Density functional theory study of platinum oxides: From infinite crystals to nanoscopic particles

For over a century, platinum oxides find technologically relevant applications in various fields ranging from catalysis to electrochemistry and nanoelectronics. We have performed a density functional theory study of the PtO, Pt3O4, and PtO2 bulk oxide phases. In our calculations, PtO and Pt3O4 present metallic character at the simple generalized gradient approximation level. The application of Hubbard corrections to the Kohn-Sham Hamiltonian opens a small gap in the electronic band structure of PtO, but not of Pt3O4, in which metallic Pt-Pt bonds are revealed by a Bader analysis of the calculated electronic structure. These results, together with the noninteger oxidation number of the Pt ions, are indicative of metallicity of the Pt3O4 phase which may be consistent with the known metallic character of platinum bronzes. Moreover, we have calculated the relative thermodynamic stabilities of platinum oxide Wulff's particles and discussed the results in the context of catalysis. Finally, we have predicted that the formation of alpha-PtO2 nanotubes could be energetically feasible. This result is of potential interest both for nanotechnological and catalytic applications and may explain the formation of curled alpha-PtO2 sheets observed in high-resolution transmission electron microscopy images.