Anisometric Charge Dependent Swelling of Porous Carbon in an Ionic Liquid

TL;DR

This study investigates the anisometric charge-dependent swelling behavior of porous carbon electrodes in an ionic liquid, revealing how potential, scan rate, and ion size influence expansion and charge storage.

Contribution

It introduces the first in situ electrochemical dilatometry analysis of porous carbon in an ionic liquid, highlighting the charge-dependent and ion-specific swelling mechanisms.

Findings

Maximum strain of 1.8% at -2 V and 0.5% at +2 V.

Expansion decreases with increasing scan rate.

Strain-charge relationship fits a quadratic function.

Abstract

In situ electrochemical dilatometry was used to study, for the first time, the expansion behavior of a porous carbon electrode in a pure ionic liquid, 1-ethyl-3-methyl-imidazolium-tetrafluoroborate. For a single electrode, an applied potential of -2 V and +2 V against the potential of zero charge resulted in maximum strain of 1.8 % and 0.5 %, respectively. During cyclic voltammetry, the characteristic expansion behavior strongly depends on the scan rate, with increased scan rates leading to a decrease of the expansion. Chronoamperometry was used to determine the equilibrium specific capacitance and expansion. The obtained strain versus accumulated charge relationship can be fitted with a simple quadratic function. Cathodic and anodic expansion data collapses on one parabola when normalizing the surface charge by the ratio of ion volume and average pore size. There is also a transient spike in the height change when polarity is switched from positive to negative that is not observed when changing the potential from negative to positive indicating the size and the shape of the ion is influencing the expansion behavior.