Electrochemical impedance spectroscopy of WO_{3} photoanodes on different conductive substrates: the interfacial charge transport between semiconductor particles and Ti surface

F. Amano, S. Koga
Journal of Electroanalytical Chemistry, 921, Article 116685, 2022, https://doi.org/10.1016/j.jelechem.2022.116685

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Particulate film electrodes of n-type semiconductor oxides are promising for photoelectrochemical (PEC) water splitting. To improve the photoanodic performance, we investigated the effect of charge transport at the interface between the oxide particles and the conductive substrate using electrochemical impedance spectroscopy (EIS) under UV-visible light irradiation. As a model oxide, we prepared tungsten oxide (WO_{3}) particle films on different conductive substrates of fluorine-doped tin oxide (FTO)-coated glass, indium tin oxide (ITO)-coated glass, and Ti plates at different calcination temperatures. The PEC properties of the WO_{3} electrodes were evaluated for water oxidation in 0.1 mol L−1 sulfuric acid. The photocurrent density of the WO_{3} films on Ti plate (Ti/WO_{3}) monotonically increased as the calcination temperature increased up to 650 °C, whereas the WO_{3} films on FTO-coated and ITO-coated glasses were, as is well known, deactivated at such high temperatures. The EIS measurements of the Ti/WO3 photoanodes revealed that the series resistance (Rs) was low even after calcination at high temperatures because the Ti surface was coated by the WO_{3} film. The charge-transfer resistance (Rct) of WO_{3} photoanodes estimated from EIS was dependent on the incident light intensity because the photocurrent density was proportional to the irradiance. We found that the Ti/WO3 photoanodes exhibited a resistance in addition to Rs and Rct. We assigned this resistance, which was not changed by the light intensity, to the interfacial charge transport resistance (Ri) between WO_{3} particles and the Ti substrate. A smaller Ri increased the photocurrent density of Ti/WO_{3} for the oxygen evolution reaction at higher applied potentials.