Electroreduction of hexaamminecobalt(III) cation on Bi(hkl) electrodes from weakly acidified LiClO4 solutions

The cyclic voltammetry and rotating disk electrode methods have been used for investigation of electroreduction kinetics of the hexaamminecobalt(III) cations on the electrochemically polished Bi planes. The rate constant for the heterogeneous electroreduction reaction of the [Co(NH3)(6)](3+) cation on the Bi(001) and Bi(01(1) over bar) planes in x M LiClO4 + 0.001 M HClO4 aqueous base electrolyte solutions has been established and the results have been compared with the data for the Ag(110), Au(hkl), and Hg electrodes as well as with the data for Bi(hkl) in x M HClO4 solutions. In the region of zero charge potential, the value of the experimental transfer coefficient alpha(exp) is slightly higher than 0.5 and depends on the crystallographic structure of the Bi plane. For more concentrated base electrolyte solutions, the values of apparent transfer coefficient alpha(app), corrected for the double-layer effect, are practically independent of the base electrolyte concentration and slightly depend on the electrode polarization. Noticeably different values of the double-layer-corrected rate constant k(het)(0) and alpha(app) for the Bi(001), Bi(01(1) over bar), Bi(111), Hg, and Ag(110) electrodes from the data for Au(hkl) planes have been explained by the different water and ClO4- adsorption energies at the metals under discussion. (C) 2006 The Electrochemical Society.