Q2. Why was the potential range limited to the temperature of Co(H)?
Owing to the fact that cobalt can be oxidized to different states, the potential range was limited to that corresponding to the thermodynamic stability of Co(H) species.
Q3. What is the effect of the splitting of the electroreduction profiles?
As the splitting of the electroreduction profiles involves a constant charge, the effect can also be ascribed to an ageing process associated with the film anodically formed.
Q4. What is the use of potentiostatic techniques combined with interference microscopy 1251?
The use of potentiostatic techniques combined with interference microscopy 1251 applied to cobalt in l--X M KOH shows three electro-oxidation reactions in the -- 1 to 0 V range.
Q5. What is the kinetic behaviour of the sandwich-type cobaltous hydroxide electrode?
The electrochemical characteristics of the sandwich-type cobaltous hydroxide electrode is sensitive to the ionic composition of the system.
Q6. What is the kinetic behaviour of the overall electrochemical interface?
In these sandwich-type structures, the relatively fast proton transfer through the film is to a great extent responsible for the kinetic behaviour of the overall electrochemical interface.
Q7. What is the effect of the potentiodynamic perturbation on the electroreduction process?
when the ageing is promoted by the potentiodynamic perturbation the splitting of the electroreduction current peak is observed (Figs. 14, 15) which makes clear the existence of at least two reactants entering the electroreduction process.
Q8. What is the electrochemical behaviour of cobalt in alkaline solutions?
the electrochemical behaviour of cobalt in alkaline solutions, within the Co/Co(II) electrode potential range, is correlated to the behaviour expected for sandwich-type electrochemical interfaces already described for various metals covered by different metal oxides and hydroxides [26-301.
Q9. What is the ageing effect of the hydrated cobaltous oxide film?
in the present case the ageing effect should be related to a kind of chemical reaction proceeding in the hydrated cobaltous oxide film, probably involving a reaccommodation of the oxygen atoms through a place exchange mechanism [47].
Q10. What is the behaviour of cobalt in alkaline solutions?
The behaviour of cobalt in alkaline solutions in the stability range of Co(I1) species, can be explained through the formation of a complex-type electrochemical interface during the potential cycling.
Q11. What is the effect of the ageing on the electroreduction current?
under both open-circuit ageing (Fig. 13) and potentiostatic ageing conditions (Figs. 10, 1 l), the electroreduction current peak potential becomes more negative as’ the corresponding ageing time increases.
Q12. What is the effect of the anodic current on the E/I profile?
The first TPS E/I display depends more remarkably on u than the following ones, and at low u they exhibit either a possible dissolution of the passivating film or its transformation into a conducting material, since after reaching E,, the reverse potential sweep shows an anodic current contribution in the potentialFig.
Q13. What is the kinetic behaviour of sandwich-type cobaltous hydroxide films?
These characteristics derive from the colloidal nature of the film which is demonstrated through the response of cobaltous hydroxide electrodes produced by colloidal precipitation on different conducting substrates [43].
Q14. What is the likely structure of the cobalt oxides in alkaline solutions?
Some authors found three different electrochemical oxidation stages of cobalt which were assigned, respectively, to the formation of Coo, Co,O, and Co304 [7], while others reported only two stages which were related to (‘:o(OH)2 and CoOOH [ 111, More recently, the passivity of cobalt in buffer borate solutions in the pH range between 7 and The authorI [ 12 171 was related to a film which is made up of different layers of hydrated cobalt oxides.
Q15. What is the kinetic behaviour of a sandwich-type electrode?
If the processes associated with the stabilized I/E profile were related to a reaction at the outer layer of the sandwich-type structure one should expect the same behaviour to be encountered with a platinum electrode covered by a cobaltous hydroxide film.
Q16. What is the kinetic behaviour of nickelous hydroxide films?
The kinetic behaviour of these films is similar to that already reported for nickelous hydroxide films, namely, both depend on their degree of hydration and on the extent of ions either occluded in the films or adsorbed on them.
Q17. What is the rate constant of the electro-oxidation process?
Following the same procedure already described for nickelous hydroxide eiectrodes 126,283, the rate constant of the ageing process, namely that of the chemical conversion of the u-species into the s-species, is estimated from the runs under potentiodynamic ageing conditions.