Role of oxygen vacancies on surface reaction of water oxidation in WO3 studied by density functional theory (DFT) and experiment

Abstract

Oxygen vacancies (Vo) play an important role on light absorption and charge separation in the semiconductor-based oxygen evolution reaction (OER). However, its role on the surface reaction in OER are not clear. Here, in this study, we investigated the role of Vo focusing on the surface reaction in OER on WO3 by using density functional theory (DFT) calculations and experiment approaches. The DFT calculations show that on (001) surface of WO3, the Vo can only be stable under ∼0.8 nm of the top surface during OER condition. Otherwise, it will be filled by the oxygen atoms from water molecules adsorbing on the top surface of the catalyst during OER. The Bader charge analysis shows there are excess electrons left by Vo can transfer to the OER intermediates and change its binding energy. Due to this, the stable Vo could reduce the overpotential of OER. To confirm this, a series of WO3 with exposed (001) surfaces containing different Vo concentrations have been synthesized by NaBH4 reduction method. The existence of Vo has been charactered by light absorption, XPS and EPR. The sample with the same Vo concentration of theoretical calculations shown best OER performance and the oxygen evolution reaches 318 μmolg−1h−1. This work gives new insights into further design OER materials based on the role of Vo on the surface reaction.