Educational kits & resources
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What is a fuel cell?
A fuel cell is an electrochemical device that combines hydrogen and oxygen to produce electricity, with water and heat as its by-product. As long as fuel is supplied, the fuel cell will continue to generate power. Since the conversion of the fuel to energy takes place via an electrochemical process, not combustion, the process is clean, quiet and highly efficient - two to three times more efficient than fuel burning.
No other energy generation technology offers the combination of benefits that fuel cells do. In addition to low or zero emissions, benefits include high efficiency and reliability, multi-fuel capability, siting flexibility, durability, scalability and ease of maintenance.
Fuel cells operate silently, so they reduce noise pollution as well as air pollution and the waste heat from a fuel cell can be used to provide hot water or space heating for a home or office.
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How does it work?
In principle, a fuel cell operates like a battery. Unlike a battery, a fuel cell does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.
A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat.
Hydrogen fuel is fed into the "anode" of the fuel cell. Oxygen (or air) enters the fuel cell through the cathode. Encouraged by a catalyst, the hydrogen atom splits into a proton and an electron, which take different paths to the cathode. The proton passes through the electrolyte. The electrons create a separate current that can be utilized before they return to the cathode, to be reunited with the hydrogen and oxygen in a molecule of water.
A fuel cell system which includes a "fuel reformer" can utilize the hydrogen from any hydrocarbon fuel - from natural gas to methanol, and even gasoline. Since the fuel cell relies on chemistry and not combustion, emissions from this type of a system would still be much smaller than emissions from the cleanest fuel combustion processes.
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Proton Exchange Membrane fuel cell (PEM)
These fuel cells operate at relatively low temperatures (about 175°F), have high power density, can vary their output quickly to meet shifts in power demand, and are suited for applications, such as in automobiles, where quick startup is required., they are the primary candidates for light-duty vehicles, for buildings, and potentially for much smaller applications such as replacements for rechargeable batteries. This type of fuel cell is sensitive to fuel impurities. Cell outputs generally range from 50 watts to 75 kW.
Direct Methanol fuel cell (DMFC)
These cells are similar to the PEM cells in that they both use a polymer membrane as the electrolyte. However, in the DMFC, the anode catalyst itself draws the hydrogen from the liquid methanol, eliminating the need for a fuel reformer. Efficiencies of about 40% are expected with this type of fuel cell, which would typically operate at a temperature between 120-190°F. This is a relatively low range, making this fuel cell attractive for tiny to mid-sized applications, to power cellular phones and laptops. Higher efficiencies are achieved at higher temperatures.
Solid Oxide fuel cell (SOFC)
Solid oxide fuel cells use a hard, non-porous ceramic compound as the electrolyte, and operate at very high temperatures - around 1800°F. One type of SOFC uses an array of meter-long tubes, and other variations include a compressed disc that resembles the top of a soup can. Tubular SOFC designs are closer to commercialization and are being produced by several companies around the world. SOFCs are suitable for stationary applications as well as for auxiliary power units (APUs) used in vehicles to power electronics.
Phosphoric Acid fuel cell (PAFC)
Phosphoric acid fuel cells are commercially available today. Hundreds of fuel cell systems have been installed in 19 nations - in hospitals, nursing homes, hotels, office buildings, schools, utility power plants, landfills and waste water treatment plants. PAFCs generate electricity at more than 40% efficiency - and nearly 85% of the steam this fuel cell produces is used for cogeneration - this compares to about 35% for the utility power grid in the United States. Phosphoric acid fuel cells use liquid phosphoric acid as the electrolyte and operate at about 450°F.
Regenerative fuel cell
Regenerative fuel cells are attractive as a closed-loop form of power generation. Water is separated into hydrogen and oxygen by a solar-powered electrolyzer. The hydrogen and oxygen are fed into the fuel cell which generates electricity, heat and water. The water is then recirculated back to the solar-powered electrolyzer and the process begins again. These types of fuel cells are currently being researched by NASA and others worldwide.
Zinc Air fuel cell (ZAFC)
In a typical zinc/air fuel cell, there is a gas diffusion electrode (GDE), a zinc anode separated by electrolyte, and some form of mechanical separators. The GDE is a permeable membrane that allows atmospheric oxygen to pass through. After the oxygen has converted into hydroxyl ions and water, the hydroxyl ions will travel through an electrolyte, and reaches the zinc anode. Here, it reacts with the zinc, and forms zinc oxide. This process creates an electrical potential; when a set of ZAFC cells are connected, the combined electrical potential of these cells can be used as a source of electric power.
Protonic Ceramic fuel cell (PCFC)
This new type of fuel cell is based on a ceramic electrolyte material that exhibits high protonic conductivity at elevated temperatures. PCFCs share the thermal and kinetic advantages of high temperature operation at 700 degrees Celsius with molten carbonate and solid oxide fuel cells, while exhibiting all of the intrinsic benefits of proton conduction in PEM and phosphoric acid fuel cells. The high operating temperature is necessary to achieve very high electrical fuel efficiency with hydrocarbon fuels. PCFCs can operate at high temperatures and electrochemically oxidize fossil fuels directly to the anode.
Microbial fuel cell (MFC)
Microbial fuel cells use the catalytic reaction of microorganisms such as bacteria to convert virtually any organic material into fuel. Some common compounds include glucose, acetate, and wastewater. Enclosed in oxygen-free anodes, the organic compounds are consumed (oxidized) by the bacteria or other microbes. As part of the digestive process, electrons are pulled from the compound and conducted into a circuit with the help of an inorganic mediator. MFCs operate well in mild conditions relative to other types of fuel cells, such as 20-40 degrees Celsius, and could be capable of producing over 50% efficiency.
Molten Carbonate fuel cell (MCFC)
Molten carbonate fuel cells use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert matrix, and operate at high temperatures - approximatelly 1,200ºF. They require carbon dioxide and oxygen to be delivered to the cathode. To date, MCFCs have been operated on hydrogen, carbon monoxide, natural gas, propane, landfill gas, marine diesel, and simulated coal gasification products. 10 kW to 2 MW MCFCs have been tested on a variety of fuels and are primarily targeted to electric utility applications.
Alkaline fuel cell (AFC)
Long used by NASA on space missions, alkaline fuel cells can achieve power generating efficiencies of up to 70 percent. They were used on the Apollo spacecraft to provide both electricity and drinking water. Alkaline fuel cells use potassium hydroxide as the electrolyte and operate at 160°F. However, they are very susceptible to carbon contamination, so require pure hydrogen and oxygen.
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 PEM
DMFC |
SOFC
PAFC |
Reg.FC
ZAFC |
PCFC
MFC |
MCFC
AFC |
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 High Efficiency
High Reliability
High Quality Power
Fuel Flexibility
Security
Modularity
Scalability
Flexible Siting
Long-lasting Battery |
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Zero-emission power
A fuel cell running on pure hydrogen is a zero-emission power source. Some stationary fuel cells use natural gas or hydrocarbons as a hydrogen feedstock, but even those produce far less emissions than conventional power plants. Fuel cell power plants are so low in emissions that some areas of the United States have exempted them from air permit requirements. Fuel cells are also very quiet, which reduces noise pollution.
Based on measured data, a fuel cell power plant may create less than one ounce of pollution per 1,000 kilowatt-hours of electricity produced - compared to the 25 pounds of pollutants for conventional combustion generating systems.
High Energy Efficiency
Because they make energy electrochemically, and do not burn fuel, fuel cells are fundamentally more efficient than combustion systems. When the fuel cell is sited near the point of use, its waste heat can be captured for beneficial purposes (cogeneration). In large-scale building systems, these fuel cell cogeneration systems can reduce facility energy service costs by 20% to 40% compared to conventional energy service.
Fuel cell power generation systems in operation today achieve 40% to 50% fuel-to-electricity efficiency utilizing hydrocarbon fuels.
Systems fueled by hydrogen can consistently provide more than 50 percent efficiency. Even more efficient systems are under development.
In combination with a turbine, electrical efficiencies can exceed 60 percent.
High Reliability/High Quality Power
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The National Power Laboratory estimates that the typical computer location experiences 289 power disturbances a year that are outside the voltage limits of the computer equipment. U.S. businesses lose $29 billion annually from computer failures due to power outages and are quickly realizing that fuel cells may help prevent not only loss of power, but also loss of dollars. Fuel cells offer clean, high quality power, crucial to an economy that depends on increasingly sensitive computers, medical equipment and machines.
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Fuel Flexibility
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Most fuel cells run on hydrogen and will continue to generate power as long as fuel is supplied. The fuel cell doesn't care where the hydrogen comes from, so a fuel cell system that includes a "fuel reformer" can generate hydrogen from diverse, domestic resources including fossil fuels, such as natural gas and coal; alcohol fuels, such as methanol or ethanol; from hydrogen compounds containing no carbon, such as ammonia or borohydride; or from biomass, methane, landfill gas or anaerobic digester gas from wastewater treatment plants . Hydrogen can also be produced from electricity from conventional, nuclear or renewable sources such as solar or wind. |
Energy Security
Hydrogen can be produced from domestic sources, eliminating the need to import foreign oil. Passenger vehicles alone consume 6 million barrels of oil every single day, equivalent to 85 percent of oil imports. If just 20 percent of cars used fuel cells, we could cut oil imports by 1.5 million barrels every day.
Modularity/Scalability/Flexibility
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The beauty of fuel cells is their versatility - since they are scalable, fuel cells can be stacked until the desired power output is reached. Larger fuel cells can be linked together to achieve megawatt outputs. Fuel cells are quiet, which allows for siting close to business or residences. They are also durable and rugged, so they can withstand any terrain or weather conditions. |
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Long-lasting, Portable Energy
Fuel cells are being developed for use with portable electronic devices such as laptops, cellular phones, and other electronic devices as they provide e a much longer operating life than a battery would, in a package of lighter or equal weight per unit of energy stored. The fuel cell doesn't require "recharging;" a liquid, solid, or gaseous fuel canister could be replaced instantly. Fuel cells also have an environmental advantage over batteries, since certain kinds of batteries require special disposal treatment. Fuel cells provide a much higher energy density, packing more energy in a smaller space.
Many organizations are working with the military to incorporate fuel cells into their equipment since soldiers are starting to carry a range of enabling electronic technologies, computers, personal radios, displays and thermal imaging, all intended to increase effectiveness, lethality and survivability.
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