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

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 *NO3. However, the formation of active hydrogen (*H) on Cu surface is difficult and insufficient, leading to the significant generation of by‐product NO2‐. 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 (FENH3: 70.4%, FENO2‐: 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 H2O dissociation to active hydrogen. The optimized hydrogen affinity validly decreases the hydrogenation kinetic energy barrier of *NO2, leading to an enhanced NH3 selectivity.