Double layer in ionic liquids: capacitance vs. temperature from atomistic simulations

TL;DR

This study combines molecular dynamics and density functional theory to analyze how temperature affects the differential capacitance at graphene-ionic liquid interfaces, revealing structural and quantum effects relevant for energy storage devices.

Contribution

It provides a detailed atomistic understanding of temperature effects on capacitance, integrating structural, electrochemical, and quantum capacitance considerations.

Findings

Temperature smears local interfacial structure and capacitance.

Interfacial bilayer model explains capacitance changes.

Quantum capacitance correction aligns simulations with experiments.

Abstract

In this study, we investigated the graphene-ionic liquid (EMImBF4) interface to clarify the effects of ambient temperature and potential on the differential capacitance. We complemented molecular dynamics simulations with density functional theory calculations to unravel the electrolyte and electrode contributions to the differential capacitance. As a result, we show: (1) the relation of characteristic saddle points of the capacitance-potential curve to the structural changes; (2) the smearing effect of temperature on the local structure and, consequently, on the capacitance; (3) rationalization of these observations with the interfacial bilayer model; and, finally, (4) how quantum capacitance correction dampens the influence of temperature and improves the agreement with the experimental data. These insights are of fundamental and practical importance for the application of similar interfaces in electrochemical energy storage and transformation devices, such as capacitors and actuators.