In addition to a very clean Pt electrode and low scan rates, as suggested above, lowering the concentration of ferro/ferricyanide can help. When you have both species in solution at relatively high concentration (whether because you start with both or you produce one from the other during experiments) you can generate Prussian-blue type of compounds on Pt electrodes which can hinder the process and separate your peaks. I'd suggest 1mM rahter than 10, to decrease the chance of these compounds having a big effect.

Hello Safdar,

there can be several causes - your electrode is maybe not clean enough, do you see some improvement in peak separation, if you make multiple CV cycles?

Also, your plate electrode is quite large, you can have significant uncompensated resistance and hence IR drop in your system. If your potentiostat has IR drop compensation, try to use it.

Also, under the circumstances of large electrode it is good to put the reference electrode close to the working electrode and also to have auxilliary electrode with larger surface area compared to working electrode.

Hi Jan Hrbac, 

Thanks a lot for useful comment.

I will repeat the experiment after cleaning the Pt plate electrodes with Conc. HNO3. I will also look for IR drop compensation option in my control software.

Regards

Good luck, Jan

Hi Jan,

I repeated the CV by washing the electrodes with conc. HNO3, and the difference is now 104 mV, instead of 170 mV. IR-compensation did not contribute any effect when was turned on. But still 104 mV is pretty much high. Isn't it? So is this because my WE and CE both are of similar size, i.e. Pt plate electrodes?

As far i concern we do this with the glassy carbon electrode to know whether the surface is clean enough or not. usually a separation of less than 120 mV  tells that the surface is clean enough to drop dry the material. 

The clean process also can be done by polishing with alumina powder as well. You can polish the Pt plate with different sizes of alumina powder and see whether you can improve the peak separation.

Hi Safdar,

What is the scan rate you use? Ferricyanide couple is preety reversible on platinum, but not completely. Try the scan rate 20-50 mV/sec, if you'll get better result. The comparable sizes of the electrodes make the potentiostat put higher voltage between the counter and reference electrodes which can slightly worsen the voltammogram shape. The polishing with alumina may help, as the colleague pointed out, alumina cleans the electrode and in adsorbed state may catalyze the electron transfer.

You did no describe how to treat Pt electrode before runing CVs. I guess that your pretreatment on Pt plate electrode may not be good enough. Normally, you can first polish Pt electrode down to 0.05 um Al2O3 slurry, then you can clean Pt electrode by successive CV cylcling in 0.5 M H2SO4 until you see the standard CV for Pt (say 50 mV/s, 50-100 cycles). You should be able to get CVs with around 70-80 mV peak separation for ferri-/feerocyanide redox couple with no much difficulty.  

You need to use 0.3 M KNO3 as an electrolyte

The method that Dr. Chi suggested will be highly useful. Take H2SO4 solution 0.5M, connect as a three electrode system, do cyclic voltamograms at 0.1V/s scan rate between -0.2 to 1.2V vs Ag/AgCl (sat) for 50cycles. Then perform CV in ferri (typical conc. 5mM ferri+1.5M KCl). Before doing this check whether your referance electrode is in good condition.

In addition to the tips given above, I would try to check the reference electrode, by measuring the potential difference to another reference electrode. If the potential difference  is o.k., you may trust the potentials indicated by your electrode. If you do not have a suited RE at hand, you may easily produce one with Hg/HgO/Na2SO4or alkaline with Hg/HgO/1M NaOH, etc. Good luck, Dirk

In addition to a very clean Pt electrode and low scan rates, as suggested above, lowering the concentration of ferro/ferricyanide can help. When you have both species in solution at relatively high concentration (whether because you start with both or you produce one from the other during experiments) you can generate Prussian-blue type of compounds on Pt electrodes which can hinder the process and separate your peaks. I'd suggest 1mM rahter than 10, to decrease the chance of these compounds having a big effect.

Whatever you do with electrode you must use a high concentration of K+ in solution. This is a must!

Standard condition to obtain CV: glassy carbon working electrode, platinum 

auxiliary electrode, Ag/AgCl reference electrode, under Ar 

10 mM K4Fe(CN)6 in 1.0 M  KNO3

I didn't notice the high concentration of ferricyanide. Lowering it or working at higher concentration of supporting electrolyte should help. Argon is, however, not necessary.

Yes, Ar is not necessary at a positive potential domain.  Ferricyanide concentration is not critical. KNO3 must be higher than 0.3 M

Dear safda,

    first the concentration is a little high. secondly, you have to polish your electrode to mirrorlike surface. third conduct the experiment at a lower scan rate. your purpose is to check the potential sata, so you can use a galssy carbon electrode. Pt plate electrode is not easy for you to pretreat.

Hope you already got the solution from above mentioned suggestions. There are  nice suggestions indeed. I would only emphasize one point, i.e.reduce the potential range and try it. Because the peak potential is greatly influenced by end potential.

Well since you just want to check if your potentiostat (system) is working, if you have a  glassy  carbon electrode, I encourage you to replace the  platinum working electrode. I once encountered almost a similar  situation when i used platinum for both  working and counter electrodes. 

I would suggest you to cross check with Ferrocene (say 10 mM in CH3CN). You must make sure your three electrodes and electrochemical cell are clean enough. Oxygen play huge role during the measurements, so you must deoxygen it before the measurements and I suggest you to flow the Ar to closed cell not less than 30 min. Good luck.  

Hi, I agree with previous suggestions of Jan Hrbac and Daniela Plana. IR compensation would be less important in aqueous solution, but the surface of working electrode is crucial. Your current reached 1 mA, it suggests that your working electrode is really large. Under these conditions you obtained probably good cyclic voltammogram.

Hi, Muhammad,

I agree with the previous comments and suggestions. Yes, to improve your results it can be recommended:

1) lower concentrations of the analyt (ferricyanide and ferrocyanide) and higher concentrations of the supporting electrolyte (but the concentration of  0.1M KNO3 could be OK)

2) pretreatment of Pt working electrodes by using alumina with sonification and then by using several cycles of this electrode in pure supporting electrolyte under checking the potential window

3) the lower surface of the working electrode (diameter of 2-3 mm) and the control of an IR compensation

4) the comparison of results by means of Au or Pt working electrodes with the same Pt electrode as the counter electrode

5) removal of oxygen does not play key role (according some papers) but we have some experience with the effect of oxygen on Ep (maybe according the type of the working electrode)

6) to check the effect of scan rates: "reversible" electrode reactions at low scan rates can become "irreversible" at high scan rates.

I saw the CV you have. I think there is no issue on potentiostat. As previously suggested, you may improve the CV by:(1) using well-polished Pt electrode; (2) lowering the concentration of the redox couple to 1.0 mM: (3) reducing the concentration of the supporting electrolyte to about 0.10 M: playing with low scan speed at 10-25 mV/s.

I think the correct way to check an electrochemical workstation is but using a resistance maybe your instrument comes with a test box if not a simple resistance can work, you can run a  CV connecting the leads to the resistance and if is working ok you should get a V but inverted signal in a E vs. t or a straight line in the i vs. E. But I think that your instrument is working ok given the CV you presented.

Such kind of CV with peak difference more than 100mV one can find by the link attached, along with statement : "The ferricyanide redox response forms the characteristic “duck” shape of a fully reversible reaction in the cyclic voltammogram (Figure 3)". They use 12 bit digital to analogue converter as output from microcontroller, which is not true linear analogue scan...  

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0023783#pone-0023783-g003

I am working on Cyclic voltammetry, I need to ask whether single cycle is enough to record CV or multiple cycles should be used to record CV?

What is the main purpose for your experiments? Do you just want to test Pt working electrode? or Do you have to use Pt as working electrode?