Poly(ethylene-co-tetrafluoroethylene)-derived radiation-grafted anion-exchange membrane with properties specifically tailored for application in metal-cation-free alkaline polymer electrolyte fuel cells

Abstract

A new class of stable poly(ethylene-co-tetrafluoroethylene)-based alkaline anion-exchange membrane (AAEM) with enhanced tensile strength has been synthesized in response to the poor mechanical properties of previously reported poly(tetrafluoroethylene-co-hexafluoropropylene) radiation-grafted AAEMs; this type of AAEM exhibits significant through-plane conductivities (up to 0.034 ± 0.004 S cm-1 at 50°C in water: conductivities that match requirements for application in fuel cells). The methanol permeabilities of this new AAEM class were found to be substantially reduced relative to Nafion-115 proton-exchange membranes; this offers the prospect that thin, low-resistance membranes may be used in direct methanol alkaline fuel cells with reduced methanol crossover. The fuel cell power performances obtained in a H2/O2 single fuel cell at 50°C with this AAEM is now within 1 order of magnitude of state-of- the-art Nafion-based fuel cells. It is evident that the alkaline ionomers are not the primary performance limiters of alkaline membrane fuel cells; performances are currently limited by the electrode architectures that have been optimized for use in PEM fuel cells but not alkaline fuel cells. The need for electrodes and catalyst structures that have been specifically tailored for use in AAEM-containing fuel cells is highlighted. © 2007 American Chemical Society.