Recently, I was trying to deposit AgCl into the surface of silver wire to make Ag/AgCl electrodes. The silver wire I used is 99% impurities and 0,3 mm in diameter. I used KCl 1 M & 3 M as electrolyte and 9 volts of voltage apply to the wire. After a few minutes, I found that the solution becomes completely black, and sure, my wire becomes darker.
Why did this happen?
As I could understand, the AgCl solution is taking electron then reduction/oxidation could take place. It means Ag2O/AgOH will make solution darker/Brownish. Similar to this event happens in Al nano powder milling which oxygen makes Al2O3 so to get Al we could use inert gasses like He,... .
I recommend fig.8 in :
Article Fabrication and evaluation of a highly durable and reliable ...
I guess if Cl2 bubbles appears then remaining K makes KOH So H2O leaves oxygen which could make Ag2O in solution or another scenario could be the oxygen diffusion (from air) into solution happens. We could check solution pH.
Dear Ali Bakhshi Muhammad Ihsan Alfikro, this black precipitate seems to be silver oxide. As a result of water reduction on the surface of the cathode, hydroxide ions are produced that precipitate the produced silver ions on the anode in the form of silver oxide. First of all, you should use 0.1 M HCl solution instead of KCl solution for the electrolysis. Since it is acidic, it precludes the formation of silver oxide. Secondly, it is recommended to operate the electrolysis at a constant current, not a constant potential. In this way, you will obtain a more uniform AgCl film on the electrode. Below you may find a few papers concerning preparation of Ag/AgCl electrode that can provide you with further details.
Article Easy-to-Make Ag/AgCl Reference Electrode
Article An improved approach for fabricating Ag/AgCl reference electrodes
Best,
Dear Muhammad
Why don't you use precipitation method to coat your silver wire with a thin layer of AgCl?
Dear Ali Bakhshi Mahdi Ghamsari
Thank you sir, for helping me realize what happened on my electroplating process. I just curious what happen to the solution.
It was amazing for having such detailed explaination & thank you so much for recommended some articles
Dear Dr. Mohammad Kooti
I would like to know more about this method, is this the same method which the wire soak to chloride solution like soaking to commercial bleach?
Some journals say that electroplating is best method used to coat silver wire
I think if you put the silver wire in a dilutd silver nitrate solution and then add a dilute solution of NaCl with gentle agitation you may be able to coat it with AgCl layer.
You perhaps need a stabilizer.
Thank you for the suggestion Dr. Mohammad Kooti
It's interesting to attempt it. Later, I would like to conduct this method to coat my wire and compare it with the electroplating one.
If you don't mind, could you please suggest some references about it?
Dear Mehdi,
I think that your mistake is the working in high voltage, and the solution is becoming dark/black due to the oxidation of Ag wire and formation of Ag2O at high voltage/current density.
To prepare a suitable and ideal reference electrode, please use constant current conditions and apply five mA on the electrode surface. Under these conditions, a suitable layer of silver chloride will be deposited on the surface of the silver electrode.
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