Dielectric relaxations and conductivity of cross-linked PVA/SSA/GO composite membranes for fuel cells
Composite membranes obtained from Poly(vinyl Alcohol) (PVA) with sulfosuccinic acid (SSA) as crosslinking agent, and two different proportions of graphene oxide (GO), were prepared to be used in Proton Exchange Membrane Fuel Cells (PEMFCs). The superficial micrographs from transmission electron microscopy (TEM) confirmed a good dispersion of GO. Fourier Transform Infrared spectroscopy (FTIR) was used to evaluate the final chemical structure. Differential Scanning Calorimetry (DSC) showed that glass transition and crystalline phase were not present in the cross-linked PVA/SSA/GO composites membranes. Thermogravimetric analysis (TGA) demonstrated that the addition of GO reduced the moisture content and increased the thermal stability of the membranes. The electrical properties of PVA/SSA and PVA/SSA/GO composite membranes and the effect of GO concentration were evaluated by means of dielectric spectra in a broad range of temperatures and frequencies. The dielectric permittivity of these membranes was significantly promoted at low filler concentration due to an interfacial polarization effect. From the analysis of the dielectric relaxation spectrum, it can be deduced that the origin of the associated molecular movements is intramolecular and occurs in the working range of the PMEFC. In addition, the direct current conductivity, the protonic conductivity, and the polarization currents were correlated to the power produced in a hydrogen monocell. It was observed that low and no high GO concentrations of filler in PVA/SSA composite membranes enhanced their performance. The systematic characterization procedure based on the study of dielectric spectra and conductivity allowed to establish a potential approach to control the addition of GO in the design of other composite membranes for PEMFC with improved properties.