In-situ reconstructed Cu/Cu₂O heterogeneous nanorods with oxygen vacancies for enhanced electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia (ENRA) is crucial for environmental pollution treatment and sustainable energy development, but the complicated reduction mechanism of ENRA leads to limited ammonia selectivity and low Faradaic efficiency. In this work, Cu/Cu₂O heterogeneous nanorods with oxygen vacancies were successfully obtained by creating Cu sites via the in-situ reconstruction of Cu₂O nanorods. These oxygen vacancies can weaken the N-O bond. The Cu sites and heterogeneous interfaces were investigated using X-ray photoelectron spectroscopy Auger spectra and transmission electron microscopy. The active species trapping experiments and density functional theory (DFT) calculations demonstrated that the Cu sites promoted the reduction of NO₃^- to NO₂^- due to their strong adsorption of NO₃^-, and the sufficient atomic hydrogen originating from Cu₂O facilitated the formation of a *NOH intermediate. In addition, abundant heterogeneous interfaces facilitated the reduction of N-containing intermediates by atomic hydrogen, leading to a high Faradaic efficiency of 84.93 % and ammonia yield of 4.58 mg/h/cm² in neutral solution. Our findings will diversify the methodologies for constructing Cu/Cu₂O electrocatalysts and provide new insight into the mechanism of ammonia synthesis from nitrate reduction.