Improving Uniformity and Reproducibility of Photoelectrochemical Water Oxidation Performance of BiVO4 Photoanodes via Selective Removal of Excess V2O5 by Electrochemical Etching

Abstract

A two-step synthesis method involving the electrodeposition of a Bi precursor and drop-casting of a V precursor is widely used to produce highly efficient BiVO4 photoanodes. This method requires a final etching step to remove excess V2O5 on top of BiVO4, and the use of chemical etching with aqueous NaOH solution is the most common. However, there is an issue with the uniformity and reproducibility of BiVO4 because of local chemical damage to the surface of BiVO4 during the etching step. Here, we present an electrochemical etching method for selective removal of excess V2O5 without any damage on BiVO4, which is based on different stability windows (in terms of pH and bias) of V2O5 and BiVO4. In contrast to the conventional chemical etching, continued etching over an optimal time causes no degradation of BiVO4 films, eliminating the causes of local fluctuation of photo-electrochemical sulfite and water oxidation performance, improving both uniformity and reproducibility. Additionally, through comparative physical and chemical analysis of BiVO4 prepared by the chemical and electrochemical etching methods, we identified loss of surface V from BiVO4 as the reason for the performance degradation in excessive chemical etching.