I use Ni Foam (as current collector) covered by ink ( 85% electroactive material, 10% carbon black, 5% PVDF and a few dorps of NMP) as an electrode in supercapacitor, in KOH 6M as an electrolyte.
It is likely some effect of one of the compounds. I would suggest studying the behaviour of your Ni and ink separately in the solution. Likely, the color comes from the ink becase I would expect Ni to form greenish compounds.
previously, the electrolyte became yellow.But now it become (blueish) greenish. how can i prevent this event?
If the solution became greenish, I would think it was due to the dissolution of Ni. What is the maximal voltage your electrode reached? Based on my experience, Ni foam can dissolve at potentials higher than 0.8 V vs. Ag/AgCl in 6 M KOH aqueous solutions.
Did you observe any pronounced peaks at ~0.6 V? The dissolution of Ni usually happens at around 0.55 V. 0.6 V is just above the limit. In this case, Ni can slowly dissolve and it may take a little long time before you can be aware of the dissolution (i.e., you first observed the solution became yellow and gradually greenish.)
It is due to the dissolution of any of your electrode constitutes, try one of the following:
1- Change the potential limits (negative and positive limits) to decide the appropriate limits.
2- decrease the concentration of KOH (during my work on Ni, 6.0 M KOH corrodes Ni electrode especially if your active material is thin enough, 1.0 M is good enough).
3- try to change the nature of the electrolyte and select the most appropriate electrolyte (KOH is not the suitable electrolyte for some active materials).
Good luck
Dear Maryam Pedram,
a (fluorescence[1]) spectroscopic study, if it is reachable, might be essential in your investigation.
1. Fluorescence spectroscopic behaviour of folic acid Article Fluorescence spectroscopic behaviour of folic acid
Dear Maryam Pedram,
In my opinion, I have found it tends to become yellow in a trial experiment.
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