Engineering bimetallic CuAu to suppress hydrogen evolution and enhance charge transfer for improved photoelectrochemical nitrogen reduction

Green ammonia synthesis from nitrogen via photocatalysis and electrocatalysis has emerged as a pivotal research focus in sustainable chemical processes. The efficient catalytic reduction of nitrogen necessitates concurrent nitrogen activation and hydrogen evolution suppression, representing a significant challenge. In this study, CuAu bimetallic-modified TiO₂ catalysts were developed and engineered to address these issues. By combining structural characterization, ultrafast photophysical studies, and DFT calculations, we demonstrate that adding Cu alters the work function of the metals and, consequently, the Schottky barrier towards TiO₂, which influences the photo-induced charge separation efficiency. Furthermore, Cu-Au binary active sites exhibit a stronger affinity for N atoms, elongating the surface-adsorbed N-N bonds and facilitating bond cleavage. These two phenomena promote the nitrogen activation process. Conversely, the addition of copper reduces the coupling of the H 1 s electron, thereby inhibiting the proton adsorption electron transfer of the *H species. The optimal alloy configuration of Cu₍₅₎Au₍₅₎ was found to balance the trade-off between nitrogen activation and hydrogen evolution suppression with maximum catalytic activity. This study reveals the combined effect of a bimetal alloy on charge transfer, nitrogen adsorption activation, and hydrogen evolution, offering insights into the enhancement of nitrogen-to-ammonia conversion.