Elaboration of nanostructured and highly proton conductive membranes for PEMFC by ion track grafting technique
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Elaboration of nanostructured and highly proton conductive membranes for PEMFC by ion track grafting technique Enrico Gallino1, Marie-Claude Clochard1, Emmanuel Balanzat2, Gerard Gebel3 and Arnaud Morin4 1
Laboratoire des Solides Irradiés, CEA-Ecole Polytechnique-CNRS, 91128 Palaiseau, France CIMAP, CEA-CNRS-ENSICAEN, 6 Boulevard du Maréchal Juin, 14050 Caen Cedex 4, France 3 CEA-DSM/INAC/SPrAM, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble, France 4 CEA-DRT/LITEN/DTH/LCPEM, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble, France 2
ABSTRACT In order to develop a novel proton conductive membrane for proton exchange membrane fuel cell (PEMFC), a poly(vinyl di-fluoride) (PVDF) matrix was irradiated with swift heavy ions (SHI) to obtain radically active cylindrical latent tracks in the polymer film. Styrene was then radiografted and further sulfonated into these irradiated cylindrical regions, leading to sulfonated polystyrene (PVDF-g-PSSA) domains within PVDF. The role of the grafting degree and fluence of irradiation of the PVDF matrix on PVDF-g-PSSA membranes properties (chemical composition, ion exchange capacity) was investigated. Then, a membrane-electrode assembly (MEA) was prepared and fuel cell tests have been performed. Our results clearly show that PVDF-g-PSSA membranes with a grafting degree of about 140%, obtained after irradiation at a fluence of 1010 ions/cm2, exhibit good conductivity values but their durability is limited to about 70 h. Decreasing the fluence leads to membranes with lower grafting yield but with fuel cell performances closer to those of 140% grafted PVDF-g-PSSA membrane and improved mechanical properties. Then, ion track grafting technique is a promising technique to obtain PEM with a good trade-off between proton conductivity and mechanical properties. INTRODUCTION Fuel cells are electrochemical systems that convert chemical energy of a fuel (i.e.: hydrogen, methanol) in a reaction with oxygen (from air for example) into electrical energy and heat with high energy efficiency and no green-house gas emission (water is the only by-product). Among the different types of fuel cells, proton exchange membrane fuel cells (PEMFC) are attractive energy sources for portable equipments (for example: laptops and mobile phones), vehicles and households. The proton exchange membrane (PEM), which works as an electrolyte to transport protons from the anode to the cathode, is the key component of PEMFC systems. The ideal PEM must fulfil specific properties such as: 1) high proton conductivities (up to -1 10 S cm-1) at high temperature (120-150°C) and low water content, 2) low gas permeability, 3) dimensional stability, 4) high mechanical strength and 5) high resistance to dehydration, oxidation, reduction and hydrolysis. Despite some serious drawbacks (high cost, conductivity losses at temperatures higher than 90°C, water swelling shortening the membrane durability), Nafion® (Dupont de Nemours) is still the reference as membrane for PEMFC [1]. Radiation induced grafting polymerization is a promisi
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