Electrochemical and XPS investigations of cobalt in KOH solutions

The electrochemical behaviour of cobalt in KOH solutions of different conce ntrations was studied. The effects of applied potential, temperature and th e presence of aggressive Cl- ions were investigated. Different electrochemi cal methods such as open-circuit potential measurements, polarisation techn iques and electrochemical impedance spectroscopy (EIS) were used. The elect rochemical behaviour of cobalt in naturally aerated KOH solutions is charac terized by three different regions according to the alkali concentration. C orrosion behaviour was observed at high concentrations (0.3-1.0 M); passiva tion at lower concentrations (0.01-0.05 M), and at intermediate concentrati ons (0.1-0.2 M) corrosion followed by passivation was recorded. The corrosi on parameters (i(corr), E-corr, and R-corr) under various conditions were c alculated. Equivalent-circuit models for the electrode-electrolyte interfac e under different conditions were proposed. The experimental impedance data were fitted to theoretical data according to the proposed models. The rele vance of the proposed models to the corrosion-passivation phenomena occurri ng at the electrode-solution interface was discussed. The electrochemical e xperimental results and discussions were supported by surface analytical te chniques.