Try to polish electrode very well or use new electrode.

It is very difficult to reach 60mV with GC electrode but you should be able to obtain 70mV...

Using lower concentration of K4Fe(CN)6 (1 mM) and good polishing

The potential difference depends on the solution pH, and also to the electrode surface. If you polished the GCE surface and decreased the solution pH, you can decreased it.

It is not possible reach to very better ∆Ep but you can substitute solution condition (pH, type of supporting electrolyte, concentration) or change your electrode

0.1 M H2SO4 and 10 cycle -1,2 to +1,2, and you have to cover electrode more electroactive layer to reduce peak potential.

it is possible to reduce peak separation for 10 or 20 mV using polishing but we have different types of GCE in the market. If you need better peak separation try with another types of GCE.

Low ur concentration to verify nernst equation

∆Ep is mainly related to the electrode material and the analyte. you can reduce the concentration of 1M KNO3 to 0.1 M (if possible try in 0.1 M KCl too). If the electrode material is not clean you will get larger ∆Ep. Try polishing more of GC electrode.

Thank you for your comments,

Ok bye keep in touch

I think you also need to check the iR drop of your cell. If the uncompensated resistance is high then you would get large difference

I think reference and working electrode should be place as close as possible and counter electrode should be place far

Make sure that the working electrode and reference electrode are as close as possible to each other. Minimize junction potentials.

I would use [Fe(edta)(H2O)]- as test sample.

It works well between pH 3-6 and should behave more reversible as compared to Ferrocyanide! Ideal supporting electrolyte here 1 M KNO3.

shall i use 10 mM concentration of [Fe(edta)(H2O)] with 1 M KNO3

Tried to check if the redox mediator and the system is ok with another electrode (even a Pt or Au disk)? If the solution or the setup is ok, polish the GC as better as you can. Don't waste too much time. If the GC surface is too much compromised for some reason, change electrode.

I think that you can read the principle of Nernstian system of Allen J. Bard and Larry R. Faulkner, 2001, Electrochemical methods, pp. 64 in the section of types of liquid junctions. May be the difference potential was occured from the concentration of electrolyte in solution and electrolyte in reference electrode so this effect can change of Ecell=Enernst+Ej.

IR drop due to positioning of RE and WE has nothing to do with values of ∆Ep for Fe 2+/Fe 3+. system.

Here the value ∆Ep tells about magnitude of reversibility of the redox system. And this value truly reflects the electronic property of the electrocatalytic surface ( Here GC used ). GC's surface property decides the reversibility of redox system and nothing else. Hence it is suggested to clean the surface with rough Watman filter paper and also condition the surface by cyclic pst conditioning between -0.2V to _+0.6V at higher Scan rates for few minutes in the supporting electrolyte

Perhaps you should try using a diffrent redox probe, because ferrocyanide its very sensityve to pH value of media, electrode surface, etc. For aqueous solution perhaps you can try 1mM solution of Ferrocenemethanol (in 0.1M KCl, it works also well when using buffers as a supporting electrolyte).

You should try the use of Hydrogen tetra cyano-mono-1, 10-phenanthroline Iron (III) complex, H [Fe (Phen) CN].2H2O. as your redox probe. The interrogation may de done in distilled water, 0.1M KCl OR 0.1M KNO3.

The problem is with the contaminated electrode surface . In the above GC electrode, even if we use Hydrogen tetra cyano-mono-1, 10-phenanthroline Iron (III) complex, H [Fe (Phen) CN].2H2O. as redox probe you may not get the ∆Ep vakues closer to 58 mV unless the surface is renewed. First we have to understand the actual phenomena occuring when using some standard redox probes ( Fe2+/Fe3+ or quinine/hydroquinone). We will get ∆Ep values closer to 58mV for single e transfer, provided the working electrode has good electronic property on the surface i.e. resistance free e- transfer between the soln and electrode surface.

I truly agree with Gareth. Try and lower the scan rate. However from my experience, I cant remember getting 60 mV though we know it is a one electron process - that is why we explain the potentials greater than 60 mV (100 mV sometimes) as a quasi-reversible system. I also concur to the fact that GC electrode sometimes get damaged or altered irreversibly

I totally agree with SUBRAMANIAN. The redox peak separation in this Fc system has nothing to do with the concentration of Fc, IR drop etc, cause the concentration of your prob and electrolyte is enough for you to avoid the problem above. And also for the scan rate, I always use around the 50 mV/s, sometime 100mV/s is okay. You problem maybe just because of unclean of GC electrode surface. It is very tricky to polish the electrode surface, if everything goes well, only 2 minutes needed, using the filter paper is a very simple and effective method, I also do recommend. certainly we cannot get 60 mV separation, but sometimes blow 100 mV is okay, most of time, we need to use other conductive material to modify the GC. Hopefully can give u some help.

Do mechanical polishing with alumina slurry and clean the surface with dd water properly. But any way for this system you will get the potential separation only less than 100 mV for 100 mV/s scan rate. Because Fe system is not a complete reversible system and we can't take it as an ideal system. You try with Ruthenium ammine complex with lower concentration. Its highly suggested system by many electrochemical experts to check the activity of the GC electrodes.

A proper way to improve the activity of the electrode is mechanical polishing only, other wise it mat affected by other treatments like potential cycling, potential holding, etc.,

The question is misunderstood by Narayanmoorthy. There is a well knonwn Fec system which gives peak difference Ep values closer to 58 mV in a good electronically conductive surface such as pure GC. The GC used by him ( may be aged one) is not showing peak separation value closer to 58 mV, but he gets about 100 mV. How to improve the GC get closer delta Ep values of 58mV on used GC with Fc system. - That is what we are discussing,. We do not want some other known system to work for the present used GC.

Actually, getting the ferrocyanide couple to be reversible on carbon is dicey. Polishing works but the CV rapidly decays during cycling. The kinetics are much better on a Pt electrode and you can get near 60 mV all day on Pt. Even gold is better than carbon.

Depending on the electrode pretreatment the heterogenous rate constant can vary several several decades.