What Is A Fuel Cell And How Does It Work? - SKengineers
WHAT IS A FUEL CELL?
A fuel cell is a device that generates electricity through
an electrochemical reaction, not combustion. In a fuel cell, hydrogen and
oxygen are combined to generate electricity, heat, and water. Fuel cells are
used today in a range of applications, from providing power to homes and
businesses, keeping critical facilities like hospitals, grocery stores, and
data centres up and running, and moving a variety of vehicles including cars,
buses, trucks, forklifts, trains, and more.
Fuel cell systems are a clean, efficient, reliable, and quiet source of power. Fuel cells do not need to be periodically recharged like batteries, but instead continue to produce electricity as long as a fuel source is provided.
A fuel cell is composed of an anode, cathode, and an electrolyte membrane. A typical fuel cell works by passing hydrogen through the anode of a fuel cell and oxygen through the cathode. At the anode site, a catalyst splits the hydrogen molecules into electrons and protons. The protons pass through the porous electrolyte membrane, while the electrons are forced through a circuit, generating an electric current and excess heat. At the cathode, the protons, electrons, and oxygen combine to produce water molecules. As there are no moving parts, fuel cells operate silently and with extremely high reliability.
Due to their chemistry, fuel cells are very clean. Fuel cells that use pure hydrogen fuel are completely carbon-free, with their only by products being electricity, heat, and water. Some types of fuel cell systems are capable of using hydrocarbon fuels like natural gas, biogas, methanol, and others. Because fuel cells generate electricity through chemistry rather than combustion, they can achieve much higher efficiencies than traditional energy production methods such as steam turbines and internal combustion engines. To push the efficiency even higher, a fuel cell can be coupled with a combined heat and power system that uses the cell’s waste heat for heating or cooling applications.
Fuel cells are also scalable. This means that individual
fuel cells can be joined with one another to form stacks. In turn, these stacks
can be combined into larger systems. Fuel cell systems vary greatly in size and
power, from combustion engine replacements for electric vehicles to
large-scale, multi-megawatt installations providing electricity directly to the
utility grid.
Benefits
at a glance -
Low-to-Zero Emissions
High Efficiency
Reliability
Fuel Flexibility
Energy Security
Durability
Scalability
Quiet Operation
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.
A block
diagram of a fuel cell -
Design
features in a fuel cell include -
The electrolyte substance, which usually defines the type of
fuel cell, and can be made from a number of substances like potassium
hydroxide, salt carbonates, and phosphoric acid.
The fuel that is used. The most common fuel is hydrogen.
The anode catalyst, usually fine platinum powder, breaks
down the fuel into electrons and ions.
The cathode catalyst, often nickel, converts ions into waste
chemicals, with water being the most common type of waste.
Gas diffusion layers that are designed to resist oxidization.
A typical fuel cell produces a voltage from 0.6 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 interconnections)
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 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.
Proton-exchange
membrane fuel cells (PEMFCs) -
Construction of a high-temperature PEMFC: Bipolar plate as
electrode with in-milled gas channel structure, fabricated from conductive
composites (enhanced with graphite, carbon black, carbon fibre, and/or carbon
nanotubes for more conductivity); Porous carbon papers; reactive layer, usually
on the polymer membrane applied; polymer membrane.
Condensation of water produced by a PEMFC on the air channel
wall. The gold wire around the cell ensures the collection of electric current.
SEM micrograph of a PEMFC MEA cross-section with a
non-precious metal catalyst cathode and Pt/C anode. False colours applied for
clarity.
In the archetypical hydrogen–oxide proton-exchange membrane
fuel cell design, a proton-conducting polymer membrane (typically nafion) contains
the electrolyte solution that 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 the synonyms
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 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 (supplying power) because the membrane is electrically insulating. On
the cathode catalyst, oxygen molecules react with the electrons (which have
travelled through the external circuit) and protons to form water.
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. 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 such as current collectors and
gaskets.
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 (MEA) is
referred to 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, and
these can be contaminated by carbon monoxide, necessitating a relatively pure
hydrogen fuel. The electrolyte could be a polymer membrane.
Proton-exchange
membrane fuel cell design issues -
Cost -
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. 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 (1.0–0.7 mg/cm2) 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. A recently published
article demonstrated how the environmental burdens change when using carbon
nanotubes as carbon substrate for platinum.
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 240,000 km (150,000 mi)) under extreme temperatures. Current
service life is 2,500 hours (about 75,000 miles). 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/L).
Limited carbon monoxide tolerance of some (non-PEDOT)
cathodes.
Phosphoric acid fuel cell (PAFC) -
Phosphoric acid fuel cells (PAFC) 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 to 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.
Solid acid fuel cell (SAFC) -
Solid acid fuel cells (SAFCs) are characterized by the use
of a solid acid material as the electrolyte. At low temperatures, solid acids
have an ordered molecular structure like most salts. At warmer temperatures
(between 140 and 150 °C for CsHSO4), some solid acids undergo a phase
transition to become highly disordered "super-protonic" structures,
which increases conductivity by several orders of magnitude. The first
proof-of-concept SAFCs were developed in 2000 using cesium hydrogen sulphate
(CsHSO4). Current SAFC systems use cesium dihydrogen phosphate (CsH2PO4) and
have demonstrated lifetimes in the thousands of hours.
Alkaline fuel cell (AFC) -
The alkaline fuel cell or hydrogen-oxygen fuel cell was
designed and first demonstrated publicly by Francis Thomas Bacon in 1959. It
was used as a primary source of electrical energy in the Apollo space program.
The cell consists of two porous carbon electrodes impregnated with a suitable
catalyst such as Pt, Ag, CoO, etc. The space between the two electrodes is
filled with a concentrated solution of KOH or NaOH which serves as an
electrolyte. H2 gas and O2 gas are bubbled into the electrolyte through the
porous carbon electrodes. Thus the overall reaction involves the combination of
hydrogen gas and oxygen gas to form water. The cell runs continuously until the
reactant's supply is exhausted. This type of cell operates efficiently in the
temperature range 343–413 K and provides a potential of about 0.9 V.[43] AAEMFC
is a type of AFC which employs a solid polymer electrolyte instead of aqueous
potassium hydroxide (KOH) and it is superior to aqueous AFC.
High-temperature
fuel cells -
Solid
oxide fuel cell -
Solid oxide fuel cells (SOFCs) use a solid material, most
commonly a ceramic material called yttria-stabilized zirconia (YSZ), 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
(800–1000 °C) and can be run on a variety of fuels including natural gas.
SOFCs are unique since in those, negatively charged oxygen
ions travel from the cathode (positive side of the fuel cell) to the anode
(negative side of the fuel cell) 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 (natural gas), 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 (heat-resistant materials made of
ceramic and metal) 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 (cerium
gadolinium oxide) 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.
Molten-carbonate fuel cell (MCFC) -
Molten carbonate fuel cells (MCFCs) require a high operating
temperature, 650 °C (1,200 °F), 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 CO2 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 United States 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 sulphur 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 (CHP) system.
Fuel Cell 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%.
Electric
storage fuel cell -
The electric storage fuel cell is a conventional battery
chargeable by electric power input, using the conventional electro-chemical
effect. However, the battery further includes hydrogen (and oxygen) inputs for
alternatively charging the battery chemically.
Efficiency
of leading fuel cell types -
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 ("output energy") to the total amount of energy that is put in
("input energy") 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 and 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 (CHP)
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
theoretical maximum efficiency of a fuel cell approaches 100%, while the
theoretical maximum efficiency of internal combustion engines is approximately
58%.
In
practice -
In a fuel cell vehicle the tank-to-wheel efficiency is
greater than 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 demonstration fuel cell electric vehicle (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. 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. As of 2019,
90% of hydrogen was used for oil refining, chemicals and fertilizer production,
and 98% of hydrogen is produced by steam methane reforming, which emits carbon
dioxide. The overall efficiency (electricity to hydrogen and back to
electricity) of such plants (known as round-trip efficiency), using pure
hydrogen and pure oxygen can be "from 35 up to 50 percent", depending
on gas density and other conditions. The electrolyzer/fuel cell system can
store indefinite quantities of hydrogen, and is therefore suited for long-term
storage.
Solid-oxide fuel cells produce 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.
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, primarily due to
the inefficiency of the oxygen reduction reaction (and ... the oxygen evolution
reaction, should the hydrogen be formed by electrolysis of water).... [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 organizations
were evaluating fuel cells to determine if they could significantly reduce the
battery weight carried by soldiers.
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 January 2014, no public company
in the industry had yet become profitable. There were 140,000 fuel cell stacks
shipped globally in 2010, up from 11,000 shipments in 2007, and from 2011 to
2012 worldwide fuel cell shipments had an annual growth rate of 85%.Tanaka
Kikinzoku expanded its manufacturing facilities in 2011. 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 (as the platinum in a regular fuel cell
costs around US$1,500, and the same amount of iron costs only around US$1.50).
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.
In 2016, Samsung "decided to drop fuel cell-related
business projects, as the outlook of the market isn't good".
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 centres, 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 CO2) for every 1,000
kW·h produced, compared to 25 pounds of pollutants generated by conventional
combustion systems.[80] 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 (1,900 L) tank at 200
pounds per square inch (1,400 kPa), and runs a Reli-On 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.
Small-scale (sub-5kWhr) fuel cells are being developed for use in residential
off-grid deployment.
Cogeneration
-
Combined heat and power (CHP) fuel cell systems, including
micro combined heat and power (MicroCHP) systems are used to generate both
electricity and heat for homes (see home fuel cell), office building and
factories. The system generates 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. 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 (40–60%
electric and the remainder as thermal). Phosphoric-acid fuel cells (PAFC)
comprise the largest segment of existing CHP products worldwide and can provide
combined efficiencies close to 90%. Molten carbonate (MCFC) and solid-oxide
fuel cells (SOFC) are also used for combined heat and power generation and have
electrical energy efficiencies 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.
Delta-ee consultants stated in 2013 that with 64% of global
sales the fuel cell micro-combined heat and power passed the conventional
systems in sales in 2012. The Japanese ENE FARM project will pass 100,000 FC
mCHP systems in 2014, 34.213 PEMFC and 2.224 SOFC were installed in the period
2012–2014, 30,000 units on LNG and 6,000 on LPG.
Fuel cell
electric vehicles (FCEVs) -
Configuration
of components in a fuel cell car -
Fuel Cell
Electric Vehicles -
Fuel cell electric vehicles (FCEVs) are powered by hydrogen.
They are more efficient than conventional internal combustion engine vehicles
and produce no tailpipe emissions—they only emit water vapor and warm air.
FCEVs and the hydrogen infrastructure to fuel them are in the early stages of
implementation. The U.S. Department of Energy leads research efforts to make
hydrogen-powered vehicles an affordable, environmentally friendly, and safe
transportation option. Hydrogen is considered an alternative fuel under the
Energy Policy Act of 1992 and qualifies for alternative fuel vehicle tax
credits.
What is a
fuel cell electric vehicle?
FCEVs use a propulsion system similar to that of electric
vehicles, where energy stored as hydrogen is converted to electricity by the
fuel cell. Unlike conventional internal combustion engine vehicles, these
vehicles produce no harmful tailpipe emissions. Other benefits include
increasing U.S. energy resiliency through diversity and strengthening the
economy.
FCEVs are fuelled with pure hydrogen gas stored in a tank on
the vehicle. Similar to conventional internal combustion engine vehicles, they
can fuel in less than 4 minutes and have a driving range over 300 miles. FCEVs
are equipped with other advanced technologies to increase efficiency, such as
regenerative braking systems that capture the energy lost during braking and
store it in a battery. Major automobile manufacturers are offering a limited
but growing number of production FCEVs to the public in certain markets, in
sync with what the developing infrastructure can support.
How Fuel
Cells Work -
The most common type of fuel cell for vehicle applications
is the polymer electrolyte membrane (PEM) fuel cell. In a PEM fuel cell, an
electrolyte membrane is sandwiched between a positive electrode (cathode) and a
negative electrode (anode). Hydrogen is introduced to the anode, and oxygen
(from air) is introduced to the cathode. The hydrogen molecules break apart
into protons and electrons due to an electrochemical reaction in the fuel cell
catalyst. Protons then travel through the membrane to the cathode.
The electrons are forced to travel through an external
circuit to perform work (providing power to the electric car) then recombine
with the protons on the cathode side where the protons, electrons, and oxygen
molecules combine to form water. See the Fuel Cell Electric Vehicle (FCEV)
infographic (PDF) to learn more about the process.
Element
One fuel cell vehicle -
Automobiles
-
By year-end 2019, about 18,000 FCEVs had been leased or sold
worldwide. Three fuel cell electric vehicles have been introduced for
commercial lease and sale: the Honda Clarity, Toyota Mirai and the Hyundai ix35
FCEV. Additional demonstration models include the Honda FCX Clarity, and
Mercedes-Benz F-Cell. As of June 2011 demonstration FCEVs had driven more than
4,800,000 km (3,000,000 mi), with more than 27,000 refuellings. Fuel cell
electric vehicles feature an average range of 314 miles between refuellings.
They can be refuelled in less than 5 minutes. The U.S. Department of Energy's
Fuel Cell Technology Program states 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 (75,000 mi) with less than 10%
degradation. In a 2017 Well-to-Wheels simulation analysis that "did not
address the economics and market constraints", General Motors and its
partners estimated that per mile travelled, 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.
In 2015, Toyota introduced its first fuel cell vehicle, the
Mirai, at a price of $57,000. Hyundai introduced the limited production Hyundai
ix35 FCEV under a lease agreement. In 2016, Honda started leasing the Honda
Clarity Fuel Cell. In 2020, Toyota introduced the second generation of its
Mirai brand, improving fuel efficiency and expanding range compared to the
original Sedan 2014 model.
Criticism
-
Some commentators believe that hydrogen fuel cell cars will
never become economically competitive with other technologies or that it will
take decades for them to become profitable. Elon Musk, CEO of battery-electric
vehicle maker Tesla Motors, stated in 2015 that fuel cells for use in cars will
never be commercially viable because of the inefficiency of producing,
transporting and storing hydrogen and the flammability of the gas, among other
reasons.
A 2019 video by Real Engineering noted that, notwithstanding
the introduction of vehicles that run on hydrogen, using hydrogen as a fuel for
cars does not help to reduce carbon emissions from transportation. The 95% of
hydrogen still produced from fossil fuels releases carbon dioxide, and
producing hydrogen from water is an energy-consuming process. Storing hydrogen
requires more energy either to cool it down to the liquid state or to put it
into tanks under high pressure, and delivering the hydrogen to fuelling
stations requires more energy and may release more carbon. The hydrogen needed
to move a FCV a kilometer costs approximately 8 times as much as the
electricity needed to move a BEV the same distance. A 2020 assessment concluded
that hydrogen vehicles are still only 38% efficient, while battery EVs are 80%
efficient.
Buses -
Toyota
FCHV-BUS at the Expo 2005
As of August 2011, there were about 100 fuel cell buses in
service around the world. Most of these were manufactured by UTC Power, Toyota,
Ballard, Hydro-genics, and Proton Motor. UTC buses had driven more than 970,000
km (600,000 mi) by 2011. Fuel cell buses have from 39% to 141% higher fuel
economy than diesel buses and natural gas buses.
As of 2019, the NREL was evaluating several current and
planned fuel cell bus projects in the U.S.
Trucks -
In December 2020, Toyota and Hino Motors, together with
Seven-Eleven (Japan), Family Mart and Lawson announced that they have agreed to
jointly consider introducing light-duty fuel cell electric trucks (light-duty
FCETs). Lawson started testing for low temperature delivery at the end of July
2021 in Tokyo, using a Hino Dutro in which the Toyota Mirai fuel cell is
implemented. Family Mart started testing in Okazaki city.
In August 2021, Toyota announced their plan to make fuel
cell modules at its Kentucky auto-assembly plant for use in zero-emission big
rigs and heavy-duty commercial vehicles. They plan to begin assembling the
electrochemical devices in 2023.
Forklifts
-
A fuel cell forklift (also called a fuel cell lift truck) is
a fuel cell-powered industrial forklift truck used to lift and transport
materials. In 2013 there were over 4,000 fuel cell forklifts used in material
handling in the US, of which 500 received funding from DOE (2012). Fuel cell
fleets are operated by various companies, including Sysco Foods, FedEx Freight,
GENCO (at Wegmans, Coca-Cola, Kimberly Clark, and Whole Foods), and H-E-B
Grocers. Europe demonstrated 30 fuel cell forklifts with Hy lift and extended
it with Hy LIFT-EUROPE to 200 units, with other projects in France and Austria.
Pike Research projected in 2011 that fuel cell-powered forklifts would be the
largest driver of hydrogen fuel demand by 2020.
Most companies in Europe and the US do not use
petroleum-powered forklifts, as these vehicles work indoors where emissions
must be controlled and instead use electric forklifts. Fuel cell-powered
forklifts can provide benefits over battery-powered forklifts as they can be
refuelled in 3 minutes and they can be used in refrigerated warehouses, where
their performance is not degraded by lower temperatures. The FC units are often
designed as drop-in replacements.
Motorcycles
and bicycles -
In 2005, a British manufacturer of hydrogen-powered fuel
cells, Intelligent Energy (IE), produced the first working hydrogen-run
motorcycle called the ENV (Emission Neutral Vehicle). The motorcycle holds
enough fuel to run for four hours, and to travel 160 km (100 mi) in an urban
area, at a top speed of 80 km/h (50 mph). 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 fuelling
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
-
In 2003, the world's first propeller-driven airplane to be
powered entirely by a fuel cell was flown. The fuel cell was a stack design
that allowed the fuel cell to be integrated with the plane's aerodynamic
surfaces. Fuel cell-powered unmanned aerial vehicles (UAV) include a Horizon
fuel cell UAV that set the record distance flown for a small UAV in 2007.
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 (PEM) fuel cell/lithium-ion
battery hybrid system to power an electric motor, which was coupled to a
conventional propeller.
In 2009, the Naval Research Laboratory's (NRL's) Ion Tiger
utilized a hydrogen-powered fuel cell and flew for 23 hours and 17 minutes.
Fuel cells are also being tested and considered to provide auxiliary power in
aircraft, replacing fossil fuel generators that were previously used to start
the engines and power on board electrical needs, while reducing carbon
emissions. failed verification] In 2016 a Raptor E1 drone made a successful
test flight using a fuel cell that was lighter than the lithium-ion battery it
replaced. The flight lasted 10 minutes at an altitude of 80 metres (260 ft),
although the fuel cell reportedly had enough fuel to fly for two hours. The
fuel was contained in approximately 100 solid 1 square centimetre (0.16 sq in)
pellets composed of a proprietary chemical within an unpressurized cartridge.
The pellets are physically robust and operate at temperatures as warm as 50 °C
(122 °F). The cell was from Arcola Energy.
Lockheed Martin Skunk Works Stalker is an electric UAV
powered by solid oxide fuel cell.
Boats -
The world's first certified fuel cell boat (HYDRA), in
Leipzig/Germany
The world's first fuel cell boat HYDRA used an AFC system
with 6.5 kW net output. Amsterdam introduced fuel cell-powered boats that ferry
people around the city's 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 Howald tswerke 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. A naval paper has
theorized about the possibility of a nuclear-fuel cell hybrid whereby the fuel
cell is used when silent operations are required and then replenished from the
Nuclear reactor (and water).
Portable
power systems -
Portable fuel cell systems are generally classified as
weighing under 10 kg and providing power of less than 5 kW. The potential
market size for smaller fuel cells is quite large with an up to 40% per annum
potential growth rate and a market size of around $10 billion, leading a great
deal of research to be devoted to the development of portable power cells.
Within this market two groups have been identified. The first is the micro-fuel
cell market, in the 1-50 W range for power smaller electronic devices. The
second is the 1-5 kW range of generators for larger scale power generation
(e.g. military outposts, remote oil fields).
Micro-fuel cells are primarily aimed at penetrating the
market for phones and laptops. This can be primarily attributed to the
advantageous energy density provided by fuel cells over a lithium-ion battery,
for the entire system. For a battery, this system includes the charger as well
as the battery itself. For the fuel cell this system would include the cell,
the necessary fuel and peripheral attachments. Taking the full system into
consideration, fuel cells have been shown to provide 530Wh/kg compared to 44
Wh/kg for lithium ion batteries. However, while the weight of fuel cell systems
offer a distinct advantage the current costs are not in their favour. while a
battery system will generally cost around $1.20 per Wh, fuel cell systems cost
around $5 per Wh, putting them at a significant disadvantage.
As power demands for cell phones increase, fuel cells could
become much more attractive options for larger power generation. The demand for
longer on time on phones and computers is something often demanded by consumers
so fuel cells could start to make strides into laptop and cell phone markets.
The price will continue to go down as developments in fuel cells continues to
accelerate. Current strategies for improving micro fuel cells is through the
use of carbon nanotubes. It was shown by Girish kumar et al. that depositing
nanotubes on electrode surfaces allows for substantially greater surface area
increasing the oxygen reduction rate.
Fuel cells for use in larger scale operations also show much
promise. Portable power systems that use fuel cells can be used in the leisure
sector (i.e. RVs, cabins, marine), the industrial sector (i.e. power for remote
locations including gas/oil wellsites, communication towers, security, weather
stations), 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. The key advantage of fuel cells in this market is the great power
generation per weight. While fuel cells can be expensive, for remote locations
that require dependable energy fuel cells hold great power. For a 72-h
excursion the comparison in weight is substantial, with a fuel cell only
weighing 15 pounds compared to 29 pounds of batteries needed for the same
energy.
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 centres,
Telecommunication
equipment and modern naval ships.
An uninterrupted power supply (UPS) 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 (e.g. a belt
clip that charges a cell phone or PDA).
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 (alcohol) in the
sample.
Carbon monoxide detector, electrochemical sensor.
Fuelling
stations -
Hydrogen fuelling station.
According to Fuel Cells Works, an industry group, at the end
of 2019, 330 hydrogen refuelling stations were open to the public worldwide. As
of June 2020, there were 178 publicly available hydrogen stations in operation
in Asia. 114 of these were in Japan. There were at least 177 stations in
Europe, and about half of these were in Germany. There were 44 publicly
accessible stations in the US, 42 of which were located in California.
A hydrogen fuelling station costs between $1 million and $4
million to build.
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