Electrochemistry of CoB alloy in 6M KOH solution

The electrochemical redox kinetics of the CoB alloy electrode was investigated in 6 M KOH solution by electrochemical impedance spectroscopy (EIS) together with cyclic voltammetry (CV). The results show that the reversible electrochemical capacity of CoB alloy electrode is from the reaction Co/Co (OH)2. The EIS reflects the following four steps in the process of Co (OH)2 → Co: the conduction step in the micropores of the electrode, two successive charge transfer steps and the diffusion of OH− away from the electrode, and the process is considered to be under the diffusion control. The EIS obtained from the process of Co → Co (OH)2 only show the responses of the conduction step and two electrochemical steps, and the second charge transfer step Co (OH)ads/Co (OH)2 is regarded as the rate-determining step in the process. However, CVs reveal that the process of Co → Co (OH)2 is entirely under the diffusion control. This inconsistency could be due to the different formation mechanisms of the oxide layer under potentiostatic and potentiodynamic conditions.