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Title: Cyclic Voltammetry as a Probe of Selective Ion Transport within Layered, Electrode-Supported Ion-Exchange Membrane Materials

Cyclic voltammetry was applied to investigate the permselective properties of electrode-supported ion-exchange polymer films intended for use in future molecular-scale spectroscopic studies of bipolar membranes. The ability of thin ionomer film assemblies to exclude mobile ions charged similarly to the polymer (co-ions) and accumulate ions charged opposite to the polymer (counterions) was scrutinized through use of the diffusible redox probe molecules [Ru(NH3)6]3+and [IrCl6]2−. With the anion exchange membrane (AEM) phase supported on a carbon disk electrode, bipolar junctions formed by addition of a cation exchange membrane (CEM) overlayer demonstrated high selectivity toward redox ion extraction and exclusion. For junctions formed using a Fumion®AEM phase and a Nafion®overlayer, [IrCl6]2−ions exchanged into Fumion®prior to Nafion®overcoating remained entrapped and the Fumion®excluded [Ru(NH3)6]3+ions for durability testing periods of more than 20 h under conditions of interest for eventualin situspectral measurements. Experiments with the Sustainion®anion exchange ionomer uncovered evidence for [IrCl6]2−ion coordination to pendant imidazolium groups on the polymer. A cyclic voltammetric method for estimation of the effective diffusion coefficient and equilibrium extraction constant for redox active probe ions within inert, uniform density electrode-supported thin films was applied to examine charge transport mechanisms.

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Journal of The Electrochemical Society
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Article No. 026520
The Electrochemical Society
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National Science Foundation
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