Electrochemical and electrochromic aspects of porous titania glass

Abstract

Electrochemical and photoelectrochemical properties of porous titania glass (PTG) electrodes in aqueous electrolytes were studied systematically paying special attention to the effects of micropores in the material. Because of its open-porous structure, current-potential characteristics of the PTG electrodes reached a steady state only after the electrolytes soaked into the micropores. The magnitude of the stationary anodic dark current was dependent upon the annealing temperature of the PTG in a hydrogen atmosphere. The dark current was found to be the consequence of charge transfer at the metal electrode (Pt) attached to the PTG back surface. The fact that the dark current decreased with increasing ionic radius of the halogen anions indicated that the mean pore radius in PTG is quite small and consistent with the reported high BET surface area. Unannealed PTG electrodes changed color from pale yellow to opaque blue-black after cathodic polarization of the electrodes in acidic solutions. This electrochromism was explained by reduction of titania on the microporous surface by hydrogen atoms.