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

Electrochemical nitrate reduction reaction (NO 3 – 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–Co 3 O 4 ) catalyst was shown to enhance ammonia production during NO 3 – RR in an alkaline electrolyte. Specifically, the Ag–Co 3 O 4 catalyst delivers an ammonia (NH 3 ) 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 Co 3 O 4 catalyst (8.8 μmol h –1 cm –2 ). The catalytic activity and selectivity of Ag–Co 3 O 4 originate from the interaction between atomically dispersed Ag and Co 3 O 4, resulting in the formation of active octahedral Co 2+ species (Co 2+ Oh ) with an unpaired e g electron, which facilitates the activation and adsorption of NO 3 – ion and promotes the *NO 2 adsorption, along with its transformation to *NO intermediate. This leads to efficient NH 4 + production, as evidenced by combined experimental and theoretical studies.