Study of the TiO2–Cr2O3 system for photoelectrolytic decomposition of water

Titanium dioxide thin films doped with up to 16 at.% of chromium were prepared by rf reactive sputtering. The effect of doping concentration on the structural, optical and electrochemical properties was studied. Modification of the electronic structure of titanium dioxide by chromium doping was established. The allowed states due to Cr were found to be situated in the forbidden band gap at about 2.5 eV below the bottom of the conduction band. Electrochemical measurements were performed in a three-electrode cell with the TiO2–Cr acting as anode. The impedance spectra and capacitance of the electrode/electrolyte interface versus voltage (Mott–Schottky plots) were recorded over a wide frequency range of 1–106 Hz. The flat band potential, effective donor density and depletion layer thickness were obtained from capacitance data as a function of the applied potential at 10 kHz.