REDUCTION OF 4,4'-BIPYRIDYL AT AG ELECTRODES - EQCM STUDIES OF FILM FORMATION AND REMOVAL

The reduction of 4,4'-bipyridyl (Bpy) has been studied at electrodepos ited Ag electrodes in 0.1 M Na2SO4 using cyclic voltammetry and the el ectrochemical quartz crystal microbalance (EQCM). A film of reduced Bp y develops on the electrode surface at high negative potentials and it s growth, development and removal can be observed and controlled by mo nitoring the mass responses. While the reduction process appears to be relatively straightforward, the re-oxidation process (as revealed in voltammograms) is complex and is generally not completed during a sing le cycle although full film removal can be accomplished by holding the potential for several minutes at -0.9 V. Cyclic voltammetric removal of thin films gives rise to a broad oxidation current stretching from -0.9 to 0.0 V, while similar removal of thicker films produces a noisy and uneven peak whose position is dependent on scan rate and potentia l and which concides with an increase in the rate of mass removal from the electrode surface. Possible processes leading to this behaviour a re discussed.