Improving the photoelectrochemical performance of WO3 photoelectrodes by controlling the pH and Na+ ion concentration through varying the number of H2WO4 precipitate washing treatments

Abstract

In this study, WO3 thin-film photoelectrodes were grown on fluorine-doped tin oxide (FTO) substrates using the spin coating method. The H2WO4 precipitate underwent various washing treatments to prepare the Na2WO4 precursor solution, which was subsequently used for growing photoelectrodes. We found that washing with the H2WO4 precipitate changed the Na + ion concentration and pH of the precursor solution containing the H2WO4 precipitate and subsequently affected the thickness, X-ray diffraction (XRD) peak intensity, optical energy bandgap, flat-band potential, and photoelectrochemical (PEC) properties of the WO3 photoelectrode. In particular, the Na + ions in the H2WO4 precipitate solution negatively affected the PEC properties by causing photogenerated electron–hole recombination and worsening the adhesion between the substrate and the WO3 thin film. Therefore, H2WO4 precipitate washing treatment is crucial for reducing the Na + ion concentration in solutions containing H2WO4 precipitate. Consequently, among the samples grown using different numbers of washing treatments, the sample grown using 12 precipitate washing treatment cycles exhibited the highest photocurrent density of 1.37 mA/cm2 and a photostability of 97.5 %. In this study, the morphological, structural, optical, electrical, and PEC properties of WO3 photoelectrodes subjected to H2WO4 precipitate washing treatment were systematically analyzed.