Sulfonic Acid-Functionalized Hybrid Proton Exchange Membranes Synthesized By Sol-Gel for Direct Methanol Fuel Cells

Organic/inorganic hybrid membranes based on (3-glycidoxypropyl) trimethoxysilane (GPTMS) and 3-mercaptopropyl trimethoxysilkane (MPTMS) have been prepared by sol-gel method and organic polymerisation, as candidate materials for proton exchange membranes in direct alcohol fuel cell (DMFC) applications. The –SH groups of MPTMS are oxidized to sulfonic acid groups, which are attributed to enhance the proton conductivity of hybrid membranes. FTIR, Raman and XPS were used to characterize and confirm the hybrid structure and oxidation reaction progress. Membranes characterization includes ion exchange capacity, water uptake, methanol permeability and proton conductivity to confirm their applicability in fuel cells. All the membranes were homogeneous thermally and chemically strong. In particular, our hybrid membranes demonstrated proton conductivities as high as 0.03 S/cm, at high temperature, while exhibiting high methanol permeability as compared to Nafion®. These results show that this kind of hybrid membranes possess high proton conductivity and a high barrier to methanol permeation due to the proton conducting path through the silica pseudo-PEO network in which sulfonic acid groups work as proton donor. Collectively, our results indicate that crosslinked MPTMS-GPTMS oxidized hybrid membranes offer great potential for use as PEMs in DMFC applications.