AC VOLTAMMETRIC MEASUREMENTS OF FAST CHARGE-TRANSFER PROCESSES AT ULTRAMICROELECTRODES

The methodology for carrying out ac voltammetric measurements with ultramicroelectrodes is discussed. Electron-transfer rate constants for the oxidation of ferrocene (FeCp2) at a Pt ultramicroelectrode and cobaltocene (CoCp2) at Hg, Au and Pt ultramicroelectrodes were measured at frequencies from 2 to 50 kHz. It was shown that the method can provide accurate information about fast interfacial charge-transfer kinetics in organic solvents. The rate of CoCP2 oxidation on Hg or Au electrodes was found to increase with a decrease in the supporting electrolyte concentration, but in the case of the Pt electrode no effect of the supporting electrolyte concentration was observed for oxidation of either CoCp2 or FeCP2. The state of the Pt-solution interface was examined by studying the H+ adsorption-desorption process in aqueous H2SO4 and the double-layer capacitance in nonaqueous media.