Cross-linker effect in ETFE-based radiation-grafted proton-conducting membranes, 2; Extended fuel cell operation and degradation analysis

Ben youcef, H.*; Gubler, L.*; Yamaki, Tetsuya; Sawada, Shinichi; Alkan Grsel, S.*; Wokaun, A.*; Scherer, G. G.*

The effect of cross-linker content on the chemical stability of poly(ethylene--tetrafluoroethylene) (ETFE)-based radiation-grafted and sulfonated membranes was investigated. An ex situ degradation test in hydrogen peroxide solution showed a strong increase in stability of crosslinked membranes compared to uncrosslinked ones. Excessive crosslinking, however, is detrimental to the chemical and mechanical properties. Furthermore, the stability of grafted membranes based on ETFE was superior to those based on poly(tetrafluoroethylene--hexafluoropropylene) (FEP). An in situ long-term test in a hydrogen/oxygen single cell over 2180 h, using an ETFE-based grafted membrane optimized with respect to cross-linker content, with a graft level of 25% was carried out. The performance of the membrane electrode assembly exhibited a voltage decay rate of 13 V/h over the testing time at a current density of 500 mA/cm and a cell temperature of 80C, while the hydrogen permeation showed a steady increase over time. This indicates that, to some extent, changes in the membrane morphology occur over the operating period. Local postmortem analysis of the tested membrane reveals that high degradation was observed in areas adjacent to the oxygen inlet and in other areas nearby.