Preparation and Electrochemical Properties of Alginate Sulfate Electrolyte Membranes.

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 (P_M). 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 P_M 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 P_M. [ABSTRACT FROM AUTHOR]