Morphology of Elastomeric Anion Exchange Membranes: A Dissipative Particle Dynamics Study

Abstract

The design and optimization of stable and highly conductive anion exchange membranes (AEMs) is essential to the development of energy and conversion technologies.1 , 2 There has been an increased interest and research to address the low stability and ionic conductivity of polymeric AEMs. However, a fundamental understanding of stability and transport in AEMs is still in its infancy3 and the effects of the choice of the cationic functional group and polymer architecture are still not known. Recently developed elastomeric AEMs4 exhibiting satisfactory chemical stability are investigated in this study. These AEMs are based on the elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS), that are functionalized with various cationic groups. Dissipative particle dynamics (DPD) is a meso-scale simulation technique5 , 6 which enables the simulation of large time- and length-scales with reasonable computational expense has been selected to investigate the morphology and dynamical behavior of such systems. The system of hydrated AEM is coarse-grained to a degree that the consideration of both chemical distinction and fine structural variants are satisfied. The structures of the DPD beads were optimized using first principles electronic structure calculations and the interaction parameters were determined using a recently developed methodology.7 The effects of several microstructural parameters including the length of the tether chains, type of the cationic group (trimethylammonium [(CH3)3NH]+; dimethylimidazolium [DMIm+]; and triphenylphosphonium [(C6H5)3PH]+ ), and the polymer architecture on the morphology and transport of anions in the aforementioned elastomeric AEMs were investigated. The effect of water content in the membrane and the effect of ion exchange capacity (IEC) were also studied. The results are compared with the widely studied proton exchange membrane Nafion.