Random and Triblock Copolymers with Phosphonium Cations for Alkaline Fuel Cells
Block copolymers are expected with highly ordered morphology, which will have interesting influence on the water uptake as well as conductivity performance. In our study, we compare tris(2,4,6-trimethoxyphenyl) phosphonium functionalized AEMs with both triblock (Figure 1. (a)) and random (Figure 1. (b)) backbone structures. The reason investigating on the bulky phosphonium cation is that attaching electron-donating functional groups (2,4,6-trimethoxyphenyl) has been tested beneficial for improvement of the chemical stability based on our previous study.5Besides, based on exploration on water uptakes, morphologies, conductivities and transport properties, Insights on block and random copolymer structures impact on fuel cell performance are developed. A further understanding of correlations between hydration number/morphology and conductivity performance are investigated. In this study, water uptake and hydration number are measured through dynamic vapor sorption (DVS). Conductivities under different relative humidity are performed by electrochemical impedance spectroscopy (EIS). Water transportation is measured by pulsed field gradient NMR (PFGNMR) and anion transportation is calculated via Mitra equation based on conductivity result. Morphologies are obtained from small angle X-ray scattering (SAXS) and atomic force microscopy (AFM).
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