Unveiling the In Situ Dissolution and Reconstruction of CoMo for Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction to ammonia (NRA) from low concentration sources is challenging due to the competing hydrogen evolution reaction. Cobalt-based catalysts have gained attention for NRA, yet their weak NO₃ ^- adsorption and limited hydrogenation of nitrogenous intermediates restrict their catalytic performance in low concentrations. Due to efficient adsorption of nitrate ions by Mo, CoMo catalysts can promote the NRA process in low-concentration nitrates. Meanwhile, various oxidation states of Mo^δ+ can promote the cracking of water molecules to provide more abundant active hydrogen. Here, a reconstructed Mo-doped β-Co(OH)₂/Co₈₅Mo₁₅ (R-Co₈₅Mo₁₅) catalyst is successfully designed and synthesized through electrochemical activation, where reconstructed OH^- species facilitate the induction of multiple Mo^δ+ oxidation states. The Mo, Co, and Mo-doped β-Co(OH)₂ distinct roles are identified by in situ spectroscopic and theoretical studies in the NRA pathway, wherein the Mo facilitates NO₃ ^- adsorption, Co accelerates ^*NO₃ to ^*NO₂ conversion, and Mo-doped β-Co(OH)₂ generates active hydrogen to promote hydrogenation of ^*NO₂ to NH₃. As a result, the R-Co₈₅Mo₁₅ catalyst exhibits excellent performance in reducing 10 mm NO₃ ^-, with a Faradaic efficiency of ≈96.01% (-0.1 V vs RHE), 95% NH₃ selectivity, and maintains exceptional stability for 1000 h at 660 mA cm^-2. Making it a promising candidate for viable electrochemical nitrate production.