The electrochemical setup and the equivalent circuit typically used for the estimation of the noise resistance using a ZRA is presented in Fig. 2a. Here, each electrode is represented by a current noise source, i1,2, in parallel with the electrode resistance, R1,2. The current measured by the ZRA is I and the potential with respect to a reference electrode (assumed noiseless) is V. The following analysis is developed for electrode resistances and, in the present form, it is strictly valid for systems where the noise impedance spectrum is flat and, consequently, the noise resistance approximate well the polarization resistance. The choice of considering the values of noise resistance rather than the noise impedance spectra has the practical advantage of simplifying the method to obtain time-resolved information. Considering a long dataset, it
is possible to evaluate the time evolution of the value of noise resistance by iteratively extracting potential and current segments, computing their variances and calculating the value of the noise resistance from Eqs. (12)–(16). If the noise resistance is unsuitable to describe a particular system, the analysis presented here can be readily extended to obtain a time-series of impedance spectra by replacing resistances with impedances and variances with power spectral densities in Eqs. (1)–(16) (the resulting equations are practically equivalent to those presented in Ref. [3]). However, given the dependency of noise impedance on frequency, in order to apply Eqs. (17)–(22), it would be necessary to consider the value of the noise impedance at each particular frequency or, alternatively, its average over a particular frequency range of interest. In most practical cases, the low-frequency limit of the impedance spectrum, or the average of the values of the impedance modulus over a pre-defined low-frequency range would be more appropriate.
The electrochemical setup and the equivalent circuit typically used for the estimation of the noise resistance using a ZRA is presented in Fig. 2a. Here, each electrode is represented by a current noise source, i1,2, in parallel with the electrode resistance, R1,2. The current measured by the ZRA is I and the potential with respect to a reference electrode (assumed noiseless) is V. The following analysis is developed for electrode resistances and, in the present form, it is strictly valid for systems where the noise impedance spectrum is flat and, consequently, the noise resistance approximate well the polarization resistance. The choice of considering the values of noise resistance rather than the noise impedance spectra has the practical advantage of simplifying the method to obtain time-resolved information. Considering a long dataset, itis possible to evaluate the time evolution of the value of noise resistance by iteratively extracting potential and current segments, computing their variances and calculating the value of the noise resistance from Eqs. (12)–(16). If the noise resistance is unsuitable to describe a particular system, the analysis presented here can be readily extended to obtain a time-series of impedance spectra by replacing resistances with impedances and variances with power spectral densities in Eqs. (1)–(16) (the resulting equations are practically equivalent to those presented in Ref. [3]). However, given the dependency of noise impedance on frequency, in order to apply Eqs. (17)–(22), it would be necessary to consider the value of the noise impedance at each particular frequency or, alternatively, its average over a particular frequency range of interest. In most practical cases, the low-frequency limit of the impedance spectrum, or the average of the values of the impedance modulus over a pre-defined low-frequency range would be more appropriate.
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