Enhanced Selective Electroreduction of Nitrate to N ₂ on N‐CuO/NF Catalysts via Chloride‐Mediated Synergistic Oxidation

The practical deployment of the electrochemical nitrate reduction reaction (eNO ₃ RR) for wastewater remediation is primarily hindered by the difficulty of achieving high N ₂ selectivity due to the complex multi‐electron transfer pathways and the formation of competing by‐products. Herein, we develop an N‐doped CuO catalyst supported on nickel foam (N‐CuO/NF) through a facile molten‐salt route followed by controlled annealing. The optimized catalyst exhibits enhanced kinetics for eNO ₃ RR, reduced charge‐transfer resistance, and an increased electrochemically active surface area. Remarkably, Cl ⁻ incorporation into the electrolyte establishes a synergistic interaction between Cl ⁻ ‐mediated anodic oxidation and the coexisting Cu ⁰ /Cu ²⁺ sites on the optimal N‐CuO/NF‐3h. This synergy enables simultaneous achievement of high nitrate‐removal efficiency (>90%) and high N ₂ selectivity (~90%) in an undivided cell. Mechanistic investigations indicate that anodically generated hypochlorous acid (HOCl) oxidizes cathodically produced NH ₄ ⁺ to N ₂ , effectively suppressing ammonia accumulation. Moreover, N‐CuO/NF‐3h demonstrates outstanding cycling stability over four consecutive cycles, with minimal activity loss (<8%) and maintained structural integrity. This work underscores the dual role of N‐doping in modulating the electronic structure of CuO and the pivotal role of Cl ⁻ in steering the reaction pathway toward N ₂ formation. The findings offer a practical strategy for selective nitrate‐to‐N ₂ conversion in wastewater treatment.