Effects of micro-phase-separated structures on proton conductivity and methanol permeability in polymer electrolyte membranes

The effects of micro-phase-separated structures in hydrocarbon-based polymer electrolyte membrane on its proton conductivity and methanol permeability were investigated to obtain a membrane with high proton conductivity and low methanol permeability. Membrane with low methanol permeability had low water content, which indicates that methanol permeated through swollen areas in the membranes. Membranes with gyroid-like structure exhibited high proton conductivity and low methanol permeability. These results indicate that continuous hydrophilic domains functioned as proton paths, therefore higher proton conductivities were shown in the structures, in which continuous hydrophobic domains existed. In contrast, continuous hydrophobic domains played a role as frameworks that prevented membranes from swelling due to water and lower methanol permeability coefficients were found in structures, in which continuous hydrophilic domains existed. Therefore, we can conclude that the most suitable structures obtaining high proton conductivities and low methanol permeability were the gyroid-like structure.