A corrosive electrolysis experiment attacked a slightly exposed Ag wire junction in the reference electrode of our Electrasyn instrument. Afterward, the Pt foil counter electrode (cathode) had raised deposits of a silvery metal when examined under an optical microscope. Naturally, I suspect the metal is silver; the only other possibility would be Pt etched from the working electrode (which I hope isn't happening). The electrode is too large to fit in our SEM without cutting so I can't easily check the surface composition. Assuming it is Ag, what would be the best way to remove it? My first impulse is to strip it off anodically but I don't know what sort of conditions would be appropriate. Hot nitric acid would get most of it, but could some contamination remain? Polishing off a thick deposit might risk damage to the foil.
Given the popularity of Ag reference electrodes, I can't be the first person to encounter this.
Dipping in 1M HCl aqueous solution will remove Ag as soluble AgCl from Pt electrodes
As your mentioned HNO3 is the best solvent to remove silver from the surface of electrode and it completely can dissolve silver. However, it is possible for part of silver to form an alloy with platinum that makes it difficult to be removed by only HNO3. I suggest using of ammonium nitrate solution after leaching with HNO3. Ammonium ions can form a complex with Ag+ and help to improve it's solubility.
Dipping in some concentrated nitric acid would do, as long as you avoid chlorides, since they would form an insoluble silver chloride. You could neutralise by a soak in NH3/NH4NO3 with even some some citric acid added in order to leach any leftover silver ions, which may be left over on the surface, as Kobra Ghobaldi mentioned, they could form water soluble silver complexes.
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