Sulphur‐Boosted Active Hydrogen on Copper for Enhanced Electrocatalytic Nitrate‐to‐Ammonia Selectivity

Abstract Electrocatalytic nitrate reduction to ammonia is a promising approach in term of pollutant appreciation. Cu‐based catalysts performs a leading‐edge advantage for nitrate reduction due to its favorable adsorption with *NO 3 . However, the formation of active hydrogen (*H) on Cu surface is difficult and insufficient, leading to the significant generation of by‐product NO 2 − . Herein, sulphur doped Cu (Cu−S) is prepared via an electrochemical conversion strategy and used for nitrate electroreduction. The high Faradaic efficiency (FE) of ammonia (~98.3 %) and an extremely low FE of nitrite (~1.4 %) are achieved on Cu−S, obviously superior to its counterpart of Cu (FE NH3 : 70.4 %, FE NO2 − : 18.8 %). Electrochemical in situ characterizations and theoretical calculations indicate that a small amount of S doping on Cu surface can promote the kinetics of H 2 O dissociation to active hydrogen. The optimized hydrogen affinity validly decreases the hydrogenation kinetic energy barrier of *NO 2 , leading to an enhanced NH 3 selectivity.