An electrochemical quartz crystal microbalance study of the adsorption of 4,4′-bipyridyl at gold electrodes

Abstract

The adsorption of 4,4′-bipyridyl (Bpy) at gold electrodes has been studied using the electrochemical quartz crystal microbalance (EQCM) technique which reveals clearly the presence of the adsorbate and the effect that it has on the behaviour of the electrode. Mass increases observed in buffer solution are removed almost completely by adsorption of Bpy which yields a constant mass response over the potential range from −0.6 to 0.6 V vs. SCE. More interesting effects are seen when the electrode surface is subjected to irreversible oxidation in the presence of Bpy. There is no significant increase in mass upon surface oxidation and the mass response also reveals that the reversal of place-exchange (where an O species is inserted into the Au lattice upon oxidation) on reduction of the oxidised surface leads to removal of a small amount of adsorbate and an irreversible loss of material from the electrode surface, possibly in the form of a gold complex. A possible mechanism has been proposed which would account for these observations. Finally, EQCM responses show clearly that adsorbed bipyridyl is easily removed from the electrode surface by washing.