Surface Heterogeneity for Oxide Formation at Pt Nanoparticles

Wang et al. performed a similar study, in which they calculated the detailed map of oxygen adsorption energies at hemispherical cubo-octahedral nanoparticles with 

In the second step, full optimizations were performed with the relaxation of all atoms in the system, where the oxygen atom was again positioned initially at all high-symmetry surface sites. Thereby, the contribution of particle relaxation to the adsorption energy could be quantified. The potential energy of adsorption after either of these steps was calculated with respect to the energy of the free O2 molecule  

The total energy of O2 was determined as —9.975 eV, using thermochemical data (Rossmeisl et al., 2005). 

From studies at extended surfaces, it is well known that undercoordination of surface atoms induces a narrowing of the d-band, causing an increase in the adsorption energy. A lattice contraction, on the other hand, induces a broadening of the d-band, which causes a decrease in the adsorption energy. Both of these effects compete on nanoparticle surfaces. As stated previously, in the case of nanoparticles, the effect of surface-atom undercoordination supersedes the lattice strain effect. 

FIGURE 3.13 A 3D map of the adsorption energy of atomic oxygen (in eV) at the surface of a hemispherical cubo-octahedral Pt nanoparticles with 92 atoms. 

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