An Electrochemical Quartz Crystal Microbalance Study of a Prospective Alkaline Anion Exchange Membrane Material for Fuel Cells: Anion Exchange Dynamics and Membrane Swelling

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• 作者：Jimmy John ; Kristina M. Hugar ; Johary Rivera-Mel茅ndez ; Henry A. Kostalik ; IV ; Eric D. Rus ; Hongsen Wang ; Geoffrey W. Coates ; H茅ctor D. Abru帽a
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：April 9, 2014
• 年：2014
• 卷：136
• 期：14
• 页码：5309-5322
• 全文大小：726K
• 年卷期：v.136,no.14(April 9, 2014)
• ISSN：1520-5126

文摘

A strategy has been devised to study the incorporation and exchange of anions in a candidate alkaline anion exchange membrane (AAEM) material for alkaline fuel cells using the electrochemical quartz crystal microbalance (EQCM) technique. It involves the electro-oxidation of methanol (CH₃OH) under alkaline conditions to generate carbonate (CO₃^{2鈥?/sup>) and formate (HCOO鈥?/sup>) ions at the electrode of a quartz crystal resonator coated with an AAEM film, while simultaneously monitoring changes in the frequency (螖f) and the motional resistance (螖R_m) of the resonator. A decrease in 螖f, indicating an apparent mass increase in the film, and a decrease in 螖R_m, signifying a deswelling of the film, were observed during methanol oxidation. A series of additional QCM experiments, in which the effects of CH₃OH, CO₃2鈥?/sup>, and HCOO鈥?/sup> were individually examined by changing the solution concentration of these species, confirmed the changes to be due to the incorporation of electrogenerated CO₃2鈥?/sup>/HCOO鈥?/sup> into the film. Furthermore, the AAEM films were found to have finite anion uptake, validating the expected tolerance of the material to salt precipitation in the AAEM. The EQCM results obtained indicated that HCOO鈥?/sup> and CO₃2鈥?/sup>, in particular, interact strongly with the AAEM film and readily displace OH鈥?/sup> from the film. Notwithstanding, the anion exchange between CO₃2鈥?/sup>/HCOO鈥?/sup> and OH鈥?/sup> was found to be reversible. It is also inferred that the film exhibits increased swelling in the OH鈥?/sup> form versus the CO₃2鈥?/sup>/HCOO鈥?/sup> form. Acoustic impedance analysis of the AAEM-film coated quartz resonators immersed in water showed that the hydrated AAEM material exhibits significant viscoelastic effects due to solvent plasticization.}