Psesudocubic Phase Tungsten Oxide as a Photocatalyst for Hydrogen Evolution Reaction

Defect and phase engineering can effectively tune the activity of photocatalysts by altering their band structure and active site configuration. Herein, we report the phase-controlled synthesis of tungsten oxide (WO₃) nanoplates via a wet-chemical approach. By adjusting the ratio of trioctylphosphine and trioctylphosphine oxide, oxygen vacancies are induced in WO₃ at a relatively low temperature, accompanying the crystal structure transition from monoclinic to orthorhombic or pseudocubic phase. The experimental results and DFT calculations reveal that the increased oxygen vacant sites in WO₃ lead to the upshift in both conduction band minimum and valence band maximum. The reformed band structure of reduced WO₃ samples (WO_3-x) enables the photocatalytic hydrogen evolution without cocatalyst at a maximum steady rate of 340 μmol g^-1 h^-1 under simulated sunlight. Our work demonstrates a simple and effective strategy of introducing oxygen vacancy to WO₃ for band structure tuning, which may be further extended to other metal oxide systems.