Polymer electrolyte membranes (PEMs) consisting of a proton-conducting hydrophilic phase and a mechanically-strong structural phase are attractive due to their potential in clean energy applications. Herein we demonstrate a new strategy of fabricating block copolymer electrolyte membranes, specifically, by blending and extracting sacrificial homopolymer into and from block copolymer to induce voids, followed by sulfonation. The morphology of these membranes was studied with in situ small angle X-ray scattering (SAXS) and cryo- scanning transmission electron microscopy (STEM) and the relationship between morphology and water uptake was established. We show clear, direct evidence of the formation of water channels in PEMs. We found that there is non-homogeneous distribution of water in the hydrophilic domains even when the membrane is fully hydrated. By tuning the porosity of the membranes, the water uptake can be optimized for improved proton conductivities, in both humid air and liquid water. Furthermore, we discovered that the presence of voids also improved the dimensional stability membranes; i.e., they are more resistant to swelling.

Nanoporous block copolymer electrolyte membranes for proton transport

248th National Meeting (2014)

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