The resistance between reference and working electrode is known as (Rs) I.e. solution resistance while charge transfer resistance (Rct), is the resistance between working electrode and solution. These are the two important values which one want to know in order to investigate the Kinetics of particular electrode.
Electrochemists are requested to suggest the recommended potential and other parameter to get EIS of samples in solution for studying OER kinetics of electrodes.
Thanking in advance.
Hi,
The Rct will be affected by the overpotential you apply, i.e. the higher the overpotential the lower the size of the semicircle in the Nyquist plot. Given that one of the main requirements for EIS is a stable system with a linear response between E and I, I would avoid the region where mass transport limitation kicks in (in you are working with RDE just collect some CVs at different rotation rates and avoid all potentials higher than the value where the CVs split). This would ease your fitting and you avoid bubble formation. Alternatively, you could use the Tafel plot to check what is the potential range with linear response of IvsE. Another reason to avoid high E is that your catalyst may peel off the surface or corrode, which means that your system is no longer stable. I used to work with Ir catalysts and an overpotential of around 270mV was a good value for me. If you're working with RDE, be careful with long term stability tests: microbubbles can get trapped in the catalyst layer leading to a false degradation effect. What is changing is just the surface area. What I think is crucial to benchmark the catalysts and make them comparable is however the normalization of their activity (current) by the available active sites. I do not know your system, but using some stripping methods (CO stripping as well as metal stripping) could be a viable option. Also the determination of the capacity by EIS could be an option, unless you're using nanoparticles supported on an inert conducting substrate. I see that knowing the Rct is important, but how can you determine a reliable value without knowing the actual surface area of your catalyst? By simply doubling your surface area you would be capable to deliver more current, but this does not make your catalyst more active, since you could simply obtain the same result by using more catalyst.
Hope that was helpful.
Thank you very much Francesco Bizzotto, your answer is really helpful for me since previously i did not know that the greater the overpotential applied in EIS studies, smaller will be the diameter of semicircle and consequently lower will be the charge transfer resistance (Rct) value. Moreover, it is known and I have also seen in many reported work that the researchers also use their observed overpotential for particular reaction say for instance OER in their EIS studies. Any way your response is highly appreciated.
Best Regards.
Sorry, I just want to correct what you stated in your last comment about the semicircle that gets larger with the overpotential, but what I said in my previous comment is the opposite: higher overpotential=lower Rct, that is smaller semicircle diameter.
Cheers, Francesco
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