Preparation of a cobalt hexacyanoferrate film-modified aluminum electrode by chemical and electrochemical methods: enhanced stability of the electrode in the presence of phosphate and ruthenium(III)

Abstract

Modification of an aluminum electrode by means of a thin film of cobalt hexacyanoferrate (CoHCF) using electroless and electrochemical procedures is described. The modification conditions of the aluminum surface, including the electroless deposition of metallic cobalt on the electrode surface from CoCl2+NaF solution and the chemical derivatization of the deposited cobalt to give a CoHCF film in 0.25 M KCl+0.25 M K3[Fe(CN)6] solution, have been determined. The modified Al electrodes prepared under optimum conditions show one or two well-defined redox couples in phosphate buffer solutions of pH 7.2, depending on the preparation procedure, due to the [CoIIFeIII/II(CN)6]–/2– system. The effect of pH, alkali metal cations, and anions of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied. Diffusion coefficients of hydrated Na+ in the film, the transfer coefficient, and the transfer rate constant for electrons were determined. The stability of the modified electrodes under various experimental conditions was studied and their high stability in the sodium phosphate buffer solutions was confirmed. Enhanced stability was observed when the modified electrode was scanned in fresh solutions of RuCl3 between 0 and 1 V for at least 20 cycles, due to the formation of mixed hexacyanoferrates of cobalt and ruthenium.