H2 Storage – Scope
H2 needs about 4 times the volume for a given amount of
energy compared to conventional liquid fuels for IC engines.
Developing safe, reliable, compact, and cost-effective
hydrogen storage technologies is one of the most
technically challenging barriers to the widespread use of
hydrogen as a form of energy.
To be competitive with conventional vehicles, hydrogen-
powered cars must be able to travel more than 300 miles
between fills.
This is a challenging goal because hydrogen has physical
characteristics that make it difficult to store in large
quantities without taking up a significant amount of space.
2
Hydrogen Storage - Requirements
An energy density similar to petrol.
Operate close to room temperature and ambient
pressures.
Release and absorb hydrogen quickly.
Cheap.
Must be safe.
Must require minimal change to infrastructure.
The performance must be adequate.
3
Hydrogen Storage Overview
Physical storage of H2
•Compressed •Metal Hydride (“sponge”)
•Cryogenically liquefied •Carbon nanofibers
Chemical storage of hydrogen
•Sodium borohydride •Methanol
•Ammonia •Alkali metal hydrides
New emerging methods
•Amminex tablets •Solar Zinc production
•DADB (Diammoniate •Alkali metal hydride slurry
of Diborane)
4
Gaseous Hydrogen Storage
H2 gas tanks are the most
proven of hydrogen storage
technologies.
Carbon-fiber-reinforced with
polymer liner.
Up to 10,000 psi (~ 70 Mpa).
High pressure tanks present
safety hazard.
Concerns over Hydrogen/tank
molecular interactions lead to
embitterment.
5
Compressed Hydrogen
Hydrogen can be compressed into high-pressure
tanks. This process requires energy to accomplish
and the space that the compressed gas occupies is
usually quite large resulting in a lower energy
density when compared to a traditional gasoline
tank
A hydrogen gas tank that contained a store of
energy equivalent to a gasoline tank would be more
than 3,000 times bigger than the gasoline tank
Hydrogen can be compressed into high-pressure
tanks. High-pressure tanks achieve 6,000 psi, and
therefore must be periodically tested and inspected
to ensure their safety
6
Underground Hydrogen Storage
Salt Caverns
Rock Storage
7
Underground Hydrogen Storage
8
Compressed H2 - Overview
Compressed hydrogen, in comparison, is quite different to store.
Hydrogen gas has good energy density by weight, but poor energy density
by volume versus hydrocarbons, hence it requires a larger tank to store.
A large hydrogen tank will be heavier than the small hydrocarbon tank
used to store the same amount of energy, all other factors remaining equal.
Increasing gas pressure would improve the energy density by volume,
making for smaller, but not lighter container tanks (see hydrogen tank).
Compressed hydrogen will require 2.1% of the energy content to power the
compressor. Higher compression without energy recovery will mean more
energy lost to the compression step. Compressed hydrogen storage can
exhibit very low permeation.
9
Liquid Hydrogen
Hydrogen does exist in a liquid state, but only at extremely cold temperatures.
Liquid hydrogen typically has to be refrigerated to 20K or -2530C.
The temperature requirements for liquid hydrogen storage necessitate
expending a minimum energy of 15.1 MJ/kg to compress and chill the hydrogen
into its liquid state.
The storage tanks have many layers and are insulated, to preserve temperature,
and reinforced to store the liquid hydrogen under pressure.
Reduced mass and especially volume needed.
Reduced cost and development of high-volume production processes needed.
Improve energy efficiency of liquefaction.
Disadvantages
The cooling and compressing process requires energy, resulting in a net loss of
about 30% of the energy that the liquid hydrogen is storing.
The margin of safety concerning liquid hydrogen storage is a function of
maintaining tank integrity and preserving the Kelvin temperatures that liquid
hydrogen requires.
Combining the energy required for the process to get hydrogen into its liquid
state and the tanks required to sustain the storage pressure and temperature
becomes very expensive comparative to other methods.
The tanks must also be well insulated to prevent boil off
Liquid hydrogen has less energy density by volume than hydrocarbon fuels
such as gasoline by approximately a factor of four.
10
Metal hydrides
Me + ½ x H2 ↔ MeHx where Me stands for a metal or metal
alloy.
Single metal hydrides MgH2 and PdH0.6 with hydrogen mass
percentages of 7.6 and 0.6 and decomposition temperatures of
330 and 25oC are well studied.
Dual metal hydrides with highest mass percentage of hydrogen
found so far is Mg2FeH6 but decomposing at 400oC.
Time needed for absorption depends not only on the alloy used
but also on grain size and lattice structure.
Additions of transitional metals such as vanadium or carbon as
additives bring down the absorption time from 30-60 min to
around a min but with marginal advantages and other
disadvantages (dealing with high pressure)
11
Formation of metal hydrides for hydrogen storage
12
Carbon Nanofibers
Complex structure
presents a large surface
area for hydrogen to
“dissolve” into
Early claim set the
standard of 65 kgH2/m2
and 6.5 % by weight as a
“goal to beat”
Research continues…
13
