Ultrastable electrocatalytic seawater splitting at ampere-level current density

Hydrogen has long been seen as a key energy vector for a carbon-neutral and sustainable future. A promising pathway to mass production of hydrogen is electrolysis of seawater—an unlimited water source—using renewable energy. However, because of the complex ion environment, direct electrolytic splitting of seawater faces major challenges, notably chlorine evolution, corrosion of electrodes and other side reactions. Here we report an earth-abundant layered double hydroxide electrocatalyst that sustains stable electrolysis of seawater over 2,800 h under an ultra-high current density of ∼1.25 A cm−2. Introduction of carbonate ions into its interlayers and surface anchoring of graphene quantum dots block unfavourable adsorption of chloride ions and contribute to increased resistance of the electrocatalyst to chloride ion corrosion. A photovoltaic-electrolysis device with the electrocatalyst as both an oxygen and a hydrogen evolution catalyst delivers a record solar-to-hydrogen efficiency of 18.1% for overall seawater splitting, along with good stability over 200 h under a high working current over 440 mA. Our work is a substantial step forwards in producing green hydrogen and achieving a sustainable energy future.