Applications of poly ionic liquids in proton exchange membrane fuel cells: A review

Poly ionic liquids (ILs), also known as polymeric ILs, are a particular class of polymers since they acquire conventional features of polymers and keep some unique characteristics of ILs, including high thermal and electrochemical stabilities and good ionic conductivity. Either IL's cation or anion can constitute the backbone of poly ILs with free mobile anion or cation, respectively. Therefore, unlike inert polymers, poly ILs are considered as charged polymers. Thus, increasing research efforts are devoted to employing poly ILs in many advanced electrochemical applications like fuel cells and batteries. The present review article concentrates on the applications of poly ILs in polymer electrolyte membrane fuel cells (PEMFCs). Firstly, a review of the different approaches to applying poly ILs in polymer electrolyte membranes (PEMs) is introduced. Also, associated properties of poly ILs membranes, such as mechanical properties, conductivity, and thermal stability are described. In addition, an assessment of their performance in PEMFC is included. Secondly, the contributions of poly ILs in improving the cathodic oxygen reduction reaction (ORR) of PEMFC either as an ionomer or a cathodic catalyst layer modified with poly IL are reviewed. Recommendations and future outlooks for improved usage and employment of poly ILs in PEMFCs are presented.