Room-Temperature Molten Salts: Protic Ionic Liquids and Deep Eutectic Solvents as Media for Electrochemical Application

Abstract

Ionic liquids (ILs) are room-temperature molten salts (RTMS) composed mostly of organic ions that may undergo almost unlimited structural variations. ILs and deep eutectic solvents (DESs) have been applied in various fields, such as electrolytes for lithium ion batteries, redox flow batteries (RFBs), electrodeposition, and electropolishing, and even in fuel cells. This chapter covers the newest aspects of H-donor ILs in applications where their transport properties (ion conductivity, diffusion, and viscosity) are exploited, for example, as electrochemical solvents for energy storage where conventional media, organic solvents (in batteries), or water (in supercapacitors) fail. Metal nanoparticles’ (NPs) formulation and stabilization in H-donor RTMS with some unique size, shape, and properties are also discussed. In these decidedly different materials, a mixture with a molecular solvent shows electroactivity that is not exhibited in more traditional systems, creating huge potential for energy storage and electrocatalysis. The remarkable recent increase in the level of interest in RTMS (protic ionic liquids, PILs, and DESs) in academics and industry is illustrated by the rapid growth in the number of publications on the topic (Fig. 1), with more than a 100-fold increase observed over the period 2004 to 2014.