I have been trying to get a background CV with 1M NaOH. As soon as I do IR compensation, the program says "Resistance is TOO HIGH". I can see bubbles forming in the GC electrode and auxillary Pt mesh. Also leaving black deposits on the GC electrode with pocket marks.
Could you please say the potential that you use to get the background? If the pH is too high, there might be oxygen evolution in GC electrode and in the counter electrode, hydrogen evolution will occur i,e., in simple alkaline water splitting will happen. If the potential is too high, the glassy carbon material itself will oxidize to form activated electrode surface.
If you're getting bubbles of gas, you're surely applying a potential in excess to what the electrolyte can take. Carbon electrodes are easily oxidised at potentials in excess of around 1 V in most solutions, but this can be significantly lower in strong alkali. The poorly defined oxidation products (maybe including graphene oxide) are base-soluble. You'll also be putting O-containing functional groups on the electrode, such as carboxylate, carbonyl, phenols, chromenes and possibly quinones (with their own rich redox chemistry) at large positive potentials.
One of the best books on this stuff remains the ancient "Electrochemistry at solid electrodes" RN Adams, though the Kissinger & Heineman "Laboratory techniques in electroanalytical chemistry" has a good chapter by McCreery on carbon electrodes. Kuwana is also worth reading.
Hydroxide ions oxidise through the loss of two electrons giving oxygen and water. Oxygen is responsible for the oxidation of carbon.
Hi Asmita,
Make sure you've cleaned all electrodes with correct methods before the test and the quality of the electrolyte you used. The black deposit formed on the electrode should be also related to side reactions in your system, other than oxygen evolution reaction at high potential.
Good luck!
Hi
I agree with all answers mentioned above. However, you have also to check your connection, especially your reference electrodes. or bubbles in your luggin capillary
I agree Alaa A.El-Shafei , mainly because you mention overpotencial and bubble evolution. Check no ohmic falls with dummy cell, as well.
carbon can be oxidized at very high potential. the applied potential may be over loaded so you should repeat your experiment and check your connections as mentioned above
The procedure to clean and activate GC electrodes, clean and highly polished with diamond paste and subsequent process with a sonicator, in NaOH to potential +1.2 V, and 10 successive cyclic sweeps, aims to functionalize the surface GC electrode. These highly oxidizing conditions, quinone and carbonyl groups are generated, among other chemical functional groups which act as redox mediators, useful systems for well defined peaks and reversible.
This has been demonstrated in my experiences with lab for p-amino phenol (PAP), and the GC electrode untreated. In this case irreversible cyclic voltammograms were obtained and poorly defined peaks.
Best results were achieved with LASER.. But this technique is expensive.
See the following references: Anjo, D et al, Anal. Chem, 61 (1989) 2603. Poon and M. Mc. Creery R.L. and Engstrom. R; Anal. Chem., 60, (1988) 1725.
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