Faradaic admittance and adsorption: a diffusion model

Abstract

When diffusion alone is the mode of mass transfer, expressions derived previously for the elements of the faradaic admittance predict that its phase angle cannot exceed π/4. Several systems show the possibility of the phase angle being greater than π/4. Laitinen and Randles had suggested that such anomalous behaviour can be explained by taking into account the correction for the contribution of the adsorbed reactants. A different model, based on diffusion, is presented in this paper and shows how the conclusions of Laitinen and Randles(e.g., the elements of the equivalent circuit, R_a and C_a, which are independent of frequency) can be obtained through this model as well. A detailed comparison between the parameters used in the two different models is made. Results for a generalised diffusion model are cited.