FILMS FORMED BY OXIDATION OF FERROCENE AT PLATINUM-ELECTRODES

Oxidation of ferrocene in acetonitrile resulted in films on Pt electro des under voltammetric conditions. Films were more readily formed with tetrabutylammonium tetrafluoroborate as the, electrolyte than with pe rchlorate salts. No films were detected when ferrocene was oxidized in aqueous 0.05 M cetyltrimethylammonium bromide (CTAB). Analysis of the films by FT-IR and Auger spectroscopy confirmed iron-containing oxida tion products on Pt, presumably from chemical reactions of ferricinium ions. Oxidation of 50-100 mM ferrocene in acetonitrile on Pt yielded insoluble precipitates. Analyses by MS, FT-IR, and UV-visible (water e xtract), suggested a mixture of oligomeric material and a small fracti on of ferricinium ions. Film formation had much less influence on volt ammograms on 12.5-mum-radius Pt microdisks than on 0.5-mm-radius Pt. T his is consistent with the smaller sensitivity of microelectrodes to c hemical reactions following charge transfer. The smaller apparent hete rogeneous, rate constants (k-degrees) found for ferrocene on macroelec trodes than on micro-electrodes could possibly be influenced by film f ormation on larger Pt electrodes. Correlations between macro- and micr oelectrode kinetic data suggest that macroelectrode k-degrees' values may be valid in a relative sense when ohmic drop is negligible. Bias i n k-degrees's on conventional-sized electrodes should be small in solu tions giving minimal film formation, such as micellar CTAB.