Abstract
This review discusses the roles of anion exchange membrane (AEM) as a solid-state electrolyte in fuel cell and electrolyzer applications. It highlights the advancement of existing fabrication methods and emphasizes the importance of radiation grafting methods in improving the properties of AEM. The development of AEM has been focused on the improvement of its physicochemical properties, including ionic conductivity, ion exchange capacity, water uptake, swelling ratio, etc., and its thermo-mechano-chemical stability in high-pH and high-temperature conditions. Generally, the AEM radiation grafting processes are considered green synthesis because they are usually performed at room temperature and practically eliminated the use of catalysts and toxic solvents, yet the final products are homogeneous and high quality. The radiation grafting technique is capable of modifying the hydrophilic and hydrophobic domains to control the ionic properties of membrane as well as its water uptake and swelling ratio without scarifying its mechanical properties. Researchers also showed that the chemical stability of AEMs can be improved by grafting spacers onto base polymers. The effects of irradiation dose and dose rate on the performance of AEM were discussed. The long-term stability of membrane in alkaline solutions remains the main challenge to commercial use.
Highlights
Modification of Anion-Exchange MembraneA conventional process “polymerization-chloromethylation-amination” is usually employed to prepare anion exchange membrane (AEM) [16]
Are inherently troublesome to shut down/start up, prone to leaking, have a high concentration gradient, and require consistent and stable output conditions
Leveraging on the knowledge of proton exchange membrane (PEM), solid-state anion exchange membrane (AEM), which offers the similar advantages of alkaline liquid fuel cell/electrolyzer, has been proposed as the replacement for liquid electrolyte
Summary
A conventional process “polymerization-chloromethylation-amination” is usually employed to prepare AEMs [16] This process is relatively mature and provides good performance for the membrane. Aside from that, a variety of cationic functional groups have been proposed for AEM applications such as quaternary ammonium, imidazolium, pyridinium, guanidinium, phosphonium and sulfonium [19,20,21,22,23,24,25,26]. AEMs are prepared through three main steps, including the polymerization of halomethyl-substituted monomers, film casting and quaternization to create the cation head group on the polymeric film. On the attempt to improve the thermo-mechanical, chemical stability, and ion conductivity properties of AEMs, various modification methods have been investigated by employing different polymers and reagents. The hydrophilic and rotatable ethylene oxide as spacer has hig affinity due to its tendency to form a hydrogen bond between ether groups and H hydrophilic property has proven to contribute to the water uptake of membrane, may result in dimensional instability of AEMs at an elevated temperature
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