Different Approaches for the Preparation of Composite Ionic Liquid-Based Membranes for Proton Exchange Membrane Fuel Cell Applications-Recent Advancements

The use of ionic liquid-based membranes as polymer electrolyte membranes for fuel cell applications increases significantly due to the major features of ionic liquids (i.e., high thermal stability and ion conductivity, non-volatility, and non-flammability). In general, there are three major methods to introduce ionic liquids into the polymer membrane, such as incorporating ionic liquid into a polymer solution, impregnating the polymer with ionic liquid, and cross-linking. The incorporation of ionic liquids into a polymer solution is the most common method, owing to easy operation of process and quick membrane formation. However, the prepared composite membranes suffer from a reduction in mechanical stability and ionic liquid leakage. While mechanical stability may be enhanced by the membrane's impregnation with ionic liquid, ionic liquid leaching is still the main drawback of this method. The presence of covalent bonds between ionic liquids and polymer chains during the cross-linking reaction can decrease the ionic liquid release. Cross-linked membranes reveal more stable proton conductivity, although a decrease in ionic mobility can be noticed. In the present work, the main approaches for ionic liquid introduction into the polymer film are presented in detail, and the recently obtained results (2019-2023) are discussed in correlation with the composite membrane structure. In addition, some promising new methods (i.e., layer-by-layer self-assembly, vacuum-assisted flocculation, spin coating, and freeze drying) are described.

Automated summary

The use of ionic liquid-based membranes as polymer electrolyte membranes in fuel cell applications has increased significantly due to the excellent properties of ionic liquids. There are three main methods for introducing ionic liquids into the polymer membrane, but each method has its drawbacks. The incorporation of ionic liquids into a polymer solution is the most common method but leads to a reduction in mechanical stability and ionic liquid leakage. Cross-linking can improve mechanical stability but may decrease ionic mobility. This article presents the main approaches for ionic liquid introduction and discusses the latest results in correlation with the composite membrane structure. In addition, some promising new methods are described.