Electrocatalytic nitrate reduction is an effective strategy to eliminate nitrate's environmental impact and produce high-value-added ammonia products. However, most of the current reports focus on preparation strategies of catalysts, with poor exploration of the mechanism. In this work, we fabricated a binding-free Cu-doped Co3O4 electrode (Cu-Co3O4) to reveal the structure-activity relationship. Cu-Co3O4 exhibited a maximum Faradaic efficiency of ammonia of up to 86.5% at -0.6 V vs reversible hydrogen electrode in a neutral electrolyte, with the corresponding yield rate of 36.71 mmol h-1 g-1. In situ electrochemical Raman spectroscopy confirmed that the structure of Cu-Co3O4 exhibits excellent stability and durability. Theoretical analysis revealed that the interaction between Cu and Co induces the d-band center position of the mono-metal oxide to shift toward the center to optimize the nitrate reduction intermediate hydrodeoxygenation free-energy change, especially of *NOx (x = 1, 2, and 3). These results offer guidelines for the electrochemical reduction of nitrate with transition metal oxide electrocatalysts.
Keywords: Co3O4; ammonia; d-band center; electrochemical reduction nitrate; intermediate.