ELECTRODISSOLUTION OF ALUMINUM THIN-FILM MICROBAND ELECTRODES

This paper discusses the electrodissolution of aluminium thin films as microband electrodes (length = 5 x 10(-3) m) in terms of mass transfer determined by voltammetry and a.c.-impedance techniques as a function of bandwidth (20 to 2000 nm) in 0.1 M NaOH solution. The anodic polarization curves of the aluminium microband electrodes show that current density is enhanced with decreasing bandwidth. The ac impedance response suggests that a steady-state diffusion layer appears the more markedly, the smaller the bandwidth. The anodic polarization curves are analysed on the basis of the combined Butler-Volmer high field approximation and the semi-cylindrical diffusion field approximation. As a result of the analysis, the electrodissolution proceeds by a mixed kinetic-mass transfer controlled reaction. The analysis also makes it possible to distinguish the semi-cylindrical diffusive mass transfer contribution to the electrodissolution from the kinetic contribution, i.e., mass transfer index linearly diminishes with decreasing bandwidth. The increased current density is attributable to the decreased mass transfer contribution, i.e., the more predominant semi-cylindrical diffusive mass transfer as compared to laminar diffusive mass transfer.