Modulating Lattice Strain and Electron Delocalization over Cu-Doped Co3O4 toward Efficient Nitrate Electroreduction

Abstract The direct electrocatalytic conversion of nitrate (NO3−) to ammonia (NH3) represents an effective strategy for wastewater remediation and nitrogen equilibrium regulation. Nevertheless, this reaction suffers from intrinsic limitations, particularly unfavorable adsorption of key reaction intermediates. Herein, we fabricate a Cu–Co3O4 catalyst with engineered Cu2+ electron delocalization and Co3O4 lattice distortion. Under optimized conditions, the catalyst exhibits an NH3 yield of 38.5 mg h−1 cm−2 and Faradaic efficiency (FE) reaching 99.4% in alkaline electrolytes. Experimental and theoretical investigations verify that Cu2+ substitute tetrahedrally coordinated Co sites in the Co3O4 lattice, triggering notable lattice distortion and electron density redistribution around Co and O centers. Such structural and electronic modulations further facilitate electron delocalization over Cu sites. The electron delocalization strengthens *NO3 adsorption, inhibits hydrogen evolution reaction, and decreases the activation barrier for *NO hydrogenation, thus accelerating the overall NO3− to NH3 conversion. Moreover, Zn–NO3− battery exhibits maximum power density (5.5 mW cm−2), with NH3 yield (1.93 mg h−1 cm−2) at 40 mA cm−2. This work provides a guiding design strategy for efficient spinel cobalt oxide catalysts for the synthesis of NH3 from NO3−.