Heterogeneous oxygen reduction

The mechanism of inhibition by the salts of the long chain fatty acids has been examined . It was concluded that, in the case of the lead salts, metallic lead was first deposited at certain points and that at these points oxygen reduction proceeded more easily, consequently the current density was kept sufficiently high to maintain ferric film formation in addition, any hydrogen peroxide present may assist in keeping the iron ions in the oxide film in the ferric condition, consequently the air-formed film is thickened until it becomes impervious to iron ions. The zinc, calcium and sodium salts are not as efficient inhibitors as the lead salts and recent work has indicated that inhibition is due to the formation of ferric azelate, which repairs weak spots in the air-formed film. This conclusion has been confirmed by the use of C labelled azelaic acid, which was found to be distributed over the surface of the mild steel in a very heterogeneous manner. ... 

In certain cases and together with the electrode reaction, in particular that of oxygen reduction at metal surfaces, a non-electrochemical regeneration mechanism operates which is heterogeneous in nature and involves the adsorbed product [165] obviously, it is very dependent on the electrode material and the available surface states. The reaction scheme is thus of the type... 

The studies of direct heterogeneous electron transfer have been carried out in most cases using cyclic and square wave voltammetry. In these studies the first of the two electrons required for the catalsftic reaction has been transferred although the authors do not see the shift of the reduction potential upon substrate addition as has been reported in Ref. [73] and is known for the reaction in solution. In all cases catalytic oxygen reduction is observed but only rarely could catalytic substrate conversion be achieved. 

Scherson, Palenscar, Tolmachev and Stefan provide a critical review of transition metal macrocycles, in both intact and thermally activated forms, as electrocatalysts for dioxygen reduction in aqueous electrolytes. An introduction is provided to fundamental aspects of electrocatalysis, oxygen reduction, and transition metal macrocydes. Since the theoretical and experimental tools used for investigation of homogeneous and heterogeneous electrocatalysis are considerably different, these topics are given separate discussion. The influence of the electrode surface on adsorbed macrocydes, and their influence on mechanism and rates of 02 reduction is treated in detail. Issues related to pyrolyzed macrocydes are also described. 

Photosensltlzatlon by electron transfer, as shown In equation 2 above, has also been observed (22,23). The occurrence of 0 (14,16) In natural waters Is good evidence that these processes are occurring, at least for oxygen reduction. With electron acceptors other than oxygen, this process Is probably similar to energy transfer in that there is a low probability for other electron acceptors to be Involved except in heterogeneous environments. 

Mamuru SA, Ozoemena KI, Fukuda T, Kobayashi N, Nyokong T (2010) Studies on the heterogeneous electron transport and oxygen reduction reaction at metal (Co, Fe)... 

Mamuru SA, Ozoemena KI (2010) Heterogeneous electron transfer and oxygen reduction reaction at nanostructured Iron(n) phthalocyanine and its MWCNTs nanocomposites. Electroanalysis 22(9) 985-994... 

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