Morphology engineering of WO3/BiVO4 heterojunctions for efficient photocatalytic water oxidation

Abstract

Four types of nanostructural WO₃/BiVO₄ heterojunctions were designed by depositing a BiVO₄ layer onto WO₃ scaffolds with different morphologies and investigated to understand the influence of heterojunction morphology on their photoelectrochemical performances. The architecture of WO₃ scaffolds was controlled by adjusting the solvents used in their solvothermal synthesis. The solvent was found to exert a great influence on the architecture of the obtained WO₃ scaffolds. Methanol leads to the formation of block-like nanostructures and ethanol facilitates the formation of nanorods, while isopropyl alcohol and ethylene glycol give rise to the formation of triangular nanowalls and 3D hierarchical nanostructures, respectively. Monoclinic WO₃ nanostructures were obtained via removal of ammonium or structural water by annealing the samples obtained at 510 °C in air. A BiVO₄ layer was then deposited on the monoclinic WO₃ scaffolds with different morphologies by spin-coating to form WO₃/BiVO₄ heterojunction films, which show significantly enhanced photocurrents compared to their corresponding bare WO₃ scaffolds. Among these WO₃/BiVO₄ nanostructure heterojunctions, the one based on a rod-like WO₃ nanostructure shows the best photoelectrochemical (PEC) performance, which can be ascribed to its optimal rod-like morphology, for the construction of WO₃/BiVO₄ heterojunction regarding efficient charge carrier transfer and collection, while the other one based on WO₃ nanowalls exhibits better stability and a higher photocurrent in a long-run test, indicating that morphology engineering significantly influences the activity and stability of WO₃-based heterojunctions.