Hicham Ben youcef

Cross-Linker Effect in ETFE-Based Radiation-Grafted Proton-Conducting Membranes I. Properties and Fuel Cell Performance Characteristics

Cross-linking of styrene grafted and sulfonated fuel cell membranes is essential to obtain well-performing and durable membranes. In this study, the properties and fuel cell performance of radiation grafted membranes based on poly(ethylene-alt-hexafluoropropylene) (ETFE) (25 μm) with different extent of cross-linking, using divinylbenzene (DVB) as a comonomer to styrene, were investigated. The water uptake and proton conductivity decrease as a function of increasing the extent of cross-linking. Also, the membranes become more brittle. Fuel cell performance is limited by the high ohmic resistance of the membrane at high degrees of cross-linking, whereas at low degrees of cross-linking the membrane-electrode interface is of poor quality. Optimum performance is obtained at an extent of cross-linking corresponding to a styrene:DVB monomer ratio (v/v) of 95:5 in the grafting solution.

Correlation between Morphology, Water Uptake, and Proton Conductivity in Radiation Grafted Proton Exchange Membranes

Fuel cells are clean and efficient electrochemical energy conversion reactors. Among the various fuel cell types under consideration, with operating temperatures ranging upto1 000 8C for thesolidoxide fuel cell (SOFC), thepolymer electrolyte fuel cell (PEFC) is particularly attractive for applications with variable load profile and intermittent operation (portable electronics, remote power sources, vehicle propulsion). PEFC typically operate at temperatures between 60 and 100 8C. In a PEFC, the electrochemical reaction of a fuel, typically H2, and O2, which is commonly taken from the ambient air, takes place in two half-cell reactions separated by an electrolyte, which is a polymeric membrane with a thickness of 20 to 200mm and proton conductivity on the order of 0.1 S cm . In the PEFC, the electrolyte membrane, allowing transport of protons from anode to cathode, serves at the same time as a separator for electrons and reactant gases. Sulfonic acid groups ( SO3H) with high dissociation constant (low pKa) tethered to the polymer provide protons as charge carriers. In such ‘‘ionomers,’’ the dissociation and formation of mobile protons requires the presence of water acting as ‘‘proton solvent.’’ The structure of water swollen proton exchange membranes (PEMs), especiallyNafion,which iswidely used S. Balog Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, 5232 Villigen PSI, Switzerland Fax: þ41 56 31