Ionic Charge Dynamics in Electrified Nanoslit Networks Through Multiscale Modeling

Porous electrodes are vital for enhancing electrochemical interface performance in applications such as energy storage devices, frequency filters, and neuromorphic systems. These applications often work under electrical inputs with rapid changes, making the understanding of ion dynamics and effects at electrode/electrolyte interfaces crucial for interpreting and predicting key electrochemical properties like capacitance and impedance of devices, especially as pore sizes decrease to the nanoscale.<br/>However, traditional macroscopic models often fail to capture the complex interactions between interfacial electrochemical potentials and the cross-scale structural configurations of conventional nanoporous materials. Additionally, scale discrepancies in microscopic simulations, due to demanding computational resources, hinder the application of nanoscale insights to macroscopic electrochemical characterizations. These challenges complicate the understanding and utilization of nano- and meso-structural impacts on ion transport dynamics.<br/>We employed multilayered graphene membranes (MGMs) and their computational representations, i.e., nanoslit networks, as novel model systems to study ion transport dynamics. Using finite element method-based numerical simulations and guided by the Poisson-Nernst-Planck theory with steric modifications, we systematically assessed the influence of nanostructures on ion movement from individual nanoslits to the entire network. We focused on cross-scale properties under dynamic electric inputs, including nanoscale in-slit ion concentration, ionic transport resistance in the nanoslit network, and global capacitance and impedance of the nanoporous electrodes.<br/>This presentation will cover several key findings and developments. We established a slit-size-dependent scaling relation as a strategy to quantitatively examine the electrode thickness effects on dynamic ion accessibility. This relation unifies the macroscopic rate capacitance behaviors and mesoscopic dynamic ion accessibility in nanoslit-based electrodes across varying electrode thicknesses, ion diffusivities, and applied voltage. The revealed notable slit size dependency of the scaling relation indicates that the conventional, macroscopic transmission line models, which overlook the interfacial electrosorbed ions, significantly underestimate the benefits of nanoconfinement effects on dynamic ion accessibility. Our findings not only enable the dynamic behaviors of a thin nanoslit network electrode to predict those of its thicker counterparts, allowing for the correlation between simulated and experimental data regarding rate capacitance in MGM-based supercapacitors, but also offer a semi-quantitative guideline for designing nanoporous electrodes under multiple structural constraint scenarios facing diverse performance metrics.<br/>Additionally, we developed a physics-informed mesoscale electrically equivalent circuit model to uncover the previously unknown effects of nanostructures and electrosorbed ions on the impedance in MGMs. The interfacial electrosorbed ions demonstrate distinct influences on ion transport within and across nanoslits, each exhibiting distinct slit-size-dependent conductivity, offering new physical insights for certain widely reported experimental outcomes. These efforts establish a connection between the electrodes' microstructure and their overall electrochemical properties, demonstrating the utility of 2D membranes and PNP-based models as effective tools for simulating and understanding the behaviors of ions at electrochemical interfaces of nanoporous materials under dynamic operational conditions. Our work also lays the groundwork for a theoretical framework aimed at digitally designing the next generation of electrochemical and ionotronic technologies.