Nitrogen-Doped Cobalt Phosphide for Enhanced Hydrogen Evolution Activity

Development of highly efficient and durable hydrogen evolution reaction (HER) electrocatalysts has a direct impact on water splitting efficiency and cost-effectiveness. In this work, N-doped CoP₂ is successfully synthesized for efficient HER in an alkaline electrolyte, which needs an overpotential of only 64 mV to drive a current density of 10 mA cm^-2, with a small Tafel slope of 47.4 mV dec^-1 and excellent stability for 15 h without any performance loss in 1 M KOH. This represents one of the best HER catalysts in the alkaline electrolyte so far. The successful doping of N into CoP₂ is confirmed using X-ray photoelectron spectroscopy, X-ray absorption near-edge structure, and scanning transmission electron microscopy characterizations. It is revealed by first-principle calculations that the partial replacement of P with N not only facilitates electron transfer but also optimizes the Gibbs free energies of H*, H₂O, and OH* adsorption on the P active sites, thus facilitating the HER process. This work highlights that anion modification of transition-metal phosphides would be an effective and feasible method to enhance their HER activities and provide new insights for the design of novel HER electrocatalysts.