Raman and NMR study of the interaction Polybenzimidazole – Phosphoric acid in membranes for fuel cells

One fundamental component of a fuel cell is the electrolyte, which separates the electrocatalytic active sites of the two electrode configurations. Phosphoric acid-doped poly(2,2’-(m-phenylene)-5,5’-bibenzimidazole) (PBI) polymers have been studied as membrane materials for the use in High Temperature Polymer Electrolyte Fuel Cells (HT-PEFC), since they can be used at temperatures as high as 200 °C without humidification. Among the many possible PBI derivatives, a very promising material is poly(2,5-benzimidazole) (AB-PBI) [1] In the present study, we report on FT-Raman and NMR investigations of AB-PBI and PBI polymer membranes doped with various concentrations of ortho-phosphoric acid. Characteristic Raman and 1D- and 2D-NMR spectra with diagnostic signals have been studied. [2, 3] Ab-initio calculations were carried out using density functional theory methods to analyse the Raman data. The information is of fundamental importance in order to elucidate the role of phosphoric acid in the conductivity mechanism of membranes based on polybenzimidazole. [1] J.N. Asensio, E.M. Sánchez and P.Gómez- Romero, Chem. Soc. Rev.39 (2010) 3210. [2] F. Conti, A. Majerus, V. Di Noto, C. Korte, W. Lehnert, D. Stolten, Phys. Chem. Chem. Phys. 14 (28) (2012) 10022. [3] F. Conti, S. Willbold, C. Korte, W. Lehnert, S. Mammi, D. Stolten, Polymer (2012) submitted