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Issue 12, 2007
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Investigations of the ex situ ionic conductivities at 30 °C of metal-cation-free quaternary ammonium alkaline anion-exchange membranes in static atmospheres of different relative humidities

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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.

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

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Publication details

The article was received on 26 Oct 2006, accepted on 15 Nov 2006 and first published on 01 Dec 2006


Article type: Paper
DOI: 10.1039/B615478F
Citation: Phys. Chem. Chem. Phys., 2007,9, 1479-1486
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    Investigations of the ex situ ionic conductivities at 30 °C of metal-cation-free quaternary ammonium alkaline anion-exchange membranes in static atmospheres of different relative humidities

    J. R. Varcoe, Phys. Chem. Chem. Phys., 2007, 9, 1479
    DOI: 10.1039/B615478F

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