AgWOS Bimetallic Oxysulfides With Synergistic Coupling of Heterovalent States and Vacancy Defects for Boosting Photocatalytic Hydrogen Evolution: An Insightful Case of the W-Doping Plus Hydrazine-Driven Design

Abstract

Recent studies have indicated that the heterovalent states and vacancy defect structures in bimetallic oxysulfide play a crucial role in pollutant reduction reactions. However, systematic investigations into the synergistic coupling between heterovalent states and vacancy defect structures during the photocatalytic hydrogen evolution reaction (PHER) remain scarce. Herein, a tungsten/oxygen (W/O) co-doped Ag₂S bimetallic oxysulfide (AgWOS) with heterovalent W⁵⁺/W⁶⁺ states and sulfur vacancy (Vs) defects was synthesized via a facile thermohydrolysis method. The combination of W-doping and hydrazine-driven conditions induces abundant Vs defects, which act as active sites for water adsorption and activation, thereby facilitating proton generation in the PHER process. Moreover, the hydrazine-driven condition promotes the formation of heterovalent W⁵⁺/W⁶⁺ states, which provide efficient electron transfer channels between W⁵⁺ and W⁶⁺ to boost PHER performance. The optimized AgWOS-2 with a balanced heterovalent n(W⁵⁺)/n(W⁶⁺) ratio and a high concentration of Vs achieves an impressive PHER rate of 1074.2 µmol·h⁻¹ and an apparent quantum efficiency of 6.21% at 420 nm in pure water. Density functional theory calculations reveal that the synergy between heterovalent states and vacancy defects lowers the water dissociation barrier, accelerates *H generation, and boosts electron transfer between W⁵⁺ and W⁶⁺. Moreover, S-3p and O-2p orbital hybridization suppresses photocorrosion and improves catalyst stability, enabling AgWOS-2 to retain 91.6% of its initial PHER activity after ten cycles. This study elucidates the synergistic interaction mechanism between heterovalent states and vacancy defects in a bimetallic oxysulfide, offering valuable insights for the rational design of efficient and durable PHER catalysts.

Keywords

bimetal oxysulfide / heterovalent states / hydrazine regulation / photocatalytic hydrogen evolution / sulfur vacancy defects

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