Journal of Electroanalytical Chemistry, Vol.615, No.2, 180-190, 2008
Diffusion-controlled potentiostatic current transients on realistic fractal electrodes
We analyze the problem of diffusion to irregular electrode whose irregularity is characterized as statistically isotropic self-affine fractals oil limited length scales. The power spectrum of a surface fractal is approximated in terms of a white noise for low wave-numbers and a power law function for the intermediate wave-numbers. This power spectrum has four fractal morphological parameters. They are fractal dimension (D-H), lower (l) and upper (L) cutoff length scales of fractality, and the proportionality factor (mu) related to topothesy or strength of toughness. Our explicit results for the potentiostatic current transient and its limiting laws are presented. These limiting laws are: (i) short time expansion, (ii) long time expansion and (iii) intermediate time expansion. The intermediate time limiting law for the current transient captures the classical anomalous power law behavior which is usually observed in experimental data. Our results show that the scaling exponent of anomalous region is dependent on D-H as well as on l and mu. These results also unravel the connection between the crossover times. and the roughness characteristics of realistic fractal surfaces. We demonstrate an excellent comparison between the theoretical results and the experimental potentiostatic current transient. Finally, we also show the localization of current density oil a tough corrugated electrode where surface corrugation is taken as a band-limited Weierstrass-Mandelbrot random function. (C) 2007 Elsevier B.V. All rights reserved.
Keywords:potentiostatic current transient;rough electrode;fractal interface;Nernstian charge transfer;diffusion-limited;anomalous behavior