Study of the Substrate Effect in the KCl Adsorption onto Single-Crystal and Polycrystalline Gold Electrodes

Electron transfer kinetics in electrochemical systems is ubiquitous to natural and industrial processes.  Thus a deep knowledge of all stages involved in the charge transfer at the electrode solution interface, which includes mass transport, adsorption and the role of the electrical double layer is highly desirable [1].  In particular, adsorption and the electrical double layer play a distinctive role in the charge transfer at electrode/solution interfaces, since they are essential part of reaction mechanisms, especially for reactions where more than one electron is transferred. Fueled by the importance of adsorption and the electric double-layer in the electrode kinetics, there has been published in the literature several works, but mainly focused on thermodynamic rather than kinetics [2-4].

Here a qualitative study of the effect of the substrate and surface heterogeneities in the adsorption of chloride ions on gold surfaces is presented.  With this goal in mind, we have performed a study of the adsorption of chloride ions at different concentrations (1 mM, 10mM 0.1M) disolved in HClO₄0.5 M on the surfaces of polycrystalline (pc) and gold (111) single crystal.  Our results include the characterization of the system by using classic electrochemical techniques, such as cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS) and the novel intermodulated techniqued called Interfacial Capacitance Modulation (MIC) [5]. 

Figure 1 shows a comparison between the typical voltammetric responses as well as the double-layer capacitance vs. polarization behavior for polycristalline and (111) gold electrodes in contact with HClO₄in absence and presence of KCl, respectively. 

After this characterization, EIS and MIC measurements are carried out.  All our results are discussed qualitatively based on the relaxation of the double layer capacitance as a function of chloride ion concentration on the electrode solution interface.

REFERENCES:

[1] F.C. Anson, Acc. Chem. Res. 8 (1975) 400.

[2] D.C. Grahame, Chem. Rev. 41 (1947) 441.

[3] J. Lipkowski, W. Schmickler, D.M. Kolb, R. Parsons, J. Electroanal. Chem. 452 399, (1998) 193.

[4] T. Pajkossy, D.M. Kolb, Electrochim. Acta 54 (2009) 3594.

[5] E.R. Larios-Durán, R. Antaño-López, M. Keddam, Y. Meas, H. Takenouti, V. Vivier. Electrochim. Acta 55, (2010) 6292.