Poly(vinyl alcohol)/sulfated β-cyclodextrin for direct methanol fuel cell applications

We report a composite membrane based on poly(vinyl alcohol) and sulfated β-cyclodextrin in this paper. TGA and SEM tests provide direct evidence of the thermal stability and the uniform structure of the composite membranes. The performances of the composite membranes are investigated in terms of swelling behavior, methanol permeability and proton conductivity as function of sulfated β-cyclodextrin content. We find that the introduction of sulfated β-cyclodextrin can reduce water uptake. The temperature dependence of proton conductivity reveals that the proton conducting activation energy of the composite membranes is similar to that of Nafion 115, in other words, both the vehicle and Grotthus mechanisms are assumed to be responsible for the composite membranes’ proton transfer. Methanol permeability decreases as the methanol feed concentration increases from 2 M to 20 M. Both proton conductivity and methanol permeability increases with increasing sulfated β-cyclodextrin. The selectivity of the composite membranes defined as the ratio of proton conductivity to methanol permeability obtains the maximum of 1.710 × 104 S s cm−3 at the composition of 17 wt.% sulfated β-cyclodextrin. The MEAs fabricate with these membranes are tested, no distinct change occurred to the composite membranes after the MEAs operating for 288 h. These data indicates the chemical and electrochemical stability of the membranes and their potential application in direct methanol fuel cells.