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.