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

Abstract

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.