The kinetics of electroreduction of hexaamminecobalt(III) cation on Bi planes in aqueous HClO 4 solutions

Abstract

The electroreduction kinetics of hexaamminecobalt(III) cations on electrochemically polished Bi planes has been studied by cyclic voltammetry and rotating disc electrode methods. The rate constant for the heterogeneous electroreduction reaction of the [Co(NH 3) 6] 3+ cation on the Bi(0 0 1), Bi(1 1 1) and Bi( 0 1 1 ̄ ) planes has been established and the results have been compared with the data for the Ag(1 1 0), Au( h k l ) and Hg electrodes [Electrocatalysis, Wiley, New York, 1998, p. 323 (Chapter 8); J. Electroanal. Chem. 498 (2001) 93; J. Am. Chem. Soc. 97 (1975) 4403; J. Electroanal. Chem. 209 (1986) 109; J. Electroanal. Chem. 223 (1987) 171]. In the region of zero charge potential, the value of the experimental transfer coefficient α exp obtained depends on the crystallographic structure of the Bi plane. α exp is only slightly higher than 0.5 for the Bi(1 1 1) and Bi(0 0 1) planes but somewhat lower than 0.5 for the electrochemically most active Bi( 0 1 1 ̄ ) plane. For more concentrated base electrolyte solutions, the values of the apparent transfer coefficient α app corrected for the double layer effect are practically independent of the base electrolyte concentration and depend slightly on the electrode polarisation. Noticeably different values of the double layer corrected rate constant and α app for the Bi(0 0 1), Bi( 0 1 1 ̄ ), Bi(1 1 1), Hg and Ag(1 1 0) electrodes from the data for the Au( h k l ) planes have been explained by the different inner layer structure, i.e. by the different water and ClO 4 − adsorption energies at the metals under discussion.