Boosting Electrochemical Ammonia Synthesis via NOx Reduction over Sulfur‐Doped Copper Oxide Nanoneedle Arrays

Abstract The electrochemical NO x reduction reactions, involving nitrate and nitrite reduction reactions (NO 3 − RR and NO 2 − RR), have emerged as promising approaches for both NO 3 − and NO 2 − removal, and ammonium (NH 3 ) synthesis under ambient conditions. However, the incorporation and stabilization of sulfur dopants in the catalysts for efficient NO x reduction are rarely explored, leading to an unclear effect of sulfur on the NO x reduction mechanism. Herein, sulfur‐doped Cu 2 O (S‐Cu 2 O) nanoneedle arrays via in situ electrochemical treatment are synthesized. The S‐Cu 2 O catalyst possesses excellent durability and selectivity for NH 3 over a wide range of potentials in NO 3 − RR, attaining a maximum NH 3 Faradaic efficiency of 94% at −0.6 V RHE and a maximum NH 3 yield as high as 1.06 mmol h −1 cm −2 . In NO 3 − RR, the sulfur dopant can accelerate the step from NO 2 − to NH 3 , contributing superior performance in NO 2 − RR and assembled Zn−NO 2 − battery device. Density functional theory (DFT) calculations reveal that the presence of sulfur can enhance the initial step of *NO 3 adsorption, lower the reaction barriers for the formation of *NHO intermediate, and activate the H 2 O dissociation process. The work sheds light on the role of sulfur in enhancing electrocatalytic performance and provides a unique perspective for understanding the NO x reduction mechanism.