Photoelectrochemical cell studied by impedance spectroscopy

The impedance of the photo-electrochemical cells using TiO2 thin film electrodes was investigated by means of complex admittance spectra within the frequency range 0.01 Hz-100 kHz, and in the presence of an electrical bias between -0.7 and 0.4 V. Plausible equivalent circuits are discussed. It was found that the impedance can be divided into two frequency ranges. Based on the determined capacitance vs. bias voltage, both flat band potential and density of donors of the TiO2 electrode have been estimated. The flat band potential with respect to a saturated calomel electrode and the density of donors were -0.64 V and 3.7x1024 m-3, respectively. The thickness of the depletion layer corresponding to 1 V voltage was equal to 46 nm