Electron transfer through single-crystal silver electrode/n-decanthiol monolayer/NaNO₃ solution interfaces

Abstract

The kinetics of Ru[(NH₃)₆]³⁺ reduction in 1 M NaNO₃ solution at Ag(210) and Ag(111) singlecrystal electrodes modified by n-decanthiol monolayer is studied by electrochemical impedance spectroscopy and cyclic voltammetry. By using these two methods, standard rate constants of the redox reaction involving Ru[(NH₃)₆]^3+/2+ redox couple in the absence and in the presence of the n-decanthiol film were estimated. The equivalent circuit describing the experimental data in the presence of the self-assembled organic monolayer and in the absence of redox reaction is an electrical circuit comprising a large resistance (∼10⁶ Ω) connected in parallel with a capacitance (∼10⁻⁸ F). Analysis of kinetic data and extrapolation of Tafel lines resulted in the determination of the rate constant at unmodified Ag-electrode, which is characteristic of very fast heterogeneous electron transfer. The calculated rate constants for n-decanthiol-modified silver singlecrystal faces (210) and (111) in 1 M NaNO₃ solution (pH 6.3) equal 4.63 × 10⁻⁵ and 3.05 × 10⁻⁵ cm/s, respectively. The results are compared with the data at hand reported by different authors for gold electrodes in indifferent electrolyte solution in the absence and in the presence of self-assembled monolayer.