(720d) Charging and Discharging Dynamics of Electrical Double Layers inside Nanopores: From Thin to Overlapping Double Layers

Electrical double layers (EDLs) play a pivotal role in electrochemical devices such as batteries, supercapacitors and capacitive desalinators. Of particular interest to these devices is a fundamental understanding of charging and discharging dynamics of EDLs within their porous electrodes. The existing models in literature typically rely on effective circuit analysis, which overlooks the effects of EDL thickness on the charging and discharging dynamics.

Here, we develop a theoretical model based on Poisson-Nernst-Planck equations to capture the effect arbitrary EDL thickness, and observe distinct physical behaviors in the thin and overlapping EDL regimes. We find that the charging dynamics of overlapping double layer is relatively independent on double layer thickness, unlike the thin double layer limit. In addition, we propose an optimal double layer thickness for maximum current density.

To mimic the widely used cyclic voltammetry experiments, we solve for our model for an applied ramp potential and derive the potential profile, current, and the capacitance of the nanopores. Our model predictions are in agreement with the experimentally observed trends for supercapacitors, and our reported analytical results can be readily applied to analyze cyclic voltammetry experiments.