M. Luisa Di Vona

Analysis of Temperature-Promoted and Solvent-Assisted Cross-Linking in Sulfonated Poly(ether ether ketone) (SPEEK) Proton-Conducting Membranes

Sulfonated poly(ether ether ketone) (SPEEK) membranes were thermally treated at temperatures between 120 and 160 degrees C. Water uptake measured at different relative humidity values or by full immersion in water between 25 and 145 degrees C was found to depend very strongly on previous thermal treatment and casting solvent. Water-uptake coefficient values as low as 10-15 even upon immersion in water at 100 degrees C were obtained with membranes treated at 160 degrees C. This effect is related to cross-linking by SO2 bridges between macromolecular chains. An important role is also played by the casting solvent: among the investigated solvents, dimethylsulfoxide (DMSO) gave the best results. A chemical kinetics model is outlined that permits the estimation of the relevant kinetic parameters, especially the activation energy of the cross-linking reaction, which was found to be about 60 kJ/mol. These results are of significant importance for the improvement of proton-exchange membrane fuel cells.

Sulfonated Polyether Ether Ketone-Based Composite Membranes Doped with a Tungsten-Based Inorganic Proton Conductor for Fuel Cell Applications

Sulfonated polyether ether ketone (SPEEK)-based composite membranes doped with hydrated tungsten oxide were prepared and studied for proton exchange membrane applications. Hydrated tungsten oxide (W O3 ·2 H2 O) was synthesized via acidic hydrolysis of sodium tungstate and its structure and physicochemical features were investigated by thermogravimetric analysis (TG), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). SPEEK/ W O3 ·2 H2 O composite membranes were prepared by mixing proper amounts of SPEEK and hydrated W O3 in dimethylacetamide as casting solvent. The composite membranes were characterized by XRD, TG-DTA, EIS, and water uptake measurements as a function of the oxide content in the membrane. In particular, XRD patterns as well as TG measurements indicated the existence of a coordinative interaction between the water molecules of tungsten oxide and the SPEEK sulfonic acid groups. This interaction lead to the enhancement of the membrane proton conductivity, as well as of their properties, from the point of view of heat resistance and water solubility. In fact, the addition of tungsten oxide resulted in higher proton conductivity, improved heat resistance, and lower water solubility.

Ormosil/Sulfonated Polyetheretherketone-Based Hybrid Composite Proton Conducting Membranes

A modified silane bearing a sulfonic acid function (sulfonated diphenylsilanediole, SDPSD) was prepared and characterized. The resulting ormosil was mixed with sulfonated polyetheretherketone (SPEEK) with high degree of sulfonation (0.9) leading to homogeneous composite membranes. The formation of the composite substantially modified the properties of SPEEK in terms of water uptake and solubility. The structural and electrochemical performance of the components and of the composite were investigated with thermogravimetric analysis, field emission scanning electron microscopy, H-1 and Si-29 nuclear magnetic resonance, both in solution and in the solid state, and electrochemical impedance spectroscopy. Both conductivity values, as high as 0.1 S cm(-1), and H-1 diffusion coefficients of the composite SPEEK/SDPSD demonstrated that it possesses good proton transport characteristics up to 120 S C, and it is then suitable for application as an electrolyte in polymer electrolyte fuel cells operating at intermediate temperature