Hydrogen Storage 1
Finally a Feasible Option for Automotive Hydrogen Fuel Cells?
Magnesium-Based Alloys for Hydrogen Storage
Kevin Forgie
E SC 414M
December 1, 2010
Hydrogen Storage 2
Introduction:
Problem Statement
The development of new materials for hydrogen storage with high hydrogen densities,
low absorption/desorption times, and relatively low reaction enthalpies is necessary to produce
practical hydrogen fuel cell vehicles.
Design Needs
The automotive industry has been dominated by internal combustion engines utilizing
fossil fuels as its means of powering the vehicle for the past 100 years. Only recently have
minor attempts been made to deviate from this theme – namely hybrid-electric vehicles, which
use batteries and gasoline, and all-electric cars. These cars have all been relatively small and
have not appealed to the general market because they lack the overall functionality that
traditional cars offer.
These attempts to get away from sole dependence on fossil fuels have come from
increasing evidence that the carbon dioxide and other greenhouse gasses produced from
combustion has had a serious effect on the planet’s atmosphere and climate. It has been shown
that the incredibly large number of automobiles in the world is a primary contributor to this
“global warming.” Thus it is necessary to develop an alternative fuel source for cars that does
not emit greenhouse gasses, but still provides the same level of performance that is obtained
from fossil fuels and internal combustion engines.
Several ideas have been considered, such as solar, nuclear, and hydrogen. Solar cars are
not desirable because the energy that can be obtained from the sun is too unreliable (on the basis
of its availability) and too weak to power a practical vehicle. Nuclear cars are not yet realistic
Hydrogen Storage 3
for matters of scale and safety. Therefore great emphasis has been placed on hydrogen fuel cell
vehicles as the best alternative to fossil fuels.
The primary limiting factor in hydrogen fuel cells is an adequate method of storage. The
US Department of Energy has set a goal of 6 weight % hydrogen and 0.045 kg H2/L as a
minimum standard for hydrogen storage methods, because this will give similar performance as a
full tank of gasoline. Gaseous and liquid hydrogen obviously have 100 wt% hydrogen, but their
densities are too low. Another option is metal-hydride compounds, which have been shown to
be able to meet these standards; the most promising of these is Magnesium-hydride (MgH2). The
main problem with metal-hydrides is a very high enthalpy for the absorption and desorption
reactions, which currently makes them impractical for mobile applications. Another important
consideration is the amount of time necessary for the reactions to take place, which have been
shown to significantly increase after many cycles. These things will have to be corrected before
metal-hydrides can be used for hydrogen cars.
Objective
This thesis examined the key aspects of Magnesium-hydride as a potential material for a
hydrogen fuel cell; specifically, the absorption and desorption rates of hydrogen in the
magnesium, the temperatures at which the reactions take place, and the overall amount of
hydrogen that can be absorbed into the magnesium. This was done with pure magnesium as a
plain solid, ball-milled solid, and powder to test the effects of differences in surface area and
texture. Magnesium was also alloyed with a small percentage of nickel and tested in those three
forms to determine if adding a similar metal will improve any of the properties. These tests and
data provided an effective characterization of magnesium-hydride as a possible material for an
automotive hydrogen fuel cell.
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Literature Review:
Hydrogen is the most abundant element in the universe, and occurs naturally on Earth
most commonly as water. Pure hydrogen can be combusted to produce energy, and in doing so,
the only byproduct is water. The water can then be broken down back into hydrogen and oxygen
through a process called electrolysis. Obviously this cycle makes hydrogen ideal as a
replacement for the fossil fuels that our world is mostly dependent upon for its energy [1]. The
only thing preventing a widespread switch to hydrogen is the ability to store an adequate amount
on board a car to give similar performance to a full tank of gasoline. Per unit volume, there is
only about 1/10 the energy of gasoline available in hydrogen. Fuel cells are expected to be more
efficient than internal combustion engines, which will make up for some of that deficit, but
development of an adequate method of storage is paramount [2]. There are many possibilities
for Hydrogen storage being studied today. Hydrogen can exist as a gas, liquid, or solid on its
own, and can also behave metallically and be alloyed with other metals. The main area of focus
on hydrogen storage is the somewhat traditional idea of a tank.
If the world were a perfect place, the switch from fossil fuels to a clean energy source for
automobiles would be as easy as changing the substance with which we fill up the tanks of our
cars. This is not the case, however. Gaseous hydrogen, which exists at room temperature and
normal atmospheric pressure, is the most efficient state to keep it in. However, it is also the least
dense form, and therefore has the least amount of hydrogen available for fuel per unit volume,
about 1x1022 atoms per cubic centimeter [3]. To compensate for this, high-pressure tanks have
been developed, storing the gas at pressures up to 70 MPa, which increases the amount of
hydrogen stored by about 65%. This is still not an adequate amount of fuel, and increasing the
pressure further does not significantly increase the amount of hydrogen stored in the tank. This
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is because at high pressures the relationship between pressure and amount of hydrogen levels off
[2]. Increasing the size of the tank is also impractical due to decreasing structural stability of the
tank as well as a significant increase in overall weight to maintain the high pressure [4].
Therefore, the logical next step is to transform hydrogen from the gaseous state into a
more dense state, such as a liquid. This is achieved by reducing hydrogen to a temperature of
less than 20K at atmospheric pressure, and results in slightly more than 4x1022 hydrogen atoms
per cubic centimeter [3]. There are two main challenges presented with this method of storage –
the large amount energy required to reach the 20K temperature and maintain it, and adequate
methods of insulation to prevent significant hydrogen evaporation and energy waste. At 4K,
hydrogen enters its solid phase, with a density of over 5x1022 atoms per cubic centimeter [3].
This form of hydrogen is still in the experimental period, as it requires a very large amount of
energy to produce and has not yet been made practical as a method of hydrogen storage.
All of these approaches have only dealt with hydrogen in its elemental form. A
promising avenue is hydrogen compounds, specifically when hydrogen behaves metallically and
forms metal hydrides. The current method in fuel cells to utilize metal hydrides is a high
pressure tank with a metal inside that will react with gaseous hydrogen to form a hydride. These
hydrides provide a higher hydrogen density, with some compounds reaching up to 7x1022 atoms
per cubic centimeter [3]. Another benefit to this method is its ability to charge and discharge the
alloy with the same hydrogen in a closed system. The main challenges presented by metal
hydrides are a low gravimetric density (hydrogen weight per tank weight) and high temperatures
that are required for the absorption and desorption of hydrogen [2]. Solutions to these problems
are being actively pursued, and it is believed that metal hydrides are a likely answer to the
question of hydrogen storage.
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The most promising metal hydride studied thus far is Magnesium Hydride (MgH2),
because it can store more hydrogen than any other metal hydride (6.5x1022 atoms per cubic
centimeter), and is fairly inexpensive. MgH2 also displays good working properties, like heatresistance, vibration absorbance, and reversible and recyclable hydrogenation reactions [3].
Despite these promising aspects, it does have problems that need to be addressed. The first of
these is the slow kinetics of the hydrogen absorption and desorption reactions. This stems from
several things.
The absorption reaction of hydrogen into magnesium occurs by the following steps. First
the reaction at the surface takes place, which is composed of physisorption, dissociation, and
chemisorption, by which the hydrogen enters the metal. Then the hydrogen diffuses below the
surface and into the bulk material lattice sites. Hydride formation occurs by nucleation and
growth [5]. For absorption, the first difficulty is magnesium’s high reactivity with air.
Oxidation on the surface forms magnesium oxide (MgO), which prevents hydrogen from
entering the lattice of the metal. This is treated by a process known as activation, in which the
metal is heated and cooled in a total vacuum or high-pressure hydrogen-only atmosphere.
Another obstacle is the slow dissociation rate of hydrogen molecules at the metal’s surface, and
the slow diffusion rate of hydrogen into the crystal lattice. This is alleviated with a high enough
hydrogen pressure, although too high of a pressure has been shown to form a stable magnesiumhydride layer at the surface that prevents further absorption into the metal [3].
The desorption reaction consists of the following steps. First, pure magnesium has to be
nucleated. Next, hydrogen atoms diffuse from the bulk lattice to the surface and recombine into
H2 molecules. The last step separates the hydride, as the hydrogen molecules then physically
desorb [5]. Diffusion is again a slow process, and desorption only occurs at high temperatures,
Hydrogen Storage 7
generally between 520K and 570K [3]. This stems from the fact that MgH2 is a relatively stable
compound, so a high amount of energy is required to break the magnesium-hydrogen bonds.
This high temperature for desorption is a very big problem for mobile (automotive) applications,
so reducing this temperature is a key area for research.
In order to address these problems, several processes have been utilized to modify
magnesium hydride. With a bulk metal, diffusion into the subsurface area slowed significantly
after the surface had absorbed a significant quantity of hydrogen. Therefore a potential method
by which the diffusion rate could be increased would be to decrease the distance over which
hydrogen must travel. This small diffusion path length is accomplished by creating small grain
and particle sizes, which also increases surface area [5]. Two processes have been effective in
doing so – ball milling MgH2 and using a thin film instead of a bulk metal.
Ball milling is a high-energy mechanical process that pulverizes and deforms the material
greatly, creating much smaller particle sizes. Ball milling for 20 hours has reduced the particle
size to 5 m, and ball milling for 200 hours reduces the particle size to 0.5 m [5]. With the
longer period of milling, reduction in the desorption enthalpy of 100K has been achieved. The
surface rates of hydrogen absorption and desorption improve greatly with the reduced particle
size and increased surface area, and the diffusion rate also increases due to the creation of defects
and micro/nanostructures in the interior of the material [3]. The major problem with ball milling
is that takes a lot of time and energy to do, and does not produce substantial amount of finished
material, which makes is unappealing for large scale applications such as the automotive
industry.
Producing a thin film of MgH2, on the order of 250 nm, rather than a bulk metal has
shown promising results as well. Thin films provide a larger surface area and faster sorption
Hydrogen Storage 8
rates. Adding a protective surface coating to prevent surface oxidation or a catalytic later to
increase performance is also possible with thin films. They give an alternative approach to ball
milling to achieve nano-structures in the material, as well as more control over its morphology
and stoichiometry. Work with thin film MgH2 has not shown any improvement in the enthalpy
of the desorption reaction, however, which still leaves it as an important factor to develop before
this can become an effective solution.
The methods discussed thus far have only attempted to modify the physical structure of
pure MgH2. While it does have the ability to hold the most hydrogen of any metal hydride, the
question arises if magnesium could be alloyed with other metals to produce better absorption and
desorption reaction kinetics and enthalpies without reducing the hydrogen storage density of the
hydride too drastically. To reduce the reaction enthalpy, the first category of these methods is
alloying magnesium with transition metals and their oxides, with the most emphasis being placed
on 3d transition metals.
One idea is to utilize elements that have a negative heat of mixing with magnesium and
therefore form stable compounds, while making dehydrogenation energetically favorable.
Mg2Ni is a very attractive and popular alloy that falls in this category. It reduces the enthalpy of
the reaction from 78 kJ/mol H2 for pure MgH2 to 65kJ/mol H2. However this is not a significant
enough drop, as the temperature of the reaction is still 470 – 500K [3]. Also, the storage
capacity of hydrogen in Mg2NiH4 is only 3.4 wt%, which is too low for practical applications
[5]. To address this, further additives to Mg2Ni were explored. One strategy is replacing a
fraction of the Ni with other 3d transition metals such as V, Cr, Fe, Co and Zn, but none of these
showed a significant improvement over Mg2Ni. Another is replacing a fraction of the Ni with
Hydrogen Storage 9
Al, Si, Ca, Co or Cu; the only one of these showing promise is Mg2NiCu – it had a significantly
reduced enthalpy of desorption but its hydrogen storage was only 3.05 wt% [5].
Mg2Ca and Mg2Si have also been investigated as possible alloys for hydrogen storage in
this category. Mg2Ca has a favorable crystal structure. The main problem with this alloy is its
tendency during hydrogenation to form calcium hydrides, which are more stable than magnesium
hydrides and therefore require a higher temperature to reverse. So far there has not been any
success in avoiding the formation of the very stable calcium hydride under moderate conditions.
Therefore, reversibly storing hydrogen in Mg2Ca (by forming MgH2 and Ca) is not yet feasible.
Mg2Si has an unfavorable, densely packed crystal structure, and does not react with hydrogen
under moderate conditions. Further additives (Li, C, Al, Ca, Co, Ni, Cu and Y) were tested for
their effectiveness. Of those, hydrogen only reacted with Ni and Cu to form hydrides, but these
were not practically reversible [5].
A second idea is to have a magnesium-based system that exhibits a positive heat of
formation for the hydride. The overall reaction enthalpy would be lowered by the formation of a
hydride that has a higher hydrogen-per-magnesium-atom ratio reduces the reaction enthalpy for
each hydrogen molecule. An example of this is Mg2FeH6. Of all known hydrides, it has the best
volumetric density of hydrogen (150kg/m3) and a decent gravimetric density of 5.3 wt%, making
it an attractive candidate. However it only showed a slight decrease in the reaction enthalpy
compared to MgH2. Two other alloys that fall into this category are Mg-Ti and Mg-Sc hydrides.
Mg-Sc is too expensive for practical applications, but Mg-Ti has shown some promise in
significantly reducing the reaction enthalpy. The Mg-Ti hydride, though, has only been shown
to form at high pressures or in thin films, thus leaving further work necessary to make it
Hydrogen Storage 10
practically applicable for automobiles [5]. A final alloy in this category is Mg-Al. Aluminum
destabilizes the MgH2 bond and forms an Mg-Al compound after dehydrogenation [3].
A third idea is to combine MgH2 with other light metal hydrides such that their
components would react exothermically upon dehydrogenation. This category is termed
Reactive Hydride Composites (RHC’s), and the most promising examples of these are
borohydride composites, made by combining MgH2 with things such as NaBH4, LiBH4, or
Ca(BH4)2. They have shown to have very high hydrogen storage capacities (>7.8 wt%) and
relatively low reaction enthalpies. Unprocessed, the sorption reactions have been shown to occur
around 500K, but this is still not a low enough temperature for practical application [5].
Therefore, more work with RHC’s is necessary.
In addition to lowering the reaction enthalpy, the sorption kinetics of MgH2 are also
improved by adding other elements or compounds. These additives are referred to as catalysts,
and there have been many successful catalysts developed already. Among the catalysts with the
most positive effect on sorption reaction kinetics of magnesium-based hydrides are carbon
nanostructures and transition-metals and compounds based on them, for example, metal oxides
[3].
The most popular transition metal is nickel, which has already been discussed as an
additive to magnesium for its ability to reduce the sorption enthalpy. The addition of nickel also
significantly increases the rate at which hydrogen is absorbed into the metal, but only slightly
improves the desorption rate. Another benefit to the Ni catalyst is its stability. Over the lifetime
of a fuel cell, the hydride will be hydrogenated and dehydrogenated many times over its lifetime.
It is important that anything added to MgH2 not have a negative effect on the metal throughout
this cycling, and it is estimated that a fuel cell car will be filled and emptied between one and
Hydrogen Storage 11
two thousand times over its lifetime. After 1500 cycles, the rates of absorption/desorption were
stable, and there was not a significant decline until after 2700 cycles. The total amount of
hydrogen able to be stored in Mg2Ni remained constant throughout the entire process [6].
Other 3d transition metals commonly used are Ti, V, Mn, and Fe. Including Ni for
comparison, desorption rates ranked highest to lowest were MgH2–V, MgH2–Ti, MgH2–Fe,
MgH2–Ni and MgH2–Mn. Mg–Ti exhibited the most rapid hydrogen absorption, followed in
order by Mg–V, Mg–Fe, Mg–Mn and Mg–Ni [5]. Metal oxides such as Nb2O5, TiO2, V2O5,
Cr2O3, Mn2O3, Fe3O4, and CuO are also common catalysts. Of these, Nb2O5 and V2O5 have been
proven the most effective, with V2O5 absorbing hydrogen three times faster than pure Mg and
desorbing hydrogen eight times faster. The effects of combining multiple catalysts have also
been examined. For example, Mg2Ni-Mn2O3 absorbed hydrogen at about the same rate as
Mg2Ni alone, however the desorption occurred at twice the rate [5].
The most recent innovation in catalysts is to design a composite of MgH2 with a carbonbased material. Carbon nanostructures have high specific area and unique absorbing properties
that make for high catalytic activity. Their use also has resulted in a substantial increase the
amount of hydrogen able to be stored in the hydride as well as a decrease in sorption
temperatures. These prominent effects can be attributed to two features of carbon: it segregates
at grain boundaries and improves hydrogen diffusion there, and it disperses well amongst the Mg
atoms and serves to shorten the diffusion path for hydrogen [3].
The idea of hydrogen as the future of alternative energy for automobiles has been around
for a long time, yet there are still major improvements needed for the hydrogen fuel cell electric
vehicle to become auto-competitive. Metal hydrides, specifically MgH2, have shown a great deal
of promise as the medium for hydrogen storage in the fuel cell. Still the challenge remains to
Hydrogen Storage 12
find the right balance of total hydrogen storage capacity, sorption reaction kinetics and
temperatures, and overall size and weight. The literature available provides the results of the
work that has been done thus far, and therefore guides future efforts. In this thesis, magnesium
and different magnesium alloys are modified by various processing techniques, and these
methods are analyzed for their success for creating a viable metal hydride.
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References
[1] Hydrogen. (n.d.). Retrieved 23 November, 2010, from Wikipedia:
http://en.wikipedia.org/wiki/Hydrogen
[2] Hirose, K., Mori, D. (2008) Recent challenges of hydrogen storage technologies for fuel cell
vehicles. International Journal of Hydrogen Energy, 34(10), 4569-4574.
doi:10.1016/j.ijhydene.2008.07.115
[3] Jain, A., Jain, I.P., Lal, C. (2009). Hydrogen storage in Mg: a most promising material.
International Journal of Hydrogen Energy, 35(10), 5133-5144.
doi:10.1016/j.ijhydene.2009.08.088
[4] Fuzhen, H., Gang, L., Rongfu, Q., Xueqin, L. (2009) The challenges of technologies for fuel
cell and its application on vehicles. 2009 IEEE 6th International Power Electronics and
Motion Control Conference, IPEMC '09, 2328-2333. DOI: 10.1109/IPEMC.2009.5157793
[5] Barkhordarian, G., Boesenberg , U., Bormann, R., Doppiu, S., Dornheim, M., Gutfleisch, O.,
Klassen, T. (2007) Hydrogen storage in magnesium-based hydrides and hydride
composites. Scripta Materialia, 56(10), 841-846. doi:10.1016/j.scriptamat.2007.01.003
[6] Bose, T. K., Dehouche, Z., Djaozandry, R., Goyette, J. (1999) Evaluation techniques of
cycling effect on thermodynamic and crystal structure properties of Mg2Ni alloy. Journal of
Alloys and Compounds, 288(1-2), 269-276. doi:10.1016/S0925-8388(99)00085-7
Hydrogen Storage 14
Annotated Bibliography:
Barkhordarian, G., Boesenberg , U., Bormann, R., Doppiu, S., Dornheim, M., Gutfleisch, O.,
Klassen, T. (2007) Hydrogen storage in magnesium-based hydrides and hydride composites.
Scripta Materialia, 56(10), 841-846. doi:10.1016/j.scriptamat.2007.01.003
This article focuses on Magnesium-based hydrides for methods of hydrogen storage.
These materials have high hydrogen storage densities and favorable kinetics (reaction
rates) for absorption and desorption of hydrogen. It has two main sections of
discussion: improving the kinetics of absorption and desorption, and reducing the
reaction enthalpy (temperature) for desorption of hydrogen. For kinetics, positive
results are attained with reducing particle and crystallite size, enlarging grain
boundaries, and adding transition metal and metal oxide catalysts. For enthalpy, adding
elements or compounds that have negative heats of mixing with magnesium or lower
overall enthalpies reduce the required temperatures; one promising avenue are
composites with borohydrides.
This article is somewhat limited in that it only deals with Mg-based hydrides.
However, it is very useful for my research because these materials appear to be
promising for hydrogen storage. It seems to be a very reliable source, and sites other
research that contribute to its findings. I will definitely refer to this article as I continue
my research.
Bose, T. K., Dehouche, Z., Djaozandry, R., Goyette, J. (1999) Evaluation techniques of cycling
effect on thermodynamic and crystal structure properties of Mg2Ni alloy. Journal of Alloys and
Compounds, 288(1-2), 269-276. doi:10.1016/S0925-8388(99)00085-7
This article focuses on a magnesium-nickel alloy and its ability to absorb/release
hydrogen after many cycles. It outlines the experiment used to analyze these properties,
and describes the results and conclusions. After 1500 cycles of loading and unloading,
the alloy remained stable and maintained fast absorption/desorption rates. After 2700
cycles, the rates were seriously slowed but the overall hydrogen-storage capacity
remained the same, as did the thermodynamic properties. Prolonged hydriding and
dehydriding cycles produce fracturing and a decrease in alloy particle size.
This article is very limited to a specific Mg-Ni alloy, however the experiment and
results are very informative. This is definitely something to look into when analyzing
materials for hydrogen storage, because the article states there will be about 2000 cycles
in a car’s lifetime. This article very clearly lays out all of the methods used in the
experiment and appears to be very credible, citing other sources’ similar experiments
and results.
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Foulkes, F.R., Karimi, S. (2002). Fuel cell cars: panacea or pipe dream? Bulletin of Science
Technology & Society, 22(4), 283-296. DOI: 10.1177/0270467602022004004
This article was not exactly what I thought it would be. It started out with a decent
summary of hydrogen fuel cell technology and how a fuel cell functions. It also
compared hydrogen fuel cells to internal combustion engines. However, the main
purpose of this article was a “life cycle analysis” of the hydrogen fuel cell, and its
overall environmental, economic, and social impacts.
The main ideas of this article are not exactly relevant to my research, though it was an
interesting and different perspective on the matter of hydrogen fuel cells. Therefore, I
will not be using much if anything from this article in my research.
Fuzhen, H., Gang, L., Rongfu, Q., Xueqin, L. (2009) The challenges of technologies for fuel
cell and its application on vehicles. 2009 IEEE 6th International Power Electronics and Motion
Control Conference, IPEMC '09, 2328-2333. DOI: 10.1109/IPEMC.2009.5157793
This article is a fairly broad and general overview of the current technology and
market for fuel cells, specifically hydrogen fuel cells and their implementation on cars.
It describes how fuel cells operate, and points out the areas in which further progress is
necessary to make a hydrogen fuel cell feasible. The author compares hydrogen fuel
cells to current automotive power sources, such as ethanol and gasoline internal
combustion engines and gas-battery hybrids. Lastly, it describes the current work on
hydrogen fuel cells, and provides opinions and advice for the future of fuel cell
technology.
This article is useful in that it provided a good background in hydrogen fuel cell
technology and its present status. It also points out where progress needs to be made,
thereby potentially guiding my further research. It is slightly limited in that it does not
get too in depth about any one topic. It was a good starting point for my research, but
does not have very much information for me to refer back to it.
Hirose, K., Mori, D. (2008) Recent challenges of hydrogen storage technologies for fuel cell
vehicles. International Journal of Hydrogen Energy, 34(10), 4569-4574.
doi:10.1016/j.ijhydene.2008.07.115
This article focuses mostly on tanks used to store hydrogen for fuel cell vehicles. It
describes the problems of simple containment methods. One is gaseous tanks, in which
the low hydrogen density in its gaseous state which requires large tanks and high
pressures to carry an adequate amount of fuel. Another is liquid hydrogen tanks, which
require very low temperatures to maintain the liquid phase and leak hydrogen over time.
The main point of this article is the idea of hybrid containment, which is a high-pressure
Hydrogen Storage 16
tank that utilizes a hydrogen-absorbing alloy that achieves higher volumetric density of
hydrogen storage. It describes an experiment that tests the hybrid containment device,
and compares the results to those of the simple containment devices.
This article was useful because it got into other methods of hydrogen storage than
simply hydrogen-absorbing (specifically magnesium-based) alloys. It was fairly
simplistic and did not cover the idea of hydrogen-storage tanks very deeply, but the
important thing for my research is that this article provides me with another avenue to
pursue for hydrogen storage.
Jain, A., Jain, I.P., Lal, C. (2009). Hydrogen storage in Mg: a most promising material.
International Journal of Hydrogen Energy, 35(10), 5133-5144.
doi:10.1016/j.ijhydene.2009.08.088
This article was a very thorough and informative discussion of magnesium-hydrides
for hydrogen storage. It started with a discussion why these materials are the most
promising for hydrogen storage. It gave examples of their shortcomings (surface
kinetics and high desorption enthalpy), as well as the methods being pursued to
overcome them (ball milling, alloying, catalyzing, forming it as a thin film). It also
gave an overall summary of the future of hydrogen fuel cells and MgH2 as a fuel cell
material.
This source was very helpful to my research. Although it was focused on one
material, it did a good job of analyzing it and comparing it to other materials. It was
very detailed and seems reliable as it cited a lot of other sources. Its conclusions about
what needs to be done with MgH2 to make it viable as a fuel cell material can guide my
research in the future. This is definitely an article I will refer to in the future.
Olk, C. H. (2004) Combinatorial approach to material synthesis and screening of hydrogen
storage alloys. Measurement Science and Technology, 16(1), 14-20. doi:10.1088/09570233/16/1/003
This article began with an overview of the difficulties with hydrogen storage alloys
and proposed that thin films could be a preferred alternative to bulk masses of alloy. It
briefly described the formation of an Mg-Fe-Ni thin film, but mostly focused on
methods for analyzing the thin film.
These methods may come in handy for analyzing sample later down the road in my
research if a study thin films for hydrogen storage. However, I had hoped it would
focus more on the actual results of the thin film analysis and its viability as a hydrogen
storage material.
Hydrogen Storage 17
Wu, Z., Xia, B. J., Xu, N. X., Yu, X. B. (2005) Improvement of activation performance of the
quenched Ti–V-based BCC phase alloys. Journal of Alloys and Compounds, 386(1-2), 258-260.
doi:10.1016/j.jallcom.2004.05.014
This article was fairly narrow in scope. It discussed how the time and energy required
to “activate” a hydrogen storage alloy are substantial, and that by ball milling the alloy
it significantly reduces the activation cost. By ball milling the alloy, it created
nanoparticles on the surface that also improved the absorption kinetics. The article only
dealt with a specific alloy, Ti–Mn–Cr–V, however its results should apply to other
alloys.