This literature review examines the viability of a hydrogen economy and addresses barriers to hydrogen fuel technology. The key barrier identified is hydrogen storage. Various storage methods are discussed, including high-pressure gas storage, liquid storage, chemical storage, and storage in porous solids, but each presents challenges like high pressures or low temperatures needed. Studies of hydrogen bus fleets show some success but high costs. Cost analyses of hydrogen vehicles show conflicting results, with estimates both above and below gasoline costs. Government support for hydrogen is discussed, but implementation has been greater in other countries than the US. There is disagreement around hydrogen's environmental impacts. The review identifies questions around implementing a hydrogen bus fleet at the University of Colorado as potential topics for further research.

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Ian Snow
ENVS 3020
9 April 2015
Literature Review on the Viability of a Hydrogen Economy
Abstract
This paper is a literature review on past and present knowledge of hydrogen fuel and fuel
cell vehicles. The purpose is to consider the possibility of both a global hydrogen economy (a
system based on hydrogen fuel and energy, rather than fossil fuels) as well as one within the
United States. The paper attempts to answer this question: what barriers exist for hydrogen fuel,
what are the known and proposed solutions for them, and is the technology ready for commercial
use in the United States?
The review includes background on the technology itself, the production of hydrogen as a
fuel, and how it is used to power vehicles. Following is a review of studies, focusing on storage
solutions, existing bus programs, monetary costs, governmental support, and finally international
support. Then follows a brief section on differing opinions, which demonstrates that there is
uncertainty within the research. Finally, there is a consideration of further questions and areas
that might spur future research.
Introduction
Although most science agrees that there is a need, or there will soon be a need, there is
not yet a great alternative to fossil fuel and coal for producing energy and fuel. While knowledge

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of renewable technologies is quickly progressing, and in many cases has reached a fully
functional capability, some of the most promising alternatives still contain uncertainties and
barriers, which hold back widespread implementation.
One such alternative is hydrogen fuel. When isolated and compressed, hydrogen as a fuel
can power vehicles and utilities. Additionally, it can be produced sustainably, using
photovoltaics powered by wind, solar, geothermal energy, etc. However, compared to “mature”
renewable sources, such as wind power, this technology still presents several barriers. This
literature review attempts to answer the question, what policies and solutions are known or
considered to overcome the barriers to hydrogen energy, and are those applicable to
implementing the technology in the United States?
Background
First, it is necessary to describe briefly the process for creating hydrogen fuel, and how it
is used to power vehicles. There are several different ways to isolate hydrogen. Some methods
like gasification and steam reforming involve extracting it from other substances such as
methane, coal, or oils (Sharma 2014). However, the simplest and most environmentally friendly
way to isolate hydrogen is to extract it from water through electrolysis. This process involves
running an electrical current through water, which breaks the water into separate hydrogen and
oxygen molecules. The attraction of this method is that the source of electricity can come from
anywhere, including renewable sources like wind and photovoltaics. Another advantage is that
“electrolysis is dispatchable” (Pyper 2014), meaning that the amount of electricity fed into the
process, and therefore the amount of hydrogen produced can be adjusted quickly according to the
energy demand on the electricity grid. The next step is to store the hydrogen in a way that can be

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useful for vehicles. This is the most controversial and difficult aspect of using hydrogen fuel, and
will be discussed in more depth later.
The next process is that of actually creating electricity from hydrogen. This can be
accomplished by using a proton exchange membrane (PEM) fuel cell. The basic shape of a fuel
cell is a two-chambered box, separated by catalysts and a selectively permeable membrane,
usually a metal in the case of hydrogen cells. The hydrogen fuel, as a liquid for example, feeds
into one side of the box and reacts with the catalyst. The protons from the hydrogen molecule are
able to pass through the membrane, while it separates electrons that must pass through an
external circuit. This is the electricity that can be diverted to power anything requiring electricity,
from a lightbulb to an engine. Meanwhile, oxygen from air feeds through the other side of the
box, which receives the hydrogen protons, producing the only byproduct of the fuel cell, which is
water (Hydrogen Fuel Co 2009). The electricity created from this process can be used to power
an electric vehicle for example. The advantage of a fuel cell over a traditional electric vehicle
(EV) however, is that the fuel can theoretically be carried on-board, allowing for a longer range,
as well as the fact that the electricity is produced without any pollution as opposed to EV
charging stations which still rely on traditionally coal-powered sources.
Review of Literature
There has been knowledge of fuel cell technology since the mid-1800s as proposed in the
journal article “Mr. Grove on the Gas Voltaic Battery” (Grove 1843). Recently however, there
has been an explosion of literature on the subject, in light of the rising issue of climate change
and because hydrogen fuel cells may be important in reversing global warming. There have since
been studies about the science of hydrogen, analyses of developmental programs, and

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governmental plans to discern the viability of personal hydrogen fueled vehicles and a “hydrogen
economy”. Many sources support the viability of the resource, both economically and in terms of
efficiency.
A good place to begin review is with the governmental writings on hydrogen.
Governmental agencies have provided research and certainly funding, but more importantly for
this review, have set goals for development in order to make the technology commercial. These
goals center on the assumption that hydrogen will need to be as effective and easy to use as
gasoline, as well as competitively cheap for consumers. Some crucial goals that have been set by
the Department of Energy (DOE) are an operating temperature of -30 to 50 degrees Celsius, a
system cost of $30 per kW (James 2012), and a storage capacity of 6 wt% (Ross 2006). This
refers to what is called the Weight Percent, meaning the ratio of the hydrogen molecule in
relation to the substance in which it is stored (Sk 2015). These all seem like reasonable goals at
first glance, a large range of temperatures, a cost still well above gasoline, and a seemingly low
wt%. However, these goals have all been set for the future, because none has yet been
successfully met.
One aspect that the literature all seems to agree upon is that the primary issue from which
most of the barriers to hydrogen stem, is storage. There are up to five types of hydrogen storage
that are usually considered. These include high-pressure storage, storing hydrogen molecules
within other chemicals, liquid storage, storage within porous solids and similarly storage within
carbon- based materials. Each aspect has its advantages, but studies on each have presented
reasons why they would not be ideal for a hydrogen economy.
High-pressure storage as a gas is the most basic of the alternatives, and has been
commercially popular for many years and applications. While there certainly are casks that can

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sufficiently hold hydrogen, the tank pressure usually ranges from 5,000 – 10,000 psi (James
2012). Certainly, there are concerns about the safety of placing these tanks on personal vehicles,
considering that people will not know how to care for them properly, and they could certainly
exacerbate the danger of auto accidents.
The next simplest method is liquid storage. This would seem a good alternative; the
infrastructure of a hydrogen economy based on this liquid form would not be too different from
the current gasoline structure. Again, the properties of hydrogen create a barrier for any simple
infrastructure however. The storage temperature for liquid hydrogen is -252.8 degrees Celsius
(Energy.gov), and evidently not conducive to a filling station.
Chemical storage within other substances have shown promising prospects as well. For
example, as study at (SLAC 2014) by Yu Lin showed that ammonia borane and the hydrogen
contained therein can be pressurized and stored at efficient levels above that of DOE standards,
at 7.5 wt%. However, this efficiency still occurs at 100 degrees Celsius, and therefore not ideal
for on-board storage.
Finally, storage within porous solids and carbon nanofibers in particular, has been the
most recent focus of research. This is because carbon compounds are light compared with
pressurized tanks and the fibers have a high surface area as well on which to carry hydrogen
molecules. One report for the International Conference on Materials Science and Technology
found that graphite flakes produced a 6 wt% efficiency at only 37 degrees Celsius. This certainly
is promising, but still only barely meets the DOE goals, which will surely change again in the
future.
Despite what seem to be many failures, there have been many studies as well as
development projects that have thus far been successful, and continue to make great strides. Most

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of the commercial progress so far has been with fleets of hydrogen buses. Worldwide there are
about 100 hydrogen fuel cell buses operating, mostly in Europe, but Canada has the most in one
country at 20 buses (Hua 2014). This Whistler bus fleet has had several incredible breakthroughs
compared with personal vehicles. For example, the fleet has been operational since October 2009
and has accumulated almost 4 million kilometers driven. More surprisingly, the fueling station
appears to have been wildly successful, capable of filling up to 15 buses per day with liquid
hydrogen, created by solar-powered electrolyzers. Evidently, public transportation is much easier
to supply and maintain than personal vehicles, without a need for many fueling stations or nearly
as many possibilities for safety concerns. Yet the implications are still promising. There have
been no notable safety incidents within the fleet and the fact that the hydrogen fuel has been
successfully produced at large quantities and varying demands, as well as entirely by renewable
sources is incredible. Similarly, buses in the US have made strides as well, some with lifetimes
of five or more years and the ability to operate for 20 hours, seven days per week. Yet the cost of
a single bus in 2013 was $2,000,000, and the DOE’s ultimate goal is set at $600,000. Hua states
that reaching the future targets requires “manufacturing at a fully commercial level”.
This raises the question of how economically viable are not only hydrogen fuel cell bus
fleets, but personal vehicles, and what steps are being taken to bring down the costs? There are
several indications that hydrogen fuel cell vehicles may indeed be close to meeting a competitive
price. For example, in 2002, the cost of a PEM fuel cell was at least $1000/kW (Jeong 2002), and
estimates at the time claimed that it would only be more profitable to use a pure fuel cell vehicle
as opposed to a hybrid if that cost were below $400. Yet in 2011, the system cost had dropped all
the way to just $48/kW, only just above the DOE target of $30. This demonstrates tremendous
progress. Additionally, there are studies showing that fuel cell systems might have a total life

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cycle cost of as low as $0.086 per mile driven (James 2012). If one conducts a simple estimate, it
is easy to see that this is not too far beyond the cost of gasoline. For example, take the regular
gas price in Boulder today, about $2.20 per gallon, and divide that by an optimistic 30 miles per
gallon fuel efficiency: the result is $0.073 per mile, just below the estimated cost of a hydrogen-
powered vehicle. However, these estimates are clearly highly dependent on criteria considered,
for there are studies, which show much less optimistic numbers. For example, considering just
the fuel itself rather than the cars, some have estimated that mass-produced hydrogen for more
than 50,000 cars, it would cost about $20/Gj (Jeong 2002). Unfortunately, a single Gj
(Gigajoule) contains about as many BTUs of energy as one sixth of a barrel of oil (IRS 1999).
This analysis would mean that a comparable barrel of hydrogen would cost at least $120,
whereas the current cost of a barrel of oil is just $52 (Nasdaq 2015). Clearly, there are many
analyses that find different conclusions about the economic viability of personal hydrogen
vehicles. However, one thing is clear among them, at some level, hydrogen fuel cells would be
more expensive currently than gasoline, although the costs have dropped drastically compared
with those of just ten years ago.
Despite this mixed optimism, there still seems to be growing and large support for
hydrogen programs in the United States. This comes mainly in the form of governmental
research and development money, as government sites like NREL have conducted much of the
research already done in this field. However, there are a few key initiatives that actually
incentivize hydrogen production, such as facets of the Economic Stabilization Act from 2008
which created tax credits for fuel cell producers of a hefty 30% of the costs per kW if installed
by 2016 (Energy.gov). In terms of vehicles, there have been strong policy initiatives as well. As
far back as 2006, the FTA began funding the bus fleet program, and provided $90 million (FTA

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2015). More recently, the California Energy Commission committed millions to a “hydrogen
highway” to build 100 fueling stations by 2023 (Pyper 2014). Clearly, the US has invested much
into this technology. The technical barriers are coming closer to resolution, and the costs are
nearing competitive levels, so the next step ought to be implementation of the technology on a
widespread scale. This would both drive down costs, and help smooth out any remaining
technological issues.
Considering the wider global scope, literature describes much higher implementation of
hydrogen than the United States. Aside from the Canadian bus fleet already described, even
several developing countries have high installed capacities such as China at 17 percent, Morocco
at 10 percent and Egypt at 15 percent (Sovacool 2009) of energy coming from renewables
including hydrogen. One country of particular interest is Iceland; which announced as early as
1999 a commitment to making its economy based on hydrogen and energy independent by 2030,
and in fact already very much depends on a hydrogen economy. This country began with only
three city buses but is quickly replacing all buses and even fishing boat fleets with hydrogen fuel
cell power. The U.S. similarly created senate bill S.665, The Hydrogen and Fuel Cell
Technology Act of 2005 which appropriated hundreds of thousands of dollars to hydrogen fuel
through 2015 (Dorgan 2005). Yet the entire framing of this bill is in the context of research,
development, and demonstrations, and is therefore nowhere as firm and significant as Iceland’s
efforts. The evident advantage that other countries and Iceland in particular enjoy however is that
they have much smaller, more concentrated populations compared to the U.S. Iceland for
example claims that there will be a need for only one filling station (Arnason 2000). Although
this is a setback for prospects in the U.S., other countries may be able to solve some of the
remaining barriers, making hydrogen fuel easier to implement in the U.S. soon.

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Differing Opinions
One area in which opinions on the merits of a hydrogen economy differ is in the
estimation of effects on the atmosphere. Some studies focus on the positive effects of CO₂
decrease, while others consider the effects of excess hydrogen buildup.
On the supporting side of a hydrogen economy, an extensive study in 1999 considered
several types of hydrogen production, storage, pollution, and compared pure fuel cells to hybrid
vehicles. The results describe that pure fuel cell vehicles result in less pollution than hybrids, and
that they might reduce CO₂ emissions in the U.S. by up to 24%. The key findings however, were
that a fuel cell fleet would leak less hydrogen and water vapor into the atmosphere than the
current gas powered fleet. These are important pollution considerations, though these molecules
are often not detrimental. This is because, as the paper suggests, these molecules may ascend and
form polar stratospheric clouds, which cause a reduction of ozone in the atmosphere, a very
severe problem (Colella 2005). However, this paper dismisses this fear in terms of hydrogen
vehicles as having no little to no proof thus far.
A study following in 2003 proposes the opposite, suggesting that hydrogen emissions
from a hydrogen fuel economy might be four to eight times the current emissions (Tromp 2003).
The implication of this difference is that of ozone reduction both directly, and indirectly simply
by the cooling of atmospheric layers. The paper also suggests the possibility of changes in the
earth’s albedo due to an increase of clouds due to water vapor emissions. Similarly to the
previous paper however, this one admits that there is uncertainty in the findings, due to
knowledge of exactly how much H₂ is currently emitted, or might be emitted by future hydrogen
technologies. Additionally, it contends that implementing technologies in 50 years as opposed to

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20 might mitigate some of the effects on ozone, as some cluorofluorocharbons are still present in
the atmosphere from before the Montreal Protocol, but will eventually be lost.
Questions for Further Research
This literature review has illuminated areas in the hydrogen economy research, which
still require work, and even present opportunities for undergraduate research. One question of
particular interest is finding the cost of implementing new hydrogen bus fleets, specifically on
the University of Colorado, Boulder campus. What would it take to replace the Buff Buses on
campus with hydrogen fuel cell buses in terms of several aspects: fueling based on the usage
loading and availability of the fleet, cost of the actual buses, any public support, possible funding
avenues, etc.?
Another area of interest comes from the papers that consider the atmospheric impacts of a
hydrogen economy. There seem to be few studies conducted in this aspect of hydrogen fuel. Yet,
the two papers considered here both agree that there are still uncertainties requiring further
knowledge of hydrogen and water vapor emissions. In addition, both papers were published
more than a decade ago. As the rest of this review has shown, hydrogen technology has changed
drastically in that time, and perhaps has improved enough to make the emission implications
negligible. It would be worthwhile to conduct another study on the byproducts of the current
PEM cells and then model those emissions within the atmosphere.

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