Dear Researchers,
I am working with a Silicon Substrate based sensor and getting CV curve with Initial and Low voltage -0.2V and High voltage 0.4. However, in the EIS test, the Nyquist plot is not giving the circular shape it's supposed to give at the beginning. I am using CHI660E and in A.C. Impedance test, do I need to set the peak voltage at which I am getting the oxidation peak? Also what should be the voltage range of CA depending on the CV parameters? Your help would be really appreciated.
Dear Tanzila Noushin ,
Hope you are well!
Please can you describe your device. What is its structure? Does it contain a pn junction?
Would you please show us the CV curve?
The semicircle complex impedance curve appears when the structure is equivalent to a parallel C-R circuit.
Best wishes
Dear Tanzila Noushin,
The potentials used for CA and EIS should be chosen based on peak potentials in CV measurements: anodic peaks, cathodic peaks, formal potential (E0= (Epa+ Epc)/2), or potentials close to the peak potentials of your material. The profile of EIS spectra is dependent on your material and applied potential chosen for performing the measurements.
Ps. You can also optimise the applied potential used, test all parameters mentioned above.
Some suggestions of articles that use EIS and the parameters used for measurements:
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Dear Abdelhalim abdelnaby Zekry ,
Thank you so much Sir for your help. I actually fitted Randle's circuit model later and by simulating it I got a semicircular shape. I am working with a silicon substrate-based screen-printed sensor with gold as WE and CE, Ag/AgCl as RE. I got a good shape earlier, but now I am getting additional small peaks and dips like the picture attached beside oxidation and reduction peak in CV. Can you please tell me the reason? I am noticed when I am working with it for a long time, it becomes like that.
Dear Wanderson Silva ,
Thank you so much for all the information and resources. It was really helpful.
Dear Tanzila Noushin
The current in the electrochemical electrodes are composed of the following current components:
- The displacement capacitive current due to due to the electrode electrolyte capacitance
- The conduction current due to the charge transfer to the surface of the electrode.
If you scan the voltage you will have displacement current because such current is proportional to dV/dt.
If you measure your electrode under static conditions you will get only the charge transport current only.
The third current may be a form of interference or man made noise current because the impedance of the electrode is high in the range of the measurement.
I see that the if you increase the voltage further the current will increase appreciably pointing out the onset of the electrochemical reactions.
The other thing is that the rapid increase and fall with the voltage may be due to
some form of interference or noise or contaminated chemicals.
For typical electrochemical electrodes performance for water analysis please see the paper in the link:Presentation The properties of electrodes and electrochemical cells for w...
Best wishes