Localized impedance measurements for electrochemical surface science

An approach for in-depth characterization of complex electrode/electrolyte interfaces based on localized impedance measurements is described in detail. The local ac probing of the interface is performed at different frequencies by means of scanning electrochemical microscopy (SECM) using ultramicroelectrodes (SECM tips) which enables visualization of dependences of the localized impedance spectra as a function of spatial coordinates. Subsequent fitting of these spectra to physical models visualize the local distribution of parameters describing the electrochemical interface, such as the electric double layer capacitance and the charge transfer resistance. Three model examples are analyzed dealing with typical situations, when the measurements are either affected or not by specific adsorption of anions at the SECM-tips. It is demonstrated that the approach holds promise for electrochemical surface science, particularly for better understanding of corrosion processes taking place at metal surfaces in aggressive, particularly aqueous electrolytes.