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).
Yuan et al. (Tue,) studied this question.