Dear doctor, I'm imaging you are referring to the Nyquist plot characteristic shape? If yes, as I'm observing in your system, you are analyzing the response of such materials deposited in a working electrodes in a determined electrolyte. You have two materials that are in the solid part of the electrochemical interface, and the impedance made at determined potential, is not involving the dissolution of any specie, where all is occurring and maintained in the interface and thus, it does not involve any diffusional phenomena. So, in summary, there is not any significance of not observing this behavior for your sensor. Otherwise, I recommend to obtain the Rct of both electrodes, because you could explain the electroanalytic behavior of both during the detection of heavy metal ions.

best

Dear Neo,

Thank you for sharing your scientific knowledge about the Nyquist plot.

In my recorded Nyquist plot, I had observed close to a perfect semicircle.

Regards,

Pasha

you are welcome! please remember that for Rct, you need to obtain the values from the electrical circuit models that better-fitted to your system, maybe a Rs-Rct-CPE model

best