How a fuel cell works: In the polymer electrolyte membrane (PEM) fuel cell, also known as a proton-exchange membrane cell, a catalyst in the anode separates hydrogen atoms into protons and electrons. The membrane in the center transports the protons to the cathode, leaving the electrons behind. The electrons flow through a circuit to the cathode, forming an electric current to do useful work. In the cathode, another catalyst helps the electrons, hydrogen nuclei and oxygen from the air recombine. When the input is pure hydrogen, the exhaust consists of water vapor. In fuel cells using hydrocarbon fuels the exhaust is water and carbon dioxide. Cornell's new research is aimed at finding lighter, cheaper and more efficient materials for the catalysts and membranes.
Tomorrow, hydrogen's use as a fuel for fuel cells will grow dramatically-for transportation, stationary and portable applications. (PlugPower 5-kW fuel cell (large cell), H2ECOnomy 25-W fuel cell (small silver cell), and Avista Labs 30-W fuel cell).
Maybe you are surprised by how close these three technologies are. This exercise points out the importance of considering the whole system, not just the car. We could even go a step further and ask what the efficiency of producing gasoline, methanol or coal is. Efficiency is not the only consideration, however. People will not drive a car just because it is the most efficient if it makes them change their behavior. They are concerned about many other issues as well. They want to know: Is the car quick and easy to refuel? Can it travel a good distance before refueling? Is it as fast as the other cars on the road? How much pollution does it produce? This list, of course, goes on and on. In the end, the technology that dominates will be a compromise between efficiency and practicality.
Hydrogen and oxygen can be combined in a fuel cell to produce electrical energy. A fuel cell uses a chemical reaction to provide an external voltage, as does a battery, but differs from a battery in that the fuel is continually supplied in the form of hydrogen and oxygen gas. It can produce electrical energy at a higher efficiency than just burning the hydrogen to produce heat to drive a generator because it is not subject to the thermal bottleneck from the second law of thermodynamics. It's only product is water, so it is pollution-free. All these features have led to periodic great excitement about its potential, but we are still in the process of developing that potential as a pollution-free, efficient energy source (see Kartha and Grimes).
Figure 5. In a proton−exchange−membrane fuel cell, hydrogen and oxygen react electrochemically. At the anode, hydrogen molecules dissociate, the atoms are ionized, and electrons are directed to an external circuit; protons are handed off to the ion−exchange membrane and pass through to the cathode. There, oxygen combines with protons from the ion−exchange membrane and electrons from the external circuit to form water or steam. The energy conversion efficiency of the process can be 60% or higher.
The Promise of Fuel Cells
• “A score of nonutility companies are
well advanced toward developing a
powerful chemical fuel cell, which
could sit in some hidden closet of
every home silently ticking off
• Theodore Levitt, “Marketing Myopia,” Harvard
Business Review, 1960
Theodore Levitt, “Marketing Myopia,” Harvard Business Review, 1960
Parts of a Fuel Cell
• Negative post of the fuel cell.
• Conducts the electrons that are freed from the hydrogen molecules so that
they can be used in an external circuit.
• Etched channels disperse hydrogen gas over the surface of catalyst.
Positive post of the fuel cell
Etched channels distribute oxygen to the surface of the catalyst.
Conducts electrons back from the external circuit to the catalyst
Recombine with the hydrogen ions and oxygen to form water.
• Proton exchange membrane.
• Specially treated material, only conducts positively charged ions.
• Membrane blocks electrons.
Special material that facilitates reaction of oxygen and hydrogen
Usually platinum powder very thinly coated onto carbon paper or cloth.
Rough & porous maximizes surface area exposed to hydrogen or oxygen
The platinum-coated side of the catalyst faces the PEM.
Fuel Cell Operation
• Pressurized hydrogen gas (H2) enters cell on
• Gas is forced through catalyst by pressure.
• When H2 molecule comes contacts platinum catalyst, it
splits into two H+ ions and two electrons (e-).
• Electrons are conducted through the anode
• Make their way through the external circuit (doing
useful work such as turning a motor) and return to the
cathode side of the fuel cell.
• On the cathode side, oxygen gas (O2) is forced
through the catalyst
• Forms two oxygen atoms, each with a strong negative
• Negative charge attracts the two H+ ions through the
• Combine with an oxygen atom and two electrons from
the external circuit to form a water molecule (H2O).
Hydrogen Fuel Cell Efficiency
• 40% efficiency converting methanol to
hydrogen in reformer
• 80% of hydrogen energy content
converted to electrical energy
• 80% efficiency for inverter/motor
• Converts electrical to mechanical energy
• Overall efficiency of 24-32%
Auto Power Efficiency Comparison
Other Types of Fuel Cells
Alkaline fuel cell (AFC)
Phosphoric-acid fuel cell (PAFC)
The phosphoric-acid fuel cell has potential for use in small stationary powergeneration systems. It operates at a higher temperature than PEM fuel cells,
so it has a longer warm-up time. This makes it unsuitable for use in cars.
Solid oxide fuel cell (SOFC)
This is one of the oldest designs. It has been used in the U.S. space program
since the 1960s. The AFC is very susceptible to contamination, so it requires
pure hydrogen and oxygen. It is also very expensive, so this type of fuel cell is
unlikely to be commercialized.
These fuel cells are best suited for large-scale stationary power generators
that could provide electricity for factories or towns. This type of fuel cell
operates at very high temperatures (around 1,832 F, 1,000 C). This high
temperature makes reliability a problem, but it also has an advantage: The
steam produced by the fuel cell can be channeled into turbines to generate
more electricity. This improves the overall efficiency of the system.
Molten carbonate fuel cell (MCFC)
These fuel cells are also best suited for large stationary power generators.
They operate at 1,112 F (600 C), so they also generate steam that can be
used to generate more power. They have a lower operating temperature than
the SOFC, which means they don't need such exotic materials. This makes
the design a little less expensive.
Advantages/Disadvantages of Fuel Cells
• Water is the only discharge (pure H2)
• CO2 discharged with methanol reform
• Little more efficient than alternatives
• Technology currently expensive
• Many design issues still in progress
• Hydrogen often created using “dirty”
energy (e.g., coal)
• Pure hydrogen is difficult to handle
• Refilling stations, storage tanks, …
Fuel Cell Energy Exchange
Fuel Cell Electric Vehicle
Although there are currently no Fuel cell vehicles available for commercial sale, over 20 FCEVs
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 (3,000,000 mi), with more than 27,000
Demonstration fuel cell vehicles have been produced with "a driving range of more than 400 km
(250 mi) between refueling". They can be refueled in less than 5 minutes.
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.“
. 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 (water, natural gas,
biomass), 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. "
Fuel Cell Application
In total there are over 100 fuel cell buses deployed around the world today. Most buses are
produced by UTC Power, Toyota, Ballard, Hydrogenics, and Proton Motor. UTC Buses have
already accumulated over 970,000 km (600,000 mi) of driving.
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.
A fuel cell forklift (also called a fuel cell lift truck or 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.
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
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.
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
(produced by Norsk Hydro), 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.
Providing power for base stations or cell sites.
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 (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.
Food preservation, achieved by exhausting the oxygen and automatically maintaining oxygen
exhaustion in a shipping container, containing, for example, fresh fish.
Smartphones, laptops and tablets.
Small heating appliances
Portable charging docks for small electronics (e.g. a belt clip that charges your cell phone or PDA).
Notebook computers for applications where AC charging may not be readily available.
Hybrid vehicles, pairing the fuel cell with either an ICE or a battery