Oxygen reduction reaction pathway

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... 

Fig. 14.9 Potential oxygen reduction reaction pathways on metallic catalysts [47]...

Studies have revealed that the type of interaction between catalyst and oxygen dictates the oxygen reduction reaction pathway and end products. The direct four-electron pathway requires dissociation of oxygen prior to the transfer of the first electron [25]. Research has demonstrated that both side-on and bridge interactions weaken the 0-0 bond to such an extent that a break is inevitable. Therefore, four-electron reduction will follow and the final product will be water. On the other hand, catalysts that cannot effectively stretch the 0-0 bond will only end up with the two-electron reduction product H2O2, which makes the catalyst unstable and degrades the fiiel cell system [31]. 

Fig. 4 (a) Oxygen reduction reaction pathways in the absence Qeft) and in the presence (right) of a contaminant. The presence of a contaminant affects the surface coverage G, oxygen reduction reaction product selectivity (j), and faradaic efficiency 0. (b) Platinum dissolution rate in the absence (top) and in the presence (bottom) of sulfur contamination either from the air intake or from the carbon support. The increased platinum dissolution rate favors a decrease in ionomer ionic conductivity. 

Catalytic oxygen reduction reaction on Co-N sites ( = 2 or 4) of graphene in acidic and alkaline media was discussed [164]. The Co atom was coordinated in an SV-like site with two or four neighboring C-atoms substituted with N-atoms. The study stressed the importance of thermo dynamic corrections and solvation effects were accounted for. Co-N sites were found to be stable in the studied range of applied electric potential, while C0-N2 sites were stable only if the external potential U < 0.45 V. The computations confirmed dual-site 2 X 2 e oxygen reduction reaction pathway on C0-N4 sites. 

Figure 6.15. Simplified schematic of the most important reaction pathways of the oxygen reduction reaction. The four-electron pathway results in the formation of water. The two-electron pathway forms hydrogen peroxide. Adsorption of molecular oxygen can form atomic oxygen (dissociative pathway) or form a superoxide species (associative pathway). The formation of Pt—OH and Pt— from water molecules represents the backward reactions of the later portion of the four-electron reduction pathway.

Oxygen reduction reaction (ORR) can occur following two different pathways. " The direct pathway involves four exchanged electrons and leads to the direct formation of water ... 

In order to understand the ORR reaction pathway, considering the general kinetics scheme of oxygen reduction reaction (Scheme... 

Scheme 5. General scheme of oxygen reduction reaction with the kinetics constant associated with each pathway.

The intercept (J) gives direct information on the variation of the ratio ki/k2, which represents a first estimation for the main pathway for the oxygen reduction reaction. A limit case for the... 

In the case of iron phthalocyanine catalyst dispersed on carbon, infrared spectroscopy measurements enabled to confirm the series mechanistic pathway for the ORR in the high overpotential domain (below 0.7 V vs RHE). Two intermediates species, 02 and H02 and two products, water (majority product) and hydrogen peroxide could be identified. However, since only few studies are led on the oxygen reduction reaction by infrared spectroscopy, a confident attribntion of the different vibrational transitions observed to a particnlar intermediate remains difficult. 

Scheme 3.1 Serial reaction pathway for oxygen reduction reaction...

Let us consider the oxygen reduction reaction (ORR) that occurs in the cathode of the polymer electrolyte membrane fuel cell (PEMFC), in an acidic environment. Although a variety of ORR mechanisms have been proposed, the four-electron pathway is primarily used to characterize the behavior of this reaction at a platinum electrode or a glassy carbon electrode coated with a platinum-based catalyst. The overall reaction is given by... 

The oxygen reduction reaction is covered in considerable detail in a review text by Kinoshita [10]. The charge-transfer reaction itself is quite complicated, and controversy still exists around the details of which of the many possible charge-transfer mechanisms determine electrode performance. The two generalized pathways that are considered are the direct four-electron reaction ... 

The oxygen reduction reaction can proceed by two pathways in aqueous electrolytes. The first one, the so-called direct pathway, involves releasing four electrons per oxygen molecule to yield HgO. The indirect pathway involves releasing two electrons to yield hydrogen peroxide (HgOg) that in successive steps can produce water. Two further pathways, which are combinations of the above, can be envisaged. The series pathway implies sequential two or... 

The oxygen reduction reaction is a multi-electron process involving numerous steps and intermediate species. As stated above, ORR may proceed via four or two electron transfer in aqueous acidic medium. The most relevant reactions pathways and their thermodynamic electrode potentials in acidic medium are shown below ... 

Wang Y, Balbuena PB (2005) Ab initio molecular dynamics simulations of the oxygen reduction reaction on a Pt(lll) surface in the presence of hydrated hydronium (H30) (H20)2 direct ot series pathway J Phys Chtan B 109 14896-14907... 

RRDE measurements with X-ray diffrac- cells. This gives tion results to investigate the detailed nature of the surface structures that are formed, particularly in coadsorption studies, for example, the influence of anion species on the UPD process. In Sect. 4.1.5, the oxygen reduction reaction (ORR) is used as a model electrochemical reaction to demonstrate the relation between the metal-O2 energetics and reaction pathway/kinetics as well as the importance of the local symmetry of surface atoms in determining the electrocatalytic properties of metal surfaces. 

Interestingly, the oxygen reduction reaction in [P666i4][Cl]/ethylene glycol mixture using a glassy carbon working electrode follows an overall 4-electron pathway (i.e. two 2-electron processes) which is of importance in the performance of air cathodes in electrochemical devices. 

A widespread interest for the electrochemical oxygen reduction reaction (ORR) has two aspects. The reaction attracts considerable attention from fundamental point of view, as well as it is the most important reaction for application in electrochemical energy conversion devices. It has been in the focus of theoretical considerations as four-electron reaction, very sensitive to the electrode surface structural and electronic properties. It may include a number of elementary reactions, involving electron transfer steps and chemical steps that can form various parallel-consecutive pathways [1-3]. 

Kattel S, Wang G (2014) Reaction pathway for oxygen reduction reaction on FeN4 embedded graphene. J Phys Chem Lett 5 452-456... 

Non-noble metal catalysts Catalysts prepared without any noble metals. As a result, the fabrication costs of such materials should be essentially lower as all basic-components are cheap. Oxygen Reduction Reaction. In this contribution, it stands for the electrochemical reduction of oxygen. The favored pathway is the... 

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