A perspective into recent progress on the tailored cationic group-based polymeric anion exchange membranes intended for electrochemical energy applications

Abstract

Anion exchange membranes (AEMs) have been widely used in electrochemical devices, such as fuel cells. This manuscript provides a comprehensive review of the recent literature on this research topic. A systematic analysis of the different trends toward the development of suitable cationic groups in AEM research, with the main goal of achieving high hydroxide conductivity and resilience under alkaline working conditions, is offered. Similar to Nafion®, state-of-the-art proton exchange membrane (PEM), AEMs with rigid hydrophobic backbones and flexible hydrophilic side groups have been shown to present high ionic conductivity. The main shortcomings of electrochemical devices utilizing PEMs are their expensive components and electrodes, chemical stability, and sensitivity to impurities. The primary challenge of AEM research is to increase the chemical and mechanical stability of the membrane under high pH and temperature conditions while maintaining high ionic conductivity as required for efficient electrochemical devices. Cations containing quaternary ammonium, phosphonium, imidazolium, guanidinium, pyrrolidinium, piperidinium, pyridinium, morpholine, triazatriangulenium, spirocyclic ionic liquids, and inorganic cations are discussed here. In addition to the synthesized cationic groups, applications of additives such as cellulose nanocrystals and chitosan in AEMs are also evaluated.