Chapter 13 - Applications of ionic liquids in fuel cells and supercapacitors

Abstract

When salts exist in liquid state, they are called ionic liquids (ILs). Unlike ordinary liquids, these are made up of ions. We know them by various other names like ionic melts or fused salts. Sometimes, they are also called liquid salts, liquid electrolytes, or ionic fluids. ILs have inimitable properties for sensing and biosensing applications which include high conductivity, thermal stability, supersensitivity, good catalytic ability, and better selectivity. Due to these properties, they find a wide range of applications that include electrochemical, optical, fluorescent, and thermometric sensors. As we look for more efficient materials in the booming and challenging area of energy conversion and storage systems like fuel cells (FCs), batteries, supercapacitors, and double-layered capacitors, the ILs are coming into the picture with vital properties like better ionic conductivity and encouraging thermal properties. They also show good chemical stability at room temperatures. These are utilized as proton exchange membrane material in the FCs and charge carriers for supercapacitors to achieve high energy density and high operating voltage. On the other hand, electrochemical capacitors which are also known as supercapacitors have seen substantial improvement in their performance with the ILs that provide a wide chemical stability window. Since they are electrochemically stable, they also exhibit high thermal stability. In addition, they also have shown low volatility and low flammability. Because of these, ILs are considered to be better alternatives. All these properties make them an effective alternative to organic solvent-based electrolytes for FCs. This chapter highlights the research and progress in finding ILs for FC and supercapacitors.