Adsorption of Ferrocene Compounds on Indium−Tin−Oxide Electrodes. Enhancement of Adsorption by Decomposition of Ferrocenium Molecules by Oxygen

Abstract

The adsorption of some substituted ferrocene molecules (Fc-R) on indium−tin-oxide electrodes has been investigated by cyclic voltammetry in acetonitrile. Adsorption occurs with carboxyl-substituted (R = −COOH and −(CH2)6COOH) and to a lesser extent with amino-substituted (R = −CH2N(CH3)2) ferrocenes. Adsorption from the neutral (ferrocene) carboxyl-substituted molecule produces layers with a coverage of 1 × 10-10 mol cm-2 which increases to 4 × 10-10 mol cm-2 from the oxidized (ferrocenium) molecule in air-saturated solution. In the latter case, adsorption occurs on a thin layer of amorphous iron oxide produced by oxidative decomposition of the ferrocenium. Electrodes modified by amorphous iron oxide layers are able to give stable monolayers from the carboxyl-terminated molecules, particularly with R = −(CH2)6COOH due to self-assembly. The layer structures are discussed on the basis of the adsorbate structure and the electrochemical parameters.