PtCo alloy

Fig. 4.13 (a) Field ion image of an ordered PtCo alloy. Co atoms do not give rise to image spots, thus only the Pt sublattice is imaged. The circular area near the center of the image is a thick layer of 90° orientation domain. (b) Field ion image of an ordered Ni4Mo where Ni atoms cither are invisible or appear much dimmer. 

Further enhancement of the specific activity of PEFC air cathode catalysts has been achieved by moving on from carbon-supported Pt to carbon-supported Pt alloy catalysts [41, 78-81]. The gain in activity per unit mass of Pt in moving over from Pt to PtCo alloy cathode catalysts is demonstrated in Fig. 43 (explanation for this enhancement in activity has been given above). With the rise by factor... 

Ball SC, Hudson S, Theobald B, Thompsett D (2006) Carbon supported Pt and PtCo alloys with improved corrosion resistance for PEMFC. 210th ECS meeting, abstract 552... 

Ball SC, Hudson SL, Hei Leung J, Russell AE, Thompsett D, Theobald BR (2007) Mechanisms of activity loss in PtCo alloy systems. ECS Trans 11 1247-1257... 

Fig. 5.25 The ferromagnetic core/diamagnetic shell nanoparticles of PtCo alloy (a) particles with various concentration of Pt atoms on the shell (b) shell order parameter in the PtCo alloy vs. particle size and temperature of ordering (c) the regular array of PtCo nanoparticles [323]...

Fig. 20.9 KMC simulation of a dealloying process. A PtCo alloy nanoparticle of approximately 8 nm diameter is exposed to an acidic solution (represented by the small spheres surrounding the surface of the nanoparticle), (a), (b), and (c) represent snapshots taken at increasing times. Co segregates to the surface and dissolves. The lowest coordination sites are the first to dissolve causing a dramatic increase of the surface roughness (Callejas-Tovar and Balbuena, unpublished results)...

In contrast, when the Pt is deposited at oblique incidence, one sidewall of the dots is coated with antiferromagnetic CoO, whereas the other side consists of a Pt-rich PtCo alloy, which is nonmagnetic (Fig. 5.3-37b). In this latter case, no direct coupling be-... 

Cobalt is used to promote CO oxidation in reformers [284, 285], suggesting PtCo alloys may be useful catalysts for H2 oxidation in the presence of CO. PtCo alloys have been proposed as improved methanol oxidation catalysts [286] because cobalt may assist with CO removal (CO is an intermediate in meflianol electrooxidation) through a mechanism analogous to the PtRu bifunctional mechanism. PtCo alloys have also been studied as improved ORR catalysts [200, 287, 288]. In addition to their improved ORR kinetics, these alloys have been shown to be more tolerant to methanol crossover in direct methanol fuel cells (DMFCs), again possibly through improved CO removal kinetics [289]. However, Stevens et al. [235] observed no impact on CO-stripping with the addition of eobalt to Pt, and explained this as due to surface cobalt dissolving away. 

Wang, H., Yuan, X., Li, D. Gu, X. Dendritic PtCo alloy nanoparticles as high performance oxygen reduction catalysts. J. Colloid Inter/. Sci. 384 (2012), pp. 105-109. 

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