Platinum catalysts cluster potentials

Little is known about the chemical nature of the recently isolated carbon clusters (C o> C70, Cg4, and so forth). One potential application of these materials is as highly dispersed supports for metal catalysts, and therefore the question of how metal atoms bind to C40 is of interest. Reaction of C o with organometallic ruthenium and platinum re nts has shown that metals can be attached directly to the carbon framework. Ihe native geometry of transition metal, and an x-ray difi action analysis of the platinum complex [(CgHg)3P]2Pt( () -C6o) C4HgO revealed a structure similar to that known for [(C4Hs)3P]2Pt( n -ethylene). The reactivity of C40 is not like that of relatively electron-rich planar aromatic molecules su( as benzene. The carbon-carbon double bonds of C40 react like those of very electron-deficient arenes and alkcnes. 

In batch and continuous tests the performance of the colloidal catalyst systems has been compared to conventional Pt/C-systems. The potential of the colloidal heterogeneous catalyst lies in the possibility of fine tuning the properties for specific applications by the addition of special dopants or poisons to the precursor. The infiuence of metal ions on the hydrogenation of o-chloronitrobenzene over platinum colloids, and the effect of metal complexes on the catalytic performance of metal clusters have also been demonstrated [133-135]. 

Direct methanol fuel cells (DMFCs) are attracting much more attention for their potential as clean and mobile power sources for the near future [1-8], Generally, platinum (Pt)- or platinum-alloy-hased nanocluster-impregnated carbon supports are the best electrocatalysts for anodic and cathodic fuel cell reactions. These materials are veiy expensive, and thus there is a need to minimize catalyst loading without sacrificing electro-catalytic activity. Because the catalytic reaction is performed by fuel gas or fuel solution, one way to maximize catalyst utilization is to enhance the external Pt surface area per unit mass of Pt. The most efficient way to achieve this goal is to reduce the size of the Pt clusters. 

Figure 13.7. Polarization curves for O2 reduction reaction on Au/Pt/C (A) and Pt/C (C) catalysts on a rotating disk electrode, before and after 30,000 potential cycles. Sweep rate 10 mV/s rotation rate 1600 rpm. Voltammetric curves for Au/Pt/C (B) and Pt/C (D) catalysts before and after 30,000 cycles sweep rates 50 and 20 mV/s, respectively. The potential cycles were from 0.6 to 1.1 V in an 02-saturated 0.1 M HCIO4 solution at room temperature. For aU electrodes, the Pt loading was 1.95 mg (or 10 nmol) on a 0.164 cm glassy carbon rotating disk electrode. The shaded area in (D) indicates the lost Pt surface area [31]. (From Zhang J, Sasaki K, Sutter E, Adzic RR. Stabilization of platinum oxygen-reduction electrocatalysts using gold clusters. Science 2007 315 220-2. Reprinted with permission from AAAS.)...

There is also scope for use of nanoparticulate Au-Pt catalysts in the fuel cells themselves [47]. Work at Brookhaven National Laboratory in New York has shown that platinum oxygen-reduction fuel cell electrocatalysts can be stabilized against dissolution under potential cycling regimes (a continuing problem in vehicle applications) by modifying Pt nanoparticles with gold clusters. 

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