Nafion, sulfated cyclodextrin, pore size distribution, proton conductivity
Direct methanol fuel cells are promising candidates for portable power sources and transport applications. One of the critical problems hindering the commercialization of DMFCs is high methanol permeation rate across proton-exchange membranes. In this study, in order to block the methanol transport through proton-exchange membranes while maintaining high proton conductivity, one approach is attempted; prepartion of Nafion/sulfated cyclodextrin (s-CD) composite membranes providing tortuous pathway of methanol and increase of reactive sites. With respect to the importance of pore size distribution of ionic cluster for Nafion membranes, the main objective is to characterize the pore size distribution of ionic clusters for composite membranes with various s-CD contents by combining NMR cryoporometry and SAXS measurements. The water uptake of composite membranes increased from 21.4% (IEC = 0.89 meq/g for pure Nafion) to 24.4% (IEC = 0.96 meq/g for 95wtNafion/5wt%s-CD) with increases in the s-CD content . From NMR cryoporometry results, it was found that the cluster size gradually increased with increase of the amount of s-CD, which is in good agreement with the results obtained by SAXS measurements. ). From ac impedance analyzer, it was shown that as the amount of s-CD in the membranes increased, the proton conductivity inreased.