Interfacial Hydrogen-Bond Networks at Bi–H2O Interfaces Govern Hydroxylamine Selectivity in Nitrate Electroreduction

Abstract

Metal–H2O interfaces strongly influence electrocatalytic selectivity. However, how interfacial H2O mediates coupled interactions among catalyst surfaces, electrolytes, and intermediates remains unresolved. Here, by combining theory and experiment on Bi–H2O interfaces, we show that pH-dependent reconstruction of the interfacial hydrogen-bond network governs hydroxylamine (NH2OH) selectivity during nitrate electroreduction. Under acidic conditions, a strengthened hydrogen-bond network induced by fully hydrogen-bonded H2O shortens proton-transfer distances and interfacial charge redistribution and promotes protonation of adsorbed NOx species while weakening *NH2OH binding, thereby favoring NH2OH formation and desorption. Under neutral conditions, the weaker hydrogen-bond network from partially hydrogen-bonded H2O suppresses *NO stabilization and protonation, enabling NO release, whereas electron transfer from interfacial H2O to Bi strengthens *NH2OH adsorption and drives its further reduction to NH3. These findings identify interfacial hydrogen-bond networks as key regulators of product selectivity at metal–H2O interfaces and provide a mechanistic basis for catalyst design for selective NH2OH electrosynthesis.