I want to ask about the response of the analyte in the EIS measurement. Bare shows a high Rct response as compared to material-modified electrodes. But when we modify the material + analyte, the Rct value response decreases. What is the reason for that? According to my knowledge, it would show a higher Rct response than material, & in CV, it shows less response than material (quenching).
Monika Antil
You're on the right track! The decrease in Rct (charge transfer resistance) upon modification with the analyte can be explained by considering the interaction between the material, the analyte, and the charge transfer process. Here's a breakdown:
Bare Electrode:
- High Rct: The unmodified electrode presents a barrier to the transfer of electrons between the electrolyte and the electrode surface. This resistance is reflected in the high Rct value observed in EIS.
Material-Modified Electrode:
- Lower Rct: Modifying the electrode material can improve the conductivity and electron transfer properties. This can lead to a decrease in Rct compared to the bare electrode.
Material + Analyte Modification:
- Decreased Rct (compared to material only): Here, the analyte likely interacts with the modified electrode in a way that further enhances electron transfer. This could be due to several reasons. The precursor/catalyst effect is that the analyte might act as a precursor or catalyst for the desired electrochemical reaction, facilitating electron transfer. Improved surface area/porosity: The presence of the analyte might create a more porous or high surface area structure on the electrode, allowing for better interaction with the electrolyte and reducing Rct. Direct electron transfer: In some cases, the analyte might be capable of direct electron transfer with the electrode, bypassing the need for the original electrode material and lowering the overall Rct.
CV (Cyclic Voltammetry) and Quenching:
- Lower current response: The observation of a lower current response in CV compared to the material alone suggests a phenomenon called quenching. This could happen due to several factors: Analyte blocking active sites: The analyte might physically block the active sites on the modified electrode, hindering the interaction between the target molecule and the electrode surface. Mediation effect: The analyte might indirectly mediate the electron transfer process, leading to a slower overall reaction rate than the direct interaction between the target molecule and the electrode material. Thanks!
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