Publication date: 31st July 2014
As an ongoing project on inexpensive, clean sources of energy, our research team is focusing its efforts to develop low-cost and non-perfluorinated alternative polymer electrolyte membranes for fuel cells (PFCs). To overcome the deficiencies of the membranes widely used as a proton exchange membrane (PEMs) we are using the approach of nanostructured polymer composites to meet the requirements of higher proton conductivity, lack of volumetric size change, and membrane-electrode assembly construction capabilities. We are studying cross-linked polymer/ceramic nanofiller composites, hybrid material obtained by adding a self-assembled molecular monolayer on a polymer film or adding well dispersed nanofibers of nanotubes of selected new nanophases to the polymer matrix. We have started preparing acids/polyvinyl alcohol (-(-CH2-CH(OH))n-) precursor membranes with various degree of polymerization and saponification, and several molar ratios of polyvinyl alcohol monomeric units to acid component. They have been reinforced with nanoparticles of various oxides. We have also prepared cross-linked acid-PVA/TiO2 nanocomposite polymer using a chemical agent based, for example, in glutaraldehyde (CHO(CH2)3CHO), for the cross-linking reaction. A preparation route based on electro-spinning techniques is allowing us to achieve well defined geometry of the active nanophases in the membranes (i.e., nanopores and nanofibers) .We are quantitatively determining how much dispersed are the nanophases on a molecular scale and aligned in the PVOH matrix and if there exist strong interfacial interactions between both components mainly by hydrogen bonding. The membranes are characterized by their mass transport and the ionic conductivity properties of polymer at different temperature and frequency values and infer their potential utility as a solid acid membrane in solid state batteries or fuel cell. Their electrochemical properties of the membranes are also evaluated in a fuel cell performance. Stress-strain measurements at constant strain rate are performed in the operating temperature range, finding a relationship between the membranes thermal and mechanical properties. Results indicate that their mechanical and proton transport properties are directly linked to a two-phase structure, where, for example, liquid-like H3PO2/H2O clusters expand to hold water molecules during swelling, whereas the solid–like polymer backbone maintains the structural stability. The electrical response of the membranes show power-law dispersive conductivity with frequency as a consequence of proton migration. This approach allow to study the effect of nanoparticles and nanosize structural elements on enhancing cooperative correlation among moving ions.
Keywords: Nanoenergy, nanoionics, polymer nanocomposites, electrochemical energy conversion.
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