Reactive hydrogen species behaviors on Cu-doped Co3O4 nanoneedles enhance nitrate electroreduction at high current density

The electrochemical conversion of nitrate, commonly found in industrial effluents and contaminated groundwater, into ammonia offers a sustainable strategy for both wastewater remediation and ammonia production. However, most existing catalysts exhibit limited activity and stability, particularly under industrial-level current density. Here we present a straightforward hydrothermal–calcination method to in situ fabricate Cu-doped Co3O4 nanoneedle arrays on three-dimensional porous copper foam (Cu-Co3O4/CF). The resulting electrode delivers an industrial-scale current density of ~ 1000 mA cm−2, a high NH3 yield rate of 58.4 mg h−1 cm−2, and a Faradaic efficiency of 98.3% at −0.5 V versus RHE. The outstanding performance under high current density highlights the significant practical potential of Cu-Co3O4/CF for large-scale applications. Density functional theory (DFT) calculations combined with experimental analysis demonstrate that Cu incorporation optimizes NO3− adsorption energy. More importantly, the doping of Cu accelerates the kinetics of the Volmer step (H2O → *H + *OH), which provides protons for the hydrogenation pathway. This promotes the selective formation of NH3 during the electrochemical nitrate reduction reaction (NO3RR). Overall, this work provides fundamental insights into designing efficient transition metal oxide catalysts for nitrate valorization.