As the charges on the redox probe and the electrode (modied material) will effect the Rct of the system under study. There are many reports in which the authors have been using the ferro (-vely charged) redox probe to compare the Rct of modified and bare electrodes. Here my Question is that The modified electrode may have +ve or -ve or nuetral charge on it, in each case we will get different Rct in the same redox probe lets say ferro. if it so, then how can we compare the Rct of the -vely charged electrode(lets say GC-Graphene oxide) and +vely/neutrally charged electrode(lets say GC-Graphene)s in a -vely charged (Ferro) redox probe?
EIS technique is capable of detecting small changes occurring at the solution–electrode interface. The interaction between a charged redox couple and the electrode surface is reflected by the charge-transfer resistance (Rct).
The choice of the redox probe depends on various parameters such as the charge, hydrophobicity/hydrophilicity, size of the redox couple, and the chemical and physical properties of the modified electrodes.
If you have a modified electrode with negative-charged and you use Fe(CN)63- /Fe(CN)64-as redox probe, there is a repulsion between the electrode and redox probe but if you use a positive charged redox probe, such as Ru(NH3)63+/ Ru(NH3)62+, you can observe a decrease in the electrostatic repulsion between the sample on electrode and redox probe, i.e. a decrease in Rct value.
The interesting thing is to watch the changes that occur when the electrode surface is modified and it is best to select the redox probe that yields higher redox changes.
In addition to the response formulated by Dr. González, I do suggest employ a neutral redox probe in your EIS experiments. For instance, ferrocene can be a good option if you are interesting for exploring chemically modified electrodes with a redox probe which do not have electric charge in the biginning. In this context, you must take into account that the solubility of ferrocene in water is less than 60uM. However, I have employed this molecule with excelent results.
Thank you very much Dear Araceli and Juan for your informative response, But my question here is are those reports reliable and are the authors sending wright message to the scientific community?
EIS measurements generally gives the Rct depending the surface modifcation. Use of additional redox probe is just to see how extent it could help the charge transfer (or it could repell as well) depending on the nature of the surface under study. You may required prior knowledge on the surface behaviour under interest.
Depends on what the authors claim. Basically the information they acquire is only valid for the system they chose to investigate. Sometimes general conclusions can be drawn.
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