High proton conductivity and low fuel crossover polymer electrolyte membranes derived from branched sulfonated poly(ether ether ketone)s and silica sulfonic acid nanoparticles

With the objective of improving water uptake and proton conductivity, silica sulfonic acid (SSA) nanoparticles were successfully prepared via the sulfonation of silica (SiO₂) with sulfuryl chloride and a series of branched sulfonated poly(ether ether ketone) (BSPEEK)-based hybrid membranes with varying contents of SSA were fabricated by the solution-casting method as proton electrolyte materials. The hybrid membranes exhibited improved water uptake, excellent thermal stability, and enhanced mechanical strength. Compared with the methanol permeability, with the incorporation of SSA particles, the proton conductivity enhanced more significantly. The selectivity of the hybrid membranes increased with the increasing SSA contents, and the highest value was 8.2 × 10⁵ S s cm⁻³, which was 2.6 times higher than that of Nafion 117. Therefore, these BSPEEK-SSA hybrid membranes could be considered as promising materials for direct methanol fuel cell applications.