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We have investigated the ion exchange capacity (IEC), water uptake, thermal and chemical stability, mechanical strength, proton conductivity, and the methanol permeability coefficient (PM) in aqueous methanol solutions for cross-linked sulfoethylcellulose (CL-SEC) membranes. The highly swollen CL-SEC membranes exhibit a high proton conductivity (σ) which is comparable to that of Nation® 112. The CL-SEC membranes also show low methanol permeability (PM) in methanol aqueous solutions. The selectivity (σ/PM)-which is a measure of the performance of polymer electrolyte membranes for direct methanol fuel cells- of the CL-SEC membranes increases with increasing the degree of cross-linking as well as the concentration of methanol solution. The value of σ/PM for the highly cross-linked membranes is at least 5 times higher than that of Nation® 112 for the methanol solutions with the concentrations of more than 1 M. The results suggest that the CL-SEC membranes are potentially applicable to polymer electrolyte membranes for direct methanol fuel cells utilizing a high concentration methanol solution as a fuel. [ABSTRACT FROM AUTHOR]

We have investigated the proton conductivity, solvent uptake, and the methanol permeability coefficient (PM) in aqueous methanol solutions of the cellulose sulfate (CS) electrolyte membranes which were prepared by sulfating regenerated cellulose membranes. The proton conductivity of the CS membranes is enhanced with increasing number of sulfate groups. Solvent uptake and PM for the CS membranes are almost independent of methanol content, and the CS membranes with higher solvent uptake show higher PM. The introduction of cross-linkage into the CS membranes not only enhances the proton conductivity but also decreases the methanol permeability because of a considerable reduction in solvent uptake. The cross-linked CS membranes exhibit a proton conductivity of 0.081 S cm-1 at room temperature, which is comparable to that of Nation 112®. The methanol permeability measured by using a 3 M methanol solution is less than half, compared with Nation 112®. [ABSTRACT FROM AUTHOR]

Alginate sulfate (AS) electrolyte membranes were prepared by sulfating sodium alginate. We have investigated the influence of the degree of substitution (DS) of sulfate groups on proton conductivity, solvent uptake in aqueous methanol solutions, and the methanol permeability coefficient (PM). DS increases with increasing molar ratio of sulfur trioxide pyridine complex (SO3 · Py) used for sulfation. Excessive DS leads to the dissolution of the AS membranes in water. The proton conductivity of the AS membranes is enhanced by increasing DS. The solvent uptake of the AS membranes decreases with increasing the methanol concentration, whereas PM is almost independent. The AS membranes show lower methanol permeability than Nafion 112® at high methanol concentrations. This is probably because the hydrophilic groups in the AS membranes are strongly hydrated with water. The introduction of cross-links into the AS membranes results in a reduction of the solvent uptake as well as PM. [ABSTRACT FROM AUTHOR]