T. D. Le, L. Zhang, S. Reculusa, G.Vignoles, N. Mano, A. Kuhn, D. Lasseux
This article reports on a procedure to predict the optimal thickness of cylindrical porous electrodes operating a single redox reaction. This is obtained from a macroscopic model for the coupled diffusion-reaction process that is first validated with voltammetry experiments of H2O2/H2O reduction reaction carried out with a series of porous electrodes elaborated in this work. An analytical solution to this model is developed in the steady regime and for electrodes featuring a thickness to mean radius ratio small enough compared to unity. An analytical expression of the optimal electrode thickness is derived corresponding to the crossover value of two asymptotic regimes characterizing the dependence of the volume current density produced by the electrode upon its thickness. The predictive tool of the optimal thickness is general, regardless the porous microsctructure. The case of the electrodes used in the reported experiments illustrates that the optimal thickness is not intrinsic to the microsctructure characterized by the size of the representative volume, its specic area and effective diffusion coefficient. It also depends on the operating conditions reflected in the kinetic number, Ki, and the thickness of the diffusion layer surrounding the electrode. The dependence of the optimal thickness on these two parameters is quite signicant in a range of very small values of Ki but remains quasi constant beyond a threshold value.