Electrosorption-Enabled Fast Ion Diffusion Along the Graphene-Electrolyte Interfaces

Modulating electronic charge transport at the interfaces of electroactive materials via external voltages is pivotal for advancing electronic transistor technology, crucial for modern information processing and intelligence systems. Inspired by the achievements in microelectronics and the vital role of ionic charge signalling in biological systems, there is an increasing interest in using external voltages to manipulate ion transport at electronic/ionic interfaces or within nanoconfined environment. However, experimentally probing ion transport along electrified electronic conductor interfaces presents significant challenges. Here, we propose an interface amplification strategy to investigate the effects of external voltage on lateral ion transport, specifically focusing on ambipolar ion permeation across electrified interfaces using reduced graphene oxide (rGO) membranes. These electronically conductive multilayered graphene membranes (MGMs), based on rGO sheets, are reconceptualized as an ensemble of numerous atomically thin sheet/electrolyte interfaces when immersed in an electrolyte solution. Our findings indicate that while the negatively charged chemical groups on rGO generally hinder ion permeation compared to bulk solutions, the application of a negative external voltage allows for unexpectedly rapid and collective permeation of both cations and anions through the membranes. We observed ion permeation rates exceeding those in bulk solutions by over three orders of magnitude for the negatively electrified membranes. By combining Poisson-Nernst-Planck simulations with various electrochemical and nanofluidic characterizations, we underscore the critical roles of ion electrosorption and ion-ion interactions in shaping ion transport dynamics at highly charged interfaces. Our research also uncovers several fundamental, unresolved questions about electrochemical interfaces, providing new insights that could drive the development of advanced electrochemical and iontronic technologies.