Water electrolysis produces hydrogen and oxygen using electricity. The hydrogen and oxygen evolution reactions are typically coupled in time and space, occurring simultaneously in electrolytic cells divided by membranes into cathodic and anodic compartments. This division increases the electrolyzers cost and limits their lifetime, efficiency and ability to use intermittent electricity from solar and wind power plants. To address these limitations, we develop novel electrochemical and chemical cycles that decouple the hydrogen and oxygen evolution reactions in time and/or place. First, we used nickel (oxy)hydroxide electrodes to mediate the hydroxide ion exchange between the cathode and anode that generate hydrogen and oxygen in separate cells, enabling safe operation without membranes. Next, we developed an electrochemical – chemical cycle that use nickel (oxy)hydroxide electrodes to generate hydrogen and oxygen in different stages with separate electrolyte flows. Nowadays, we use bromide/bromate ions to store oxygen in one cell and release it in another cell, enabling continuous operation without membranes. These processes provide disruptive opportunities (as well as new challenges) to reshape century-old water electrolysis to fit for green hydrogen production using renewable electricity.
