Proton exchange membrane (PEM) hydrogen electrolysis is a technology used for splitting water molecules into hydrogen and oxygen by using electricity. The origins of the development of PEM electrolyzers lie in the 1950s space race, but not to provide hydrogen. Rather, PEM was a solution for providing a dependable supply of oxygen for astronauts in manned space flight. PEM contains anode and cathode electrodes that are separated by a solid ion conductive solid polymeric membrane. This solid polymeric membrane will only allow positive ions to pass through, hence the term proton (H+) exchange membrane.