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

Electrocatalytic nitrate reduction reaction (NO₃RR) has shown great potential in ecofriendly ammonia synthesis. However, the multiple electron and proton transfers in the NO₃RR present a fundamental barrier to precise reaction control, thus leading to low Faradaic efficiency (FE) and limited ammonia (NH₃) selectivity. In this work, we addressed the above challenge of the NO₃RR by achieving kinetic equilibrium through a synergistic strategy, where oxygen vacancy (OV) tuning promotes the deoxygenation step and structural reconstruction facilitates the hydrogenation steps. To investigate the intrinsic structure-performance relationship of the NO₃RR, we systematically probed the reconstruction of CuCo₂O₄ with gradient OV levels. Scanning electron microscopy (SEM) and in situ Raman spectroscopy indicated that CuCo₂O₄ with different OV levels all transformed into a Co(OH)₂/CuCo₂Ox heterostructure. Further mechanism studies, involving dynamic analysis and density functional theory (DFT) calculations, mutually confirmed that OV facilitated adsorption of NO₃⁻, and Co(OH)₂ (generated via structural reconstruction) enabled an efficient supply of active hydrogen (*H). The dual factors synergistically modulated the deoxygenation process (NO₃⁻ to NO₂⁻) along with sequential hydrogenation (NO₂⁻ to NH₃) steps in NO₃RR. This work provides a new method for designing high-performance dynamic electrocatalysts capable of kinetic equilibrium, thereby attaining superior NH₃ FE of 96.2% at -0.3 V vs reversible hydrogen electrode (RHE).