Synthesis and evaluation of all-block-sulfonated copolymers as proton exchange membranes for fuel cell application

A new series of all-block-sulfonated copolymers were prepared as proton exchange membrane (PEM) materials. The backbone of these block copolymers consisted of poly(ether ether ketone) (PEEK) and polybutadiene (PB) chains. Sulfonate groups were successfully introduced into all blocks by two sulfonation methods. sPEEK-b-sPB exhibited good thermal stability and could be cast into transparent, tough and flexible membranes. Due to the sulfonation of all blocks, the mechanical properties of membranes were largely enhanced and could be controlled by the sulfonation level. TEM images showed spherical ionic domains and large ionic aggregates in membranes. Ionic channels and networks formed by the connected sulfonate groups in PB chains were observed as well. The proton conductivity was also improved because of the sulfonated PEEK segments. The above results demonstrated all-block-sulfonated copolymers could be one prospective choice in PEM fuel cell applications.