Co-Cu dual active sites for synergistic electrochemical nitrate reduction to ammonia

Electrochemical nitrate (NO₃^-) reduction to ammonia (NRA) is a promising strategy for converting harmful NO₃^- into valuable ammonia. Herein, the energy barrier of NRA is dropped dramatically from 21-38 kWh kg^-1 for direct eight-electron reduction to 0.23 kWh kg^-1 using a dual-site Co₃O₄/Cu₂O catalyst. An impressive Faradaic efficiency of 99.17 %, NH₄⁺ yield rate of 0.87 mmol h^-1 cm^-2, and NO₃^- removal of 97 % are achieved at -0.3 V; these results are considerably better than those observed for Cu₂O sites and Co₃O₄ sites and surpasses those yielded by reported nonprecious metal electrocatalytic systems. Theoretical calculations indicate that the strong interaction between NO₃^- and the Co₃O₄/Cu₂O catalyst is crucial toward NO₃^- reduction. This interaction increases the number of available adsorption sites for NO₃^-, accelerates the reduction of adsorption-state NO₂^- (NO₂*) to NO* , and facilitates the selective transformation of NO* to NOH* . The synergistic interaction between Co₃O₄ and Cu₂O enhances the adsorption of reaction intermediates, enabling an efficient and stable electrochemical reaction.