A fuel cell is a device that converts the chemical energy from a fuel into electricity
through a chemical reaction with oxygen or another oxidizing agent.
Hydrogen produced from the steam methane reforming of natural gas is the most common fuel, but
for greater efficiency hydrocarbons can be used directly such as natural gas and alcohols
like methanol. Fuel cells are different from batteries in that they require a continuous
source of fuel and oxygen/air to sustain the chemical reaction whereas in a battery the
chemicals present in the battery react with each other to generate an electromotive force.
Fuel cells can produce electricity continuously for as long as these inputs are supplied.
The first fuel cells were invented in 1838. The first commercial use of fuel cells came
more than a century later in NASA space programs to generate power for probes, satellites and
space capsules. Since then, fuel cells have been used in many other applications. Fuel
cells are used for primary and backup power for commercial, industrial and residential
buildings and in remote or inaccessible areas. They are also used to power fuel-cell vehicles,
including forklifts, automobiles, buses, boats, motorcycles and submarines.
There are many types of fuel cells, but they all consist of an anode, a cathode and an
electrolyte that allows charges to move between the two sides of the fuel cell. Electrons
are drawn from the anode to the cathode through an external circuit, producing direct current
electricity. As the main difference among fuel cell types is the electrolyte, fuel cells
are classified by the type of electrolyte they use followed by the difference in startup
time ranging from 1 sec for PEMFC to 10 min for SOFC. Fuel cells come in a variety of
sizes. Individual fuel cells produce relatively small electrical potentials, about 0.7 volts,
so cells are "stacked", or placed in series, to increase the voltage and meet an application's
requirements. In addition to electricity, fuel cells produce water, heat and, depending
on the fuel source, very small amounts of nitrogen dioxide and other emissions. The
energy efficiency of a fuel cell is generally between 40–60%, or up to 85% efficient in
cogeneration if waste heat is captured for use.
The fuel cell market is growing, and Pike Research has estimated that the stationary
fuel cell market will reach 50 GW by 2020.
History
The first references to hydrogen fuel cells appeared in 1838. In a letter dated October
1838 but published in the December 1838 edition of The London and Edinburgh Philosophical
Magazine and Journal of Science, Welsh physicist and barrister William Grove wrote about the
development of his first crude fuel cells. He used a combination of sheet iron, copper
and porcelain plates, and a solution of sulphate of copper and dilute acid. In a letter to
the same publication written in December 1838 but published in June 1839, German physicist
Christian Friedrich Schönbein discussed the first crude fuel cell that he had invented.
His letter discussed current generated from hydrogen and oxygen dissolved in water. Grove
later sketched his design, in 1842, in the same journal. The fuel cell he made used similar
materials to today's phosphoric-acid fuel cell.
In 1939, British engineer Francis Thomas Bacon successfully developed a 5 kW stationary
fuel cell. In 1955, W. Thomas Grubb, a chemist working for the General Electric Company,
further modified the original fuel cell design by using a sulphonated polystyrene ion-exchange
membrane as the electrolyte. Three years later another GE chemist, Leonard Niedrach, devised
a way of depositing platinum onto the membrane, which served as catalyst for the necessary
hydrogen oxidation and oxygen reduction reactions. This became known as the "Grubb-Niedrach fuel
cell". GE went on to develop this technology with NASA and McDonnell Aircraft, leading
to its use during Project Gemini. This was the first commercial use of a fuel cell. In
1959, a team led by Harry Ihrig built a 15 kW fuel cell tractor for Allis-Chalmers, which
was demonstrated across the U.S. at state fairs. This system used potassium hydroxide
as the electrolyte and compressed hydrogen and oxygen as the reactants. Later in 1959,
Bacon and his colleagues demonstrated a practical five-kilowatt unit capable of powering a welding
machine. In the 1960s, Pratt and Whitney licensed Bacon's U.S. patents for use in the U.S. space
program to supply electricity and drinking water. In 1991, the first hydrogen fuel cell
automobile was developed by Roger Billings. UTC Power was the first company to manufacture
and commercialize a large, stationary fuel cell system for use as a co-generation power
plant in hospitals, universities and large office buildings. UTC Power continues to be
the sole supplier of fuel cells to NASA for use in space vehicles, having supplied fuel
cells for the Apollo missions, and the Space Shuttle program, and is developing fuel cells
for cell phone towers and other applications. Types of fuel cells; design
Fuel cells come in many varieties; however, they all work in the same general manner.
They are made up of three adjacent segments: the anode, the electrolyte, and the cathode.
Two chemical reactions occur at the interfaces of the three different segments. The net result
of the two reactions is that fuel is consumed, water or carbon dioxide is created, and an
electric current is created, which can be used to power electrical devices, normally
referred to as the load. At the anode a catalyst oxidizes the fuel,
usually hydrogen, turning the fuel into a positively charged ion and a negatively charged
electron. The electrolyte is a substance specifically designed so ions can pass through it, but
the electrons cannot. The freed electrons travel through a wire creating the electric
current. The ions travel through the electrolyte to the cathode. Once reaching the cathode,
the ions are reunited with the electrons and the two react with a third chemical, usually
oxygen, to create water or carbon dioxide.
The most important design features in a fuel cell are:
The electrolyte substance. The electrolyte substance usually defines the type of fuel
cell. The fuel that is used. The most common fuel
is hydrogen. The anode catalyst breaks down the fuel into
electrons and ions. The anode catalyst is usually made up of very fine platinum powder.
The cathode catalyst turns the ions into the waste chemicals like water or carbon dioxide.
The cathode catalyst is often made up of nickel but it can also be a nanomaterial-based catalyst.
A typical fuel cell produces a voltage from 0.6 V to 0.7 V at full rated load. Voltage
decreases as current increases, due to several factors:
Activation loss Ohmic loss
Mass transport loss. To deliver the desired amount of energy, the
fuel cells can be combined in series to yield higher voltage, and in parallel to allow a
higher current to be supplied. Such a design is called a fuel cell stack. The cell surface
area can also be increased, to allow higher current from each cell. Within the stack,
reactant gases must be distributed uniformly over each of the cells to maximize the power
output. Proton exchange membrane fuel cells
In the archetypical hydrogen–oxide proton exchange membrane fuel cell design, a proton-conducting
polymer membrane separates the anode and cathode sides. This was called a "solid polymer electrolyte
fuel cell" in the early 1970s, before the proton exchange mechanism was well-understood.
On the anode side, hydrogen diffuses to the anode catalyst where it later dissociates
into protons and electrons. These protons often react with oxidants causing them to
become what are commonly referred to as multi-facilitated proton membranes. The protons are conducted
through the membrane to the cathode, but the electrons are forced to travel in an external
circuit because the membrane is electrically insulating. On the cathode catalyst, oxygen
molecules react with the electrons and protons to form water.
In addition to this pure hydrogen type, there are hydrocarbon fuels for fuel cells, including
diesel, methanol and chemical hydrides. The waste products with these types of fuel are
carbon dioxide and water, when hydrogen is used the CO2 is released when methane from
natural gas is combined with steam in a process called steam methane reforming to produce
the hydrogen, this can take place in a different location to the fuel cell potentially allowing
the hydrogen fuel cell to be used indoors for example in fork lifts.
The different components of a PEMFC are; bipolar plates,
electrodes, catalyst,
membrane, and the necessary hardware.
The materials used for different parts of the fuel cells differ by type. The bipolar
plates may be made of different types of materials, such as, metal, coated metal, graphite, flexible
graphite, C–C composite, carbon–polymer composites etc. The membrane electrode assembly
is referred as the heart of the PEMFC and is usually made of a proton exchange membrane
sandwiched between two catalyst-coated carbon papers. Platinum and/or similar type of noble
metals are usually used as the catalyst for PEMFC. The electrolyte could be a polymer
membrane. Proton exchange membrane fuel cell design
issues Costs. In 2013, the Department of Energy estimated
that 80-kW automotive fuel cell system costs of US$67 per kilowatt could be achieved, assuming
volume production of 100,000 automotive units per year and US$55 per kilowatt could be achieved,
assuming volume production of 500,000 units per year. In 2008, professor Jeremy P. Meyers
estimated that cost reductions over a production ramp-up period will take about 20 years after
fuel-cell cars are introduced before they will be able to compete commercially with
current market technologies, including gasoline internal combustion engines. Many companies
are working on techniques to reduce cost in a variety of ways including reducing the amount
of platinum needed in each individual cell. Ballard Power Systems has experimented with
a catalyst enhanced with carbon silk, which allows a 30% reduction in platinum usage without
reduction in performance. Monash University, Melbourne uses PEDOT as a cathode. A 2011
published study documented the first metal-free electrocatalyst using relatively inexpensive
doped carbon nanotubes, which are less than 1% the cost of platinum and are of equal or
superior performance. Water and air management. In this type of
fuel cell, the membrane must be hydrated, requiring water to be evaporated at precisely
the same rate that it is produced. If water is evaporated too quickly, the membrane dries,
resistance across it increases, and eventually it will crack, creating a gas "short circuit"
where hydrogen and oxygen combine directly, generating heat that will damage the fuel
cell. If the water is evaporated too slowly, the electrodes will flood, preventing the
reactants from reaching the catalyst and stopping the reaction. Methods to manage water in cells
are being developed like electroosmotic pumps focusing on flow control. Just as in a combustion
engine, a steady ratio between the reactant and oxygen is necessary to keep the fuel cell
operating efficiently. Temperature management. The same temperature
must be maintained throughout the cell in order to prevent destruction of the cell through
thermal loading. This is particularly challenging as the 2H2 + O2 -> 2H2O reaction is highly
exothermic, so a large quantity of heat is generated within the fuel cell.
Durability, service life, and special requirements for some type of cells. Stationary fuel cell
applications typically require more than 40,000 hours of reliable operation at a temperature
of −35 °C to 40 °C, while automotive fuel cells require a 5,000-hour lifespan)
under extreme temperatures. Current service life is 7,300 hours under cycling conditions.
Automotive engines must also be able to start reliably at −30 °C and have a high power-to-volume
ratio. Limited carbon monoxide tolerance of some
cathodes. Phosphoric acid fuel cell
Phosphoric acid fuel cells were first designed and introduced in 1961 by G. V. Elmore and
H. A. Tanner. In these cells phosphoric acid is used as a non-conductive electrolyte to
pass positive hydrogen ions from the anode to the cathode. These cells commonly work
in temperatures of 150 to 200 degrees Celsius. This high temperature will cause heat and
energy loss if the heat is not removed and used properly. This heat can be used to produce
steam for air conditioning systems or any other thermal energy consuming system. Using
this heat in cogeneration can enhance the efficiency of phosphoric acid fuel cells from
40–50% to about 80%. Phosphoric acid, the electrolyte used in PAFCs, is a non-conductive
liquid acid which forces electrons to travel from anode to cathode through an external
electrical circuit. Since the hydrogen ion production rate on the anode is small, platinum
is used as catalyst to increase this ionization rate. A key disadvantage of these cells is
the use of an acidic electrolyte. This increases the corrosion or oxidation of components exposed
to phosphoric acid. High-temperature fuel cells
SOFC
Solid oxide fuel cells use a solid material, most commonly a ceramic material called yttria-stabilized
zirconia, as the electrolyte. Because SOFCs are made entirely of solid materials, they
are not limited to the flat plane configuration of other types of fuel cells and are often
designed as rolled tubes. They require high operating temperatures and can be run on a
variety of fuels including natural gas. SOFCs are unique in that negatively charged
oxygen ions travel from the cathode to the anode instead of positively charged hydrogen
ions travelling from the anode to the cathode, as is the case in all other types of fuel
cells. Oxygen gas is fed through the cathode, where it absorbs electrons to create oxygen
ions. The oxygen ions then travel through the electrolyte to react with hydrogen gas
at the anode. The reaction at the anode produces electricity and water as by-products. Carbon
dioxide may also be a by-product depending on the fuel, but the carbon emissions from
an SOFC system are less than those from a fossil fuel combustion plant. The chemical
reactions for the SOFC system can be expressed as follows:
Anode Reaction: 2H2 + 2O2− → 2H2O + 4e− Cathode Reaction: O2 + 4e– → 2O2−
Overall Cell Reaction: 2H2 + O2 → 2H2O SOFC systems can run on fuels other than pure
hydrogen gas. However, since hydrogen is necessary for the reactions listed above, the fuel selected
must contain hydrogen atoms. For the fuel cell to operate, the fuel must be converted
into pure hydrogen gas. SOFCs are capable of internally reforming light hydrocarbons
such as methane, propane and butane. These fuel cells are at an early stage of development.
Challenges exist in SOFC systems due to their high operating temperatures. One such challenge
is the potential for carbon dust to build up on the anode, which slows down the internal
reforming process. Research to address this "carbon coking" issue at the University of
Pennsylvania has shown that the use of copper-based cermet can reduce coking and the loss of performance.
Another disadvantage of SOFC systems is slow start-up time, making SOFCs less useful for
mobile applications. Despite these disadvantages, a high operating temperature provides an advantage
by removing the need for a precious metal catalyst like platinum, thereby reducing cost.
Additionally, waste heat from SOFC systems may be captured and reused, increasing the
theoretical overall efficiency to as high as 80%–85%.
The high operating temperature is largely due to the physical properties of the YSZ
electrolyte. As temperature decreases, so does the ionic conductivity of YSZ. Therefore,
to obtain optimum performance of the fuel cell, a high operating temperature is required.
According to their website, Ceres Power, a UK SOFC fuel cell manufacturer, has developed
a method of reducing the operating temperature of their SOFC system to 500–600 degrees
Celsius. They replaced the commonly used YSZ electrolyte with a CGO electrolyte. The lower
operating temperature allows them to use stainless steel instead of ceramic as the cell substrate,
which reduces cost and start-up time of the system.
MCFC
Molten carbonate fuel cells require a high operating temperature, 650 °C, similar to
SOFCs. MCFCs use lithium potassium carbonate salt as an electrolyte, and this salt liquefies
at high temperatures, allowing for the movement of charge within the cell – in this case,
negative carbonate ions. Like SOFCs, MCFCs are capable of converting
fossil fuel to a hydrogen-rich gas in the anode, eliminating the need to produce hydrogen
externally. The reforming process creates CO
2 emissions. MCFC-compatible fuels include natural gas, biogas and gas produced from
coal. The hydrogen in the gas reacts with carbonate ions from the electrolyte to produce
water, carbon dioxide, electrons and small amounts of other chemicals. The electrons
travel through an external circuit creating electricity and return to the cathode. There,
oxygen from the air and carbon dioxide recycled from the anode react with the electrons to
form carbonate ions that replenish the electrolyte, completing the circuit. The chemical reactions
for an MCFC system can be expressed as follows: Anode Reaction: CO32− + H2 → H2O + CO2
+ 2e− Cathode Reaction: CO2 + ½O2 + 2e− → CO32−
Overall Cell Reaction: H2 + ½O2 → H2O As with SOFCs, MCFC disadvantages include
slow start-up times because of their high operating temperature. This makes MCFC systems
not suitable for mobile applications, and this technology will most likely be used for
stationary fuel cell purposes. The main challenge of MCFC technology is the cells' short life
span. The high-temperature and carbonate electrolyte lead to corrosion of the anode and cathode.
These factors accelerate the degradation of MCFC components, decreasing the durability
and cell life. Researchers are addressing this problem by exploring corrosion-resistant
materials for components as well as fuel cell designs that may increase cell life without
decreasing performance. MCFCs hold several advantages over other fuel
cell technologies, including their resistance to impurities. They are not prone to "carbon
coking", which refers to carbon build-up on the anode that results in reduced performance
by slowing down the internal fuel reforming process. Therefore, carbon-rich fuels like
gases made from coal are compatible with the system. The Department of Energy claims that
coal, itself, might even be a fuel option in the future, assuming the system can be
made resistant to impurities such as sulfur and particulates that result from converting
coal into hydrogen. MCFCs also have relatively high efficiencies. They can reach a fuel-to-electricity
efficiency of 50%, considerably higher than the 37–42% efficiency of a phosphoric acid
fuel cell plant. Efficiencies can be as high as 65% when the fuel cell is paired with a
turbine, and 85% if heat is captured and used in a Combined Heat and Power system.
FuelCell Energy, a Connecticut-based fuel cell manufacturer, develops and sells MCFC
fuel cells. The company says that their MCFC products range from 300 kW to 2.8 MW systems
that achieve 47% electrical efficiency and can utilize CHP technology to obtain higher
overall efficiencies. One product, the DFC-ERG, is combined with a gas turbine and, according
to the company, it achieves an electrical efficiency of 65%.
Comparison of fuel cell types Efficiency of leading fuel cell types
Glossary of Terms in table: Anode: The electrode at which oxidation takes
place. For fuel cells and other galvanic cells, the anode is the negative terminal; for electrolytic
cells, the anode is the positive terminal. Aqueous solution: a: of, relating to, or resembling
water b : made from, with, or by water. Catalyst: A chemical substance that increases
the rate of a reaction without being consumed; after the reaction, it can potentially be
recovered from the reaction mixture and is chemically unchanged. The catalyst lowers
the activation energy required, allowing the reaction to proceed more quickly or at a lower
temperature. In a fuel cell, the catalyst facilitates the reaction of oxygen and hydrogen.
It is usually made of platinum powder very thinly coated onto carbon paper or cloth.
The catalyst is rough and porous so the maximum surface area of the platinum can be exposed
to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the membrane in
the fuel cell. Cathode: The electrode at which reduction
occurs. For fuel cells and other galvanic cells, the cathode is the positive terminal;
for electrolytic cells, the cathode is the negative terminal.
Electrolyte: A substance that conducts charged ions from one electrode to the other in a
fuel cell, battery, or electrolyzer. Fuel Cell Stack: Individual fuel cells connected
in a series. Fuel cells are stacked to increase voltage.
Matrix: something within or from which something else originates, develops, or takes form.
Membrane: The separating layer in a fuel cell that acts as electrolyte as well as a barrier
film separating the gases in the anode and cathode compartments of the fuel cell.
Molten Carbonate Fuel Cell: A type of fuel cell that contains a molten carbonate electrolyte.
Carbonate ions are transported from the cathode to the anode. Operating temperatures are typically
near 650 °C. Phosphoric acid fuel cell: A type of fuel
cell in which the electrolyte consists of concentrated phosphoric acid. Protons are
transported from the anode to the cathode. The operating temperature range is generally
160–220 °C. Polymer Electrolyte Membrane: A fuel cell
incorporating a solid polymer membrane used as its electrolyte. Protons are transported
from the anode to the cathode. The operating temperature range is generally 60–100 °C.
Solid Oxide Fuel Cell: A type of fuel cell in which the electrolyte is a solid, nonporous
metal oxide, typically zirconium oxide treated with Y2O3, and O2− is transported from the
cathode to the anode. Any CO in the reformate gas is oxidized to CO2 at the anode. Temperatures
of operation are typically 800–1,000 °C. Solution: a: an act or the process by which
a solid, liquid, or gaseous substance is homogeneously mixed with a liquid or sometimes a gas or
solid, b : a homogeneous mixture formed by this process; especially : a single-phase
liquid system, c : the condition of being dissolved
For more information see Glossary of fuel cell terms
Theoretical maximum efficiency The energy efficiency of a system or device
that converts energy is measured by the ratio of the amount of useful energy put out by
the system to the total amount of energy that is put in or by useful output energy as a
percentage of the total input energy. In the case of fuel cells, useful output energy is
measured in electrical energy produced by the system. Input energy is the energy stored
in the fuel. According to the U.S. Department of Energy, fuel cells are generally between
40–60% energy efficient. This is higher than some other systems for energy generation.
For example, the typical internal combustion engine of a car is about 25% energy efficient.
In combined heat and power systems, the heat produced by the fuel cell is captured and
put to use, increasing the efficiency of the system to up to 85–90%.
The theoretical maximum efficiency of any type of power generation system is never reached
in practice, and it does not consider other steps in power generation, such as production,
transportation and storage of fuel and conversion of the electricity into mechanical power.
However, this calculation allows the comparison of different types of power generation. The
maximum theoretical energy efficiency of a fuel cell is 83%, operating at low power density
and using pure hydrogen and oxygen as reactants According to the World Energy Council, this
compares with a maximum theoretical efficiency of 58% for internal combustion engines. While
these efficiencies are not approached in most real world applications, high-temperature
fuel cells can theoretically be combined with gas turbines to allow stationary fuel cells
to come closer to the theoretical limit. A gas turbine would capture heat from the fuel
cell and turn it into mechanical energy to increase the fuel cell's operational efficiency.
This solution has been predicted to increase total efficiency to as much as 70%.
In practice The tank-to-wheel efficiency of a fuel-cell
vehicle is greater than 45% at low loads and shows average values of about 36% when a driving
cycle like the NEDC is used as test procedure. The comparable NEDC value for a Diesel vehicle
is 22%. In 2008 Honda released a demonstration fuel cell electric vehicle with fuel stack
claiming a 60% tank-to-wheel efficiency. It is also important to take losses due to
fuel production, transportation, and storage into account. Fuel cell vehicles running on
compressed hydrogen may have a power-plant-to-wheel efficiency of 22% if the hydrogen is stored
as high-pressure gas, and 17% if it is stored as liquid hydrogen. Fuel cells cannot store
energy like a battery, except as hydrogen, but in some applications, such as stand-alone
power plants based on discontinuous sources such as solar or wind power, they are combined
with electrolyzers and storage systems to form an energy storage system. Most hydrogen,
however, is produced by steam methane reforming, and so most hydrogen production emits carbon
dioxide. The overall efficiency of such plants, using pure hydrogen and pure oxygen can be
"from 35 up to 50 percent", depending on gas density and other conditions. While a much
cheaper lead–acid battery might return about 90%, the electrolyzer/fuel cell system can
store indefinite quantities of hydrogen, and is therefore better suited for long-term storage.
Solid-oxide fuel cells produce exothermic heat from the recombination of the oxygen
and hydrogen. The ceramic can run as hot as 800 degrees Celsius. This heat can be captured
and used to heat water in a micro combined heat and power application. When the heat
is captured, total efficiency can reach 80–90% at the unit, but does not consider production
and distribution losses. CHP units are being developed today for the European home market.
Professor Jeremy P. Meyers, in the Electrochemical Society journal Interface in 2008, wrote,
"While fuel cells are efficient relative to combustion engines, they are not as efficient
as batteries, due primarily to the inefficiency of the oxygen reduction reaction.... [T]hey
make the most sense for operation disconnected from the grid, or when fuel can be provided
continuously. For applications that require frequent and relatively rapid start-ups ... where
zero emissions are a requirement, as in enclosed spaces such as warehouses, and where hydrogen
is considered an acceptable reactant, a [PEM fuel cell] is becoming an increasingly attractive
choice [if exchanging batteries is inconvenient]". In 2013 military organisations are evaluating
fuel cells to significantly reduce the battery weight carried by soldiers.
Applications
Power Stationary fuel cells are used for commercial,
industrial and residential primary and backup power generation. Fuel cells are very useful
as power sources in remote locations, such as spacecraft, remote weather stations, large
parks, communications centers, rural locations including research stations, and in certain
military applications. A fuel cell system running on hydrogen can be compact and lightweight,
and have no major moving parts. Because fuel cells have no moving parts and do not involve
combustion, in ideal conditions they can achieve up to 99.9999% reliability. This equates to
less than one minute of downtime in a six-year period.
Since fuel cell electrolyzer systems do not store fuel in themselves, but rather rely
on external storage units, they can be successfully applied in large-scale energy storage, rural
areas being one example. There are many different types of stationary fuel cells so efficiencies
vary, but most are between 40% and 60% energy efficient. However, when the fuel cell's waste
heat is used to heat a building in a cogeneration system this efficiency can increase to 85%.
This is significantly more efficient than traditional coal power plants, which are only
about one third energy efficient. Assuming production at scale, fuel cells could save
20–40% on energy costs when used in cogeneration systems. Fuel cells are also much cleaner
than traditional power generation; a fuel cell power plant using natural gas as a hydrogen
source would create less than one ounce of pollution (other than CO
2) for every 1,000 kW·h produced, compared to 25 pounds of pollutants generated by conventional
combustion systems. Fuel Cells also produce 97% less nitrogen oxide emissions than conventional
coal-fired power plants. One such pilot program is operating on Stuart
Island in Washington State. There the Stuart Island Energy Initiative has built a complete,
closed-loop system: Solar panels power an electrolyzer, which makes hydrogen. The hydrogen
is stored in a 500-U.S.-gallon tank at 200 pounds per square inch, and runs a ReliOn
fuel cell to provide full electric back-up to the off-the-grid residence. Another closed
system loop was unveiled in late 2011 in Hempstead, NY.
Fuel cells can be used with low-quality gas from landfills or waste-water treatment plants
to generate power and lower methane emissions. A 2.8 MW fuel cell plant in California is
said to be the largest of the type. Cogeneration
Combined heat and power fuel cell systems, including Micro combined heat and power systems
are used to generate both electricity and heat for homes, office building and factories.
The system generates constant electric power, and at the same time produces hot air and
water from the waste heat. As the result CHP systems have the potential to save primary
energy as they can make use of waste heat which is generally rejected by thermal energy
conversion systems. A typical capacity range of home fuel cell is 1–3 kWel / 4–8 kWth.
CHP systems linked to absorption chillers use their waste heat for refrigeration.
The waste heat from fuel cells can be diverted during the summer directly into the ground
providing further cooling while the waste heat during winter can be pumped directly
into the building. The University of Minnesota owns the patent rights to this type of system
Co-generation systems can reach 85% efficiency. Phosphoric-acid fuel cells comprise the largest
segment of existing CHP products worldwide and can provide combined efficiencies close
to 90%. Molten Carbonate and Solid Oxide Fuel Cells are also used for combined heat and
power generation and have electrical energy efficiences around 60%. Disadvantages of co-generation
systems include slow ramping up and down rates, high cost and short lifetime. Also their need
to have a hot water storage tank to smooth out the thermal heat production was a serious
disadvantage in the domestic market place where space in domestic properties is at a
great premium. Fuel cell electric vehicles
Automobiles Although there are currently no fuel cell
vehicles available for commercial sale, over 20 fuel cell electric vehicle prototypes and
demonstration cars have been released since 2009. Demonstration models include the Honda
FCX Clarity, Toyota FCHV-adv, and Mercedes-Benz F-Cell. As of June 2011 demonstration FCEVs
had driven more than 4,800,000 km, with more than 27,000 refuelings. Demonstration fuel
cell vehicles have been produced with "a driving range of more than 400 km between refueling".
They can be refueled in less than 5 minutes. The U.S. Department of Energy's Fuel Cell
Technology Program claims that, as of 2011, fuel cells achieved 53–59% efficiency at
one-quarter power and 42–53% vehicle efficiency at full power, and a durability of over 120,000 km
with less than 10% degradation. In a Well-to-Wheels simulation analysis, that "did not address
the economics and market constraints", General Motors and its partners estimated that per
mile traveled, a fuel cell electric vehicle running on compressed gaseous hydrogen produced
from natural gas could use about 40% less energy and emit 45% less greenhouse gasses
than an internal combustion vehicle. A lead engineer from the Department of Energy whose
team is testing fuel cell cars said in 2011 that the potential appeal is that "these are
full-function vehicles with no limitations on range or refueling rate so they are a direct
replacement for any vehicle. For instance, if you drive a full sized SUV and pull a boat
up into the mountains, you can do that with this technology and you can't with current
battery-only vehicles, which are more geared toward city driving."
Some experts believe, however, that fuel cell cars will never become economically competitive
with other technologies or that it will take decades for them to become profitable. In
July 2011, the chairman and CEO of General Motors, Daniel Akerson, stated that while
the cost of hydrogen fuel cell cars is decreasing: "The car is still too expensive and probably
won't be practical until the 2020-plus period, I don't know."
In 2012, Lux Research, Inc. issued a report that stated: "The dream of a hydrogen economy
... is no nearer". It concluded that "Capital cost ... will limit adoption to a mere 5.9
GW" by 2030, providing "a nearly insurmountable barrier to adoption, except in niche applications".
The analysis concluded that, by 2030, PEM stationary market will reach $1 billion, while
the vehicle market, including forklifts, will reach a total of $2 billion. Other analyses
cite the lack of an extensive hydrogen infrastructure in the U.S. as an ongoing challenge to Fuel
Cell Electric Vehicle commercialization. In 2006, a study for the IEEE showed that for
hydrogen produced via electrolysis of water: "Only about 25% of the power generated from
wind, water, or sun is converted to practical use." The study further noted that "Electricity
obtained from hydrogen fuel cells appears to be four times as expensive as electricity
drawn from the electrical transmission grid. ... Because of the high energy losses [hydrogen]
cannot compete with electricity." Furthermore, the study found: "Natural gas reforming is
not a sustainable solution". "The large amount of energy required to isolate hydrogen from
natural compounds, package the light gas by compression or liquefaction, transfer the
energy carrier to the user, plus the energy lost when it is converted to useful electricity
with fuel cells, leaves around 25% for practical use."
Despite this, several major car manufacturers have announced plans to introduce a production
model of a fuel cell car in 2015. In 2013, Toyota has stated that it plans to introduce
such a vehicle at a price of less than US$100,000. Mercedes-Benz announced that they would move
the scheduled production date of their fuel cell car from 2015 up to 2014, asserting that
"The product is ready for the market technically. ... The issue is infrastructure." At the Paris
Auto Show in September 2012, Hyundai announced that it plans to begin producing a commercial
production fuel cell model in December 2012 and hopes to deliver 1,000 of them by 2015.
Other manufacturers planning to sell fuel cell electric vehicles commercially by 2016
or earlier include General Motors, Honda, and Nissan.
The Obama Administration sought to reduce funding for the development of fuel cell vehicles,
concluding that other vehicle technologies will lead to quicker reduction in emissions
in a shorter time. Steven Chu, the United States Secretary of Energy, stated in 2009
that hydrogen vehicles "will not be practical over the next 10 to 20 years". In 2012, however,
Chu stated that he saw fuel cell cars as more economically feasible as natural gas prices
have fallen and hydrogen reforming technologies have improved.
Buses
As of August 2011, there were a total of approximately 100 fuel cell buses deployed around the world.
Most buses are produced by UTC Power, Toyota, Ballard, Hydrogenics, and Proton Motor. UTC
Buses had accumulated over 970,000 km of driving by 2011. Fuel cell buses have a 39–141%
higher fuel economy than diesel buses and natural gas buses. Fuel cell buses have been
deployed around the world including in Whistler, Canada; San Francisco, United States; Hamburg,
Germany; Shanghai, China; London, England; São Paulo, Brazil; as well as several others.
The Fuel Cell Bus Club is a global cooperative effort in trial fuel cell buses. Notable Projects
Include: 12 Fuel cell buses are being deployed in the
Oakland and San Francisco Bay area of California. Daimler AG, with thirty-six experimental buses
powered by Ballard Power Systems fuel cells completed a successful three-year trial, in
eleven cities, in January 2007. A fleet of Thor buses with UTC Power fuel
cells was deployed in California, operated by SunLine Transit Agency.
The first Brazilian hydrogen fuel cell bus prototype in Brazil was deployed in São Paulo.
The bus was manufactured in Caxias do Sul and the hydrogen fuel will be produced in
São Bernardo do Campo from water through electrolysis. The program, called "Ônibus
Brasileiro a Hidrogênio", includes three additional buses.
Forklifts A fuel cell forklift is a fuel cell powered
industrial forklift truck used to lift and transport materials. Most fuel cells used
for material handling purposes are powered by PEM fuel cells.
In 2013 there were over 4,000 fuel cell forklifts used in material handling in the USA, of which
only 500 received funding from DOE. Fuel cell fleets are operated by a large number of companies,
including Sysco Foods, FedEx Freight, GENCO, and H-E-B Grocers. Europe demonstrated 30
Fuel cell forklifts with Hylift and extended it with HyLIFT-EUROPE to 200 units, with other
projects in France and Austria. Pike Research stated in 2011 that fuel-cell-powered forklifts
will be the largest driver of hydrogen fuel demand by 2020.
PEM fuel-cell-powered forklifts provide significant benefits over both petroleum and battery powered
forklifts as they produce no local emissions, can work for a full 8-hour shift on a single
tank of hydrogen, can be refueled in 3 minutes and have a lifetime of 8–10 years. Fuel
cell-powered forklifts are often used in refrigerated warehouses, as their performance is not degraded
by lower temperatures. Many companies do not use petroleum powered forklifts, as these
vehicles work indoors where emissions must be controlled and instead are turning to electric
forklifts. In design the FC units are often made as drop-in replacements.
Motorcycles and bicycles In 2005 a British manufacturer of hydrogen-powered
fuel cells, Intelligent Energy, produced the first working hydrogen run motorcycle called
the ENV. The motorcycle holds enough fuel to run for four hours, and to travel 160 km
in an urban area, at a top speed of 80 km/h. In 2004 Honda developed a fuel-cell motorcycle
that utilized the Honda FC Stack. Other examples of motorbikes and bicycles
that use hydrogen fuel cells include the Taiwanese company APFCT's scooter using the fueling
system from Italy's Acta SpA and the Suzuki Burgman scooter with an IE fuel cell that
received EU Whole Vehicle Type Approval in 2011. Suzuki Motor Corp. and IE have announced
a joint venture to accelerate the commercialization of zero-emission vehicles.
Airplanes Boeing researchers and industry partners throughout
Europe conducted experimental flight tests in February 2008 of a manned airplane powered
only by a fuel cell and lightweight batteries. The fuel cell demonstrator airplane, as it
was called, used a proton exchange membrane fuel cell/lithium-ion battery hybrid system
to power an electric motor, which was coupled to a conventional propeller. In 2003, the
world's first propeller-driven airplane to be powered entirely by a fuel cell was flown.
The fuel cell was a unique FlatStackTM stack design, which allowed the fuel cell to be
integrated with the aerodynamic surfaces of the plane.
There have been several fuel-cell-powered unmanned aerial vehicles. A Horizon fuel cell
UAV set the record distance flown for a small UAV in 2007. The military is especially interested
in this application because of the low noise, low thermal signature and ability to attain
high altitude. In 2009 the Naval Research Laboratory's Ion Tiger utilized a hydrogen-powered
fuel cell and flew for 23 hours and 17 minutes. Fuel cells are also being used to provide
auxiliary power in aircraft, replacing fossil fuel generators that were previously used
to start the engines and power on board electrical needs. Fuel cells can help airplanes reduce
CO 2 and other pollutant emissions and noise.
Boats
The world's first fuel-cell boat HYDRA used an AFC system with 6.5 kW net output. Iceland
has committed to converting its vast fishing fleet to use fuel cells to provide auxiliary
power by 2015 and, eventually, to provide primary power in its boats. Amsterdam recently
introduced its first fuel-cell-powered boat that ferries people around the city's famous
and beautiful canals. Submarines
The Type 212 submarines of the German and Italian navies use fuel cells to remain submerged
for weeks without the need to surface. The U212A is a non-nuclear submarine developed
by German naval shipyard Howaldtswerke Deutsche Werft. The system consists of nine PEM fuel
cells, providing between 30 kW and 50 kW each. The ship is silent giving it an advantage
in the detection of other submarines. Portable power systems
Portable power systems that use fuel cells can be used in the leisure sector, the industrial
sector, and in the military sector. SFC Energy is a German manufacturer of direct methanol
fuel cells for a variety of portable power systems. Ensol Systems Inc. is an integrator
of portable power systems, using the SFC Energy DMFC.
Other applications Providing power for base stations or cell
sites Distributed generation
Emergency power systems are a type of fuel cell system, which may include lighting, generators
and other apparatus, to provide backup resources in a crisis or when regular systems fail.
They find uses in a wide variety of settings from residential homes to hospitals, scientific
laboratories, data centers, telecommunication equipment and modern naval
ships. An uninterrupted power supply provides emergency
power and, depending on the topology, provide line regulation as well to connected equipment
by supplying power from a separate source when utility power is not available. Unlike
a standby generator, it can provide instant protection from a momentary power interruption.
Base load power plants Solar Hydrogen Fuel Cell Water Heating
Hybrid vehicles, pairing the fuel cell with either an ICE or a battery.
Notebook computers for applications where AC charging may not be readily available.
Portable charging docks for small electronics. Smartphones, laptops and tablets.
Small heating appliances Food preservation, achieved by exhausting
the oxygen and automatically maintaining oxygen exhaustion in a shipping container, containing,
for example, fresh fish. Breathalyzers, where the amount of voltage
generated by a fuel cell is used to determine the concentration of fuel in the sample.
Carbon monoxide detector, electrochemical sensor.
Fueling stations
There were over 85 hydrogen refueling stations in the U.S. in 2010.
As of June 2012 California had 23 hydrogen refueling stations in operation. Honda announced
plans in March 2011 to open the first station that would generate hydrogen through solar-powered
renewable electrolysis. South Carolina also has two hydrogen fueling stations, in Aiken
and Columbia, SC. The University of South Carolina, a founding member of the South Carolina
Hydrogen & Fuel Cell Alliance, received 12.5 million dollars from the United States Department
of Energy for its Future Fuels Program. The first public hydrogen refueling station
in Iceland was opened in Reykjavík in 2003. This station serves three buses built by DaimlerChrysler
that are in service in the public transport net of Reykjavík. The station produces the
hydrogen it needs by itself, with an electrolyzing unit, and does not need refilling: all that
enters is electricity and water. Royal Dutch Shell is also a partner in the project. The
station has no roof, in order to allow any leaked hydrogen to escape to the atmosphere.
The current 14 stations nationwide in Germany are planned to be expanded to 50 by 2015 through
its public private partnership Now GMBH. Japan also has a hydrogen highway, as part of the
Japan hydrogen fuel cell project. Twelve hydrogen fueling stations have been built in 11 cities
in Japan, and additional hydrogen stations could potentially be operational by 2015.
Canada, Sweden and Norway also have hydrogen highways being implemented.
Markets and economics
In 2012, fuel cell industry revenues exceeded $1 billion market value worldwide, with Asian
pacific countries shipping more than 3/4 of the fuel cell systems worldwide. However,
as of October 2013, no public company in the industry had yet become profitable. There
were 140,000 fuel cell stacks shipped globally in 2010, up from 11 thousand shipments in
2007, and from 2011 to 2012 worldwide fuel cell shipments had an annual growth rate of
85%. Tanaka Kikinzoku Kogyo K.K. expanded its production facilities for fuel cell catalysts
in 2013 to meet anticipated demand as the Japanese ENE Farm scheme expects to install
50,000 units in 2013 and the company is experiencing rapid market growth.
Approximately 50% of fuel cell shipments in 2010 were stationary fuel cells, up from about
a third in 2009, and the four dominant producers in the Fuel Cell Industry were the United
States, Germany, Japan and South Korea. The Department of Energy Solid State Energy Conversion
Alliance found that, as of January 2011, stationary fuel cells generated power at approximately
$724 to $775 per kilowatt installed. In 2011, Bloom Energy, a major fuel cell supplier,
said that its fuel cells generated power at 9–11 cents per kilowatt-hour, including
the price of fuel, maintenance, and hardware. Industry groups predict that there are sufficient
platinum resources for future demand, and in 2007, research at Brookhaven National Laboratory
suggested that platinum could be replaced by a gold-palladium coating, which may be
less susceptible to poisoning and thereby improve fuel cell lifetime. Another method
would use iron and sulphur instead of platinum. This would lower the cost of a fuel cell.
The concept was being developed by a coalition of the John Innes Centre and the University
of Milan-Bicocca. PEDOT cathodes are immune to monoxide poisoning.
Research and development August 2005: Georgia Institute of Technology
researchers use triazole to raise the operating temperature of PEM fuel cells from below 100 °C
to over 125 °C, claiming this will require less carbon-monoxide purification of the hydrogen
fuel. 2008 Monash University, Melbourne uses PEDOT
as a cathode. 2009 Researchers at the University of Dayton,
in Ohio, show that arrays of vertically grown carbon nanotubes could be used as the catalyst
in fuel cells. 2009: Y-Carbon began to develop a carbide-derived-carbon-based
ultracapacitor, which they hoped would lead to fuel cells with higher energy density.
2009: A nickel bisdiphosphine-based catalyst for fuel cells is demonstrated.
2013: British firm ACAL Energy develops a fuel cell that it says runs for 10,000 hours
in simulated driving conditions. It asserts that the cost of fuel cell construction can
be reduced to $40/kW. See also
References
Further reading Vielstich, W., et al, ed.. Handbook of fuel
cells: advances in electrocatalysis, materials, diagnostics and durability. Hoboken: John
Wiley and Sons. Gregor Hoogers. Fuel Cell Technology – Handbook.
CRC Press. James Larminie; Andrew Dicks. Fuel Cell Systems
Explained. Hoboken: John Wiley and Sons. Subash C. Singhal; Kevin Kendall. High Temperature
Solid Oxide Fuel Cells-Fundamentals, Design and Applications. Elsevier Academic Press.
Frano Barbir. PEM Fuel Cells-Theory and Practice. Elsevier Academic Press.
EG&G Technical Services, Inc.. Fuel Cell Technology-Handbook, 7th Edition. U.S. Department of Energy.
Matthew M. Mench. Fuel Cell Engines. Hoboken: John Wiley & Sons, Inc.
Noriko Hikosaka Behling. Fuel Cells: Current Technology Challenges and Future Research
Needs. Elsevier Academic Press. External links
Fuel Cell Today – Market-based intelligence on the fuel cell industry
Fuel starvation in a hydrogen fuel cell animation Animation how a fuel cell works and applications
Fuel Cell Origins: 1840–1890 TC 105 IEC Technical standard for Fuel Cells
EERE: Hydrogen, Fuel Cells and Infrastructure Technologies Program
Thermodynamics of electrolysis of water and hydrogen fuel cells
2002-Portable Power Applications of Fuel Cells US Fuel Cell Council
DoITPoMS Teaching and Learning Package- "Fuel Cells"
Solar Hydrogen Fuel Cell Water Heating