Background: Thermodynamically a specific voltage is required to split water into hydrogen and oxygen. In practice the actual potential required to oxidize water is greater than the thermodynamic potential. The additional energy requirement or overpotential is dependent on the catalyst used and the electrode materials used in the reaction chamber.

Hydrogen is being developed as an electrical energy storage medium. Hydrogen is produced, then compressed or liquefied, stored, and then converted back to electrical energy or heat or used as an input to (industrial) processes. Hydrogen can be used as a fuel for portable (vehicles) or stationary energy generation. Compared to pumped water storage, CAES and batteries, hydrogen has the advantage that it is a high energy density fuel that can be fed into the grid, stored or converted in ammonia and then stored. Hydrogen can be directly converted to electrical energy using an electrolyser.