Electroless deposition of Pt at a Pd electrode by reaction with sorbed H in Pd/H

In the course of cycling a Pt electrode into the platinum surface oxide formation and reduction region in an aqueous Cl− ion solution, using a Pd ∣ H reference electrode, it was found that the Pd surface becomes coated with Pt. It is shown that this phenomenon arises from electroless deposition of Pt from Pt anodically dissolved from the Pt working electrode; the adsorbed H at Pd ∣ H is the reducing agent. These observations provide a warning that care must be exercised in the use of Pd ∣ H as a reference electrode.