Two-component electrolyte solutions with dipolar cations on a charged electrode: Theory and computer simulations

TL;DR

This paper presents a theoretical model and molecular dynamics simulations to explore how introducing dipolar organic cations into the electric double layer can modify electrode interface structures, potentially enhancing electrochemical device performance.

Contribution

The study develops a new theoretical framework predicting the replacement of alkali cations with dipolar organic cations in the EDL, supported by simulation validation.

Findings

Dipolar cations influence the EDL at high surface charge densities.

Theoretical predictions align qualitatively with molecular dynamics results.

Effective cation replacement occurs above 30 μC/cm² surface charge.

Abstract

The development of advanced electrochemical devices for energy conversion and storage requires fine tuning of electrode reactions, which can be accomplished by altering the electrode/solution interface structure. Particularly, in case of an alkali-salt electrolyte the electric double layer (EDL) composition can be managed by introducing organic cations (e.g. room temperature ionic liquid cations) that may possess polar fragments. To explore this approach, we develop a theoretical model predicting the efficient replacement of simple (alkali) cations with dipolar (organic) ones within the EDL. For the typical values of the molecular dipole moment ($2-4~D$) the effect manifests itself at the surface charge densities higher than 30 $\mu C/cm^2$. We show that the predicted behavior of the system is in qualitative agreement with the molecular dynamics simulation results.