I use copper foil as an electrode in the process of CO2 reduction reaction. When I opened the cell after the process of applying - 1.3 volts vs RHE on the foil for an hour, I noticed a black layer on it. The copper has likely oxidized during the process. The weird thing is that the current was negative and stable just like usual. So what could be the reason for its oxidation? The foil is a piece of others that have been polished, cleaned and annealed and used as before with no problems. Same case for electrolyte which is from the same bottle of 0.5M KHCO3 solution.
when i run cyclic voltammetry on carbon electrodes i have noticed that the negative current generally refers to a reducing current, now there is oxidation happening here on the electrode which would suggest that the reduction is happening elsewhere probably the electrolyte. Since reduction means the loss of oxygen, there is a chance that the oxygen upon being released from the CO2 is getting enough time to oxidize the copper foil before recombing to form O2 and bubbling out of solution.
What is the counter electrode (anode)? You could be dissolving the anode and plating it out on the cathode. Also, just to clarify, as the computer formating of the question wasn't clear, the Cu electrode was at negative 1.3 V vs RHE, correct?
Yes Mr. Ken Hardee, it is negative 1.3vl v vs RHE (or negative 1.93 v vs Ag/AgCl) . The counter electrode is Pt, which I believe it's unlikely to desolve in my electrolyte, and the reference electrode is Ag/AgCl in saturated KCl solution.
At first I doubted the liquid products of the CO2RR to be the cause of changing the PH, or the local PH high increase on the foil surface due to proton depletion, however the potential is high that the PH can not drag it to the oxidation values even if PH is 14. This is really baffling.
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