Polarization Effects on the Surface Chemistry of ${\mathrm{PbTiO}}_3$-Supported Pt Films

To demonstrate a new paradigm of dynamical control of surface structure and reactivity, we perform density functional theory calculations of the adsorption of several molecules and atoms to the surface of ultrathin Pt(100) films supported on ferroelectric ${\mathrm{PbTiO}}_3$. We show that reorienting the polarization direction of the substrate can dramatically change the chemisorption energies of CO, O, C, and N and alter the reaction pathways for dissociation of CO, ${\mathrm{O}}_2$, ${\mathrm{N}}_2$, and NO. We discuss the structural and electronic effects of a polarized substrate on the metal surface, and we suggest potential applications in tunable catalysis.

Figure 1

Atomic structure and induced charge density (in $\mathrm{m}{e}^{-{\AA }^3}$) for the $\mathrm{PbO}/\mathrm{Pt}$ interfaces. Pb, Ti, O, and Pt atoms are shown as cyan, blue, red, and gray spheres, respectively. The $P^{-}$ and $P^{+}$ interfaces are on the left and the right, respectively. The contour plot axes are chosen to show the surface cations and anions and their bonds to the Pt atoms. The general trends of interfacial charge rearrangement are similar for the analogous ${\mathrm{TiO}}_2/\mathrm{Pt}$ interfaces; for illustration, see Ref. 22.

Figure 2

Platinum $d_{z^2}$ and $d_{xz/yz}$ DOS as a function of ${\mathrm{PbTiO}}_3$ film thickness for one monolayer of Pt above the $P^{-}$ (left) and the $P^{+}$ (right) PbO-terminated ${\mathrm{PbTiO}}_3$, with $m=1–5$ oxide unit cells. The shaded gray curve shows the corresponding DOS for Pt(100). Regardless of the ${\mathrm{PbTiO}}_3$ film thickness, the electronic structure of the interfacial Pt layer remains almost constant, suggesting that the Pt surface reactivity is also independent of the substrate thickness.

Figure 3

(a)–(d) Chemisorption energies for CO [26], O, C, and N as a function of polarization direction and Pt thickness for the $\mathrm{PbO}/\mathrm{Pt}$ interfaces. Red plus signs indicate the $P^{+}$ interface, and blue minus signs represent the $P^{-}$ interface. The zero of energy corresponds to $E_{\mathrm{chem}}$ on unsupported Pt(100). (e)–(h) Site-preference energies for CO, O, C, and N. The solid black lines give $E_{\mathrm{site}}$ for the adsorbates on unsupported Pt(100). Points above the dotted lines represent a change in the preferred bonding site relative to Pt(100).