(Keynote) Interrogation of the Interfacial Capacitance By a Double Modulation Technique

Abstract

The description of the electrochemical interface is usually based on the assumption that the faradaic impedance is in parallel with the double layer capacitance, in other word, it is supposed that the double layer charging is independent of the faradaic current.1 This approach was criticized by Delahay et al.2 in the 60’s and later, Anson et al.3 established by a transient potential-time measurement that the double layer exhibits relaxation processes when the equilibrium is modified by a fast coulostatic charge injection. Feldberg4 also performed a quantitative approach by digital simulation of the non-steady-state Gouy–Chapman model and showed that two relaxations of the double-layer can take place when a charge is injected into the interface: the first relaxation was related to neutralization of the overall charge on the electrode; the second one, slower, was related to the redistribution of the ions in the diffuse layer towards the steady-state profile given by the solution of the Poisson–Boltzmann equation. The aim of this work is to revisit the kinetic aspects of adsorption processes which play a determining role in the behavior of reaction intermediates in electrode reactions based on the use of Electrochemical Impedance Spectroscopy (EIS) and by modulation of the interfacial capacitance (MICTF). The MICTF technique proposed few years ago by Antaño-Lopez et al.5,6 consisted in a double excitation technique for determining simultaneously two spectra: the traditional electrochemical impedance and the frequency response of the interfacial capacitance modulated by the same EIS signal. In principle, the MICTF measurement can be compared to the transient approach developed by Anson et al.3 but taking advantage of the frequency domain for improving the signal-to-noise ratio especially in the low and very low frequency ranges. This measurement can be performed by the simultaneous application of two sinewave-potential perturbations: the first one in high frequency domain and the other one by scanning the low frequency domain at which traditional EIS can be performed.5,7 After the presentation of the technique, the description of an ideally polarizable electrode (Hg in NaBr and KCl) for different concentrations of the electrolyte will be discussed. In a last part, the most recent work on the relaxation of the interface formed between an ionic liquid and an electrode will be presented. 1 J.H. Sluyters, On the impedance of galvanic cells I. theory, Recl. Trav. Chim. Pays-Bas 79 (1960) 1092–1100. 2 P. Delahay, Electrode processes without a priori separation of double-layer charging, J. Phys. Chem. 70 (7) (1966) 2373–2379. 3 F. Anson, R.F. Martin, C. Yarnitzky, Creation of nonequilibrium diffuse double layers and studies of their relaxation J. Phys. Chem. 73 (1969) 1835. 4 S.W. Feldberg, Theory of relaxation of the diffuse double layer following coulostatic charge injection J. Phys. Chem. 74 (1970) 87. 5 R. Antaño-Lopez, M. Keddam, H. Takenouti, Electrochim. Acta 46 (2001) 3611. 6 E. R. Larios-Durán, R. Antaño López, M. Keddam, Y. Meas, H. Takenouti, V. Vivier, Electrochim. Acta 55 (2010) 6292. 7 A. Battistel, F. La Mantia. Electrochim. Acta 176 (2015) 1484-1491.