Co-Reduction of Electrochemically Active [Co(H2O)6]2+ and [CoCl(H2O)5]+ Complexes onto Gold Electrode

Abstract

The work comprises results of the studies of the mechanism and kinetics of the co-reduction of hexaaquacobalt(II) and pentaaquachlorocobalt(II) complexes in chloride solutions at pH = 3. The studies were preceded by the thermodynamic analysis of the electrolyte. Electrolyte stability was determined by UV – Vis absorbance measurements. Electrochemical examinations were performed by cyclic voltammetry (CV) combined with Electrochemical Quartz Crystal Microbalance (EQCM). The M/z values determined by electrogravimetric measurements indicated that the reduction process occurs in one step 2-electron reduction reaction. Although the low pH value (pH = 3) electrogravimetric tests also indicate the process of Co(OH)2 precipitation. Deposition of Co takes place only in the overpotential deposition range. The examined reactions were diffusion controlled. The diffusion coefficient of Co2+ ions was determined by using the Berzins – Delahay equation.