Preparation And Properties Of Composite Sulfonated Poly(Aryl Ether Ketone Sulfone) Proton Exchange Membranes

Proton exchange membrane fuel cells are popular as energy conversion devices with high energy conversion efficiency, high power density and low pollution. Proton exchange membranes not only transfer protons but also isolate the oxidant and fuel as the key components of PEMFCs. The proton conductivity of the commercially available PEMs for PEMFCs(e.g, Nafion?) sharply decreases above 80 ?C due to the severe water loss. Thus, we developed two kinds of composite membranes to improve proton conductivity at medium-high temperature or low relative humidity.Sulfonated poly(arylene ether ketone sulfone) containing pendant amino groups(AmSPAEKS)/phosphotungstic acid(HPW) composite membranes with different HPW content were prepared by the solution blend method as proton exchange membrane(PEM) for proton exchange membrane fuel cells(PEMFCs) operation at medium-high temperature. FT-IR showed that there was acid-base interaction between the amino groups and HPW, as well as HPW and the sulfonic groups. These interactions could stabilized HPW in composite membranes which was confirmed by SEM images. The water uptake and thermal stability of the composite membranes were improved compared with the Am-SPAEKS membranes. The water retention capacity and the mechanical property of the composite membranes also met the requirement of proton exchange membranes. The proton conductivity of the AmSPAEKS/HPW30% composite membranes reached to 0.091 S cm-1 at 120 ?C. These results indicated that the composite membranes had higher proton conductivity at medium-high temperature conditions.A series of sulfonated poly(aryl ether ketone sulfone)/poly(vinylidene fluoride) phosphotungstic acid(SPAEKS/PVDF-HPW) composite membranes were prepared and characterized by FT-IR. No phase separation was observed by scanning electron microscopy. The HPW particles are evenly dispersed in the membranes, probably because the microporous structure of PVDF stabilized the dispersion of HPW particles in the membranes. Thermogravimetric analysis showed that the thermal stability of the membranes increased with increase in HPW content. Moreover, the composite membranes exhibited outstanding oxidative stability. The methanol permeability coefficient of the SPAEKS/PVDF-HPW10% membrane at 20 ?C was 1.68×10-7 cm2 s–1, and the highest proton conductivity of the membrane at 80 ?C was 0.098 S cm-1, slightly lower than that of Nafion? 117. However, the relative selectivity of the membrane was higher than that of Nafion? 117. The swelling ratio of the membrane at 80 ?C was 16%, and the methanol uptake of the membrane at room temperature was only 10.2%, much lower than those of Nafion? 117. The results indicate that the SPAEKS/PVDF-HPW membranes can be used as an alternative proton exchange membrane for direct-methanol fuel cells(DMFCs).