Hello,
I am trying to perform cyclic voltammetric studies using Versastat 3 Potentiometer. For the first study, I have used a Pt wire with diameter 1.6mm as working electrode, a Pt sheet as counter electrode and Ag/AgCl as the reference electrode. The electrolyte is 10mM of pottasium ferricyanide in 0.1M KCl supporting electrolyte. As I connect my cell to the potentiostat I have seen that there is an overload which stops the measurement. The potential window I am using is +0.6V to -0.6V with a scan rate of 100mV/s scan rate. What can be the probable reasons of this overload and what can I do to avoid it?
First of all, please check the basics:
1) Is the cell assembled correctly? Please make sure that none of the electordes are in contact with each other, each electrode is connected to the correct terminal of the potentiostat, etc.
2) Is the control software and experiment configured correctly? A current cut-off may be included in the experiment and would stop the experiment with an "overload" message. Also, is the current range set to "auto"? While I used to work with a much older Princeton potentiostat, I have little experience with the Verastat line of potentiostats. AFAIR, sometimes it was better to set a current range by hand - please verify if setting the current range to a bit more than you are seeing in the experiment, which yields the "overload" message, helps.
3) What is the operating potential window of your supporting electrolyte (KCl/H2O?)? The potentials you are applying might be sufficient for decomposition of water / KCl or for an electrode reaction of the oxygen dissolved in the electrolyte solution.
Should this not help or the current in the CV be above the range the potentiostat can handle (unlikely, but possible), you may want to use a much thinner working electrode.
You have good suggestions from Tomasz. I recommend you to verify the current range setting first.
check the potential range and the current range. if possible upload the image of parameter file here.
Thank you Tomasz, Cornel and Zahid for your suggestions. I could finally measure the CV. I changed my reference electrode and yes indeed the current range was set to Auto. So I corrected it. Hoever, the CV curves that I have obtained are very noisy. I am attaching a picture of the CV curve at various scan rates. What could be the cause of the noise that I am observing?
1.The noise is high because the current range manually set is too high. Choose 10 microA as range. It is also possible to set the potentiostat for a higher damping (higher integration time). I don't know the Versastat, tell me to search more, if you need further help.
2. You have another problem: a bias of -0.5 microA in current values recording. You may verify this also with a dummy cell ( measurement on a resistor in CA mode: you must record 0.000000.... A for 0.00000... V) . Only the manufacturer may solve this correction.
There's not really much I can add to Cornel's suggestions, apart from some other possible "culprits" of your current noise (please check the adequacy of the current range first - this is the most likely culprit):
Electrical filter (e.g. automatic compensation of high/low-frequency current oscillations) settings - in some cases they can tend to over-compensate and cause such noise.
Possible mechanical oscillations of your experimental cell - the current spikes at 0.0V (for 40mV/s) and +0.15V (10mV/s) look like they have been caused by some sudden mechanical shock. Although unlikely, a constant vibration of your setup could also result in such noise.
As to the current issue, pointed out by Cornel, a "less severe" possibility is that either the electrolyte or some contaminant undergoes a reaction below 0.0V and you are seeing the onset of a voltammetric peak. This is possible both due to the fact that the current value changes with the scan rate and because your high-potential end of the CV is relatively close to a 0.0uA current.
Nevertheless, it is always good to check your potentiostat on a resistor system to ensure that it is always working correctly (a handy setup is to link two identical resistors in series, i.e.: -R1-R1- and connect the electrode terminals of the potentiostat so that WE and CE are on the opposite ends and your RE is attached in between the two linked resistors like so: WE-R1-(RE)-R1-CE).
As suggested put the current range and potential range properly. Secondly i would suggest to increase the concentration of supporting electrolyte to 1 M.
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