Mesoscale dynamics of electrosorbed ions in fast-charging carbon-based nanoporous electrodes

Electrosorption, the accumulation of electrolyte ions at charged interfaces, is a common phenomenon across various electrochemical systems. Its impact is particularly pronounced in nanoporous electrodes owing to their high surface-to-volume ratios. Although electrosorption alters the ion distribution at the electrode-electrolyte interface through the formation of an electrical double layer, the effects of electrosorbed ions on the charge storage dynamics in nanoporous electrodes and their ability to improve charging processes have often been overlooked. Here we use a multilayered reduced graphene oxide-based membrane as a model nanoporous electrode material, integrating numerical simulations with experimental insights. We monitor the spatiotemporal distribution of electrosorbed ions and electrical potentials across the nanopore network during fast charging of symmetrical laboratory-scale cells using aqueous and non-aqueous electrolyte solutions. This method allowed us to quantitatively assess how features of the nanoporous electrode mesostructure, such as nanoslit size, the distribution of nanoslit sizes and electrode thickness, dynamically influence ion electrosorption and the local electrical and chemical potentials across the network. Our findings reveal that the mesostructure of nanoporous electrodes influences how migration and diffusion currents, mediated by electrosorbed ions, respond to charging rates.