A hydrogen electrolyzer is a device that uses electrolysis to split water into hydrogen and oxygen gas. It consists of two electrodes, usually made of a non-reactive material such as graphite, separated by an electrolyte such as aqueous potassium hydroxide. An electrical current is passed through the electrodes, causing the water molecules to split into hydrogen and oxygen atoms. The hydrogen gas is collected at the cathode, while the oxygen gas is collected at the anode.