I'm using acidic and basic piranha (H2SO4+H2O2 and NH3+H2O2 respectively) in a two steps procedure, rinsing with miliQ water after each piranha solution. The fact is that the silver foil looks pretty clean after that but some high current redox couples appear in the voltagrams when just measuring the curve on a phosphate buffer (pH6). I'm using a cell with a Ag/AgCl ref electrode and Pt counter electrode.
So I've measured after cleaning with both and each piranha solutions, and the redox couple is always around -450mV.
Attached are 4 plots that show what I say above.
I don't remember the Ag CV, but are you sure that this is not your expected profile? or have you tried to clean it by CV in acid solution?
A new silver working, clean it with ethanol to remove any finger residuals or oils.
Need to sonicate in ethanol after with dd. water. Then dry it under nitrogen flow
Polarize the silver foil in dilute acid (0.01 M HClO4) cathodically to voltages where hydrogen gas evolves (reduction of H+). Let the bubbling occur for about 15-30 minutes. Silver surfaces can appear clean after polishing but subsurface reducible materials remain trapped. Evolution of hydrogen gas should get rid of any of these and yield a truly clean surface. We routinely clean our silver electrodes this way to assure reproducibility in cyclic voltammetry and other electrochemical techniques.
Thank you John! Do you think it may work just with 0.01 M HCl? I guess is the 2H+ ---> H2 reaction which matters here. What potentials do I have to apply? Should I use a graphite electrode for the anode?
Yes, 0.01 M HCl will work. The voltage needed to get hydrogen gas evolving will be between -1 and -2 volts relative to a silver/silver chloride reference electrode and depending on the acid content of solution. Even neutral water will evolve hydrogen at more negative voltages. Whatever your electrolyte or reference electrode just dial the potential negatively until you see hydrogen bubbling.
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