I am currently running some electrochemistry experiments, including LSV and EIS. According to Ohm's law, the larger current responses the smaller impedance. What is the relationship between the LSV and EIS? When I measured in the LSV that the current was getting larger and larger, the resistance in the EIS should not be getting smaller and smaller. Does anyone have any about the basic of these techniques?
Thank you a lot.
The original Ohm's law as applied to simple resistors can be generalized to complex impedances, but even then you need to account for frequency dependence and phase shift between the variable voltage and variable current. The generalized form still assumes time invariance of the system's response to the electric excitation. On the other hand, electrochemical experiments are commonly conducted on reactive systems. During the LSV, the system's response becomes anomalous (non-ohmic) whenever the potential difference between the electrodes triggers some electrochemical reaction. Identifying such potentials is usually the purpose of the voltage sweep in LSV. On the other hand, the voltage in EIS is kept sufficiently low to stay within the range of linear relationship between the (complex) voltage and response current amplitudes. In that case, the purpose is to study responses of the (complex) impedance to the AC frequency. Analysis of such spectra yields information about the equivalent electrical circuit describing the system's response, particularly, the equivalent resistors and capacitors.
The original Ohm's law as applied to simple resistors can be generalized to complex impedances, but even then you need to account for frequency dependence and phase shift between the variable voltage and variable current. The generalized form still assumes time invariance of the system's response to the electric excitation. On the other hand, electrochemical experiments are commonly conducted on reactive systems. During the LSV, the system's response becomes anomalous (non-ohmic) whenever the potential difference between the electrodes triggers some electrochemical reaction. Identifying such potentials is usually the purpose of the voltage sweep in LSV. On the other hand, the voltage in EIS is kept sufficiently low to stay within the range of linear relationship between the (complex) voltage and response current amplitudes. In that case, the purpose is to study responses of the (complex) impedance to the AC frequency. Analysis of such spectra yields information about the equivalent electrical circuit describing the system's response, particularly, the equivalent resistors and capacitors.
You can indeed compare to some extent data from voltammetry and EIS. First you can obtain the potential which you could use in the EIS experiments, in general this is the equilibrium potential. The peak currents from the voltammetry or the integrated current of the voltammetric peaks will show a linear relationship with the (faradayic) capacitance obtained in the EIS measurements. EIS is based on phase information of the AC current, and everything can be calculated from this. Basic information is a bode plot, at the lower end of the frequency range all current will be in phase and will correspond to the capacitance (1/Z) as frequency increases a shift in phase angle will become apparent, this resembles a bell shaped curve. Initially the faradayic or capacitive reaction at the electrode can keep up with the frequency of the AC signal, and the current is in phase, at higher freq. this is not the case and the current is out of phase. At a certain frequency the current is in phase again as there is no longer a capacitive reaction, Z in the bode plot will now be equal to the solution resistance
Best regards, Mike
It depends on the purpose of your analysis. If you find a cathodic/anodic peak, then you can compare EIS plot at that potential versus EIS in another peak and compare the two plot. You can obtain plenty of qualitative information, such as the diffusion of the electroactive species during the electrochemical reaction...
There can be a huge amount of possibility, but keep in mind that you must verify that at the potential at which EIS is analyzed you must make sure that you are in the linear range of the Butler-Volmer equation otherwise you should not use EIS
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