Preparation Of SPPESK/PWA And Its Surface-Modified Composite Proton Exchange Membranes

Proton Exchange Membrane (PEM) is one of the key components of proton exchange membrane fuel cell. Though commercial Nafion membrane has high chemical stability, its high cost, high fuel permeability and dramatically reduced proton conductivity at high temperature make it unable to satisfy the demands of operation under high temperature and low humidity. Sulfonated poly (phthalazinone ether sulfone ketone)(SPPESK) is a kind of non-fluorinated sulfonic acid membrane material with good swelling resistance and low methanol permeability. However, the proton conductivity of SPPESK needs further improvement compared with other sulfonated materials about the same sulfonation degree.Organic-inorganic modification is an effective method to improve the comprehensive performance of membrane. In this work, SPPESK/PWA hybrid membranes were prepared by blending SPPESK with highly-conductive and highly-stable inorganic solid phosphotungstic acid (PWA) to increase the proton conductivity. SPPESK/PWA-PANI(PPy) composite membranes were fabricated with further surface polymerization on hybrid membrane. PWA was effectively immobilized in the composite membranes with less decrease in proton conductivity. Meanwhile, the swelling resistance and mechanics were enhanced.In order to increase the proton conductivity of SPPESK membrane, we prepared a series of SPPESK/PWA organic-inorganic hybrid membranes with different PWA contents blending in SPPESK. As for hybrid membrane with a5:5content ratio of PWA to SPPESK, the water uptake is up to185%-192%,1.5times higher than SPPESK membrane; the proton conductivity is0.085S/cm at20℃,1.5times higher than SPPESK membrane and close to the value of SPPESK membrane at90℃; but the weight loss ratio is6.96%after immersed in water for20days, higher than SPPESK membrane.In order to limit the loss of PWA, SPPESK/PWA-PANI composite membranes were fabricated by surface polymerization with aniline. The swelling ratio decreased a lot while proton conductivity decreased a little. As for composite membrane with five-time polymerization, the swelling ratio is only13%which is1/3of hybrid membrane; the proton conductivity is0.133S/cm, lower than hybrid membrane but28%higher than SPPESK membrane; the weight loss ratio is0.32%, one order magnitude lower than hybrid membrane (5.39%) and the value is20.38%,42%lower than hybrid membrane when immersed under high temperature. As the loss of PWA under high temperature needs to be further restricted, SPPESK/PWA-PPy composite membranes were prepared by surface polymerization with pyrrole. Similar to PANI membrane, the swelling ratio decreased a lot and proton conductivity decreased a little, but the weight loss ratio declined dramatically. As for composite membrane with five-time polymerization, the swelling ratio is only16%which is41%of hybrid membrane; the proton conductivity is0.113S/cm, lower than hybrid membrane but still higher than SPPESK membrane; the weight loss ratio is0.26%which is close to SPPESK membrane, and the value is9.51%when immersed under high temperature, only1/4of hybrid membrane and53%lower than SPPESK/PWA-PANI-5membrane; the tensile strength is33.48MPa,13%higher than hybrid membrane,68%higher than SPPESK/PWA-PANI-5membrane and reaches three times of SPPESK membrane.