Local Electrochemical Impedance Spectroscopy: Towards an Improvement in the Low Frequency Domain

The ability to probe surface reactivity at the local scale has led to a new understanding of the electrochemical reactivity in relation to the surface microstructure. Among the various techniques developed in recent years, local electrochemical impedance spectroscopy (LEIS) takes advantage of using a transient approach to locally characterize a stationary electrochemical system without the need to add any redox mediator in solution. The principle of LEIS was pioneering by Isaacs et al. [1, 2]. The local current density, , is obtained from the local potential difference in solution, , measured with a probe which consisted in three reference microelectrodes positioned close to the interface of interest, as depicted in Fig. 1. Whatever the mode of operation, the spatial resolution of the technique is governed by the following parameters [3, 4]: - The diameter of each microelectrode used for sensing the local potential in solution; - The distance between the two potential microprobes (the smaller the distance, the smaller the potential difference) [5]; - The distance between the dual probe and the substrate is an important parameter to be considered. Due to the potential distribution in the electrochemical cell, the difference in potential to be measured will be smaller if the probe is positioned far from the substrate. This may result in difficulties in measuring properly LEIS response in the low frequency domain, as regularly encounter, for instance, in coating degradation application. In the present work, we reported a new experimental setup that allows the measurement of local electrochemical impedance response of an interface in a wide frequency range, including the low frequency domain which is discussed. Proofs of concept with model systems, as well as passive materials and coatings are presented. Keywords:Local electrochemical impedance spectroscopy; low frequency measurements; electrochemical instrumentation; micro-electrochemistry. References [1] R.S. Lillard, P.J. Moran, H.S. Isaacs, A novel method for generating quantitative local electrochemical impedance spectroscopy, J. Electrochem. Soc., 139 (1992) 1007-1012. [2] F. Zou, D. Thierry, H.S. Isaacs, A high-resolution probe for localized electrochemical impedance spectroscopy measurements, J. Electrochem. Soc., 144 (1997) 1957-1965. [3] V.M.-W. Huang, S.-L. Wu, M.E. Orazem, N. Pebere, B. Tribollet, V. Vivier, Local electrochemical impedance spectroscopy: A review and some recent developments, Electrochim. Acta, 56 (2011) 8048-8057. [4] O. Gharbi, K. Ngo, M. Turmine, V. Vivier, Local electrochemical impedance spectroscopy: A window into heterogeneous interfaces, Current Opinion in Electrochemistry, 20 (2020) 1-7. [5] C.P.d. Abreu, C.M.d. Assis, P.H. Suegama, I. Costa, M. Keddam, H.G. de Melo, V. Vivier, Influence of probe size for local electrochemical impedance measurements, Electrochim. Acta, 233 (2017) 256-261. Figure 1