Bismuth vanadate photoanodes for water splitting deposited by radio frequency plasma reactive co-sputtering

Abstract

Photoactive bismuth vanadate (BiVO4) thin coatings were deposited on fluorine-doped tin oxide glass by plasma reactive sputtering from Bi2O3 and vanadium (V) radio frequency (RF) powered targets. The films were characterized by x-ray diffraction, scanning electron microscopy, energy dispersion spectroscopy, and UV-vis spectroscopy. The effects that the power density supplied to the Bi2O3 target, the post-annealing treatment, and the film thickness have on the structural features and on the photoelectrochemical (PEC) performances of the so obtained BiVO4 film-based photoelectrodes were investigated. Their PEC performance in water splitting was evaluated in a three-electrode cell by both incident photon to current efficiency and linear sweep voltammetry measurements under AM 1.5 G simulated solar light irradiation. A monoclinic phase of BiVO4, which is more photoactive than the tetragonal BiVO4 phase, was obtained by optimizing the power density supplied to the Bi2O3 target, i.e., by tuning the Bi:V:O atomic ratio. The best PEC performance was obtained for a stoichiometric 1:1 Bi:V atomic ratio, attained with 20 W power supplied to the Bi2O3 target and 300 W power supplied to the vanadium target, and an optimal 200 nm thickness of the BiVO4 film, with a 0.65 mA/cm2 photocurrent density attained at 1.23 V versus standard calomel electrode, under simulated solar light. These results show the suitability of plasma reactive sputtering with two RF powered electrodes for the deposition of BiVO4 photoanodes for water splitting.