A
fuel cell is a device that converts the
chemical energy from a fuel into electricity through a chemical reaction of positively charged hydrogen ions with oxygen or another
oxidizing agent. Fuel cells are different from
batteries in that they require a continuous source of fuel and oxygen or air to sustain the chemical reaction, whereas in a battery the chemicals present in the battery react with each other to generate an
electromotive force (emf). Fuel cells can produce electricity continuously for as long as these inputs are supplied.