Construction of bimetallic CoCu@BC for sustainable ammonia synthesis with minimal nitrite accumulation

Abstract

The electrochemical nitrate (NO₃⁻) reduction reaction (NO₃RR) is hindered by nitrite (NO₂⁻) accumulation and the competing hydrogen evolution reaction, limiting the faradaic efficiency (FE) and selectivity of ammonia (NH₃) production. Herein, we report a cobalt–copper catalyst supported on biomass carbon (CoCu@BC) that achieves a high NH₃ FE of 97.15% with an NH₃ yield of 367.33 μmol h⁻¹ mg_cat⁻¹, while maintaining an NO₂⁻ FE of only 0.26% and NO₂⁻ concentrations below 10 μg mL⁻¹. In situ Fourier transform infrared spectroscopy confirms the presence of *NH₂ and the absence of NO₂⁻ on the catalyst surface, indicating enhanced hydrogenation toward NH₃ formation. In situ X-ray absorption fine structure analysis further demonstrates the structural stability of CoCu@BC during the reaction, supporting its sustained performance over 120 hours. Density functional theory calculations reveal that the heterogeneous Co–Cu interface optimizes the reaction energy barrier for *NO₃ to *NO₂ conversion, facilitating rapid reaction kinetics and enabling highly efficient and selective NH₃ synthesis.