High-Performance Ammonium Cobalt Phosphate Nanosheet Electrocatalyst for Alkaline Saline Water Oxidation

The development of highly efficient electrocatalysts toward the oxygen evolution reaction is imperative for advancing water splitting technology to generate clean hydrogen energy. Herein, a two dimensional (2D) nanosheet ammonium cobalt phosphate hydrate (NH₄CoPO₄·H₂O) catalyst based on the earth-abundant non-noble metal is reported. When used for the challenging alkaline saline water electrolysis, the NH₄CoPO₄·H₂O catalyst with the optimal thickness of 30 nm achieves current densities of 10 and 100 mA cm^-2 at the record low overpotentials of 252 and 268 mV, respectively, while maintaining remarkable stability during the alkaline saline water oxidation at room temperature. X-ray absorption fine spectra reveal that the activation of Co (II) ions (in NH₄CoPO₄·H₂O) to Co (III) species constructs the electrocatalytic active sites. The 2D nanosheet morphology of NH₄CoPO₄·H₂O provides a larger active surface area and more surface-exposed active sites, which enable the nanosheet catalyst to facilitate the alkaline freshwater and simulated seawater oxidation with excellent activity. The facile and environmentally-benign H₂O-mediated synthesis route under mild condition makes NH₄CoPO₄·H₂O catalyst highly feasible for practical manufacturing. In comparison with noble metals, this novel electrocatalyst offers a cost-effective alternative for economic saline water oxidation to advance water electrolysis technology.