Electron engineering of nickel phosphide for Ni^δ+ in electrochemical nitrate reduction to ammonia

The electrochemical reduction of nitrate to ammonia (ENRA) provides an efficient approach to remove nitrate pollution and achieve ammonia production simultaneously. Herein, inspired by bio-enzyme in denitrifying bacteria, a carbon-coated nickel phosphide (NiPC) nanosheet derived from metal-organic frameworks (MOFs) is proposed as an efficient catalyst for ENRA. Through electron engineering, controllable Ni^δ+ in nickel phosphide is achieved by regulating the degree of phosphating, which enhances its activity for the hydrogenation of nitrate. As the result, Ni^δ+ becomes one of dominating factors determining the efficiency of the ENRA reaction in nickel phosphide. The optimal NiPC catalyst exhibits impressive property toward ENRA: NH₄⁺ Faraday efficiency of 96.68%, NH₄⁺ selectivity of 99.04%, and nitrate conversion rate of 90.43% under low nitrate concentration (200 mg·L⁻¹). This work opens a new avenue for the design of next-generation catalysts through electron engineering for ENRA.