Influence of Platinum Precipitation on Properties and Degradation of Nafion~® Membranes

摘要

In this study, the role of Pt concentration and distribution in the membrane on ionomer degradation was investigated. Nafion~® membranes were impregnated with different mass fraction of Pt via ion-exchange and operated as membrane electrode assemblies (MEAs) at open circuit voltage (OCV). Various MEAs with known Pt concentration were characterized by electrochemical in-situ measurements regarding both, membrane properties and ionomer degradation. Additionally, Pt particle distribution in the membrane cross sections was analyzed. The presence of Pt precipitations was found to influence ionic conductivity and the sensitivity of cell performance for humidification. Ionomer decomposition increased with concentration and surface area of Pt deposits as well as distance between particles. The comparison between Pt precipitated artificially and during operation showed a considerable difference in particle distribution and extent of internal membrane humidification due to water formation at Pt sites.