Yang Yun1, Nicolas Pilet2, Udo D. Scwarz2, and Eric I. Altman3. (1) Department of Chemical Engineering, Yale University, PO Box 208260, New Haven, CT 06520, (2) Department of Mechanical Engineering, Yale University, PO Box 208284, New Haven, CT 06520, (3) Chemical Engineering, Yale University, P.O. Box 208260, New Haven, CT 06520-8260
Ferroelectric polarization creates high energy surfaces that are expected to reduce their surface energy by reconstructing or adsorbing compensating charges. Because opposite charges must be screened on opposite surfaces, different surface atomic structures and reactivities are anticipated. Since the polarization can be changed by applying an electric field, this suggests switchable surface chemical properties. We previously found that this effect can be exploited to alter how strongly polar molecules adsorb on LiNbO3 surfaces. To determine if ferroelectric polarization can alter the catalytic properties of supported metals, the interaction of Pd with LiNbO3 was characterized using electron diffraction, photoelectron spectroscopy (XPS and UPS), ion scattering spectroscopy (ISS), atomic force microscopy, and CO temperature programmed desorption (TPD). Positively poled LiNbO3 surfaces behave like many other oxides. The Pd atoms aggregate into nanoparticles, with the smallest nanoparticles exhibiting XPS peak shifts that can be associated with a size effect. CO adsorption on these nanoparticles is largely unaffected by the size of the nanoparticles, the LiNbO3 support, and annealing. In contrast, preliminary results suggest that Pd behaves very differently on negatively poled LiNbO3. In this case, the Pd photoemission peak shifts persist to higher Pd coverages and annealing causes the Pd peak intensity to decrease; annealing has no effect on Pd on positively poled LiNbO3. Further, we find that modest heating to just 600 K severely attenuates the ability of the Pd to adsorb CO.