A fuel cell is an electrochemical device that uses hydrogen and oxygen to produce DC electricity, with water and heat as byproducts. Although similar to batteries, fuel cells are different in that they require a continual replenishment of the reactants (hydrogen and oxygen).

A typical fuel cell element consists of a cathode and anode separated by an electrolytic membrane material. As hydrogen gas flows across the anode, electrons are stripped from the hydrogen and flow through an external circuit, reentering the fuel cell at the cathode. At the same time, positively charged hydrogen ions migrate across the membrane to the cathode, where they combine with oxygen and the returning electrons to form water and heat.