New Crystal Structures Identified for PtO and PtO$_2$ using Density Functional Theory Calculations

Platinum plays an important role in catalysis and electrochemistry, and it has been known that the direct interaction of oxygen with Pt surfaces can lead to the formation of platinum oxides (PtO$_x$), which can affects 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$_x$ ($1 \leq x \leq 2$). 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 Moore and Pauling (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 tends to form octahedron motifs in PtO$_x$ even at lower O composition by the formation of Pt$-$Pt bonds.