A
fuel cell is an
electrochemical cell that produces
electricity from a fuel tank. The electricity is generated through
the reaction, triggered in the presence of an electrolyte, between
the fuel (on the anode side) and an oxidant (on the cathode side).
The reactants flow into the cell, and the reaction products flow
out of it, while the electrolyte remains within it. Fuel cells can
operate virtually continuously as long as the necessary flows are
maintained.
Fuel cells are different from conventional electrochemical cell
batteries in that they consume
reactant from an external source, which must be replenished – a
thermodynamically
open system.
By contrast, batteries store electrical energy chemically and hence
represent a thermodynamically closed system.
Many combinations of fuels and oxidants are possible. A hydrogen
fuel cell uses
hydrogen as its fuel and
oxygen (usually from air) as its oxidant.
Other fuels include
hydrocarbons and
alcohols. Other oxidants include
chlorine and
chlorine
dioxide.
Design
A fuel cell works by
catalysis, separating
the component
electrons and
protons of the reactant fuel, and forcing the
electrons to travel through a
circuit, hence converting them to
electrical power. The catalyst typically comprises a
platinum group metal or alloy. Another catalytic
process puts the electrons back in, combining them with the protons
and oxidant to form waste products (typically simple compounds like
water and carbon dioxide).
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 (voltage drop due to
resistance of the cell components and interconnects)
- Mass transport loss (depletion of reactants at catalyst sites
under high loads, causing rapid loss of voltage)
To deliver the desired amount of energy, the fuel cells can be
combined in
series and
parallel circuits, where series yields higher
voltage, and parallel allows a higher
current to be supplied. Such a design is
called a
fuel cell stack. Further, the cell surface area
can be increased, to allow stronger
current from each cell.
Proton exchange fuel cells
In the archetypal hydrogen–oxygen
proton exchange membrane fuel
cell (PEMFC) design, a proton-conducting polymer membrane, (the
electrolyte), separates the
anode and
cathode sides. This
was called a "solid polymer electrolyte fuel cell" (SPEFC) in the
early 1970s, before the proton exchange mechanism was
well-understood. (Notice that "polymer electrolyte membrane" and
"proton exchange mechanism" result in the same
acronym.)
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 is commonly
referred to as multi-facilitated proton membranes (MFPM). The
protons are conducted through the membrane to the cathode, but the
electrons are forced to travel in an external circuit (supplying
power) because the membrane is electrically insulating. On the
cathode catalyst, oxygen
molecules react
with the electrons (which have traveled through the external
circuit) and protons to form water — in this example, the only
waste product, either
liquid or
vapor.
In addition to this pure hydrogen type, there are
hydrocarbon fuels for fuel cells, including
diesel,
methanol
(
see: direct-methanol
fuel cells and
indirect
methanol fuel cells) and chemical hydrides. The waste products
with these types of fuel are
carbon
dioxide and water.
[[Image:condensation.jpg|400px|thumb|Condensation of water produced
by a PEMFC on the air channel wall. The gold wire around the cell
ensures the collection of electric current.]]
The materials used in fuel cells differ by type. In a typical
membrane electrode
assembly (MEA), the electrode–
bipolar
plates are usually made of
metal,
nickel or
carbon
nanotubes, and are coated with a
catalyst (like
platinum,
nano iron powders or
palladium) for higher efficiency.
Carbon paper separates them from the
electrolyte. The electrolyte could be
ceramic or a
membrane.
Proton exchange membrane fuel cell design issues
- Costs. In 2002, typical fuel cell systems cost US$1000 per
kilowatt of electric power output. In 2008, the Department of
Energy reported that fuel cell system costs in volume production
are $73 per kilowatt. The goal is $35 per kilowatt. In 2008 UTC
Power has 400 kW stationary fuel cells for $1,000,000 per
400 kW installed costs. The goal is to reduce the cost in
order to compete 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 have experiments
with a catalyst enhanced with carbon
silk which allows a 30% reduction (1 mg/cm² to
0.7 mg/cm²) in platinum usage without reduction in
performance. Monash
University, Melbourne
uses PEDOT as a cathode.
- The production costs of the PEM (proton exchange membrane). The
Nafion membrane currently costs $565.92/m².
In 2005 Ballard Power Systems announced that its fuel cells will
use Solupor, a porous polyethylene film
patented by DSM.
- Water and air management (in PEMFCs). 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 (-31 °F to
104 °F), while automotive fuel cells require a 5,000 hour lifespan
(the equivalent of 150,000 miles) 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 (-22 °F) and have a high power to volume
ratio (typically 2.5 kW per liter).
- Limited carbon monoxide
tolerance of the cathode.
High temperature fuel cells
(SOFC)
In a
solid oxide fuel cell
(SOFC) design, the anode and cathode are separated by an
electrolyte that is conductive to oxygen ions but non-conductive to
electrons. The electrolyte is typically made from zirconia doped
with yttria.
In general, on the cathode side, oxygen catalytically reacts with a
supply of electrons to become oxygen ions, which diffuse through
the electrolyte to the anode side. On the anode side, the oxygen
ions react with hydrogen to form water and free electrons. A load
connected externally between the anode and cathode completes the
electrical circuit.
The real SOFC can be fed by other fuels than hydrogen (even without
hydrogen at all). The general working principle of SOFC is passing
oxygen ions through the electrolyte by the oxygen pressure
difference between cathode and anode sides. In the case of air, the
oxygen partial pressure at cathode side is about 0.021MPa, whereas
at anode side can reach values much lower (10
−22MPa).
Many various factors have an additional influence on obtained
voltage: temperature, pressure, electrolyte type and thickness,
fuel utilization factor, and so on.
SOFC performance modelling is related to the multi-physic processes
taking place on the fuel cell surfaces. Heat transfer together with
electrochemical reactions, mass and charge transport are conducted
inside the cell. The SOFC models found in the literature are based
mainly on mathematical descriptions of these physical, chemical,
and electrochemical properties. The SOFC models developed thus far
are mainly based on the Nernst equation, activation, ohmic, and
concentration losses. Moreover, most of the equations used require
the addition of numerous factors which are difficult or impossible
to determine. There are many parameters which impact cell working
conditions, e.g. electrolyte material, electrolyte thickness, cell
temperature, inlet and outlet gas compositions at anode and
cathode, anode and cathode porosities etc. The Artificial Neural
Network (ANN) can be applied to simulate an object’s behaviour
without an algorithmic solution merely by utilizing available
experimental data. Simultaneously, the ANN can make model more
general, whichmeans that model gives accurate results for other
data thanused in training processes.
MCFC
Molten carbonate fuel
cells (MCFCs) operate in a similar manner, except the
electrolyte consists of liquid (molten) carbonate, which is a
negative ion and an oxidizing agent. Because the electrolyte loses
carbonate in the oxidation reaction, the carbonate must be
replenished through some means. This is often performed by
recirculating the carbon dioxide from the oxidation products into
the cathode where it reacts with the incoming air and reforms
carbonate.
Unlike proton exchange fuel cells, the catalysts in SOFCs and MCFCs
are not poisoned by carbon monoxide, due to much higher operating
temperatures. Because the oxidation reaction occurs in the anode,
direct utilization of the carbon monoxide is possible. Also, steam
produced by the oxidation reaction can
shift carbon monoxide and
steam reform hydrocarbon fuels inside
the anode. These reactions can use the same catalysts used for the
electrochemical reaction, eliminating the need for an external fuel
reformer.
MCFC can be used for reducing the CO2 emission from coal fired
power plants as well as gas turbine power plants.
History
Sketch of William Grove's 1839 fuel
cell
The principle of the fuel cell was discovered by German scientist
Christian Friedrich
Schönbein in 1838 and published in one of the scientific
magazines of the time. Based on this work, the first fuel cell was
demonstrated by Welsh scientist and barrister Sir
William Robert Grove in the February
1839 edition of the
Philosophical Magazine and Journal of
Science and later sketched, in 1842, in the same journal. The
fuel cell he made used similar materials to today's
phosphoric-acid fuel cell.
In 1955, W. Thomas Grubb, a chemist working for the General
Electric Company (
GE), 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.It wasn't until 1959 that
British engineer
Francis Thomas
Bacon successfully developed a 5 kW stationary 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 US 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 (hydrogen and oxygen being
readily available from the spacecraft tanks).
United Technologies
Corporation's
UTC Power subsidiary 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
market this fuel cell as the PureCell 200, a 200 kW system
(although soon to be replaced by a 400 kW version, expected
for sale in late 2009). UTC Power continues to be the sole supplier
of fuel cells to NASA for use in space vehicles, having supplied
the
Apollo missions, and currently
the
Space Shuttle program, and
is developing fuel cells for automobiles, buses, and cell phone
towers; the company has demonstrated the first fuel cell capable of
starting under freezing conditions with its
proton exchange membrane automotive
fuel cell.
Types of fuel cells
!Fuel Cell Name
!Electrolyte
!Qualified Power (W)
!Working Temperature (°C)
!Electrical efficiency
!Status
!Cost per Watt
|-
| |Metal hydride fuel cell
|Aqueous alkaline solution (e.g.potassium hydroxide)
|
|style="background:#ddddff;text-align:right;" | above -20
(50% Ppeak @ 0°C)
|
|
|-
| |Electro-galvanic fuel cell
|Aqueous alkaline solution (e.g., potassium hydroxide)
|
|style="background:#ddffdd;text-align:right;"|under 40
|
|
|-
| |Direct formic acid fuel cell (DFAFC)
|Polymer membrane (ionomer)
|style="background:#ffffdd;text-align:right;"|to 50 W
|style="background:#ddffdd;text-align:right;"|under 40
|
|style="background:#ffffdd;text-align:right;"|Commercial/Research
|-
| |Zinc-air battery
|Aqueous alkaline solution (e.g., potassium hydroxide)
|
|style="background:#ddffdd;text-align:right;"|under 40
|
| Mass production
|-
| |Microbial fuel cell
|Polymer membrane or humic acid
|
|style="background:#ddffdd;text-align:right;"|under 40
|
|style="background:#ddddff"|Research
|-
| |Upflow microbial fuel cell (UMFC)
|
|
|style="background:#ddffdd;text-align:right;"|under 40
|
|style="background:#ddddff"|Research
|-
| |Regenerative fuel cell
|Polymer membrane (ionomer)
|
|style="background:#ddffdd;text-align:right;"|under 50
|
|
|-
| |Direct borohydride fuel cell
|Aqueous alkaline solution (e.g., sodium hydroxide)
|
|style="background:#ddffdd;text-align:right;"|70
|
|style="background:#ddddff"|Commercial
|-
| |Alkaline fuel cell
|Aqueous alkaline solution (e.g., potassium hydroxide)
|style="background:#ffffdd;text-align:right;"|10 kW to 100 kW
|style="background:#ddffdd;text-align:right;"|under 80
|style="background:#ddffdd;text-align:right;"|Cell: 60–70%
System: 62%
|
|-
| |Direct methanol fuel cell
|Polymer membrane (ionomer)
|style="background:#ffffdd;text-align:right;"|100 mW to 1 kW
|style="background:#ffffdd;text-align:right;"|90–120
|style="background:#ffdddd;text-align:right;"|Cell: 20–30%
System: 10–20%
|
|-
| |Reformed methanol fuel cell
|Polymer membrane (ionomer)
|style="background:#ffffdd;text-align:right;"|5 W to 100 kW
|style="background:#ffffdd;text-align:right;"|(Reformer)250–300
(PBI)125–200
|style="background:#ffdddd;text-align:right;"|Cell: 50–60%
System: 25–40%
|
|-
| |Direct-ethanol fuel cell
|Polymer membrane (ionomer)
|style="background:#ffffdd;text-align:right;"|up to 140 mW/cm²
|style="background:#ffffdd;text-align:right;"|above 25
? 90–120
|
|style="background:#ddddff"|Research
|-
| |Proton exchange membrane fuel cell
|Polymer membrane (ionomer) (e.g., Nafion or Polybenzimidazole fiber)
|style="background:#ddffdd;text-align:right;"|100 W to 500 kW
|style="background:#ffffdd;text-align:right;"|(Nafion)50–120
(PBI)125–220
|style="background:#ffffdd;text-align:right;"|Cell: 50–70%
System: 30–50%
|
|$30–35 per watt
|-
| |RFC - Redox
|Liquid electrolytes with redox shuttle & polymer membrane (Ionomer)
|style="background:#ddffdd;text-align:right;"|1 kW to 10 MW
|
|
|style="background:#ddddff"|Research
|-
| |Phosphoric acid fuel cell
|Molten phosphoric acid (H3PO4)
|style="background:#ddffdd;text-align:right;"|up to 10 MW
|style="background:#ffdddd;text-align:right;"|150-200
|style="background:#ffffdd;text-align:right;"|Cell: 55%
System: 40%
Co-Gen: 90%
|
|$4–$4.50 per watt
|-
| |Molten carbonate fuel cell
|Molten alkaline carbonate (e.g., sodium bicarbonate NaHCO3)
|style="background:#ddffdd;text-align:right;"|100 MW
|style="background:#ffdddd;text-align:right;"|600-650
|style="background:#ffffdd;text-align:right;"|Cell: 55%
System: 47%
|
|-
| |Tubular solid oxide fuel cell (TSOFC)
|O2--conducting ceramic oxide (e.g., zirconium dioxide, ZrO2)
|up to 100 MW
|style="background:#ffdddd;text-align:right;"|850-1100
|style="background:#ddffdd;text-align:right;"|Cell: 60–65%
System: 55–60%
|style="background:#ddddff"|Commercial/Research
|-
| |Protonic ceramic fuel cell
|H+-conducting ceramic oxide
|
|style="background:#ffdddd;text-align:right;"|700
|
|style="background:#ddddff"|Research
|-
| |Direct carbon fuel cell
|Several different
|
|style="background:#ffdddd;text-align:right;"|700-850
|style="background:#ddffdd;text-align:right;"|Cell: 80%
System: 70%
|
|-
| |Planar Solid oxide fuel cell
|O2--conducting ceramic oxide (e.g., zirconium dioxide, ZrO2 Lanthanum Nickel Oxide La2XO4,X= Ni,Co, Cu.)
|style="background:#ddffdd;text-align:right;"|up to 100 MW
|style="background:#ffdddd;text-align:right;"|850-1100
|style="background:#ddffdd;text-align:right;"|Cell: 60–65%
System: 55–60%
|
|-
| |Enzymatic Biofuel Cells
|Any that will not denature the enzyme (usually aqueous buffer).
|
|style="background:#ddffdd;text-align:right;"|under 40
|
|style="background:#ddddff"|Research
|-
|}
Efficiency
Fuel cell efficiency
The efficiency of a fuel cell is dependent on the amount of power
drawn from it. Drawing more power means drawing more current, which
increases the losses in the fuel cell. As a general rule, the more
power (current) drawn, the lower the efficiency. Most losses
manifest themselves as a voltage drop in the cell, so the
efficiency of a cell is almost proportional to its voltage. For
this reason, it is common to show graphs of voltage versus current
(so-called polarization curves) for fuel cells. A typical cell
running at 0.7 V has an efficiency of about 50%, meaning that 50%
of the energy content of the hydrogen is converted into electrical
energy; the remaining 50% will be converted into heat. (Depending
on the fuel cell system design, some fuel might leave the system
unreacted, constituting an additional loss.)
For a hydrogen cell operating at standard conditions with no
reactant leaks, the efficiency is equal to the cell voltage divided
by 1.48 V, based on the
enthalpy, or
heating value, of the reaction. For the same cell, the
second law efficiencyis equal to cell
voltage divided by 1.23 V. (This voltage varies with fuel used, and
quality and temperature of the cell.) The difference between these
numbers represents the difference between the reaction's
enthalpyand
Gibbs free
energy. This difference always appears as heat, along with any
losses in electrical conversion efficiency.
Fuel cells do not operate on a thermal cycle. As such, they are not
constrained, as combustion engines are, in the same way by
thermodynamic limits, such as
Carnot
cycleefficiency. At times this is misrepresented by saying that
fuel cells are exempt from the laws of thermodynamics, because most
people think of thermodynamics in terms of combustion processes
(
enthalpy of formation). The
laws of thermodynamics also hold for chemical processes (
Gibbs free energy) like fuel cells, but
the maximum theoretical efficiency is higher (83% efficient at 298K
in the case of hydrogen/oxygen reaction) than the
Otto cyclethermal efficiency (60% for compression
ratio of 10 and specific heat ratio of 1.4). Comparing limits
imposed by thermodynamics is not a good predictor of practically
achievable efficiencies. Also, if propulsion is the goal,
electrical output of the fuel cell has to still be converted into
mechanical power with the corresponding inefficiency. In reference
to the exemption claim, the correct claim is that the "limitations
imposed by the second law of thermodynamics on the operation of
fuel cells are much less severe than the limitations imposed on
conventional energy conversion systems". Consequently, they can
have very high efficiencies in converting
chemical energyto
electrical energy, especially when they
are operated at low power density, and using pure hydrogen and
oxygen as reactants.
In should be underlined that fuel cell (especially high
temperature) can be used as a heat source in conventional heat
engine (gas turbine system). In this case the ultra high efficiency
is predicted (above 70%).
In practice
For a fuel cell operating on air (rather than bottled oxygen),
losses due to the air supply system must also be taken into
account. This refers to the pressurization of the air and
dehumidifying it. This reduces the efficiency significantly and
brings it near to that of a compression ignition engine.
Furthermore fuel cell efficiency decreases as load increases.
The tank-to-wheel efficiency of a
fuel
cell vehicleis about 45% at low loads and shows average values
of about 36% when a driving cycle like the NEDC (
New European Driving Cycle) is
used as test procedure. The comparable NEDC value for a Diesel
vehicle is 22%.In 2008 Honda released a car (the
Honda FCX Clarity) 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. In addition to the production losses, over 70% of US'
electricity used for hydrogen production comes from
thermal power, which only has an efficiency of
33% to 48%, resulting in a net increase in carbon dioxide
production by using hydrogen in vehicles .
Fuel cells cannot store energy like a battery, but in some
applications, such as stand-alone power plants based on
discontinuous sources such as
solaror
wind power, they are combined with
electrolyzersand storage systems to
form an energy storage system. The overall efficiency (electricity
to hydrogen and back to electricity) of such plants (known as
round-trip efficiency) is between 30 and 50%, depending on
conditions. While a much cheaper
lead-acid batterymight 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(m-CHP) 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.
Fuel cell applications
Configuration of components.
Fuel cells are very useful as power sources in remote locations,
such as spacecraft, remote weather stations, large parks, rural
locations, 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 around one minute of down
time in a two year period.
Micro combined heat and
powersystems such as
home fuel
cellsand
cogenerationfor office
buildings and factories are in mass production phase. The
stationary fuel cell
applicationgenerates constant electric power (selling excess
power back to the grid when it is not consumed), and at the same
time produces hot air and water from the waste heat. A lower
fuel-to-electricity conversion efficiency is tolerated (typically
15-20%), because most of the energy not converted into electricity
is utilized as heat. Some heat is lost with the exhaust gas just as
in a normal
furnace, so the combined heat
and power efficiency is still lower than 100%, typically around
80%. In terms of
exergyhowever, the process
is inefficient, and one could do better by maximizing the
electricity generated and then using the electricity to drive a
heat pump.
Phosphoric-acid fuel cells(PAFC)
comprise the largest segment of existing CHP products worldwide and
can provide combined efficiencies close to 90% (35-50% electric +
remainder as thermal)
Molten-carbonate fuel cellshave
also been installed in these applications, and
solid-oxide fuel cellprototypes
exist.
Since 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. In this application, batteries would have to be largely
oversized to meet the storage demand, but fuel cells only need a
larger storage unit (typically cheaper than an electrochemical
device).
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 gallon tank
at 200 PSI, and runs a ReliOn fuel cell to provide full electric
back-up to the off-the-grid residence. The SIEI website gives
extensive technical details.
The world's first Fuel Cell Boat
HYDRAused an AFC system with 6.5 kW net
output.
In 2003, the world's first propeller driven airplane to be powered
entirely by a fuel cell was flown (the first fuel cell powered
aircraft was the Space Shuttle). The fuel cell was a unique
FlatStack
TMstack design which allowed the fuel cell to
be integrated with the aerodynamic surfaces of the plane.
Suggested applications
Hydrogen transportation and refueling
The GM 1966 Electrovan was the automotive industry's first attempt
at an automobile powered by a hydrogen fuel cell. The Electrovan,
which weighed more than twice as much as a normal van, could travel
up to 70 mph for 30 seconds.
The 2001
Chrysler Natriumused its
own on-board hydrogen processor. It produces hydrogen for the fuel
cell by reacting
sodium
borohydridefuel with
Borax, both of which
Chrysler claimed were naturally occurring in great quantity in the
United States. The hydrogen produces electric power in the fuel
cell for near-silent operation and a range of 300 miles without
impinging on passenger space.
Chrysleralso
developed vehicles which separated hydrogen from gasoline in the
vehicle, the purpose being to reduce emissions without relying on a
nonexistent hydrogen infrastructure and to avoid large storage
tanks.
The first
public hydrogen refueling station was opened in Reykjavík
, Iceland
in April
2003.This station serves three buses built by
DaimlerChryslerthat are in service in the
public transportnet of Reykjavík.
The
station produces the hydrogen it needs by itself, with an
electrolyzing unit (produced by Norsk Hydro
), and does not need refilling: all that enters is
electricity and water.Royal
Dutch Shellis also a partner in the project. The station has no
roof, in order to allow any leaked hydrogen to escape to the
atmosphere.
In 2003 President George Bush proposed the Hydrogen Fuel Initiative
(HFI), which was later implemented by legislation through the 2005
Energy Policy Act and the 2006 Advanced Energy Initiative. These
aimed at further developing hydrogen fuel cells and its
infrastructure technologies with the ultimate goal to produce
commercial fuel cell vehicles by 2020. By 2008, the U.S. had
contributed 1 billion dollars to this project.Nice, Karim, and
Jonathan Strickland. "How Fuel Cells Work." How Stuff Works. 30
Oct. 2008. 3 Nov. 2008
/auto.howstuffworks.com/fuel-efficiency/alternative-fuels/fuel-cell.htm>.
In May 2009, however, the
Obama
Administrationannounced that it will "cut off funds" for the
development of fuel cell
hydrogen
vehicles, since other vehicle technologies will lead to quicker
reduction in emissions in a shorter time. The
US Secretary of Energyexplained that
hydrogen vehicles "
will not be practical over the next 10 to 20
years", and also mentioned the challenges involved in the
development of the required infrastructure to distribute hydrogen
fuel. Nevertheless, the U.S. government will continue to fund
research related to
stationary fuel
cells. The
National
Hydrogen Associationand the
U.S.Fuel Cell Councilcriticized this
decision arguing that "
...the cuts proposed in the DOE hydrogen
and fuel cell program threaten to disrupt commercialization of a
family of technologies that are showing exceptional promise and
beginning to gain market traction."
In 2005 the British firm Intelligent Energy produced the first ever
working hydrogen run
motorcyclecalled the
ENV(Emission Neutral Vehicle). The motorcycle
holds enough fuel to run for four hours, and to travel 100 miles in
an urban area, at a top speed of 50 miles per hour. In 2004
Hondadeveloped a
fuel-cell motorcyclewhich utilized the
Honda FC Stack.
The
Type 212 submarinesof the
German and Italian navies use fuel cells to remain submerged for
weeks without the need to surface.
Boeingresearchers and industry partners throughout
Europe conducted experimental flight tests in February 2008 of a
manned
airplanepowered only by a fuel cell
and lightweight
batteries. The
Fuel Cell Demonstrator Airplane, as it was called, used a Proton
Exchange Membrane (PEM) fuel cell/
lithium-ion batteryhybrid system to
power an electric motor, which was coupled to a conventional
propeller.
In 2007,
the Revolve Eco-Rally (launched by HRH Prince of Wales)
demonstrated several fuel cell vehicles on British roads for the
first time, driven by celebrities and dignitaries from Brighton to
London's Trafalgar
Square
.Fuel cell powered race vehicles, designed
and built by university students from around the world, competed in
the world's first hydrogen race series called the
2008 Formula Zero
Championship, which began on August 22, 2008 in Rotterdam, the
Netherlands. More races are planned for 2009 and 2010. After this
first race, Greenchoice Forze from the university of Delft (The
Netherlands) became leader in the competition. Other competing
teams are Element One (Detroit), HerUCLAs (LA), EUPLAtecH2 (Spain),
Imperial Racing Green (London) and Zero Emission Racing Team
(Leuven).
The
California Hydrogen
Highwayis an initiative by the
California Governorto implement a series
of
hydrogen refueling stationsalong
that state. These stations are used to refuel
hydrogen vehiclessuch as fuel cell
vehicles and hydrogen combustion vehicles. As of July 2007
California had 179 fuel cell vehicles and twenty five stations were
in operation, and ten more stations have been planned for assembly
in California. However, there have already been three hydrogen
fueling stations decommissioned.
Japan
also has a
hydrogen highway, as part
of the Japan hydrogen
fuel cell project.Twelve
hydrogen fueling stationshave been built in
11 cities in Japan.
Canada
, Sweden
and Norway
also have
hydrogen highways
implemented.
There are numerous prototype or production cars and buses based on
fuel cell technology being researched or manufactured by motor car
manufacturers. In 2008,
Hondareleased a
hydrogen vehicle, the
FCX Clarity. Meanwhile there exist also
other examples of bikes and bicycles with a hydrogen fuel cell
engine.
A few companies are conducting hydrogen fuel cell research and
practical
fuel cell bustrials.
Daimler AG, with thirty-six experimental
units powered by
Ballard Power
Systemsfuel cells completing a successful three-year trial, in
eleven cities, in January 2007.
There are also fuel cell powered buses currently active or in production, such as a fleet of Thor buses with UTC Power fuel cells in California, operated by SunLine Transit Agency. The Fuel Cell Bus Club is a global cooperative effort in trial fuel cell buses.
The first
Brazilan
hydrogen fuel cell
bus prototype will begin operation in São Paulo
during the first semester of
2009.The hydrogen 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" (Brazilian Hydrogen
Autobus), includes three additional buses.
Market structure
Not all geographic markets are ready for SOFC powered m-CHP
appliances. Currently, the regions that lead the race in
Distributed Generation and deployment of fuel cell m-CHP units are
the EU and Japan.
Fuel cell economics
Also, it must be noted that regarding the concept of the
hydrogen vehicle, burning/
combustionof hydrogen in an
internal combustion
engine(IC/ICE) is often confused with the electrochemical
process of generating electricity via fuel cells (FC) in which
there is no combustion (though there is a small byproduct of heat
in the reaction). Both processes require the establishment of a
hydrogen economy before they may be considered commercially viable,
and even then, the aforementioned energy costs make a hydrogen
economy of questionable environmental value. Hydrogen combustion is
similar to petroleum combustion, and like petroleum combustion,
still results in nitrogen oxides as a by-product of the combustion,
which lead to smog. Hydrogen combustion, like that of petroleum, is
limited by the
Carnot efficiency,
and is completely different from the hydrogen fuel cell's chemical
conversion process of hydrogen to electricity and water without
combustion. Hydrogen fuel cells emit only water during use, while
producing carbon dioxide emissions during the majority of hydrogen
production, which comes from natural gas. Direct
methaneor
natural
gasconversion (whether IC or FC) also generate carbon dioxide
emissions, but direct hydrocarbon conversion in high-temperature
fuel cells produces lower carbon dioxide emissions than either
combustion of the same fuel (due to the higher efficiency of the
fuel cell process compared to combustion), and also lower carbon
dioxide emissions than hydrogen fuel cells, which use methane less
efficiently than high-temperature fuel cells by first converting it
to
high purity hydrogenby steam
reforming.
Nowadays low temperature fuel cell stacks
proton exchange membrane fuel
cell(PEMFC),
direct
methanol fuel cell(DMFC) and
phosphoric acid fuel cell(PAFC)
use a
platinumcatalysts. Impurities create
catalyst poisoning(reducing activity and
efficiency) in these low-temperature fuel cells, thus
high hydrogen purityor higher catalyst
densities are required. Although there are sufficient platinum
resources for future demand, most predictions of platinum running
out and/or platinum prices soaring do not take into account effects
of thrifting (reduction in catalyst loading) and recycling.
Recent
research at Brookhaven National Laboratory
could lead to the replacement of platinum by a
gold-palladium coating
which may be less susceptible to poisoning and thereby improve fuel
cell lifetime considerably.Current targets for a transport
PEM fuel cells are 0.2 g/kW Pt – which is a factor of 5 decrease
over current loadings – and recent comments from major
original equipment
manufacturers(OEMs) indicate that this is possible. Also it is
fully anticipated that
recyclingof fuel
cells components, including platinum, will kick in.
High-temperature fuel cells, including molten carbonate fuel cells
(MCFC's) and
solid oxide fuel
cells(SOFC's), do not use platinum as catalysts, but instead
use cheaper materials such as nickel and nickel oxide. They also do
not experience catalyst poisoning by carbon monoxide, and so they
do not require high-purity hydrogen to operate. They can use fuels
with an existing and extensive infrastructure, such as natural gas,
directly, without having to first reform it externally to hydrogen
and CO followed by CO removal.
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.
- 2006: Staxon introduced
an inexpensive OEM fuel cell module for system integration. In 2006
Angstrom Power, a British Columbia
based company, began commercial sales of portable devices using
proprietary hydrogen fuel cell technology, trademarked as "micro
hydrogen."
See also
References
Further reading
- Vielstich, W., et al. (eds.) (2009). Handbook of fuel
cells: advances in electrocatalysis, materials, diagnostics and
durability. 6 vol. Hoboken: Wiley, 2009.
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