Synthesis of nanoporous tin oxide layers by electrochemical anodization

Nanoporous tin oxide layers were electrochemically synthesized by a voltage-controlled anodization of the metallic tin electrodeposited on the surface of Cu plate. As-prepared structures consist of number of stacked nanoporous layers separated from each other by thin gaps and the atomic ratio of Sn and O was found to be 1:1. An evolution of morphology of nanoporous tin oxide layer during anodization was investigated in detail. It was found that the oxide layer formed during the initial stage of anodizing is non-porous or exhibits a tiny pores, much smaller than those observed in the inner oxide layer. Under certain conditions (especially at higher anodizing potentials and temperatures), the nanopores in the outer layer widen with time of anodization. On the other hand, nanochannels diameter in the inner oxide layer remain almost constant. The effects of anodizing potential, temperature and electrolyte concentration on structural features of the oxide layer were deeply investigated. It was found that time required for a complete metallic tin oxidation shortens with increasing both anodizing potential and temperature. In addition, the increase in the maximum current density with increasing anodizing potential and temperature was observed. Moreover, the higher temperature, electrolyte concentration and potential applied during anodization, the larger nanochannels and thinner walls of the oxide layer are formed due to the more effective field-assisted dissolution of the oxide at the oxide/electrolyte interface and more vigorous oxygen evolution during anodizing. (C) 2012 Elsevier Ltd. All rights reserved.