Synergistic effect of Co and Co₆Mo₆C for electroreduction of nitrate to ammonia on Co-MOF derived Co₆Mo₆C/Co/NC

Electrocatalytic nitrate reduction reaction (e-NO₃RR) offers a promising alternative method for nitrogen cycling and ammonia (NH₃) production under ambient conditions. However, the method is still in the dilemma of lowering the reaction overpotential and increasing the reaction activity. We successfully developed the composition-adjustable Co₆Mo₆C/Co/N-doped carbon (NC) catalysts by in situ carbonization of Co-based metal-organic framework (MOF) with the constrained phosphomolybdic acid. After adjusting the ratio of Co⁰ and Co₆Mo₆C, Co₆Mo₆C/Co/NC-3 could satisfy both NO₃⁻ conversion at low potential and NH_x hydrogenation, and synthesize ammonia efficiently through the synergistic effect of Co⁰ and Co₆Mo₆C. It achieved an ammonia yield rate as 1233.2 µg·h⁻¹·mg_cat⁻¹ and Faradaic efficiency of NH₄⁺ 93.6% at −0.33 V vs. reversible hydrogen electrode (RHE). Importantly, density functional theory (DFT) calculations and experimental results have demonstrated for the first time the excellent adsorption of nitrite (NO₂⁻) by the Mo sites of Co₆Mo₆C during e-NO₃RR, avoiding the undesirable accumulation of NO₂⁻.