Photoelectrochemical measurements were carried out in three-electrode configuration (CIMPS workstation, Zahner-Elektrik GmbH & Co. KG, Germany). 0.1 M sodium phosphate buffer solution containing 0.1 M sodium sulfite was used as electrolyte for photocurrent and electrochemical impedance spectroscopy (EIS) measurements. The circular irradiation area was 0.283 cm 2 and the intensity of simulated solar LED white light source was 100 mW cm -2 . EIS measurements were conducted in the frequency range between 0.1 Hz and 10 KHz with a perturbation amplitude of 10 mV at open circuit potential (OCP). Mott-Schottky plots were measured at a frequency of 500 Hz in 0.5 M Na2SO4 solution in three electrode configuration. Ag/AgCl (3 M NaCl) and Pt wire were used reference and counter electrodes, respectively and the potential of the Ag/AgCl reference electrode was +0.251 V.