Nafion/Sulfonated Montmorillonite Composite:  A New Concept Electrolyte Membrane for Direct Methanol Fuel Cells

An organic species bearing an organic sulfonic acid (HSO3-) was grafted onto the surface of montmorillonite (MMT) by silane condensation, and the composite membranes were cast together with Nafion. The performance of the Nafion/HSO3−MMT composite membranes for direct methanol fuel cells (DMFCs) was evaluated in terms of methanol permeability, proton conductivity, and cell performance. The methanol permeability of the composite membrane decreased dramatically with increasing content of HSO3−MMT in the composite membrane. By rendering proton conductivity to MMT by functionalization with an organic sulfonic acid, the proton conductivity of the composite membrane was lowered only slightly from that of pristine Nafion 115. The combination of these effects led to a significant improvement in the performance of DMFCs made with Nafion/HSO3−MMT composite membranes.