Gelation, Clustering and Crowding in the Electrical Double Layer of Ionic Liquids

TL;DR

This paper extends a theory of ion associations in ionic liquids to the electrical double layer, revealing a transition from gel-like clustering to crowded free ions as electrode charge increases, relevant for energy storage devices.

Contribution

It develops and applies a theoretical framework to describe ion associations in the electrical double layer of ionic liquids, highlighting a gelation to crowding transition.

Findings

Predicts a transition from gelled to crowded ion regimes with increasing electrode charge.

Describes a transition similar to overscreening to crowding in ionic liquids.

Provides insights into interfacial properties relevant for supercapacitors.

Abstract

Understanding the bulk and interfacial properties of super-concentrated electrolytes, such as ionic liquids (ILs), has attracted significant attention lately for their promising applications in supercapacitors and batteries. Recently, McEldrew \textit{et al.} developed a theory for reversible ion associations in bulk ILs, which accounted for the formation of all possible Cayley tree clusters and a percolating ionic network (gel). Here we adopt and develop this approach to understand the associations of ILs in the electrical double layer at electrified interfaces. With increasing charge of the electrode, the theory predicts a transition from a regime dominated by a gelled or clustered state to a regime dominated by free, crowded ions. This transition from gelation to crowding is conceptually similar to the overscreening to crowding transition.