Abstract
Many electrochemical processes for energy conversion are more facile in base than in acid. But, there are no good commercial anion exchange membranes (AEM), that are chemically stable, have dimensional stability in water, and still have high ion conductivities resulting in reasonable area specific resistances as thin films. In collaboration with the University of Massachusetts, Amherst we have developed an innovative polymer system that can be tuned for almost any application needing an AEM in electrochemical engineering. The material is a symmetrical ABA triblock polymer with a facile synthesis amenable to large-scale production. The A blocks are the ridged ion conducting hydrophilic blocks and are derived from polymethylchlorostyrene (PCMS) and functionalized with next generation C6 ring cations that give the polymers some of the highest know chemical stability so far observed. Here we functionalize the materials via quaternization of the PCMS with methylpyrrolidinium (MPRD) cations. We can process the A block to control swelling. In addition we can easily achieve ion exchange capacities >2.0meq g-1 which leads to phase separated materials with ionic conductivities > 0.1 S cm-1. The material phase separates into a short range lamella morphology as confirmed by TEM and SAXS. The B block is based on cycloctene or cycloctadiene and is designed to be very soft, so soft in fact that it melts at 50°C. The mechanical properties of the B block are then easily tuned by careful control of a photocrosslinking chemistry involving a dithiol. Through control of the A and B block lengths and the cross-linking steps we can achieve AEMs that can be as little as 10 μm in thickness with some of the highest ionic conductivity, chemical stability, control of swelling, and device ready mechanical properties. Because the material is solvent castable it also makes an excellent starting point to develop ionomers for the electrodes in fuel cells and other devices. We are supplying the material to ProtonOnSite for testing in electrolysis devices, the Army Research Laboratory for testing in fuel cells and JCESR for testing in redox flow batteries, and we will present the results of these studies and discuss the path forward to making our material device ready.
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