This process uses a cell with a cathode, an anode, and an electrolyte based in a solution of caustic salts. When voltage is applied, water decomposes in the alkaline solution. Hydrogen is formed at the cathode and oxygen at the anode. Between the two electrodes is a membrane that only allows negatively charged ions of oxygen and hydrogen (OH-) to pass through, which separates the gases.

PEMs, or proton exchange membranes, do not require a liquid electrolyte. Water is pressed through a stack of two electrodes and a polymer membrane, which only allows positively charged hydrogen protons to pass through. Platinum is usually used as a catalyst here. Though this process is more expensive than Alkaline, it responds faster to changes in the electrical current.

More expensive than Alkaline but responds faster to changes in electrical current.

Like alkaline electrolysis, anion exchange membranes, or AEMs, allow negatively charged ions (OH-) to pass through the membrane. A major advantage is that AEMs avoid the costly precious metals required as catalysts in PEM electrolysis.