Polymer-bound antioxidants in grafted membranes for fuel cells

Proton conducting membranes for fuel cells containing antioxidants were synthesized by radiation grafting. Styrene and a "linker" monomer were pre-irradiation cografted onto an ETFE base film of 25 mm thickness. Tyramine, a phenol type antioxidant, was subsequently covalently attached to the "linker" units, and the styrene units were sulfonated. FTIR and SEM-EDX analyses of the synthesized films and membranes were performed to confirm uniform grafting, functionalization and sulfonation steps. The obtained membranes were characterized in terms of ion exchange capacity (IEC), water uptake and through-plane conductivity. The cografted membranes were assembled into a fuel cell and tested under accelerated aging conditions to assess their chemical stability. The membranes containing the tyramine moieties degraded substantially less compared to membranes lacking these phenolic groups. Post-test FTIR and IEC analyses confirmed the results of the fuel cell test, which supports the notion that the polymerbound antioxidants effectively mitigate oxidative aging of the polymer electrolyte in a fuel cell.