Interfacial engineering of 2D Nb₂C MXene/copper electrode for selective electrochemical nitrate-to-nitrogen conversion

Background Electrochemical nitrate reduction is a promising approach for mitigating nitrogen pollution in water. However, the development of electrocatalysts that simultaneously achieve high activity, N₂ selectivity, and operational stability remains a major challenge. Methods A two-dimensional (2D) Nb₂C MXene-modified copper mesh electrode (Nb₂C/Cu) was fabricated via a simple coating method. The morphology, structure, and surface properties of the composite were characterized using FESEM-EDS, HR-TEM, XRD, BET, and XPS, whereas LSV and EIS were employed to probe its electrochemical characteristics. The electrochemical nitrate reduction performance was systematically evaluated in a dual-chamber electrolytic cell under various operating conditions. Significant findings The optimized Nb₂C/Cu electrode achieved 93 % nitrate conversion, 92 % N₂ selectivity, a Faradaic efficiency of 81.35 %, and a low energy consumption of 0.067 kWh/g-N. The electrode maintained good performance over five consecutive reuse cycles while suppressing the formation of NO₂⁻ and NH₄⁺ by-products. Electrochemical analyses revealed that the Nb₂C/Cu interface enhances electron transfer and reduces charge-transfer resistance, thereby suppressing the competing hydrogen evolution reaction and promoting selective nitrate-to-nitrogen conversion.