Electrochemical and electrochemically modulated reflectance AC voltammetry studies of electron transfer kinetics between attached redox centers and a mirror gold electrode

• Published in: Journal of the Electrochemical Society 2000-09, Vol.147 (9), p.3461-3466
• Main Authors: BREVNOV, Dmitri A, FINKLEA, Harry O
• Format: Article
• Language: English
• Subjects: Chemistry; Electrochemistry; Electrodes: preparations and properties; Exact sciences and technology; General and physical chemistry; Other electrodes
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1393920

Small amplitude electrochemical ac voltammetry (ACV) is employed to investigate kinetics of electron transfer between Ru redox centers attached to the electrode surface via C sub 10 alkanethiols and gold mirror electrodes. The equations for faradaic admittance of strongly adsorbed electroactive species in the case of a Langmuir isotherm are applied to determine the total coverage of redox centers ( theta total) kinetic parameters: the standard rate constant (k sub s ) and transfer coefficient, k sub s appears to increase and theta total appears to decrease as the perturbation frequency increases. In a separate experiment, large amplitude ACV is performed simultaneously with electrochemically modulated reflectance ac voltammetry (EMR ACV) on the same electroactive monolayer/electrode system. The electromodulation reflectance coefficient (X) is defined in the frequency domain as a ratio of ac electroreflectance to both dc electroreflectance and the interfacial ac potential (E exp inter ). X is shown to be a more useful quantity than the ratio of ac electroreflectance to dc electroreflectance for representation of the electroreflectance data. X is found to be exactly out-of-phase with the faradaic admittance at the wavelength region (410-440 nm) corresponding to the absorption band of the reduced form of the Ru complex. Therefore, the ac electroreflectance signal is dominated by the modulation of the electrode coverage of a given redox state with E exp inter . Electrochromic effects are negligible. Accurate calculation of k sub s from EMR ACV data is complicated because of the nonlinear relationship between the faradaic ac current and large amplitude E exp inter . Thus, under our experimental conditions, ACV is the preferred method to determine k sub s .