A transition in the kinetics of electroreduction of anodically formed cobalt oxides. Influence of potentiostatic ageing

✍ Scribed by C.A. Gervasi; J.R. Vilche; P.E. Alvarez

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 622 KB
• Volume: 41
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(95)00329-0

✦ Synopsis

The kinetics of the electroreduction of oxide layers prepared through controlled anodisation of high purity polycrystalline cobalt electrodes in carbonate-bicarbonate buffers, has been analysed with special emphasis laid on the influence of potentiostatic ageing during passive film formation. The present results reveal the occurrence of an ageing process related to the reaction product formed in the second oxidation stage. The ageing process of the anodically formed cobalt passive layers appears as an apparent increasing irreversibility of the electroreduction reaction. Longer times of ageing also result in the thinning of the oxide layer through partial chemical dissolution. The transition of the growth mechanism for the new phase from a 3-D to a 2-D electroreduction process is related to the magnitude of the rate constant orthogonal to the surface and the time of potentiostatic ageing. Physical limit for the growing phase in the vertical direction can be reached at relatively short times during the potentiostatic current transient experiments. The calculated values of the height of the growing phase during electroreduction conditions correlates well with the thickness of the anodic film.