Physical interpretation of cyclic voltammetry for measuring electric double layer capacitances

This paper aims to develop a model for simulating the electric double layer dynamics in CV measurements while simultaneously accounting for transport phenomena in both the electrode and the electrolyte. It also aims (i) to identify the dimensionless parameters that govern the CV measurements, (ii) to provide a physical interpretation of the shape of CV curves, and (iii) to investigate the effect of the electrode electrical conductivity on the predicted double layer capacitance. The transient double layer dynamics was simulated using the modified Poisson-Nernst-Planck (MPNP) model with a Stern layer and accounting for the presence of the electrode. A dimensional analysis was performed and four dimensionless numbers governing the CV measurements were identified. This study established that the hump in CV curves for electrodes with large radius of curvature was due to the saturation of ion concentration near the electrode surface before reaching the maximum potential. It also demonstrates that CV curves became symmetric for large ion diffusion coefficient due to rapid ion transport. This study confirmed that the EDL capacitance retrieved from CV measurements is constant for low scan rates and corresponds to the capacitance under equilibrium conditions. Larger ion diffusion coefficient and electrode electrical conductivity led to larger EDL capacitance at large scan rates corresponding to better charging performance. (C) 2012 Elsevier Ltd. All rights reserved.