Semi-crystalline sulfonated poly(ether ketone) proton exchange membranes: The trade-off of facile synthesis and performance

Improving the performance of proton exchange membranes (PEMs) through the synthesis of sulfonated polymers with elaborate molecular structures has received extensive approval. However, the tedious synthetic process and consequently high costs restrain their possible substitution for Nafion, a classic PEM material. Herein, a series of semi-crystalline sulfonated poly(ether ketone)s with fluorene-based units were prepared via direct copolymerization of commercially available monomers and followed post-sulfonation, namely SPEK-FD-x, where × represents the molar ratio of the fluorene-containing monomer to the employed bisphenol monomers. The entire synthetic pathway was facile without involving hardly accessible materials. Subsequently, various properties of SPEK-FD-x membranes were investigated and further compared with Nafion 117. Due to the formation of the well-defined hydrophilic-hydrophobic microphase separation morphology and the reinforcement of the PEK crystalline regions, the SPEK-FD-x membranes exhibited outstanding proton conductivity, resistance for methanol permeation, as well as dimensional, thermal, oxidative, and mechanical stability. Among them, the overall behavior of the SPEK-FD-25 membrane was comparable to or even greater than that of Nafion 117, most importantly, it also performed decently in both H2/air fuel cells and direct methanol fuel cells. Therefore, with the straightforward synthesis and superior performance, the SPEK-FD-x membranes may serve as a promising alternative to Nafion.