Influence of Probe Size and Probe Position for Local Electrochemical Impedance Spectroscopy

Local electrochemical impedance spectroscopy (LEIS) has received a significant attention these last two decades mainly for corrosion applications [1, 2]. The assessment of local current density in solution requires the measurement of at least 3 local potentials in the electrolytic solution using 3 independent micro-reference electrodes positioned close to the electrochemical interface. Then, the different contributions of the local current density (namely the normal and the radial components) are obtained using the Ohm’s law. The spatial resolution is mainly governed by the probe size, the distance between the two independent potential probes (i.e. silver micro-wires), and the distance between the probes and the interface. Interestingly, resolutions in the micrometre range have already been reported [3], but the apparition of two main drawbacks accompanies the diminution of the probe dimension.

First, a non-negligible capacitance is observed in the high-frequency domains corresponding to a coupling capacitance between two of the micro-wires, as shown in Fig. 1. 

Second, the position of the reference electrode for measuring the potential and calculating the local impedance plays a significant role [4]. Indeed, depending on the location of the probe for measuring the potential, the measurement may be insensitive to local heterogeneity. As a result, such a measurement is no longer a local impedance measurement since it is obtained as a ratio of global potential to local current density.

In this paper, we present experimental results on platinum electrode and on the steel / copper system in order to characterize the influence of the probe size and the probe positioning. A specific attention will be paid to data analysis, and some guidelines for performing LEIS measurements (probe characterisation and probe positioning) will be presented.

[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) 1007-12.

[2] 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) 8048-57.

[3] I. Annergren, D. Thierry, F. Zou, Localized electrochemical impedance spectroscopy for studying pitting corrosion on stainless steels, J. Electrochem. Soc. 144 (1997) 1208-15.

[4] E. Bayet, F. Huet, M. Keddam, K. Ogle, H. Takenouti, Local electrochemical impedance measurement: scanning vibrating electrode technique in ac mode, Electrochim. Acta 44 (1999) 4117-27.

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Fig. 1: dual probe used for measuring local electrochemical impedance spectroscopy and equivalent circuit used for taking into account the stray capacitance ascribed to this setup.