Hi

you must be prepared a solution contain K4[Fe(CN)6]/K3[Fe(CN)6)] (1 mM) contain 0.1 M KCl.

After preparation of  solution, you can be get good signal in potential windows -0.2-0.9V vs. Ag/AgCl/KClsat

best regards

The reduction peak potential appears to be at about -0.4 V while the oxidation peak potentials are around 0.65 V. It looks like you either have a huge iR drop in your measurements or the charge transfer kinetics are very slow. What potential sweep rate have you used?

Given data is not complete but According to the figure it seems that you have both oxidation and reduction peaks with iR  drop and kinetic problems that may be due to the:

1) Nature of SWCNT: Lower edge plane regions in comparison to base plane… compare the electrode behavior with GCE or MWCNT electrode

2) High scan rates

3) Insufficient cleaning of electrode surface

4) Inappropriate solution