The beauty of Solid Oxide Fuel Cells is that the stack is fully reversible: the same stack that is used to convert hydrogen and oxygen into electricity and water vapour, can be used to split water into hydrogen and oxygen using electricity. In a SOE, water vapour is fed to the cathode side where, thanks to the electricity input (more precisely, to the external voltage applied), it is split into hydrogen and oxygen ions. The oxygen ions can move through the membrane and reach the anode where they form oxygen and release the electrons that can travel through the external electrician circuit connecting anode and cathode.