Insights into Electrochemical Nitrate Reduction to Nitrogen on Metal Catalysts for Wastewater Treatment
Weijian Duan, Ying Li, Yangjie Ou, Haorui Tuo, Tian Li, Yihui Zhu, Hengyi Fu, Wenxiao Zheng, Chunhua Feng
Abstract
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.