Surface modification of expanded polytetrafluoroethylene to reinforced composite membranes for proton exchange membrane fuel cells

The study reports on the fabrication of reinforced composite membranes via hydrophilic surface modification of highly hydrophobic and porous expanded polytetrafluoroethylene (ePTFE) using argon plasma treatment and silane coupling. These processes create amine end group, functionalized onto ePTFE surface, thus improving hydrophilicity. It enables impregnation of Nafion ionomer dissolved in a polar aprotic solvent as well as water/alcohol mixture solvent. The optimal silane coupling concentration is systematically determined and facilitates uniform grafting of amine-functionalized silane without the pore blockage of ePTFE. The resulting reinforced composite membranes show improved mechanical, chemical, and dimensional stabilities and comparable proton conductivity. However, their membrane ohmic resistance is slightly higher than that of a commercial Nafion membrane (N211), leading to slightly reduced fuel cell performance. Note, the processes of this study prove versatile, accommodating partially fluorinated polymers in aprotic polar solvents with ePTFE, holding its potential for creating alternative reinforced composite.