Synergistic interaction of phosphorus vacancies and cobalt species in cobalt phosphide to enhance electrocatalytic nitrate reduction

Electrocatalytic nitrate reduction (e-NO₃RR) offers a sustainable approach for ammonia synthesis and water purification. Transition metal phosphides (TMP) provide active hydrogen (*H), but are influenced by competitive hydrogen evolution reactions (HER). Meanwhile, vacancy engineering of electrocatalysts accelerates the kinetic process of reaction by modulating the electronic structure of the catalyst and lowering the energy barriers of the reaction. In this work, we constructed a phosphorus-vacancy-rich Co_xP/Co-V_p/NF catalyst through KBH₄ etching, which achieved a Faraday efficiency (FE) exceeding 90 % and an ammonia yield rate of 6190.94 μg h⁻¹ cm⁻². The catalyst demonstrated 80.07 % NO₃⁻ conversion over 13 h with 78.65 % NH₄⁺ selectivity. In situ spectroscopy and Density Functional Theory (DFT) calculations reveal that Co_xP, V_p and Co⁰ three-phase synergistically optimize *H utilization: Co^δ+ in Co_xP facilitates the adsorption of NO₃⁻, enriching the reactants, while P^δ− adsorbs a certain amount of *H and stabilizes intermediate electron transfer. Simultaneously, Co⁰ spontaneously reduces NO₃⁻ to NO₂⁻ while suppressing HER. V_p enhances hydrogen adsorption and the hydrogenation of intermediates through charge redistribution, collectively optimizing the production of NH₃.The present work provides new ideas and strategies for e-NO₃RR ammonia production.