Bulk structures of PtO and PtO${}_2$ from density functional calculations

Platinum plays an important role in catalysis and electrochemistry, and it is known that the direct interaction of oxygen with Pt surfaces can lead to the formation of platinum oxides (PtO${}_x$), which can affect the reactivity. To contribute to the atomistic understanding of the atomic structure of PtO${}_x$, we report a density functional theory study of the atomic structure of bulk PtO${}_x$ ($1\le x\le 2$). From our calculations, we identified a lowest-energy structure (GeS type, space group $Pnma$) for PtO, which is 0.181 eV lower in energy than the structure suggested by W. J. Moore and L. Pauling [J. Am. Chem. Soc. 63, 1392 (1941)] (PtS type). Furthermore, two atomic structures were identified for PtO${}_2$, which are almost degenerate in energy with the lowest-energy structure reported so far for PtO${}_2$ (CaCl${}_2$ type). Based on our results and analysis, we suggest that Pt and O atoms tend to form octahedron motifs in PtO${}_x$ even at lower O composition by the formation of Pt-Pt bonds.

Figure 1

Atomic structures of the PtO, PtO${}_{1.33}$, and PtO${}_2$ compositions, in which the Pt and O atoms are indicated by gray (large) and red (small) balls. The unit cells are indicated by solid black lines. The structure type, crystalline system, space group, and formation energy $\Delta H$ are indicated below the unit cells.

Figure 2

Total and local density of states (LDOS) for PtO${}_x$ for the structures shown in Fig. 1 in arbitrary units. The black (solid), red (dotted), and blue (dashed) lines are the total DOS, Pt LDOS, and O LDOS, respectively. The vertical dashed lines indicate the Fermi level (zero energy).