Controllable synthesis of nanostructured bismuth vanadate thin films as an efficient catalyst for photoelectrochemical water splitting

This work focuses on the variation of solvents/additives as a key factor in hydrothermal and solvothermal syntheses of nanocrystal BiVO 4 films. All synthesized films successfully formed the BiVO 4 monoclinic phase, which was confirmed by XRD, XPS, XANES and EDS techniques. The physico-chemical characteristics of these solvents/additives have dramatic impacts on the crystal morphologies and surface crystal planes. Using ethanol and ethylene glycol gives plate-like BiVO 4 with {121} as a dominant facet. On the other hand, preparations with low pH and higher polar solvents result in {010}-dominated nanocrystals. The effects of the three solvent molecules including water, methanol, and ethanol are investigated by computations. Interestingly, the adsorption energy of each solvent molecule on various facets is different, leading to diverse exposure of the lattice planes. Overall, the photoanodes with plate-like particles give better catalytic activities. These films have higher-index {121} exposed facets, more oxidative (110) plane and better charge transfer properties. The photoelectrochemical photocurrent switching effects are also observed with varied switching potentials, suggesting that the (110) and (040) planes are the controlling parameters. The obtained knowledge from this work may be useful for the fabrication of photoelectrodes with expanded fields of application. The choice of solvents and additives used in the preparation of BiVO 4 films had a critical influence on the preferred orientation of the crystal planes, the surface morphology, and, consequently, the photoelectrochemical properties.