Electron Transfer through Single-crystal Silver Electrode/n-Decanthiol Monolayer/NaNO3 Solution Interfaces

The kinetics of Ru[(NH3)(6)](3+) reduction in 1 M NaNO3 solution at Ag(210) and Ag(111) single-crystal 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 (similar to 10(6) Omega) connected in parallel with a capacitance (similar to 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 single-crystal faces (210) and (111) in 1 M NaNO3 solution (pH 6.3) equal 4.63 x 10(-5) and 3.05 x 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.