The influence of water-induced crystallization on the photoelectrochemical properties of porous anodic tin oxide films

Abstract

Nanoporous SnOx films with ultra-small channels (<20nm in diameter) were synthesized by one-step anodic oxidation of Sn foil in 1M sodium hydroxide. Then, as-prepared materials were immersed in distilled water for various durations (2–120h) to find out whether a simple soaking process can affect the photoelectrochemical performance of such kind of photoanodes. It was confirmed that during exposure to water, spontaneous crystallization of the amorphous SnOx matrix into rutile-type SnO2 occurs via a dissolution–redeposition process, which results in a gradual loss of the initial porous morphology and thinning of the anodic film. Moreover, due to the formation of less defective, more stoichiometric, and crystalline SnO2-x, gradual widening of the semiconductor band gap, the cathodic shift of the flat band and onset potentials, as well as decrease in the donor density are observed. All these factors are the reason for the significant deterioration of the photoelectrochemical performance of SnOx photoanodes during their exposure to water. Therefore, it was confirmed that even slight differences in the experimental procedure, especially sample washing, drying, and storage, can result in meaningful changes in the composition, and the photoelectrochemical properties of anodically generated tin oxide films.