Sulfonated polybenzimidazole membranes

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technology of fuel cells too expensive for a large scale. ∗ ... main characteristics of this material. ..... [24] M. Mulder, Basic Principles of Membrane Technology,.

Journal of Membrane Science 188 (2001) 71–78

Sulfonated polybenzimidazole membranes — preparation and physico-chemical characterization P. Staiti∗ , F. Lufrano, A.S. Aricò, E. Passalacqua, V. Antonucci CNR — TAE, Institute for Transformation and Storage of Energy, Via Salita S. Lucia No. 5, 98126 S. Lucia, Messina, Italy Received 19 October 2000; received in revised form 31 January 2001; accepted 01 February 2001

Abstract The preparation of sulfonated polybenzimidazole by sulfuric acid treatment on pre-formed polybenzimidazole membranes was investigated. This polymer, which is originally a thermal resistant and insulating material is transformed by the chemical treatment into a proton conductor. The modified material is stable at temperatures close to 400◦ C. The proton conductivity of the sulfonated membrane at 160◦ C and 100% r.h. is 7.5 × 10−5 S/cm. The low conductivity is explained by protonation of nitrogen in the imidazolium ring, as evidenced by FT-IR analysis, which lowers the proton mobility. Hydrogen bridge bonds are formed between nitrogen in the imidazole and oxygen of sulfonic group creating a more regular structure in the material which becomes insoluble in polar solvent such as dimethyl sulfoxide. These modifications of the material have been observed in the X-ray diffraction patterns, which evidence an incipient crystalline structure of the sulfonated polybenzimidazole. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Solid polymer electrolyte; Conductive membrane; Proton conduction; Polybenzimidazole; Sulfonation

1. Introduction There is a great interest in the development of thermally stable proton conductive membranes (up to 200◦ C) having lower cost with respect to those currently used for fuel cell applications [1–4]. Actually, the polymer electrolyte fuel cells (PEFCs) operate at temperatures