The electrochemical behaviour of cobalt in alkaline solutions part II. The potentiodynamic response of Co(OH)2 electrodes

Abstract

The potentiodynamic behaviour of Co(OH)2 hydroxide electrodes is studied in the potential range related to the appearance of Co(III) and Co(IV) species. The corresponding electrochemical reactions involve relatively fast proton transfer processes occurring at potentials close to those predicted from thermodynamics. Sandwich-type structures of the eleclrode/film/solution interface are assumed in the interpretation of the processes. They probably include configurational changes of reactants and products participating in the various electrochemical reactions.

Redox and electrochemical water splitting catalytic properties of hydrated metal oxide modified electrodes

“…13. These rather complex voltammetric profiles are typical of those generally observed in the literature, 217,[224][225][226][227] and there seems to be fairly good agreement regarding the interpretation of the various peaks. The approach most often adopted is based on that of Behl and Toni 224 who compared the observed peak potentials with thermodynamic data.…”

“…À1.0 V associated with the reduction of Co(II) species. 217,226,227,232 As previously described, Liu et al 226 have attributed the increasing reversibility achieved with increasing film thickness to redox processes in the vicinity of the hydrous oxide surface. The contrast between this behaviour and the irreversibility noted during the earlier stages of film formation reinforces the concept of the initially formed oxide or inner regions of a thick film being difficult to reduce.…”

“…Gomez Meier et al 227 also allude to the complex hydrous nature of the anodic oxide formed on Co in alkaline solution. These authors view the oxide growth process in terms of the formation of 'sandwich-type' structures, with a Co/CoO/ Co(OH) 2 'sandwich' formed at lower potentials.…”

“…Šimpraga 225 noted that the ratio of the charges associated with this set of corresponding anodic and cathodic peaks in 0.5 M NaOH at 298 K became unity after approximately 15 cycles in the potential range of À1.125 to À0.325 V. Similar observations have also been made by other workers. 217,226,227 This behavior has been attributed to the stabilization of the developing anodic film with respect to the dissolution process of eqn (47), so that after a number of cycles the anodic peak in the potential region of À0.6 to À0.8 V should be almost entirely due to a solid state process.…”

“…Furthermore, on the basis of a perceived correlation between their voltammetric peak data and the predictions of thermodynamics, Gomez Meier et al 227 conclude that, in the formation of the anodic film on Co, the electrochemical reactions involve fast proton transfers and that the advance in the degree of oxidation of the metal is accompanied by a deprotonation and change in the water content at different parts of the complex electrochemical interface.…”