Characterization of changes in the electronic structure of platinum sub-nanoclusters supported on graphene induced by oxygen adsorption†

Abstract

As the sizes of noble metal catalysts, such as platinum, have been successfully minimized, fundamental insights into the electronic properties of metal sub-nanoclusters are increasingly sought for optimizing their catalytic performance. However, it is difficult to rationalize the catalytic activities of metal sub-nanoclusters owing to their more complex electronic structure compared with those of small molecules and bulky solids. In this study, the adsorption of molecular oxygen on a Pt₁₃ sub-nanocluster supported on a graphene layer was analyzed using density functional theory. Unlike bulk Pt, the Pt₁₃ sub-nanocluster has multiple adsorption sites, and the adsorption energy depends strongly on the type of adsorption site. The O₂ adsorption energy does not correlate with the transferred charge between O₂ and the Pt₁₃ moiety; therefore, to elucidate the differences in the adsorption sites, we propose an original approach for analyzing the electronic structure change in metal sub-nanoclusters caused by molecular adsorption. Our analysis of the integrated local density of state (LDOS) revealed that O₂ adsorption on the Pt₁₃ sub-nanocluster has a distinct feature, different from that on a smaller Pt₂ cluster or rather a larger Pt slab. The change in the electronic structure of the Pt₁₃ moiety was primarily observed near the Fermi level, different from that of the Pt slab whose DOS was distributed over a wide energy range. Furthermore, the change in the integrated LDOS correlated well with the O₂ adsorption energy on the Pt₁₃ sub-nanocluster.