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.