Intrinsically oxygen reduction

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Wang JX, Markovic NM, Adzic RR. 2004. Kinetic analysis of oxygen reduction on Pt(ll 1) in acid solutions Intrinsic kinetic parameters and anion adsorption effects. J Phys Chem B 108 ... 

The high theoretical efficiency of a fuel cell is substantially reduced by the finite rate of dynamic processes at various locations in the cell. Substantial efficiency losses at typical operating temperatures occur already in the anodic and cathodic catalyst layers due to the low intrinsic reaction rates of the oxygen reduction and, in the case of the DMFC, of the methanol oxidation reaction. (The catalytic oxidation of hydrogen with platinum catalysts is very fast and thus does not limit PEFC performance.) In addition, at low temperatures, turnover may be limited by noble metal catalyst poisoning due to sulfur... 

Wang Z, Jia R, Zheng J, Zhao J, Li L, Song J, Zhu Z (2011) Nitrogen-promoted self-assembly of N-doped carbon nanotubes and their intrinsic catalysis for oxygen reduction in fuel cells. ACS Nano 5(3) 1677-1684... 

Fouda-Onana F, Bah S, Savadogo O (2009) Palladium-copper alloys as catalysts fra the oxygen reduction reaction in an acidic media I Correlation between the ORR kinetic parameters and intrinsic physical properties of the alloys. J Electroanal Chem 636(1-2) 1-9... 

Abstract In this chapter, we review recent works of dealloyed Pt core-shell catalysts, which are synthesized by selective removal of transition metals from a transition-metal-rich Pt alloys (e.g., PtMs). The resulted dealloyed Pt catalysts represent very active materials for the oxygen reduction reaction (ORR) catalysis in terms of noble-metal-mass-normalized activity as well as their intrinsic area-specific activity. The mechanistic origin of the catalytic activity enhancement and the stability of dealloyed Pt catalysts are also discussed. 

More recently, Wang et al. [28] derived an intrinsic kinetic equation for the four-electron (4e ) oxygen reduction reaction (ORR) in acidic media, by using free energies of activation and adsorption as the kinetic parameters, which were obtained through fitting experimental ORR data from a Pt(lll) rotating disk electrode (RDE). Their kinetic model consists of four essential elementary reactions (1) a dissociative adsorption (DA) (2) a reductive adsorption (RA), which yields two reaction intermediates, O and OH (3) a reductive transition (RT) from O to OH and (4) a reductive desorption (RD) of OH, as shown below [28] (Reproduced with permission from [28]). 

Wang JX, Uribe FA, Springer TE, Zhang JL, Adzic RR (2008) Intrinsic kinetic equation for oxygen reduction reaction in acidic media the double Tafel slope and fuel cell applications. 

Major contributions to the development of the macrokinetic or macrohomogeneous theory of porous electrodes were made by Yu, A, Chizmadzhev and Yu, G, Chirkov [25-27], In these works the importance of the interplay of oxygen diffusion and interfacial kinetics had already been realized. For oxygen reduction electrodes, a large electrocatalytically active surface area per unit volume,, has to compensate for the smallness of the intrinsic activity per unit... 

The oxygen storage capacity of ceria can benefit from either type of defect. In some cases, such as with the introduction of Ca +, Mg " ", Gd " ", La " ", and Pr " +, the increased OSC is obtained chiefly through the creation of extrinsic type defects. In other cases, such as when Zr is used as a dopant, promoting the kinetics of Ce" + reduction, increases the intrinsic oxygen vacancies and enhanced oxygen storage [99]. 

Before concluding, it should be noted that the Heikes formula should be used also only if a plateau is reached for the S(T) curve. This is not always the case as an increase in S can be observed for some misfits or in Na cCoOi. This increase has not been investigated in detail so far, and it would be very important to understand if this is really an intrinsic increase or if it is related to some oxygen reduction as T increases, depending on the measuring atmosphere. 

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