Water electrolysis(also called water splitting) is the decomposition of water into oxygen and hydrogen gas due to the passage of an electric current. This technique can be used to make hydrogen gas, a main component of hydrogen fuel, and breathable oxygen gas. It ideally requires a potential difference of 1.23 V to split water. However, real water electrolyzers require higher voltages for the reaction to proceed. The part that exceeds 1.23 V is called overpotential, and represents any kind of loss and nonideality in the electrochemical process.
Electrocatalysts can facilitate this reaction.