Electrocatalytic Oxygen Reduction Reaction

Oxygen (O2) is the most abundant element in the Earth s crast. The oxygen reduetion reaetion (ORR) is also the most important reaction in life processes such as biological respiration, and in energy converting systems such as fuel cells. ORR in aqueous solutions occurs mainly by two pathways the direct 4-electron reduction pathway from O2 to H2O, and the 2-electron reduction pafliway from O2 to hydrogen peroxide (H2O2). In non-aqueous aprotic solvents and/or in alkaline solutions, the 1-electron reduction pathway from O2 to superoxide (O2 ) can also occur. 

To assist readers, we first provide an overview of the following background information the major electrochemical O2 reduction reaction processes, simple ORR kinetics, and conventional techniques for electrochemical measurements. 

In Table 2.1, the reduction pathways such as the I-, 2-, and 4-electron reduction pathways have unique significance, depending on the applications. In fuel cell proeesses, the 4-eleetron direct pathway is highly preferred. The 2-electron reduction pathway is used in industry for H2O2 production. The 1-electron reduction pathway is of importance in the exploration of the ORR mechanism. 

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Isogai S, Ohnishi R, Katayama M, Kubota J, Kim DY, Noda S, Cha D, Takanabe K, Domen K (2012) Composite of TIN nanoparticles and few-walled carbon nanotubes and its application to the electrocatalytic oxygen reduction reaction. Chem Asian J 7 286-289... 

Zheng JS, Zhang XS, Li P, Zhou XG, Yuan WK (2008) Microstructure effect of carbon nanofiber on electrocatalytic oxygen reduction reaction. Catal Today 131(l-4) 270-277... 

Song C, Zhang J (2008) Electrocatalytic oxygen reduction reaction. In Zhang J (ed) PEM fuel cell electrocatalysts and catalyst layers. Springer, London, pp 89-134... 

FIGURE 7.7 Theoretically derived volcano for the electrocatalytic Oxygen Reduction Reaction in acidic media. Experimental data points are indicated by solid or filled circles. PtjY is an improved alloy catalyst discovered by computational catalyst screening. Reprinted with permission from Ref. [74]. Nature group. 

Keith JA, Jacob T (2010) Theoretical studies of potential-dependent and competing mechanisms of the electrocatalytic oxygen reduction reaction on Pt (111). Angew Chemie Int Ed 49 9521-9525... 

In 2005, Cui and co-workers studied the electrocatalytic oxygen reduction reaction by electrodepositing Pt nanoparticles on MWNTs. A significant positive shift in oxygen reduction potential and a concurrent increase in oxygen reduction current have been observed. Pt nanopartides deposited on MWNTs also exhibited enhanced transfer rates of dectrons as wdl as stability for methanol oxidation. ... 

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