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

作者：John Jimmy; Hugar Kristina M; Rivera Melendez Johary; Kostalik Henry A; Rus Eric D; Wang Hongsen; Coates Geoffrey W; Abruna Hector D^*

来源：Journal of the American Chemical Society, 2014, 136(14): 5309-5322.

DOI：10.1021/ja4117457

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 (CO32-) and formate (HCOO-) ions at the electrode of a quartz crystal resonator coated with an AAEM film, while simultaneously monitoring changes in the frequency (Delta f) and the motional resistance (Delta R-m) of the resonator. A decrease in Delta f, indicating an apparent mass increase in the film, and a decrease in Delta 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-, and HCOO- were individually examined by changing the solution concentration of these species, confirmed the changes to be due to the incorporation of electrogenerated CO32-/HCOO- 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- and CO32-, in particular, interact strongly with the AAEM film and readily displace OH- from the film. Notwithstanding, the anion exchange between CO32-/HCOO- and OH- was found to be reversible. It is also inferred that the film exhibits increased swelling in the OH- form versus the CO32-/HCOO- 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.

• 出版日期2014-4-9