Oxygen reduction reaction mechanism

Two mechanisms have been proposed for carbon-catalyzed ORR. On a glassy carbon electrode, the following reaction mechanism has been proposed [2]  

On pyrolytic graphite electrodes, the first reaction was also proposed as Reaction 2.19, followed by  

The active sites in N-doped carbon are carbon atoms adjacent to the N atom. Using a cluster model, Sidik et al. [24] did theoretical calculations and found that carbon radical sites adjacent to the substitutional N showed strong bonding ability to adsorbed OOH, favoring the production of H2O2 [24], which improves its catalytic activity. 

Pre-treatment of carbon materials can significantly improve their catalytic activity towards ORR and change their electrochemical behavior. A variety of treatment methods have been used, including polishing the electrode, radio frequency plasma treatment, heating at low pressures, in situ laser irradiation, vacuum heat treatment, chemical oxidation, and electrochemical oxidation [25-28]. 

Pretreated carbon also affects the activity of other catalysts supported on it. For example, pretreatment of a carbon support followed by deposition of Pt on it and 

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Yu L, Pan X, Cao X, Hu P, Bao X. Oxygen reduction reaction mechanism on nitrogen-doped graphene a density functional theory study. J Catal 2011 282 183-90. 

Tripkovic V, Skulason E, Siahrostami S, Norskov JK, Rossmeisl J. The oxygen reduction reaction mechanism on Pt(lll) from density functional theory calculations. Electrochim Acta 2010 55 7975-81. 

Olson TS, Pylypenko S, Fulghum JE, Atanassov P (2010) Bifunctional oxygen reduction reaction mechanism on non-platinum catalysts derived from pyrolyzed porphyrins. J Electrochem Soc 157 B54—B63... 

Chen R, Li H, Chu D, Wang G (2009) Unraveling oxygen reduction reaction mechanisms on carbon-supported Fe-phthalocyanine and Co-phthalocyanine catalysts in alkaline solutions. J Phys Chem C 113(48) 20689-20697... 

First-Principles Insights in ORR Catalysis for PEMFC 21.3.1 Oxygen Reduction Reaction Mechanism... 

Figure 2.16. The oxygen reduction reaction mechanism on Pt [42]. (Reprinted from Surface Seience Reports, 45(4-6), Markovi N. M. and Ross P. N., Surface science studies of model fuel cell electrocatalysts, 117-229, 2002, with permission from Elsevier.)...

Key words polymer electrolyte membrane fuel cell, direct methanol fuel cell, oxygen reduction, reaction mechanism, core-shell, platinum-fiee. 

The mechanism of the oxygen reduction reaction is by no means as fully understood as the h.e.r., and a major experimental difficulty is that in acid solutions (pH = 0) E02/H20 = 1 23, which means that oxygen will start to be reduced at potentials at which most metals anodically dissolve. For this reason accurate data on kinetics is available only for the platinum metals. In the case of an iridium electrode at which oxygen reduction is relatively rapid, a number of reaction sequences have been proposed, of which the most acceptable appear to be the following ... 

CATALYTIC ACTIVITY THE OXYGEN REDUCTION REACTION 3.4.1 Reaction Mechanism... 

Antoine O, Bultel Y, Durand R. 2001. Oxygen reduction reaction kinetics and mechanism on platinum nanoparticles inside Nafion . J Electroanal Chem 499 85-94. 

The impedance polarization performance of LSM electrode is closely related to the mechanism and kinetics of the oxygen reduction reactions. 02 reduction at SOFC cathodes is the most heavily studied subject, and this subject is sufficiently broad and complex to warrant its own review. Interested readers should consult the recent excellent articles by Adler [1] and Fleig [55], Here, only the polarization performance and its influencing factors are discussed. 

The mechanism of anodic hydrogen oxidation is much simpler than that of oxygen reduction. Reaction pathways would be the reverse of the Volmer-Heyrovsky or the Volmer-Tafel mechanism, that is, with anodic adsorption... 

Figure 13. Mechanism of the first electron transfer in an oxygen reduction reaction.

In practice, in all fuel cells that involve the utilization of 02 from air (Section 13.4.5), the oxygen reduction reaction [Eqs. (13.4) and (13.24)] is always rate determining for terrestrial applications. One can seejust how important it is to attempt to develop electrocatalysts for the cathodes of fuel cells on which the enhanced current density is high and Tafel slope is low and the efficiency of energy conversion, therefore, maximal. The direct relation of the mechanism of oxygen reduction and the associated Tafel parameters to the economics of electricity production and transportation is thus clearly seen. 

Figure 5.3. Electrode potential effects on ORR impedance spectra using GDE AC frequency range 6 x 104 to 6 x 10 3 Hz. Electrode potentials (versus SCE) ( ) 0.54 V (+) 0.49 V (x) 0.44 V (o) 0.39 V [6], (Reprinted from Journal of Electroanalytical Chemistry, 499, Antoine O, Bultel Y, Durand R. Oxygen reduction reaction kinetics and mechanism on platinum nanoparticles inside Nafion , 85-94, 2001, with permission from Elsevier.)...

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