Long-term durability of radiation-grafted PFA-g-PSSA membranes for direct methanol fuel cells

Poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether)-graft-poly(styrene sulfonic acid) (PFA-g-PSSA) membranes were prepared by γ-ray radiation-induced grafting of styrene onto 50μm PFA films and a subsequent sulfonation. The properties of the PFA-g-PSSA membranes such as ion exchange capacity, water uptake, proton conductivity, and methanol permeability were evaluated and compared with commercial Nafion 115 membrane. The characteristic properties and direct methanol fuel cell (DMFC) performances with PFA-g-PSSA membrane were better than that with the Nafion 115 membrane. The power density of the single cell with PFA-PSSA30, PFA-PSSA50, PFA-PSSA80 membranes having different degree of grafting (DOG), and Nafion 115 membranes was 113, 123, 118, and 111mWcm^-2 at 0.4V, respectively. To study the long-term durability of the prepared membrane electrode assembly (MEA) with a PFA-PSSA50 membrane, the single cell was tested for 2066h in a galvanostatic mode under a constant load 150mAcm^-2 and at a temperature of 60°C. The performance loss of the MEA after 2066h operation was about 26.8%. Before and after the long-term performance test, the degradation of MEA with PFA-g-PSSA membrane was investigated by polarization curve technique, electrochemical impedance spectroscopy, TEM, X-ray diffraction, and ion exchange capacity.