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

To solve the severe accumulation of nitrite during nitrate reduction on Cu, S-doped Cu nanorod arrays (Cu−S NAs) were designed via an electrochemical conversion strategy. The high FE of ammonia (98.3 %) and an extremely low FE of nitrite (1.4 %) can be achieved on Cu−S NAs. The introduction of S can significantly decrease the energy barrier of H₂O dissociation to *H, leading to a favorable hydrogenation of *NO₂ and enhanced 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 *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.

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