Hydrogen generation from renewable energy sources will play a key role in the concerted endeavor to constrain climate change. One environmentally friendly route, powered by sunlight, is the photoelectrochemical water splitting cell (PEC). This technology employs electrodes coated with thin films of semiconductor materials to capture light and generate charge carriers that directly drive the water splitting reaction. Bismuth vanadate is a promising metal oxide semiconductor, as it absorbs visible light, and is abundant, non-toxic and cost-effective. The present study investigates the formation of bismuth vanadate thin films by the aerosol deposition (AD) method. Operating with layer formation at room temperature, AD offers advantages over other routes for the fabrication of photoactive thin film coatings, as no binders or sintering processes need to be applied. Furthermore, compared to traditional cold spraying, micrometer-sized particles can be used, resulting in coatings with thicknesses below 1 µm. Additionally, the lower kinetic energy of the feedstock powder particles enables the use of delicate substrates, such as FTO-coated glass, expanding the range of possible PEC device configurations. The process parameters explored in this study had considerable influence on the resulting coating microstructure, which in turn showed a significant impact on the photoelectrochemical performance.

In order to enable mass production of photocatalytically active electrodes for direct conversion of solar energy into hydrogen, abundant materials and inexpensive preparation methods are needed. BiVO4 photoelectrodes prepared by aerosol deposition satisfy these requirements, in addition offering reasonable photocurrent densities, and can potentially contribute to the establishment of a prospective economy based on hydrogen as energy source. Nevertheless, in order to allow the economically feasible implementation of BiVO4 electrodes for direct water splitting, there is need for further improvement of the electrodes efficiency. In particular, an increased understanding of factors limiting the photocurrent is needed. In this work, BiVO4 photoelectrodes, prepared by aerosol deposition of BiVO4 particles on FTO-substrates, were investigated by surface photovoltage (SPV) as well as photocurrent and Mott-Schottky measurements. Surface photovoltage spectroscopy under front and back illumination gives evidence of limitation of charge transport by a significant lower mobility of electrons compared to holes, leading to a nearly tenfold higher photocurrent, when illuminated from the back, compared to illumination from the front. Furthermore, the presence of traps for holes as well as for electrons on the BiVO4 surface has been confirmed by transient surface photovoltage spectroscopy and their influence on the photocurrent is discussed. Figure 1

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