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 number
1. Consequently, they have shown improved catalytic activities toward a number of reactions
2, including formic acid electro-oxidation
3, and Suzuki coupling reaction
4. 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.
References
1. Ruditskiy A, Peng HC, Xia YN. Shape-Controlled Metal Nanocrystals for Heterogeneous Catalysis. Annual Review of Chemical and Biomolecular Engineering, Vol 7. 2016;7:327-348.
2. Zhang JA, Langille MR, Personick ML, Zhang K, Li SY, Mirkin CA. Concave Cubic Gold Nanocrystals with High-Index Facets. Journal of the American Chemical Society. Oct 2010;132(40):14012-14014.
3. Huang XQ, Zhao ZP, Fan JM, Tan YM, Zheng NF. Amine-Assisted Synthesis of Concave Polyhedral Platinum Nanocrystals Having {411} High-Index Facets. Journal of the American Chemical Society. Apr 2011;133(13):4718-4721.
4. Jin MS, Zhang H, Xie ZX, Xia YN. Palladium Concave Nanocubes with High-Index Facets and Their Enhanced Catalytic Properties. Angewandte Chemie-International Edition. 2011;50(34):7850-7854.
