Electrochemistry at Well-Characterized Bimetallic Surfaces - Fuel Cell Catalysis: A Surface Science Approach - page 261

Figure 8.15 (a) TEM micrograph of a Pt nanoparticle supported on carbon and the corre-
sponding cubo-octahedral model. (b) Snapshot of equilibrium Pt 3 Ni octahedral nanoparticles
containing 586 atoms simulated at 600K, exterior and cross-sectional views with (111) facets.
as a change in the surface coverage of underpotentially deposited hydrogen as well as
oxide species (Figs. 8.13b and 8.14).
The attenuated oxide formation boosts the activity for the ORR, and for
Pt 3 Ni(111)-skin we found the highest activity that has ever been observed on cathode
catalysts [Stamenkovic et al., 2007a], with a specific activity 10-fold higher than
Pt(111) and 90-fold higher than state-of-the-art Pt/C catalysts. Therefore, a critical
goal in ORR electrocatalysis is to prepare PtM nanoparticles with electronic and mor-
phological properties similar to those of the nanosegregated Pt 3 Ni(111) structure.
Given that the contribution of the (111) plane is maximized in an octahedral particle
(Fig. 8.15) consisting of 8 (111) facets, 12 (111) - (111) step-edges, and 6 vertices, syn-
thesis of uniform alloys of Pt 75 M 25 octahedra with the Pt-skin structure is the ultimate
goal [Wang et al., 2005]. These procedures are difficult, but, based on indications
obtained from Monte Carlo simulations, such syntheses with metals may eventually
be possible. An additional challenge involves preserving the Pt-skin-like surface
composition in the particles.
8.3.3 Bimetallic Systems by Thin Film Deposition
In addition to the establishment and understanding of activity trends on nanosegre-
gated surfaces, it has been anticipated that finding relationships between chemical
and electronic properties of thin metal films of Pt group metals deposited over 3d
and 5d elements has the potential to open up new opportunities in the quest to