The capacitance, spectral response, and volt‐ampere characteristics of lightly reduced TiO2 photo-electrochemical electrodes were all significantly altered by immersion in concentrated acids or by operation at sufficiently negative voltages. These changes, which were reversible, were attributed to diffusion of protons along the c‐axis channels of rutile. There was an apparent threshold voltage for appreciable accumulation of protons which were presumed to enter the crystal as H atoms.

Characterized Semiconductor Electrodes. II . Room Temperature Diffusion in a Single Crystal Rutile Electrode. Harris, L.A., Gerstner, M.E., Wilson, R.H.: Journal of the Electrochemical Society, 1979, 126[5], 850-5