During performing CV of a GCE or modified GCE, we rise the potential in the first half of the cycle and reduce it in reverse half. During the first half, what is the nature of charge on GCE or modified GCE, similarly what is the charge during reverse cycle.
For, Eg- In Fe redox couple, for a graphene coated GCE, Ox. of Fe2+ is seen at 0.25V whereas in bare GCE, Ox. is seen at 0.3V. How does the charge on GCE plays a critical role here? Please explain.
Dear Sai Prasad Nayak
When the potential raised from a value where no charge transfer occurs to a redox active solution species, to one in which charge transfer occurs, the oxidation reaction proceeds then the concentration of the redox active species will be lowered at the electrode surface followed by decreases in charge transfer rate. This case leads to build up a concentration gradient between the near zone to electrode surface and the bulk of the solution. This means that the oxidation process at electrode surface is at unsteady-state condition between the rate of diffusion and the rate of charge transfer.
Now when the concentration gradient increases as the electrode is continue at a potential value sufficient to allow charge transfer, diffusion of redox active species from the bulk solution of high and constant concentration to regions of low concentration near the electrode surface start to develop a steady-state condition between diffusion and electron transfer, where the rate of diffusion matches the rate of charge transfer.
I hope the above explanations are helpful to stand on the function of working electrode charge changes with rising potential.
Best regards
Thanks for the answer. The above answer deals with concentration gradient of electroactive species and charge transfer. But, I wanted to know, Is there any charged species on GCE independent of what occurs in electrolyte? If yes, with the application of potential (in CV) what occurs to these charge on GCE without considering the species in electrolyte?
Dear Sai Prasad Nayak
Regarding your above feedback, my answer to your question "is there any charged species on GCE independent of what occurs in electrolyte?" is "yes there " and its depends on the type of the applied methodology for the pretreatment preparation and modification of the GCE and thus its surface composition and structure.
In this respect, I take your example for Fe3+/2+ redox system, as the affected by the graphene modification, since the graphene acts as a “getter and sink” for solvent impurities and for species desorbed from the GCE surface during the pretreatment and cleaning stage leaving the electrode surface clean. These charged species are independent of what occurs in electrolyte until CV potential rising. In this stage the graphene continue remaining as the sink for trapping impurities comes from the solution of redox species. In addition, removal of these impurities would be expected to increase the adsorption of solution redox species which normally compete with impurities for adsorption sites on electrode surface. For that, the oxidation potential with graphene coated GCE lower than that of bare GCE.
Best regards
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