Selective Removal of Excess V2O5 Via Electrochemical Etching for Reproducible Photoelectrochemical Water Oxidation Performance of BiVO4 Photoanodes

Abstract

Monoclinic bismuth vanadate (BiVO4) is a promising candidate for photoanodes of photoelectrochemical (PEC) water oxidation due to its ability of visible light absorption, suitable valance band edge position and chemical stability under neutral electrolyte conditions. Among various fabrication methods for BiVO4, two-step process consisting of electrodeposition of Bi-based film followed by drop casting of V containing precursor solution to form to BiVO4 has been shown to produce BiVO4 photoanodes with high photoelectrochemical water oxidation performance. However, a careful removal of excess V2O5 is necessary in this fabrication method. The most common method of removing excess V2O5 is chemical etching by NaOH solution. However, in often cases, unwanted dissolution of BiVO4 occurs along with the etching of V2O5, which results in poor reproducibility of the PEC performance. Here, we developed a simple yet very selective etching method for the removal of excess V2O5 without any damage to BiVO4, which is based on electrochemical etching. BiVO4 photoanodes prepared by our electrochemical etching resulted in very reproducible PEC performance. Physical and chemical analyses of BiVO4 films after different etching methods (chemical vs. electrochemical) revealed that the loss of surface vanadium is the source of the fluctuation in PEC water oxidation performance. Details of material characterizations and electrochemical analyses will be presented.