The University of British Columbia
Faculty of Applied Science
1 LETTER OF TRANSMITTAL
Dylan Stephanian
University of British Columbia
6350 Stores Road,
Vancouver, B.C.
V6T 1Z4
March 31, 2010
Mr. Randall Kerr
Faculty of Applied Science
University of British Columbia
5000 – 2332 Main Mall
Vancouver BC
V6T 1Z4
Dear Mr. Kerr
Subject: Formal Report Assignment for APSC 201
Our group has prepared the following document on the safe storage of hydrogen in
response to your request for a formal report in Applied Science 201 section 206.
The enclosed report, entitled “Hydrogen Storage” considers the advantages and
disadvantages of four primary hydrogen storage methods. We will outline hydrogen
safety considerations as well as storage in tanks, micropores and sodium
borohydride before making recommendations regarding the most appropriate
storage technologies for certain applications.
It is our hope that this report will exceed the expectations for this assignment. If you
have any questions or concerns, please contact Dylan Stephanian at
d.stephanian@gmail.com.
Thank you,
Davis Wuolle, Dylan Stephanian, Jerry Zhao, Justin Park and Katherine McLauchlan
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
HYDROGEN STORAGE
Submitted to Mr. Randall Kerr
By Katherine McLauchlan, Justin Park,
Davis Wuolle & Jerry Zhao
The University of British Columbia
Applied Science 201
Wednesday March 21, 2010
HYDROGEN STORAGE
2 The University of British Columbia
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3 ABSTRACT
The report we are presenting explores the options available for the storage of
hydrogen for energy transfer. The current developments surrounding hydrogenbased energy transfer technology enables us to launch a fascinating excursion into
the safety related issues surrounding hydrogen storage and transport. This report is
an informative inquiry into the current innovations in hydrogen storage, which is an
important aspect of the budding hydrogen fuel industry.
Additionally, we will outline the advantages and disadvantages of several
hydrogen storage technologies relative to the challenges each of them face.
Although there is currently no dominant form of storage, we have analyzed and
discovered a number of viable storage methods.
HYDROGEN STORAGE
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4 TABLE OF CONTENTS
ABSTRACT
II
LIST OF FIGURES
V
GLOSSARY
VI
LIST OF ABBREVIATIONS
X
1.0 INTRODUCTION
12
2.0 SAFETY FACTORS AFFECTING HYDROGEN STORAGE
13
2.1 INTRODUCTION
13
2.2 RISKS
13
2.2.1 FIRE & EXPLOSION
13
2.2.2 HYDROGEN POSTING
15
2.2.3 TANK RUPTURE
16
2.2.4 CRYOGENIC RISKS
17
2.3 CONCLUSION
18
3.0 STEEL STORAGE
18
4.0 COMPOSITE STORAGE
19
4.1 ADVANTAGES OF STORAGE TANK STRUCTURE
19
4.2 STORAGE TANK STRUCTURE
20
4.3 MATERIAL PROPERTIES
21
4.4 WEAKNESSES OF COMPOSITE STORAGE TANKS
22
4.4.1 HIGH TEMPERATURE LOADING
22
4.4.2 CRYOGENIC LOADING
23
4.5 CONCLUSION
5.0 MICROPORE STORAGE
5.1 CARBON NANOTUBE
5.1.1 ADVANTAGES OF CARBON NANOTUBE
HYDROGEN STORAGE
24
24
24
25
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5 5.1.2 DISADVANTAGES OF CARBON NANOTUBE
5.2 MICROSPHERE
26
27
5.2.1 ADVANTAGES OF MICROSPHERE
27
5.2.2 DISADVANTAGES OF MICROSPHERE
29
6.0 SODIUM BOROHYDRIDE
29
6.1 INTRODUCTION TO SODIUM BOROHYDRIDE
29
6.2 HYDROGEN STORAGE USING
30
SODIUM BOROHYDRIDE
6.3 ADVANTAGES
30
6.4 DISADVANTAGES
31
6.5 CONCLUSIONS
31
7.0 CONCLUSION
32
LIST OF REFERENCES
33
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6 LIST OF FIGURES
FIGURE 1.
Carbon nanotube magnified under a microscope.
FIGURE 2.
Microspheres magnified under a microscope.
FIGURE 3.
A diagram of a storage tank utilizing carbon fibre.
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7 GLOSSARY
Activation Energy
The amount of energy required for a chemical
reaction to occur.
Adsorb
To gather (a gas, liquid, or dissolved substance)
on a surface in a condensed layer: Charcoal will
adsorb gases.
Adsorption
See Adsorb.
Aqueous solution
A chemical solution in which the solvent is water.
That is, a solution in which a volume of one or
more chemical compounds are dissolved in a
greater volume of water.
Atmosphere
A conventional unit of pressure, the normal
pressure of the air at sea level, about 14.7
pounds per square inch (101.3 kilopascals), equal
to the pressure exerted by a column of mercury
29.92 in. (760 mm) high. Abbreviation: atm.
Bond
The attraction between atoms in a molecule or
crystalline structure.
By-products
Products of a chemical reaction created in
addition to the desired product(s).
Chemisorption
Adsorption involving a chemical linkage between
the adsorbent and the adsorbate.
Coefficient of Thermal
The measure of the rate of dimension change of
Expansion
a material with respect to constant pressure and
temperature change.
Composite
An artificially made material that consists of
multiple phases that are chemically different and
separated by distinct interfaces.
Corrosion
HYDROGEN STORAGE
Deterioration of a material as a result of chemical
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8 reactions with its operating environment.
Cryogenic
Concerning the effects of extremely low
temperatures.
Delamination
A failure in a laminated structure characterized by
the separation or loss of adhesion between the
structure’s individual sections.
Diffusivity
A relative measure of a gas's ability to spread, or
intermingle in the atmosphere.
Elastic Modulus
A measure of the stiffness of a material under the
condition that the deflection of the material due to
loading is non-permanent. Measured by taking
force divided by area divided by % elongation.
Emissivity
The amount of energy, as a percentage or
fraction, that is released to the surrounding
environment in the form of radiation.
Enthalpy
A quantity associated with a thermodynamic
system, expressed as the internal energy of a
system plus the product of the pressure and
volume of the system, having the property that
during an isobaric process, the change in the
quantity is equal to the heat transferred during
the process.
Explosive Range
Range of concentrations in air required to cause
an explosion in the presence of an ignition
source.
Fatigue
A method of failure due to fluctuating and cyclic
loading of a structure under relatively low stress
levels.
Fatigue Life
HYDROGEN STORAGE
The total number of loading cycles that will cause
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9 a structure to fail, given a specified and repeated
loading condition.
Filament Winding
A process by which continuous reinforcing fibres
are accurately positioned in a predetermined
pattern to form a hollow(usually cylindrical) shape.
The fibres are first fed through a polymer bath
and then are continuously wound onto a spool.
Flammability range
Range of concentrations in air required to cause
a fire, in presence of an ignition source.
Heat transfer
The process whereby heat moves from one body
or substance to another by radiation, conduction,
convection, or a combination of these methods.
Hydrogen Embrittlement
The process whereby metals become brittle or
fracture with exposure to hydrogen, common
when hydrogen is present in forming processes
or at high pressures.
Ideal Gas Law
The relationship between pressure, volume,
temperature and quantity of a gas, neglecting the
interaction between gas particles.
Joules
A unit of work or energy, equal to the work done
by a force of one newton when its point of
application moves through a distance of one
meter in the direction of the force.
Liquefied Hydrogen
Hydrogen cooled or compressed to liquid phase.
Matrix
The phase in a composite or two-phase alloy
structure that is continuous or completely
surrounds the other phase.
Micrometer
Millionth part of a meter. (10-6m)
Mole
Base unit for measuring quantities of a
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10 substance. Equal to 6.02 x 1023 particles.
Molecular Weight
The mass of one mole of a substance expressed
in grams; gram molecule.
Molecular-Surface
Total surface area of a molecule where elements
can penetrate through the surface.
Molecule
The smallest physical unit of an element or
compound, consisting of one or more like atoms
in an element and two or more different atoms in
a compound.
Nanometer
One billionth of a meter. (10-9m)
Polymer
A compound of high molecular weight. Its
structure consists of chains of small repeating
units.
Saturating
See Saturation.
Saturation
To cause a substance to unite with the greatest
possible amount of another substance, through
solution, chemical combination, or the like.
Specific Strength
The ratio of tensile strength to the weight of a
material with respect to the weight of water.
Thermal shock
Failure of a material due to a sudden change in
temperature.
Thermosetting Polymer
A compound of high molecular weight that, once
having hardened by a chemical reaction, will not
soften of melt when subsequently heated.
HYDROGEN STORAGE
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11 LIST OF ABBREVIATIONS
H2
Hydrogen
LH2
Liquid Hydrogen
CH2
Compressed Hydrogen
CO
Carbon Monoxide
CO2
Carbon Dioxide
NaBH4
Sodium Borohydride
Nm
Nanometer
Psi
Pounds per Square Inch
PPM
Parts per Million
PPB
Parts per Billion
STP
Standard Temperature and Pressure
Wt%
Weight Percent
HYDROGEN STORAGE
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12 1.0 INTRODUCTION
Hydrogen has come to the forefront as a clean and reliable form of energy
as concerns about the environment become more and more important.
Hydrogen does not create greenhouse gas and this is attractive to an
environmentally conscious consumer base. Further, increasing recognition
of eco system degradation and dwindling reserves force the world to rethink
our reliance on fossil fuel sources. While hydrogen is potentially very useful
as a fuel, complex concerns regarding safe and affordable storage are of
great significance.
Public concerns regarding hydrogen risks are not unfounded, but
certainly blown out of proportion. This report outlines the major safety
concerns and what can be done about them.
This report covers the risks and advantages associated with storing
hydrogen and the various methods that are currently in use or development.
Hydrogen can be stored physically or chemically. Physical storage includes
steel, composite, and micropores. Chemical storage is possible by synthesis
of sodium borohydride.
A thorough understanding of hydrogen safety and storage will
facilitate the implementation of a hydrogen based energy system.
Knowledge will allow engineers to make the correct choices and foster
public and political support for a transition away from fossil fuels.
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13 2.0 SAFETY FACTORS AFFECTING HYDROGEN STORAGE
2.1 INTRODUCTION
Hydrogen (H2) transportation and storage is associated with several safety
concerns, which must be taken seriously if it is going to be used on a large
scale. The most well known is the potential to explode or burn. While the risk
of ignition is inherent in any fuel, what matters is how well we can mitigate
this risk. Equally, if not more dangerous is the possibility of H2 poisoning in
enclosed spaces, where H2, a colourless, odourless gas can collect
undetected. A third danger in common H2 storage methods, is tank rupture.
This danger is particularly important when considering transportation, as the
possibility of rupture due to a collision is much higher than in stationary
tanks. Finally, when using liquefied H2, the extremely low temperatures
present several potential dangers, and high fire risks.
2.2 RISKS
2.2.1 FIRE & EXPLOSION
The Hindenburg is the hydrogen disaster that captured the public's
imagination, and rightfully so. The idea of a car, bus, or air plane
spontaneously exploding is completely terrifying equally unacceptable.
However, one incident does not tell us the whole story. Most importantly, it's
quite likely that H2 had little or nothing to do with the Hindenburg fire (Bain,
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14 2004). Compared to the hydrocarbons that are currently and commonly
used - Gasoline, Natural Gas and Jet-A - H2 seems relatively innocuous.
The safe handling of hydrogen requires careful consideration of a few
key properties of hydrogen. Most of these chemical properties are safety
advantages, but some pose risks. Key chemical properties are as follows:
•
Very low molecular weight (2g per mole, or 2g per 22.4l at STP)
•
Broad flammability range (4 to 75% in air) (Hord, 1978)
•
Broad explosive range (18.3 to 59% in air) (Hord, 1978)
•
Colourless, odourless
•
Low flame emissivity
•
High reactivity
Hydrogen's low molecular weight means that in the case of a leak, it
is not likely to collect in any significant quantities. This is the key to most
hydrogen safety practices. Simply ensuring that any enclosed areas are
sufficiently vented will prevent or significantly reduce the risk of fire or
explosion. The downside of course, is that only 4% H2 in air is required to
cause a fire. In combination with the fact that H2 is colourless, odourless,
highly reactive and disperses quickly, it would not take long to create a
disaster in a closed space, particularly one with readily available ignition
sources (Hord, 1978). This 4% limit can also be a blessing. Since the
explosive range is narrower than the flammability range, the gas is more
likely to burn off that explode. Finally, if the H2 did catch fire, it is less likely to
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15 cause damage than any hydrocarbon. H2, when compared to an equivalent
volume of hydrocarbon, will radiate only very slightly more energy, but for a
significantly shorter period of time (Hord, 1978). So, anything damaged
would likely have to be IN the flame (Scott, 2007). All this is not to dismiss a
real and present danger lightly, but just to say that it should not be a reason
to write off H2 as a fuel.
2.2.2 HYDROGEN POISONING
Hydrogen gas, like any other gas, can and will displace the oxygen we need
to breath. This phenomenon is called H2 poisoning and can be extremely
dangerous. Here, three properties are the keys to both the danger and risk
mitigation:
•
Low molecular weight
•
Lack of colour and odour
•
High diffusivity
Once again, the low weight and high diffusivity is a huge advantage. It
means that H2 is unlikely to collect in high enough quantities to pose a
danger, in a ventilated space. Despite the lack of colour and odour, H2
detection systems have been available for more than 30 years, and are
capable of detecting concentrations as low as 0.03 Parts Per Billion (PPB),
though detection levels of 10 to 100 Parts Per Million are more reasonable
(Christofides et al, 1989). The installation of these detectors in enclosed
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16 spaces is entirely feasible and would be a sufficient solution to this problem.
detectors, similar to current CO or CO2.
2.2.3 TANK RUPTURE
As with any compressed gas, tank rupture with H2 fuel poses a serious risk.
This danger presents itself in several forms:
i.
In extreme circumstances, tank rupture can lead to the tanks being
propelled uncontrollably at high speeds. Although this is unlikely, it
must be considered when installing and building tanks. It would not
be difficult to compensate for at the design stage, by ensuring that
tanks fail reliably and are well secured.
ii.
Sudden catastrophic tank failure has also been known to occur,
causing significant damage and loss of life. This can be caused by
hydrogen embrittlement of metals, poor tank design, insufficient
construction or lack of maintenance but is most likely to be some
combination of these factors (F. Rigas and S. Sklavounos, 2005).
iii.
In more likely scenarios, tank punctures and the rapid expansion of
the escaping gas will cause a steep drop in the surrounding
temperature as per the ideal gas law. There is no easy way to prevent
this sudden temperature change. On the other hand, steps can be
taken to ensure damage caused by the failure is minimized, using
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17 materials that are not susceptible to thermal shock and distancing or
insulating people from tanks where possible.
2.2.4 CRYOGENIC RISKS
Liquid Hydrogen (LH2) is the most energy dense and therefore the most
useful form of H2 (Scott, 2007). Unfortunately, liquefaction requires
temperatures around -253°C. This presents a few problems.
At such low temperatures, most materials used for LH2 storage tanks
become very brittle. This embrittlement does increase the risk of tank rupture
when subject to impact.
i.
At any given pressure, there is a temperature above which H2 will
absolutely not remain liquid. At this point, all the LH2 present in the
tank will transform to gas, nearly instantaneously. Since gaseous H2,
this can have spectacular, and explosive results (Rigas, 2005).
occupies 851 times the volume of LH2
ii.
When spilled, LH2 will boil off almost immediately, creating risks
similar to gaseous H2. Though, due to behaviour similar to that of a
heavy gas, LH2 concentrations at ground level can remain high,
increasing the risk of H2 poisoning or explosion. Despite this, LH2 will
still vaporize and disperse orders of magnitude faster than any fuel
currently in use (Hord, 1978).
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18 iii.
If equipment used in the handling of LH2 is not properly insulated, the
extreme cold can be a hazard. The very cold temperatures can cause
both severe cases of frostbite and very quickly condense other
vapours, including air. These liquefied gases can, in fact, be very
flammable (Scott, 2007).
2.3 CONCLUSION
Despite the dangers associated with the storage of H2, it is a far safer way of
transporting energy than any hydrocarbon fuel currently in use. With proper
regulation and forethought, all the scenarios presented above can be
overcome.
3.0 STEEL STORAGE
The use of steel tanks is not commonly used to store hydrogen. Steel tanks
are impractical due to hydrogen embrittlement*, a process in which metals
such as steel become brittle and fracture with exposure to hydrogen. A steel
tank, as a result, would need to be coated on the inside to prevent this
process from occurring. The requirement of a lining increases maintenance
costs, leakage rates, and material costs, further reducing feasibility.
Additionally, Steel tanks are heavy, and therefore the amount of hydrogen
stored would only constitute 0.5-1% by weight (Cahan). For portable use of
hydrogen, any energy supplied by the hydrogen itself would be greatly
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19 The University of British Columbia
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overshadowed by the energy required for tank transport. It is evident there
are many setbacks caused by weight, space and cost.
However, the use of steel tanks does provide a reliable way of storing
hydrogen in stationary settings, primarily for university laboratory work. The
duration of a standard steel tank under these conditions can be 30 years or
more since impact rupture is not an issue and cracks and leaks can be
easily monitored by trained technicians. Hydrogen at a pressure of 5000
psi*, is the maximum pressure the steel tank is able to safely withstand in
this type of setting (Cahan).
4.0 COMPOSITE STORAGE
4.1 ADVANTAGES OF COMPOSITE STORAGE TANKS
Composite storage tanks are an attractive option for Hydrogen storage and
transport, be it a fuel tank on board a fuel cell automobile or a stationary
storage system. Unlike their metal counter parts, composite tanks are quite
light but still supply satisfactory strength under high pressure conditions.
Another edge that composite materials hold over metals is higher resistance
to
corrosion
and
higher
fatigue
life
(Hu,
Sundararaman,
Menta,
Chandrashekhara, and Chernicoff, 2008, p. 233). Unlike forms of chemical
storage, using composite tanks is much simpler and less expensive with
respect to storage and transport (Hu et al., 2008, p. 234). The desirable
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20 properties of Composite storage tanks are the result of optimization of the
structure of the composite and the selection of distinct materials that make
up the composite using their properties.
4.2 STORAGE TANK STRUCTURE
Many different structures are available for use in composite storage tanks.
However, many forms of storage tanks have been pushed aside due to lack
of manufacturing experience or their novelty. As safety is the primary
concern on the subject of Hydrogen storage, providers prefer tried-and-true
manufacturing techniques that are more reliable. Filament winding is a welldeveloped process that is already widely used for manufacturing composites
(Hu et al., 2008, p. 234), and can thus be utilized to support the needs of a
large-scale industry like automotive fuel storage and transport. The most
commonly seen composite tanks consist of a filament-wound, composite
matrix with an internal lining that serves as a hydrogen permeation barrier
(Neel, 2002, pg. 4). Other standard features on the tank may include light
weight impact resistant domes on both ends of the tank, a reinforced shell
that covers the composite matrix, and a manual or electric valve for access
to the fuel. The composite is usually composed of many layers of Epoxy
matrix containing helically wound carbon fibres. The permeation barrier is
constructed from aluminum or a high molecular weight polymer (Hu et al.,
2008, p. 234). The impact domes, reinforce shell, and valves can be made
HYDROGEN STORAGE
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21 from a wide variety of viable materials and are generally not considered part
of the tanks specialized design.
FIGURE 1. A diagram of a storage tank utilizing carbon fibre. Source: Dr.
Neel Sirosh, 2002, (www.qtww.com)
4.3 MATERIAL PROPERTIES
Carbon fibers are chosen due to their high elastic modulus and strength,
which can carry high loads even when combined with a matrix that
compromises some of their properties. Carbon fibres also exhibit higher
corrosion and specific strength than metals. As fibres cannot perform in any
aspect of loading other than pure tension, the Epoxy matrix is implemented
to keep the fibres aligned to the loading condition. Epoxy displays high
strength and adhesion for a polymer and adds to the corrosion resistance of
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22 the resulting composite (Hu, Chen, Sundararaman, Chandrashekhara, and
Chernicoff, 2008, p. 2738). Aluminum alloys and oxides have shown to
greatly reduce Hydrogen permeation and are used as internal linings
alongside ultra-high molecular weight polymers which exhibit similar
hydrogen permeation properties (Hollenberg, Simonen, Terlain, and Kalinin,
1994, p. 2).
4.4 WEAKNESSES OF COMPOSITE STORAGE TANKS
Major safety issues with composite tanks are related to high pressure
loading under extreme temperatures. In the event of accidental fire exposure
or similar situations, the high internal pressure may cause catastrophic failure
of the composite by rupture. Composite tanks may also Another
shortcoming of composite tanks is the higher cost compared to their metal
counter parts. Due to the rarity of composite tanks in the present, it is often
difficult to detect and repair damaged specimens due to lack of experience.
This may prove hazardous and costly should a damaged tank remain in
operation.
4.4.1 HIGH-TEMPERATURE LOADING
As Epoxy is a thermosetting polymer, it does not soften appreciably as it is
heated. Excessive heating at extreme temperatures will, however, result in
degradation of the polymer and the eventual delamination of the entire
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23 composite structure(Hu et al., 2008, p. 234). Even before degrading, the
matrix will begin combusting if oxygen is present at 140°C (Hu et al., 2008,
p. 234). Without the polymer to support the fibres, the load-bearing capacity
of the composite plummets and becomes susceptible to rupture. Above
288°C, the epoxy matrix will also begin to deflect under loading, weakening
the entire structure of the composite (Hu et al., 2008, p. 2740).
4.4.2 CRYOGENIC LOADING
Hydrogen can also be stored in its liquid state, below -253°C. While more
Hydrogen can be stored due to the higher density of the liquid phase, the
storage medium is also put under cryogenic conditions. Such temperatures
result in the strengthening of both the fibres and the Epoxy matrix. However,
this transition to greater strength also reduces the ductility of the Epoxy. As
Epoxy has a positive coefficient of thermal expansion, and Carbon
possesses a negative one, residual stresses in the composite structure can
built up as the Carbon expands while the Epoxy attempts to contract(Choi
and Sankar, 2005, p. 1078).. These residual stresses, combined with the
embrittlement of epoxy under cryogenic conditions may result in the
formation of micro-cracks within the matrix (Choi et al., 2005, p. 1078).
These micro cracks may lead to failure of the composite should they expand
and interlink.
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24 4.5 CONCLUSION
When exposed to extreme temperatures, using Composite Hydrogen tanks
for prolonged periods of time may prove to be hazardous. However, this
weakness can be viewed as only a slight issue under controlled
environments and definitely does not overrule the efficiency and reliability of
Composites as possible Hydrogen storage mediums.
5.0 MICROPORE STORAGE
Currently, almost all the cars on the road are being fuelled by some form of
fossil fuel. Sooner or later we will run out of fossil fuel reserve in about
twenty year or so. Therefore it is critical to find a reliable fuel source for
vehicles. One of the methods that have taken interest of automotive industry
is micropore storage. It has been around for about a decade but it has
taken a great deal of interest from the automotive industry, looking for
alternative ways to store hydrogen in high volume to weight ratio and safety.
There are 2 main methods being researched upon to improve the weight
percent of hydrogen, carbon nanotube method and microsphere method
and both of them have distinct advantages and disadvantages.
5.1 CARBON NANOTUBE
Carbon nanotube was discovered in 1991 by Sumio Iijima. It is a hollow
cylindrical structure; a sheet of carbon atom has been rolled up to make
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25 such shape. It is usually 1.2 to 1.4 nm (nanometer) in diameter, which is
about 50000 times smaller than a strand of human hair. Virtue of their large
surface to volume ratios, nanotubes are able to adsorb considerable amount
of hydrogen in molecular state via weak molecular-surface interactions.
Physisorption is preferred, as it would moderate the pressure and
temperature required for the respective uptake and release of hydrogen.
Heat transfer is not a major problem because physisorption bonds are weak,
typically with enthalpies of adsorption of -10 ~ -20 KJ/mole and you do not
need to spend large amount of energy to split the hydrogen molecules.
Storing hydrogen in the tube is done by heating up hydrogen and carbon
nanotubes in a pressurised compartment and hydrogen molecules will break
up into individual molecules and will permeate into the hollows of the tube.
5.1.1 ADVANTAGES OF CARBON NANOTUBE
Through the storing of hydrogen with physisorption, release of hydrogen can
be simply done by just heating up the nanotubes. Nanotubes indicate
potential up to 7.5 wt% hydrogen storage capacity for this material through
chemisorption by saturating the C-C double bonds in the nanotube walls
and forming C-H bonds.
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26 FIGURE 2. Carbon nanotube magnified under a microscope. Source: University of
Cambridge, Department of Material Sciences and Metallurgy, 2010
(www.msm.cam.ac.uk)
5.1.2 DISADVANTAGES OF CARBON NANOTUBE
It has been discovered only for about 20 years, so the amount of weight
percent storage and the mechanism through which hydrogen is stored in
this material is not well-defined. Toxic and current technology limit keeps
the industry from mass producing. Mass production being impossible as of
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27 now, the cost of the final product would be very high. The most expensive
kind one can purchase is about $83 per gram.
5.2 MICROSPHERE
Microsphere is a tiny sphere measuring up to up about 5 micrometers in
diameter with wall thickness of few microns thick. Each of the spheres
contains only few molecules of hydrogen, however, since each sphere is
really small, concentration of the spheres would. A thimble contains
approximately 4 million spheres. In order to store hydrogen in the empty
spaces of the sphere, hydrogen and spheres are heated up in a pressurised
container up to 350oC and in 272 to 409 atmospheres. (2007 Holland,
Provenzano) During the heating, the hydrogen will permeate through the
small pores into the sphere. (2004, Ewing) When it cools down, the pores
will shrink and the molecules will be trapped inside, allowing for storage. In
order to release the molecules for fuel usage, the spheres can be simply
heated up, and then the pores will expand, allowing the molecules to pass
through so they can be freed.
5.2.1 ADVANTAGES OF MICROSPHERE
Since few molecules of hydrogen can be stored in a sphere, each can act as
a pressure vessel and this is important in safe storage because breakage of
one or two spheres would release only small amount of hydrogen, so there
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28 would be no danger of a tank containing the spheres would explode.
Refuelling a tank would be as easy as pumping out “used”, in other words
empty spheres, and pumping in new spheres into the fuel tank.
FIGURE 3. Microspheres magnified under a microscope. Source: The
Suslick Research Group, 2010, (http://www.scs.uiuc.edu)
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
29 This is a very similar process as refuelling the current vehicle fuel tank, so
the consumers would not be taken aback by a new method of fuel storage
and refuelling. Also it is not a fire hazard when it is suspended in a solid
material, which is an assurance that some believe that hydrogen is a volatile
substance.
5.2.2 DISADVANTAGES OF MICROSPHERE
As of now, it is costlier than compressed hydrogen, which is the most
common method of storing hydrogen, but as the microsphere method
becomes more wide spread, its cost will go down. Also, to make a sphere,
a right type of glass and purity has to be found or else the hydrogen cannot
permeate between the spaces. Regarding the porosity, the sizes of the
pores need to be right, or else, the hydrogen might escape through the
pores or won’t be able to permeate through the pores at all.
6.0 SODIUM BOROHYDRIDE
6.1 INTRODUCTION TO SODIUM BOROHYDRIDE
Sodium Borohydride (NaBH4) is a chemical method of storing hydrogen fuel
indirectly. It supplies hydrogen fuel at the site of use through a chemical
reaction. The use of sodium borohydride provides many safety an portability
advantages; however, it does currently present some drawbacks which limit
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
30 its use. At present, sodium borohydride is being used as a hydrogen fuel
storage method primarily in concept commercial vehicles.
6.2 HYDROGEN STORAGE USING SODIUM BOROHYDRIDE
The use of sodium borohydride is not what one would consider a
conventional method of hydrogen storage. Instead of storing pure (H2),
hydrogen is locked in a stable chemical compound, sodium borohydride
(NaBH4). This can be compared to storing the unstable chemicals sodium
and chlorine in the compound NaCl (pure table salt). When pure hydrogen is
needed to burn, a catalyst is added to an aqueous solution of sodium
borohydride (Wu, 2003). This causes a chemical reaction which produces
pure hydrogen (H2) and NaBO2, a byproduct which can be recycled back
into sodium borohydride (Wu, 2003). Additionally, this reaction is
controllable, does not require a significant amount of activation energy and
releases heat energy as it moves forward.
6.3 ADVANTAGES
Sodium borohydride can is a very safe method of storing hydrogen for use
as fuel. It can be kept in an aqueous solution at room temperature, is nonflammable and requires no pressurization (Wu, 2003). The reaction to
release hydrogen from sodium borohydride is non-volatile and produces no
harmful by-products (Wu, 2003). Therefore, sodium borohydride can be a
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
31 safe and effective method of storing and extracting hydrogen in portable
contexts, such as in vehicles and portable generators.
6.4 DISADVANTAGES
While sodium borohydride can be very safe and effective, it faces certain
drawbacks. Firstly, the energy density sodium borohydride is too low; the
amount of energy stored does not warrant the weight of the fuel, making it
relatively costly to transport for the energy gain. This can be a problem in
cars, for example, where driving around with a full tank greatly reduces fuel
efficiency due to the fuel’s weight. Secondly, the costs of producing sodium
borohydride are high. The fuels complexity and high energy state mean it
uses a large quantity of energy to manufacture (Wu, 2003). Therefore, the
cost of sodium borohydride will only rise with increasing energy costs. The
only way to reduce the costs of sodium borohydride is increased efficiency.
6.5 CONCLUSIONS
Though sodium borohydride may be suitable for some portable applications,
the amount of energy it requires to produce and move will limit its usability
for other applications. That being said, the safety of sodium borohydride is a
key feature and could lead to its widespread use in vehicles and portable
generators.
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
32 7.0 CONCLUSION
Hydrogen is emerging as a clean and reliable form of energy, and is
attractive for its renewability and minimal environmental impact. To render
this new fuel a viable replacement for fossil fuels, there have been many
innovations in steel, composite, micropore, and sodium borohydride storage
technology.
There are hazards associated with the use of hydrogen. However, the
public image of hydrogen as extremely dangerous is exaggerated. Simple
and effective techniques are available to sufficiently mitigate risks and allow
the use of hydrogen without serious concern for public safety.
In the near future, composite and micropore storage are the most
promising available methods for use in automotive and aerospace
applications. These methods have two main advantages; high fuel to weight
ratios and relatively low production costs. Once the cost of mass production
can be overcome, sodium borohydride will become a safe and reliable
method of storage in any setting. Although steel manufacturing is a mature
industry, keeping costs low, it is incompatible with hydrogen and therefore
should not be seriously considered as a main method of storage.
By proper application of the various storage technologies and
attention to potential safety risks, hydrogen can overcome the current fossil
fuel monopoly on portable energy and lead the way to a better future.
HYDROGEN STORAGE
The University of British Columbia
Faculty of Applied Science
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Faculty of Applied Science
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