Magnetically Coupled Circuits to Capture Dynamics of Ionic Transport in Nanopores

TL;DR

This paper introduces magnetically coupled circuits to better model ionic transport in nanopores, capturing oscillations and complex impedance behaviors that traditional resistor-capacitor models overlook.

Contribution

It demonstrates that magnetically coupled inductor-resistor circuits and dual Warburg elements more accurately represent ionic transport dynamics in nanopores.

Findings

Diffusivity asymmetry causes two-turn Nyquist plots.

Magnetically coupled circuits outperform simple RC models.

Two Warburg elements better fit impedance responses.

Abstract

Ionic transport within charged nanopores is commonly represented by resistor-capacitor transmission line circuits, where charging electrical double layers are modeled as capacitors, and the resistance to ionic current is modeled as resistors. However, these circuits fail to account for oscillations observed in experimental Nyquist plots of impedance, which are attributed ad hoc to effects such as complex porous structures or chemical reactions. Here, we show that diffusivity asymmetry between ions in confinement - overlooked in previous studies - produces Nyquist plots with two turns. Additionally, we demonstrate that ionic transport is more accurately described by magnetically coupled inductor-resistor circuits than by a simple resistor-capacitor circuit. Our results show that an impedance response of ionic transport in nanopores for arbitrary Debye lengths is better captured by two Warburg elements in parallel than a single Warburg element.