a fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent . hydrogen is the most common fuel, but hydrocarbons such as natural gas, and alcohols like methanol, are sometimes used.
individual fuel cells produce relatively small electrical potential, about 0.7 volts, so cells are stacked, or placed in series, to increase the voltage and meet an application's requirements. in addition to electricity, fuel cells produce water, heat and, depending on the fuel source, very small amounts of nitrogen dioxide and other emissions.
the energy efficiency of a fuel cell is generally between 40 to 60%, or up to 85% efficient in cogeneration if waste heat is captured for use.
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