Conditioning or reviving a Ag/AgCl electrode:
If an electrode needs to be 'revived' after abuse or prolonged storage, the first step is to disassemble the electrode and remove the silver wire from the electrode shell that surrounds it. The 'frit' which electrically connects the inside filling solution to the outside world should be replaced (if it is Vycor® ) or cleaned to insure that ionic transport across the inside/outside interface is facilitated.
The procedure, below, is the one generally followed by this web site's author, but a similar procedure is outlined in Sawyer, Sobkowiak, & Roberts.
The old silver chloride coating can be removed by soaking the wire in conc. ammonium hydroxide. Nitric acid may be used to roughen the silver surface. Once the wire has been cleaned and rinsed, the electrode must be anodized or re-coated with AgCl. If a 'low resistance' (i.e., high leak rate) frit is used this anodization can be done after the electrode is reassembled and refilled with fresh filling solution (the author's preference!) This not only coats the silver wire, but also insures that the filling solution is saturated with AgCl. The assembled electrode (or just the silver wire) should be placed in a beaker containing the filling solution. For a wire that is a few cm long and 0.05 cm diameter, a current of about 10 uA applied overnight is generally adequate. A platinum counter electrode completes the circuit. A galvanostat can be used if one is handy: A 9V battery in series with a 1Megohm resistor will also suffice. Be sure that the silver wire is at a positive voltage with respect to the counter electrode to anodize (oxidize) it! In the author's experience the resulting coating should be a smooth, dull, and slightly off-white.
If you have not already done so, reassemble the electrode and allow the renewed reference electrode to 'equilibrate' overnight for best stability. Store the electrode with the frit in the filling solution. If a low leakage 'fiber plug' or cracked glass junction is used, DI water can be used to store the electrode. However, this is not recommended for storage if Vycor® or other 'high leak rate' junctions are employed since that can lead to the dilution of the filling solution!