Alkaline water electrolysis is the oldest way of making hydrogen from water & electricity. It passes current through a strong potassium hydroxide solution, producing hydrogen at one electrode & oxygen at the other. It uses cheap nickel & steel rather than rare metals, so it is the lowest-cost electrolysis technology. It is slightly less efficient & slower to respond to changing power than membrane systems, & its raw hydrogen needs purifying for fuel cells. Major suppliers include thyssenkrupp nucera, Nel, John Cockerill & fast-growing Chinese manufacturers.