1H NMR spectroscopy of degraded perfluorosulfonic acid membranes: A simple methodology for detecting onset of degradation

Abstract

Perfluorosulfonic acid (PFSA) polymer electrolyte membranes (PEMs) used in fuel cells undergo chemical degradation when exposed to radicals formed during electrochemical reactions. One of the products or intermediates formed during the degradation was reported to be proton-exchangeable groups such as CF2OH and COOH. However, the 1H magic angle spinning nuclear magnetic resonance (MAS NMR) spectra of Nafion PEMs degraded chemically through the Fenton reaction revealed that CF2H was generated. Furthermore, the accompanying depletion of SO3H in the Nafion PEMs reduced the water contents of Nafion PEMs even under water saturation conditions. Our results are consistent with recent thermal degradation results of CF2H generation via SO3H substitution with H. While very simple, the 1H MAS NMR spectroscopic analysis was demonstrated to be a powerful technique for determining degradation of PFSA membrane such as Naion and Aquivion when other techniques, such as 19F MAS NMR spectroscopy, failed to show any degradation evidence. Hence, this method is potentially useful for investigating various PFSA PEMs for initial degradation evidence before analyzing their in-depth degradation mechanisms.