Oxygen reduction reaction models

Zhu L, Susac D, Teo M, Wong KC, Wong PC, Parsons RR, Bizzotto D, Mitchell KAR, Campbell SA (2008) Investigation of CoSa-based thin films as model catalysts for the oxygen reduction reaction. J Catal 258 235-242... 

Schneider A, Colmenaies L, Seidel YE, Jusys Z, Wickman B, Kasemo B, Behm RJ. 2008. Transport effects in the oxygen reduction reaction on nanostructuied, planar glassy carbon supported Pt/GC model electrodes. Phys Chem Chem Phys 10 1931-1943. 

The most important electrokinetic data pertinent to fuel cell models are the specific interfacial area in the catalyst layer, a, the exchange current density of the oxygen reduction reaction (ORR), io, and Tafel slope of ORR. The specific interfacial area is proportional to the catalyst loading and inversely proportional to the catalyst layer thickness. It is also a strong function of the catalyst layer fabrication methods and procedures. The exchange current density and Tafel slope of ORR have been well documented in refs 28—31. 

The DNS model can be deployed subsequently on the liquid water blocked CL structure pertaining to a saturation level for the evaluation of the hindered oxygen transport. In brief, the DNS model is a top-down numerical approach based on a fine-scale CFD framework which solves point-wise accurate conservation equations for species and charge transport in the CL with appropriate source terms due to the oxygen reduction reaction (ORR) directly on the CL microstructures.25-27 67 The conservation equations for proton, oxygen and water vapor transport, respectively, are given by 25-27 68... 

Anderson and his coworker carried out a series quantum chemistry studies of oxygen reduction reactions.52-57 Anderson and Abu first studied reversible potential and activation energies for uncatalyzed oxygen reduction to water and the reverse oxidation reaction using the MP2/6-31G method. The electrode was modeled by a non-interacting electron donor molecule with a chosen ionization potential (IP). The primary assumption is that when the reactant reaches a point on the reaction path where its electron affinity (EA) matched the donor IP, an electron transfer is initialized. The donor s IP or reactant s EA was related to the electrode potential by,... 

A detailed model for the oxygen reduction reaction at semiconductor oxide electrodes has been developed by Presnov and Trunov [341, 345, 346] based on concepts of coordination chemistry and local interaction of surface cation d-electrons at the oxide surface with HO, H20, and 02 acceptor species in solution. The oxygen reduction reaction is assumed to take place at active sites associated with cations at the oxide surface in a higher oxidation state. These cations would act as donor-acceptor reduction (DAR) sites, with acceptor character with respect to the solid by capture of electrons and donor electronic properties with respect to species in solution. At the surface, the long-range oxide structure is lost and short-range coordination by hydroxide ions and water molecules in three octahedral positions may occur [Fig. 16(b)], One hydroxide ion can compensate coulombically for the excess charge on surface M2+ cations with two coordinated water mole-... 

In this chapter we review studies, primarily from our laboratory, of Pt and Pt-bimetallic nanoparticle electrocatalysts for the oxygen reduction reaction (ORR) and the electrochemical oxidation of H2 (HOR) and H2/CO mixtures in aqueous electrolytes at 274—333 K. We focus on the study of both the structure sensitivity of the reactions as gleaned from studies of the bulk (bi) metallic surfaces and the resultant crystallite size effect expected or observed when the catalyst is of nanoscale dimension. Physical characterization of the nanoparticles by high-resolution transmission electron microscopy (HRTEM) techniques is shown to be an essential tool for these studies. Comparison with well-characterized model surfaces have revealed only a few nanoparticle anomalies, although the number of bimetallics... 

Many catalyst layer models have appeared in the literature during the last few years [15, 16, 17, 18, 19,20, 21]. This observation partly explains the complications associated with this topic. Still, much work remains to be completed since many effects have not yet been included, such as proton surface diffusion (outside the ionomer, [22,23]) and ionomer density (water content effect), which effectively and respectively increases/modifies the reactive surface area. The surface-sensitive nature of Pt catalysts on the oxygen reduction reaction rate [24] and electrochemical promotion (a catalytic effect, [25]) represent other examples which can also affect the reaction rate and surface area. All these effects are further compounded by the potential presence of hquid water which effectively modifies the reaction front, access to speeifie eatalyst particles and surface properties. 

The oxygen reduction reaction has received a large amount of attention recently, from both modeling and experimental investigations, due to its importance in the development of fuel cell systems [74,103,122-125]. The rate of corrosion reactions may be controlled by either the anodic or cathodic process, depending upon which of the two half-cell reactions is rate limiting. This combination is elaborated further in the following text. 

Fig. 11.5 Potential energy surface profile for the oxygen reduction reaction at the standard hydrogen electrode potential scale the proton was modeled by two shells of water molecules, H 0H2(H20)3(H20),5, and the data in parentheses are Gibbs free energies [50]...

Hyman MP, Medlin JW (2007) Effects of electronic stmeture modifications on the adsorption of oxygen reduction reaction intermediates on model Pt(l 1 l)-alloy surfaces. J Phys Chem C 111(45) 17052-17060... 

Nesselberger M, Ashton S, Meier JC, Katsounaros I, Mayrhofer KJJ, Arenz M (2011) The particle size effect on the oxygen reduction reaction activity of pt catalysts influence of electrolyte and relation to single crystal models. J Am Chem Soc 133(43) 17428-17433... 

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. 

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