Electrodeposition of oxyanion films as universal chloride ion-repelling layers for efficient and stable seawater oxidation at ampere-level current density

Abstract

Seawater splitting is an environmentally friendly pathway for hydrogen production, helping to resolve the conflict between the growing hydrogen energy demand and freshwater scarcity. However, abundant chloride ions in seawater cause the chlorine oxidation reaction (ClOR), leading to severe anode corrosion and increased energy consumption. We developed an oxyanion film electrodeposition strategy to form a universal Cl⁻-repelling layer on electrocatalyst surfaces, allowing efficient and stable seawater oxidation at high current densities. Among several oxyanion films (sulfate, phosphate and carbonate), the Ni–Co layered double hydroxide catalyst with sulfate modification (NiCo-LDH@Sulfate) demonstrated the best seawater oxidation activity and stability (1 A cm⁻² with 381 mV overpotential; stable activity at 600 mA cm⁻² for 330 hours). In-depth explorations indicate that the high electrostatic potential generated by the oxyanion films can effectively repel Cl⁻ and inhibit the ClOR. The oxyanion films can also improve oxygen evolution reaction (OER) activity by accelerating the generation of the OER active centers and changing the coordination intensity between the catalytic centers and the OER intermediates. Impressively, this strategy enables ultrafast formation of a protective layer within 5 min and can be applied to a wide range of OER array electrodes, thus providing groundbreaking guidance for the industrialization of seawater splitting.