Unveiling Ionized Interfacial Water-Induced Localized H* Enrichment for Electrocatalytic Nitrate Reduction

Electrocatalytic nitrate reduction reaction (NO₃RR) is a process that requires the participation of eight electrons and nine protons. The regulation of active hydrogen (H*) supply and a deep understanding of related processes are necessary for improving the ammonia yield rate and Faradaic efficiency (FE). Herein, we synthesized a series of atomically precise copper-halide clusters Cu₂X₂(BINAP)₂ (X=Cl, Br, I), among which the Cu₂Cl₂(BINAP)₂ cluster shows the optimal ammonia FE of 94.0 % and an ammonia yield rate of 373 μmol h^-1 cm^-2. In situ experiments and theoretical calculations reveal that halogen atoms, especially Cl in Cu₂Cl₂(BIANP)₂, can significantly affect the distance of alkali metal-ionized water on the catalyst surface, which can promote the water dissociation to enhance the localized H* enrichment for the continues hydrogenation of nitrate to ammonia. This work explains the role of H* in the hydrogenation process of NO₃RR and the importance of localized H* enrichment strategy for improving the FEs.