Electrochemical reduction of Rh(bpy)33+ at Hg/phosphate electrolyte interface

The electrochemical reduction of tris(2,2′-bipyridine)rhodium(III), Rh(bpy)33+, in phosphate buffer solutions was investigated by cyclic voltammetry, alternating current voltammetry, chronoamperometry and exhaustive electrolysis. The cyclic voltammograms exhibit a series of sharp peaks indicating surface confined processes. The major features of the electroreduction are strong adsorption of Rh(bpy)33+, participation of mercury in the electroreduction process and the simultaneous loss of bipyridine ligand. The complex forms condensed layer in a narrow potential region around −0.8 V vs. Ag/AgCl. The chemical bond between Rh(bpy)33+ and mercury is required for the formation of binuclear complex of rhodium(II), [Rh2bpy3(H2O)Cl]3+, at the potentials about −0.9 V. At the potential of −1.1 V further reduction of [Rh2bpy3(H2O)Cl]3+ leads to the concomitant oxidation of the mercury electrode, resulting in a mixed Rh(I)–Hg(II) complex and elemental rhodium deposited on the electrode.