Oxygen evolution electrode passivation

Passivation looks different when observed under galvanostatic conditions (Fig. 16.2b). The passive state will be attained after a certain time t when an anodic current which is higher than is applied to an active electrode. As the current is fixed by external conditions, the electrode potential at this point undergoes a discontinuous change from E to Ey, where transpassive dissolution of the metal or oxygen evolution starts. The passivation time t will be shorter the higher the value of i. Often, these parameters are interrelated as... 

Deactivation, or "passivation , behavior has been found to be a feature of the oxygen evolution process on these electrodes [284], While apparently not related to oxide dissolution, the loss of activity for oxygen evolution is evidently related to the formation of a hydrated Co-rich oxide multilayer film over a significant portion of the LaosBojCoOg electrode surface [284]. Lowering of the electrode potential restored the initial activity for oxygen evolution. Further study of this deactivation process in warranted since similar deactivation processes may occur at other oxide catalysts. 

Electrolytic Oxidation I. Electrode Potential.—A series of stable potentials is difficult to obtain at an anode in the presence of a depolarizer the potential generally rises rapidly from the low value, at which the anode dissolves, to the high value for passivity and oxygen evolution. Since a platinum electrode is nearly always passive, however, it is possible to obtain graded potentials to a limited extent the data quoted in Table LXXXVI were recorded for the oxidation of an acid solution of... 

The dominating process depends on the band structure of the oxide, the film thickness, and the electrode potential. Cathodic reactions usually take place via the CB, while anodic processes at high potentials (e.g. oxygen evolution) obey the VB-mechanism. Figure 13 shows some Tafel diagrams for ETR at passive iron... 

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