Scanning electrochemical microscopy combined with fast fourier transform impedance spectrometer for local electrochemical impedance measurements

Abstract

EIS is a powerful, non-destructive and informative technique, which has been successfully applied for the characterization of biosensor surfaces [1]. However, conventional EIS based techniques represent only averaged response of the entire electrochemical system. In order to get more advanced mapping of electrochemical system scanning electrochemical microscopy (SECM) merged with EIS (SEIM) eventually could be applied. In SEIM based technique localized impedance measurements could be performed in the range of frequencies when the surface of interest is scanned by ultramicroelectrode (UME). The result of SEIM could be visualized by mapping one of calculated parameters, e. g. charge transfer resistance or double layer capacitance as a function of 3D coordinates [2,3]. Fundamental aspects of SEIM were investigated comparing UME responses while it was approaching to different surfaces e.g.: (i) insulator surface, (ii) conducting surface not-connected to electric circuit, and (iii) conducting surface, which was connected to electric circuit and was held at constant potential [4]. By this research it has been shown that the admittance of the UME located at relatively small distance from the surface of interest mostly depends on the distance between UME and the surface and on interfacial properties of the surface. Therefore the SEIM based imaging is informative even without any redox mediators. Using SECM, combined with Fast fourier transform (FFT) impedance spectrometer, the impedance spectra could be registered at very high speed. In the frequency range between 1.5 Hz and 25 kHz the measurement time of the electrochemical impedance spectrum continues 1.3 s. This combined technique allows to obtain additional information to common measurements of impedance spectra: system-generated noise, and reliability of spectra. Thus, this technique is very informative, reliable, and suitable for measurements of quickly changed processes in the electrochemical cell. Combined with SECM, this technique could be applied for local characterization of not-stabile surfaces.