I was trying to deposit hydroxide form of ZnCo2O4 through electrodeposition technique. In this regard I have taken Zn(NO3)2 · 6H2O and Co(NO3)2 · 6 H2O in a 1:2 molar ratio in a 40 ml DI water. Deposition potential was kept at -0.9V. However, current initially started to decreases but after few second it started to increase. Almost nothig deposited on the ITO glass. Any idea why this is happening?
I have used 3 electrode system as below configuration
Working Electrode: ITO Glass, Counter Electrode: Pt wire, Reference Electrode: Ag/AgCl
Possibly you are cleaning the ITO electrode, provided the counter electrode is not limiting or fouled. Of course it's not abnormal that current increases during electrodeposition as surface area increase vs. difusion becomes more significant even if deposition is minimal or unstable.
Check the position of the ITO-coated side where it should meet the counter electrode
Check the quality and percentage of DI used
In addition, there are two possible reasons for the phenomenon you described. The small amount of material deposited in the early stage catalyzed the reduction of nitrate, or HER. If it is the latter, a large increase in bubbles generated on the electrode will be observed. If the bubble does not appear or does not increase, it is the former.
There could be multiple reasons, as stated in all the answers above.
In addition to the above explanations, the change in current could be due to
- a change in the initial electrode surface area.
- some impurities in the electrolyte/ in-homogeneity in the electrolyte mix.
- increase in the electrolyte temperature
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