Maria Geormezi

The interaction of H3PO4 and steam with PBI and TPS polymeric membranes. A TGA and Raman study

Thermogravimetric analysis (TGA) and Raman spectroscopic experiments were carried out in order to study the interaction of H3PO4 and steam with the chemical structure of polybenzimidazole (PBI) and pyridine bearing aromatic polyethers (TPS). The interaction of the polymers with H3PO4 causes a blue Raman shift on the imidazole and the pyridine bands, which is larger for the imidazole ring. It has been found that one H3PO4 molecule is needed to neutralize one imidazole group, while ca. five H3PO4 molecules are necessary for full protonation of the pyridine group. This observation is reflected on the hydration procedure of the imbibed membranes at high temperatures (150–170 °C) as this was studied by TGA. At low acid doping levels (130–150 wt%) the hydrolysis of pyrophosphoric acid into ortho-phosphoric acid is not reversible in the case of PBI, thus indicating that the chemical structure influences the chemical equilibrium of the hydrolysis reaction. The evaporation rate of H3PO4 increases with increasing steam partial pressure and is lower in the case of PBI than in TPS. Nevertheless in all cases the evaporation rate is by a factor of two lower than that of the pure phosphoric acid under the same steam partial pressure.

Influence of the Molecular Structure on the Properties and Fuel Cell Performance of High Temperature Polymer Electrolyte Membranes

High Temperature PEM Fuel Cells (130 C-200 C) offer the distinct advantages over traditional Low Temperature PEMs. Polymeric materials of specific properties should be used as electrolytes for high temperature MEAs in order to withstand the strong conditions during the fuel cell operation. Current research interest focuses on the development of new polymers with tailored basic sites that could improve the acid–base interactions of the membranes in order to acquire high proton conductivity (~10S/cm) at temperatures ranging between 150°C and 200°C Herein we present our approach to the synthesis of monomers and copolymers containing basic groups having high molecular weights, increased solubility and the ability to form complexes with strong acids. Different polymeric structures have been used in order to examine the influence of the detailed polymeric structure on the final membrane properties. It was found that the phosphoric acid doping ability is dramatically influenced by the presence of the polar groups, as well as the detailed copolymer structure. Even small differences on the pyridine content resulted in drastic difference on the phosphoric acid level in some cases as showed in Fig. 1.