Abstract
This review highlights advancements made in anion exchange membrane (AEM) head groups, polymer structures and membrane synthesis methods. Limitations of current analytical techniques for characterizing AEMs are also discussed. AEM research is primarily driven by the need to develop suitable AEMs for the high-pH and high-temperature environments in anion exchange membrane fuel cells and anion exchange membrane water electrolysis applications. AEM head groups can be broadly classified as nitrogen based (e.g. quaternary ammonium), nitrogen free (e.g. phosphonium) and metal cations (e.g. ruthenium). Metal cation head groups show great promise for AEM due to their high stability and high valency. Through “rational polymer architecture”, it is possible to synthesize AEMs with ion channels and improved chemical stability. Heterogeneous membranes using porous supports or inorganic nanoparticles show great promise due to the ability to tune membrane characteristics based on the ratio of polymer to porous support or nanoparticles. Future research should investigate consolidating advancements in AEM head groups with an optimized polymer structure in heterogeneous membranes to bring together the valuable characteristics gained from using head groups with improved chemical stability, with the benefits of a polymer structure with ion channels and improved membrane properties from using a porous support or nanoparticles.
Highlights
Ion exchange membranes (IEM) are semi-permeable membranes composed of ionic head groups attached to polymer matrices [1]
anion exchange membranes (AEM) research is driven by the need to develop anion exchange membranes (AAEMs) for fuel cells and water electrolysis applications since presently there are no suitable AAEMs which can stably operate in the high-pH and hightemperature environments of anion exchange membrane fuel cells (AEMFC)/anion exchange membrane water electrolysis (AEMWE)
AEMFC/AEMWE are a promising source of clean energy and have several operational benefits compared to PEMFC/PEMWE, mainly in that catalysts can be platinum free
Summary
Ion exchange membranes (IEM) are semi-permeable membranes composed of ionic head groups attached to polymer matrices [1]. This technique combines the beneficial characteristics of the polymer (high ion conductivity) and porous support (mechanical strength and reduced membrane swelling) to produce membranes with improved performance [100] While this method may involve repeated pouring and immersion steps, the literature sources have reported the ability to obtain both cation and anion exchange membranes with high IEC [97, 98, 101]. Heterogeneous membranes synthesized using porous supports or inorganic nanoparticles are promising methodologies to achieve AEM with high IEC without compromising mechanical strength This methodology still uses volatile organic solvents, which suggests further research is needed to develop IEM synthesis pathways that can minimize harsh solvent usage. By stretching membrane samples in a universal testing machine, various physical properties like tensile strength, stress–strain curves and elongation at break can be determined [103, 116, 125]
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