Surface Engineering on Ag-Decorated Co3O4 Electrocatalysts for Boosting Nitrate Reduction to Ammonia

Electrochemical nitrate reduction reaction (NO3-RR) offers an alternative pathway toward ambient ammonia production and nitrogen balance restoration, requiring efficient catalysts. In this study, a silver-decorated cobalt oxide (Ag-Co3O4) catalyst was shown to enhance ammonia production during NO3-RR in an alkaline electrolyte. Specifically, the Ag-Co3O4 catalyst delivers an ammonia (NH3) yield rate of 52 μmol h-1 cm-2 with a Faradaic efficiency of 88% at −0.32 V versus RHE. The activity is 6 times higher than that of the conventional Co3O4 catalyst (8.8 μmol h-1 cm-2). The catalytic activity and selectivity of Ag-Co3O4 originate from the interaction between atomically dispersed Ag and Co3O4, resulting in the formation of active octahedral Co2+ species (Co2+Oh) with an unpaired eg electron, which facilitates the activation and adsorption of NO3- ion and promotes the *NO2 adsorption, along with its transformation to *NO intermediate. This leads to efficient NH4+ production, as evidenced by combined experimental and theoretical studies.