Effect of Added MoO3 and Tungsten on Photoelectrochemical Behavior of Thermally Decomposed W03 Electrodes

Abstract

Polycrystalline WO₃ was synthesized by the thermal decomposition of ammonium paratung: state. The optical property and the photoelectrochemical behavior of the WO₃ and WO₃ added with MoO₃ or metalic tungsten were investigated. The effects of added MoO3 and tungsten on the anodic oxygen evolution reaction were measured in acidic aqueous solutio ns under illumination with a high-pressure mercury lamp. The additive/WO₃ molar ra tios for MoO₃ and tungsten were 0.1 and 0.05, respectively. The optical band gap was measured by an UV-VIS spectrophotometer with an integrating sphere, and the values of both MoO₃/WO₃ and W/WO₃ systems were ca.2.6 eV.
For WO₃ electrodes of W/WO₃ molar ratio 0.005, the photocurrent of oxygen evolution had a maximum value and it was 1.5 times larger than that for the pure WO₃ polycry stalline electrode. In a concentration ranges of below 0.01, the increase in photocurrent corresponded to the change in their donor concentration obtained from Mott-Schottky plo ts. In the higher concentration ranges of additives, the photocurrent was decreased by the formation of carrier traps and recombination centers.
These results suggest that the anodic photocurrent of oxygen evolution is due to bandband excitation of the impurity bands arising from the lattice defects of oxygen and the addition of tungsten or MoO₃.