Preparation and Characterization of Stable Ionomers and Ionomer Membranes for Fuel Cells

✍ Scribed by S. Mitov; B. Vogel; E. Roduner; H. Zhang; X. Zhu; V. Gogel; L. Jörissen; M. Hein; D. Xing; F. Schönberger; J. Kerres

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 289 KB
• Volume: 6
• Category: Article
• ISSN: 1615-6846
• DOI: 10.1002/fuce.200600034

✦ Synopsis

Abstract

Membranes based on sulfonated arylene polymers and their cross‐linked blends were prepared. Embedding the ionomers into textile or porous PTFE matrix and/or doping with ZrP nanoparticles reduced the swelling, and improved the thermal stability. PTFE reinforcement led to an excellent single cell performance, which is promising for PEMFC applications. Some of the membranes performed better than Nafion®. The net methanol crossover correlates with the membrane thickness and composition, but surprisingly, suppression of the methanol crossover alone, does not enhance U/I performance. ESR experiments of oxidative degradation of the monomer by OH^•^ at pH > 10 leads to phenoxyl and semi‐quinone radicals. The study focuses on the case where O~2~^•–^ or ^1^O~2~ are the damaging species, i.e. above pH 11.7, and the dominant reaction is that involving the aromatic ring. Under conditions of fuel starvation, the acid protons get depleted, which may lead to high local pH values, even in an overall acidic environment. It is therefore important to be aware of the entirely different form of degradation chemistry at high pH. In the presence of both HO^•^ radicals and oxygen, complete degradation of the aromatic rings can be observed, within hours. In view of this, perfluorinated membranes are more inert. Cross‐linked arylene polymer blend membranes and PTFE‐reinforced arylene ionomer membranes can be regarded as promising for further development, due to their high stability and excellent PEMFC performance.