Properties and structure of SPEEK proton exchange membrane doped with nanometer CeO2 and treated with high magnetic field

The membranes of sulfonated polyetheretherketone(SPEEK) doped with rare earth metal oxide nanometer cerium oxide (CeO2) were prepared for direct methanol fuel cell (DMFC) application, which was treated by parallel or perpendicular high magnetic field of 6 Teslas (T) at 100°C. The proton conductivity of membrane specimens increased with temperature raised from 20 to 60°C and decreased with increasing CeO2 contents. The proton conductivity of membrane specimens under treatment with high magnetic field was better than that without treatment. The membrane specimens treated with perpendicular magnetic field demonstrated better proton conductivity than those treated with parallel magnetic field. The methanol permeation coefficient of membrane specimens decreased with increasing CeO2 contents and furthermore reduced by about 20% after treated with perpendicular high magnetic field. The water uptake of membrane specimens decreased with CeO2 doping, but would not be influenced by the magnetic field. Fourier transform infrared spectroscopy (FTIR) and small-angle X-ray scattering (SAXS) revealed certain reaction between oxygen anion in sulfonic groups and cerium cation in the CeO2 which dispersed evenly in the membranes but formed small conglomerates as shown by the atomic force microscopy (AFM) images. X-ray diffraction (XRD) proved the stability of the crystal structure of the nanometer CeO2 in polymer membranes, indicating that the reaction occurred only at the interface between SPEEK resin and CeO2 particles.