Cation adsorption by mesoporous titania photoanodes and its effect on the current-voltage characteristics of photoelectrochemical cells

Current-voltage curves recorded during the study of photoelectrochemical cells functioning in the presence of aqueous electrolytes contain a characteristic anodic current feature, which may interfere in the interpretation of the results. This anodic current is observed at negative potentials and it derives from the adsorption of cations into the mesoporous structure of nanoparticulate titania photoanodes. The shape and the height of the peak depends on the size of the cation, its concentration, the thickness of the titania film and the nature of the counter ion and the corresponding pH. This anodic current is similar to the one observed in other works during ion storage and electrochromism studies with mesoporous titania. In the presence of an organic sacrificial agent, like ethanol, adsorption of cationic species is still strong but it decreases at higher organic content.