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 (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 H₂O dissociation to active hydrogen. The optimized hydrogen affinity validly decreases the hydrogenation kinetic energy barrier of *NO₂, leading to an enhanced NH₃ selectivity.