SANDIA REPORT

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Hydrogen Storage for Vehicular Applications:

Technology Status and Key Development Areas (U)

S. L. Robinson, J. L. Handrock

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SAND94-8229
Unlimited Release
Printed April 1994

HYDROGEN STORAGE FOR VEHICULAR APPLICATIONS:

TECHNOLOGY STATUS AND KEY DEVELOPMENT AREAS

S. L. Robinson and J. L. Handrock

Engineering for Transportation and Environment Department
Structural Mechanics Department
Sandia National LaboratoriedCalifornia

Abstract

The state-of-the-art of hydrogen storage technology is reviewed, including gaseous, liquid, hydride,
surface adsorbed media, glass microsphere, chemical reaction, and liquid chemical technologies. The
review of each technology includes a discussion of advantages, disadvantages, likelihood of success,
and key research and development activities. A preferred technological path for the development of
effective near-term hydrogen storage includes both current DOT qualified and advanced compressed
storage for down-sized highly efficient but moderate range vehicles, and liquid storage for fleet
vehicle applications. Adsorbate media are also suitable for fleet applications but not for intermittent
uses. Volume-optimized transition metal hydride beds are also viable for short range applications.
Long-teim development of coated nanoparticulate or metal matrix high conductivity magnesium
alloy, is recommended. In addition, a room temperature adsorbate medium should be developed to
avoid cryogenic storage requirements. Chemical storage and oxidative schemes present serious
obstacles which must be addressed for these technologies to have a future role.

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 ..

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produced from the best available original
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 Table of Contents
Executive Summary 6
Introduction 7
Hydrogen Storage Goals 8
Hydrogen Storage Options: State-of-the-& 8
High Pressure Gaseous Storage 9
Liquid Storage 10
Hydride Storage 11
Surface Adsorbed Media Storage 12
Glass Microsphere Storage 13
Chemical Reaction and Liquid Chemical Storage 14
Conclusions 15
Preferred Development Options 15

Appendix
Review of Developments in Hydrogen Storage and Delivery System Technology 23
High Pressure Gaseous Storage 23
Pressure Vessel Development 23
Balance of Plant 26
Liquid Storage 28
Hydride Storage 30
Hydride Materials 31
Hydride Bed Designs 32
Surface Adsorbed Media Storage 33
Glass Microsphere Storage 37
Chemical Reaction and Liquid Chemical Storage 39
A. Iron Reduction/Oxidation Storage 39
B. Liquid Chemical Storage 43

References 44

5
 EXECUTIVE SUMMARY

The state-of-the-art of bulk hydrogen storage for vehicular applications is reviewed. The intent is to
identify key development needs and desirable technologies to support near-term (less than 10
years) and far-term (15 years and beyond) hydrogen storage requirements for a spectrum of
vehicular applications. We consider the hydrogen storage options of storage as high pressure gas;
(including microspheres and cryogenic gas), storage as liquid, storage as metal hydrides, storage on
adsorbate media, and others such as chemical reaction. The various technologies are compared to
the Department of Energy storage goals, which are a weight efficiency of 7 wt % hydrogen and a
volumetric density of 70 kg hydrogedcubic meter.
In defining the preferred research paths, and therefore the supporting or enabling technology
development tasks, the discriminating factors were the following:
Is the technology appropriate for near or far term payoff?
What are the prospects of technical success?
(achieving weight and volume density, dormancy)
What are the prospects for economic success?
How does the technology fit with volume and weight sensitive applications?
What must be done to assure both safety, and the perception of safety?
In the near term, compressed gas storage using either current Department of Transportation vessels
or advanced pressurized storage is viable for highly efficient, down-sized commuter or town
vehicles. Compressed gas storage may also afford interim support of large fleet-type vehicles such
as buses. For fleet applications, cryogenic compressed gas also offers advantages, although its
utility in personal vehicles will be limited unless highly efficient cooling, insulation, and control
devices are developed. Advanced hydride bed designs with improved volume efficiency (to about
50% that of the bulk hydride) may also support highly efficient, down-sized commuter or town
vehicles. Transition metal hydrides are capable of supplying hydrogen in improved beds today,
provided a high efficiency (miles per gallon) vehicular standard is achieved. Liquid hydrogen
storage is suitable today for fleet-type, professionally maintained vehicles. Glass microsphere
storage, which suffers from low volumetric storage density, may be useful to volume-insensitive
vehicles. However, other technologies may be more suitable. Adsorbate media are unsuitable todiiy
for personal vehicles because of the cryogenic requirements, the need for a pressure vessel, and the
lack of dormancy, but may be usable for fleet applications today. Chemical storage media have
many difficulties, including the need to recycle masses of material, and the heavy, costly reforming
equipment. The highest hydrogen density carrier, liquid ammonia, is toxic in low concentrations
and therefore unacceptable.
In the future, nanoparticulate coated magnesium hydride, or coated metal matrix high conductivity
hydride, having reduced absorption and release temperatures, offers safety, weight and volume
efficiency provided the many technical obstacles can be overcome. Superabsorbent carbon needs
development so that near room temperature absorption occurs, otherwise the cryogenic cooling and
control requirements will hinder its acceptance in private vehicles. These hindrances may be
acceptable in fleet vehicles. Microsphere technology should address stronger, more perfect spheres
to allow and increase in storage pressure. Currently considered hydrogen-bearing media, or
chemical reaction media, are deficient. Clearly breakthroughs are needed, making this a long-term
option at best.

6
 Introduction
Hydrogen is currently being investigated in the USA, Japan and Germany for use in alternatively
fueled vehicles. For the USA, hydrogen offers the potential for (a) freedom from pollution,
including greenhouse gases, (b) independence from foreign fuel sources, and (c) potential system
efficiencies in excess of those currently realized. The candidate hydrogen-using power sources
include, hydrogen-air fuel cells, hydrogen-burning internal combustion engines, and internal
combustion engines using hydrogen-natural gas blends such as hythane (5% hydrogen in
methane).
While it is unlikely that hydrogen will serve as a large-scale commercial vehicular fuel in this
century, there are additional opportunities for the application of hydrogen on a significant scale.
Some of these applications are as a vehicular fuel, although many are not. The space station, space
shuttle, and advanced discrete monitoring devices all require hydrogen storage. Self-monitoring
("smart") containers for high value cargo may also use hydrogen storage. Unmanned undersea
vehicles have requirements which mate well with hydrogen use, and advanced hydrogen storage
technology also has application to battery packs used in satellites, etc. which require high power,
long life and very high reliability. The dual-use nature of developments in hydrogen storage
technology may be of benefit to the United States Department of Energyhlefense Programs
(USDOEIDP), National Aeronautics and Space Administration (NASA) and Department of
Defense (DoD). Therefore, although this paper concerns hydrogen storage technologies in terms
of vehicular applications, many of these technologies would support a variety of possible end-use
options.
Numerous system level reviews have been published recently [ 1-41 and in the near past [5-71
concerning hydrogen storage options. The dominant hydrogen storage issues are:
Storage parameters
Weight efficiency (%hydrogen to total weight), volume density (kg hydrogedunit
volume) and dormancy, that is, time until energy is required to maintain storage.
Safety
We assume that no lessening of current safety standards is acceptable.
Fuel-cycle costs
This includes generation cost, and parasitic energy loss or energy cost such as
material recycling.
System costs
System costs are driven by the complexity of the chargddischarge cycle, materials,
and other technology costs.
These issues will be treated in turn for each of the currently known hydrogen storage technologies.
The specific technology will be introduced and its advantages and disadvantages discussed. The
requirements for full development of the technology to the point of utility and the development
opportunities will then be considered.
Systems analysts have also attempted to match requirements to vehicular characteristics, including
weight, duty cycle, carrying capacity or payload, etc. Several different hydrogen storage
technologies will likely be required to address the unique requirements of both light-duty and
heavy-duty vehicles, since weight and volume sensitivity vary considerably. For example, the
sensitivity to weight and volume of a variety of vehicular applications has been portrayed [4] as
shown in Figure 1. It is apparent from the figure that no single storage medium is necessarily

7
appropriate for all applications, and research and development on several technologies may be
appropriate. Technologies deemed unsuitable for use in personal vehicles may prove suitable for
heavy-duty fleet-type commercial vehicles, such as a storage mode having poor dormancy, but
having a continuous and high fuel demand. Use of LH2 (liquid hydrogen) in buses would be such
an example.
In addition to the weight and volume sensitivity of vehicular applications portrayed in Figure 1, the
additional factor of technological advances in vehicles must be considered. As an example,
Lovins[8] has postulated a revolution in vehicle construction techniques which would incorporate
vehicle downsizing to subcompact dimensions, the use of lightweight composite materials instead of
steel as structural and body materials, and the implementation of series-hybrid electric-drive power
plants sized to average rather than peak power demands. Peaking power would be provided by high
power-density batteries. Such a power plant would use an internal combustion engine of about 10-
20 kW capacity, in a point-tuned optimized engine, running a generator. Propulsion would be by
switched-reluctance electric motors at the drive wheels. Lovins asserts that, application of "state of
the shelf'' technology is capable of producing fully satisfactory automobiles which consume 0.4
-
MJ/km ( 600 BTU/mile), which is less than the 2 M J h (3000 BTU/mile) common today
(approximately 30 mpg) in compact and subcompact automobiles. Lovins' prognostications are
more optimistic than the targets recently set by the administration, its National Laboratories and
commercial partners in the US Car alliance. Their goal is an 82 mpg (0.725 M J h ) consumer-
acceptable four-person vehicle. Leaving aside the questions of safety, manufacturing, the need for a
hydrogen infrastructure, and compatibility with existing vehicles, hydrogen as a fuel becomes a
more viable option for such a highly efficient vehicle since the fuel storage requirement is greatly
diminished. Rather than storing 7 kg of hydrogen to achieve a 550 km (340 miles) range, as
identified in the DOE Hydrogen Plan [SI,it would be necessary only to store 2.8 kg or less of
hydrogen to achieve that range in an 82 mpg-equivalent vehicle. In this scenario, many of the
decision points for choosing an appropriate hydrogen storage technology would shift dramatically.
In this review, we consider the hydrogen storage options of storage as high pressure gas (including
microspheres and cryogenic gas), storage as liquid, storage as metal hydrides, storage on adsorbate
media, and others such as chemical reaction. In the remainder of this report, the storage goals are
reviewed, hydrogen storage technologies are evaluated, and potential high pay-off research and
development activities are identified. We also attempt to chart desirable development pathways for
both the near future and more distant technologies. The appendix contains a detailed description of
each storage technology, a listing of advantages and disadvantages, and a discussion of key
development activities.

Hydrogen Storage Goals

The primary technological limitation which has been repeatedly identified in hydrogen utilization is
the storage of adequate quantities of hydrogen (enabling significant vehicle ranges, etc.). The
storage concern arises since, while hydrogen is energy-rich on a weight basis, it is relatively energy-
poor on a volumetric basis (by comparison for example with gasoline). The Department of Energy
has established a goal [9] under the Matsanuga Hydrogen Implementation Act for efficiency of
hydrogen storage of a volumetric density of 70 kg Hdm3 (4lbs Hift3) and 7 wt % gravimetric
density. It should be noted that the volumetric density goal is approximately 70% of the highest
hydrogen density found in nature, for example in methanol and liquefied ammonia.

Hydrogen Storage Options: State-of-the-Art

The current hydrogen storage options discussed are high pressure gas, liquid hydrogen, hydrides,
activated carbon, glass microspheres, and chemical reaction and liquid chemical storage. Table I
summarizes our view of the advantages and disadvantages of each storage method. Figure 2(A and

8
B) provides a comparison of volumetric and gravimetric densities for the various hydrogen storage
options, with .the system volume normalized to 1 kg of hydrogen. The effects on mass and volume
of appropriate safety factors, system controls, etc. are included in these estimates of system
performatlce.

High Pressure Gaseous Storage

High pressure gaseous storage is a relatively simple technology on the surface, offering dormancy,
easy filling and requiring only appropriate valving and metering to supply product. It has the
disadvantages of low volumetric densities and the perception of being excessively hazardous. For
this reason, it is often seen as a transitional stage of hydrogen storage development. However, the
excellent safety record of Compressed Natural Gas (CNG) vehicles should mitigate some of the
perception of hazard associated with compressed gaseous fuels. Moreover, storage and handling are
required for any hydrogen system, indicating a need for handling technology development and
standardization.
The design and qualification of highly efficient storage containers to meet all foreseeable
environmental, structural and safety requirements is not straight forward. A number of issues need
to be dealt with. Both vessels and distribution system must be hydrogen embrittlement-resistant (see
a related white paper [lo]). There is an upper bound in the practical or useful pressure imposed by
hydrogen embrittlement, fatigue effects, structural material limits and construction quality, and
pumping efficiency losses (which rise rapidly above 55 MPa or 8000 psi). Detailed design and
analysis work is required to assess the materials-manufacturing quality-pressure-costs tradeoffs.
Questions such as on-board pressurization vs. station-based pressurization must be addressed.
Department of Transportation (DOT)-qualified vessels are probably necessary to address both
perceptual risk problems and hypothetical hazards. However, DOT does not at present own the
regulatory problem of hydrogen fuel storage for vehicular propulsion. Ballard Power Systems of
Vancouver Canada is using DOT-qualified natural gas vessels to fuel its fuel-cell powered bus.
Frank Lynch and Associates of Denver CO are reportedly operating vehicles on hythane, also stored
in DOT-qualified natural gas vessels. Further demonstrations would be valuable.
Hydrogen density is known to increase greatly with decreasing temperature as shown in Figure 3,
suggesting that cryogenic hydrogen technologies deserve exploration. A related concept of high
pressure plus liquid storage was originally advanced by Kuhn[3] which is discussed later. A more
detailed assessment of the potential for cryogenic compressed gas storage should be performed.
Technolow Assessment
Some storage of compressed gas may be necessary for all hydrogen technologies. Safe hydrogen
gas handling equipment and infrastructure will be mandatory but from a consumer perspective is not
yet developed. The potential for achieving high storage densities by using pressures of 20.7-69
MPa (3000-10,000psi) is limited by the compressibility of the gas, fatigue, hydrogen embrittlement,
and mechanical energy and safety considerations. Never the less, if highly efficient hydrogen-using
vehicles become available, gas storage is viable for at least short- to moderate range applications.
Cryogenic gas storage has the potential of 50-100% increases in storage densities, but it must be
compared to liquid hydrogen.
Key Recommendations
Assess the cost-materials-construction quality-pressure tradeoff for a conceptual design
delivery system for compressed gas storage, integrating metallurgical, manufacturing, and non-
destructive test data bases.
Assess methane (natural gas) - qualified DOT vessels for hydrogen storage use.

9
 Develop a DOT-qualified advanced composite high pressure gaseous hydrogen vessel, using
improved textile-based polymer matrix composite technology and improved matrix toughening
technology. Analyze and verify long-term structural performance.
Investigate the effects of hydrogen exposure on composite liner materials.
Develop conceptual cryogenic gas storage designs and perform cost and technical trade-off
analyses.

Liquid Storage
Liquid hydrogen has been extensively demonstrated as a motor vehicle fuel by Los Alamos National
Laboratory, BMW, Nissan and others. An often-raised primary objection is that greater than 304;
of the fuel energy (12.5 kwhrkg) is required to liquefy hydrogen, decreasing system efficiency
significantly. (Research into magnetic liquefaction technology may diminish this cost.) This energy
penalty may be acceptable given the potentially high efficiency of hydrogen-using engines or fuel
cells, the possibility of recovering some of the liquefaction energy, and the anticipated environmenltal
and public health improvements resulting from decreased pollution accompanying a switch to
hydrogen fuel. Liquid storage offers moderately high storage weight densities, although the volume
is more than triple that of gasoline for equivalent BTU content. Some automotive analysts believe
that the volume represents a safety concern, although BMW successfully demonstrated 130 liter
tankage in a large automobile, which endured collisions without releasing hydrogen [lo]. Dormancy
is poor since the boil-off rate even with superior insulation is unacceptably high (ca. l.S%/day).
Venting of an expensive fuel is possibly unacceptable, and would require catalytic
combustiodflaring to avoid hazardous accumulations. Fractional losses are inversely related to thle
tankage size, and so light vehicles are at a disadvantage. Recent advances in thermal design and
shielding using boil-off gases may greatly improve the performance of even small tanks. Systems
for collectiiig the boil-off add greatly to the complexity, weight and cost of the system. However,
they would needed to obtain long dormancy periods. High-pressure dewars to contain the boil-off
have been suggested[3], but these only extend the "lockup" time to about 10 days, at the cost of a
very strong, high pressure tank with extensive and costly insulation and highly reliable valving.
Finally, consumer-oriented liquid hydrogen use would entail cryogenic hazards requiring safety
education, intelligent error-resistant refueling stations, and robust systems. The rigorous training of
operators and the detailed handling of liquid during transport and delivery of merchant liquid
hydrogen stands as testimony to these requirements [ 101. Liquid hydrogen is appropriate to
regularly scheduled, professionally maintained vehicle applications. BMWs automated filling
station [26] facilitates the fueling step. However, using liquid hydrogen extensively in the family
automobile still presents serious technical and social obstacles.
Technolopv Assessment
Commercial experience in handling and delivering large volumes of liquid hydrogen has been good,
although it relies upon careful training and strict procedures. It is doubtful that this level of rigor
could be transferred en masse to the driving public. Furthermore, dormancy of the containment is
inadequate for infrequently used vehicles, releases are unacceptable, catalytic burning technology
has not been demonstrated, and the acceptability of flaring and expensive fuel gas has yet to be
demonstrated. Fleet applications would be most suitable. Adequate ruggedness and resistance to
failure of vehicular LH2 containers have been demonstrated.
Key Recommendations
*Investigate techniques for extending dormancy; develop and demonstrate equipment.
*Develop a safe and easy to use refueling capability.
*Investigate techniques for improving weight and volume storage efficiencies.

10
Hydride Storage
Hydride storage of hydrogen has been demonstrated in vehicles by both Mercedes-Benz and Mazda,
although their vehicle ranges were severely limited because of volume and weight inefficiencies
associated with existing or current hydride state-of-the-art technology. Hydride storage avoids high
pressure concerns since hydrides are stable with relatively low gas overpressures. The theoretical
volume density of the materials themselves is high, and they exhibit unlimited dormancy provided
the necessary temperature and overpressure are maintained. However, it is anticipated that hydrides
will be readily poisoned by impure gas (oxygen) altering the kinetics and losing capacity. In
addition, certain hydrides may be pyrophoric or at least oxidize rapidly in an accidental release. The
ideal hydride absorbs and desorbs hydrogen near room temperature, has an equilibrium pressure
slightly above atmospheric pressure, is lightweight, but is highly dense in hydrogen. Unfortunately,
light hydrides bond ionically and require high temperatures, while the covalently bonded hydrides
which hydride and dehydride near ambient temperatures are heavy and are generally transition
metals. A combination of these traits is sought in laboratories worldwide. Now, a significant
opportunity exists to advance the state of the art, combining low temperatures and overpressures with
light weight. Superficial coatings applied to magnesium would facilitate low temperature charging
and discharging (by permitting hydrogen sorption and dissociation at low temperatures) and would
decrease the negative aspects of poisoning and pyrophoricity. Improved safety is expected with
such a system due to the low temperature and pressure and the coating which should be less air-
reactive than the magnesium alone. Never the less, safety will need to be demonstrated.
In addition, a significant effort to improve hydride bed design should be undertaken, using
computational models of heat and mass transfer, and confirmation through experiment. Storage bed
design efforts should include powdered metal hydride beds and porous metal matrix hydride beds
with superior heat transfer properties. The primary purpose of this work would be to achieve
improved volume density, up to 50% of the density of monolithic hydride. This work would have
applicability not just to hydrogen storage for fuels, but also to hydride heat pumps, which could play
a role as CFC-free air conditioning devices, as hydrogen storage media in advanced batteries, and as
hydrogen compressors.
Technology Assessment
Low temperature (transition metal) hydrides are too heavy for efficient vehicular use, and light
hydrides generally require unsuitably high temperatures for functioning. The basic hydrogen
binding mechanism is at the root of this effect. Alloying may partially blend the requirements,
however at the expense of weight increase and capacity loss. Magnesium metal, coated with a
hydrogen-adsorbing transition metal, is a good possibility for obtaining low temperature hydridind
dehydriding behavior, with small increase in weight and a small loss in capacity.

Key Recommendations
Develop a lower operating temperature, and a poisoning- and oxidation-resistant magnesium
(alloy) hydride material.
Develop a safe and easy to use refueling capability.
Design an optimized maximum volume efficiency hydride bed using both powdered hydride
and metal matrix hydrides.
Evaluate safety characteristics of candidate hydride beds.
Evaluate needed gas purity requirements for extended bed lifetimes, and regeneration methods.
Surface Adsorbed Media Storage
Of the various surface adsorbing media activated carbon is the most common and generally accepted
as the best performing for hydrogen storage, though recent advances in carbon aerogel technology
appear promising. Activated carbon has a very porous structure, allowing hydrogen molecules to 1%
condensed (adsorbed) onto the surface while gaseous hydrogen fills available void spaces.
Adsorption is enhanced by a reduction in temperature and by an increase in pressure. There are,
however, inherent limits in the total amount of hydrogen (hydrogen to carbon ratio) which can
effectively be adsorbed. Also, with continued increase in pressure the amount of additional
hydrogen adsorbed significantly decreases (approaches saturation) and the amount of hydrogen
stored in the carbon void spaces surpasses that adsorbed on the surface (at about 5.6 MPa or 810
psi, for AX-31M superactivated carbon) [ 101. As temperature decreases active cooling and
containment costs increase. Effective insulation can minimize cooling needs. However, this occurs
at the expense of system weight and volume storage densities. Studies have shown that moderate
storage densities can be achieved at 150 K and 5.6 MPa (810 psi) [12]. Utilizing recent advances in
composite pressure vessel technology a proto-typical storage system was developed having weight
and volume storage densities of 4.1 wt % H2 and 14.0 kg H g m 3 respectively [12].
The most significant need in the use of surface adsorbed media for hydrogen storage is the
development of a higher efficiency and/or room temperature adsorbent material. Future storage
densities of 8 - 10 wt % and 50 k g m 3 are often cited, but these are currently goals and may or maLy
not prove obtainable. Several activities are currently in progress to investigate various means of
improving the density and/or adsorptive capabilities of carbon.
A variety of other design, reliability, and safety issues are also yet to be resolved. The use of carbon,
while lowering the required operating pressure, adds net weight reducing efficiency. Extended
dormancy requires active cooling and significant insulation to minimize heat influx. Refrigeration
equipment must be carried on-board the vehicle, adding weight and complexity, consuming fuel arid
further reducing efficiency. Activation of the carbon must take place in-situ, or activated carbon
must be loaded into vessels, presenting handling and contamination problems. The surface can be:
readily poisoned by oxygen or other impurities. Relief devices and/or pressure vessel overdesign
will be required to guard against warm-up, both of which add complexity to and decrease efficiency
of the system.
Cost, while difficult to estimate because of the lack of a storage medium with suitable performance
characteristics, will likely exceed that of compressed gas systems, likely be greater than refrigerated
liquid systems, and likely be much less than hydride systems.
Technology Assessment
The major disadvantages of utilizing surface media adsorption for hydrogen storage are low
demonstrated storage densities (especially volumetric) on a usable scale and the need for active
cooling and control. The primary focus of this technology should be the development of higher
efficiency and/or room temperature adsorbent materials, including full scale storage density
demonstrations.
Key Recommendations
Develop a higher efficiency and/or a room temperature absorbent material.
Develop a safe and easy to use refueling capability.
Develop an active cooling and control system.
Address safety concerns.

12
Glass Microsphere Storage
Hollow glass microspheres have been proposed as a hydrogen storage technique for vehicular
applications due to good dormancy characteristics and intrinsic safety against catastrophic hydrogen
release. For utilization, microspheres would be loaded off-vehicle by subjecting them to high
pressure hydrogen at elevated temperature. Having the capability of being pumped or poured, the
charged microspheres could be loaded into a storage vessel of virtually any shape. To release
hydrogen for use the spheres would be reheated. The permeation characteristics of the microspheres
are such that while not in use, extended periods of dormancy can be achieved. Once the flow of
hydrogen out of the spheres is insufficient to power the vehicle the spent spheres must be removed
and replaced by fully charged ones. Glass microspheres are resistant to poisoning by atmospheric
gases, and are expected to be intrinsically safe against hydrogen fires under accident conditions
since only a small quantity of hydrogen can be released at a given time.
A significant amount of research on the use of glass microspheres for hydrogen storage has been
completed by Robert J. Teitel Associates (RJTA) under contract by the US. Department of Energy
through Brookhaven National Laboratory [13-161. In their studies RJTA obtained weight and
volume bed (not system) densities of 5.3 wt % H2 and 12 kg H2/m3, respectively, at fill conditions
of 300OC and 3500 psi. Ultimately, Brookhaven National Laboratory Project Management Staff
concluded[ 161 "The use of commercial grade hollow-glass microspheres for high pressure
hydrogen storage has been shown to be cost ineffective." This conclusion was based upon costs
associated with the initial material, microsphere breakage, low hydrogen storage densities, low
fraction of recoverable hydrogen, and fill and release energy requirements. More recently, Ontario
Research Foundation has investigated the use of cylindrical glass microcapsules for hydrogen
storage [ 171. Through process refinements microcapsules with axial tensile strengths of over 100
ksi were produced. Hydrogen storage capacities of over 2 wt % were achieved at moderate charging
pressures and temperatures. Lawrence Livermore National Laboratory is working on the
development of glass microspheres with a pressurization capability of 62 MPa (9000 psi) at 5000C
[ 181. If successful, this increased capability could significantly improve storage bed characteristics,
with 10% weight and 20 kg Hgm3 volume densities possible.
The primary disadvantage of glass microsphere storage is poor volumetric efficiency. Even if the
development of higher pressurization spheres proves successful, high pressure pumping efficiencies
may significantly limit overall system performance improvements. A secondary, but none the less
significant, disadvantage is the necessity of processing spent microspheres. It is unlikely that the
limitations of glass microsphere hydrogen storage can be overcome sufficiently to make this
technology suitable for passenger vehicular application, where volumetric efficiency and refueling
ease are critical. However, with volumetric efficiency improvements, this technology may be suitable
to fleet applications with low volume sensitivity, where refueling concerns are less important. The
microspheres do not present an inhalation hazard, although fragmented debris would be a concern.
Technology Assessment
The technical risks associated with glass microsphere storage utilization are minor. However,
uncertainty in the ability to achieve suitable performance characteristics is significant. Development
of improved microsphere bed performance is warranted since this is the limiting factor in terms of
future utilization. Uncertainty in terms of scaling between laboratory and full scale utilization is
minimal, and so full scale demonstration activities are not needed at this time.
Key Recommendations
Explore new materials and development of processes to manufacture economically attractive
microspheres.
Perform a total system energy balance including recycle, transport, energy costs, etc.

13
Chemical Reaction and Liquid Chemical Storage
Chemical reaction and liquid chemical storage technologies are most appropriate for applications
which are not weight sensitive. Chemical reaction hydrogen generation methods, such as oxidation
of sponge iron, offer claimed high volumetric efficiencies of storage (A1kg H2/m3) but at a severe
weight penalty (2 wt % H2). In practice, it is difficult to achieve total oxidation of the medium and,
therefore, the claimed volumetric and weight efficiencies. Refueling would probably involve
exchanging standardized tanks; any remaining unreacted finely divided particulate would be
potentially pyrophoric and hazardous. Assertions about industrial scale reduction and recycling of
the oxidizable medium have not been substantiated, and the potential mass of recycled iron is of the
order of 150 million tons per year. Furthermore, the generation process itself requires energy input,
lowering the overall efficiency of the system. Arthur D. Little Cop. estimates that these losses
could be well over 10%[4]. The use of improved catalysts may reduce elevated temperature
requirements, but these catalysts have not as of yet been developed.
Liquid chemical storage methods based upon storage and cracking of napthenes to aromatics, such
as cracking of methylcyclohexane to toluene and hydrogen require large volumes of liquid to be
recycled through the fueling system and represent dead weight to be carried on board. Large
volumes of toxic chemicals must be stored. Complex, heavy and expensive chemical cracking
equipment must be carried onboard to generate hydrogen. Furthermore, the higher the hydrogen
density, the greater the cracking temperature requirements. Dramatic improvements are required to
equal other storage methods in weight and volume efficiency, and in cost. One possible liquid
carrier is methanol, a high hydrogen density liquid at 12.5% by weight and about 100kg H2/m3.
Methanol may be reformed to yield hydrogen, and DOE programs are underway to evaluate
candidate technologies. Complex, though not necessarily heavy equipment, is required. System
controls and thermal management will require a high degree of engineering development. System
efficiencies of about 7.5 wt % H2 and 42 kg H2/m3 are estimated. Liquefied ammonia is more
dense in hydrogen (17%) and could be chemically cracked to yield hydrogen and nitrogen, but it is
toxic in low concentrations and does not readily disperse, adding a new and probably unacceptable
hazard.
Technologv Assessment
The iron reductiodoxidation storage technique has the potential for moderately high volumetric
storage densities. To achieve this potential the development of an effective catalyst which
operates at near ambient temperatures is required. Upon development, storage performance
characteristics should be evaluated using full scale demonstrations. Low weight storage
densities and the substantial quantities of iron required will likely limit the application of this
technology to niche markets. Most techniques of hydrogen storage as chemical media are
unacceptable in weight, volume, or complexity. It is not clear that the extensive development and
breakthroughs required to overcome these deficiencies can be realized.
Key Recommendations
Develop appropriate sensors and microprocessor control to manage catalytic reforming of
methanol and methane.
Develop an economical and effective catalyst for catalytic reforming of methanol and methane.
Design, manufacture and test a prototype methanoYmethanehydrogen generatiodstorage
system.
Develop an economical and environmentally sound method of sponge iron production.
Investigation of refueling logistics (fuel replacement, spent fuel disposition).

14
 Conclusions
The current state-of-the-art of hydrogen storage technology has been reviewed, the advantages and
disadvantages of each storage technique summarized, and a listing of potential research and
development activities has been presented. In defining the preferred research paths, and therefore
the supporting or enabling technology development tasks, the discriminating factors were the
following:
Is the technology appropriate for near or far term payoff?
What are the prospects of technical success?
(achieving weight and volume density, dormancy)
What are the prospects for economic success?
How does the technology fit with volume and weight sensitive applications?
What must be done to assure both safety, and the perception of safety?
The following discussion summarizes the conformance of these requirements and the enabling
technologies, with the intent of identifying the preferred technological and investment path for
short- and long-term hydrogen storage development.
We assume that mandated pressures for near-zero, zero emissions, and greenhouse gas free power
plants will accelerate a trend towards hydrogen andor electrically powered vehicles. We have not
treated the problems of the primary energy sources for hydrogen or electrical power generation, and
the byproducts from those processes. However, it is apparent that the relative importance of
minimizing localized pollutant emissions versus distant emissions will need to be considered. Also,
technologies which increase greenhouse gas emissions will need to be evaluated for their overall
desirability. These considerations should ultimately be added to those above.
Two hydrogen-fueled transportation options need to be considered: the near future (1-10 years) and
the distant (greater than 15-20 years) future. In the short term, highly modified internal combustion
engines and low technology storage solutions make sense (which does not imply that attempts to
apply fuel cell technologies to large vehicles, such as buses, is premature) to develop engineering
experience, public familiarity, and to demonstrate hydrogen as a potential solution to transportation
problems in impacted air basins. This approach will also emphasize the developing need for a
hydrogen infrastructure, and perhaps stimulate alternatives to an extended infrastructure such as
distributed generation. The transition to long-term technologies is somewhat approximate, but we
consider that in the long term, the introduction of fuel cells, lighter but more robust automobile
bodies, and many small innovations will make personal vehicles many-fold more efficient than is
currently the case.

Preferred Development Options

In the near-term, hydrogen vehicles fueled by hydrogen from either high pressure gas or transition
metal hydride storage may compare favorably with electric vehicles on cost, range, and performance.
This is especially so in small, highly efficient (low fuel consumption) vehicles. Advanced high
pressure storage in composite vessels is a high-certainty technology, although the ultimate
performance limits, especially volumetric efficiency, are sufficiently low that over the long term,
other technologies promise better performance. However, since there are uncertainties in
developing those technologies, and since there will continue to be a need for some (limited) volume

15
of compressed hydrogen storage, for start-up and transient demands, some attention to compressed
gas storage is appropriate.
The development of high-efficiency vehicles will significantly reduce the quantity of hydrogen
needed and the required weight and volume. Even now, subcompact 'town cars' may require less
than 1 kg of hydrogen (occupying less than 80 liters 2.8 ft3 and weighing less than 20 kg) to
achieve range (greater than 160 km) and performance superior to current electric vehicles.
Compressed hydrogen storage is probably unlikely to provide the 500+ kM range expected in
general purpose vehicles because of the volume requirements. Perceptions of the safety of
compressed hydrogen will undoubtedly benefit from the large number of CNG vesseldvehicles oin
the road. In order to improve weight and volume performance and safety, it is appropriate to pursue
developments in the toughening of matrix materials and application of textile technologies to the
fiber reinforcing materials.
Hydride storage media using transition metal hydrides have been developed, and vehicle-based
hydride beds have been engineered by Mercedes-Benz and Mazda, followed by fleet
demonstrations. In the near-future, transition metal hydrides may be useful for small, highly
efficient vehicles having short ranges, especially if the vehicle structure does not allow sufficient
crush space to protect a compressed gas tank. Improvements in bed volume efficiency would make
them attractive for small vehicles. Over the long term, a suitable lightweight hydride must be
developed if required dormancy, high density, safe hydrogen storage for personal vehicles is to be
obtained. High surface area magnesium, coated with appropriate hydrogen dissociating metals, is
the most promising long-term approach to obtaining both high volumetric and mass storage
densities. While the development of this technology carries high risk, the payoffs are
correspondingly high. The development of more volumetrically efficient hydride beds requires
innovative geometries and extensive thermal modeling and testing, and should interact extensively
with the materials development. While the goal seems to be technically achievable, the realization of
the technology is too distant for economics to be considered.
Liquid storage is appropriate for fleet-type applications, since regular schedules and professional
training in liquid handling are required. There have been numerous demonstrations of liquid
hydrogen handling and use. Dormancy problems, the necessity of fuel-venting and the losses
associated with small vessels contribute to this recommendation. Automation of filling and
handling as pioneered by BMW are essential to acceptance of liquid storage in general purpose
vehicles. Similarly, a solution to the boil-off and venting requirements is essential. It is difficult to
see a role for high pressure liquid storage in these applications.
Cryogenic storage of hydrogen gas has great potential today for fleet-type applications if
satisfactory high-efficiency cryogenic cooling devices and superinsulators become economically
attractive. As with liquid storage, small containers suitable for personal vehicles will pay a thermal
efficiency penalty resulting in economic penalties. These technologies represent moderate risk
items.
In the long-term development arena, adsorbate media, represented by superactivated carbon and
carbon aerogels, offer moderately high energy densities. Currently these media require a cryogenic
system to maintain the adsorbed state (that is, dormancy), and also require an overpressure of 5.6
MPa (810 psi), necessitating a pressure vessel. Analysis therefore shows that the addition of the
adsorbate and the cooling requirement reduces the weight efficiency of storage compared to
compressed gas storage. Scale-up has not been demonstrated. Efficiency and performance
characteristics should be evaluated from full scale demonstrations followed by the determination of
system requirements through a conceptual design. The development of a higher efficiency and a
room temperature absorbent material is needed. This includes a more complete understanding of the
fundamental mechanisms by which the adsorption process occurs. Without room temperature

16
adsorption, cooling requirements prevent the attainment of significant dormancy, making the
technology suitable only for fleet-type operations. The development of room temperature adsorbate
media paces the future acceptability of this technology.
Current high-performance glass microspheres are too expensive, and the volumetric efficiency is
still too low even with high (62 MPa) fill pressures to be useful in any but volume-insensitive
applications. Therefore, glass microsphere performance and production methodology should be
addressed if microsphere storage development is to proceed. It is not clear where microsphere
storage will be applicable, since other options are available even for volume-insensitive vehicles.
Steam oxidation of iron has the potential for moderately high volumetric efficiency, requiring
catalyst development and extensive process engineering to perform at near-ambient temperatures.
Even at full potential the technology cannot provide weight efficient performance. It may be
suitable for niche market applications which are relatively weight insensitive (such as locomotives),
but probably does not have general applicability. Most techniques of hydrogen storage as chemical
media (methanol, methylcyclohexane) which are reacted to yield hydrogen are inefficient in weight,
volume, or entail complex technologies to recover hydrogen. These technologies need extensive
development and breakthrough thinking in catalyst development, sensor development and process
controls. However, it is not clear that these inefficiencies can be economically overcome for mobile
applications. Ammonia, often cited as a high hydrogen density carrier, is probably unacceptable
due to its toxicity in low concentrations. Clearly, a breakthrough in the choice of hydrogen-bearing
storage medium is required, making all of these options long-term at best. As a stationary source of
hydrogen, natural gas reforming has good potential as a distributed hydrogen source, since the
natural gas infrastructure is well developed.

17
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19
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Figure 2A. System Weight and Volume per Kilogram Hydrogen for Various Storage Technologies.

20
200

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All Comwsite

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Current compressed from commercial products
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Microspheres estimate includes vessel, tank, Heat Exchangers
All pressure vessels have a safety factor of 3 on burst

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0.5 1 2 5 10 20

Gravimetric Density, wt. % H2

Figure 2B. Comparison of Hydrogen Storage Densities.

21
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22
 APPENDIX
REVIEW OF DEVELOPMENTS IN
HYDROGEN STORAGE AND DELIVERY SYSTEM TECHNOLOGY
In the following, we discuss the system requirements, and the state of the art for each particular
technology, including advantages and disadvantages. Safety issues, including DOT qualification and
other factors, and reliability issues associated with each technology, are also discussed. Finally, a
number of potential technological improvements resulting in performance improvements are
identified.

Hiph Pressure Gaseous Storage

Pressure vessel development
High pressure gaseous storage is conceptually a relatively simple technology, offering extended
dormancy and requiring only tankage and appropriate valving and metering to deliver product.
Filling a container is straightforward in theory, although in practice achieving leak-free couplings,
freedom from contamination by air, and satisfactory pumping rates at high pressures are important
design considerations. In practice, the design and qualification of highly efficient storage containers
is not straight forward. Furthermore, the vessel and distribution system must be hydrogen
embrittlement-resistant. The materials and techniques for handling high pressure hydrogen are well-
known and require somewhat more expensive materials and procedures than compressed natural
gas. The purity of the hydrogen has a dominant effect in the manifestation of hydrogen
embrittlement.
Storage of acceptable quantities of hydrogen in gaseous form (which we define as 7 kg, the DOE
target for a hydrogen-fueled vehicle [9]) requires pressures exceeding that of the current natural gas
3000 psi (20.7 MPa) standard in order to avoid excessively large storage containers. For example, at
3000 psi, 7 kg of hydrogen will occupy 462 liters (16.3 ft3) exclusive of the vessel, while at 8000 psi
(55 MPa) the gas occupies 208 liters (7.35 ft3). DeLucchi [11 has stated that storage to 8000 psi is
feasible. Safety, pumping costs, and engineering constraints, discussed below, must be considered to
determine whether this pressure represents an optimal or a desirable design point.
The safety concerns arising from increased containment pressure stem from the increasing
mechanical work (Pressure x Volume = Energy) contained in the gas. As pressure increases, the gas
becomes non-ideal, e.g. a given pressure increment results in less gas being stored than the previous
identical pressure increment. A useful figure of merit for the mechanical hazard is the stored
mechanical energy at different pressures, assuming a constant quantity of gas. Increasing pressure
from 3000 to 8000 psi ( 21-55 MPa), as in the previous example, and using a constant quantity (at
Standard Temperature and Pressure) of gas, causes only a few percent increase in contained
mechanical energy, since the compressibility deviates only slightly from ideal, e.g. the volume
decrease counterbalances the increased energy per unit volume. For 7 kg, the magnitude of the
energy is significant, that is, 13.1 x 106 ft-lbs, or the equivalent of 9.24 lbs of TNT. On an equivalent
BTU basis, hydrogen tankage would contain approximately three times the mechanical energy as
would natural gas. In practice, the extraordinary thermodynamic efficiency with which hydrogen may
be used in optimized applications (fuel cells, optimized internal compression engines) means that very
little additional mechanical energy is contained compared to compressed natural gas storage. Above
55 MPa (8000 psi), the increasingly non-ideal behavior of compressed hydrogen causes unacceptably
large increases in contained mechanical energy.

23
The engineering constraints which limit compressed gas storage arise primarily from considerations
of vessel performance in off-normal operating conditions. DOT requires that fuel storage containers
fail in benign ways when subjected to deliberate burst testing, fire, gunfire and impact. In the latter
cases, this involves leak-before-burst response. Appropriate factors of safety, which include static
fatigue, cyclic fatigue, and environmental considerations, must be selected. These factors interact
strongly with vessel design, mateiials, and duty cycle. Since composite vessel tankage is considered
as the only weight-viable option for vehicular applications, we will consider their behavior. Low
performance vessels (the volumetric and gravimetric efficiencies are low), such as fiberglass with
polyester resin over an aluminum liner, offer a benign burst mode. The use of Kevlar filaments over
aluminum improves storage efficiency, and at low stresses the vessels fail benignly. At high stresses,
their burst failure modes can shift to fragmentation. High performance (Pressure x Volume / Weight
>1 x 106 inches) carbodepoxy vessels, which offer high volumetric ( about 20 kg/m3) and gravimetric
(about 10 wt % H2) efficiencies, may fail burst and gunfire tests. Burst failures occur because of the
very high energies released by the high strength fibers into the matrix material which lacks sufficient
toughness to absorb the energy. Gunfire testing for example induces shock waves [191emanating
from the point of penetration that exceed the fracture toughness of the matrix. Mitigation of these
vessel response modes while maintaining high storage efficiencies is not straightforward. Pressure
down-rating these vessels will alter the failure modes but is not cost-effective, and greatly diminishes
storage efficiencies. Simple hybridizing, by layering a tough composite layer such as Kevlar and E-
glass inside the carbordepoxy layers, is effective but also reduces efficiencies significantly.
Alternative approaches are needed.
The development of analytical methods can minimize the reliance on expensive testing for technical
guidance. Modeling can provide mechanistic insight into failure modes, reduce the scope of required
(expensive) testing, and supply an understanding of design alternatives and limitations. Three-
dimensional finite element models can be used to analyze (1) the dependence of vessel burst strength
on fiber selection and lay-up process, (2) liner thickness-overwrap design tradeoffs, and (3) response
of pressure vessels to quasi-static localized penetration. The primary issues are stress distribution
and the response to localized cracking. The first goal is to predict the evolution of subcritical damage
to failure in a quasi-static loading mode. Dynamic behavior predictions must follow. Fabricators of
high performance composite vessels recognize the value in developing this approach, but there is
currently no centralized effort to fund and coordinate the many facets of this effort.
In the interim, detailed testing will remain crucial to the development of high performance alternatives.
Alternative resin matrices, fibers, and lay-up processes must be explored, often in combination. For
example, Spectra@ fibers (a linear polyethylene fiber with a low glass transition temperature polyester
resin matrix) offer improved toughness and strength at high deformation rates typical of impact or
gunfire penetration. These fibers also offer static strengths comparable to many high performance
graphite fibers and are currently in use in ballistic body armor. Techniques which should be
investigated for use in pressure vessels would include hybridizing lay-ups, hybridized fiber
construction, and 3-dimensional fiber weaves. Further experimentation in improved fiber-matrix
bonding should be conducted, that is, processes such as plasma treatment and chemical pre-
conditioning of carbon or other fiber tows, should be examined in detail. Tougher matrix materials
are highly desirable. Work has proceeded in this area for some time, and although it has not brought
significant benefits as yet, any initiatives in this arena should be considered for support, since matrix
toughness is a primary limiting factor in the response to impact, penetration and fiber failures.
Monolithic liners are commonly used in small composite vessels. However, large vessels may require
joined liners. Joints in either metallic or non-metallic liner materials have the potential for defects.
Joining techniques for candidate liner materials must be further developed, defects characterized and
controlled, and their consequences known. Since permeation of hydrogen will be a major issue, the
development of low permeation barrier materials is crucial. Since most testing is done at low
pressure, and since candidate barrier materials are likely to be pressure sensitive, testing equipment
will be needed for measuring permeation at full rated vessel pressures. Molecular alignment through
processing or welding may become instrumental in controlling permeation. A multiple barrier
approach may also be fruitful. Thin layers of metallic materials applied to the inner liner material
surface may be adequate for permeation minimization, although such coatings must adhere to the liner
over a wide temperature range.
Normal working environments for a high pressure vessel include the potential of hydrogen
embrittlement of the vessel wall. Hydrogen is known to severely effect the mechanical behavior of
most metals. Its effects on organic composite materials is not known, although it is anticipated that
there will be no effect. Accelerated chemical interaction phenomena need to be examined for liner
materials and for strength members. Some composite vessels use liners of aluminum alloys, and their
response to cyclic pressure fatigue in hydrogen needs to be examined. Aluminum is normally only
little affected by hydrogen; its protective oxide layer excludes hydrogen from contact and solution in
the metal. Vessel design to avoid plastic strains at corners, flanges, etc. is imperative to avoid rupture
of the protective oxide coating.
A related hydrogen storage technique is cryogenic storage of hydrogen gas. Hydrogen density as a
function of pressure and temperature approaches or exceeds that of liquid hydrogen over a range of
temperatures and pressures (Figure 3, from [20]); utilizing this density to advantage requires a high
degree of development of containment vessels and insulation in order to operate in the 50-100 K
temperature range. The actual choice of pressure and temperature is somewhat complex. For
example, at 34.5 MPa (5000 psi) and 77 K, the density of the gas is equivalent to that of LH2; at
higher pressure and/or lower temperature the density exceeds that of LH2. This is achieved without
paying the full energy cost of liquefaction, and with less heat influx and reduced insulation
requirements compared to LH2. Lowering the temperature while raising pressure would allow
increased density, up to approximately 96 kg H2/m3 (6 lbs/ft3) at 69 MPa (10,000 psi) and 30-40 K;
the practicality of these conditions is suspect since the thermally related design problems are like
LH2, and the system energetics become similar to that of LH2 because of the high compression
requirements. In addition, cryogenic pressurization technology appears to be undeveloped. At the
somewhat higher liquid nitrogen temperature (77 K), the technology is well developed and much of it
could be applied to hydrogen handling. The addition of high pressure, pressure reliefs and active
cooling complicate the problem but are not insurmountable.
For gaseous cryogenic hydrogen storage at temperatures below 77 K, a highly capable and heavily
insulated pressure vessel is required. The pressure vessel technology problem is similar to that
discussed previously, except for the consideration of thermal expansivity and mechanical mismatch
between liner and strength member should metallic liners be required. Insulation technologies (multi-
layer, perlite and aerogels for example) exist to hold heat leakage to the watt level, however the cost of
these insulations must be significantly decreased to be practical. A highly reliable cryogenic pressure
relief is required to guard against overpressure caused by warm-up, otherwise the vessel must be
capable of containing the room temperature gas. This is probably an unrealistic expectation for the
following reason. Warming from 77 K and 34.5 MPa (5000 psi) to 293 K, results in a gas pressure
of 190 MPa (27600 psi), and requires a pressure vessel of ca. 276 MPa (40 ksi) proof test capability
at an internal volume of 100 liters if it is to meet common code requirements for pressure vessels.
The cryogenic relief valve becomes a serious consideration below 90 K, since oxygen can condense,
freezing a valve and also providing a highly oxidative medium. Any satisfactory cryogenic device will
not expose valving to air, piimarily because of heat leakage but also to avoid these possibilities.
Finally, active cooling is necessary to achieve significant dormancy times. Typical cryogenic coolers
needed to achieve this temperature are expensive, bulky and inefficient. Electrically driven cooling,
e.g., cuirently available Peltier junction devices, are capable of removing only milliwatt quantities of
heat leakage and are likely to be inefficient. These devices need development to the watt level. LLNL,
has conceptualized the "Intellitank", [2 11 a microprocessor controlled cryotank composed of
composite materials, having a thermally conductive lining and using Peltier junction cooling devices.

25
This design concept responds to the dormancy, active cooling and gas delivery requirements. Most
of the vessel design considerations were discussed previously; thermally conductive liners may
require detailed development to avoid excessive m a s and volume, thereby compromising the
performance efficiencies of the tank. Further development of the components of the "Intellitank" is
desirable, in part because it would also be applicable to adsorbate media discussed later. The
temperatures could be higher, which would have advantages for avoiding "freezeup" and condensation
of air,and diminished thermal influx. A preliminary conceptual design, incorporating strength
member, insulation, valving, pressure reliefs etc. should be performed to compare to ambient
temperature storage as high pressure gas. The figures of merit would be estimated cost and weight
and volume efficiencies of storage. To be attractive, significant improvements would be necessary
over ambient temperature gas storage.
A few comments are in order on the high pressure storage of hythane, that is, blends of natural gas
and hydrogen, such as hythane 5 which is 5% (by BTU's) hydrogen in methane. The blending of
hydrogen and methane has the potential to provide an exceptionally clean-burning fuel, albeit a fuel
which continues to exhibit greenhouse gas emissions. In the absence of oxygen or carbon monoxide,
most of the hydrogen embrittlement effects exhibited by pure hydrogen must be mitigated [22-24:1 in
these blends. Compressibility is anticipated to decrease, and therefore the BTU content of the gas
stored at the Natural Gas Vessel standard 3000 psi ((20.7 MPa) will decrease. In order to provide
vehicular range, there appears to be a need to increase storage pressure and quantity, just as is the case
for hydrogen gas.

Balance of Plant
Balance of plant is that part of the system between the storage device and the energy conversion
device. The primary engineering issues for balance of plant are,
reliable and safe containment/delivery of hydrogen gas,
controlled conversion of gas from storage (cryogenic if applicable) or high pressure
containment to moderate pressure compressed gas, from hydride bed, etc.
efficiency of operation, e.g recovery of compression energy or heating of cryogenic gas,
for example.
With all storage devices and energy conversion devices, hydrogen gas must be handled at pressures
from roughly 0.3 MPa (fuel cell) to 7 MPa (fuel injection for internal mixture formation in an
internal combustion engine). (A discussion of the effects of hydrogen on the materials used in
existing qualified (DOT) natural gas containers is found in [2 13)
A primary issue in reliability and safety is design for hydrogen embrittlement. The choice of
appropriate materials is crucial. Hydrogen embrittles most structural materials in the anticipated
service environment, which consists of pressure cycles, mechanical fatigue cycles, and temperature
cycles. Increasing the hydrogen pressure, as for example in a fuel-injected internal combustion
engine, will accelerate hydrogen embrittlement and inevitably conflicts in material requirements will
arise. In addition, fittings and seals must be hydrogen-embrittlement and hydrogen-accelerated
fatigue resistant. Depending upon the service pressure, shielding or double containment of high
pressure fittings may be necessary, yet accessibility and inspectability must be provided. Inertial
and electrical shutoffs would be required in order to isolate gas in small volumes. Similarly,
mounting of lines, etc., to prevent failure in the event of collision should be addressed. Minimal
volumes and venting requirements must be established in order to preclude
ipitioddeflagratioddetonation events in case of leakage; illuminant materials to allow detection o F
underhood hydrogen flames, normally invisible, should be considered. Finally, hydrogen sensors
need further development, to preclude false a l m s of leakage.

26
Mitigation of hydrogen embrittlement by trace oxygen should be explored. Small amounts of
oxygen in hydrogen or in hydrogenhatural gas mixtures apparently mitigates most hydrogen
effects on susceptible steels [22,24]. Oxygen doped hydrogen could be labeled "safety grade"
hydrogen. Although oxygen is incompatible with hydride beds and possibly superactivated carbon
beds, the addition of oxygen to compressed gas might be satisfactory. Removal of oxygen, for use
in a fuel cell, could be performed by passing the gas over a hot filament. The additional few ppm of
water would not pose difficulties in maintaining fuel cell moisture balance.
Other plant development needs include reliable systems for
1. the controlled feed of hydrogen from cryogenic apparatus;
2. development of refueling capabilities with positive and fail-safe interlocks, discussed under
each storage option;
3. assessment and design of energy recovery devices such as turbochargers for pressurization
of fuel cell air supply using compressed hydrogen gas;
4. development of lower temperature ( d 5 0 K) refrigerant systems for cryogenic storage
techniques.

Technolow Assessment
Some storage of compressed gas may be necessary for all hydrogen technologies. Safe hydrogen
gas handling equipment and infrastructure will be mandatory, but from a consumer perspective is not
yet developed. The potential for achieving high storage densities by using pressures of 21-69 MPa
(3OOO-10,000 psi) is limited by the compressibility of the gas, fatigue, hydrogen embrittlement, and
mechanical energy and safety considerations. However, if highly efficient hydrogen-using vehicles
become available, gas storage is viable for at least short- to moderate range applications. Cryogenic
storage has the potential of 50-100% increases in storage densities, but must be compared to liquid
hydrogen storage.
State of the Art
Advantages
System is relatively simple and inexpensive.
Ready availability of gas at almost any flow rate desired.
Technology is well in hand to field demonstration vehicles.
Long dormancy without energy input or active control circuitry requirements.
Disadvantages
Low weight and volume storage efficiency.
DOT approved storage vessels are too large and heavy for efficient storage.
Significant pumping losses above 55 MPa (8000 psi).
Safety concerns associated with high pressure gas storage.
Key Research and Development Activities
1. Development of a demonstration pressure vessel and delivery system,
Utilizing existing technology develop a demonstration pressure vessel and delivery (valve,
metering and fill devices) system. Design constraints are to develop a system which can:

1) supply hydrogen to a fuel cell to safely operate a lightweight vehicle

- 2.5 - 7.0 kg hydrogen capacity
- flow rates to 0.5 dsec
- minimum 5 wt % efficiency
- minimum 15 kg/m3 volume density

27
 2) be used to evaluate peiformance changes caused by modification of hydrogen storage
components.
2. Assess methane qualified DOT vesse1s for hvdrogen storage use,
Any pressure vessel selected for high pressure gaseous hydrogen storage will require DOT
qualification for road use applications. An assessment of methane qualified DOT vessels for
use in hydrogen storage should be completed to identify likely vessel candidates and expected
performance characteristics for near term utilization. Specific areas of assessment should
include:
- short and long term hydrogen compatibility
- cyclic loading effects
- hydrogen embrittlement
3. DeveloD a DOT-aualifiable advanced composite high Dressure gaseous hydrogen vessel,
To maximize volumetric and weight energy density efficiencies for high pressure gaseous
hydrogen storage some form of composite pressure vessels will likely be required. Evaluate
composite pressure vessel technology with the goal of identifying potential candidates for high
pressure gaseous hydrogen DOT qualification. Vessel performance criteria should include:
- 2.5 - 7.0kg hydrogen capacity
- flow rates to 0.5 g/sec
- minimum 6 wt efficiency
- up to 34.5-55 MPa (5000 - 8000 psi) fill pressure
- operation at a suitably high safety factor (2.25-3.0) and DOT qualifiable
Activities shall include:
Assess composite pressure vessel technology for potential suitable candidates
- armoring efficiency and effectiveness
- multi-layer crack retardation construction
- alternative polymer matrix materials
Select the most promising candidates for further evaluation
Fabricate prototype vessels
Conduct safety and DOT burst and projectile tests
Evaluate peiformance characteristics
Document findings including identification of technical activities needed to further
vessel design and performance
4. Investigate the effects of hvdrogen exposure on composite vessel liner materials,
The use of polymeric liners in composite pressure vessels may provide an opportunity for
increasing the performance of high pressure hydrogen containers. However, combined high
cycle fatigue and high pressure hydrogen environments may lead to accelerated liner failure,
especially at joints. Investigation of these issues and determination of appropriate safety factor
ratings should be completed. This investigation should include the identification and testing of
low permeability polymeric liner materials.

Liauid Storage
Liquid hydrogen has been extensively studied as a motor vehicle fuel, and vehicles have been
operated on LH2 in Japan, Geimany and the USA. It is often considered to be the ideal means of
high-pressure injection of hydrogen into engines for internal mixture formation due to the cooling
effects and prevention of "hot spot" preignition; hence there is much interest in cryogenic storage
systems for liquid hydrogen. Moderately high hydrogen storage densities are attainable, that is 15-

28
20 wt % and ca. 30 kg H2/m3; however, on an equal energy basis an LH2 system is 6-8 times the
volume of gasoline. On an equivalent range basis, it is believed to be 5-6 times as voluminous[ 11.
Kukkonen has observed that this volume presents difficulties in safe containment [25], although
BMW has not substantiated this observation for its L H ~ f u e l e dvehicles. Dormancy is poor since
the boil-off rate even with superior insulation is equal to or in excess of 1.5-2%/day. Fractional
losses are inversely related to the tankage size, and so light vehicles are at a disadvantage. BMW
achieved 1.8%/day in a 130 liter tank [26]. Recent advances in thermal design, shielding using boil-
off gases, and insulating materials (such as aerogels) may improve the performance of even small
tanks. However, boil-off will remain a technical obstacle and an expensive problem for small,
infrequently used vehicles. While systems for collecting the boil-off add greatly to the complexity,
weight and cost of the system, they will need to be incorporated for long dormancy periods. Finally,
cryogenic hazards exist which would require robust systems. BMW's automated filling system
apparently solves this problem, although demonstration of high use reliability is required.
An economic trade-off between the costs of hardware to mitigate boil-off losses, and the costs of
simply venting gas can be made. At 6-8 $/Gigjoule, a commonly cited production cost range for
hydrogen fuel gas from reformation of natural gas, a capital cost of $2000-3000 might be born for
reducing or eliminating boil-off losses, which is within reason for vehicular sized systems. Attempts
to develop reliable catalytic systems to oxidize boil-off gas were reported a decade ago, but no new
work seems to have been performed since then. BMW has chosen to flare the gas instead. The
poor dormancy of liquid hydrogen may be partially overcome through the placement of a pressure
vessel within a liquid hydrogen cryostat. Cryostats vent at about 2.5 bar, but actual failure pressures
may be several hundred bar. A pressure capability of 345 bar (5 hi)will extend dormancy to three
to five days[3]. The primary disadvantages are those of liquid hydrogen with the addition of
potentially very high stored mechanical energy (due to the volume phase change).

Technolo gv Assessment
Commercial experience in handling and delivering large volumes of liquid hydrogen has been good,
although it relies upon careful training and strict procedures. It is doubtful that this level of rigor
could be transferred en masse to the driving public. Furthermore, dormancy of the containment is
inadequate for infrequently used vehicles, releases are unacceptable, and catalytic burning
technology has not been demonstrated. Fleet applications would be most suitable. Adequate
ruggedness and resistance to failure of vehicular LH2 containers have been demonstrated.
State of the Art
Advantages
Moderately high weight and volume energy densities.
Storage has been demonstrated.
Refueling experience exists.
Disadvantages
Liquefaction of hydrogen is relatively expensive.
Hydrogen being lost due to evaporation during dormancy and refueling must be captured or
used.
Safety concerns associated with handling cryogenic liquids.
Hybrid cryogenic/pressure vessel systems have high stored energy.
Kev Research and Development Activities
1. InvestiPate techniques for extending dormancv/develop and demonstrate ea-uipment
The goal is to achieve 7 days dormancy and to limit losses (not by venting) to less than l%/day
thereafter. This may be achieved through improved insulation and through hybrid systems
incorporating moderate pressure storage, coupled with active cooling using the fuel cell to power
a refrigeration unit.
2. Develop a safe and easy to use refueling c a ybilitv,
The refueling system would require recovery of boil-off for economic and safety reasons, as well
as secure couplings and interlocks. Much of this technology exists requiring primarily
refinements.
3. Investigate techniques for improvinp weipht and volume storage efficiencies,
In a hybrid pressure vessefliquid hydrogen container, the optimal ullage volume must be
reconsidered. However, weight will increase with the additional pressure capacity, necessitating
system trade-offs. Insulation requirements must be addressed in an actively cooled system.
4.Address safetv concerns associated with crvogenic liauid utilization,
Cryogenic safety, storage vessel and pressure controlhelief, reliability and, ultimately, crash
safety need to be addressed. This concern should be integrated into the above activities.

-
Hydride Storage
Hydride storage avoids the concerns of high pressure storage, since candidate hydrides are stable
with low gas overpressures. It also avoids the cryogenic related-concerns of activated media storage
and LH2 storage. The theoretical volume density of the materials themselves is high (about 100-115
kg/m3), and they exhibit long doimancy. Hydride storage for fixed site and mobile applications
have been demonstrated several times, as summarized most recently and completely by DeLuchi [ 21.
However, current hydride mateiials exhibit several shortcomings:
Hydrides are readily poisoned by impure gas [2] but can be regenerated by high temperature
vacuum treatment. This treatment may or may not be compatible with the containment
vessel.
Hydrides are expected to be pyrophoric in accidental releases due to the high area of very
clean (oxide free) metal surface.
Hydrides which readily exchange gas in and out at low temperatures are generally transition
metals or their alloys, but these alloys exhibit low (1 to 2 wt %) weight efficiency. High
weight efficiency hydrides (magnesium, 7.6 wt %) require high temperatures to discharge at
usable rates and are exceedingly slow to charge at low (room) temperatures. Previous
attempts to reduce the tempemture for charginddischarging hydrogen by alloying
magnesium, usually with nickel [25],have been unsatisfactory due to the resulting 50% loss
in capacity and increased weight (most alloying elements are heavier than magnesium).
Current hydride bed designs are inefficient, e.g. they obtain 1/3 of the theoretical H2 storage
density. There are a number of sources for these losses. A volume expansion allowance for
the formation of the hydride is necessary. Allowances must be made for particle
decrepitation and wedging, which may swell vessels upon repeated cycling. Heat exchange
manifolding requires 10-20% of the volume. Designing for a specific gas discharge rate
requires a balance between thermal requirements (thermal diffusivity of finely divided

30
 hydrides is low) and the need for small hydride particles to obtain significant mass flow.
Pour densities of fine particles as perfect spheres seldom exceeds 60 % of theoretical
density. The last factor is amenable to improvement and is discussed later.
The cost of metal hydrides is high.

Hydride Materials
It is possible to minimize most of the listed technical shortcomings through an ordered approach to
hydride design based on understanding the sources of the limitations. First of all, in order to obtain
high storage density parameters, a low 2 hydride material must be the basis, implying magnesium.
Magnesium suffers from slow hydrogen adsorption and release kinetics [28], requiring high
sorption and release temperatures, ca. 350-4oooC. Two processes decrease the discharging or
charging rates: surface dissociation of the hydrogen and hydrogen diffusion through a magnesium
hydride shell formed during the hydriding process. A coating which diminishes the activation
barrier to hydrogen dissociation will facilitate the charginddischarging process, making the
dissociation kinetics that of the coating material. The coating material may be a high permeability
material such as palladium [29,3 13 or a normal metal such as nickel [311. The coating should
withstand volumetric expansion during hydride expansion. The lowering of hydriding temperatures
from 350-400OC to near room temperature would be expected to prevent diffusion of the surface
layer into the magnesium. Second, hydrogen must diffuse through the hydride layer inhibiting
hydride formation at thicknesses ca. 0.6-1.3 pm [29]. Therefore, particle diameters from 10 nm-500
nm should facilitate full hydriding of particles at maximum rates. A complete review of these
phenomena has been published by Selvan et al[32]. Since particle cracking during hydriding
typically occurs on grain boundaries [33], small single crystal particulate should be tolerant of the
hydride volume expansion and not crack readily. Vessel design should not require additional
volume to allow for decrepitation if the particulate is resistant to decrepitation. Thus a suitable low Z
material, with a very fine particulate size of 10 nm - 500 nm, coated with a normal metal coating
selected for compatibility during hydride phase change expansion, would be expected to exhibit high
volume efficiency and hydiidinddehydiiding kinetics similar to that of the coating material.
Additional benefits of coated magnesium hydride are likely. The presence of a catalytic coating such
as palladium over the magnesium would diminish the possibility of fire upon vessel rupture,
improving the safety of hydride beds. In addition, it would improve resistance to poisoning by
oxygen or by carbon monoxide [34] which we believe would be reversible and would be amenable to
easier clean-up and re-activation processes than the typical very high temperature processing and
multiple hydriding steps currently required.
Alloying of magnesium can still play a role in the design of the hydride. The equilibrium
overpressure can be tailored to meet demands by judicious additions of nickel or aluminum.
However, in each case the overall weight efficiency of the hydride will diminish, making it less
attractive for weight sensitive applications. Lower weight efficiency hydrides with tailored
characteristics may find other applications than the stringent conditions which a vehicular
environment imposes.
Innovative new hydride materials may be formed by aqueous chemistry, and this route has been
touted to obtain size distributions of particulate like that of multiple-hydride/dehydride cycled
materials [35]. In aqueous electrochemical techniques, hydrogen-hydrogen bonds are not broken as
is the case in gas-phase hydriding, which removes an activation energy from the initial hydride
forming step. Thus hydride forming reactions are available using borohydride compounds which
mimic electrochemical reactions [34], reduction of intermetallics by alcohols [36,37] or by hydrazine
in KOH [38]. The borohydride techniques have been used successfully to make many hydrides and
should be considered for scale-up. Alternative electrochemical schemes should be evaluated as well.

31
Hvdride Bed Designs
Hydride bed efficiencies, stated in terms of energy densities on both a weight and volume basis,
represent a loss of 65-75% of the hydrogen density of the host hydride metal. Heat transfer
limitations are the primary driver of this aspect of hydride bed design. Convective models [39,4Q[
and one- and two-dimensional conduction models 141-431 have been applied to hydride bed design.
Some differences in assigning importance of variables exist between the models. More importantly,
convective models have not incorporated detailed knowledge of heat transfer as a function of
hydrogen concentration and hydrogen pressure and do not at this time consider hysteresis. Their
applicability Seems limited to AB5 (such as lanthanum-nicke1)and FeTi hydrides, which due to their
weight are of limited value to hydrogen storage for transportation. Of the two approaches, the
conduction models most fully account for the specific properties of hydride materials, thermal
properties as a function of composition, temperature and hydride composition and appear to offer
the most promise as design tools for optimization of conventional bed designs.
The single-most important obstacle to applying conduction models to hydride bed design appears to
be the prediction of the effective thermal conductivity for extremely fine particulate sizes in hydrid!e
beds and correlation with measurement, Effective thermal conductivity is decreased as particle size
is diminished, and since reaction pressures exceed one atmosphere while particle sizes are small,
packed bed thermal analysis becomes inadequate. Recently, improvements in the correlation of
theoretical and experimental thermal diffusivities have been made [MI. Conduction-based models
imply that theimal path length reductions and improved effective thermal diffusivity are required,
necessitating some innovative design approaches. The thermal diffusivity problem will magnify
should nano-phase palladium or nickel-coated magnesium become a viable material. Adequate
models must be developed, otherwise the design of efficient hydride beds for this material, having
the needed energy density, will be strictly a hit-or-miss process and optimized designs will be
elusive. In addition, innovative material schemes of depositing hydridable material on high
conductivity substrates, while achieving low pressure loss gas flow and adequate delivery rates, need
to be explored. Analyses [45] of porous metal-matrix hydride beds using high conductivity
substrates predict 40-fold thermal conductivity improvements. Such bed designs will be important
for hydride systems having high heats of hydride formation such as magnesium [45].
Combining an improved magnesium hydride-based material with new bed designs, high storage
densities and high performance, consistent with safety, are attainable with the application of the best
design and materials science tools. Hydride storage densities of 50 kg Hdm3 and 5 wt % H2,
approaching DOE'S goals of 70 kg H2/m3 and 7 wt H2 should be possible.
Technologv As sessment
Low temperature (transition metal) hydrides are too heavy for vehicular uses, and light hydrides
generally require unsuitably high temperatures for functioning. The basic hydrogen binding
mechanism is at the root of this effect. Alloying may partially blend the requirements, at the
expense of weight increase and capacity loss. Magnesium metal, coated with a hydrogen-adsorbing
transition metal, is a good possibility for obtaining low temperature hydridind dehydriding
behavior, with small increase in weight and a small loss in capacity.
State of the Art
Advantages
The hydride bed can be repeatedly recharged.
High volumetiic energy density compared to some technologies; potentially higher volumetric
energy density.
Long dotmancy periods are readily available.
Low overpressure means no significant mechanical energy to contain.
No significant pumping/pressurizing costs.

32
Disadvantages
Thermal management is required during charging and discharging hydrogen.
High system weight and low volumetric energy density (current technologies) compared to
potential performance.
Gas impurities can substantially decrease hydride bed life.
A light, high hydrogen density, low temperature hydride currently does not exist.
Finely divided clean metal powders are potentially pyrophoric.
Gas- and coolant-flow requirements prohibit achieving near-theoretical efficiencies.

Kev Research and Development Activities

1, Develon a lower oDeratinp temwrature coated magnesium (alloy) hydride.
Experimental programs to destabilize the hydride by alloying while retaining hydrogen storage
should be combined with hydrogen dissociation stimulating coatings on nanophase particulate.
This is a medium to long term program. Included is an assessment of the critical gas punty
requirements (02,CO), re-activation, etc.
2. Design an optimized volume efficient hydride bed for (coated) magnesium powder. and for
porous metal matrix hvdride using coated maenesium,
There are significant volumetric efficiency gains needed in packaging hydride reactors. This
effort would require both metal matrix hydride development, and optimized bed development
using computational techniques and experiment.
3. Develop a safe and easv to use refueling cmabilitv,
Refueling rates control and thermal management will require integration between refueling
stations and storage beds. The avoidance of oxygen contamination will require positive sealing
and evacuation of filling lines. These systems will need to be interlocked and reliable. The
efficient management and reuse of 'waste' heat from hydride beds and fuel cells or engines will
improve the thermodynamic efficiency of the system. A conceptual design is appropriate using
parametrically stated hydride properties followed by experimental confirmation.
4. Evaluate safety characteristics of candidate hydride beds.
The consequences of loss and/or dispersion of containment of the finely divided hydride
powders should be explored analytically and experimentally. Engineered solutions may then be
developed including compartmentalization,etc. Confidence in the tractability of the problem will
enable continued development of the technology.

Surface Adsorbed Media Storape

The storage of hydrogen on surface adsorbing media has been proposed as an alternative to the
more traditional techniques of compressed gas, liquid, and hydride storage. Of the various surface
adsorbing media, activated carbon is the most common and generally accepted as the best
performing for hydrogen storage, though recent advances in carbon aerogel technology appear
promising.
Activated carbon has a very porous structure, yielding a high surface area and void space fraction.
During cryoadsorption hydrogen molecules are condensed (adsorbed) onto the surface of an
activated carbon particulate while gaseous hydrogen fills available void spaces. The
hydrogedcarbon bond on the carbon surface is relatively weak, and so adsorption is enhanced by a
reduction in temperature. Adsorption is also enhanced by an increase in pressure. There are,

33
however, inherent limits in the total amount of hydrogen which can effectively be adsorbed. The
primary factor governing adsorption is the total amount of surface area available on the carbon.
Also, with continued increase in pressure the amount of additional hydrogen adsorbed significantly
decreases and the amount of hydrogen stored in the carbon void spaces surpasses that adsorbed 011
the surface (this occurs at about 6.5 MPa (8 10 psi) for AX-31M superactivated carbon) [113. As
temperature decreases active cooling and containment costs increase. For this reason an operating
temperature of at least 150 K, the lower bound of that sustainable with freon based refrigeration
systems, is typically desired. Effective insulation can minimize cooling needs; this is done, however,
at the expense of system weight and volume storage densities. When hydrogen is required for use:,a
modest increase in temperature will release it from the carbon surface.
Syracuse University has expended considerable effort in the research of cryoadsorption of hydrogen
onto carbon particulate [ 11,12,46]. Studies showed that 14 kg H2/m3 C storage densities could be
achieved at 150 K and 5.6 MPa (8 10 psi) [ 121. Utilizing recent advances in composite pressure
vessel technology a proto-typical storage system was developed [12]. The storage system was
constructed of a fiberlepoxy filament wound vessel with a 6061-T6 aluminum liner and had an
internal volume of 16.5 liters and a weight of 3 kg. Hydrogen was loaded onto the bed at a pressure
of 8.1 MPa (1 180 psi) and a temperature of 150 K. Following charging, the vessel pressure was
reduced to an operating level of 5.6 MPa. The vessel contained 2400 g of carbon, which was able to
adsorb about 230 g of hydrogen. The storage system had weight and volume storage densities of
0.041 kg H2kg system (4.1 wt %) and 14.0 kg H g m 3 system, respectively. The system weight
calculation was based upon the weight of the hydrogen, carbon, and storage vessel, but the system
volume calculation was based only upon the internal volume of the vessel. Based upon the external
vessel volume the calculated storage density decreases to 12.5 k d m 3 system, which still does not
include insulation or cooling and temperature regulating and metering equipment. While the
densities achieved are well below goals stated in the DOE Hydrogen Plan, the development of a
storage system within an order of magnitude of an actual use size gives the most accurate indication
to date of what storage densities can reasonably be expected utilizing this technology. Realistic
sizing studies can now begun to be made for vehicular applications.
Kuhn [3] estimates that a storage system with the ability to contain 15 lbs of hydrogen at 5.5 MPa
(800 psi) could do so with 4.8% weight percentage (usable hydrogedtotal system weight) and
require 15 cubic feet of volume (includes tankage, insulation, and heat exchangers). Based upon
these calculations he concludes that an 800 psi cryoadsorption system is not feasible. By increasing
the storage pressure to 34.5 MPa (5000 psi) he estimates the weight percentage could be increased
to 6.4 % and the required volume reduced to 7.8 cubic feet. But he notes that at these pressures
73% of the hydrogen is stored as compressed gas, making cryoadsorption systems heavier and only
slightly more compact than a 150 K, 34.5 MPa (5000 psi) compressed gas system. He concludes
that utilization of carbon in high pressure, low temperature systems is not advantageous due to
increased complexity and cost. Young [ 121 calculates that a graphite composite tank holding 1300 g
of compressed gaseous hydrogen at 20.7 MPa (30()0 psi) and 25OC would only be about 9%
heavier than a carbon adsorption vessel (including fuel) with the same hydrogen storage capacity.
This difference is minimal considering weight for insulation, cooling devices, and pressure relief
devices are not included in the cryoadsoiption calculation.
The most significant need in the use of surface adsorbed media for hydrogen storage is the
development of a higher efficiency andor room temperature adsorbent material. While
cryoadsorption of hydrogen onto carbon has the benefit of minimal temperature (compared to LH:2)
and pressure (compared to compressed gas storage) requirements, it is still less attractive than other
storage techniques on a hydrogen density storage basis, especially volumetrically. Future storage
densities of 8- 10 wt %I and 50 k d m 3 are often cited, but these are current goals and may or may not
prove obtainable. Several activities are cumntly in progress to investigate various means of
improving the performance of carbon adsorption materials. In these studies the goal is to improve

34
 the density and/or the adsorptive capabilities of the carbon. Improving carbon density increases the
amount of hydrogen stored in a given volume but also results in a weight penalty. Improving
adsorptive capability increases both the volume and weight storage density.
Surface area is the primary factor governing the amount of hydrogen a particular type of carbon can
. adsorb. However, Noh et al. have shown that different carbons having the same surface area can
have significantly different adsorption capabilities [46]. This led them to investigate
Modification/Metal Assisted Cold Storage (MACS) for improving the storage performance of
superactivated carbons [46]. This concept involves modifying the surface of carbon, either by
changing its acidity or impregnating it with metal. In either case, the goal is to increase the amount
of hydrogen which can be adsorbed on the carbon surface. They found that by increasing the
acidity, and therefore the surface oxygen complexes which act as adsorption sites, from 0.1 to 0.4
milliequivalents NaOWg of Witco carbon hydrogen uptake was increased from about 24 to 29 g
H 2 k g C at 25 atm, a 20% increase. They also found that by impregnating the surface of carbon
with an active transition metal such as Pd (1%) or PtK (5%), an increase in adsorption of 7 - 20% in
comparison to the support carbon was achieved. Further work needs to be completed in utilizing
these techniques in the development of an activated carbon with performance characteristics suitable
for vehicular applications.
Syracuse University has achieved hydrogen storage densities of 12-13% by carbon weight utilizing
a new carbon in conjunction with improved activation processes [ 121. To achieve these results,
however, the storage temperature must be reduced to 77 K. Furthermore, considering that carbon
only constitutes about half the weight of a filled storage vessel, the overall improvement in weight
density is still unclear. Obviously a reduction in storage temperature increases active cooling
requirements, and, therefore, costs. These costs must be weighed against increases in performance.
Allied Signal claims to have achieved moderate adsorption storage densities (2 wt %) at room
temperature and elevated pressure (13.8 MPa or 2000 psi) [47]. Further improvements are needed,
however, to reach storage density levels practical for vehicular applications.
The National Renewable Energy Laboratory [27] has called for the investigation of the hydrogen
storage capabilities of AX-21 carbon. This material has a surface area of ca. 3000 m2/g, a
characteristic which could yield favorable hydrogen storage densities.
Increased attention is being given to the use of carbon aerogels for hydrogen storage. The high
surface area of this class of material shows promise for obtaining acceptable storage densities.
Lawrence Livermore National Laboratory has been investigating the effects of composition,
formulation, pyrolysis temperature, and chemical activation on storage capability [48]. Tests on 19
different carbon aerogels at 5.6 MPa (800 psi)) and 77 K were completed, with several materials
having bed storage densities of greater than 4.3 wt % and 19.8 kg HYm3 [48]. While actual system
storage densities will be significantly less than those of the bed alone, future work may yield
acceptable performance characteristics.
Advocates of cryoadsorption hydrogen storage point out that pressure requirements are well below
that for compressed gaseous storage and cooling requirements are much less than that required for
liquid hydrogen storage. It remains to be seen, however, if this technique in fact incorporates the
advantages or disadvantages of these other techniques. Furthermore, a variety of other design,
reliability, and safety issues are yet to be resolved. The use of carbon, while lowering the required
operating pressure, adds weight compared to a simple pressure vessel. Extended dormancy requires
refrigeration equipment and significant insulation to be carried on-board the vehicle, adding weight,
reducing efficiency, and consuming fuel.
Activation of the carbon must take place in-situ, or activated carbon must be loaded into vessels,
presenting handling and contamination problems. The surface can be readily poisoned by oxygen

35
or other impurities. Relief devices and/or pressure vessel overdesign will be required to guard
against warm-up, both of which add complexity to and decrease efficiency of the system.
The cost of a practical cryoadsorption storage system is difficult to estimate because development of
a storage media with suitable performance characteristics has not been sufficiently developed to
allow operating conditions to be adequately defined. The cost of utilizing current materials will
exceed that of compressed gas systems due to carbon and active cooling requirements. It will likely
also be more costly than liquid cooled systems because the cost of reduced cooling requirements
will probably not offset the cost of carbon and material processing for refueling activities. It will
likely be much less expensive than hydride systems due to the use of a less expensive fuel carrier.
However, before more defrntive cost comparisons can be made an adsorbing material with suitable
performance characteristics must be developed.
Technolow Assessment
The major disadvantages of utilizing surface media adsorption for hydrogen storage are low
demonstrated storage densities (especially volumetric) on a usable scale and the need for active
cooling and control. The primary focus of this technology should be the development of higher
efficiency and/or room temperature adsorbent materials, including full scale storage density
demonstrations.
State of the Art
Advantages
Moderate weight energy densities.
Moderate operating pressure levels.
Potential for higher energy densities with further development.
Disadvantages
Low volumetric energy density.
System not demonstrated at full size.
Active cooling is required for operation and extended dormancy.
Heating is required to release hydrogen supply for use.
Absorption of gaseous impurities (including oxygen) readily occurs, reducing efficiency.
Handling and contamination problems exist during the refueling process.
Key Research and Development Activities
1. Development of a higher efficiency andor room temperature absorbent material,
The cryogenic requirements for adsorption need to be reduced and the density of storage
increased. This includes more fully understanding the fundamental mechanisms by which the
hydrogedcarbon adsorption process occurs. The addition of a gas over pressure to improve
volumetric efficiency should be explored. Prototype systems using current materials should be
built to explore the design requirements for cooling, dormancy, safety, cost and efficiency, etc,
Efficiency and performance characteristics should be evaluated from full scale demonstrations.
2. Development of a safe and easy to use refuelin? capability.
Couplings, gas metering, ovefflow or heated gas recovery, and the cooling capacity of the storage
system, all must be developed prior to fielding demonstration vehicles. The activation of carbon
beds may be incompatible with efficient composite vessels. Development of the
loadindactivation sequence and techniques for mass production of the carbon bedvessel
combination is needed.

36
 3. DeveloDment of an active coolinP and control svstem,
A highly efficient system for cryogenic maintenance must be developed for operation and to
obtain extended dormancy.
4. Address safetv concerns,
Accidental loss of containment and/or dispersion of carbon and hydrogen should be simulated
C
and studied experimentally. Cryogenic apparatus requirements for thermal isolation, and for
robust reliability, must be developed.
5. Evaluate needed gas puritv rea uirements for extended bed lifetimes,
The rate at which impure gas causes loss of capacity should be characterized in order to set
punty requirements. Regeneration techniques should be developed and characterized.

-
Glass Microsphere Storape
Hollow glass microspheres have been proposed as a hydrogen storage technique for vehicular
applications due to good dormancy characteristics and intrinsic safety against catastrophic hydrogen
release. For utilization microspheres would be loaded off vehicle by subjecting them to high
pressure hydrogen at elevated temperature. Having the capability of being pumped or poured, the
charged microspheres could be loaded into a storage vessel of virtually any shape. To release
hydrogen for use the spheres would be reheated. The permeation characteristics of the microspheres
are such that while not in use extended periods of dormancy can be achieved. Once the flow of
hydrogen out of the spheres is insufficient to power the vehicle the spent spheres must be removed
and replaced by fully charged ones. Glass microspheres are resistant to poisoning by atmospheric
gases, and are expected to be intrinsically safe against hydrogen fires under accident conditions
since only a small quantity of hydrogen can be released at a given time.
A significant amount of research on the use of glass microspheres for hydrogen storage has been
completed by Robert J. Teitel Associates (RJTA) under contract by the US. Department of Energy
through Brookhaven National Laboratory [13-16]. In 1979 RJTA evaluated several commercial
grades of glass microsphere, including Fillite 200/7 and 30017 and 3M D32/4500. Evaluations
completed included pressurization, filling and dispersion, cyclic, and storage tests. Based upon this
work 3M grade D32/4500 displayed the best overall performance, and was therefore selected for
more detailed characterization studies. Following are some of the key findings of the evaluation for
bed characteristics of as received 3M D32/4500 microspheres [14].

Bed characteristics for fill conditions of 300OC for e 1 hr at a fill pressure of 24.1 MPa (3500 psi.)
55% of the stored hydrogen was available at 200OC, while 70% was available at 250OC.
A weight density of 5.3 wt % H2 (bed) was achieved.
A volume density of 12 kg H2/m3 (bed) was achieved.
A storage half-life of 110 days was achieved.
Microsphere sizes ranged from 5 to 60 microns, with an average of 27.7 microns.
Bulk density was 0.2 d c c or 200 kdrn3.
Packing fraction was 0.63.
Other findings
During crush tests 96% of the microspheres survived under a 24.1 MPa (3500 psi)
nitrogen over pressure, while only 50% survived at 41.4 MPa (6000 psi).
Cyclic pressurization at a given amplitude did not generate further microsphere failures.
Debris from a failing microsphere can cause other microspheres in the vicinity to fail.
Pressure gradients of 34.5 MPa (5000 psi) across microsphere walls caused failure.

37
From the bed characteristics listed above, we estimate that a weight density of 4 - 4.5 wt % H2 and a
volume density of 8 - 9 kg/m3 could be obtained in an engineered system including heating,
manifolding, and container with low pressure capability.
Following the initial studies described above, additional commercial sources of glass microsphere
were evaluated with the goal of gaining an understanding of how microsphere bed designs could be
optimized to maximize high pressure hydrogen storage and delivery performance [ 15,161. Eight
different sources of glass microspheres were evaluated, including 3M grades D32/4500 (two lots),
A38/4000, and B38/4000, Emerson & Cuming grades EC-202, EC-SI, EC-HAS, and EC-HASY,
and Fillite grade 200/7. The various microsphere grades were screened based upon storage,
breakage, and cost considerations. The screening procedure included chemical, surface and
microscopic analyses, density, pressure, and hydrogen flow measurements, crush tests, and fill-
dispersion tests. From this screening process two grades, 3M D32/4500 and Emerson & Cuming,
EC-HAS, were chosen for performance optimization studies. During these studies the effects on
performance by particle size separation, surface treatment, stress relief heat treatment, and over
pressurization treatment processes were evaluated. This phase of the study was not completed due:
to a redirection of the program. However, from the work which was completed the following
conclusions were made [ 161:
For commercial microspheres fill pressure is limited by strength.
Glass composition must be modified to improve microsphere dispensation characteristics
for suitable vehicular application.
Unacceptable breakage of off-the-shelf microspheres occurs for 400 atm room
temperature hydrogen storage fill-dispense cycles.
Preliminary studies indicate that particle densities (0.35 - 0.42 dcc, aspect ratios of 34 -
40) suitable for operation up to 40.5 MPa (5900 psi) can be extracted from off-the-shelf
microspheres.
Ultimately, Brookhaven National Laboratory Project Management Staff concluded that [161 "The
use of commercial grade hollow-glass microspheres for high pressure hydrogen storage has been
shown to be cost ineffective." This conclusion was based upon costs associated with the initial
material, microsphere breakage, low hydrogen storage densities, low fraction of recoverable
hydrogen, and fill and release energy requirements.
More recently, Ontario Research Foundation has investigated the use of cylindrical glass
microcapsules for hydrogen storage [17]. The focus of this work was the development of hollow
fiber fabrication processes and the measurement of ensuing microcapsule properties. Since storage
pressure is primarily controlled by microcapsule dimensions and material tensile strength these
attributes were the primary focus of the development program. The ability to increase storage
pressure would allow an increase in storage volume and weight densities. The microcapsule material
chosen was fused silica due to its favorable hydrogen permeability, strength, and hydrofluoric (HE:)
acid etching characteristics. Processes examined included shellac coating for retardation of aging
effects, fiber end-sealing for strengthening, and HF etching for dimensional control and
strengthening. Through process refinements microcapsules with axial tensile strengths of over 100
ksi were produced. Hydrogen storage capacities of over 2 wt % were achieved in laboratory tests at
moderate charging pressures and temperatures [ 171.
Lawrence Livermore National Laboratory is working on the development of glass microspheres wtth
a pressurization capability of 62.1 MPa (9000 psi) at 500OC [18]. If successful, this increased
capability could significantly improve storage characteristics of the bed, with 10% weight and 20 kg
HYm3 volume densities possible. System densities of 7 wt 3' % H2 and 13 kg Hdm3 would be
obtainable.

38
 The primary disadvantage of glass microsphere storage is poor volumetric efficiency. Even if the
development of higher pressurization spheres proves successful, high pressure pumping efficiencies
may significantly limit overall system performance improvements. A secondary, but none the less
significant, disadvantage is the necessity of processing spent fuel. Increased refueling time will
definitely be inconvenient for customers, but increased cost resulting from supplier processing may
be prohibitive.
*
It is unlikely that the limitations of glass microsphere hydrogen storage can be overcome sufficiently
to make this technology suitable for passenger vehicular applications where volumetric efficiency
and refueling ease are critical. However, with volumetric efficiency improvements, this technology
may be suitable to bulk fleet applications where refueling concerns are less important.
Technoloy Assessment
The technical risks associated with glass microsphere storage utilization are minor. However,
uncertainty in the ability to achieve suitable bed performance characteristics are significant.
Development of improved microsphere performance characteristics are warranted since this is
the limiting factor in terms of future utilization. Uncertainty in terms of scaling between
laboratory and full scale utilization is minimal, and so full scale demonstration activities are not
needed at this time.
State of the Art
Advantages
Intrinsically safe against catastrophic hydrogen release.
A weight density of 5.3% is currently achievable (bed density).
Good dormancy characteristics.
Microspheres may be poured to fit nearly any shape.
Resistant to poisoning by atmospheric gases.
Disadvantages
Low volumetric storage efficiencies.
Spent fuel requires processing.
Heat is required to charge the spheres, as well as to release hydrogen for use.
Level of glass particulate inhalation hazard undetermined.
The maximum practical fill pressure is about 41 MPa (6000 psi) due to pumping costs.
Kev Research and Development Activities
1, Development of improved glass microsphere performance characteristics,
Development of microsphere beds with characteristics suitable for vehicular applications is
needed. The key element in this activity is the development of higher strength microspheres.

Chemical Reaction and Liquid Chemical Storage

Iron Reduction/Oxidation Storage
A patented hydrogen generatiodstorage method based upon the oxidation of sponge iron has been
proposed as an environmentally safe, cost effective alternative to typical hydrogen storage techniques
[49]. An overview of the technique is given below, summarized from the detailed descriptions of
[2,49,50]. Feed stock (sponge iron) and steam (H20) are produced by reducing iron oxide (Fe304)
with either hydrogen (H2) or carbon monoxide (CO) gas as follows:

39
If carbon monoxide is used as the reducing gas the reaction becomes exothermic, requiring no heat
input. However, if hydrogen gas is used as the reducing agent the reaction becomes endothermic,
requiring the addition of heat for completion. Both reactions occur at about the same temperature
(800-11 W C ) and are nearly thermally balanced once initiated.
After production, the iron feed stock is loaded as a powder into either steel or reinforced plastic
cylinders and placed onto the vehicle. To generate hydrogen for vehicular use the reduction process
is reversed. Sponge iron is oxidized with steam at a temperature typically between 600and 9oOOC.
Hydrogen and iron oxide are produced as follows:

If a catalyst is used the required reaction temperature can be reduced to 100-2oooC. A further
reduction in reaction temperature to about 25OC may be possible with the use of a very efficient but
likely costly catalyst [2]. DeLuchi [2] notes that for practical implementation a balance must be
struck between the extremes of using a costly catalyst requiring negligible heat input and using no
catalyst, requiring significant heat input and adding to system complexity. For fuel cell applications
the catalyst would be necessary since tail gas temperatures (80-110%) are inadequate for production
of high temperature steam.

700 watt-hourslpound 39 g H2/kg

51 watt-hourdcubic inch or 78.7 k g H m 3
$O.Ol(/kW-Hr same
3.9 % H2 equivalent! same

370 watt-hourdpound 20.7 g H2kg

27 watt-hourdcubic inch 41.6 kg HYM3
$0.18/kW-Hr same
2.06 wt %H2 equivalent same
The proposed reduction/oxidation process clearly has several advantages over other, more traditional,
hydrogen storage techniques. The production of hydrogen on demand reduces the inherent safety
concerns associated with long term storage of significant quantities of hydrogen. The oxidation
reaction occurs at ambient pressure, eliminating high pressure safety concerns. (In exchange for the
reduction of one hazard, however, the presence of finely divided, oxidizable iron powder presents
two safety concerns in the event of cell rupture and dispersal, that is pyrotechnic oxidation and
dispersdhnhalation of fine particulate.) The hydrogen produced will be of high purity provided the

40
iron and water are sufficiently pure, making it suitable for fuel cell use. Finally, Maceda and Wills
[50] claim that this technique represents a significant opportunity for the development of a very
economical system.
There remain, however, a variety of technical and practical issues which must be resolved by ongoing
research and development activities. The initial reduction process used to generate the sponge iron
feed stock requires very high temperature (800-1 lOoOC), resulting in a variety of high temperature
design issues and expenses. To a lesser degree the elevated temperature generation of hydrogen on
board also requires additional mechanical design considerations. Furthermore, the generation
process itself requires energy input, lowering the overall efficiency of the system. Arthur D. Little
Corp. estimates that these losses could be well over 10% [4]. The use of improved catalysts may
reduce elevated temperature requirements, but these catalysts have not as of yet been developed.
Also, concern has been raised that during the oxidation process only surface iron is reacted, thereby
greatly reducing reaction effciencies[4]. Additional processing steps may be necessary to obtain
near-theoretical reaction efficiency. Furthermore, it is possible that iron powder, necessarily fine to
improve surface area exposure to maintain efficiency, may tend to pack together upon repeated use
[43. Finally, the response to vibration and shock in the vehicular environment are uncharacterized,
and may result in compaction.
Further difficulties may arise during the engineering of a prototype system. For instance, it is not
clear how efficient the oxidation process will be on the scale necessary for vehicular applications.
The iron powder must be easily loaded in a configuration which allows effective oxidation. After
use the iron oxide must be easily removed and processed.
It is unclear whether the reduction of spent iron oxide fuel would occur at local refueling sites
(service stations) or at centrally located reprocessing facilities where chemicals such as carbon
monoxide could be more safely handled. While local processing would eliminate shipping and
transportation costs, economies of scale may preclude the feasibility of local processing sites.
Issues of refueling(wh0 does it, how long it takes), tank exchange, couplings, purging, etc. have not
been addressed. Multiple tankage will probably be necessary to avoid "running out", increasing the
number of exchanges required. A major obstacle to full-scale implementation of the technology is
the mass of recycle material. R. Williams [51] has calculated the amount of recycled sponge iron to
sustain the US. light vehicle fleet to be 700 million tons per year, assuming high efficiency vehicles.
New production quantity is about 50 million tons per year. The transportation and infrastructure
costs would be exorbitant. If this problem is not solved, sponge iron oxidation may forever be a
niche market commodity.
It is difficult to estimate what the cost of an iron based system would be. The quoted hydrogen
storage cost of $0.1Skilowatt-hour is definitely superior to many storage techniques. This value
does not cover auxiliary system costs such as plumbing, catalysts, and spent fuel removal or the cost
of incomplete reaction. From a system perspective, it does not include the fuel economy cost of the
low weight efficiency. For example, the DOE target 7 kg of hydrogen would require a storage
system weight of ca. 350 kg, roughly equivalent to a 2 mpg decrease in gasoline equivalent in today's
vehicles. Consideration of all additional costs would appreciably raise the projected energy costs.
Work on the iron reductiordoxidation process is in the early developmental stage. Further
developmental effort will help resolve remaining unknowns, many of which are related to system
implementation on a scale suitable to vehicular use. These unknowns include actual system
performance and cost, the most effective means of sponge iron production, logistics of adequate
refueling operations, the overall system complexity, and the mass of material which must be handled.

41
Technolow Assessmen€
The iron reduction/oxidation storage technique has the potential for moderately high volumetric
storage densities. To achieve this potential the development of an effective catalyst which
operates at near ambient temperatures is required. Upon development, storage performance
characteristics should be evaluated using full scale demonstrations. Low weight storage
densities and the substantial quantities of iron required will likely limit the application of this
technology to niche markets.

state of the Art

Advantages
On-demand hydrogen generation rather than storage.
Avoids storage of significant quantities of hydrogen.
Operates at ambient pressure.
Potentially volume efficient compared to other hydrogen storage techniques.
Disadvantages
Elevated temperature operation requires additional design considerations.
Replacement of solid material required for refueling.
A catalyst may be required to achieve acceptable reaction temperatures and efficiencies.
An onboard energy supply is required.
Necessity for processing spent fuel(iron oxide) implies infrastructure with unquantified
concerns.
Low weight efficiency as a hydrogen storage medium implies vehicular efficiency loss.
Unproven oxidation efficiency on a scale necessary for vehicular applications.
Potential safety concerns stem from oxidizable fine particulate.
Key Research and Development Activities;
1. Develooment of an economical and effective catalyst,
Development of a more effective, lower temperature catalyst is required to yield necessary
improvements in the overall efficiency of the system. Studies should be completed to assess the
degree of reaction of the oxidation process and to establish a suitable means of processing
unreacted particulate. The catalyst mateiial must be relatively inexpensive to make the system
economically viable.
2, Development of an economical and environmentally sound method of sponge iron
production,
Development of an economical and environmentally sound method of sponge iron production is
needed. Processing temperature and user distribution requirements of the fuel may make the
technique too costly.
3. Investigation of refueling logistics (fuel replacement. soent fuel disposition2
Logistics for refueling should be investigated, followed by a demonstration. Requirements for
assuring availability of fuel and handling of unreacted particulate must be established.

4. Desim. manufacture and testing of a prototype hydrogen generation/storage svstem,

To date only laboratoiy reduced scale experiments have been completed utilizing this hydrogen
storage/delivery technique. Performance characteristics should be evaluated on a full scale
system to allow a more comprehensive assessment of the technology to be completed.

42
Liquid Chemical Storage
There are currently several candidate liquid chemical systems under consideration.
Methylcyclohexane can be stored onboard a vehicle, and can then be catalytically cracked to yield
hydrogen and toluene. The toluene is returned to a storage tank for later rehydrogenation. As with
the iron oxidation concept, this material represents an inert mass to be carried with the vehicle,
diminishing the overall system efficiency. Toluene is toxic and heavier than air, and so represents a
significant accidental release hazard. The hydrogen density of the medium is lkg Hg18 kg of
methylcyclohexane, that is, 5.55 wt %, and about 43 kg/m3 volumetric density. Taube [52,53] cites a
700 kg dehydrogenation system. Thus the system weight efficiency is very low, and only
locomotives or other heavy vehicles could utilize this technology. Breakthrough improvements in
cost and weight are needed, with the probable result that efficiencies would only equal that of
systems using other more benign components.
Methanol can also be reformed to produce hydrogen. The methanol reformer (which must be
carried onboard to generate the hydrogen) is under development. Bentley [4] estimates that an
advanced methanol refoimer system, assuming 80%efficiency and no onboard water storage, would
achieve about 7.5 wt % and 42 kdm3 volumetric hydrogen density. Methanol is also toxic, but is
probably only marginally different from gasoline in its hazards. Ammonia is an excellent example
of a high hydrogen-density chemical medium. The technology to crack ammonia has not been
applied to vehicular concerns; indeed its toxicity would argue against its extensive use.
Technolopy Assessment
Most techniques of hydrogen storage as chemical media are unacceptable in weight, volume, or
complexity. It is not clear that the extensive development and breakthroughs required to
overcome these deficiencies can be realized.
State of the AIT
Advantages
Potentially high volumetric efficiencies.
Disadvantages
Low weight energy density.
Incomplete reaction.
Significant on-board heat requirements.
Potentially pyrophoric powders.
Complex reformer technologies.
Kev Research and Development Activities
1. Analyze proposed storage svstems.
Alternative media such as chemical hydrides should continue to be analyzed, and the total energy
balance of these systems studied from the practical perspective of design and development.
Otherwise, a significant technology could be overlooked. These efforts are very long-term, in
excess of ten years.
2. Develop appropriate catalvsts. sensors and microprocessor control to manage reforming of
methanol and methane,
Satisfactory stationary reforming equipment could provide the means to sidestep hydrogen
infrastructure questions; that is, reforming of methane could be distributed, avoiding long-range
transport of hydrogen. Methanol reforming to hydrogen has relevance to biomass schemes,
although it would be probably less distributed than methane reforming. Microprocessor control
 is available, provided affordable catalysts can be developed, and sensor development and process
control can be established.

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46
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