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I have been experimenting with electrolysis for producing oxyhydrogen and using potassium carbonate $(\ce{K2CO3})$ as an electrolyte. After several hours of electrolysis, I noticed that the plates began to tarnish and after 24 hours, are now dark brown. The plates are made of 316 stainless steel and the electrolyte remains clear.

When I chose to use $\ce{K2CO3}$, I thought that it would not decompose during electrolysis but now I suspect that it is decomposing and electroplating the stainless steel plates with carbon. If this is the case, will this have an adverse effect on the plates ability to conduct and produce oxyhydrogen? Also, is $\ce{CO2}$ being produced?

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Since the carbonate radical is covalently bonded, it probably is not being decomposed electrolytically. Much more likely is that iron in the stainless steel is being removed and oxidized, leaving a thin film of "rust" on the plates.

A few ways you can prove this:

  1. Immerse the browned plates in oxalic acid, which will slowly dissolve iron oxides, but leave carbon untouched.

  2. Substitute platinum electrodes -- admittedly expensive, but Pt is the "gold" standard for electrodes. They should not discolor.

  3. Spray the browned plates with a solution of potassium ferricyanide. If free iron is present, a blue color ("Prussian blue") appear.

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  • $\begingroup$ Titanium could also be used for anodes. $\endgroup$ May 28, 2022 at 18:57

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