Dependence of oxygen dissociative adsorption on platinum surface structures

We carry out density functional theory-based calculations to investigate the oxygen $\left({\mathrm{O}}_2\right)$ dissociative adsorption on two platinum (Pt) surfaces, viz., Pt(111) and Pt(001). We calculated the corresponding total energies, for varying ${\mathrm{O}}_2$ center-of-mass distances from the Pt surface, and varying O-O interatomic distances. Our calculation results show that the ${\mathrm{O}}_2$ dissociative adsorption progresses much more easily on Pt(001) than on Pt(111). These results are in good agreement with experimentally observed differences and trends in reactivities of Pt(001) and Pt(111).

Figure 1

(Color online) (a) and (b) shows schematic depiction of the ${\mathrm{O}}_2\text{‐}\mathrm{Pt}$ system with the coordinates $Z$ and $r$ as indicated. (c) and (d) show the possible symmetric ${\mathrm{O}}_2$ dissociative adsorption sites. (a) and (c) correspond to ${\mathrm{O}}_2∕\mathrm{Pt}\left(001\right)$. (b) and (d) correspond to ${\mathrm{O}}_2∕\mathrm{Pt}\left(111\right)$.

Figure 2

Calculated potential energies for ${\mathrm{O}}_2$ dissociation at the bridge site [in the configuration 1:H-B-H, as depicted in Fig. 1c] as a function of the O-O distance $r$ and the ${\mathrm{O}}_2$ c.m. distance $Z$ from the Pt(001) surface. The O-O bond is oriented parallel to the Pt(001) surface. The ${\mathrm{O}}_2$ is constrained to dissociate over the indicated site in a parallel orientation and a planar geometry. The equilibrium gas phase O-O distance is $\approx 1.2\mathrm{\AA }$. Energies are given in electronvolts relative to the values at $(Z=5.0\mathrm{\AA },r=1.2\mathrm{\AA })$. We can see a potential minimum at $(Z=1.0\mathrm{\AA },r=2.8\mathrm{\AA })$, which is denoted as $\alpha$.

Figure 3

Calculated potential energies for ${\mathrm{O}}_2$ dissociation at the bridge site [in the configuration 1:H-B-F, as depicted in Fig. 1d] as a function of the O-O distance $r$ and the ${\mathrm{O}}_2$ c.m. distance $Z$ from the Pt(111) surface. The O-O bond is oriented parallel to the Pt(111) surface. The ${\mathrm{O}}_2$ is constrained to dissociate over the indicated site in a parallel orientation and a planar geometry. The equilibrium gas phase O-O distance is $\approx 1.2\mathrm{\AA }$. Energies are given in electronvolts relative to the values at $(Z=5.0\mathrm{\AA },r=1.2\mathrm{\AA })$. We can see a potential minimum at $(Z=1.5\mathrm{\AA },r=2.0\mathrm{\AA })$, which we denote as $\beta$.

Figure 4

(Color) Contour plot of the charge distribution taken along a cut through the plane depicted by the broken line in the inset, (a) before and (b) after ${\mathrm{O}}_2$ dissociation on Pt(001). (b) corresponds to case indicated by $\alpha$ in Fig. 2. Contour spacing is $0.2\text{electrons}∕\mathrm{\AA }$, with the origin indicated by the red line.

Figure 5

(Color) Contour plot of the charge distribution taken along a cut through the plane depicted by the broken line in the inset, (a) before and (b) after ${\mathrm{O}}_2$ dissociation on Pt(111). (b) corresponds to case indicated by $\beta$ in Fig. 3. Contour spacing is $0.2\text{electrons}∕\mathrm{\AA }$, with the origin indicated by the red line.