High-Temperature One-Step Synthesis of Efficient Nanostructured Bismuth Vanadate Photoanodes for Water Oxidation

Bismuth vanadate (BiVO ₄ ) is a promising photoanode material for photoelectrochemical water splitting due to its well-suited valence band edge and comparatively narrow band gap. First insights on the high-temperature and scalable synthesis of efficient nanostructured BiVO ₄ photoanodes for water oxidation are provided. Nanostructured BiVO ₄ films with a tunable optical density and porosity ranging from 12% to 80% are synthesized in few seconds by direct deposition of flame-made BiVO ₄ nanoparticle aerosols. The impact of the BiVO ₄ film structural properties on the photooxidation performance has been systematically investigated by a set of electrochemical and physical characterizations indicating key directions for its morphological optimization. It is found that the BiVO ₄ water oxidization performance is mainly determined by two competitive factors, viz., accessible surface area and carrier conductivity through the grain boundaries. Optimization of these two factors increases the photocurrent densities by more than three times resulting in ≈1.5 mA cm ⁻² for sulfite oxidation and ≈1 mA cm ⁻² for water oxidation with a FeOOH/NiOOH co-catalyst at 1.0 V vs the reversible hydrogen electrode (RHE) under simulated 1 sun illumination. These findings provide novel insights into the structure–activity relationships of high-temperature synthesized BiVO ₄ photoanodes for solar-powered water splitting and introduce a scalable and low-cost approach for their rapid nanofabrication.