Mitigating Membrane Degradation: Investigation of Lifetime and Fluoride Emission Rate from Modified Short-Side-Chain and Long-Side-Chain PFSA Membrane Electrode Assemblies during High Temperature Open Circuit Voltage Hold

The incorporation of radical traps in the membrane or electrode of a fuel cell MEA based on perfluorosulfonic acid (PFSA)type ionomers has emerged as an important development enabling much increased fuel cell lifetime. Effective radical scavengers include transition metal ions and their oxides, in particular of cerium. We have developed novel nanofibre-networks comprising inorganic and organic polymer radical trap materials for incorporation either within the membrane or at the membrane electrode interface of MEAs comprising long-side-chain (LSC) and short-side-chain (SSC) PFSA membranes. MEAs were submitted to open circuit voltage hold testing at 50% relative humidity and 90 °C and the voltage decay and fluoride and sulfur emission rates were monitored with time. MEAs were investigated post-mortem for evidence of Pt migration (SEM-EDX), cerium migration where relevant, and PFSA backbone modification (¹⁹F NMR, Raman and XPS spectroscopies). The results show that non-protected SSC PFSA MEAs have a significantly lower (factor >20) fluoride emission rate on OCV hold than non-protected LSC PFSA MEAs, and the interpretations of this finding will be discussed. Implementing a nanofibre PFSA network enriched with cerium oxide nanoparticles at the membrane electrode interface at the anode side further reduces the FER of SSC PFSA MEAs, such that fluoride emission rate of anode-protected Aquivion® E79-03S MEAs is 300 times lower than that of non-protected Nafion®-212. These results will be compared in this presentation with those obtained on embedding a polymer nanofibre radical scavenger within PFSA membranes such as to establish a ranking of the effectiveness of CeOx type and alternative polymer type radical scavengers in reducing fluoride loss and membrane thinning, and extending MEA lifetime.