Functionalizing Biomaterials to Be an Efficient Proton-Exchange Membrane and Methanol Barrier for DMFCs

Biobased materials capable of transforming into selective proton-exchange composite membranes (PEMs) are highly favored for use in direct methanol fuel cells (DMFCs) because of their low cost and abundance. Here, a polysaccharide and a clay have been functionalized together to make a highly proton selective PEM. Use of chitosan and clay composites ensured limited methanol crossover and thereby high measured performance via efficient fuel convertibility. In this study, sulfonated natural nanocomposite PEMs made of chitosan and sodium–montmorillonite (CS-MMT) were characterized for their water swelling, proton conductivity and methanol permeability parameters. The CS-MMT membrane with a proton conductivity of 4.92 × 10–2 S cm–1 and a power density of 45 mW/cm2 showed a measured methanol crossover current density (J) of <100 mA/cm2. For higher methanol concentrations (4, 6 and 8 M), fuel loss was ∼4 times less in comparison with commercially successful PEMs, such as Nafion 117.