It puzzles me when I try to repeat EIS experiments. The same experimental conditions are used, unless the bare electrode is cleaned between each run. Different EIS data is obtained in terms of the charge transfer resistance, and usually it decreases in the 2nd run and 3rd run and stays the same after the 3rd run.
Does anyone know why? And which run should I use as "the" result? To me, in the literature, people rarely talk about the reproducibility and the results they show are mostly based on one-time experiments.
look if your systems changes a lot during measurements it means that your electrode is not clean at the atomic level.EIS experiments on bare electrode are very reproducible. Also you have to ensure that your electrochemical cell is clean, and never use organics (etanol, acetone) to wash your electrode and electrochemical cell.Only Millipore water. Clean your electrode very well: first polyshing on microcloth pads with Diamond suspension (to push hard on it as circle shape), sonicate in MilliQwater 20 minutes, than electrochemically cleaning in aq. HClO4 (run at least 100 CVs , until you get the CV specific for clean electrode). After that you can use it for EIS experiments (freshly cleaned , not next day!). After this procedure every experiment that you perform is very reproducible. Let me know how it works.M
I think the "degree" of reproducibility depens a lot on the reaction that you are studying. I think that for most publication you should interpret the data as a trend and not to take into account the exact reported values. And maybe some kind of adsoprtion reactions or surface conditioning takes place in your first 3 runs. As long as your EIS spectra stay the same after the 3 run, you should take the forth run as "the" result . This happens sometimes also with CV measurements. Good luck.
I use Ferri-Ferro couple in KNO3. Au electrode is used as working electrode in this case. I'm not sure if there's adsorption happening on the surface. Is there any other possible causes?
Yes this does happen sometimes in CV, but not in this setup, I ran both CV and EIS, no big differences were found in CV.
Please check the potential prior to each experiment, it should be same for each experiment while you are checking the reproducibility. Effect of adsorption can not not be ignored during the experiment, It might be a cause for non reproducibility. During experiment the system may catch up some unwanted electrical noise from surroundings, in that case put your system in Faraday cage to minimize electrical noise.
look if your systems changes a lot during measurements it means that your electrode is not clean at the atomic level.EIS experiments on bare electrode are very reproducible. Also you have to ensure that your electrochemical cell is clean, and never use organics (etanol, acetone) to wash your electrode and electrochemical cell.Only Millipore water. Clean your electrode very well: first polyshing on microcloth pads with Diamond suspension (to push hard on it as circle shape), sonicate in MilliQwater 20 minutes, than electrochemically cleaning in aq. HClO4 (run at least 100 CVs , until you get the CV specific for clean electrode). After that you can use it for EIS experiments (freshly cleaned , not next day!). After this procedure every experiment that you perform is very reproducible. Let me know how it works.M
You don't mention what kind of sensor you are using, but if the electrode surface is modified, maybe conditioning effects take place during the first 3 runs. In this case try a conditioning step before carrying out your measurement by immersing your electrode into the electrolyte solution that you are using (you must optimize the duration of this step). In addition you must ensure that your electrodes are in the same place every time you perform measurements (the distance between them must be constant).
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