Interfacial ordering and accompanying divergent capacitance at ionic liquid-metal interfaces

TL;DR

This paper develops a theoretical framework for ionic liquid-metal interfaces, predicting a voltage-driven charge ordering transition that explains anomalous capacitance behaviors observed experimentally and in simulations.

Contribution

It introduces a new theory capturing strong inter-ionic correlations and predicts a first-order transition and charge ordering at interfaces, aligning with recent experimental and simulation findings.

Findings

Predicts a fluctuation-induced first-order transition at the interface

Shows charge density ordering driven by applied voltage

Explains anomalous differential capacitance phenomena

Abstract

A theory is constructed for dense ionic solutions near charged planar walls that is valid for strong inter-ionic correlations. This theory predicts a fluctuation-induced, first-order transition and spontaneous charge density ordering at the interface, in the presence of an otherwise disordered bulk solution. The surface ordering is driven by applied voltage and results in an anomalous differential capacitance, in agreement with recent simulation results and consistent with experimental observations in a wide array of systems. Explicit forms for the charge density profile and capacitance are given. The theory is compared with numerical results for the charge frustrated Ising model, which is also found to exhibit a voltage driven first-order transition.