The effect of Donnan potentials on the apparent formal potentials of polymer-bound metal ions has been investigated for recast Nafion films and for spin-cast Nafion films on graphite electrodes. For the probe ions Ru(NH3)6 3+/2+ and Ru(bpy)3 3+/2+, the behavior generally correlates with Donnan potentials expected for ideally permselective domains, and plots of the apparent E°′ vs ionic strength (μ) have slopes of 59 mV/(decade increase in μ) for 1:1 monovalent electrolytes. The observed reaction entropies, ΔSobsdave been determined as a function of solution ionic strength. The measured ΔSobsd values are found to consist of the intrinsic reaction entropy for the reaction and an entropy of transfer term. The latter term arises from the permselectivity properties of the Nafion films. Extraction of the intrinsic reaction entropy, ΔSrc, yields a revised interpretation of the reaction entropy behavior of Ru complexes in Nafion films. The pH vs E1/2 properties of Nafion-bound Ru(NH3)5(H2O)3+/2+, Ru(NH3)5(isna)3+/2+ (isna = isonicotinic acid), and Ru(NH3)5(pz)3+/2+ (pz = pyrazine) have been investigated, and apparent pka, values have been determined for these complexes. Apparent pKa, values in Nafion are generally higher than those in aqueous media by 1.5-2 pK units.
|Number of pages||5|
|Journal||Journal of Physical Chemistry|
|Publication status||Published - 1988|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry