Sulfonated poly(etheretherketone) and sulfonated polyvinylidene fluoride-co-hexafluoropropylene based blend proton exchange membranes for direct methanol fuel cell applications

Abstract

In this work, blend membranes based on sulfonated poly(etheretherketone) (SPEEK) and sulfonated polyvinylidene fluoride-co-hexafluoropropylene (SPVDF-co-HFP) with a 10 wt% concentration of a polymer blend in solution were prepared by a solution casting method. The PEEK and PVDF-co-HFP were sulfonated with a direct sulfonation method to reach sulfonation degrees of 68% and 31%, respectively. The different weight ratios of the blend polymers were synthesized and a weight ratio of 20 wt% PVDF-co-HFP and SPVDF-co-HFP exhibited the best properties in terms of a few essential membrane properties such as membrane swelling, liquid uptake, thermal and mechanical stability, methanol permeability, proton conductivity and DMFC performance. The prepared blend membranes presented excellent swelling and methanol barrier properties while the proton conductivities were acceptable. Also, the effect of the casting solvent on the morphology and properties of the prepared membranes was investigated. The membranes cast on N-methyl-2-pyrrolidone (NMP) showed the best results compared to the others. The SPEEK/SPVDF-co-HFP blend membrane cast in NMP had good interaction and showed the highest proton conductivity of 35.7 S cm⁻¹ for 10 wt% SPVDF-co-HFP and the highest power density of 43.02 mW cm⁻² for 20 wt% SPVDF-co-HFP, among all of the prepared membranes, at room temperature.