Electrolysis

When two electrodes are placed in water with a voltage difference between them, an electric field is created in the water. Hydrogen ions are attracted toward one electrode, while OH⁻ ions are drawn toward the other. At the electrode where H⁺ ions accumulate (the cathode, which has a negative voltage), an excess of electrons allows the H⁺ ions to combine with electrons, forming hydrogen molecules. At the other electrode, where OH⁻ ions accumulate (the anode, with a positive voltage), the electrons are transferred to the electrode, allowing the formation of water molecules and the release of oxygen molecules. This process is sustained as more water molecules (H₂O) dissociate into H⁺ and OH⁻ ions, maintaining the cycle. Without the applied voltage, the dissociation and recombination of H⁺ and OH⁻ ions continue naturally, but at equilibrium, with no net production of gases. The electrolysis of one mole of water yields one mole of hydrogen gas and half a mole of oxygen gas, both in their diatomic forms. Water electrolysis is commonly used to generate oxygen, such as on the International Space Station. The hydrogen produced can also be stored and later used in a fuel cell to generate both energy and water.