Anomalous Electrochemical Behavior of 1,4-Benzoquinone upon the Addition of Silver Ion

A cyclic voltammogram of 1,4-benzoquinone showed a couple of redox waves in aqueous solution. Upon adding a trace amount of silver ion, the cyclic voltammogram exhibited an anomalous behavior: a shift of the reduction peak toward a negative potential and the appearance of a new re-oxidation peak at a much more positive potential. This anomalous electrochemical behavior was investigated in terms of both interactions in bulk and on the electrode surface using some kinds of metal-ion additives and some working-electrode materials. It is suggested that the underpotential deposition of silver ion is primarily responsible for the anomalous electrochemical behavior of 1,4-benzoquinone. This was demonstrated by a measurement of cyclic voltammograms using a silver-deposited electrode at an underpotential.