Greetings,
I am using electrochemical impedance spectroscopy to study photoelectrochemical properties of my sample SiO2@TiO2 (core@shell) on Autolab device and Nova software.
In the Nyquist plot, there are two semi-circles. There is a tiny one at very first high frequency and a big clear one at smaller frequency.
I am stuck at the step of modelling an equivalent circuit that fit my experimental Nyquist and Bode plots. Particularly, in the Bode phase plot, I think the highest peak in low frequency range might be attributed to the big semi-circle. However, I have no idea for the middle peak and the lowest peak recorded at higher frequency.
I tried many ubiquitous models such as Randles circuit, etc but couldn't get any.
Could you please help me to overcome the obstacle?
Thank you
Dear Duong V. Quach
I see two sets of data...
Warburg element correponds to a semi-inifnite diffusion mechanism so I do not think this is what is happening on your sample.
You should try to go to lower frequencies.
Using R+R/Q+R/Q for the low impedance data and R/Q+R/Q for the high impedance data should do the trick.
I hope this helps,
Best regards,
Nicolas
Dear Sourav Roy
Thank you for responding. But, I am not sure Origin could help to build an eq. circuit.
Regards,
Dear Duong V. Quach ,
I think you may have measuring errors at the small phase values which may have more effects on the low frequency parts of the complex impedance chart. You must measure the DC resistance directly. This measurement can be accomplished by adjusting the DC operating point at I and V and the you increases the the current by an incremental value and measure the increase in the voltage of the device. Then you can can calculate the small signal resistance at the this DC condition by dividing dV/dI. This will give you an important point on the real axes from which you can judge whether the right part is in error or not.
If the plot is semicircle then it can easily be fitted with a parallel R- C circuit which is connected din series with aperies resistance RS.
Best wishes
Here you can have different models of the Randle circuit which are preferably editable and easy to fit the data.
http://www.abc.chemistry.bsu.by/vi/analyser/program/program.htm
Install this EIS Spectrum Analyser software and perform your data analysis.
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