Photoelectrochemical Investigations of Passive Films on Titanium Electrodes

Photoelectrochemical investigations were performed with passivated titanium electrodes. Passive films were formed in 1M H₂SO₄ at constant potential, U_ox with U_ox being varied between 4 and 105V. The results of photocurrent spectra and the potential dependence of the photocurrent suggest a distinction of four different types of film behavior depending on the thickness of the passive film. The most important changes in photoelectrochemical data occur below U_ox= 30V. An amorphous-crystalline transition of the passive film can be assumed. This is inferred from the change of the optical transitions with thickness and the potential dependence of the photocurrent which seems to obey the Poole-Frenkel effect for thinner films. The changes observed with thicker films can be related to an increasing long range order in the passive film. The results demonstrate that photoelectrochemistry is a suitable in situ technique for determining important properties of Passive films including structurally related ones.