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Application of Stoynov's 4-D analysis for nonstationary impedance spectra corrections of thin poly(o-ethoxyaniline) modified Pt electrode

Stoynov's 4-D analysis has been applied for corrections of nonstationary impedance spectra of poly(o-ethoxyaniline)POEA modified Pt electrode measured using conventional EIS technique at the potential of conducting to insulating conversion of polymer. The series of nine sequentially measured impedance spectra of Pt/POEA electrode showed significant increase with operating time of experiment, implying not only time-varying system but also nonstationarity, i.e. time changes within time interval of the single impedance spectrum measurement. Correction procedure for nonstationarity, comprising three mathematical steps, was applied to each of sequentially measured impedance spectrum. In the first step of the procedure, central times of data acquistion at each frequency point were determined, referred to the operating time of experiment and as the fourth variable included into impedance data sets of all experimentally measured IS. In the second step of the procedure, the operating time function of measured real and imaginary impedance parts at iso-frequency points was built up and “frozen“ at starting times of each impedance spectrum measurement. In the last step of the procedure, nine instantaneous impedance spectra were calculated using extrapolation/interpolation method. Comparison between measured and instantaneous impedance spectra showed differences that indicate overestimation of all charge transfer and charge transport resistances and underestimation of charge pseudocapacitance values for not corrected vs. corrected IS of Pt/POEA electrode.

electrochemical impedance spectroscopy ; Stoynov's 4-D analysis ; nonstationarity ; poly(o-ethoxyaniline) modified electrode

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