Diffusion layer in well-ordered clay-modified electrodes

Abstract

Recently [l] we demonstrated that there is a correlation between reduction currents for Fe(CN),3at spin-coated clay-modified electrodes (SPCME) and literature values for low-angle X-ray diffraction data of well-oriented SWy-1 montmorillonite. We suggested that the ratio of the maximum current (peak or plateau) obtained for the reduction of Fe(CN),3at CME to the peak current obtained at a bare electrode (R = Z pcme/Zpbare) during single sweep cyclic voltammetry could give quantitative information about clay platelet face-face interlayer distances [2]. These ratio measurements may shed light on the mechanism of long-range swelling in clays, which is important for understanding the role of the double-layer charge vs. surface hydration in interlayer forces. As the film thickness varies considerably with electrolyte concentration and speciation, the diffusion layer may or may not reside within the film for a fixed scan rate as the electrolyte concentration is varied. This could affect the validity of the correlation between the peak currents and interlayer spacing. It is, therefore, important to demonstrate that the diffusion layer resides within the film, regardless of changes in film thickness with film swelling, for all experimental conditions. In this paper, we map out systematically the conditions under which the diffusion layer will reside uniformly within the film, irrespective of changing film thickness.