Understanding the Selectivity Differences of NO Electroreduction on Ag and Au Electrodes

Although noble metals Ag and Au have similar chemical reactivities, their catalytic selectivity for NO electroreduction is significantly different. Namely, hydroxylamine is often considerably produced on Ag while not observed on the Au electrode. In this study, first-principles calculations and the electric field controlling constant potential (EFC-CP) method are adopted to unveil the underlying reasons. We first reveal a distinct NO* adsorption configuration, vertical on Ag and inclined on Au, leading to different reduction pathways to NOH* and HNO*, respectively. Via complete electrochemical barrier calculations and detailed kinetic analysis, we find the hydroxylamine selectivity difference between Ag and Au is mainly induced by adsorption strength of NH₂OH*. On Ag, the obtained NH₂OH* prefers to desorb and produce hydroxylamine, while NH₂OH* is bonded strongly to Au and favors further reduction to ammonia. The study advances our understanding of factors regulating product selectivity, providing crucial insights for designing NO electroreduction catalysts toward hydroxylamine production.