Oxygen reduction, electrocatalysts

Guerin S, Hayden BE, Pletcher D, RendaU ME, Suchsland J-P. 2006a. A combinatorial approach to the study of particle size effects on supported electrocatalysts oxygen reduction on gold. J Comb Chem 8 679-686. 

Keywords electrocatalysts, oxygen reduction, hydrogen oxidation, fuel cells. 

On most of the electrocatalysts, oxygen reduction takes place by the formation of high-energy intermediate, peroxide, which is then further reduced to H2O. This is probably a consequence of the high stability of the 0—0 bond, which has a dissociation energy of 494 kj mol. In contrast, the dissociation energy of the 0—0 bond in H2O2 is only 146 kJ mor In order to obtain maximum efficiency and to avoid corrosion of carbon supports and other materials by peroxide, it is desired to achieve a... 

Tiibutsch H, Koslowski U, Dorbandt I (2(X)8) Experimental and theoretical modeling of Fe-, Co-, Cu-, Mh based electrocatalysts oxygen reduction. Electrochim Acta 53 2198-2209... 

Role of Cathode Electrocatalysts—Oxygen Reduction Reaction (ORR)... 

Alkaline Fuel Cell. The electrolyte ia the alkaline fuel cell is concentrated (85 wt %) KOH ia fuel cells that operate at high (- 250° C) temperature, or less concentrated (35—50 wt %) KOH for lower (<120° C) temperature operation. The electrolyte is retained ia a matrix of asbestos (qv) or other metal oxide, and a wide range of electrocatalysts can be used, eg, Ni, Ag, metal oxides, spiaels, and noble metals. Oxygen reduction kinetics are more rapid ia alkaline electrolytes than ia acid electrolytes, and the use of non-noble metal electrocatalysts ia AFCs is feasible. However, a significant disadvantage of AFCs is that alkaline electrolytes, ie, NaOH, KOH, do not reject CO2. Consequentiy, as of this writing, AFCs are restricted to specialized apphcations where C02-free H2 and O2 are utilized. 

Several activities, if successful, would strongly boost the prospects for fuel ceU technology. These include the development of (/) an active electrocatalyst for the direct electrochemical oxidation of methanol (2) improved electrocatalysts for oxygen reduction and (2) a more CO-tolerant electrocatalyst for hydrogen. A comprehensive assessment of the research needs for advancing fuel ceU technologies, conducted in the 1980s, is available (22). 

One factor contributing to the inefficiency of a fuel ceU is poor performance of the positive electrode. This accounts for overpotentials of 300—400 mV in low temperature fuel ceUs. An electrocatalyst that is capable of oxygen reduction at lower overpotentials would benefit the overall efficiency of the fuel ceU. Despite extensive efforts expended on electrocatalysis studies of oxygen reduction in fuel ceU electrolytes, platinum-based metals are stiU the best electrocatalysts for low temperature fuel ceUs. 

Carbon shows reasonable electrocatalytic activity for oxygen reduction in alkaline electrolytes, but it is a relatively poor oxygen electrocatalyst in acid electrolytes. A detailed discussion on the mechanism of... 

The overpotentials for oxygen reduction and evolution on carbon-based bifunctional air electrodes for rechargeable Zn/air batteries are reduced by utilizing metal oxide electrocatalysts. Besides enhancing the electrochemical kinetics of the oxygen reactions, the electrocatalysts serve to reduce the overpotential to minimize... 

Binary systems of ruthenium sulfide or selenide nanoparticles (RujcSy, RujcSey) are considered as the state-of-the-art ORR electrocatalysts in the class of non-Chevrel amorphous transition metal chalcogenides. Notably, in contrast to pyrite-type MS2 varieties (typically RUS2) utilized in industrial catalysis as effective cathodes for the molecular oxygen reduction in acid medium, these Ru-based cluster materials exhibit a fairly robust activity even in high methanol content environments of fuel cells. 

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... 

Solorza-Eeria O, EUmer K, Giersig M, Alonso-Vante N (1994) Novel low-temperature synthesis of semiconducting transition metal chalcogenide electrocatalyst for multielectron charge transfer Molecular oxygen reduction. Electrochim Acta 39 1647-1653... 

Alonso-Vante N, Malakhov IV, Nikitenko SG, Savinova ER, Kochubey DI (2002) The structure analysis of the active centers of Ru-containing electrocatalysts for the oxygen reduction. An in situ EXAFS study. Electrochim Acta 47 3807-3814... 

Lee JW, Popov BN (2007) Ruthenium-based electrocatalysts for oxygen reduction reaction—a review. J Solid State Electrochem 11 1355-1364... 

Lee K, Zhang L, Zhang J (2007) Ternary non-noble mefal chalcogenide (W-Co-Se) as electrocatalyst for oxygen reduction reaction. Electrochem Commun 9 1704-1708... 

Gochi-Ponce Y, Alonso-Nunez G, Alonso-Vante N (2006) Synthesis and electrochemical characterization of a novel platinum chalcogenide electrocatalyst with an enhanced tolerance to methanol in the oxygen reduction reaction. Electrochem Commun 8 1487-1491... 

In this section, we summarize the kinetic behavior of the oxygen reduction reaction (ORR), mainly on platinum electrodes since this metal is the most active electrocatalyst for this reaction in an acidic medium. The discussion will, however, be restricted to the characteristics of this reaction in DMFCs because of the possible presence in the cathode compartment of methanol, which can cross over the proton exchange membrane. 

Stamenkovic V, Mun BS, Mayrhofer KJJ, Ross PN, Markovic NM, Rossmeisl J, Greeley J, Nprskov JK. 2006. Changing the activity of electrocatalysts for oxygen reduction by tuning the surface electronic structure. Angew Chem Int Ed 45 2897. 

Zhang J, Vukmirovic MB, Sasaki K, Nilekar AU, Mavrikakis M, Adzic RR. 2005a. Mixed-metal Pt monolayer electrocatalysts for enhanced oxygen reduction kinetics. J Am Chem Soc 127 12480-12481. 

Fernandez JL, Raghuveer V, Manthiram A, Bard AJ. 2005a. Pd-Ti and Pd-Co-Au electrocatalysts as a replacement for platinum for oxygen reduction in proton exchange membrane fuel cells. J Am Chem Soc 127 13100-13101. 

Lee K, Savadogo O, Ishihara A, Mitsushima S, Kamiya N, Ota K-I. 2006. Methanol-tolerant oxygen reduction electrocatalysts based on Pd-3D transition metal alloys for direct methanol fuel cells. J Electrochem Soc 153 A20-A24. 

Murthi VS, Urian RC, Mukeijee S. 2004. Oxygen reduction kinetics in low and medium temperature acid environment Correlation of water activation and surface properties in supported Pt and Pt alloy electrocatalysts. J Phys Chem B 108 11011-11023. 

Mustain WE, Kepler K, Prakash J. 2007. CoPd, oxygen reduction electrocatalysts for polymer electrolyte membrane and direct methanol fuel cells. Electrochim Acta 52 2102-2108. Nagy Z, You H. 2002. Applications of surface X-ray scattering to electrochemistry problems. Electrochim Acta 47 3037-3055. 

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