Oxygen Vacancy Modulation in CuCo ₂ O ₄ : Structural Reconstruction-Driven Kinetic Equilibrium for Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction reaction (NO 3 RR) has shown great potential in ecofriendly ammonia synthesis. However, the multiple electron and proton transfers in the NO 3 RR present a fundamental barrier to precise reaction control, thus leading to low Faradaic efficiency (FE) and limited ammonia (NH 3 ) selectivity. In this work, we addressed the above challenge of the NO 3 RR by achieving kinetic equilibrium through a synergistic strategy, where oxygen vacancy (O V ) tuning promotes the deoxygenation step and structural reconstruction facilitates the hydrogenation steps. To investigate the intrinsic structure–performance relationship of the NO 3 RR, we systematically probed the reconstruction of CuCo 2 O 4 with gradient O V levels. Scanning electron microscopy (SEM) and in situ Raman spectroscopy indicated that CuCo 2 O 4 with different O V levels all transformed into a Co(OH) 2 /CuCo 2 O x heterostructure. Further mechanism studies, involving dynamic analysis and density functional theory (DFT) calculations, mutually confirmed that O V facilitated adsorption of NO 3 –, and Co(OH) 2 (generated via structural reconstruction) enabled an efficient supply of active hydrogen (*H). The dual factors synergistically modulated the deoxygenation process (NO 3 – to NO 2 – ) along with sequential hydrogenation (NO 2 – to NH 3 ) steps in NO 3 RR. This work provides a new method for designing high-performance dynamic electrocatalysts capable of kinetic equilibrium, thereby attaining superior NH 3 FE of 96.2% at −0.3 V vs reversible hydrogen electrode (RHE).