Fuel cells produce electricity by utilizing the power generated from electrochemical reactions. They use external sources of chemical energy such as hydrogen and oxygen to produce energy. Electrochemical reactions in the fuel cells oxidize hydrogen, which reacts with oxygen to form water and release electrons. The electrons then flow through the external circuit producing an electric current. All fuel cells are based on a standard design wherein two electrodes are separated by an electrolyte. The electrolyte carries electrically charged particles. A catalyst is used to speed up or accelerate the electrochemical reaction within the fuel cells. Fuel cells can be used in small devices that are powered by a few watts of electricity and also in large power plants that produce megawatts (MW) of electrical energy. Fuel cells are categorized by the nature of the electrolyte used in them.

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