Novel branched sulfonated poly(ether ether ketone)s membranes for direct methanol fuel cells

•Br-SPEEK were obtained via two-step polymerization.•The polymer exhibited higher degree of branching values.•The membrane showed improved mechanical strength, excellent dimensional stability.

In this article, novel branched sulfonated poly(ether ether ketone)s (Br-SPEEK) containing various amounts of 1,3,5-tris(4-fluorobenzoyl)benzene as the branching agent have been successfully prepared. Compared with the traditional linear polymer membranes, the membranes prepared by Br-SPEEK showed improved mechanical strength, excellent dimensional stability and superior oxidative stability with similar proton conductivity. Notably, the Br-SPEEK-10 membrane began to break after 267 min in Fenton's reagent at 80 °C, which was 4 times longer than that of the L-SPEEK. Although the proton conductivity decreased with the addition of the branching agent, satisfying methanol permeability value was observed (down to 6.3 × 10−7 cm2 s−1), which was much lower than Nafion 117 (15.5 × 10−7 cm2 s−1). All the results indicated that the novel branched sulfonated poly(ether ether ketone)s membrane was potential candidate as proton conductive membranes for application in fuel cells.