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Electrocatalytic nitrate reduction reaction (NO 3 RR) to harmless nitrogen (N 2 ) presents a viable approach for purifying NO 3 – -contaminated wastewater, yet most current electrocatalysts predominantly produce ammonium/ammonia (NH 4 + /NH 3 ) due to challenges in facilitating N–N coupling. This study focuses on identifying metal catalysts that preferentially generate N 2 and elucidating the mechanistic origins of their high selectivity. Our evaluation of 16 commercially available metals reveals that only Pb, Sn, and In demonstrated substantial N 2 selectivity (79.3, 70.0, and 57.0%, respectively, under conditions of 6 h electrolysis, a current density of 10 mA/cm 2, and an initial NO 3 – -N concentration of 100 mg/L), while others largely favored NH 4 + production. Comprehensive experimental and theoretical analyses indicate that NH 4 + -selective catalysts (e.g., Co) exhibited high water activity that enhances • H coverage, thereby promoting the hydrogenation of NO 3 – to NH 4 + through the hydrogen atom transfer mechanism. In contrast, N 2 -selective catalysts, with their lower water activity, promoted the formation of N-containing intermediates, which likely undergo dimerization to form N 2 via the proton-coupled electron transfer mechanism. Enhancing NO 3 – adsorption was beneficial to improve N 2 selectivity by competitively reducing • H coverage. Our findings highlight the crucial role of water activity in NO 3 RR performance and offer a rational design of electrocatalysts with enhanced N 2 selectivity.
Duan et al. (Mon,) studied this question.