Enhanced electrochemical nitrate reduction on copper nitride with moderate intermediates adsorption

Nitrate in surface and underground water caused systematic risk to the ecological environment. The electrochemically reduction of nitrate into ammonia (NO₃RR), offering a sustainable route for nitrate containing wastewater treatment and ammonia fertilizer conversion. Exploration of catalyst with improved catalytic activity with lower energy barriers is still challenging. Here, we report a copper nitride (Cu₃N) catalyst with moderate *NO_x and *H₂O intermediates adsorptions showed enhanced NO₃RR performance. Density functional theory calculations reveals that the unique electronic structure of Cu₃N provides efficient active sites for NO₃RR, thus enabled balanced adsorption of *NO₃ and *H₂O (ΔE descriptor), sufficient active hydrogen, and moderate intermediate (*NO₃ → HNO₃, *NH₂→*NH₃) adsorption energy. Notably, the in-situ analysis technology revealed potential-driven reconstruction and rehabilitation of Cu₃N, forming possible nitrogen vacancy, thus implied for better mechanism understanding. The NO₃RR activity of Cu₃N surpasses that of most recent catalysts and demonstrates superior stability and implies the application for NH₄⁺ fertilizer recovery, which maintaining an NH₃ Faradaic efficiency of 93.1 % and high yield rate of 2.9 mg cm²h^-1 at -0.6 V versus RHE. These findings broaden the application scenarios of Cu₃N catalyst for ammonia synthesis and provide strategy on improving NO₃RR performance.