Extraordinarily Efficient Conduction in a Redox-Active Ionic Liquid

TL;DR

This paper reveals that iodine-enhanced ionic liquids exhibit exceptionally high conductivity due to a combination of physical diffusion and Grotthuss bond-exchange mechanisms, providing new insights into charge transport in viscous systems.

Contribution

It demonstrates the significant role of the Grotthuss mechanism in ionic liquid conductivity and introduces a quantitative model combining diffusion and bond-exchange processes.

Findings

Iodine addition drastically increases ionic liquid conductivity.

Grotthuss mechanism significantly contributes to charge transport.

A new model quantitatively describes conduction in these systems.

Abstract

Iodine added to iodide-based ionic liquids leads to extraordinarily efficient charge transport, vastly exceeding that expected for such viscous systems. Using terahertz time-domain spectroscopy, in conjunction with dc conductivity, diffusivity and viscosity measurements we unravel the conductivity pathways in 1-methyl-3-propylimidazolium iodide melts. This study presents evidence of the Grotthuss mechanism as a significant contributor to the conductivity, and provides new insights into ion pairing processes as well as the formation of polyiodides. The terahertz and transport results are reunited in a model providing a quantitative description of the conduction by physical diffusion and the Grotthuss bond-exchange process. These novel results are important for the fundamental understanding of conduction in molten salts and for applications where ionic liquids are used as charge-transporting media such as in batteries and dye-sensitized solar cells.