Dear All,
I want to calculate the electrochemical impedance of electrolyte-electrocatalyst interphase using Autolab. I am confused how to select the overpotential or potential vs Ag/AgCl. In a paper researchers selected fixed value of 270 mV for 5 different catalysts. I am working on 6-7 materials how to chose potential value what is the purpose of it?? I should be at onset of Faradaic process or something else??? It should be same for all catalysts???
Second, How to calculate impedance of electrolyte. Do i need to perform the same experiment (mentioned above) without catalyst coating or something else??
1. You have to run a CV to decide the correct option for the imposed potential. For a better understanding I suggest you to try to run EIS at OCP, at onset of Faradaic process, at peak maxima and at half maxima. I imagine that your interest it to see the catalyst at work, thus I recommend to consider the last options.
2. Working EIS at a fixed potential for all materials is not more informative than a CV.
3. The electrolyte resistance may be seen at high frequency (R1, before the first semicycle) and is not dependent on the working electrode condition.
1. You have to run a CV to decide the correct option for the imposed potential. For a better understanding I suggest you to try to run EIS at OCP, at onset of Faradaic process, at peak maxima and at half maxima. I imagine that your interest it to see the catalyst at work, thus I recommend to consider the last options.
2. Working EIS at a fixed potential for all materials is not more informative than a CV.
3. The electrolyte resistance may be seen at high frequency (R1, before the first semicycle) and is not dependent on the working electrode condition.
Dear Baber,
Usually, EIS carried out at OCV to under stand the interface. Depending on your bulk resistance may understand the conductivity of the system. While to conduct the EIS, amplitude of frequency should have a nominal voltage (~ 10 mV)
Dear Babar,
If you comparing the catalysts for a particular reaction. You can perform the CV and you can choose the potential for your region of interest (e.g. to compare the charge-transfer resistance between electrodes).
But for comparison you can run all the sample at OCV . The electrolyte resistance is calculated from the high frequency resistance from EIS and it is same for all the electrodes.
For more clarification see the attached paper.
The electrostatic (Coulomb) force is conservative, which means that the work done, on Q, is independent of the path taken; this is, exactly, analogous to the gravitational force, both in the absence of dissipative forces, such as friction. However, such an "AC-friction" (analogy) is, ordinarily (apart when: Zreal=0), the core of the EIS measurements. In standard EIS measurements, a common (DC, electric potential) reference is the (cell's) OCP, because the (DC-part of the) "friction" (iDC=0uA) is near "zero", as a rule.
So, the "EIS standard" (Z-spectra, at VDC=OCP) is, always, the 1st EIS to be measured, because we provoke, as a rule, the minimum system (cell) perturbation, both in DC and AC (low ampl.: 1 to 5mV) terms. Supplementary, EIS, at other (fixed) VDC, might be useful, if we have to analyze some specific reactions' dynamics of the WE, in a 3-electrode cell. However, note, that when VDC is far from the OCP, we provoke, we enter in a, commonly, non conservative electrochemical force field, and, as a rule, we provoke a non linear system (cell).
Such a sequence of EIS-set of coming spectra (members of the set), succeeding in parametric steps (of, say, 10mV), bring a new, collateral, rewarding CV[1], also.
1. a new, secondary, low(er) rate, equivalent CV, based on the EIS polarization parameters; it is, actually, a virtual CV if we bring together the sequence of, near DC, polarization parameters of the (essentially the same rate) EIS spectra.
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