Chemistry through

Hydrogen
Clean Energy for the Future

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 This book was carefully produced. Nevertheless the author and publisher do not warrant the information contained therein to be free
of errors. Readers are advised that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate.

Published by
Heliocentris Academia GmbH, Berlin, Germany
www.heliocentris.com

Editors: Ted Lister and Dr. Henrik Colell

Production Manager: Brian Cook

Die Deutsche Bibliothek – CIP-Cataloguing-in-Publication-Data

A catalogue record for this publication is available from Die Deutsche Bibliothek

Averil Macdonald and Martyn Berry:

Chemistry through Hydrogen – Clean Energy for the Future (volume 2)/ Averil Macdonald; Martyn Berry.
7th Edition 2013
Berlin: Heliocentris Academia GmbH, 2000-2013
ISBN 978-3-935161-01-5 (ISBN 3-935161-01-8)
NE: Macdonald, Berry

Also published in this series:

ISBN 978-3-935161-00-8 (Science through Hydrogen - Clean Energy for the Future (volume 1))
ISBN 978-3-935161-02-2 (Physics through Hydrogen - Clean Energy for the Future (volume 3))
ISBN 978-3-935161-03-9 (Energy through Hydrogen - Research Notes (volume 4))
ISBN 978-3-935161-04-6 (Hydrogen Technology and Fuel Cells - Course Program for Secondary Schools (volumes 1-4))

© Heliocentris Academia GmbH, Rudower Chaussee 29, 12489 Berlin, Germany, 2013

©Heliocentris Academia International GmbH, Rudower Chaussee 30, 12489, Germany, 2017

All material and substances used in the printing and production of the book are harmless for the environment.

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form –
by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written
permission from the publisher. Registered names, trademarks, etc. used in this book, even when not specifically marked as
such, are not to be considered unprotected by law.

Graphic design and layout: Designation.com Ltd, Reading, UK

Revision and Production: Zech Dombrowsky Design, Berlin

Printed in Germany

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 Preface
This is one of a set of 4 books that tackle the subject of an energy economy based
on hydrogen technology. This is an area that is likely to grow massively in the coming
century as pressure on existing fossil fuel stocks grows, and mankind becomes
increasingly sensitive to environmental concerns. These books seem almost unique in
science education as they have been written by two experienced and active science
educators but with the full support and co-operation of a company and of individuals
working at the cutting edge of the field.

Book 1 Physics through Hydrogen – Clean Energy for the Future To accompany these teaching resources the authors have
broadly covers the physics-based aspects of the topic at the written a fourth book ‘Energy through Hydrogen – Research
post-16 level while its sister, Book 2 Chemistry through Hydrogen Notes’. This contains extensive background material covering
– Clean Energy for the Future is written at the same level but the theory of hydrogen technology, its potential for
covers the chemistry of the subject. Book 3 Science through exploitation in the coming years, and a variety of issue-based
Hydrogen – Clean Energy for the Future is aimed at the pre-16 articles covering social concerns, pollution, the environment,
level and takes a more environmental view of the subject economics and engineering.
matter.
It has been my privilege to work in a small way with Averil
These books have been written with an eye on current and Martyn on this project; I have enjoyed seeing their work
syllabuses specifications but the content should be useful in unfold and have learned a lot. I hope that readers will find
a variety of courses. The authors have also made a point of the books both useful and exciting.
stressing transferable skills – research, comprehension,
Information Technology, etc – and the importance of Acknowledgments
cutting-edge technology and its impact on our quality of life.
The authors would like to thank Brian Cook from
Heliocentris, Berlin without whose drive and enthusiasm
Each book has a core of experimental work, both set
the project would never have got off the ground
experiments and open ended investigations. This is designed
to support the hydro-Genius kit produced by
Heliocentris – consisting of a solar cell, water electrolyser
and fuel cell – but can be done with other suitable apparatus. Ted Lister

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 Heliocentris
Post-16 level Chemistry
Hydrogen - clean energy for the future
We enter the third Millennium greedy for energy and endangering
the planet with pollution – the Energy Crisis is upon us. After
centuries where the sources of power have been carbon based,
and now that our reserves of these fuels are failing, is hydrogen
set to be the fuel of the 21st Century?
This book provides teaching resources which explain how Solar
Hydrogen Technology works, how a range of fuel cells can provide
for different needs from transport to household and industry, and
asks whether hydrogen technology really can deliver.

Key features: • M
 aterial enabling independent learning
relevant to ‘research and report’
• A
 n up to date context for addressing
assignments or case studies.
a range of Chemistry topics.
• L
 inks to environmental issues leading
• A
 variety of practical activities which
to consideration of the spiritual, moral
demonstrate key Chemistry concepts.
and cultural impact of scientific
• O
 pportunity for extended practical advances.
investigations or projects.
• D
 evelopment of economic and
• A
 ssignments targeting data industrial understanding related to
interpretation and analysis. advances in Chemistry.
• O
 pportunity for developing team • A
 dditional background material is
working skills. provided in accompanying book of
• A
 selection of resources and assignments ‘Research Notes’ for more substantial
addressing key comprehension and research or for general interest detailing
communication skills. the most recent advances in hydrogen
technology.

4 Heliocentris • post-16 level chemistry

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 Contents
Part 1 Part 2
Prepared experimental and teaching Written assignments targeting key skills
sessions targeting syllabus requirements 1. Fuel cells : past and present pg96 – 97
and laboratory skills 2. The third century of power pg98 – 99
1. The greenhouse effect pg12 –17 3. Batteries vs fuel cells
2. The electrolysis of water pg18 –23 – where does the future lie? pg100 –101
3. The Avogadro constant pg24 –29 4. Zero emission vehicles pg102 –103
4. The characteristic curve 5. The first hydrogen gas station pg104 –105
of the electrolyser pg30 –35 6. Carbon nanofibres pg106 –107
5. The Faraday efficiency of the
electrolyser pg36 –41
6. The characteristic curve of the Conclusion/Bibliography pg108–109
fuel cell pg42 –47
7. The efficiency of a fuel cell pg48 –53
8. Faraday’s first law using
a fuel cell pg54 –59
9. Rates of reactions at the
electrode pg60 – 61
10. The characteristic curve of
the methanol fuel cell pg62 – 67
11. The effect of varying concentrations
on the methanol fuel cell pg68 –73
12. The dismantlable fuel cell:
Impact of catalyst load on the
characteristic curve pg74–79
13. Impact of the gas supply on the
characteristic curve of the fuel cell pg80 – 85
14. Team project: Comparing the
hydrogen fuel cell with the
methanol fuel cell pg86 ­– 87
15. Theoretical principles behind
fuel cells pg88– 93

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 Overview: Target specification sections:
This resource pack supports the
The specification sections addressed
Heliocentris hydro-Genius apparatus.
include:
This offers a hydrogen fuel cell with
hydrogen supplied by the photovoltaic • Environmental considerations.
electrolysis of water, with an optional • The chemistry of Group 4.
dismantlable fuel cell and a direct
• Chemical bonding.
methanol fuel cell.
• Delocalisation of electrons.
• Part 1 provides 15 prepared sessions covering
a range of topics required in Chemistry • Electrolysis.
specifications. Photocopiable worksheets • The Avogadro constant.
enable students to undertake practical
• Oxidation and reduction.
investigation of Chemistry principles. These
may be undertaken individually or in groups as • Rates of reaction.
part of on-going experimental work, or they • Catalysis.
may inform a more substantial practical
• C
 alculation: quantitative electrolysis, enthalpy
investigation or project for formal summative
changes, rates.
assessment. Opportunities for data analysis
arise naturally from these investigations. The • Industrial, economic and social factors.
teachers' worksheets may be photocopied at
the teacher's discretion for the help and Subject specific experimental skills:
guidance of students.
The experimental guides give students
the opportunity to develop skills in
• P
 art 2 provides photocopiable worksheets • Basic circuit design and assembly.
with written assignments which develop key
• U
 se of preliminary work to determine
communication skills. Working through these,
appropriate techniques and what to measure.
students will begin to appreciate how
Chemistry has contributed to the development • Manipulation of variables, and optimisation.
of hydrogen technology and its potential uses, • Data logging and use of spreadsheets.
and to evaluate the benefits and drawbacks of
• Data analysis and interpretation.
such advances to society and the environment.
The assignments include comprehension • E
 valuation of experimental techniques and
exercises and 'research and report' or quality of results.
presentation activities - which may be undertaken • Manipulation of gases.
as groups to develop team working skills.

6 Heliocentris • post-16 level chemistry

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 Key skills: Spiritual, moral and cultural issues:
The development of the key skills of Meaningful study will consider the wider
communication, application of number and implications of a subject, for example the social,
information technology now forms a major historical, economic, industrial or environmental
element of achievement at post-16 level, and the issues. The development of alternative energy
nature of assessment in examinations has sources is very topical. By tracing the history of
changed to reflect this. The development of hydrogen technology from its discovery in 1839,
students' personal skills of working with others, considering why it was abandoned until the
problem solving and improving their own learning 1960s, its use in manned space flight and how
is also important. The range of tasks offered in environmental legislation has contributed to its
this resource enables students to practice a wide recent revival and subsequent rapid advance,
range of skills while studying Chemistry, for example: students will encounter all of these wider issues
and develop a greater appreciation of the nature
• Comprehension
of scientific research, and of the interaction of
• Data interpretation and analysis science and society. Discussion of the need for
• Reading, extracting and collating material environmental protection, and why large
companies are investing heavily in hydrogen
• Presenting information in different forms
technology, invites students to develop their own
• Producing written reports views on the future of alternative energy sources
• Making poster presentations based upon sound scientific arguments.

• Making verbal presentations

• Discussion and debates
• Working with others
• Independent learning

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 experimental sessions

Part 1
Experimental sessions
These sessions cover a range of topics from post-16 Chemistry specifications
addressed within the context of sustainable energy supplies.

Using this section: Contents:

E1. The greenhouse effect pg12 – 17
The laminated sheet provided with each kit may be
Students devise a method for observing the greenhouse
photocopied and issued to students for guidance.
effect in a gas jar, first without a black surface to absorb
The Student Guides. Students are guided in planning, visible radiation and re-emit IR, and then with one.
undertaking and evaluating the experiment. Preparatory and Results are analysed graphically and experimental
follow-up questions ensure that the experimental work has technique is evaluated.
a firm theoretical basis and is set in a real-life context. The
students develop experimental skills of circuit design and E2. The electrolysis of
assembly as well as laboratory, IT, data analysis and report water pg18 – 23
writing skills. The guides may be photocopied for student use. The solar module and PEM electrolyser are introduced,

The Teacher Guides offer specific information regarding the and used to find the relative volumes of gases produced

learning objectives of each experiment, details of the during the electrolysis of water. The gases are positively

experimental set-up and the anticipated learning outcomes. identified. Experimental technique is evaluated.

There is also a full explanation of the underpinning theory

and how to interpret the data. If students require additional E3. The Avogadro
support when undertaking their investigation then constant pg24 – 29
photocopied sub-sections of the teacher guides may be Knowledge of the charge on the electron allows
offered at the teacher’s discretion, for example to prompt determination of the Avogadro Constant, L, by use of
students or specify precisely the circuit design or how the the PEM electrolyser. The need for repeat runs of the
experiment might be done. experiment is stressed and also precision in calculation.
Experimental technique is evaluated.
Key chemistry specification requirements targeted:
• Electrolysis and oxidation and reduction
• Catalysis
E4. The characteristic curve
• Quantitative chemistry of the electrolyser pg30 – 35
• Group 4 and d-block chemistry Students investigate the effect of changing the voltage
• Economic and environmental factors across the electrolyser and observe the resulting current
values. Results are displayed graphically and
Subject specific experimental skills: experimental technique is evaluated.
• Basic circuit design and assembly
• Adapting apparatus to fit the task
• Recording, analysing and interpreting data
• Manipulation of variables and optimisation
• Evaluation of techniques and the quality of results
• Manipulation of gases

8 Heliocentris • part1 – experimental sessions

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 P1
E5. The
 Faraday efficiency of E10. The characteristic curve of the
the electrolyser pg36 – 41 methanol fuel cell pg62 – 67
The actual volume of hydrogen produced during The methanol fuel cell is introduced. Students
electrolysis is compared with the volume theoretically investigate how the voltage and current vary as the
obtainable. Repeated runs and precision in calculation value of the resistance changes. Results are displayed
are stressed. Experimental technique is evaluated. graphically, and compared with the characteristic curve
for the hydrogen fuel cell. Experimental technique is
E6.The characteristic evaluated.
curve of a fuel cell pg42 – 47
The PEM fuel cell is introduced. Students investigate E11. The effect of varying
how the voltage and current vary as the value of the concentrations on the
resistance load changes. As the hydrogen fuel cell is the methanol fuel cell pg68 – 73
reverse of the electrolyser, the two characteristic curves Students investigate the behaviour of the methanol fuel
may be compared. Results are displayed graphically and cell when different concentrations of aqueous methanol
experimental technique is evaluated. are used. The characteristic and power curves are
displayed graphically. Students are encouraged to
E7.The efficiency of the consider the processes within the fuel cell which lead
fuel cell pg48 – 53 to the observed shape of the curves. Experimental
Students compare the actual volume of hydrogen used technique is evaluated.
by the fuel cell with the theoretical volume required for
production of a certain amount of electricity. Extension E12. The dismantlable fuel cell:
work on energy efficiency, and also on the link between Impact of catalyst load on the
the power developed by the cell and its efficiency, is characteristic curve pg74–79
suggested. Precise calculation is required. Experimental The dismantlable fuel cell is introduced. Students gain
technique is evaluated. experience in manipulation as they dismantle and
reassemble the cell. The characteristic curves of the cell
E8. Faraday’s first law using are found for different catalyst loads on the membrane
a fuel cell pg54 – 59 and displayed graphically. Students are encouraged to
Students test the application of Faraday’s first law to a consider the implications of their observations for
fuel cell by investigating how the volume of hydrogen commercial fuel cells. Experimental technique is
used by the cell varies: (1) with time, keeping the current evaluated.
constant; (2) with the current produced by the cell,
during a constant time interval. Results are analysed E13. Impact of the gas supply on
graphically and experimental technique is evaluated. the characteristic curve of the
fuel cell pg80 – 85
E9. The rates of reactions at Students use the dismantlable fuel cell to control the
the electrode pg60 – 61 rate at which oxygen can reach the cathode, and display
Results of previous experiments are used to broaden the resulting characteristic curves graphically. They are
students’ experience of calculation; for example, to find encouraged to consider the implications of their
the rate of discharge of hydrogen ions at the cathode, observations for commercial fuel cells. Experimental
the rate of production of hydrogen at the membrane, technique is evaluated.
and the rate of production of water in the cell.

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 experimental sessions continued

E14. Team project: Comparing the E15. Theoretical principles behind

hydrogen
 and methanol fuel cells pg88 – 93
fuel cells pg86 – 87 A resource for experiments 6-14. Aspects covered
One group of students investigates the hydrogen fuel include the general characteristics of the fuel cell, the
cell and another the methanol fuel cell. (Alternatively, principles of operation, the structure of the membrane/
the results from previous experiments may be used). electrode assembly, the significance of the shape of the
A list of points to use in comparing the two cells is characteristic curve, and the implications for
drawn up, and each point discussed and its importance commercial use.
assessed, including the implications for commercial use
of the cells. A report is then written by each student.

10 Heliocentris • part1 – experimental sessions

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 P1

11

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 teachers guide

The greenhouse effect

Apparatus required: • Scissors
• -10 ºC – 110 ºC thermometer
• Lamp, 60 or 100 Watt
(identical if more than one)
• Glass gas jar (or identical gas jars) approx
• Piece of A4 paper, pencil
15 cm tall, 7.5 cm outside diameter
• Black paper
• Strong cardboard

Fig. 1

Safety: Please follow the operating instructions.

Gas jar becomes warm.
A full risk analysis must be undertaken before beginning any experiment.

12 the greenhouse effect • teacher guide

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 Et1
Instructions 5. Place the centre of the gas jar cover about one-third of the inside
above the other mark, and put the diameter of the jar. Use fingers to fit
1. Cut a piece of flat cardboard to fit
cardboard and thermometer on the the paper as closely as possible to
over the gas jar, allowing about 1 cm
gas jar so that the thermometer is in the inside of the jar.
overhang all round.
the centre of the gas jar. 9. Using the same marks on the paper,
2. In the centre of the cardboard pierce
6. Record the temperature in the gas repeat instructions (4), (5) and (6),
a small round hole. It must be tight
jar, switch on the lamp, and record making sure that the black paper at
around the thermometer. Push the
the temperature every minute for the back of the inside of the gas jar
thermometer through the hole so
10 minutes. directly faces the lamp.
that its bulb is 5 cm below the
7. Either remove the cardboard and 10.On the same piece of graph paper,
cardboard when placed on the gas jar.
thermometer and allow the gas jar plot the temperature (on the
3. Make two pencil marks 10-15 cm
and thermometer to cool down fully vertical axis) against time for both
apart on a piece of A4 paper.
to room temperature, or use an the experiments.
4. Place the lamp so that the front
identical gas jar and thermometer.
surface of the bulb is directly above
8. Cut a strip of black paper to fit in
one of the marks and about 10 cm
the gas jar to just below the
above the surface of the paper,
cardboard, and wide enough to
facing directly ahead.

Table of results: with no black paper in the gas jar

Time/minutes 1 2 3 4 5 6 7 8 9 10

Temperature/ºC

Table of results: with black paper in the gas jar

Time/minutes 1 2 3 4 5 6 7 8 9 10

Temperature/ºC

Evaluation
1. Comment on the shape of the
curves.
2. Comment on the difference between
the two curves.

chemistry through hydrogen • clean energy for the future 13

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 teachers guide continued

Learning objective
• the basis of the ‘greenhouse effect’

Interpretation Typical results Extension

Some of the radiation from the lamp (60 W bulb, 10 cm between bulb and This experiment could be used as a
is reflected off the glass and some is centre of gas jar). lead-in to a discussion of why the
absorbed as it passes through the ‘greenhouse effect’ in the Earth’s
glass. The gas jar and the air in it atmosphere is necessary (otherwise
gradually warm up. Earth’s surface would be about 30ºC
The greenhouse effect depends colder than it is), but any increase in
on a surface absorbing visible radiation, the effect is likely to be harmful.
becoming warmer and radiating in the Students are asked to consider these
IR region of the spectrum. Visible light points in the question at the end of the
can pass through glass but IR radiation student guide E1.
cannot, so the inside of the greenhouse
(or glass gas jar) warms up quicker.
The black paper absorbs visible light
and emits IR.

14 the greenhouse effect • teacher guide

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 Et1
notes

chemistry through hydrogen • clean energy for the future 15

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 student guide

The greenhouse effect

Apparatus required: • Strong cardboard

• Scissors
• Lamp, 60 or 100 Watt
• -10 ºC – 110 ºC thermometer
• Glass gas jar (or identical gas jars) approx
(identical if more than one)
15 cm tall, 7.5 cm outside diameter
• Piece of A4 paper, pencil
• Black paper

Safety: Please follow the operating instructions.

Gas jar becomes warm.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
A surface which absorbs visible light and becomes
warm re-emits radiation of a longer wavelength than
visible, i.e. in the infra-red (IR) region of the spectrum.
When Earth is warmed by solar radiation, the
re-emitted IR is absorbed by certain molecules as
they vibrate, in particular water, carbon dioxide, and
methane. The absorbed energy is spread around the
rest of the molecules of the atmosphere by collisions,
so that the atmosphere is warmed up.

A greenhouse works because visible light can largely

get through glass, but the IR re-emitted by the
warmed-up surfaces in the greenhouse cannot get
out again through the glass.

Objectives
To investigate whether the heating of air in a confined space is accelerated by a
surface which absorbs visible light, and hence to study one of the factors responsible
for the ‘greenhouse effect’.

16 the greenhouse effect • student guide

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 E1
Procedure Results, records
• Use the equipment and materials
provided, to devise a method for
and evaluation
1. Draw a diagram to show your
Question
irradiating the gas jar and the air experimental arrangement.
inside it with visible light, without • Why is the ‘greenhouse effect’
2. Devise a suitable results table to
and then with a black surface inside in the atmosphere important
record your data, either on paper
the jar, and following any change in for maintaining life on Earth,
or a spreadsheet.
the temperature of the air within and what are the likely
the gas jar. 3. Plot the curves for the temperature problems if the effect is
of the air in the gas jar (on the increased?
vertical axis) against time.

4. Comment on the shape of the

curves, and on the difference
between the two curves.

5. Evaluate the experimental

techniques you used, identifying any
precautions taken and any difficulties
encountered and how they were
overcome.

6. Suggest further improvements for

the experiment. (You may have
access, for example, to a
temperature sensor coupled to a
computer).

chemistry through hydrogen • clean energy for the future 17

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 teachers guide

The electrolysis of water

Apparatus required: Additional components:

• Solar module • Lamp 100 – 150 Watt
• Electrolyser • Distilled water (about 100 cm3 )
• Fuel cell • 2 small test tubes
• Load measurement box • 2 wooden splints or spills
• Connecting leads • Bunsen burner
• 2 long tubes
• 2 short tubes
• 2 tubing stoppers

Fig. 1
(purging)

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

18 the electrolysis of water • teacher guide

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 Et2
Instructions distilled water to the 0 ml mark. the gases released from the
Adjust the solar module so that electrolyser. Then put the rotary
1. Set up the apparatus as shown in
there is a constant current to the switch on the load measurement box
fig. 1. Make sure the electrolyser is
electrolyser of between 200 to 300 mA. to 3Ω for 3 minutes. The ammeter
connected with the correct polarity.
The solar module and the light must display of the load measurement box
2. Check that the gas tubes are
be positioned so that a steady gas should show that a current is
correctly connected between the
production can be observed. flowing. Purge the system again with
electrolyser and the fuel cell.
4. Purge the complete system, the rotary switch ‘OPEN’ for
Adjust the rotary switch to ‘OPEN’.
consisting of the electrolyser, fuel 3 minutes.
3. Make sure both gas storage cylinders
cell, and tubes for 5 minutes with
of the electrolyser are filled up with

Fig. 2
(measurement)

Note to the teacher:

If the students are fully conversant with the electrolysis of water, this experiment
could be done as a preliminary to the experiment on the characteristic curve of the
fuel cell (experiment 6), as the apparatus and the first part of the method (as far as
instruction 6) are identical.

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 teachers guide continued

Instructions continued electrical connections to the fuel stopper from it, and immediately
cell by setting the rotary switch to put it as far as possible into the
5. Disconnect the solar module from
‘OPEN’. The fuel cell has consumed test tube before releasing the gas.
the electrolyser, and close both the
all the stored hydrogen (10 ml). Remove the plastic tube and
short tubes at the gas outlets of the
Measure the volume of consumed immediately put a burning splint
fuel cell with the stoppers.
oxygen. to the mouth of the test tube.
6. Reconnect the solar module to the
9.  Remove the stoppers from the (It is easier if there are two people
electrolyser, and store the gases in
tubes of the fuel cell after the involved!)
the gas storage cylinders.
experiment. 13. Leaving the hydrogen tube from
Disconnect the power supply of the
10. Disconnect the tubes from the the electrolyser open, but with the
electrolyser when the hydrogen has
electrolyser to the fuel cell, fit short stopper still in the oxygen tube,
reached the 10 ml mark. Now read
tubes to the electrolyser and put pass the current through the
the volume of oxygen which has
stoppers in them. Repeat electrolyser until 10 cm3 oxygen
been collected in the same time.
instruction (6) to fill the hydrogen has been collected.
7. Adjust the rotary switch at the load
storage cylinder to the 10 ml mark. 14.Repeat (12), but this time using the
measurement box to a resistance of
11. Light a Bunsen burner at least one oxygen tube from the electrolyser
1Ω. A current flows and the fuel cell
metre away from the apparatus. and holding the test tube
consumes the stored hydrogen.
12.H
 olding a test tube upside down, horizontal, and immediately
8. When the level of water in the
pinch the tube from the hydrogen pushing a glowing (not burning)
hydrogen storage cylinder returns to
storage cylinder and remove the splint well inside the test tube.
the 0 ml mark, disconnect the

Draw out your own results table

Table of results: Decomposition of water in the electrolyser Table of results: Consumption by the fuel cell

Volume of hydrogen = 10 cm3 = (10 ml) Consumption of hydrogen = cm3

Volume of oxygen = cm3 Consumption of oxygen = cm3

Results of gas identification tests:

Evaluation 3. D
 etermine the ratio of the gases which gas is produced at which
consumed by the fuel cell during electrode during electrolysis of water.
1. Measure the respective gas volumes.
operation.
2. Determine the ratio of the gas
4. E
 xplain how you have made sure
volumes released during electrolysis.

20 the electrolysis of water • teacher guide

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 Et2
Learning objectives
• the gases, and relative gas volumes, produced during the electrolysis of water
• that the fuel cell uses these gases in the same relative volumes
• the interconversion of light energy, electrical energy, and chemical energy

Interpretation

Sample results: Decomposition of water in the electrolyser Sample results: Consumption by the fuel cell

Volume of hydrogen ≈ 10 cm3 Volume of hydrogen ≈ 10 cm3

Volume of oxygen ≈ 5 cm3 Volume of oxygen ≈ 5 cm3

The experiments carried out This proves that this electrochemical

demonstrate the decomposition of reaction is reversible.
water in a ratio of 2 volumes of The first reaction (electrolysis)
hydrogen gas to 1 volume of oxygen. requires electrical energy, whereas the
second reaction (fuel cell) releases
2H2O(l) ➝ 2H2(g)+ O2(g) electrical energy. In any such energy
cycle there will inevitably be losses.
In the fuel cell, the reverse of The conversion of one form of energy
electrolysis takes place, i.e. the gases to another is never 100% efficient. The
stored during electrolysis are fuel cell, however, is a more efficient
reconverted into water. energy converter than the internal
2H2(g)+ O2(g) ➝ 2H2O(l) combustion engine by a factor of about
two.

notes

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 student guide

The electrolysis of water

Apparatus required: Additional components:

• Solar module • Lamp 100 – 150 Watt
• Electrolyser • Distilled water (about 100 cm3 )
• Fuel cell • 2 small test tubes
• Load measurement box • 2 wooden splints or spills
• Connecting leads • Bunsen burner
• 2 long tubes • Photocopy of the diagram on the
• 2 short tubes laminated sheet in the hydro-Genius kit
• 2 tubing stoppers

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
‘Electrolysis’ means the breaking-up (‘-lysis’) of a substance by
passing electricity through it. There is a great difference between
ordinary metallic conduction, in which there is no observable
change in the metal except that it may get hot and even melt, and
electrolytic conduction, in which the substance which is
doing the conducting is chemically broken up.

In conventional electrolysis, the electrolyte must be molten or in

solution in water, so that ions in the electrolyte are able to
move through the liquid to the electrodes.
The conductivity of pure water is normally very low, and electrolysis of water using
conventional methods is not possible. Both the electrolyser and the fuel cell in the kit use
a solid polymer membrane, with the reactions at the electrodes being catalysed by
very fine particles of precious metals, usually platinum.

Objectives
To find the relative volumes of gases produced during the electrolysis of water, to
positively identify the gases, to observe how the fuel cell uses these gases, and to
become familiar with the kit, its components, and how they work.

22 the electrolysis of water • student guide

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 E2
Procedure Results, records
• Assemble the kit as shown in the
diagram in the teachers’ notes.
and evaluation
1. Draw a circuit diagram and explain
Question
It is vitally important that all the its arrangement.
connections are correctly made; • Write the equations for the
2. Record your results in a suitable
the polarity of the electrolyser overall processes occurring in
table.
and fuel cell must be correct. each of the electrolyser and
Check with the teacher before 3. Draw conclusions from your results. the fuel cell and explain the
proceeding. link between these equations
4. Evaluate the experimental
and your results.
• Purge the apparatus of air for 5 techniques you use, identify any
minutes by using gases generated in precautions taken, and describe
the electrolyser, with the switch at any difficulties encountered and
‘OPEN’. Then switch to 3Ω for how they were overcome.
3 minutes, then purge for another 5. Suggest improvements for the
3 minutes with the switch ‘OPEN’. experiment. Extension work
• Devise a method for collecting the Explain what is meant by ‘oxidation’
gases in the gas storage cylinders in and 'reduction'.
the electrolyser. Note the volume
ratio. Which process is happening at each
electrode in the electrolyser and the fuel
• When the hydrogen storage cylinder
cell? (The research note book will help).
is full, disconnect the solar module
from the electrolyser and switch to
Write an equation for the process
1Ω. The fuel cell will consume the
occurring at each electrode.
gases; note the ratio of gases
consumed.
Explain each of the terms in bold type
• Then devise a method for safely in the introduction.
collecting and identifying a sample of
each gas. Check with your teacher Discuss how the experiment
before proceeding. demonstrates the conversion of energy
from one form to another.

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 teachers guide

The Avogadro constant

Apparatus required: Additional components:

• Solar module • Lamp 100 – 150 Watt
• Electrolyser • Distilled water
• Load measurement box
• Connecting leads
• 1 short tube
• 1 tubing stopper
• Stop watch

Fig. 1

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

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 Et3
Instructions (200-300 mA) and that gas is being during the time; if so, record the
steadily given off. When all is ready, average.
1. Set up the apparatus as shown in fig.1.
break the circuit, close the short 5. Release the hydrogen so that the
Make sure all connections have the
tube on the hydrogen side of the level of water in the storage cylinder
correct polarity. Adjust the rotary
electrolyser with a tubing stopper, returns to 0 ml, and repeat
switch of the load measurement box
reconnect the circuit, and start the instructions 3 to 5.
to ‘SHORT CIRCUIT’.
timer. 6. Repeat at least once more if time
2. Make sure both the gas storage
4. Record how long it takes to collect allows.
cylinders of the electrolyser are filled 3
10.0 cm (=10 ml) of hydrogen, and
with distilled water to the 0 ml mark.
record the constant current. There
3. Make sure that a constant current is
may be minor fluctuations in current
produced by the solar cell

Table of results: (Make your own results table)

Volume of hydrogen collected each

Current/A Time/s Charge/C
time = 10.0 cm3 (= 10 ml)
Electric charge/C = Current/A · Time/s Run 1

Run 2
Average electric charge required to
release 10.0 cm3 hydrogen = ............C Run 3

Evaluation 3. From your results, calculate how

many coulombs are needed to release
1. Write the electrode equation for the
one mole of hydrogen gas, H2.
cathode reaction in the electrolyser.
4. Using the value for the charge on the
2. State how many moles of electrons
electron, calculate the number of
are needed to release one mole of
electrons in one mole of electrons,
hydrogen gas (= 24,000 cm3 at room
and hence the Avogadro constant.
temperature and pressure).
(The charge on an electron is
e = 1.60 · 10–19 C).

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 teachers guide continued

Learning objective
• that the value of the Avogadro constant can be found by an electrolytic method

Interpretation Therefore L amounts to:

The accepted value for L is
The equation for production of
6.02 · 1023 mol–1 (to 3 significant
hydrogen in the electrolyser is:
which equals 2 moles of electrons. figures).
2H+(aq) + 2e– ➝ H2(g)
The accepted value for the charge on
This shows that two moles of electrons
One mole of any species contains an a mole of electrons (the Faraday
are needed in order to produce one
Avogadro constant, L, of particles. constant) is 96,500 C (to 3 significant
mole of hydrogen gas.
If e is the charge on one electron: figures).
This method should produce a value for
Sample results:
L within 10% of the accepted value.
10.0 cm3 of hydrogen was produced by:
0.280 A flowing for 276 s.
Therefore the amount of electric charge
Extension
The charge on one electron e is:
is: The experiment can be repeated, using
e = 1.60 · 10–19 C.
Q = 0.280 A · 276 s = 77.2 C. the anode reaction:
The amount of electric charge needed for 2H2 0(l) ➝ 02(g) + 4H+(aq) + 4e–
1 mole of hydrogen gas (i.e. 24,000 cm3
at room temperature and pressure) is:

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notes

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 student guide

The Avogadro constant

Apparatus required: Additional components:
• Solar module • Lamp 100 – 150 Watt
• Electrolyser • Distilled water
• Load measurement box • Photocopy of the diagram on the
• Connecting leads laminated sheet in the hydro-Genius kit
• 1 short tube
• 1 tubing stopper
• Stop watch

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
A full risk analysis must be done before beginning any experiment.
Solar module becomes hot.

Introduction
The number of atoms or other entities which is
contained in one mole of any substance is known
as the Avogadro constant, L, the units of
which are mol-1.

By considering the electron as a particle with a

definite electric charge, we can use electrolysis
to find a value for the Avogadro constant.

The charge on the electron, e, was first measured by Robert Millikan between 1909
and 1913. The value is now known to 7 places of decimals (1.6021892 · 10-19 C),
but in this experiment we shall use the value of e to three significant figures only.

Objectives
To find the value of the Avogadro constant, L, by an electrolytic method.

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 E3
Procedure Results, records
• Assemble the solar cell, lamp,
electrolyser and load measurement
and evaluation
1. Draw a circuit diagram and explain
Question
box as shown in the diagram in the its arrangement.
teachers notes, but without the • Give reasons why the value
2. Construct a suitable results table.
tubing stopper. you obtain for the Avogadro
3. Use your results, together with the constant, L, is likely to be
• All connections must be correctly
equation for the cathode reaction in different from the accepted
made, with the correct polarity.
the electrolyser and the value for the value.
Check with your teacher before
charge on the electron, to find a
proceeding. Collect hydrogen with
value for the Avogadro constant.
the switch at ‘SHORT CIRCUIT’.
4. Evaluate the experimental
• Investigate the amount of electric
charge required to release 10.0 cm3
techniques used in your experiment, Extension work
identify any precautions taken, and
(= 10 ml) of hydrogen gas, and then Repeat the experiment, using oxygen
describe any difficulties encountered
calculate the amount needed to rather than hydrogen.
and how they were overcome.
release 1 mole of hydrogen gas.
(Remember that a single 5. Suggest any ways in which the
measurement is unlikely to be experimental procedure may be
reliable, and that charge/C = improved.
current/A · time/s).

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 teachers guide

Characteristic curve
of the electrolyser

Apparatus required: Additional components:

• Electrolyser • Lamp 100 – 150 Watt
• Solar module • Distilled water
• Load measurement box
• Connecting leads

Fig. 1

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

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 Et4
Instructions measurement box to ‘SHORT Table of results:
(make your own results table)
CIRCUIT’.
1. Set up the apparatus as shown in fig. 1.
2. Adjust the current of the solar module
• Make sure all connections have the Voltage /V Current / mA
by variation of the light intensity, e.g.
correct polarity. The positive
by rotating the solar module to
terminal of the power-supply unit
different angles with respect to the
must be connected to the positive
incident light. Use different current
terminal of the electrolyser, and
values, starting at small currents of
the negative terminal of the power
approx. 10 mA through to approx.
supply to the negative terminal of
350 mA (depending on the type of during electrolysis, and note the
the electrolyser. Fill the electrolyser
lamp). Record the electrolyser's values in a table of measurements,
cylinders with distilled water to the
voltage. Take at least 8 sets of as shown above.
0 ml mark.
measurements of voltage and current
• Adjust the rotary switch of the load

Evaluation
1 Plot the current-voltage (IV)
characteristic curve of the
electrolyser, with current on the
vertical axis.
2. Interpret the IV characteristic curve.

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 teachers guide continued

Learning objectives
• the relationship between current and voltage in the electrolyser
• that electrolysis needs a minimum voltage before it can happen

Interpretation electrodes reaches the level of the the depositing of metals; however, they
external air pressure, and gas bubbles are particularly large when gases
begin to rise at the electrodes. (H2, O2, Cl2) are released.
A further increase in the external In practical applications, the aim
voltage leads to continuous gas is to keep overpotential to a minimum.
production and a steep rise in the It is important in this context to use
electrolysis current strength. very good, active electrode and
The minimum voltage at which electrolyte materials.
the splitting of water begins is called The PEM electrolyser has no
the decomposition voltage. For our liquid electrolyte. The function of the
Characteristic curve of the electrolyser electrolyser, this voltage is equal to the electrolyte is taken over by a special
cell voltage of the H2//H2O//O2 proton-conducting membrane (PEM =
The current-voltage curve shows that a
electrochemical cell under standard Proton Exchange Membrane). This
current only starts to flow at a certain
conditions. This value is 1.23 volts. membrane has roughly the acidity of
voltage, and that it then rises –
1/2 O2(g) + 2H+ (aq) + 2e H2O(l) 1 mol dm–3 sulphuric acid. Only
continuously. What is the value of the
E = +1.23 V precious metals can be used as
voltage at which a current starts to
From the figure above, it appears electrode material in acidic
flow?
that the release of hydrogen and environments. The oxygen side of the
The initial application of a small
oxygen at the electrodes is being PEM electrolyser membrane is coated
voltage does not cause an electrolysis
obstructed. with a special ruthenium-iridium alloy,
current leading to the release of
The difference between the the hydrogen side with platinum. Very
hydrogen at the cathode and oxygen
theoretical decomposition voltage and small amounts of both catalysts are
at the anode (e.g. nothing appears to
the decomposition voltage that is applied directly to the membrane in the
happen at 1 volt).
determined experimentally is termed form of tiny particles. The current is
The gases that may form at a
overpotential or overvoltage. conducted to the outside using high-
small voltage are initially adsorbed on
The overpotential is a function of grade stainless steel electrodes.
the surface of the electrodes; an
the electrode material, the texture of In electrolysis, the catalytic
electrochemical cell develops. This cell
the electrode surfaces, the type and activity of the electrodes is normally
has a certain voltage known as the
concentration of the electrolyte, the the decisive factor in minimising
polarisation voltage, which causes a
current density (current strength per operational voltage and thus increasing
current. This internal current acts in the
unit area of electrode surface) and the efficiency.
opposite direction to the electrolysis
temperature.
current. More gas is adsorbed if the
Overpotentials are small in the
external voltage is increased. At a
case of electrode reactions that lead to
certain voltage, the gas pressure at the

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notes

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 student guide

Characteristic curve
of the electrolyser

Apparatus required: Additional components:

• Electrolyser • Lamp 100 – 150 Watt
• Solar module • Distilled water
• Load measurement box • Photocopy of the diagram on the
• Connecting leads laminated sheet in the hydro-Genius kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
When a direct current (D.C.) supply is connected to an
electrolytic cell, electrolysis will not start until the voltage
reaches a particular value.

A characteristic curve shows how the current through the

cell varies with the voltage.

Objective
To use the solar module to investigate how the current through
the electrolyser varies with the voltage applied, and to find the
minimum voltage at which electrolysis begins.

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 E4
Procedure Results, records
• Assemble the appropriate
components as shown in the teacher
and evaluation
1. Draw a circuit diagram and explain
Questions
guide, with a lamp, so that the its arrangement.
current and voltage through the • The theoretical minimum
2. Construct a suitable results table for
electrolyser can be measured at voltage required for the
recording your data, either on paper
the same time. splitting of water is 1.23 V.
or as a spreadsheet.
• How does this compare with
• All connections must be correctly
3. Plot the characteristic curve for the the voltage which you have
made, with correct polarity.
electrolyser (with current on the found?
Check with your teacher before
vertical axis), and find the minimum • If there is a difference between
proceeding.
voltage at which electrolysis begins. the two values, can you explain
how the difference arises?
4. Comment on the shape of the curve.

5. Evaluate the techniques used in your

experiment, identify any precautions
taken, and describe any difficulties
you encountered and how they were
overcome.

6. Suggest any ways in which the

experimental procedure might be
improved.

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 teachers guide

Faraday efficiency
of the electrolyser

Apparatus required: • 1 tubing stopper

• Stop watch
• Solar module
• Electrolyser
Additional components:
• Load measurement box
• Connecting leads • Lamp 100 – 150 Watt
• 1 short tube • Distilled water

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Fig. 1

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 Et5
Instructions  Take three measurements, using
Fig. 2 the same time period (e.g. t = 180 sec)
1. Set up the apparatus as shown in
and use the average volume of the
fig. 1. Make sure all the connections
hydrogen collected for your
have the correct polarity.
calculations.
Adjust the rotary switch of the load
measurement box to ‘SHORT CIRCUIT’.
2. Make sure both the gas storage
cylinders of the electrolyser are filled
with distilled water to the 0 ml mark.
3. Make sure a constant current is
Close the short tube on the
produced by the solar cell and the
hydrogen side of the fuel cell using
power-supply unit (approx. 200 –
one of the tubing stoppers
300 mA), measure the voltage, and
(see fig. 2). When a current flows,
record the volume of hydrogen
the released hydrogen will be stored
released during a given time.
in the storage cylinder.

Table of results: Draw out your own table

t= s Vol1 = cm3 Volaverage = cm3

V= V Vol2 = cm3

I= mA Vol3 = cm3

Evaluation
1. Determine the Faraday efficiency
of the electrolyser.
2. Determine the energy efficiency.

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 teachers guide continued

Learning objectives
• that use of the molar volume of a gas and the Faraday constant allows calculation of
the volume of gas which should be released in electrolysis
• that the efficiency of the electrolyser can be found by comparing the observed
and theoretical volumes of hydrogen produced

Interpretation 1 mol H2 requires 2 mol electrons. of the hydrogen generated and the
1 mol H2 occupies 24,000 cm3 at room electrical energy used.
Calculation of the Faraday
temperature and pressure. The energy released when 1 mole
efficiency of the electrolyser:
1 C = 1 A for 1 s. of H2 gas is burned under usual room
The Faraday efficiency is determined
conditions is 286 kJ.
from the volume of hydrogen found by
The theoretical volume VolH (th.) is: (i.e. ∆Hc(H2) = -286 kJ mol–1)
experiment and the volume of 2

hydrogen calculated from theory:

So in our worked example above the
 olH (exp.) / VolH (th.)
η=V electrical energy needed for the release
2 2

The Faraday efficiency should be close of 6.7 cm3 is:

to 1 (100 %). The efficiency is: Eel = V · I · t
The volume of hydrogen to be  olH (exp.) / VolH (th.)
η=V Eel = 1.6 V · 0.300 A · 180 s = 86.4 J
2 2
expected theoretically can be
η = 6.7 cm3 / 6.72 cm3
calculated from Faraday's second law. The energy released by burning 6.7 cm3
η ≈ 1.0 i.e. very nearly 100%.
One modern form of this law is: To of hydrogen is:
liberate one mole of a substance
The Faraday efficiency of the
requires one, two, three (or some other
electrolyser shows how much of the
whole number) moles of electrons.
electric charge is converted in the
For hydrogen, the equation is:
desired reaction. In commercial
2H+(aq)+2e– ➝ H2(g) electrolysers, the Faraday efficiency
Therefore the energy efficiency is:
Therefore 1 mole of hydrogen must be close to one (100%). A Faraday
molecules requires 2 moles of efficiency much smaller than one would
electrons. 1 mole of any gas occupies mean that secondary reactions were
24,000 cm3 (24 litres) at room taking place in the system (e.g.
– which is unusually high. The usual
temperature and pressure. 1 mole of corrosion). This would be a great
value found is lower, but energy
electrons = 96,500 coulombs. disadvantage, since it would not only
efficiency varies with voltage. As the
shorten the service life of the
voltage is raised, the amount of
Worked example: electrolyser, but also necessitate a
hydrogen released increases, but
t = 180 s Vol1 = 6.7 cm3 higher energy input.
energy efficiency drops. For commercial
V = 1.6 V Vol2 = 6.6 cm3
electrolysers an optimum set of
I = 300 mA Vol3 = 6.8 cm3 Calculation of the energy efficiency
conditions must therefore be found.
VolH (average) = 6.7 cm3 of the electrolyser:
2

The energy efficiency of the electrolyser

is the ratio between the energy content

38 faraday efficiency of the electrolyser • teacher guide

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 Et5
notes

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 student guide

Faraday efficiency
of the electrolyser

Apparatus required: • Stop watch

• Solar module
Additional components:
• Electrolyser
• Load measurement box • Lamp 100 – 150 Watt
• Connecting leads • Distilled water
• 1 short tube • Photocopy of the diagram on the
• 1 tubing stopper laminated sheet in the hydro-Genius kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
In a particular electrolytic cell, the passage of a definite
amount of electricity should release or deposit a definite
amount of a substance (usually a gas or a metal).

The Faraday efficiency of an electrolytic cell can be

expressed as the ratio of the amount of substance found
by experiment and the amount calculated from theory.

In this experiment the substance produced is hydrogen.

Objectives
To compare the actual volume of hydrogen produced during electrolysis of water with
the volume which should in theory have been produced by passing a certain amount
of electricity, and so to calculate the Faraday efficiency of the cell.

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 E5
Procedure Results, records
and evaluation
• Assemble the appropriate
components, as shown in the 1. Draw a circuit diagram and explain
Questions
teacher’s notes, with a lamp, so that its arrangement.
the current and voltage through the • Why must the efficiency of
2. Construct a suitable results table for
electrolyser can be measured at the any commercial electrolyser be
recording data, either on paper or as
same time. Ensure that the current as close as possible to one
a spreadsheet.
produced by the solar module is (i.e. 100%)?
constant and that the switch on the 3. Use your results to calculate the • What may be happening in
load measurement box is on ‘SHORT Faraday efficiency. the electrolyser if its Faraday
CIRCUIT’. 4. Evaluate the techniques used in your efficiency is much less than
experiment, identify any precautions 100%?
• All connections must be correctly
made, with the correct polarity. taken, and describe any difficulties

Check with your teacher before you encountered and how they were

proceeding. overcome.

• Investigate the volume of hydrogen 5. Suggest any ways in which the

produced by passage of a known experimental procedure might be

current (between 200 – 300 mA) for improved.

a known time (say 3 minutes) and

compare it with the volume which in
theory should have been produced
by the same amount of electricity.
(Remember that a single measurement
is unlikely to be reliable).

Extension work The amount of energy released when Use the information given to calculate
1 mole of hydrogen gas is burned at the energy efficiency of the electrolyser.
The energy efficiency of the electrolyser
room temperature and pressure is
is the ratio between the energy content
286 kJ, i.e. ∆Hc(H2)=-286 kJ mol–1. (Note: The energy efficiency varies with
of the hydrogen produced and the
1 mole of any gas occupies voltage. You may have time to
amount of electrical energy needed to
24,000 cm3 at room temperature and investigate this).
produce it.
pressure.
The electrical energy used (J)=
voltage · current · time (V · A · s) .

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 teachers guide

Characteristic curve
of the fuel cell

Apparatus required: • 2 long tubes

• 2 short tubes
• Solar module
• 2 tubing stoppers
• Electrolyser
• Fuel cell
Additional components:
• Load measurement box
• Connecting leads • Lamp 100 – 150 Watt
• Distilled water

Fig. 1 (purging)

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

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 Et6
Instructions 3Ω for 3 minutes. The ammeter display
Fig. 2 (storing)
of the load measurement box should
1. Set up the apparatus as shown in fig.1.
show that a current is flowing. Purge the
Make sure all connections have the
system again with the rotary switch
correct polarity.
‘OPEN’ for 3 minutes.
2. Check that the gas tubes are
5. Disconnect the solar module from
correctly connected between the
the electrolyser, and close both the
electrolyser and the fuel cell.
short tubes at the gas outlets of the
Adjust the rotary switch to ‘OPEN’.
fuel cell with the stoppers (see fig.2).
3. Make sure both of the gas storage
6. Reconnect the solar module to the
cylinders of the electrolyser are filled ‘OPEN’ position, then decrease the
electrolyser, and store the gases in
up with distilled water to the 0 ml resistance stepwise by turning the rotary
the gas storage cylinders. Disconnect
mark. Adjust the solar module so that switch to the right. For each resistance,
the power supply of the electrolyser
there is a constant current to the record the values for voltage and current
when the hydrogen has reached the
electrolyser of between 200 to 300 mA. after you have waited for 30 sec. Put the
10 ml mark.
The solar module and the light source values in the results table. The last
7. Remove the connecting leads from
must be positioned so that steady gas measurements should be taken in the
the solar module to the electrolyser,
production can be observed. positions ‘LAMP’ and ‘MOTOR’.
and use them to connect the
4. Purge the complete system, consisting 9. After recording of the characteristic
voltmeter of the load measurement
of the electrolyser, fuel cell and tubes, curve, reset the rotary switch of the
box with the fuel cell (see fig. 3).
for 5 minutes with the gases released load measurement box to ‘OPEN’,
8. Record the characteristic curve by varying
from the electrolyser. Then put the rotary and remove the stoppers from the
the resistance using the rotary switch of
switch on the load measurement box to tubes of the fuel cell.
the load measurement box. Start in the

Fig. 3 (recording the characteristic curve)

Table of results: Draw out your own table

Resistance (R)/Ω Voltage (V)/V Current (I)/mA

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 teachers guide continued

Evaluation 3. E
 nter the voltage and current values voltage/V · current/A).
for each of the motor and lamp in 5. Calculate the power consumption for
1. Draw the VI characteristic curve
the VI characteristic curve. each of the motor and lamp and
of the fuel cell.
4. D
 raw a power/current (PI) diagram. enter the values into the PI diagram.
2. Interpret the characteristic curve.
(Remember that power/W =

Learning objectives
• that voltage drops as the current taken from the fuel cell increases
• the comparison between the characteristic curves of the electrolyser and the fuel cell

Interpretation dependent on the volume and purity of Experiment variations:

the input gases. The more current is In a further experiment, you can
drawn from the fuel cell, the lower the remove the tube from the oxygen inlet
voltage becomes. There is an nozzle of the fuel cell and so operate
exponential increase in the current as the fuel cell with oxygen from air. The
the voltage drops. hydrogen comes, as before, from the
If the operating point of the electrolyser’s storage cylinder.
electric motor is entered in the PI
diagram, it can be seen that the motor
does not run at the optimum point, i.e.
Characteristic curve of the fuel cell some hydrogen is being wasted. More
power can therefore be drawn from the
In order to understand the
fuel cell.
characteristic curve of a fuel cell, recall
In practice, efforts are made to
the characteristic curve of the
draw as much current as possible from
electrolyser (see Et4). The processes in
the fuel cell (i.e. maximum output).
the fuel cell are the reverse of those Characteristic curve with oxygen or air
However, the efficiency of the fuel cell
that take place in electrolysis. In the
declines at high current values This results in a dip in the characteristic
electrolysis of water, at least 1.23 V
(see Et7), so that the task is to find an curve at higher currents as a result of
must be applied before the water begins
optimum operating point (high the reduced oxygen supply (see the
to split; as a rule the voltage which is
efficiency, high output). typical diagram above).
needed is higher because of
The experiment shows that the current
overpotential (see Et4, interpretation).
rises exponentially at low overpotential
In the case of a fuel cell (which is
(near the off-load voltage). Here, it is
an electrochemical cell), a lower voltage
the catalytic reactions at the electrodes
than expected is generated for the
which determine the size of the current.
same reasons. Here, too, the
At high overpotentials, i.e where the
characteristic curve is affected by the
actual voltage is widely different from
materials used for the electrodes and
the 'off-load' voltage of about 0.9 V, the
the catalysts, the internal resistance,
supply and the concentration of the
the temperature and the volume of
Power curve of the fuel cell gases are the decisive factors
hydrogen and oxygen being supplied.
determining the behaviour of the fuel
At very small or zero current, the
cell. Depending on the gas supply, this
voltage across the fuel cell is approx.
can lead to large deviations in the size
0.9 V. This voltage is called the off-load
of the current.
voltage (by analogy with a battery). In
the case of the fuel cell, it is very

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notes

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 student guide

Characteristic curve
of the fuel cell

Apparatus required: • 2 short tubes

• Solar module • 2 tubing stoppers
• Electrolyser
• Fuel cell Additional components:
• Load measurement box • Lamp 100 – 150 Watt
• Connecting leads • Distilled water
• 2 long tubes • Photocopy of the diagram on the
laminated sheet in the hydro-Genius kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
A hydrogen fuel cell is the exact opposite of a water
electrolyser. For a fuel cell, a characteristic curve shows
how the electric current produced by the cell varies
with voltage.

Objectives
By using hydrogen and oxygen generated
photovoltaically, to investigate how the current
produced by the cell varies with the voltage.

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 E6
Procedure Results, records
and evaluation
• Assemble the appropriate
components, as shown in the 1. Draw a circuit diagram and explain
Questions
teacher’s notes, with a lamp, and its arrangement.
use the gases produced by the • The theoretical maximum
2. Construct a suitable results table for
electrolyser to remove all air from voltage for a hydrogen fuel cell
recording your data, either on paper
the apparatus (‘purging’). is 1.23 V.
or as a spreadsheet.
• How does this compare with
• All connections must be correctly 3. Plot the characteristic curve (VI) for the voltage which you have
made, with the correct polarity. the cell (with voltage on the vertical found?
Check with your teacher before axis), and find the maximum voltage • If there is a difference between
proceeding. obtainable from the fuel cell. Place the two values, can you explain
• The current to the electrolyser the lamp and motor on the curve. how the difference arises?
should be 200 – 300 mA. Pass gases 4. Comment on the shape of the curve.
through the entire system for 5
5. Plot the power curve (PI) for the cell
minutes, then switch to 3Ω for 3
(with power in mW on the vertical
minutes, then purge for 3 more
axis). Place the ‘LAMP’ and ‘MOTOR’
minutes with the switch ‘OPEN’.
on the curve. Extension work
• Then adjust the apparatus so that
6. Comment on the shape of the curve. Remove the oxygen tube which
the current and voltage produced by
connects the electrolyser to the fuel
the fuel cell can be measured at the 7. Evaluate the techniques used in your
cell, and repeat the experiment using
same time, using gases stored in the experiment, identify any precautions
air rather than pure oxygen.
electrolyser to power the cell. taken, and describe any difficulties
you encountered and how they were
Plot the characteristic curve with air as
• Investigate how the current and overcome.
the oxidant.
voltage vary as the value of the
8. Suggest any ways in which the
resistance load is altered. Start in
experimental procedure may be Explain the difference between the curve
the ‘OPEN’ position, then decrease
improved. obtained using air and the curve
the resistance stepwise. For each
obtained using oxygen.
resistance wait 30 s before noting
the voltage and current. Take
measurements for ‘LAMP’ and
‘MOTOR’.

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 teachers guide

The efficiency of a fuel cell

Apparatus required: • 2 long tubes

• Solar module • 2 short tubes
• Electrolyser • 2 tubing stoppers
• Fuel cell Additional components:
• Load measurement box
• Lamp 100 – 150 Watt
• Connecting leads
• Distilled water
• Stop watch

Safety:
Fig. 1 (storing)
Please follow the operating instructions.

Wear protective goggles and keep

ignition sources at a distance when
experimenting.
Solar modul becomes hot.

A full risk analysis must be undertaken

before beginning any experiment.

Important:
Set up and purge the apparatus exactly as for the experiment on the characteristic curve
of the fuel cell (experiment 6). Follow the first four instructions there precisely.
Then follow the instructions below.

Instructions the power supply of the electrolyser of 5 minutes. Determine the leakage rate
when the hydrogen has reached in ml of hydrogen per minute.
1. Disconnect the solar module from the
the10 ml mark. 4. Reconnect the solar module to the
electrolyser, and close both the short
3. Since the whole system always has a electrolyser and store the gases in
tubes at the gas outlets of the fuel
certain leakage rate because of its tubes the gas storage cylinders. Disconnect
cell with the stoppers (see fig. 1).
and seals, a blank measurement must be the power supply of the electrolyser
2. Reconnect the solar module to the
made first. Record the loss of hydrogen when the hydrogen has reached
electrolyser and store the gases in
from the hydrogen storage cylinder, the10 ml mark.
the gas storage cylinders. Disconnect
without load at the fuel cell, over a period

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 Et7
5. Remove the connecting leads from the record the figures for voltage and
solar module to the electrolyser and current at the fuel cell. Move the rotary
use them to connect the voltmeter of switch to ‘OPEN’ after the 180 seconds.
the load measurement box to the fuel 6. Repeat steps 4 and 5 twice, and
cell (see fig. 2). Adjust the resistance to calculate the average value for the
3Ω. Record the volume of hydrogen amount of hydrogen consumed. After
consumed by the fuel cell from the the measurement, move the rotary
electrolyser’s hydrogen storage cylinder switch to ‘OPEN’ and remove the
in 180 seconds. Also measure and stoppers from the tubes of the fuel cell.

Fig. 2 (determination of efficiency)

Table of results: Fuel cell without load -blank measurement (draw out your own table) Evaluation
t = 5 min 1. Calculate the average volume of
hydrogen, and subtract the volume
Volume loss of hydrogen from storage: Vol = cm3 of hydrogen lost through leakage.

Leakage rate of system: Vol/t = cm3/min 2. Determine the Faraday efficiency

of the fuel cell.
Table of results: Fuel cell with load 3. Determine the energy efficiency
of the fuel cell.
R= Ω I= mA Vol3 = cm3

t= s Vol1 = cm3 Volaverage = cm3

(consumed
V= V Vol2 = cm3 hydrogen)

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 teachers guide continued

Learning objectives
• that comparison of the actual and theoretical volumes of hydrogen used by the cell
enables calculation of the cell’s Faraday efficiency
• that comparison of the electrical energy produced by the cell and the energy
released by combustion of the hydrogen used enables calculation of the energy
efficiency of the cell

Interpretation Therefore 24,000 cm3 H2 gives Energy efficiency = electrical energy /

(2 · 96,500 C) = 193,000 C. theoretical energy content of the
Worked example:
consumed hydrogen.
In this experiment, the fuel cell delivers The molar enthalpy change of
Blank measurement:
233 mA (= 0.233 A) for 180 s. combustion of hydrogen at
t = 5 min
Therefore the theoretical volume of room temperature and pressure
Vol = 1.5 cm3
hydrogen consumption is: is -286 kJ mol–1.
Leakage rate: Vol/t = 0.3 cm3/min
which is 0.9 cm3 in 180s.
Therefore the energy released by
combustion of 5.6 cm3 H2 is:
Fuel cell with load:
R = 3Ω
Therefore the efficiency is:
t = 180 s Vol1 = 6.5 cm3
η = VolH2 (th.)/ VolH (exp.)
V = 0.74 V Vol2 = 6.6 cm3 2
η = 5.2 cm3 / 5.6 cm3
I = 233 mA Vol3 = 6.4 cm3
η = 0.93 (93%) The energy efficiency is:
Volaverage = 6.5 cm3
The Faraday efficiency of the fuel cell
(consumed hydrogen
can be less than one for the following
from storage)
reasons:
• The fuel cell consumes
1. Competing, simultaneous
5.6 (6.5–0.9) cm3 of hydrogen in 180
electrochemical reactions in the fuel
s to supply a current of 233 mA.
cell, which supply fewer electrons for
the same volume of consumed Therefore the energy efficiency of the
Determination of the Faraday
hydrogen. fuel cell at 0.74 V is 47%.
efficiency of the fuel cell
2. Chemical reaction between hydrogen
The Faraday efficiency is the ratio
and oxygen at the catalysts (catalytic Experiment variation:
between the theoretical volume of
oxidation/ combustion). 1. Determine the energy efficiency as a
hydrogen consumed by the load at
3. Hydrogen and oxygen recombination, function of the current flowing
a certain current flow and the
or diffusion, by leakage through the through the fuel cell.
experimentally determined
electrolyte membrane. 2. Set the fuel cell to currents between
consumption of hydrogen.
100 and 500 mA by varying the
η = VolH (th.) / VolH (exp.)
2 2 Extension resistance.
The Faraday efficiency should be 1 (100%). 3. Do not exceed 500 mA!
Determination of the energy
The expected theoretical 4. Determine the current-dependent
efficiency of the fuel cell
consumption of hydrogen can be efficiency and interpret the result.
The energy efficiency of the fuel cell is
calculated. As current increases - i.e. as power
the ratio between the electricity
H2 ➝ 2H+ + 2e–, therefore 1 mole increases - efficiency decreases. This
obtained and the theoretical energy
hydrogen gas gives 2 moles of has major consequences in the design
content of the consumed hydrogen.
electrons. One mole of electrons has a of fuel cells for vehicles: an optimum
charge equal to 96,500 C. point on the power/efficiency curve has
to be found.

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notes

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 student guide

The efficiency of a fuel cell

Apparatus required: • 2 short tubes

• 2 tubing stoppers
• Solar module
• Electrolyser
Additional components:
• Fuel cell
• Load measurement box • Lamp 100 – 150 Watt
• Connecting leads • Distilled water
• 2 long tubes • Photocopy of the diagram on the
• Stop watch laminated sheet in the hydro-Genius kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
The Faraday efficiency of a fuel cell is the ratio between
the theoretical amount of hydrogen used by the cell at
a particular current flow and the amount of hydrogen
found by experiment.

Objectives
To compare the actual volume of hydrogen used by the
fuel cell with the volume which should in theory have
been used to produce a certain amount of electricity,
and so to calculate the Faraday efficiency of the cell.

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 E7
Procedure • Using a resistance of 3Ω investigate
the volume of hydrogen used by the
• Assemble the appropriate
components, as shown in the
cell, in a definite period of time Question
(say 3 minutes), and note the voltage
teacher’s notes, with a lamp, and
and current being produced by the
use the gases produced by the • Give reasons why the Faraday
cell during this time. (Remember that
electrolyser to remove all air from efficiency of a fuel cell is likely
a single measurement may be
the apparatus (‘purging’), exactly to be less than one (i.e. less
unreliable).
as for experiment 6. than 100%).
• Compare the volume which you have
• All the connections must be
measured with the volume of
correctly made, with the correct
hydrogen which should have been 3. Use your results to calculate the
polarity. Check with your teacher
consumed to produce this amount Faraday efficiency.
before proceeding.
of electricity.
4. Evaluate the techniques used in your
• Store gases in the electrolyser, close
experiment, identify any precautions
the exit tubes from the fuel cell, and Results, records taken, and describe any difficulties
measure the rate at which hydrogen
and evaluation you encountered and how they were
leaks from the apparatus over a
1. Draw a circuit diagram and explain overcome.
period of 5 minutes. This leakage
rate must be allowed for in its arrangement. 5. Suggest any ways in which the
subsequent calculations. 2. Construct a suitable table for experimental procedure might be
recording data, either on paper or improved.
• Adjust the apparatus so that the
current and voltage produced by the as a spreadsheet.
fuel cell can be measured at the
same time, using gases stored in the
electrolyser to power the cell.

Extension work Use the information given above to

calculate the energy efficiency of the
1. The energy efficiency of the fuel cell
fuel cell.
is the ratio between the electrical
energy obtained and the calculated
2. (This would be especially appropriate
energy content of the hydrogen used.
if there is more than one group, each
with a kit).
The electrical energy produced / (J)
Investigate how efficiency of the fuel
= voltage /(V) · current/(A) · time/(s).
cell varies with the current.
The amount of energy released when 1
(Note: Do not exceed 500 mA).
mole of hydrogen gas is burned at room
(Note: As power (P=V · I) increases,
temperature and pressure is 286 kJ.
efficiency decreases. This has
(i.e. ∆Hc(H2) = -286 kJ mol–1)
consequences for makers of fuel-cell
1 mol of any gas occupies 24,000 cm3
cars; an optimum point has to be
at room temperature and pressure.
found).

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 teachers guide

Faraday’s first law

using a fuel cell
Apparatus required: • 2 long tubes
• 2 short tubes
• Solar module
• 2 tubing stoppers
• Electrolyser
• Fuel cell
Additional components:
• Load measurement box
• Connecting leads • Lamp 100 – 150 Watt
• Stop watch • Distilled water

Fig.1 (purging)

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

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 Et8
Instructions: supply when the hydrogen has the rotary switch to successively set
reached the 10 ml mark. different current levels by selecting
1. Set up the apparatus as shown in fig.1.
7. Since the whole system always has different resistances (10, 5, 3 and 1Ω).
Make sure all connections have the
a certain leakage rate because of For each resistance value, record in
correct polarity.
its tubes and seals, a blank table 2 the volume of hydrogen
2. Check that the gas tubes are
measurement must be made first. consumed by the fuel cell from the
correctly connected between the
Record the loss of hydrogen from the electrolyser’s hydrogen storage
electrolyser and the fuel cell.
hydrogen storage cylinder, without cylinder during 120 s. After each
Adjust the rotary switch to ‘OPEN’.
load at the fuel cell, over a period of individual measurement, adjust the
3. Make sure both gas storage cylinders
5 minutes. Determine the leakage rotary switch to the ‘OPEN’ position
of the electrolyser are filled up with
rate in cm3 of hydrogen per minute. and refill the hydrogen storage
distilled water to the 0 ml mark. Adjust
8. Reconnect the electrolyser to the cylinder to the 10 ml mark as
the solar module so that there is a
solar module and refill the hydrogen described in section 8.
constant current to the electrolyser of
storage cylinder up to the 10 ml 12. After the final measurement, adjust
between 200 to 300 mA. The solar
mark. Then disconnect the power the rotary switch to ‘OPEN’ and
module and the light source must be
supply to the electrolyser again. remove the stoppers from the tubes
positioned so that steady gas
9. In order to examine the first part of the fuel cell.
production can be observed.
of Faraday’s first law, set a 13. Correct the measured values by
4. Purge the complete system, consisting
constant current by adjusting the subtracting the leakage rate.
of the electrolyser, fuel cell and tubes,
rotary switch of the load
for 5 minutes with the gases released Fig. 2 (storing)
measurement box to a resistance
from the electrolyser. Then put the rotary
of 3Ω. Now record the volume of
switch on the load measurement box to
hydrogen consumed by the fuel cell
3Ω for 3 minutes. The ammeter display
from the electrolyser’s hydrogen
of the load measurement box should
storage cylinder for 4 minutes (60 to
show that a current is flowing. Purge the
240 s in 60 s steps). Record your
system again with the rotary switch
results in table 1. Then rotate the
‘OPEN’ for 3 minutes.
switch to the ‘OPEN’ position.
5. Disconnect the solar module from the
10.R
 econnect the electrolyser to the
electrolyser, and close both the short
solar module and refill the hydrogen
tubes at the outlet nozzles of the fuel
storage cylinder up to the 10 ml
cell using the stoppers (see fig.2).
mark. Then disconnect the solar
6. Reconnect the electrolyser with the
module again.
solar module. The electrolyser will now
11. In order to examine the second
store gas in the storage cylinders.
part of Faraday's first law, use
Disconnect the electrolyser’s power

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 teachers guide continued

Table of results: Fuel cell without load - blank measurement (draw out your own tables)

Volume of hydrogen lost from storage in 5 min = cm3

Leak rate of system = cm3/min

Table 1:
Evaluation:
R= Ω = constant
1. Plot the recorded data from results
I= mA = constant tables 1 and 2 (hydrogen
consumption versus time and
Time / s VolH /cm3 VolH (corrected)/cm3 hydrogen consumption versus
2 2

current).
2. Investigate the connection between
the volume of hydrogen consumed
and the quantity of electricity (in
Table 2: Coulombs) produced (Faraday's first
law).
t= s = constant

Resistance/Ω Current/mA VolH /cm3 VolH (corrected)/cm3

2 2

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 Et8
Learning objectives
• that the volume of hydrogen used by a fuel cell is proportional to time,
with the current being constant
• ... and is also proportional to current, during a constant time interval
• ... and that therefore a fuel cell obeys a form of Faraday’s first law

Interpretation Sample results:

Graph 1 shows that the volume of

hydrogen consumed is proportional to
the time (at a constant current).
Therefore: Vol ∝ t
Graph 2 shows the straight line
relationship between the volume of
hydrogen consumed and the various
currents produced (at constant time).
(1) C
 onsumption of hydrogen as a (2) Consumption of hydrogen as a
Therefore: Vol ∝ I
function of time – Faraday’s first law function of current produced by the
If Vol ∝ t and Vol ∝ I, then: Vol ∝ It (part1) fuel cell – Faraday’s first law (part 2)
It follows that because:
It = charge (Coulombs), volume of
We can now see that an exactly similar
hydrogen consumed ∝ amount of
law applies to the opposite process to
electricity produced.
electrolysis, which occurs in the
Faraday’s first law relates to
hydrogen fuel cell:
electrolysis, and states:
The amount of hydrogen which is
The amount of a substance produced
consumed in a fuel cell is proportional
by a cathode or anode reaction in
to the quantity of electricity produced.
electrolysis is directly proportional to
the quantity of electricity passed
through the electrolytic cell.

notes

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 student guide

Faraday’s first law

using a fuel cell
Apparatus required: • 2 short tubes
• 2 tubing stoppers
• Solar module
• Electrolyser
Additional components:
• Fuel cell
• Load measurement box • Lamp 100 – 150 Watt
• Connecting leads • Distilled water
• 2 long tubes • Photocopy of the diagram on the
• Stop watch laminated sheet in the hydro-Genius kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
Faraday’s first law states: The amount of a substance
produced at a cathode or anode during electrolysis is
directly proportional to the quantity of electricity passed
through the electrolytic cell.

A re-worded form of the law should apply to a

hydrogen fuel cell: The amount of hydrogen which is
consumed in a fuel cell is directly proportional to the
quantity of electricity produced.

Objective
To investigate how the volume of hydrogen used by the fuel cell varies: (1) with time, the
current produced being kept constant; (2) with the current produced, during a constant
time interval; and so to test whether Faraday's first law applies to the fuel cell.

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 E8
Procedure current by using a resistance of 3Ω,
and investigate the rate at which
• Assemble the appropriate
components, as shown in the
hydrogen is used from the storage Questions
cylinder. (Starting with hydrogen at
teacher’s notes, with a lamp, and use
10 ml mark, measure the volume
the gases produced by the electrolyser • Write equations to represent
used after each minute for 4 minutes).
to remove all air from the apparatus the reactions occurring at the
(‘purging’). • Then (refilling the hydrogen storage, anode and cathode in each of
with the switch at ‘OPEN’, before the electrolyser and the
• All connections must be correctly
each run) use different resistances hydrogen fuel cell.
made, with the correct polarity.
(10, 5, 3, 1Ω) to investigate how the • Use the equations to explain
Check with your teacher before
volume of hydrogen consumed varies why you expected Faraday’s
proceeding.
with the current produced by the first law to apply to the fuel cell.
• Purge the complete system for 5 cell, using a constant time interval
minutes with the switch at ‘OPEN’. Put (say, 2 minutes).
the switch box to 3Ω for 4. Use these graphs to test the validity
3 minutes: the ammeter display should Results, records of Faraday’s first law for the fuel cell,
show that a current is flowing. Switch and evaluation 5. Evaluate the techniques used in your
back to ‘OPEN’ and purge for 3 more
1. Draw a circuit diagram and explain experiment, identify any precautions
minutes.
its arrangement. taken, and describe any difficulties
• Store gases in the electrolyser, close you encountered and how they were
2. Construct suitable tables for
the exit tubes from the fuel cell, and overcome.
recording data, either on paper or as
measure the rate at which hydrogen
a spreadsheet. 6. Suggest any ways in which the
leaks from the apparatus over a
experimental procedure might be
period of 5 minutes. This leakage 3. Use your results to plot graphs of (1)
improved.
rate must be allowed for in volume of hydrogen consumed vs
subsequent calculations. time (at constant current) and (2)
volume of hydrogen consumed vs
• Using gases stored in the electrolyser
current (for a constant time interval).
to power the cell, set a constant

Extension work
Use your results and the electrode
equation in the fuel cell to calculate the
number of moles of hydrogen required
to produce 96,500 C of electric charge.
(1 mole of any gas occupies 24,000 cm3
at room temperature and pressure; the
Faraday constant = 96,500 C mol–1).

Comment on the result of your

calculation.

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 student and teacher guide

Rates of reactions
at the electrode

Teachers may wish to use data accumulated from measurements using the
electrolyser and/or the hydrogen fuel cell to broaden experience of calculation in
their students.

The data for this section can be obtained from any experiment in which the rate
at which hydrogen is being produced by the electrolyser, or
being consumed by the hydrogen fuel cell, is being measured.

This section could be used as • The Avogadro constant

an extension for the following • The Faraday efficiency of the electrolyser
experiments: • The efficiency of a fuel cell
• Faraday’s first law using a fuel cell

Additional data Typical calculations might include:

• The rate of production of hydrogen
• The area of the membrane in both
at the membrane, in mol cm–2 hr–1;
the electrolyser and the fuel cell can
• The rate of production of water in
be assumed to be 10 cm2.
the fuel cell, in mol hr–1 and hence in
• Assume that the Faraday efficiency
cm3 hr–1.
of both the electrolyser and the fuel
The results of these calculations may
cell is 1 (100 %).
then be used to discuss points about
the design and operation of fuel cells.

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 E9
Sample calculations: The rate of production of H2 is One mole H2O has a mass of
4.05 · 10–4 mol cm–2 hr–1; see part (a). (2 · 1.0) g+ (16.0) g = 18 g, and a
1. It was found that with a current of
Therefore 4.05 · 10–4 mol H2 requires volume of 18 cm3.
220 mA, 10.0 cm3 of hydrogen was
8.10 · 10–4 mol of H+(aq) ions.
released in the electrolyser in 370 s.
This is the amount of H+ ions Therefore the volume of water
(a) Calculate the rate of production of
discharging on 1 cm2 of cathode produced per hour is:
hydrogen at the membrane, in mol cm–2
surface in one hour. Vol = 18 cm3mol–1· 4.05 · 10–3 mol
hr–1. (1 mole of any gas at room
Vol = 0.073 cm3
temperature and pressure occupies
Therefore the number of hydrogen ions
24,000 cm3).
discharged per unit area per second is:

If 10.0 cm3 H2 is produced in

Possible extensions
370 s, then in 1 hr the volume of (many others are
hydrogen will be: possible):
Calculate the volume of water
(measured at room temperature)
2. If all the hydrogen produced in the produced per hour by a 100 kW
Therefore the amount of hydrogen is: hydrogen fuel cell operating at an
electrolyser (see data at the start of (1))
Therefore the rate of production of energy efficiency of 0.5 (50%). The
is used in the fuel cell, calculate the
amount and volume of water produced molar enthalpy change of combustion
in the fuel cell in one hour. of hydrogen is -286 kJ mol–1.
(Ar(H) = 1.0; Ar(O) = 16.0) If a commercial electrolyser operates at
hydrogen at the membrane is
85% efficiency, calculate the amount of
4.05 · 10–3 mol hr–1. As the membrane
If 10 cm3 H2 is used in 370s, the electrical energy (in kWh) needed to
has an area of 10 cm2, the rate of
consumption of H2 in 1 hour is: produce 1.0 m3 of hydrogen gas at
production per unit surface area is:
room temperature and pressure. (The
Faraday constant = 96,500 C mol­­–1;
1 mole of gas at room temperature
The equation for formation of water is: and pressure occupies 24,000 cm3.)
2H2(g) + O2(g) ➝ 2H2O(l)

(b) Calculate the number of hydrogen Therefore 1 mole hydrogen gives one
ions being discharged on the cathode mole water.
per unit area per second. (The Avogadro The amount of hydrogen consumed in
constant is L = 6.02 x 1023 mol–1). one hour is:

The equation for the cathode process is:

2H+(aq) + 2e– ➝ H2(g)
Therefore 2 moles of hydrogen ions
are needed to produce 1 mole of H2 Therefore in one hour 4.05 · 10–3 mol

molecules. water is produced.

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 teachers guide

Characteristic curve of
the methanol fuel cell

Apparatus required: Additional components:

• Methanol fuel cell • Methanol
• Stock bottle with methanol solution • Distilled water
(1.0 mol dm-3 )
• Load measurement box
• Connecting leads
• Stoppers for tank

Fig. 1

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
A full risk analysis must be undertaken before beginning any experiment.

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Instructions
Fig. 2
Before starting the experiments,
the teacher has to prepare a 1 mol
dm-3 (1M) solution of methanol in
distilled water. This solution has to
be filled into the appropriate stock
bottle. One filling is sufficient for
4–5 experiments. To make the
methanol solution, add deionised
water to 4.0 cm3 methanol until the
total volume is 100 cm; stir
thoroughly.

1. Set up the apparatus as shown in

fig.1. Turn the switch of the load
measurement box to ‘OPEN’.
2. Fix the nozzle to the stock bottle
filled with 1 mol dm-3 (1M) methanol
solution and fill up the fuel cell’s
tank to the upper edge (fig. 2). the switch to ‘OPEN’ for 3 more waited for 60 seconds. Put the
Make sure no air bubbles are in minutes before starting the values in the results table. Take the
the tank. Tap the cell gently on a experiments. The fuel cell should last measurement with the switch in
hard surface to release any that are now be ready for use. the ‘MOTOR’ position.
there. Seal the tank using the plugs. 4. Record the characteristic curve of 5. After recording the characteristic
3. Wait for 5-10 minutes, with the the fuel cell by varying the resistance curve, reset the switch of the load
switch of the load measurement box using the rotary switch of the load measurement box to ‘OPEN’. At the
‘OPEN’. You should then observe an measurement box. Start in the end of the experiment, remove the
off-load voltage of about 500 mV on ‘OPEN’ position, then increase the stoppers from the tanks, replace
the voltmeter. Adjust the resistance resistance stepwise from 1Ω to them in their containers, and pour
for 2 minutes to 3Ω by using the 200Ω. For each value of the the methanol solution down the sink
switch. You should observe a current resistance, record the values for with plenty of cold water.
of about 40 mA on the ammeter. Set voltage and current after you have

Table of results: Draw out your own table

Resistance, R /Ω Voltage, V /V Current, I /mA Power, P/mW

Evaluation 3. Enter the operating voltages and 5. Calculate the motor’s power
currents of the motor in the VI consumption and enter the values
1. Draw the VI characteristic curve of
characteristic curve. in the PI diagram.
the fuel cell.
4. Draw a power-current (PI) diagram.
2. Interpret the characteristic curve.
(Power/W = voltage/V · current/A)

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 teachers guide continued

Learning objectives
• that voltage decreases as the current taken from the fuel cell increases
• the comparison between the characteristic curves of the hydrogen and methanol fuel cells

Interpretation long as sufficient fuel is supplied, the

fuel cell continues to deliver a current.
During the recording of the fuel cell’s
The theoretical voltage of a
characteristic curve, variations in
methanol fuel cell is 1.21 V. In practice,
voltage and current can occur. These
depending on the current load, the
variations are quite normal. They
voltage is somewhere between 0.6 and
depend on the history of the cell
0.2 V. The electrode material (catalyst),
(e.g. duration of operation before the
the internal resistance, the temperature,
relevant experiment, dryness of the
as well as the amount of methanol at
membrane, waiting period since filling
the anode and the amount of oxygen
with methanol.)
from the air at the cathode, all influence
the magnitude of the current.
difference is that both electrodes are
At very small or no current drain,
made of very precious metal, i.e.
the fuel cell shows a voltage of 0.5 to
platinum or ruthenium. At these metal
0.6 V. This voltage is called the off-load
electrodes catalysed chemical reactions
voltage (as for the battery). The more
take place; the metals themselves are
current is drawn from the fuel cell, the
not subject to reaction.
smaller the voltage becomes. As the
At the anode the fuel, in this case
voltage decreases, the current
methanol, is supplied; at the cathode,
Characteristic curve of the methanol increases exponentially.
oxygen from the air is fed in.
fuel cell
The following reactions occur:
In order to understand the Anode:
characteristic curve of a fuel cell, it is CH3OH(l) + H20(l)
helpful to recall the fundamental ➝ CO2(g) + 6H+(aq) + 6e–
principles of a battery. Cathode:
A battery consists of 2 separate 1.5 O2(g)+ 6H+(aq) + 6e–
half-cells, which often contain metals ➝ 3H2O(l)
or alloys as the electrodes. These Overall reaction:
electrodes are subject to different CH3OH(l) + 1.5 02(g) Power curve of the methanol fuel cell
chemical reactions when the battery ➝ CO2(g) + 2H2O(l)
If the power of the electric motor
generates current. Both electrodes are The oxidation of methanol at
is entered in the PI diagram, it can be
changed chemically, and eventually no the anode causes emission of
seen that the motor does not run at
more reaction is possible and the battery electrons. These electrons pass through
the optimum point; i.e. more power can
is discharged. In any battery or fuel cell, the external circuit, and return to the
be drawn from the methanol fuel cell.
the anode is where oxidation occurs and cathode to reduce the oxygen from the
In commercial practice, efforts
electrons are released into the external air. The hydrogen ions produced at the
are made to draw as much current as
circuit. The anode therefore becomes anode pass through the electrolyte
possible from the fuel cell (i.e.
the negative terminal. Reduction occurs (here, the proton conducting
maximum output). However, the
at the cathode as electrons flow in from membrane) towards the cathode. At the
efficiency of the fuel cell declines at
the external circuit; the cathode anode the oxidation product is CO2. At
high current values, so it is necessary
therefore becomes the positive terminal. the cathode oxygen is reduced to water.
to find an optimum operating point
The methanol fuel cell also In contrast to the battery, the fuel
(high efficiency, high output).
consists of 2 half-cells. The major cell is not used up and discharged. As

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Extension After filling the fuel cell, the > 500 mV 10 min. after the cell is filled
electrolyte membrane bulges slightly, with methanol. The reasons mentioned
Sample calculation
whereas it shrinks slightly when it is dry. above may delay the start-up. The
As one dm–3 of 1.0 mol dm–3 (1.0 M)
This behaviour is unpredictable and voltage can vary strongly, and may be
aqueous methanol contains 1.0 mol
cannot be influenced. As a result, limited to 400 mV.
CH3OH, then 10.0 cm3 (which is the
variations in the cell’s current can If this happens, the following
approximate capacity of the fuel tank)
occur, or the start-up time, particularly procedures are recommended in order
contains 0.01 mol. The molar enthalpy
when the cell has been dry for a long to improve the voltage and stabilise the
change of combustion of methanol is
period, may be extended. system, so ensuring reliable data.
-726 kJ mol–1.
The tank and the porous electrode 1. Wait for a few more minutes before
Therefore 0.01 mol would release 7.26 kJ.
structure always contain tiny bubbles of starting the experiment. Shake the
If the constant power output of
oxygen from the air. Directly after filling, cell several times or tap it lightly on
the cell is 8.0 mW, then the time taken
this may lead to development of a hard surface. Usually, this
to provide 7.26 kJ of energy is:
potentials from competing reactions. increases the voltage to more than
Consequently the off-load voltage will not 500 mV.
reach its maximum value. The instructions 2. Connect the fuel cell to the load
therefore contain the advice that no air measurement box and set the
Therefore, assuming an efficiency of
bubbles must be left in the tank. switch to 1Ω for 2 minutes. After
30%, the cell should run for 75 h. This
The oxidation of methanol is a that, wait 3 more minutes with the
is not possible in practice with this
complex reaction. The final product is rotary switch in the ‘OPEN’
methanol fuel cell, as carbon dioxide
CO2. However, small amounts of position. The off-load voltage
builds up in the anode tank and is
preoxidation products are formed, e.g. should now be above 500 mV.
difficult to remove.
methanoic acid, HCOOH. Any such Only rarely will the off-load
materials affect the potential at the voltage not exceed 500 mV after such
Tips and tricks methanol anode, and may lead to a treatment. If it does stay below 500 mV,
for operating the reduction of both voltage and current. you can nevertheless perform your
methanol fuel cell All the above effects may lead to experiments, e.g. drive the electric

The voltage and current of a methanol fluctuations in voltage and current from motor. When the cell is next used (it

fuel cell depend much more on how the one experiment to another. This is having dried out in between), this

cell has been treated than they would quite normal. problem most probably will not re-

for a hydrogen fuel cell. The off-load voltage (with the occur.

Here are some of the reasons for this. switch at ‘OPEN’) should have reached

notes

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 student guide

Characteristic curve of
the methanol fuel cell

Apparatus required: Additional components:

• Methanol fuel cell • Methanol
• Stock bottle with methanol solution • Distilled water
(1.0 mol dm-3 ) • Photocopy of the diagram on the laminated
• Load measurement box sheet in the methanol fuel cell kit
• Connecting leads
• Stoppers for tank

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
A full risk analysis must be undertaken before beginning any experiment.

Note:
The one mol dm-3 (1.0 M) methanol solution used in this experiment must be prepared
by the teacher

Introduction
A suitably constructed fuel cell can use methanol as
a fuel, with the methanol in dilute aqueous solution.

The behaviour of the methanol fuel cell differs from that

of the hydrogen cell. The methanol is oxidised directly
to carbon dioxide. (Note: The direct methanol fuel cell
is not the same as a cell using reformed methanol).

Objectives
To investigate how the current produced by the
methanol fuel cell varies with the voltage.

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 E10
Procedure ‘OPEN’. You should then observe an
off-load voltage of about 500 mV on
It will be necessary to read
carefully the instructions on loading
the voltmeter. Adjust the resistance Questions
for 2 minutes to 3Ω by using the
and starting-up the methanol fuel
switch. You should observe a current
cell which are provided with the • What are the major differences
of about 40 mA on the ammeter. Set
methanol fuel cell kit. in behaviour between the
the switch to ‘OPEN’ for 3 more
hydrogen fuel cell and the
• All connections must be correctly minutes before starting the
methanol fuel cell?
made, with the correct polarity. experiments. The fuel cell should
• Discuss briefly the advantages
Check with your teacher before now be ready for use.
and disadvantages of each
proceeding.
• Investigate how the current and type for commercial use.
• Set up the apparatus as shown in the voltage vary as the value of the
teachers’ notes. Turn the switch of resistance load is altered stepwise
the load measurement box to ‘OPEN’. from 1Ω to 200Ω. After switching to 6. Comment on the shape of the curve.
• Fix the nozzle to the stock bottle a new resistance, wait for 60s before
7. Evaluate the techniques used in your
filled with 1 mol dm-3 (1M) methanol taking readings.
experiment, identify any precautions
solution and fill up the fuel cell’s taken, and describe any difficulties
tank to the upper edge. Seal the Results, records you encountered and how they were
tank using the plugs. Make sure no and evaluation overcome.
air bubbles are in the tank. Tap the
1. Draw a circuit diagram and explain 8. Suggest any ways in which the
cell gently on a hard surface to
its arrangement. experimental procedure may be
release them.
2. Construct a suitable results table for improved.
• The fuel tank of the cell must be
recording your data, either on paper
carefully loaded (so that there are no Note: It may be convenient to combine
or as a spreadsheet.
air bubbles) and stoppered. The cell this experiment with experiment 11,
must then be connected to the load 3. Plot the characteristic curve (VI) for
The effect of varying concentrations on
measurement box so that the current the cell (with the voltage on the
the methanol fuel cell.
and voltage produced by the fuel cell vertical axis) and find the maximum
can be measured at the same time. voltage obtainable from the methanol
The start-up procedure must be fuel cell.
followed before any readings are 4. Comment on the shape of the curve.
taken.
5. Plot the power curve (PI) for the cell
• Wait for 5-10 minutes, with the (with power in mW on the vertical axis).
switch of the load measurement box

Extension work The formation of gas makes it difficult At the maximum of its power curve,
to keep this small laboratory direct how long should your methanol fuel
You may notice a bubble of gas
methanol fuel cell running continuously cell run on a single (10.0 cm3) filling of
appearing at the top of the fuel tank
for very long periods. We can, however, 1.0 mol dm-3 (1.0 M) aqueous methanol,
after the fuel cell has been running for
do a calculation to work out how long assuming an energy efficiency of 30%?
some time (1 hr). What do you think this
the cell should be able to run! (The molar enthalpy change of
gas is?
combustion of methanol,
∆ Hc (CH3OH), is -726 kJ mol-1).

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 teachers guide

The effect of varying

concentrations on the
methanol fuel cell

Apparatus required: • Pipette

• Tank stoppers
• M ethanol fuel cell
• Load measurement box
• Stock bottle with 0.25 mol dm–3 (0.25M)
• Connecting leads
methanol solution
• Stock bottle with 0.5 mol dm–3 (0.5M)
Additional components:
methanol solution
• Stock bottle with 1.0 mol dm–3 (1.0 M) • Methanol
methanol solution • Distilled water

Fig. 1

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
A full risk analysis must be undertaken before beginning any experiment.

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 Et11
Instructions solution, first make 4.0 cm3 of 1-4. Follow exactly the instructions
methanol up to 100 cm3 with given in instructions 1–4 in the
Before starting the experiments,
deionised water and stir. This is previous experiment, except that
the teacher has to prepare the
now a 1 mol dm–3 (I.0 M) solution. the first solution used should
required solutions of methanol
Put 50 cm3 of this into the correct be 0.25 mol dm–3 methanol.
(1 mol dm–3, 0.5 mol dm–3
stock bottle. To the other 50 cm3, 5. Reset the switch of the load
0.25 mol dm–3) in distilled water.
add 50 cm3 deionised water and measurement box to ‘OPEN’, remove
The preparation of the 0.5 and
stir. Put 50 cm3 of this mixture into the stoppers from the tanks and
0.25 mol dm–3 solution is best done
the 0.5 M bottle. To the other 50 cm3, pour the methanol solution down
by accurate dilution of the 1.0 mol
add 50 cm3 deionised water and stir. the sink with plenty of cold water.
dm–3 solution. The solution must be
Put 50 cm3 of this mixture into the 6. Repeat steps 1–5, first with the 0.5
put into the appropriate stock
0.25 M bottle and pour the rest down mol–3 (0.5 M) methanol solution, and
bottles. One filling is sufficient for
the sink. then with the 1.0 mol dm–3 (1.0 M)
4–5 experiments. To make up the
methanol solution.

Table of results: Draw out your own table

0.25 mol dm–3 (0.25 M) 0.5 mol dm–3 (0.5 M) 1.0 mol dm–3 (1.0 M)

Resistance/Ω Voltage/V Current/mA Voltage /V Current/mA Voltage /V Current / mA

Evaluation 2. Draw the PI diagrams (power versus 3. Interpret the results.

current) for the different methanol
1. On the same piece of graph paper,
concentrations.
draw the VI characteristic curves
(Remember that power/W =
of the fuel cell at the different
voltage/V · current/A, so that power/
methanol concentrations.
mW = voltage/V · current/mA).

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 teachers guide continued

Learning objectives
• that the performance of the methanol fuel cell depends on the concentration
of the methanol solutions
• that the shape of the characteristic curve can be explained in terms of catalytic
processes and diffusion within the cell as well as by resistance

Interpretation towards the electrode (transport by

diffusion), e.g. by how much methanol
During the experiment variations in
arrives at the catalyst in a given time.
voltage and current can occur. These
The above experiment clearly
variations often happen. They depend
demonstrates the last effect. The
on the history of the cell (e.g. duration
magnitude of the current depends
of operation before the relevant
directly on the methanol concentration.
experiment, dryness of the membrane,
This current is called ‘diffusion current’,
waiting period since filling with
because it is determined by transport
methanol.)
of reactant to electrode.
This all has relevance for the
commercial application of the
methanol fuel cell, for example in cars.
Research is directed towards attaining
a maximum power density for the fuel
catalytic processes at the electrode
cells. The power curve indicates that in
(i.e. the type of, amount of, and
practice the highest possible methanol
distribution of the catalyst).
concentration should be used.
Characteristic curve of the methanol Furthermore the entire resistance of
Compared with the technical
fuel cell as a function of the methanol the cell (i.e. the metal, membrane,
concentration (sample results) development of the hydrogen fuel cell,
electric contacts, etc) influences the
the methanol fuel cell is still far behind.
The experiments show that the magnitude of the current. If the
The direct methanol fuel cell shows
magnitude of the current depends on resistance becomes too large, the fuel
many advantages because of its simple
the amount of methanol in the cell clearly loses performance.
technical structure (current generation
solution. This can be observed from the At higher current density, the
direct from a fluid fuel), so in many
graph; for instance, at the line drawn at magnitude of the current is also
places development is under way for
0.1 V it can be seen that the current is influenced by transport of reactants
practical applications. The major target
roughly proportional to the methanol
is to increase the fuel cell’s power
concentration.
density and lifetime. An important
A VI curve like the one of a
consideration is that the methanol fuel
methanol fuel cell can usually be
cell releases carbon dioxide to the
separated into three different parts,
atmosphere, although far less than an
as the following diagram shows.
internal combustion engine of equal
At voltages close to the off-load
power.
voltage, the current increases
Tips and tricks for operating the methanol
exponentially as the voltage decreases.
Power curve of the methanol fuel cell as
fuel cell: see the end of the notes for the previous
The magnitude of the current in this
a function of the methanol concentration experiment.
part of the graph is determined by the

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notes

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 student guide

The effect of varying

concentrations on the
methanol fuel cell

Apparatus required: • Pipette

• Tank stoppers
• M ethanol fuel cell
• Load measurement box
• Stock bottle with 0.25 mol dm–3 (0.25M)
• Connecting leads
methanol solution
• Stock bottle with 0.5 mol dm–3 (0.5M)
Additional components:
methanol solution
• Stock bottle with 1.0 mol dm–3 (1.0 M) • Methanol
methanol solution • Distilled water
• Photocopy of the diagram on the laminated
sheet in the methanol fuel cell kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
The aqueous methanol solutions used in this experiment should be prepared by the
teacher.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
This experiment follows on from experiment 10,
the characteristic curve of the methanol fuel cell,
and it may be convenient to combine the two.

Objectives
To investigate the behaviour of the methanol fuel cell
when different concentrations of aqueous methanol
are used.

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Procedure Results, records
It will be necessary to read carefully
the instructions on loading and
and evaluation
1. Draw a circuit diagram and explain
Questions
starting-up the methanol fuel cell, its arrangement.
as for experiment 10. • What processes occurring in
2. Construct a suitable results table for
the fuel cell might affect the
• All connections must be correctly recording your data, either on paper
nature of the characteristic
made, with the correct polarity. or as a spreadsheet.
curve?
Check with your teacher before
3. Plot the characteristic curve (VI) for • What evidence for these
proceeding.
each methanol concentration on the processes is provided by your
• The fuel tank of the cell must be same graph (with the voltage on the results?
carefully loaded (so that there are no vertical axis).
air bubbles) and stoppered. The cell
4. Comment on the curves obtained.
must then be connected to the load
measurement box so that the current 5. Plot the power curve (PI) for each
and voltage produced by the fuel cell methanol concentration on the same
can be measured at the same time. graph (with power in mW on the
The start-up procedure must be vertical axis).
followed before any readings are 6. Comment on the curves obtained.
taken.
7. Evaluate the techniques used in your
• It has found to be better for the experiment, identify any precautions
operation of the methanol fuel cell if taken, and describe any difficulties
lower concentrations are used first in you encountered and how they were
this experiment. The sequence overcome.
therefore should be: first, 0.25 mol
8. Suggest any ways in which the
dm–3 (0.25 M) methanol, then 0.5
experimental procedure may be
mol dm–3 and finally 1.0 mol dm–3.
improved.
• For each concentration, investigate
how the current and voltage vary as
the value of the resistance load is
increased stepwise from 1Ω to 200Ω.
After switching to a new resistance,
wait for 60 s before taking readings.

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 teachers guide

The dismantlable fuel cell

– impact of catalyst load on
the characteristic curve
Apparatus required: Components from science kit,
solar hydrogen technology:
• D ismantlable fuel cell with membrane
0.3 mg/cm2 Pt, hydrogen and oxygen • Solar module
cover plates, mounted according to • Electrolyser
illustrated set-up instruction • Connecting leads
• Additional membrane 0.1 mg/cm2 Pt • 2 long tubes
(the membrane is marked) • 2 short tubes
• Hexagon key • 2 tubing stoppers
• Spanner • Load measurement box

Additional components:
• Lamp 100 – 150 Watt
• Distilled water

Fig. 1 (purging)

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

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Instructions 3 minutes. The ammeter display of the ‘OPEN’ position, then decrease the
load measurement box should show that resistance stepwise by turning the
Important note to the teacher:
a current is flowing. Purge the system rotary switch to the right. For each
The operating instructions and
again with the rotary switch ‘OPEN’ for 3 resistance, record the values for
diagrams for the dismantlable fuel
minutes. voltage and current after you have
cell extension kit to the solar
5. Disconnect the solar module from waited for 30 sec. Put the values in
hydrogen technology kit are
the electrolyser, and close both the the results table.
required, so that the fuel cell can
short tubes at the gas outlets of the 9. After recording the characteristic
be efficiently taken apart and put
fuel cell with the stoppers (see fig.2). curve, reset the rotary switch of the
together again, and so that it may
load measurement box to ‘OPEN’,
be operated safely.
and remove the stoppers from the
Perform the first experiment with Fig 2 (storing)
tubes of the fuel cell.
the membrane containing 0.3 mg/cm2
10. Dismantle the fuel cell exactly
of Pt catalyst. Make sure the two cover
according to the illustrated
plates are 7 mm apart.
operating instructions booklet,
1. Set up the apparatus as shown in fig.1.
and replace the membrane by the
Make sure all connections have the
one containing 0.1 mg/cm2 of Pt
correct polarity.
catalyst. Make sure the two cover
2. Check that the gas tubes are
plates are 7 mm apart.
correctly connected between the
11. Purge the apparatus, and store the
electrolyser and the fuel cell.
gas, exactly as before. When the
Adjust the rotary switch to ‘OPEN’.
6. Reconnect the solar module to the fuel cell is ready, repeat instructions
3. Make sure both of the gas storage
electrolyser, and store the gases in 8 and 9 above.
cylinders of the electrolyser are filled
the gas storage cylinders. Disconnect 12. After the experiment, dismantle the
up with distilled water to the 0 ml mark.
the power supply of the electrolyser fuel cell using the operating
Adjust the solar module so that there is
when the hydrogen has reached the instructions booklet, and
a constant current to the electrolyser
10 ml mark. assemble it again with the
of between 200 to 300 mA. The solar
7. Remove the connecting leads from membrane containing 0.3 mg/cm2 Pt
module and the light source must be
the solar module to the electrolyser, catalyst, so returning to the original
positioned so that steady gas
and use them to connect the set-up.
production can be observed.
voltmeter of the load measurement
4. Purge the complete system, consisting of
box with the fuel cell.
the electrolyser, fuel cell and tubes, for 5
8. Record the characteristic curve, by
minutes with the gases released from the
varying the resistance using the
electrolyser. Then put the rotary switch
rotary switch of the load
on the load measurement box to 3Ω for
measurement box. Start in the

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 teachers guide continued

Table of results: Draw out your own table

0.1 mg/cm2 Pt catalyst 0.3 mg/cm2 Pt catalyst

Resistance/Ω Voltage /V Current/mA Voltage /V Current / mA

Evaluation
1. On the same graph paper, draw the VI (voltage–current) characteristic curve of the fuel cell with each catalyst loading.
2. Draw the PI (power-current) curves.
3. Interpret the results.

Learning objectives
• that the performance of the hydrogen fuel cell depends to a great extent on the
nature
of the catalyst, i.e. particle size, and the amount per unit area
• that changing the amount of catalyst per unit area (keeping particle size constant)
affects the power output of the fuel cell
• ... but the effect is not directly proportional to the catalyst loading

Interpretation Extension:
Use the 0.47Ω resistance provided in
the dismantlable fuel cell kit (simply
plug it into one of the connector points
of the cell), and find the VI and PI
curves of the new assembly as before.
Comment on how these curves
compare with those already obtained.
Power output of the fuel cell as a
[Increasing the internal resistance is
function of catalyst loading
found to reduce the power output; fuel
Characteristic curve of the fuel cell as a
function of catalyst loading (sample cells should therefore be designed to
results) It can be seen here that, although minimise internal resistance].
lowering the catalyst loading (keeping For further discussion of the effect of
For general interpretation of the VI and particle size the same) has some effect resistance, see experiment 11 in the
PI curves, see the characteristic curve of the on power output, the power does not Physics book.
fuel cell, experiment 6. drop in proportion to the catalyst

In the early days of hydrogen fuel cells, loading. A dramatic lowering of catalyst

the cost of the platinum (or other loadings without much loss in power

platinum-group metal) catalyst was a density has helped make fuel cells

major part of the cost of a fuel cell commercially viable. This point is

assembly. discussed further in the Research

Note Book on ‘Getting the cost down’.

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notes

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 student guide

The dismantlable fuel cell

– impact of catalyst load on
the characteristic curve

Apparatus required:
• D ismantlable fuel cell with membrane 0.3 • Electrolyser
mg/cm2 Pt, hydrogen and oxygen cover • Connecting leads
plates, mounted according to illustrated • 2 long tubes
set-up instruction • 2 short tubes
• Additional membrane 0.1 mg/cm2 Pt • 2 tubing stoppers
(membrane marked) • Load measurement box
• Hexagon key
• Spanner Additional components:
 • Lamp 100 – 150 Watt
Components from science kit, solar • Distilled water
hydrogen technology: • Photocopy of the diagram on the laminated
• Solar module sheet in the dismantlable fuel cell kit

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction
The performance of a hydrogen fuel cell depends to a
considerable extent on the nature of the catalyst, the size
of the catalyst particles, and the amount of catalyst per unit
area of the membrane electrolyte assembly.

In this experiment, the two membranes contain the same

catalyst distributed over the membrane in the same
particle size, but in different quantities.
Objectives
To investigate how the characteristic curve of a hydrogen fuel cell changes with
different catalyst loadings.

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Procedure resistance value, wait for 30 seconds Extension:
before taking the readings.
Important note: It will be necessary Use the 0.47Ω resistance provided in
to follow carefully the operating • Dismantle the fuel cell, following the dismantlable fuel cell kit to
instructions and diagram for the the instructions precisely, and fit the investigate how the internal resistance
dismantlable fuel cell extension kit to membrane which has 0.1 mg/cm2 of of the cell affects its performance.
the solar hydrogen technology kit. platinum.
It is essential that the fuel cell • Purge the apparatus as before and
is efficiently and carefully taken
apart and put together again, and
then again investigate how the
current and voltage vary as the value
Question
that the membranes are not of the resistance load is altered.
damaged in any way. • From your observations, what

Results, records suggestions can you make

• All connections must be correctly
about the ideal membrane
made, with the correct polarity. and evaluation
catalyst loading in commercial
Check with your teacher before
1. Draw a circuit diagram and hydrogen fuel cells?
proceeding.
explain its arrangement.
• Assemble the appropriate
2. Construct a suitable results table for
components, with a lamp, and using
recording your data, either on paper
the fuel cell containing the
or as a spreadsheet.
membrane with 0.3 mg/cm2 of
platinum. Use the gases produced 3. On the same graph, plot the
by the electrolyser to remove all air characteristic curve (VI) for the cell
from the apparatus (‘purging’). Purge (with voltage on the vertical axis) for
the complete system for 5 minutes both membranes.
with the switch at ‘OPEN’. Put the 4. Comment on the curves obtained.
switch box to 3Ω for 3 minutes: the
5. On another graph, plot both power
ammeter display should show that a
curves (PI) for the membranes (with
current is flowing. Switch back to
power in mW on the vertical axis).
‘OPEN’ and purge for 3 more minutes.
Then adjust the apparatus so that 6. Comment on the curves obtained.
the current and voltage produced by 7. Evaluate the techniques used in your
the fuel cell can be measured at the experiment, identify any precautions
same time, using gases stored in the taken, and describe any difficulties
electrolyser to power the cell. you encountered and how they were
• Investigate how the current and overcome.
voltage vary as the value of the 8. Suggest any ways in which the
resistance load is altered stepwise experimental procedure may be
from ‘OPEN’ to 1Ω. For each improved.

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 teacher guide

Impact of the gas supply on

the characteristic curve
of the fuel cell

Apparatus required: Components from science kit,

solar hydrogen technology:
• D ismantlable fuel cell with membrane
0.3 mg/cm2 Pt, hydrogen and oxygen • Electrolyser
cover plates, mounted according to • Solar module
illustrated set-up instruction • Load measurement box
• Cover plate with air inlet slits • Connecting leads
• Hexagon key • 2 long tubes
• Spanner • 2 short tubes
• 2 tubing stoppers

Additional components:
• Lamp 100 – 150 Watt
• Distilled water

Safety:
Fig. 1 (recording the characteristic curve using oxygen)
Please follow the
operating instructions.
Wear protective goggles
and keep ignition sources
at a distance when
experimenting.
Solar module becomes
hot.
A full risk analysis must
be undertaken before
beginning any experiment.

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Instructions
Fig. 2 (recording the characteristic curve using air supplied through the nozzles)
Important: Set up and purge the
apparatus, and store the gases,
exactly as for the experiment on the
characteristic curve of the fuel cell,
experiment 6. Follow the first seven
instructions there precisely. Then
follow the instructions below.
Perform the experiment with the
membrane containing 0.3 mg/cm2 of Pt
catalyst. Make sure the two cover
plates are 7 mm apart.
1. Record the characteristic curve, using
the set up in fig.1, by varying the
resistance with the rotary switch of
the load measurement box. 5. Dismantle the fuel cell exactly each measurement point before
Start in the ‘OPEN’ position, then according to the illustrated operating reading the values for the
decrease the resistance stepwise by instructions, and replace the oxygen characteristic curve.
turning the rotary switch to the right. cover plate by the one equipped with 7. After the experiment, dismantle the
For each resistance, record the air inlet slits. Make sure the two fuel cell using the operating
values for voltage and current after cover plates are 7 mm apart. instructions booklet, and assemble
you have waited for 30 sec. 6. The fuel cell is now supplied with it again with the oxygen cover plate.
Put the values in the results table. oxygen from the air which enters the This will return the cell to the original
2. After recording the characteristic fuel cell through the air inlet slits. set-up.
curve, reset the rotary switch of the The experiment is repeated,
load measurement box back to including purging the apparatus with
‘OPEN’ and remove the stoppers only hydrogen being taken from the
from the tubes of the fuel cell. electrolyser’s storage cylinders (see
3. Now remove the tubes on the fig 3). Wait for approx. 1 minute at
oxygen side of the fuel cell. The
oxygen for the fuel cell now has to Fig. 3 (recording the characteristic curve using air supplied through inlet slits)
come from air, which enters the fuel
cell through the nozzles. The
experiment is repeated, including
purging the apparatus, with only
hydrogen being taken from the
electrolyser’s storage cylinders
(See fig.2).
4. Record measurements as described
in point 1, but at each resistance
value wait for 2 minutes before
reading the values of voltage and
current, because reaching
equilibrium using air takes longer
than with oxygen.

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 teacher guide

Table of results: Draw out your own table

Oxygen Air through nozzles Air through inlet slits

Resistance/Ω Voltage/V Current/mA Voltage /V Current/mA Voltage /V Current / mA

Evaluation
1. On the same graph paper, draw the
three VI characteristic curves of the
fuel cell, and label the curves
according to the different oxygen/air
supply.
2. On another piece of graph paper,
draw the three power curves (PI).
3. Interpret the results.

Learning objective
• t hat the behaviour of the fuel cell depends on the supply of oxidant (in this case,
oxygen, either from the electrolyser or from air)

Interpretation
The curves show that the power
available from the cell is influenced by
gas diffusion. It depends on the rate at
which oxygen can reach the cathode.
Diffusion of oxygen from the air
through the gas nozzles in the oxygen
cover plate is very slow; diffusion
through the cover plate with air inlet Characteristic curve as a function of Power output as a function of oxygen
oxygen supply supply
slits is faster, but cannot equal the
supply of oxygen from the electrolyser.

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notes

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 student guide

Impact of the gas supply on

the characteristic curve
of the fuel cell
Apparatus required:
• Solar module
• D ismantlable fuel cell with membrane
• Load measurement box
0.3 mg/cm2 Pt, hydrogen and oxygen
• Connecting cables
cover plates, mounted according to
• 2 long tubes
illustrated set-up instruction
• 2 short tubes
• Cover plate with air inlet slits
• 2 tubing stoppers
• Hexagon key
• Spanner
Additional components:
 omponents from science kit, solar
C • Lamp 100 – 150 Watt
hydrogen technology: • Distilled water
• Photocopy of the diagram on the
• Electrolyser
laminated sheet in the dismantlable
fuel cell kit

Safety: Please follow the operating instruction.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Introduction

One of the factors which affects the performance of a fuel cell

is the rate at which the gases are supplied. In this experiment
the rate at which the oxidant, oxygen, supplied by the
electrolyser or oxygen in air, can get to the cathode is
controlled. Unless there is a positive pressure behind the
oxygen to assist the process – as is the case when the
oxygen is being produced in the electrolyser – oxygen can
only reach the cathode by diffusion.
Objectives
To investigate the dependence of the characteristic curve of the hydrogen fuel cell
on the supply of oxygen.

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Procedure resistance value wait for two
minutes before reading the values
Important note: It will be necessary
to follow carefully the operating
of voltage and current. Questions
instructions and diagrams for the • Then dismantle the fuel cell,
dismantlable fuel cell extension kit following the instructions precisely, • What do your results tell you
to the solar hydrogen technology and replace the oxygen cover plate about the design of
kit. by the one equipped with air inlet commercial fuel cells?
slits (fig. 3 in teacher guide). Make • Why did you have to wait for
• All connections must be correctly sure the two cover plates are 7 mm different time intervals before
made, with the correct polarity. apart. Repeat the experiment, after taking readings during the
Check with your teacher before purging etc., but at each resistance three experimental runs?
proceeding. value wait for about one minute
before reading the values of voltage
• Assemble the appropriate
and current. 8. Suggest any ways in which the
components, with a lamp, and using
experimental procedure may be
the fuel cell containing the
membrane with 0.3 mg/cm2 of Results, records improved.

platinum. Use the gases produced by and evaluation

the electrolyser to remove all air from 1. Draw a circuit diagram and explain
the apparatus (‘purging’), exactly as its arrangement.
for experiment 6. Then adjust the
2. Construct a suitable results table for
apparatus so that the current and
recording your data, either on paper
voltage produced by the fuel cell can
or as a spreadsheet.
be measured at the same time, using
gases stored in the electrolyser to 3. On the same graph, plot the
power the cell (see fig.1 in teacher characteristic curve (VI) for the cell
guide). (with voltage on the vertical axis) for
all three arrangements.
• Investigate how the current and
voltage vary as the resistance load is 4. Comment on the curves obtained.
altered stepwise from ‘OPEN’ to 1Ω.
5. On another graph, plot all three
For each resistance value, wait for 30
power curves (with power in mW on
seconds before taking the readings.
the vertical axis).
• Then remove the tubes on the
6. Comment on the curves obtained.
oxygen side of the fuel cell, so that
air can only get into the cell through 7. Evaluate the techniques used in your

the nozzles (fig.2 in teacher guide). experiment, identify any precautions

Repeat the experiment after again taken, and describe any difficulties

purging the apparatus and refilling you encountered and how they were

the hydrogen store in the overcome.

electrolyser. Vary the resistance as

described above, but at each

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 student and teacher guide

Team project: comparing

the hydrogen fuel cell
with the methanol fuel cell

This activity can be used when both a hydrogen fuel cell kit and a methanol fuel
cell kit are available, and when students have not already performed the
experiments mentioned below.

One group should use the hydrogen cell, and another group the
methanol cell.

Suitable experiments for making • T

 he characteristic curve (and power curve)
comparisons are: of the hydrogen fuel cell, experiment 6.
• The characteristic curve (and power curve)
of the methanol fuel cell, experiment 10.

Safety: Please follow the operating instructions.

Wear protective goggles and keep ignition sources at a distance when experimenting.
Solar module becomes hot.
A full risk analysis must be undertaken before beginning any experiment.

Objectives
To make comparisons between the hydrogen fuel cell and the methanol fuel cell.

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 E14
Procedure Results, records 3. It is expected that the team will be

and evaluation able to think of other points.

Each group should carry out their
experiment by following the procedures 1. The recommendations concerning 4. Each point should be discussed and
detailed in the section which deals with recording and evaluating results its importance assessed. The
that experiment, especially producing which are made in the student guide Research Notes and other resource
the characteristic and power curves. to the appropriate experiment material may be used.

should be followed by each group. 5. Each student should then write a

2. The members of the two groups brief report. The report should

should then, as a team, draw up a provide a balanced view, supported

list of points to use in comparing by evidence, of the advantages and

the two cells. disadvantages of each of the two


Such a list might include, for example: types of cell.

• Ease of fuelling.
• Problems in operation.
• The shapes of the characteristic
curves.
• The shapes of the power curves.
• The implications for commercial
use of each point of comparison.

notes

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 student and teacher guide

Theoretical principles
behind fuel cells
1. Principles of operation and general characteristics

Fuel cells are highly efficient electrochemical electricity generators. The principle of the
fuel cell is much simpler than that of conventional power generation, since the cell
converts the carrier of chemical energy directly into electrical energy.

Fig. 1 The fuel cell compared to conventional power-generation processes

The basic principle behind the fuel cathode with the oxidant; the accepting the electrons. The flow of
cell is the direct generation of electrolyte connects the two electrons through the external circuit
electricity using a fuel (e.g. electrodes. can be used to perform work.
hydrogen) and an oxidant (oxygen) The fuel is oxidised at the anode The transfer of charge within the
in an electrochemical process. (negative pole). The electrons released fuel cell is carried out by the movement
A fuel cell consists of two during this process flow via the external of the ions through the electrolyte.
electrodes and the electrolyte. The circuit to the cathode (positive pole).
anode is supplied with the fuel and the Here the oxidant is reduced by

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Hence, like a battery or an accumulator,
Fig. 2 Principle of operation of
the fuel cell
a fuel cell supplies energy from an
electrochemical process. The essential
difference between a fuel cell and the
others is, however, that the electrodes
of the fuel cell are not chemically
changed, i.e. the fuel cell cannot be
discharged.

Comparison between the battery, the accumulator and the fuel cell

Similarities: They all generate electrical energy from chemical energy by an

electrochemical reaction.

Differences:
• Battery: becomes discharged once all of one of the reactants is used up.
• Accumulator: the electrochemical reaction is reversible; it can be re-charged after
becoming discharged.
• Fuel cell: can be used without discharging; it can be refuelled with reactants
as required.

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 student and teacher guide continued

2. P
 rinciples of operation of the fuel cell, which can be demonstrated by the
‘dismantlable fuel cell’

The dismantlable fuel cell uses polymer electrolyte membrane technology. The term
polymer electrolyte membrane fuel cell (PEMFC) refers to the proton-conductive
polymer membrane that serves as the electrolyte. The term PEM can also stand for
‘proton exchange membrane.’

The PEM fuel cell operates with hydrogen and oxygen. The electrochemical conversion
of energy inside the PEM fuel cell is the exact reversal of water electrolysis.

At the anode, hydrogen molecules are

Fig. 3 Principles of operation of a PEM fuel cell
oxidised to positively charged hydrogen
ions, releasing electrons. The hydrogen
ions diffuse through the ion-conducting
polymer electrolyte membrane
(electrolyte) to the cathode.
At the cathode, the hydrogen ions
react with oxygen and the electrons
supplied via the external circuit, forming
water.
If the anode and cathode are
connected by an external circuit (e.g. an
electric motor), the electrons flow from
the anode to the cathode (electric
current).

Anode: 2H2 → 4 H+ +4 e– Oxidation (release of electrons)

Cathode: O2 + 4 H+ +4 e– → 2 H2O Reduction (absorption of electrons)

Overall reaction: 2H2 + O2 → 2 H2O ∆ H = -286 kJ mol-1 (at 25ºC)

A single cell’s maximum theoretical for an individual cell is 1.23 volts.

voltage depends on the thermodynamic The maximum theoretical voltage
data applicable to the reaction between for a hydrogen fuel cell is therefore
hydrogen and oxygen to form water. 1.23 V.
Under standard conditions, the figure

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 E15
Current conduction losses (overvoltage) a finely distributed platinum catalyst simultaneous contact with the gas, the
occur during operation, e.g. as a result (approx. 0.1 – 0.5 mg of platinum per proton conductors (polymer electrolyte
of reaction inhibition because of 2). The membranes coated in this
cm membrane), and the electron
insufficient catalyst (experiment 12), way are subsequently press-bonded conductors (electrodes). This is where
internal resistance, or insufficient gas with porous carbon electrodes to the electrochemical reactions take
diffusion (experiment 13). In practice, create electrical contact on both sides place (fig. 4, right).
this leads to lower cell voltages, which of the membrane. Hydrogen and oxygen are catalytically
generally lie between 0.4 and 0.9 volts By contact pressure, the polymer converted during the reaction; the
for an individual cell. electrolyte membrane partially extends electrodes themselves remain
The membrane electrode into the porous electrode structures, unaffected. The platinum particles
assembly (MEA) is the heart of a PEM forming the gas/catalyst/electrolyte function as catalytic centres whose
fuel cell. The membrane is coated with interface. The catalyst must have effectiveness increases with surface area.

Fig. 4 Cross-section of a (polymer electrolyte) membrane electrode assembly, illustrating the processes taking
place during the fuel-cell reactions

The electrolyte membrane functions electricity conductors must ensure gas The current/voltage characteristic
like an ion exchanger. The protons of supply and water removal, i.e. they curve of a fuel cell
the acidic groups which are attached to must be gas- and water-permeable. The current/voltage characteristic curve
the polymer chains present in the The electric current obtainable and the power curve of the
membrane are mobile. When it is from a fuel cell is a function of the dismantlable fuel cell can be
humidified, the membrane conducts surface area of the electrodes, and can determined in the experiments.
2.
protons between the anode electrode reach values of up to 2 A/cm In addition, the influence of specific
and the cathode electrode. parameters on the shape of the
The electric contact between the characteristic curve can also be
MEA and the external circuit is made examined in experiments 12 and 13.
via special-steel perforated plates. In
large-scale fuel cells, too, these

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 student and teacher guide continued

Overvoltage depends on various excessive power losses. In the

factors. The size of the contributions extension to experiment 12 (see also
from these factors determines the Physics book Et11) the difference is
shape of the characteristic curve, as a simulated by a plug-in resistance, i.e.
function of current conduction. The the behaviour of the characteristic
individual factors are as follows: curve relative to total resistance is
examined.
1. Penetration overvoltage
– influence of the catalyst 3. Diffusion overvoltage – influence
At low currents and at voltages close to of the transport of material
the thermodynamic maximum voltage, At higher currents, the input of the
the shape of the characteristic curve is gases through the porous electrode
determined by the catalytic processes structure (fig. 4) becomes decisive.
taking place at the electrodes. This is Diffusion overvoltage occurs when the
shown here by an exponential increase gases at the catalyst are used up more
Fig. 5 Current/voltage characteristic
curve of a fuel cell divided into three in current as the voltage drops and quickly than they can diffuse to the
areas: catalysis, resistance of the fuel therefore the overvoltage increases. catalyst. A typical symptom of diffusion
cell and transport of the reactants
The main factor which determines the overvoltage is when the voltage/current
What does the shape of such a value of the current is the speed of the characteristic curve suddenly dips. The
characteristic curve tell us? catalytic conversion of the gases H2 fuel cell’s voltage declines very quickly
The thermodynamically maximum and O2, i.e the speed with which the as the current rises, and the electrode
voltage that a hydrogen/oxygen fuel cell electrons pass through the border is ‘starved’ of gas.
can deliver is taken from the between the Pt catalyst and the The instructions for experiment
electrochemical series and is 1.23 volts. electrolyte. This fundamental process is 13 describe how to measure the
Actual cell voltages are always lower shown in fig. 4. The overvoltage characteristic curve in air operation
than this. The difference between the involved is termed penetration mode. The curve dips at approx. 40 mA,
measured cell voltage and the overvoltage. a typical example of diffusion
thermodynamic voltage is called overvoltage. When the air end plate is
overvoltage or overpotential. The size 2. Internal resistance – influence of installed, the voltage is almost as high
of the overvoltage is the decisive the fuel cell’s structure as in oxygen operation, i.e. the fuel cell
parameter that determines a fuel cell's Every fuel cell has an internal resistance receives enough oxygen from the air.
efficiency. (electrolyte, electricity conductors, The aim of all fuel cell
interior structure, external wiring) which development is to minimise these
is recorded as ohmic voltage drop at three factors which contribute towards
high currents. In this case, the voltage/ overvoltage by using: (1) better
current characteristic curve is linear, i.e. electrocatalysts, (2) highly conductive
voltage falls in proportion to the materials and contacts, and (3)
increase in current. optimised electrode structures and gas
This resistance must be kept very ducts.
small, particularly in large fuel cells,
because it otherwise results in

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notes

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 assignments

Part 2
Written assignments
Written assignments targeting key skills

Using these assignments: Contents:

These assignments cover a range of more general topics and 1. Fuel cells:
lend themselves to class work or homework to consolidate past and present pg96–97
the theory covered previously. Each one is self-contained and A brief overview of fuel cells from their origin in 1839,
they may be used in any order or combination. They aim to their use on all manned space flights, and their promise
provide opportunities for the development of communication of non–polluting, sustainable energy. The article discusses
skills by offering extended reading and questions requiring recent progress following developments in catalyst
extended written answers. Team-working skills are developed technology, thanks to catalytic converters on cars.
in poster preparation and debate/discussion exercises.

2. The third century

of power pg98–99
The consequences of continued global reliance on fossil
fuels, and the social, economic and environmental
possibilities offered by hydrogen technology.

3. Batteries or fuel cells

– where does the
future lie? pg100–101
The limitations of batteries : size, cost, disposal,
compared with the possibility of continuous-use fuel
cells, including miniature cells for consumer devices.

4. Zero emission
vehicles pg102–103
How Californian ‘zero emission’ legislation has led to
massive investment in fuel cell powered rather than
battery powered vehicles. Recent technological
developments and possibilities for the future are considered.

5. Hydrogen gas station pg104­­–105

F  rom the Independent on Sunday, 9 January 2000.

6. Carbon nanofibres pg106–107

A recently-developed material which might solve the
problem of storing hydrogen for vehicles.

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 P2

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 written assignment

Fuel cells:
past and present
In 1839 William Grove, a 28 year old Scottish physicist who later went on to become a
barrister and judge, demonstrated the world’s first ‘fuel cell’ (or ‘gas battery’ as he called
it) at The Royal Institution in London.

Grove, a friend of Michael Faraday, had between the USA and the former Soviet fuel cell needed about 16 grams of
been experimenting on the electrolysis Union in the 1960s that real interest in platinum per kilowatt produced. This
of sulphuric acid. This involves putting fuel cells was revived, and they have been would cost $180 at today’s prices.
a voltage across two platinum used in every manned space flight since. Modern fuel cells work out to $6 - $8
electrodes immersed in the acid. This worth of platinum per kilowatt. Further
causes the positive hydrogen ions and The National Aeronautics and Space improvements are likely to reduce even
the negative sulphate and hydroxide Administration (NASA) developed fuel more the amount of platinum required,
ions in the electrolyte (sulphuric acid) cells as the ideal supply of both power but researchers have yet to find a
to drift to the cathode and anode and drinking water. They used an suitable substitute for platinum or
respectively. Hydrogen is produced at alkaline fuel cell, which enables other platinum metals at either
the cathode and oxygen at the anode. hydrogen and oxygen to be brought electrode.
This movement of charge carriers is an together in an alkaline electrolyte where
electric current in the liquid, and results they recombine to produce pure water As fuel cells generating 250 kW or more
in bubbles of hydrogen appearing at as well as generating a small voltage. If are now entering the market, systems
the cathode as the positive hydrogen larger voltages are required, the fuel using renewable energy sources are
ions pick up electrons. Similarly, cells are simply stacked together like a poised to provide large amounts of
bubbles of oxygen appear at the anode. club sandwich - they are connected in continuous electricity with no polluting
series. The total output voltage is the emissions. ✪
What surprised Grove was that when he sum of the individual cell voltages.
disconnected the apparatus it seemed to Carbon was typically used for the
work backwards, and he observed that he electrodes, but a coating of platinum is
was now generating a voltage of around 1 required to ensure the chemical
volt. It seemed that (in modern terms) the reaction proceeds efficiently.
hydrogen molecules were returning to the
electrode and giving up their electrons. The high cost of the platinum catalysts
These electrons were travelling round the used in fuel cells restricted them to
circuit to the positive electrode and there space and military applications for
they were reducing the oxygen. On the many years. However, recent work on
way round the circuit the electrons could catalytic converters for cars has
power electrical apparatus. resulted in deposition techniques
Unfortunately the materials that Grove where much less platinum is required.
used were unstable, and when Werner For example, particles only 10 atoms in
von Siemens developed rotary electrical diameter can now be deposited on the
generators the interest in fuel cells electrodes of modern fuel cells using
dwindled. It wasn’t until the ‘space race’ solid polymer electrolytes. In 1986 a

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 Fuel cells: past and present
1

Questions
1. Explain what an ion is.
2. Electrolytes conduct electricity. Describe the difference in the way in which electrolytes
and metals conduct.
3. During electrolysis, why do the ions drift to the anode and cathode as described?
4. Explain, using ion-electron equations to describe the processes happening at each electrode,
why the ratio of hydrogen to oxygen in this electrolysis is always 2:1.
5. The theoretical maximum output of a hydrogen/oxygen fuel cell is 1.23 V. If seven fuel cells, each
capable of working at 60% of the theoretical maximum, are connected in series, what will be the total
output voltage?
6. Using the information in the text, calculate the amount of platinum required in a modern fuel cell
to generate the 10 kW needed to power a large household.
7. Calculate by what factor the amount of platinum used has been reduced since 1986.

Activity
Using the research notes and any other sources available to you, construct a poster which shows
the different types of fuel cell and the uses to which they can be put.

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 written assignment

The third century

of power
‘I sell here, Sir, what all the world desires to have. Power!’ Matthew Boulton made James
Watts’ steam engine into an industrial tool, and for the next 100 years the industrial
world’s source of power was coal. For another 100 years, since Daimler first put an
internal combustion engine on to a horseless carriage, it has been oil. Now
DaimlerChrysler plan to be turning out 100,000 engines based upon hydrogen fuel cells,
to power the Mercedes A class as well as other cars, by 2005. The third century of
power seems likely to be driven by hydrogen.

After centuries during which the its power! This represents a transition sulphur compounds. About 1% by mass
sources of power have been getting to a world in which we are no longer of coal is sulphur; this is almost entirely
‘dirtier’, from wind and water to coal restrained by lack of resources but still locked in compounds, but when the
and oil, hydrogen technology could be have an improved standard of living. coal is burned sulphur dioxide is
the first step towards reversing that It could take 50 – 100 years to achieve, released.
trend. However, hydrogen will not be but the impact of fuel cells will be felt
burnt in conventional engines. Instead, long before that. These reserves of coal could, however,
it will power fuel cells whose sole be turned into a supply of hydrogen –
by-product is water. This will give us Alternatively, if we continue to rely rich gas which would be well suited to
zero-emission cars, and effective use upon fossil fuels, global consequences fuel cells. The challenge is to
of renewable resources for continuous may be even more extreme. It is decarbonise the coal during
supplies of electricity. estimated that from 1995 to 2015 the gasification, a process which would
demand for energy will grow by 54% produce carbon dioxide alongside the
With no emission of noxious gases or world wide, and by 129% in developing fuel gas. Engineers and chemists need
carbon dioxide the impact should be Asia. China and India currently have to develop techniques for sequestering
dramatic: a drastic decline in air two of the lowest per capita rates of the carbon dioxide gas, that is,
pollution, in acid rain, in oil spills and electricity usage. It is expected that separating it permanently from the
eventually in the greenhouse gases. they may satisfy an exploding demand environment. The advent of the
Global reliance on Middle Eastern oil for energy by tapping their vast coal hydrogen era offers developing
would end and international trade reserves, which are among the dirtiest countries a chance to benefit from their
balances would be realigned. of fossil fuels. The effects of the natural resources without jeopardising
Decentralised power plants would pollution produced would be grave. the environment. ✪
emerge, with the disappearance of the
National Grid and a complete make- Coal is not just carbon. Ordinary
over of the electricity-utility industry. bituminous coal when heated in the
Some even predict a scenario in which absence of air loses up to 30% of its
your house is plugged into your car for mass as coal gas, water, ammonia, and

98 the third century of power

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 The third century of power
2

Activities
1. 
Debate
Using the various assignments in this book, and any other sources of information, debate the motion:
‘By 2020 hydrogen will drive the world’.
2. 
Essay
Contrast how different life might be, both locally and globally, in the year 2050 if hydrogen technology
delivers what it promises, compared with what may happen if present trends continue.
3. 
Discussion
Is it right for other governments and international organisations to put pressure on developing
countries, such as India and China, to opt for hydrogen technology rather than using their reserves
of fossil fuels in conventional engines and generators? How might they be encouraged to adopt this
route?

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 written assignment

Batteries vs fuel cells

– where does the future lie?
The charge transfer within the fuel cell occurs by the movement of ions from one
electrode to the other through the electrolyte, while the electrons flow between the
electrodes via the external circuit. So a fuel cell supplies electrical energy in the same
way as a battery. However, the reactants in a fuel cell are the hydrogen fuel and the
oxidant (oxygen from the air) which are constantly supplied to the electrodes, whereas
in the battery the reactants are the materials (e.g. nickel oxyhydroxide, NiOOH, and
cadmium) used as the electrodes. The difference is, therefore, that the electrodes in
the fuel cell do not deteriorate and electrical energy is generated as long as the fuel is
supplied; whereas, in a battery, the material at the electrodes is used up. (In rechargeable
batteries the reaction can be reversed and the electrodes restored to their original state).

All fuel cells consists of a membrane round the external circuit while the alkaline fuel cells (AFCs), phosphoric acid
(or electrolyte) sandwiched between protons (hydrogen ions) drift through fuel cells (PAFCs), and direct methanol
two electrodes,but there is a variety of the Nafion membrane (electrolyte). fuel cells (DMFCs) (A DMFC oxidises
fuel cells which differ in the electrolyte At the other electrode, the returning methanol at the anode to form carbon
they use. It is the Polymer Electrolyte electrons combine with protons coming dioxide, protons – which pass through
Membrane or Proton Exchange through the electrolyte and with oxygen the membrane to the cathode – and
Membrane (PEM) fuel cell which is to form pure water – the only waste electrons, which pass through the
showing the most promise at the product of the process! external circuit). High temperature fuel
moment. cells include molten carbonate fuel cells
A single cell is only 2.5 mm thick and (MCFCs) and solid oxide fuel cells
The membrane or electrolyte is a typically 20–30 cm square, although (SOFCs). The high temperature cells
polymer (i.e. Nafion). This is miniature cells are being developed typically suit stationary power generation
sandwiched between the electrodes, which could easily provide power for a applications, such as supplying both heat
which are specially treated carbon mats range of devices currently powered by and power to homes and offices –
coated with platinum at around 0.1 – batteries: e.g. cellular phones; laptop so-called ‘co-generation’.
0.5 mg cm-2 Pt . The method of computers; personal stereos.
bonding allows the polymer membrane Hydrogen for a fuel cell may be generated
to extend into the porous carbon Single fuel cells produce only about by electrolysis of water and provided
electrodes to ensure maximum surface 1 volt, but by stacking the cells, directly, or it can be extracted from, for
area contact. connected in series, voltages of about example, natural gas or petrol via a
200 V can be attained. The maximum process called reformation. One
The platinum acts as a catalyst, current that can be drawn from the fuel advantage of the high temperature cells
speeding up the reactions at the two cell depends upon the surface area of is that they can use natural gas or
electrodes. Hydrogen fuel is fed to one the electrodes. At present the untreated coal gas directly as a fuel
–2,
electrode, where the reaction results in maximum current density is 2.0 A cm without needing a separate reformer, by a
it losing electrons and becoming for a PEM type fuel cell. process called Direct Internal Reforming.
+
positive ions (H ). The electrons travel Other low temperature fuel cells include Recent work on hydrogen fuel storage

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 Batteries vs fuel cells – where does the future lie?
3
has focused on cartridges of metal size, but at a lower cost and weight.
hydrides or carbon nanotubes which The reason is the greater energy density
absorb and store hydrogen for later of methanol, and the fact that batteries
extraction. have to store both reactants as bulky
solids whereas fuel cells take the
Until now batteries have been the only second reactant (oxygen) from the air.
choice for low power consumer Fuel cells are easily replenished by
products, but they are heavy and adding an ampoule of methanol or a
expensive and expire without warning, cartridge of solid hydride. ✪
and they also require disposal or
recharging. A methanol fuel cell would
provide power for 20 times longer than
a nickel cadmium battery of the same

Questions
1. 
From the information in the article draw a schematic labelled diagram which shows how
a fuel cell operates.
2. 
From the information in the article draw a table, or construct a poster, which compares and contrasts
fuel cells and batteries. Include reference to the way they work and their respective advantages and
disadvantages.
3. 
A house may require about 10 kW. At 240V what is the total current drawn? What surface area of fuel
cell might supply this current? How much platinum would be required to catalyse this reaction?
(Power/W = voltage/V x current/A).
4. What is meant by ‘reformation’, in the context of fuel cells?
5. 
Identify the main advantage of high temperature fuel cells. What do you see as their main drawback,
particularly in the area of consumer electronics?
6. 
Explain why, for purely environmental reasons, it is better to use hydrogen as a fuel for a fuel cell rather
than reformed natural gas, methanol or petrol.

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 written assignment

Zero emission vehicles

– the fuel cell car
Up to 60% of the air pollution in our cities is caused by transport emissions, and the
threat of California’s zero-emissions laws has provided a spur in recent years for
companies to take hydrogen technology seriously for powering the next generation
of zero-emission cars. But will fuel cells ever compete in a head to head contest with
internal combustion engines (ICEs)?

Present generation cars using the internal nearly every major car manufacturer in jams. The on-road performance of
combustion engine are becoming cleaner the world announced a programme to prototypes already looks promising.
and more efficient, but the recent rapid build a fuel cell car. DaimlerChrysler Ford’s P2000HFC zero emission vehicle
growth in the number of vehicles on the plan to be producing 100,000 fuel cell is slightly larger than a Mondeo and
roads has off-set these advances. In 1996 cars within 5 years. Their prototype weighs 1520kg. It can accelerate from
there were some 634 million vehicles on Necar 4 has fuel cells mounted under the 0 – 62 mph (0 – 100kph) in 14 seconds.
the roads of the world, an increase of floor, with a compressor to maintain the By comparison a 1.8 litre Mondeo will
30% on a decade earlier. Collectively they gases at the electrodes at pressure to take 10.7 seconds, whereas a typical
emitted 3.7 billion tonnes of carbon increase efficiency. Air and the hydrogen diesel model takes 14.7 seconds.
dioxide during the year. In addition to the fuel are conditioned by a humidifier and a
possible effects on the climate through heat exchanger, while a condenser Fuel cell stacks already power zero
increased emission of this ‘greenhouse captures waste water. The liquid-hydrogen emission buses in Vancouver and
gas’, the health hazards posed by the fuel is stored in a cryogenic tank. An air- Chicago, and a 40 ft (12 m) vehicle
emission of nitrogen oxides and other cooled radiator eliminates waste heat. powered by a 205 kW fuel cell has a
compounds are well established. By range of 250 – 350 miles ( 400 –
contrast, the reaction between hydrogen Unlike batteries – in which one of the 560 km) before refuelling.
and oxygen in a fuel cell produces no materials contained in the battery is
noxious gases, and either little or no used up – fuel cells can run for as long The initial problem for purchasers of
carbon dioxide, depending on the source as the hydrogen or other fuel is fuel cell cars will be the lack of a
of hydrogen used. supplied. Their conversion of direct hydrogen infrastructure (filling stations)
chemical energy to electrical energy is and the difficulties of storing the gas.
In 1990 the California Air Resources very efficient, typically reaching 40 – A 500 km journey would require about
Board passed legislation requiring that 50%, at full load, which compares very 3 kg hydrogen. Although this doesn’t
10% of the cars on its roads must be favourably with the internal combustion sound much, the volume at room
zero-emission (emit no pollutants) by engines of today’s cars. These temperature and pressure is 36,000 dm3
2003. Early developments on zero- theoretically reach 35%, but in practice - the volume of several cars! Even if the
emission cars concentrated on battery average around 15% due to friction gas is compressed at 200 atm
technology, but the weight, uncertain losses in the engine and traffic (2 x 104 kPa) the volume would still be
durability and limited range of the congestion. One reason for the 180 dm3. Liquid hydrogen must be
batteries caused development of superior performance is that, for maintained at about 20 K (-253 ºC),
battery-powered cars to stall. example, fuel cells do not have to idle and the cryogenic tanks are heavy and
Consequently, during the early 1990s, when the car is stationary in traffic expensive. Recent developments have

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 Zero emission vehicles – the fuel cell car
4
focused on metal hydrides which has a lower energy content than petrol stations already exist. Either individual
absorb and store hydrogen for later in terms of energy released per unit cars could carry on-board reformers, or
extraction. Graphite nanofibres have mass, the higher efficiency of the fuel the reformation could take place at the
also been suggested as suitable cell engine allows the use of methanol filling station for those cars requiring
carriers. Recent work claims that they without sacrificing vehicle range. This hydrogen. A fuel cell car running on
are capable of absorbing and retaining would result in an ultra-low emission petrol would provide between 1.5 and
up to 30 dm3 of molecular hydrogen vehicle rather than a zero emission 2.3 times higher fuel economy than the
per gram of carbon at room one, due to the emissions from the same car burning petrol in an ICE.
temperature. This would allow reformation process. Again, an
molecular hydrogen to be transported infrastructure for refuelling with As cars need about 50 kW to accelerate,
in a liquid-like state without need for methanol would have to be developed. another possibility is the hybrid car,
refrigeration or high volume. More Direct methanol fuel cells (DMFCs) can with a 15 kW fuel cell backed up by a
development work is required on this. also be used, in which methanol is battery for periods of peak demand.
oxidised at the anode to carbon dioxide.
An alternative to using hydrogen However, even if early fuel cell vehicles
directly is to use methanol to produce Reformers to strip the hydrogen from are powered by methanol or petrol, the
hydrogen by a technique called the hydrocarbons in petrol, giving use of fossil fuel to provide hydrogen is
‘reformation’. Methanol has the minimum emissions, are another seen by many researchers in this field
advantage that it is liquid at room possible development; this would have as simply a transition to hydrogen
temperature and, although methanol the advantage that the petrol filling production from sustainable sources. ✪

Questions
1. Estimate the number of vehicles on the roads in 1986.
2. What is, currently, the average output of carbon dioxide per vehicle per day?
3. Carbon dioxide is not considered to be toxic or a health hazard. Explain its effect in the environment,
and so explain why carbon dioxide emissions from vehicles are a cause for concern.
4. Explain why the typical efficiency of an internal combustion engine car is only about 15%, whereas in
theory it reaches 35%. Why does a fuel cell car not suffer a similar drop in efficiency?
5. Explain how it is possible that ‘higher efficiency allows the use of methanol without sacrificing vehicle
range’.
6. Suggest processes by which hydrogen may be produced from ‘sustainable sources’.
7. The formulae of hydrogen, methanol and octane (as in petrol) are H2, CH3OH, and C8H18 respectively.
Write full equations for the complete combustion of each of these fuels in air. What information do
these equations give us about the effects of using these materials as fuels?
8. The values of the standard molar enthalpy changes of combustion of hydrogen, H2, methanol, CH3OH, and
octane, C8H18, are, respectively -286 kJ mol–1 , -726 kJ mol–1, and -5470 kJ mol–1. How much energy will be
released by burning 1.0 kg of each of the above materials? [Ar(C) = 12.0, Ar(H) = 1.0, Ar(O) = 16.0] Comment
on your answer.

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 written assignment

The first hydrogen gas

station
Article from the Independent on Sunday, by Geoffrey Lean, 9th January 2000

Hydrogen gas station opens way for

world’s first fume-free car
The world’s first hydrogen filling station the state government and seven giant century oil accounted for just 2.4 per cent
will open in the summer – and, companies. Shell, Arco and Texaco will of the energy used in the United States, for
predictably, it will be in California. jointly fund it, while DaimlerChrysler, example. But over the last 100 years – and
Ford, Honda and Volkswagen will mostly in the last 50 – the world has
The opening of the station will herald provide and service the vehicles. burned up half of all the oil laid down in
the move away from economies fuelled the earth’s crust over many millions of
by oil, coal and gas to ones powered by Beginning with 16 vehicles – but, the years.
the sun. The station, which will provide parties hope, soon catering for a fleet of
hydrogen to fuel cars and buses, is to 30 cars and 10 buses – the station may New oil reserves are becoming
be opened beside a freeway in mark the beginning of the end of the increasingly hard to find and exploit.
Sacramento, the capital of California, world’s brief binge on fossil fuel, And though there is still plenty of coal
as the result of a partnership between particularly oil. At the beginning of this and gas, all fossil fuels emit air

So what are the alternative fuels?

Ethanol Methane LPG Electricity Hydrogen

Stage of Made from sugar Used in form of This mixture of Used mostly in Prototype vehicles
cane in Brazil as compressed propane and towns – battery being produced
development
substitute for natural gas. butane powers development is the as big companies
petrol, but no Substitute for around 8,000 fleet key to increasing invest heavily in
longer supported diesel in larger vehicles on range. Expected cars with fuel cells
by government vehicles, such as Britain’s roads breakthrough soon powered by the
buses, in towns already gas

Advantages Less polluting, Much cleaner Cleaner than Quiet. Very clean – emits
Renewable than diesel petrol or diesel No pollution only water.
from vehicle

Disadvantages Engines run poorly Not suitable for May be less safe Pollution from Expensive at
and don’t last as cars as the tank is or abundant than power stations to present. May be
long. Expensive too heavy methane provide charge safety problems

Future potential ✪ (out of ten) ✪✪✪✪ ✪✪✪✪ ✪✪✪✪✪✪✪ ✪✪✪✪✪✪✪✪✪

104 the first hydrogen gas station

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 Hydrogen gas station – first fume-free car
5
pollution that damages health and is or wind power. As a result, the institute The Icelandic government is working
the main driving force behind global believes, it will be the key to a new world with the two companies to change its
warming. economy based on renewable energy. fishing fleet over to hydrogen and has
launched a plan to convert the country
Hydrogen fuel, by contrast, produces no First it will have to overcome one major entirely to a ‘hydrogen economy’ over
pollution. The new filling station will fuel safety drawback – it is highly explosive. But the next two decades.
cars run by fuel cells – originally the companies in the partnership point out
developed for the space programme – that petrol is explosive too, and that it has Meanwhile Shell and BP are investing
which produce only electricity and water. been mastered safely nevertheless. massively in solar and wind power.

The authoritative Washington-based John Smith, the chairman of General The Worldwatch Institute concludes:
Worldwatch Institute reports: ‘Today’s Motors, predicted at the 1998 Detroit ‘The next century may be as profoundly
top fuel cells are roughly twice as Motor Show that: ‘No company will be shaped by the move away from fossil
efficient as conventional engines, have able to survive in the 21st century if it fuel as this one was marked by the
no moving parts, require little relies solely on internal combustion move towards them. Markets can shift
maintenance, are nearly silent, and engines.’ His company Ford and abruptly in the next few years, drying
emit only water vapour’. DaimlerChrysler plan to put hydrogen up sales of conventional power plants
vehicles on the market within four years. and cars in a matter of years and our
At first the hydrogen will come from more industries, homes and cities could be
conventional fuels such as natural gas, DaimlerChrysler has embarked on an transformed in ways we can only begin
methanol or even petrol, but the eventual £870m partnership with a leading fuel to anticipate.’. ✪
aim is to produce it from water using solar cell company, Ballard Power Systems.

Questions
1. Is the headline completely correct?
2. What is meant by the phrase ‘the world’s brief binge on fossil fuel’? In particular,
why is the word ‘brief’ used?
3. Discuss the sentence which begins ‘ And though there is still plenty of coal....’. In particular, consider
the statement that ‘air pollution..... is the main driving force behind global warming’.
4. Consider the properties of hydrogen. In what ways may hydrogen be safer than petrol as a fuel for vehicles?
5. Briefly explain why John Smith felt it necessary to say what he said at Detroit.
6. (a) Among the alternative fuels (see Box), ethanol is described as a substitute for petrol. It has in fact
been used as an extender for petrol, rather than as a substitute. Explain the difference between the
two underlined words. (b) What is the link between ethanol and solar energy?
7. What aspects of battery development will influence whether battery-electric vehicles will become
competitive with petrol or fuel cell engines? (See Box, under Electricity).
8. Imagine you are an Icelandic government official. Summarise briefly the main features of your plan to
convert the country to a ‘hydrogen economy’ within 20 years.

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 written assignment

Carbon nanofibres
(The following passage is mostly adapted from material published by Professor Terry
Baker, Professor Nelly Rodriguez and their colleagues at Northeastern University, Boston.)

In the early 1990s a new type of fibrous It has been possible to grow 100 g of normal temperatures, and which can
carbon was developed by a research the nanofibres in a single experiment. release the gas easily.
team at Northeastern University. This It is possible that, if the method can be
was achieved by decomposing scaled up, commercial amounts could The Northeastern University research
hydrocarbons, such as ethene, in a be grown at a price less than the price team’s data showed that if the
mixture with hydrogen, on the surface of graphite. The fibres are immensely nanofibres were carefully pretreated to
of a metal catalyst at temperatures strong and have much better chemical drive off any adsorbed gases, the
between 400 – 800 ºC. The regularity and physical characteristics than the material could hold up to 30 dm3 of
of the particles in the fibres – i.e. their carbon fibres used in current composite molecular hydrogen per gram of carbon
crystallinity –is determined by the lightweight/high strength materials. at room temperature.
nature of the catalyst particles, the
hydrocarbons/hydrogen ratio, and the The interlayer spacing of the graphite Other researchers have so far
reaction conditions. Catalysts used platelets is 0.34 nm; hydrogen (January 2000) been unable to produce
have included, among many others, molecules have a diameter of 0.29 nm. nanofibre material which absorbs more
iron, iron-nickel, and copper-cobalt. Hydrogen can therefore not only than about 3 dm3 of hydrogen per
adsorb on edges but also fit into the gram.✪
The nanofibres are built up from slits between platelets, whereas larger
graphite platelets arranged in a highly- molecules like oxygen and nitrogen
ordered form around the fibre axis. cannot. Because the material is almost
Depending on materials and conditions, entirely micro-porous, almost all of it
the nanofibres can be from 5 to 100 μm can be used for hydrogen storage. Also,
long and between 5 and 10 nm in the delocalised electrons in the
diameter. The ordered platelets lead to graphite platelets help the development
a huge number of edges, which can act of strong van der Waals’ – type forces
as active sites for adsorption. The which hold the hydrogen quite strongly
resulting surface area is immense, and even at room temperature. The
can be as high as 700 m2 g–1. Very hydrogen is released at room
careful control of materials and temperature by a reduction of pressure,
conditions leads to a ‘herringbone’ or the material can be warmed.
pattern of platelets, with the layers of
graphite separated by 0.34 nm. Subtle The storage of hydrogen in fuel cell
changes in experimental conditions powered vehicles has been a problem.
leads to platelets arranged Carbon nanofibres are said to provide
perpendicular to the fibre axis or a lightweight, relatively inexpensive
parallel to it. material which can hold large amounts
of hydrogen at moderate pressure and

106 carbon nanofibres

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 Carbon nanofibres
6

Questions
1. Why is the word nanofibres used for the material?
2. What is the ratio between the length and the width of the nanofibres discussed here?
3. Explain the phrase ‘delocalised electrons in the graphite platelets’.
4. How many moles of carbon atoms are there in 100 g of nanofibres?
5. What, according to the reports, is the possible maximum surface area of one mole of carbon in the
form of nanofibres?
6. (a) From the data presented here, what volume of hydrogen (measured at room temperature and
pressure) can be held in one mole of carbon in the form of nanofibres?
(b) What is the mass of this amount of hydrogen?
7. The Northeastern University team has published a large number of valuable research papers on
catalysis and its applications over many years, and there is no question of their results being due to
misrepresentation or incompetence. Yet other research workers have so far (January 2000) failed to
produce nanofibre materials which can hold more than about 10% of the hydrogen reported by the
Northeastern workers.
From careful reading of the text, and by thinking about the nature of the material and the way in which
it is made and treated, can you suggest why the original results have been difficult to reproduce?
8. Even if the original results cannot be reproduced, could the results reported by other workers lead to
a commercially viable method of storing hydrogen in cars? Explain your reasoning.

Activity
Discussion: Why is it so important to be able to store large quantities of hydrogen in a small volume?

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 ... in conclusion
To the student

We hope that through using this book, together with its companion books and the Heliocentris kits, you have learned a lot about the
trapping and use of solar energy, about fuel cell technology, and about the hydrogen economy. We have explained why we believe
that knowledge about these matters is vitally important for the future of our planet and for all who live on it.
We also hope that all the material has helped you in your learning of important sections of physics and chemistry, and that
it will serve you well in any exams you have to take, and also in any projects which you may have to do.
We believe in the absolute need for as many people as possible to understand basic scientific principles; and we believe
also that solar energy and hydrogen will play a major part in everyone’s future.
And it is perhaps our greatest wish that you have enjoyed the work and will wish to learn more, and that some of you may
eventually contribute – by working in the fields of renewable energy sources and sustainable development as scientists, engineers, or
economists - to making the world a healthier, happier and safer place for our successors to live in.

The following list of books and other resources will help

if you wish to find out more:

Books:
K. Kordesh and G. Simader, Fuel Cells and their Applications, New York: VCH, 1996.
A. Appleby, F. Foulkes, Fuel Cell Handbook, Van Nostrand and Reinhold, 1989.
J. Hirschnhofer et al, Fuel Cells: A Handbook, Morgantown Energy Technology Center, 1994.
Michael Peavy, Fuel from Water: Energy Independence With Hydrogen, Merit Products, 1998.
L. Blomen, M. Mugerwa (eds.), Fuel Cell Systems, Plenum Publishing Corp, 1994.
Jim Motavalli, Forward Drive: The Race to Build the Car of the Future, Sierra Cub Books, 2000.
Tom Koppel, Powering the Future: The Ballard Fuel Cell and the Race to Change the World, John Wiley and Sons, 1999.
James S. Cannon, Sharene L. Azimi (Editor), Harnessing Hydrogen: The Key to Sustainable Transportation, Inform, 1995.
J. O'M. Bockris, Energy Options - Real Economics and the Solar-Hydrogen Systems, Halsted Press, New York, 1980.

D. Hart, Hydrogen power: the commercial future of the ultimate fuel, Financial Energy Publishing, London, 1997.
P. Hoffmann, The Forever Fuel: The story of hydrogen, Westview Press, Boulder, Colorado, 1982
P. Hoffmann, International Directory of Hydrogen Energy and Fuel Cell Technology, The Hydrogen Letter Press, Rhinecliff, New York
J. M. Ogden, R. H. Williams, Solar Hydrogen: Moving Beyond Fossil Fuels, World Resources Institute, Washington, DC, 1989
H. W. Pohl, Hydrogen and Other Alternative Fuels for Air and Ground Transportation, Wiley, Chichester, 1995
Edward W. Justi, Solar Hydrogen Energy System, Plenum Publishing Corp, 1987

108 Heliocentris • post-16 level chemistry • conclusion/bibliography

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 Journals/Magazines:
Hydrogen and Fuel Cell Letter, www.mhv.net/hfcletter/.
New Scientist, www.newscientist.com.
Green Chemistry, www.chemsoc.org/greenchem.
Education in Chemistry, www.chemsoc.org/gateway/eic.htm.
Scientific American, www.sciam.com.
Fuel Cell Industry Report, Scientific American Newsletters, New York.
International Journal of Hydrogen Energy, Pergamon.
Fuel Cell News, Fuel Cell Institute, Washington DC.

Articles:
H. Colell and B.Cook, Fuel Cells – power for the future, Education in Chemistry, 36 (5), 1999, pp. 123.
T. Ralph and G. Hards, Powering the cars and homes of tomorrow, Chemistry and Industry, 4 May 1998, p337.
The third age of fuel/At last, the fuel cell, The Economist, 25-31 October 1997, p16 and p89.
The future of fuel cells, etc, Scientific American, July 1999, p56 –75
A. Wilson and N. Malin, ‘Fuel Cells: A Primer on the Coming Hydrogen Economy,’, Environmental Building News (8:4) April 1999
pp. 1, 7-12, April 1999. Available from Environmental Building News, Brattleboro, Vermont, USA.
C. Christenson, ‘Fuel Cell System Technologies and Application Issues,’ Energy Business & Technology Sourcebook 1996, pp. 258-261,
1996. Available from Fairmont Press.
R. Barlow, ‘Residential Fuel Cells: Hope or Hype?,’ Home Power (No. 72), Aug/Sept 1999, pp. 20-29. Available from Home
Power, Ashland, Oregon, USA.

Useful Organisations:
• U.S. Environmental Protection Agency (material on global warming) – www.epa.gov/global warming • U.S. Union of
Concerned Scientists – www.ucsusa.org • Austrian Energy Agency (European fuel cell strategy, in English) –
www.eva.wsr.ac.at/opet/fcstrategy.htm • Friends of the Earth – www.foe.co.uk • Royal Society of Chemistry Green
Chemistry Network – www.chemsoc.org/gcn • British Association for the Advancement of Science – www.britassoc.org.uk

Fuel Cell Internet Resources:

A list of internet links for further research on hydrogen technology and fuel cells.
Heliocentris Academia International GmbH – http://www.heliocentrisacademia.com • Los Alamos National Laboratory –
http://education.lanl.gov/resources/h2/ • Center for Renewable Energy and Sustainable Technology (CREST) –
http://solstice.crest.org/index.shtml • Energy Efficiency and Renewable Energy Network (EREN), U.S. Department of Energy
– http://www.eren.doe.gov/ • American Hydrogen Association – http://www.clean-air.org
• Electric Power Research Institute – http://www.epri.com • Electrochemical Analysis and Diagnostic Laboratory –
http://www.cmt.anl.gov • Fuel Cell Commercialization Group – http://www.ttcorp.com/fccg • National Renewable Energy
Laboratory (NREL) – http://www.nrel.gov • National Energy Technology Laboratory (NETL) – http://www.fetc.doe.gov
• National FuelCells Research Center – http://www.nfcrc.uci.edu • Office of Scientific and Technical Information, U.S.
Department of Energy – http://apollo.osti.gov/html/osti/ • Fuel Cells 2000 – http://www.fuelcells.org • E-sources: online
journal on energy and environment – http://www.e-sources.com/

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