An Atomistic View of Platinum Cluster Growth on Pristine and Defective Graphene Supports.

Density functional theory (DFT) is used to systematically investigate the electronic structure of platinum clusters grown on different graphene substrates. Platinum clusters with 1 to 10 atoms and graphene vacancy defect supports with 0 to 5 missing C atoms are investigated. Calculations show that Pt clusters bind more strongly as the vacancy size increases. For a given defect size, increasing the cluster size leads to more endothermic energy of formation, suggesting a templating effect that limits cluster growth. The opposite trend is observed for defect-free graphene where the formation energy becomes more exothermic with increasing cluster size. Calculations show that oxidation of the defect weakens binding of the Pt cluster, hence it is suggested that oxygen-free graphene supports are critical for successful attachment of Pt to carbon-based substrates. However, once the combined material is formed, oxygen adsorption is more favorable on the cluster than on the support, indicating resistance to oxidative support degradation. Finally, while highly-symmetric defects are found to encourage formation of symmetric Pt clusters, calculations also reveal that cluster stability in this size range mostly depends on the number of and ratio between PtC, PtPt, and PtO bonds; the actual cluster geometry seems secondary.

Adsorption, activation, and dissociation of oxygen on doped oxides.

Charge transfer in the presence of dopants is relevant for the adorption and activation of small molecules, such as O2 . Scanning tunneling microscopy and DFT calculations provide evidence for the formation of strongly bound superoxo species on chemically inert, Mo-doped CaO films. This oxygen surface species shows a high propensity to dissociate. Dopants could also be important for the activation of hydrocarbons on inert oxides.