Pt-Co alloys

Paulus UA, Wokaun A, Scherer GG, Schmidt TJ, Stamenkovic V, Radmilovic V, Markovic NM, Ross PN. 2002. Oxygen reduction on carbon-supported Pt-Ni and Pt-Co alloy catalysts. J Phys Chem B 106 4181-4191. 

Besides using Pt-Ru or Pt-Co alloy anodes, CO poisoning can be mitigated by elevating the operating temperature. However, temperature dependencies of the HOR rates in the presence of CO with relevance to PEFC operation have been scarcely reported. One of the difficulties is correction of the change in H2 concentration [H2] in the... 

Beard BC, Ross PN. 1990. The structure and activity of Pt-Co alloys as oxygen reduction electrocatalysts. J Electrochem Soc 137 3368-3374. 

Bismuth-Manganese Alloy, developed at the Naval Ordnance Laboratory, White Oak,Md, is a suitable substitute for permanent magnets Alnico or the expensive Pt-Co alloy. The Bi -Mn alloy can be used in various electronic devices(Ref 3). The Bi-Mn alloy known as "Bismanol , prepd by powder metallurgy techniques, is claimed to possess a coercive force of 3000 oersteds(Ref 5)... 

Pt/Co alloys have been suggested and have proved to have a superior activity to Pt for oxygen reduction due to a higher exchange current density [16]. The Tafel slope for oxygen reduction for Pt/ Co catalysts is the same as for Pt catalysts (60 mV per decade). Further work on Ag and Co catalysts is being undertaken to replace some or the entire Pt in the electrodes. 

Ross,33 and Beard and Ross34 had also been interested in electrocatalytic properties of Pt-3d transition metal binary-alloys, with a view that stable intermetallics could be formed. It was also their view that the catalytic enhancement shown by Pt-V, Pt-Cr, and latterly Pt-Co was due to the surface roughening of the platinum crystallites caused by leaching of the non-platinum elements from the surface. In the case of the Pt-Co alloy, they believed that a more stable alloy is formed that protects against further alloy degradation. 

Paulus, U. A. Wokaun, A. Scherer, G. G. Schmidt, T. J. Oxygen Reduction on Carbon-Supported Pt-Ni and Pt-Co Alloy Catalysts. Journal of Physical... 

III. CASE STUDY Pt-Co ALLOY ELECTROCATALYSTS FOR OXYGEN REDUCTION... 

The divergence between the elemental composition at the topmost layer and that in the bulk is appreciated best when the atom-percent composition of Pt (or Co) at the alloy surface is plotted as a function of the monolayer-percent composition of Pt (or Co) in the bulk. Such a plot, which represents the phase diagram of the outermost-layer Pt-Co alloy, is shown in Fig. 7 the open circles are data for when Ptwas deposited initially, whereas the... 

The two-dimensional order of the Pt-Co alloys was investigated by low-energy electron diffraction. The results, in terms of LEED patterns are shown in Fig. 8. First, the fact that distinct LEED spots are observed indicates that the alloy interface is well-ordered. Figure 8a shows a typical LEED pattern for alloys that contained greater than 75 atom-percent of Pt the hexagonal pattern is reminiscent of a pure Pt(lll) surface. At such high Pt surface concentrations, the outermost layer is most likely heterogeneous, populated by comparatively wide Pt(lll) domains. Fig. 8b shows that a different LEED pattern is obtained when the Pt Co atom-percent ratio is 3 1. Under these conditions, it may be post-... 

Figure 8. FEED patterns of the annealed Pt-Co alloys at points in the surface phase diagram where (a) the outermost layer is predominantly PtsCo, and (b) the topmost layer is essentially pure Pt. 

The primaiy emphasis in this review article is to showcase the use of LEISS to examine the outermost layers of Pt-Co alloys in order to correlate interfacial composition with electrocatalytic reactivity towards oxygen reduction. In some instances, it is desirable to compare the properties of the outermost layer with those of the (near-surface) bulk an example is when it becomes imperative to explain the unique stability the alloyed Co under anodic-oxidation potentials. In such cases. X-ray photoelectron spectroscopy and temperature-programmed desorption may be employed since both methods are also able to generate information on the electronic (binding-energy shift measurements by XPS) and thermochemical (adsorption enthalpy determinations by TPD) properties at the sub-surface. However, an in-depth discourse on these and related aspects was not intended to be part of this review article. 

To showcase the strengths of the combined LEISS-EC approach, recent results on the study of Pt-Co alloys as enhanced oxygen cathodes for fuel cells are presented. Through the use of LEISS, hitherto unknown phenomena have come to light. The more significant observations are ... 

In 2009, Hirunsit and Balbuena published AIMD simulations of aPt(lll)- and a Pt-Co-alloy-water interface and oxygen [226]. Different oxygen coverages were investigated as well as surface reconstruction effects due to different coverages of the adsorbed oxygen. Additionally, an electric field (-0.51 to +0.51 V/A) was applied on the surface but no spontaneous water dissociation or oxygen reduction was observed. Only the reorientation of the water molecules from O-down to H-down orientations was observed, as previously found [201, 202] and is already discussed in Sect. 4.4.1. 

Hirunsit P, Balbuena PB (2009) Surface atomic distribution and water adsorption on Pt-Co alloys. Surf Sci 603(6) 912-920... 

Salgado, J.R.C., Antolini, E., and Gonzalez, E.R. (2005) Carbon supported Pt-Co alloy as methanol-resistant oxygen-reduction... 

Kobayashi, M., Hidai, S., Niwa, H., Harada, Y., Oshima, M., Horikawa, Y., Tokushima, T., Shin, S., Nakamori, Y., and Aoki, T. (2009) Co oxidation accompanied by degradation of Pt-Co alloy cathode catalysts in polymer electrolyte fuel cells. Phys. Chem. Chem. Phys., 11, 8226-8230. 

Koh S, Leisch J, Toney MF, Strasser P (2007) Stracture-activity-stability relationships of Pt-Co alloy electrocatalysts in gas-diffusion electrode layers. J Phys Chem C 111(9) 3744-3752... 

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