W-Doped BiVO₄ Photoanodes for Light-to-Chemical Energy Conversion

Renewable energy and related systems are an indispensable part of our future. The urgent need to tackle climate change and the energy crisis has driven the search for innovative alternative technologies to replace current polluting and energy-intensive ones. Photoelectrochemical (PEC) advanced oxidation systems offer the possibility to convert light energy into chemical energy and store it in the form of valuable chemical compounds, e.g., oxidants and hydrogen. In this study, the performance of sol-gel-derived W-doped BiVO₄ in photoelectrolysis of aqueous sulfate solutions was investigated. W-doping was found to have a significant impact on the PEC activity of the material, with optimal results achieved using 1-5 atom % of the dopant. Fluorescence lifetime imaging microscopy revealed variations in material quality, which were attributed to the defects in the BiVO₄ crystal lattice introduced by W-doping. The double maxima observed in the incident photon-to-current efficiency maps and applied-bias photon-to-current efficiency plots were explained by the dopant-related introduction of electronic states, which require lower energy input for their excitation and participation in the interfacial charge transfer reactions. Analysis of the charge separation efficiencies in the bulk and on the surface of the layers revealed that separation in the bulk is the limiting factor for all the studied materials, whereas W-doping reduces the charge carrier recombination at the photoelectrode surface. The latter effect was ascribed to the superficial position of BiVO₄ lattice defects introduced by W-doping. Light-driven generation of persulfate and hydrogen was demonstrated.