A Photoelectrochemical study of Bismuth Vanadate Photoanodes for Solar Water Splitting

Abstract

Bismuth Vanadate (BiVO4) is a promising photoanode in the field of solar water splitting due to its low cost of synthesis, low toxicity, good stability and high theoretical photocurrent density. However, several reports on this material have shown poor photocurrent densities, poor photon conversion efficiencies, high surface recombination and slow kinetics at the BiVO4/electrolyte interface. In order to identify and address these issues, a review of the properties of this material and the research carried out on it is provided, followed by a thickness dependent study to make an overall characterisation of the material in terms of morphology, phase and photoelectrochemical performance. We also confirm the high surface recombination and slow kinetics at the BiVO4/H2O interface, while shedding light on the reported mechanisms of slow electron transport and photocurrent enhancement by an interfacial SnO2 layer (hole mirror effect). Electrochemical impedance spectroscopy measurements determine a capacitance with magnitudes similar to a depletion-region capacitance with a capacitive peak at ~0.75 V vs VRHE, related to the V4+/V5+ redox couple, which made the estimation of the actual flatband potential difficult.