Increasing the Operating Temperature of Nafion Membranes with Addition of Nanocrystalline Oxides for Direct Methanol Fue
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Increasing the Operating Temperature of Nafion Membranes with Addition of Nanocrystalline Oxides for Direct Methanol Fuel Cells Vincenzo Baglio1, 3, Alessandra Di Blasi1, Antonino S. Arico’1, Vincenzo Antonucci1, Pier Luigi Antonucci2, Francesca Serraino Fiory3, Silvia Licoccia3, Enrico Traversa3 1 CNR-TAE Institute, via Salita S. Lucia sopra Contesse 98126 Messina, Italy 2 University of Reggio Calabria, Località Feo Di Vito, 89100 Reggio Calabria, Italy 3 University “Tor Vergata”of Rome, via della Ricerca Scientifica, 00133 Roma, Italy ABSTRACT Composite Nafion membranes containing various amounts of TiO2 (3%, 5% and 10%) were prepared by using a recast procedure for application in high temperature Direct Methanol Fuel Cells (DMFCs). The electrochemical behaviour was compared to that of a membraneelectrode assembly (MEA) based on a bare recast Nafion membrane. All the MEAs containing the Nafion-titania membranes were able to operate up to 145°C, whereas the assembly equipped with the bare recast Nafion membrane showed the maximum performance at 120°C. A maximum power density of 340 mW cm-2 was achieved at 145°C with the composite membrane in the presence of oxygen feed, whereas the maximum power density with air feed was about 210 mW cm-2.
INTRODUCTION Liquid-fueled Solid-Polymer-Electrolyte Fuel Cells represent a promising alternative to hydrogen based devices as electrochemical power sources for application in portable systems and in electric cars, due to their simplicity of design. However, despite the practical system benefits, the power density and the efficiency of Direct Methanol Fuel Cells (DMFCs) are low compared to Polymer Electrolyte Fuel Cells (PEFCs) operating with hydrogen because of the slow oxidation kinetics of methanol and the methanol cross-over through the membrane [1-5]. In the last years, significant efforts have been addressed to the development of polymer membranes for DMFCs in order to increase their operation temperature. At present, the electrolyte widely used in this field is Nafion, due to its excellent stability, high protonic conductivity at temperatures close to 100°C and good mechanical strength. The main problems associated with this electrolyte are the membrane dehydration at temperatures higher than 100°C, which is a prerequisite for a suitable electro-oxidation of small organic molecules (e. g. CO, methanol, ethanol, etc.), and the methanol cross-over, resulting in a performance decay and a loss of fuel efficiency. An increase in the operation temperature up to 150°C is highly desirable to enhance the kinetics of methanol oxidation. Various approaches have been proposed to solve these problems and allow the operation of liquid-feed solid polymer electrolyte fuel cells at elevated temperatures (higher than 120°C). Recently, the use of Nafion membranes containing finely dispersed nanocrystalline ceramic oxide powders (silica) has been proposed [6-7]. The role of the oxide powders is to improve the water retention, allowing fuel cell operation at 145°C with the oxygen hu
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