(561f) Surface Reconstruction of Pd Concave Icosahedra: Atomic-Scale Mechanisms from First-Principles and Experiments

Elnabawy, A. - Presenter, University of Wisconsin-Madison
Roling, L., Stanford University
Xia, Y., Georgia Institute of Technology
Mavrikakis, M., University of Wisconsin-Madison
Concave surfaces exhibit a large density of high-index facets, such as steps, edges, and kinks. These structural features offer sites of high surface energy, and low coordination number1. Consequently, they have shown improved catalytic activities toward a number of reactions2, including formic acid electro-oxidation3, and Suzuki coupling reaction4. A common aspect of this diverse set of reactions is that they take place at low temperatures (<100 °C), which does not compromise the structural integrity of the as-synthesized concave structures. However, a myriad of structure-sensitive catalytic processes take place at much higher temperatures. Therefore, acquiring an atomic-level understanding of the mechanisms by which the concave surface structures transform into more common surface facets at elevated temperatures is of paramount interest. Here, we focus on the atomic surface reconstruction of Pd concave icosahedra to regular icosahedra. Applying self-consistent periodic density functional theory (PW91-GGA) to an atomistic model of a concave icosahedron edge, we quantify activation energy barriers for key steps responsible for the surface reconstruction, including step deformation and adatom diffusion. Our calculated energetics are surmountable at the temperatures at which the reconstruction experimentally takes place, as observed by in situ high-resolution transmission electron microscopy (HRTEM). Combining experimental and theoretical methods, we offer insight into the mechanism of surface reconstruction of Pd concave icosahedra to regular icosahedra, which offers an opportunity to rationally design thermally-durable concave nanoparticles.


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