Polymer films on electrodes. 20. An ESR study of several spin probes incorporated into nafion

The oxidative electrochemistry of protonated 2,2,6,6-tetramethylpiperidine-1-oxyl (Tempamine, TP) has been surveyed with Pt/Nafion modified electrodes. Protonated TP was shown to incorporate into Nafion films at pH lower than 9. Its oxidation is a reversible, one-electron process occurring at E_1/2 = 0.54 V vs. SCE on Pt/Nafion electrodes (ca. 120 mV less positive than E_1/2 on bare Pt) and independent of the pH in the range 4-8. The ESR spectrum of Nafion-confined TP showed that the rotational correlation time was in the slow tumbling region and was estimated to be 1.2 × 10^-8 s. This reveals an unusual anchoring effect by Nafion which had not been observed previously. The ESR spectra of some additional Nafion-confined spin probes such as vanadyl, manganese(II), and the cation radical of N,N,N′,N′-tetramethyl-1,4-phenylenediamme (TMPD) were also surveyed. The results indicate that the motion of a given cation within Nafion is determined by the nature of the cation itself.