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Investigations of the ex situ ionic conductivities at 30 degrees C of metal-cation-free quaternary ammonium alkaline anion-exchange membranes in static atmospheres of different relative humidities

Varcoe, JR (2007) Investigations of the ex situ ionic conductivities at 30 degrees C of metal-cation-free quaternary ammonium alkaline anion-exchange membranes in static atmospheres of different relative humidities PHYS CHEM CHEM PHYS, 9 (12). 1479 - 1486. ISSN 1463-9076

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Abstract

This article presents the first systematic study of the effect of Relative Humidity (RH) on the water content and hydroxide ion conductivity of quaternary ammonium-based Alkaline Anion-Exchange Membranes (AAEMs). These AAEMs have been developed specifically for application in alkaline membrane fuel cells, where conductivities of >0.01 S cm–1 are mandatory. When fully hydrated, an ETFE-based radiation-grafted AAEM exhibited a hydroxide ion conductivity of 0.030 ± 0.005 S cm–1 at 30 °C without additional incorporation of metal hydroxide salts; this is contrary to the previous wisdom that anion-exchange membranes are very low in ionic conductivity and represents a significant breakthrough for metal-cation-free alkaline ionomers. Desirably, this AAEM also showed increased dimensional stability on full hydration compared to a Nafion®-115 proton-exchange membrane; this dimensional stability is further improved (with no concomitant reduction in ionic conductivity) with a commercial AAEM of similar density but containing additional cross-linking. However, all of the AAEMs evaluated in this study demonstrated unacceptably low conductivities when the humidity of the surrounding static atmospheres was reduced (RH = 33–91%); this highlights the requirement for continued AAEM development for operation in H2/air fuel cells with low humidity gas supplies. Preliminary investigations indicate that the activation energies for OH– conduction in these quaternary ammonium-based solid polymer electrolytes are typically 2–3 times higher than for H+ conduction in acidic Nafion®-115 at all humidities.

Item Type: Article
Uncontrolled Keywords: ELECTROLYTE FUEL-CELLS, IONOMER MEMBRANES, TRANSPORT
Divisions: Faculty of Engineering and Physical Sciences > Chemistry
Depositing User: Mr Adam Field
Date Deposited: 27 May 2010 14:43
Last Modified: 23 Sep 2013 18:34
URI: http://epubs.surrey.ac.uk/id/eprint/1698

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