Charge relaxation dynamics of an electrolytic nanocapacitor

TL;DR

This study uses a novel lattice Boltzmann method with a variable relaxation time to simulate ion relaxation in nanocapacitors, revealing oscillatory behaviors and plasma-like oscillations influenced by EDL overlap and confinement.

Contribution

Introduces a new MSDRT-based lattice Boltzmann approach for accurately modeling charge relaxation dynamics in electrolytic nanocapacitors, capturing nanoscale effects.

Findings

Oscillatory ionic current density at large EDL overlaps

Observation of plasma-like spatial oscillations under nanoscale confinement

Enhanced stability and accuracy of LB simulations with MSDRT

Abstract

Understanding ion relaxation dynamics in overlapping electric double layers (EDLs) is critical for the development of efficient nanotechnology based electrochemical energy storage, electrochemomechanical energy conversion and bioelectrochemical sensing devices as well as controlled synthesis of nanostructured materials. Here, a Lattice Boltzmann (LB) method is employed to simulate an electrolytic nanocapacitor subjected to a step potential at t = 0 for various degrees of EDL overlap, solvent viscosities, ratios of cation to anion diffusivity and electrode separations. The use of a novel, continuously varying and Galilean invariant, molecular speed dependent relaxation time (MSDRT) with the LB equation recovers a correct microscopic description of the molecular collision phenomena and enhances the stability of the LB algorithm. Results for large EDL overlaps indicated oscillatory behavior for the ionic current density in contrast to monotonic relaxation to equilibrium for low EDL overlaps. Further, at low solvent viscosities and large EDL overlaps, anomalous plasma-like spatial oscillations of the electric field were observed that appeared to be purely an effect of nanoscale confinement. Employing MSDRT in our simulations enabled a modeling of the fundamental physics of the transient charge relaxation dynamics in electrochemical systems operating away from equilibrium wherein Nernst-Einstein relation is known to be violated.