Optimizing Oxidation State of Octahedral Copper for Boosting Electroreduction Nitrate to Ammonia

Electrocatalytic nitrate reduction reaction (NITRR) is a potential candidate for efficient ammonia (NH3) production under ambient conditions in the aqueous media, whereas the direct nine-proton and eight-electron transfer result in low Faraday efficiency and product selectivity. Here, we report that electrochemical NITRR produces NH3 catalyzed by surface oxygen-modified copper nanoparticles wrapped in layered graphitized carbon (Cu@C). The characterization results reveal that Cu@C-800 possesses an optimal oxidation state and exhibits the highest NH3 production Faradaic efficiency of 78 ± 0.9% and a corresponding rate of 51.7 ± 0.6 mmol h–1 g–1 at −0.9 V versus reversible hydrogen electrode. The incorporation of surface oxygen species endows to enhance the binding energy of *NO3 and reduce the energy barrier of *NO to *NOH, the potential rate-determining step. These findings offer a reference for designing efficient catalysts for NITRR to NH3 under ambient conditions.