PROTON EXCHANGE SULFONATED POLY(ETHER ETHER KETONE)/FUNCTIONALIZED SILICA COMPOSITE MEMBRANES IN DMFCs

The present paper focuses on improving the water-holding ability of sulfonated poly (ether ether ketone) (SPEEK) (degree of sulfonation, DS = 55.1%) membranes. Functionalized silica (silica sol (SiO2) and silica powder with sulfonic acid groups (SiOx-S)) were chosen as the hygroscopic additive, respectively. SPEEK/SiO2, SPEEK/SiOx-S composite membranes were obtained by casting a homogeneous mixture of SiO2 (or SiOx-S) and SPEEK in N,N-dimethylacetamide onto glass plate and then evaporating the solvent at 60 degrees C. The decrease in both the swelling degree and the methanol permeability and the improvement in the conductivity at a high temperature and a low humidity of the membranes were a dose-dependent result of addition of the SiO2 and SiOx-S powders. Pure SPEEK membranes swelled 52.6% at 80 degrees C, whereas the SPEEK/SiO2 (15 wt%) and SPEEK/SiOx-S (15 wt%) membranes swelled only 26.2% and 27.3% at the same temperature, respectively. From room temperature to 80 degrees C, SPEEK/SiO2 (20 wt%) and SPEEK/SiOx-S (20 wt%) membranes had methanol permeability of about two order of magnitude lower than that of Nafion (R) 115. At 120 degrees C and 40% relative humidity (RH), the conductivity of pure SPEEK membranes is only 2.6 X 10(-4) S.cm(-1), and that of SPEEK/SiO2 (20 wt%) membranes is about 2.0 x 10(-3) S.cm(-1), while that of SPEEK/SiOx-S (20 wt%) composite membranes reaches 1.0 x 10(-2) S.Cm-1, which is close to that of Nafion (R) 115. DMFCs single cell performance of SPEEK/SiO2 (20 wt%) and SPEEK/SiOx-S (20 wt%) membranes was better than that of pure SPEEK membranes because they had good dimensional stability and no separation of catalyzers and membranes in membrane electrode assembles.