Catalysis oxygen reduction

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. 

Lewera A, Inukai J, Zhou WP, Cao D, Duong HT, Alonso-Vante N, Wieckowski A (2007) Chalcogenide oxygen reduction reaction catalysis X-ray photoelectron spectroscopy with Ru, Ru/Se and Ru/S samples emersed from aqueous media. Electrochim Acta 52 5759-5765... 

Gao F, El-Deab M, Okajima T, Ohsaka T. 2005. Electrochemical preparation of a Au crystal with peculiar morphology and unique growth orientation and its catalysis for oxygen reduction. J Electrochem Soc 152 A1226-A1232. 

Hence, catalysis related challenges for SOFC cathode are the development of cathode specifications, i.e., material and microstructure, having high catalytic activity for oxygen reduction at 600 °C, high electron and ion conductivity, and a low sensitivity for poisoning by volatile Cr species. Again, as for the anode, cost and compatibility related requirements have to be considered. 

Fuel cells (continued) metal catalysis, cathodic oxygen reduction, 40 127... 

H. Kohler and W. Gopel, Catalysis of the oxygen reduction on W18O49 electrodes by OH induced surface-states— A study based on XPS UPS and electromotive-force measurements,... 

Bonakdarpour, A., Fleischauer, M. D., Brett, M. J., and Dahn, J. R. Columnar support structures for oxygen reduction electrocatalysts prepared by glancing angle deposition. Applied Catalysis A General 2008 349 110-115. 

Most of the catalysts employed in PEM and direct methanol fuel cells, DMFCs, are based on Pt, as discussed above. However, when used as cathode catalysts in DMFCs, Pt containing catalysts can become poisoned by methanol that crosses over from the anode. Thus, considerable effort has been invested in the search for both methanol resistant membranes and cathode catalysts that are tolerant to methanol. Two classes of catalysts have been shown to exhibit oxygen reduction catalysis and methanol resistance, ruthenium chalcogen based catalysts " " and metal macrocycle complexes, such as porphyrins or phthalocyanines. ... 

The reaction process in oxygen reduction on chelate catalysts however is less easily explained. A number of experimental results have been obtained which do not accord with Beck s mechanism of "redox catalysis . 

Some other catalytic events prompted by rhodium or ruthenium porphyrins are the following 1. Activation and catalytic aldol condensation of ketones with Rh(OEP)C104 under neutral and mild conditions [372], 2. Anti-Markovnikov hydration of olefins with NaBH4 and 02 in THF, a catalytic modification of hydroboration-oxidation of olefins, as exemplified by the one-pot conversion of 1-methylcyclohexene to ( )-2-methylcycIohexanol with 100% regioselectivity and up to 90% stereoselectivity [373]. 3. Photocatalytic liquid-phase dehydrogenation of cyclohexanol in the presence of RhCl(TPP) [374]. 4. Catalysis of the water gas shift reaction in water at 100 °C and 1 atm CO by [RuCO(TPPS4)H20]4 [375]. 5. Oxygen reduction catalyzed by carbon supported iridium chelates [376]. - Certainly these notes can only be hints of what can be expected from new noble metal porphyrin catalysts in the near future. 

The phenomenon of bioelectrical catalysis with direct electron transfer from electrode to enzyme active site was primarily observed in the study of electrochemical oxygen reduction in the presence of a copper-containing oxidase - laccase, adsorbed on electrodes of different origins. This work was developed with peroxidase and hydrogenase application as the working components [2],... 

Gasteiger H, Kocha S, Sompalli B, Wagner F, (2005). Activity benchmarks and requirements for Pt, Pt-alloy and non-Pt oxygen reduction catalysts for PEMFCs , Applied Catalysis B Environmental, 56 9-35... 

Figure 3.3.14 Experimental ORR activity of dealloyed Pt-Cu and Pt-Ni core-shell nanoparticle ORR catalysts compared to a pure-Pt nanoparticle catalyst. All three catalyst particles are supported on a high surface area carbon material indicated by the suffix 1C. The shift of the j-E curve of the core-shell catalysts indicates the onset of oxygen reduction catalysis at a more anodic electrode potential (equivalent to a lower overpotential) and hence represents improved ORR reactivity compared to pure Pt.

Attempts to support models of the catalytic activity and the operative mechanism with results of theoretical considerations have been reported for the oxygen reduction [iii] and hydrogen oxidation [iv]. Electrocatalytic electrodes are indispensable parts of fuel cells [v]. A great variety of electrocatalytic electrodes has been developed for analytical applications [vi]. See also electro catalysis, catalytic current, -> catalytic hydrogen evolution, catalymetry. 

Nilekar AU, Xu Y, Zhang J, Vukmirovic MB, Sasaki K, Adzic RR, Maviikakis M (2007) Bimetallic and ternary alloys for improved oxygen reduction catalysis. Top Catal 46 276... 

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