Dear Dr Ahmed

Actually, your question needs more clarification

Such as

1-what your material is? each material has a working principle

2-what application you are working for?

each application has its mechanism and it has a specific measurement technique

for example why you did choose 3-electrode system

I suggest you try the 2-electrodes system and see?

in addition to you can magnify the part at High frequency and check may be you have a tiny semicircle at the point of Rs

Yours

Ahmed A. Aboalhassan

Thanks for your reply.

Answering your questions:

1. My material is trimetallic PdAuIr nanoparticles supported on graphite.

2. I am using it as an electrocatalyst to oxidise ethanol in basic solution.

3. Using an auxiliary electrode is necessary to allow reduction while only oxidation is happening at the working electrode. This will prevent electrons to flow between the reference and working electrodes leading to high input impedance.

Dear Dr Ahmed,

I suggest you to try 4-electrode system since your work requires auxiliary electrode

Please, check the following links for more information

https://www.gamry.com/application-notes/electrodes-cells/two-three-and-four-electrode-experiments/

https://www.ecochemie.nl/download/Applicationnotes/Autolab_Application_Note_EC08.pdf

and the following paper

" One-pot synthesis of PtIr tripods with a dendritic surface as an efficient catalyst for the oxygen reduction reaction"

Additionally, up to my knowledge, metallic materials have no capacitance behavior.

best of luck in your future work

Ahmed A. Aboalhassan

1. Add a cyclic voltammogram to support your explanation.

2. Explore a lower frequency range.

3. In your explanation you may see in different ways what happens at lower vs. higher frequency (your surface is blocked at low frequency only).