Electrochemical aspects of pressure reduction of aqueous Cobalt(II) by hydrogen

The reduction of Co(II) by hydrogen on an aluminium electrode in acetate-sulphate aqueous solutions was examined using potentiostatic measurements in a three-electrode system. Measurements were performed at varying cobalt concentrations at 453 K and at varying temperatures at a cobalt concentration of 30 g/l. Thereafter, the oxidation of hydrogen on an aluminium electrode in acetate aqueous solutions was examined at 453 K and varying partial pressures of hydrogen and at varying temperatures at a hydrogen pressure of 3.0 MPa. Polarization curves were taken at an initial pH (pHo) of 6.2, mixing rate of 450 min−1, and a constant rate of potential change of 10 mV/s. From the resultant anodic and cathodic curves the exchange current density of the overall reaction was evaluated and found to correlate with the rate constants of pressure reduction of aqueous Co(II) by hydrogen determined in a previous kinetic study. The overall process was found to comprise two electrochemical half reactions on the aluminium surface: Co2++2e−=Co and H2−2e−=2H+.