Membranes for Direct Alcohol Fuel Cells
This chapter is devoted to summarize and discuss the main properties of ionomeric membranes used in direct alcohol PEM fuel cells. Although Nafion is the proton exchange membrane commonly used in methanol and other direct alcohol fuel cells, other proton
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Membranes for Direct Alcohol Fuel Cells Horacio R. Corti
Abstract This chapter is devoted to summarize and discuss the main properties of ionomeric membranes used in direct alcohol PEM fuel cells. Although Nafion is the proton exchange membrane commonly used in methanol and other direct alcohol fuel cells, other proton and alkaline membranes are being investigated in order to improve the efficiency of DAFC. The goals in the development of this critical component of DAFC are: low cost, long durability, low alcohol permeability and high electrical conductivity. The last two properties can be combined in a single parameter, the membrane selectivity that accounts for the ratio between the proton and alcohol transport through the membrane. This parameter can be compared to that measured for Nafion to define a relative selectivity, which is a primary parameter to evaluate the potentiality of a ionomer material to be used in alcohol feed fuel cells. The vast catalogue of polymeric materials reviewed here included Nafion composite with inorganic and organic fillers, and non-fluorinated proton conducting membranes such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly (vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. Anionexchange membranes are also discussed because of the facile electro-oxidation of alcohols in alkaline media and because of the minimization of alcohol crossover in alkaline direct alcohol fuel cells. The performance of different types of membranes in direct alcohol fuel cells, mainly methanol, are summarized and discussed in order to identify the most promissory ones. The lack of correlation between the relative selectivity and fuel cell performance of the membranes indicates that the architecture of the three
H.R. Corti (*) Departamento de Fı´sica de la Materia Condensada, Centro Ato´mico Constituyentes, CNEA, and INQUIMAE (Universidad de Buenos Aires – CONICET), Buenos Aires, Argentina e-mail: [email protected] H.R. Corti and E.R. Gonzalez (eds.), Direct Alcohol Fuel Cells: Materials, Performance, Durability and Applications, DOI 10.1007/978-94-007-7708-8_6, © Springer Science+Business Media Dordrecht 2014
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phases region is a decisive factor to take into account in the design of enhanced performance membrane-electrode assemblies.
6.1
Introduction
The studies on membranes for DAFC follow the same pattern as reported in Chap. 1 for DAFC. Around 90 % of the most of 4,000 works cited by Scopus till the end of 2012, correspond to direct methanol, while only 10 % deals with membranes for direct ethanol fuel cells. In both case, for DMFC and DEFC membranes, there is a maximum in the number of publications in 2009, as can be seen in Fig. 6.1. Several reviews on membranes for DMFC fuel cells have been published in the last decade [1–9], starting with that by Kreuer [1], discussing the differences between Nafion and sulfonated polyether ketone membranes. According to Fig. 6.1, reviews published till 2006 [1–4] cover only one third of the ionomeric memb
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