NMR Studies of Proton Transport in Anhydrous Polymer Electrolytes for High Temperature Fuel Cells

✍ Scribed by H. A. Every; L. D. Ionescu; M. P. de Heer; Y. Álvarez-Gallego; G. J. M. Janssen

• Publisher: John Wiley and Sons
• Year: 2008
• Tongue: English
• Weight: 314 KB
• Volume: 8
• Category: Article
• ISSN: 1615-6846
• DOI: 10.1002/fuce.200800004

✦ Synopsis

Abstract

This paper presents an NMR study of the dynamic processes related to proton transport in a new polymer consisting of two blocks – poly(2,6‐diphenylphenol) (P3O) and an imidazole functionalised poly(2,6‐dimethylphenol) (imi‐PPE) – and subsequently doped with polyphosphoric acid (PPA). From ^1^H and ^31^P NMR relaxation and diffusion measurements of the individual homopolymers and block copolymer, it was observed that addition of PPA significantly enhanced the mobility of imi‐PPE and the imi‐block copolymer, but not of P3O. The similarity in ^1^H T~2~ values between imi‐PPE and the imi‐block copolymer suggests that the relaxation behaviour in the block copolymer is dominated by the imi‐PPE phase. ^1^H diffusion in P3O and the imi‐block copolymer were comparable to pure PPA, suggesting that the proton diffusion is similar in each case. For imi‐PPE, the diffusion coefficients were several orders of magnitude lower, reflecting a restricted diffusion process that is not indicative of the proton mobility. For all three polymers, the ^31^P T~2~ relaxation behaviour and inability to measure ^31^P diffusion coefficients imply hindered translational motion of the phosphonate groups. From these results, it can be concluded that hydrogen bonds between the phosphoric acid and the polymer form a network that facilitates proton transport via a hopping mechanism.