A First-Principles Study of Surface-Dependent Synergy between H2O and O2 on Silver-Based Oxide Semiconductors

Abstract

Silver-based ternary oxides, including Ag3PO4, β-Ag2MoO4, and the α- and γ-Ag2WO4 polymorphs, are promising photocatalysts for generating reactive oxygen species (ROS). In this work, density functional theory calculations were employed to disclose the atomic site-specific electronic properties governing the activation of coadsorbed O2 and H2O molecules, a key step in ROS formation, at these semiconductor surfaces. We found that O2 activation, as characterized by O–O bond weakening, is enhanced by H2O coadsorption on Ag3PO4(110), β-Ag2MoO4(110), and α-Ag2WO4(100), whereas the opposite trend is observed on β-Ag2MoO4(111) and α-Ag2WO4(001). Electronic structure analyses corroborate this surface-dependent behavior. These results reconcile contrasting views on the role of H2O by demonstrating its critical dependence on surface structure and intrinsic reactivity, providing crucial insights for the rational design and optimization of Ag-based semiconductor photocatalysts through controlled surface exposure or humidity management.