Photoelectrochemical Properties of Gallium-nitride-based Photoanode in Tandem Cell Analyzed by AC Impedance Method

This study used an AC impedance method to quantitatively analyze the internal resistance in a tandem cell with a gallium-nitride (GaN) based photoanode for the water splitting reaction. Impedance spectra of the whole system (two-electrode cell) and the photoanode cell (three-electrode cell) were analyzed by using an R-C equivalent circuit, and the ohmic resistance in the system and the charge transfer resistance in the photoanode cell were clarified. From the AC impedance measurement performed 1 min after light irradiation, it was found that the internal resistance of the photoanode cell was the dominant resistance in the system and the charge transfer resistance in the photoanode cell accounted for over 90 % of the internal resistance. In addition, the results indicate that the charge transfer resistance depends on the number of electron-hole pairs generated in the GaN-based photoanode.