Highly durable PFSA membranes

Perfluorosulfonic acid (PFSA) polymers are extensively applied for preparing the membrane of proton exchange membrane fuel cells (PEMFCs) because of their considerably higher chemical stability over hydrocarbon-based polymers. However, even PFSA polymers suffer from decomposition caused by the hydroxyl radicals under low humidity conditions. Additionally, a critical breakdown of the membranes occurs at high temperatures when using conventional PFSA polymers, which have glass transition temperatures of around 80 °C. Therefore, operational conditions of PEMFCs are limited to low temperatures (below 80 °C) and high humidity conditions (ca 100% RH (relative humidity)). Highly durable PFSA membranes have been developed, which can operate for more than 6000 h at 120 °C and 50% RH. This achievement has opened up a new era of operating PEM fuel cells in the temperature range of near freezing to 120 °C under low and high humidity conditions for an extended period of time. In this article, a unique philosophy is presented along with guiding principles for developing highly durable PFSA membranes and their performances. Keywords: PEMFC; membrane; perfluorosulfonic acid (PFSA) polymer; degradation; hydroxyl radical; hydrogen peroxide; high temperatures; low humidity; ionical cross-linking; radical quencher