Ex-situ NMR and Raman studies of H3PO4 and H2O uptake of polybenzimidazole membrane for PEMFC

: Polybenzimidazole (PBI) doped with H3PO4 is the most commonly used membrane mate-rial for high-temperature polymer fuel cells. Despite this fact, only less is known on the chemical equilibria of all species inside the membrane as a function of the com¬position of the ternary system PBI - H3PO4 - H2O. This in¬clu¬des details on the proton transfer pro¬ces-ses, on the dominant conduc¬tion me¬cha¬nisms and on the con¬densation equilibria, lea-ding to the formation of di¬phos¬pho¬ric acid and higher homo¬logues species. In this study Raman and NMR spectroscopy is used to in¬vestigate the chemical inter¬ac-tions between H3PO4, H2O and PBI vs. the H3PO4 doping level. We could ob¬tain in¬forma-tion on the H-bond formation between H3PO4 and the polymer chains, on tauto¬me¬ric pro-ces¬ses as well as on the presence of not directly bounded H3PO4 at high do¬ping levels [1,2]. Investigations were performed with uncrosslinked and cross¬linked m-PBI and AB-PBI. [1] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, and D. Stolten, Phys. Chem. Chem. Phys. 14, 10022-10026 (2012) [2] F. Conti, S. Willbold, S. Mammi, C. Korte, W. Lehnert, and D. Stolten, New J. Chem. 37, 152-156 (2013)