Photoanodes on titanium substrates: one-step deposited BiVO₄ versus two-step nano-V₂O₅ films impregnated with Bi^₃+

One-step deposition of photoelectrochemically active BiVO₄ (monoclinic) from a polyethylene glycol (PEG300) precursor paint onto titanium substrates is demonstrated to lead to more complex multioxide phase films. Photocurrents in 0.5 M Na₂SO₄ remain relatively low when compared to those reported on tin-doped indium oxide (ITO) substrates, possibly due to the effect of detrimental underlying titanium oxide phases or mixed phases. For comparison, the one-step deposition is demonstrated also for the direct formation of V₂O₅ nanocrystalline films, which also exhibited low photoelectrochemical activity. Impregnation of nanocrystalline V₂O₅ with aqueous Bi³⁺ is shown to cause substantial recrystallization with formation of much more photoactive BiVO₄. In particular, on low-temperature (high surface area) nano-V₂O₅ (400 °C) and after further mild annealing at 400 °C much improved photoelectrochemical water oxidation activity (ca. 0.3 mA cm⁻² at 1.0 V vs Ag/AgCl (KCl (3 M) at 0.1-W cm⁻² xenon lamp radiation) is observed. This opens up a new mild temperature two-step route for BiVO₄ photocatalysts on practical titanium substrates.