Structures, Thermal Stability, and Chemical Activity of Crown-Jewel- Structured Pd-Pt Nanoalloys Yang Yang, † Zheng Zhao, † Rong Cui, ‡ Hao Wu, ‡ and Daojian Cheng* ,†,‡ † State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People’s Republic of China ‡ Changzhou Institute of Advanced Materials, Beijing University of Chemical Technology, Changzhou 213164, People’s Republic of China * S Supporting Information ABSTRACT: In this work, the equilibrium structures, thermal stability, and chemical activity of crown-jewel (CJ)-structured Pd-Pt nanoalloys with highly symmetric cuboctaheral (Cubo), decahedral (Dec), and icosahedral (Ico) structures are studied by using molecular simulation based on the Gupta empirical potential and density functional theory (DFT) calculations. It is found that both the melting temperature and stability of CJ-structured Pd-Pt nanoalloys with the same size follow the order of Ico > Dec > Cubo, which agrees with the rule that the more stable the cluster, the higher the melting point. In addition, the melting temperature of CJ-structured Pd-Pt nanoalloys with the same morphology is of the same linear behavior with the inverse diameter of the clusters, which is consistent with the Pawlow’s law. The adsorption properties of O on these Pd-Pt nanoalloys are studied to model the chemical activity of these nanoalloys. For the CJ-structured Pd 12 Pt 43 , the adsorption strength of O follows the order of Dec < Cubo < Ico, and the adsorption strength per O atom decreases slightly with increasing coverage of the O atom. In addition, the adsorption strength of O on the CJ-structured Pd 12 Pt 43 is stronger than that on the CJ-structured Pd 12 Pt 135 . Our results show that the structures, thermal stability, and chemical activity of CJ-structured Pd- Pt nanoalloys are size- and morphology-dependent, which would shed new light on the design of CJ-structured nanoalloys as catalysts. 1. INTRODUCTION Bimetallic clusters (or “nanoalloys”) occupy a very important place among nano-objects because they are the building blocks of nanoscience. The rich diversity of compositions, structures, and properties of nanoalloys has led to their widespread applications in catalysis. 1 To achieve a high catalytic activity, special structures of nanoalloys have been found and studied, 2 such as the core-shell, 3-5 onion-like, 6-9 and crown-jewel (CJ) 10,11 structures. In particular, the CJ structure, where one kind of metal atom (single atom) is controllably assembled at the special position on the surface of the nanoalloys, has been considered to be promising for the catalytic applications. For example, Au-Pd nanoalloys with CJ structure, 10,11 where the Pd clusters serve as the crowns and the Au atoms serve as jewels decorating the top position of the Pd clusters, were prepared based on the galvanic replacement process, showing excellent catalytic activity for aerobic glucose oxidation. It is obvious that nanoalloys with the CJ structure are worth studying deeply as a potential catalyst. However, data is still scarce for the CJ-structured nanoalloys. Pt-based nanoalloys have been considered to be promising catalysts for fuel cell cathodes. It is well-known that Pt-based nanoalloys can reduce the utilization of Pt and also improve the catalytic ability. 12-15 Among these systems, Pd-Pt nanoalloys have been widely studied, showing enhanced catalytic activity toward the oxygen reduction reaction (ORR). 16,17 For example, Lim et al. 17 found that Pd-Pt nanoalloys are 2.5 times more active than the Pt/C catalyst for the ORR. Zhang et al. 18 found that the ORR activity on carbon-supported Pd-Pt nanoalloys is 5-8 times higher than that on carbon-supported pure Pt catalyst. It is well-known that structural models can strongly affect not only the thermodynamics but also the catalytic activity and selectivity of metal clusters. 19 In our previous work, Pd 43 Pt 12 with a three-shell onion-like structure exhibits the highest relative stability, the highest melting point, and good catalytic activities toward the ORR among these 55-atom Pd- Pt clusters. 20 Therefore, it is also interesting to study Pd-Pt nanoalloys with the CJ structure, which could be a promising ORR electrocatalyst. However, little work has been done on the Special Issue: Current Trends in Clusters and Nanoparticles Conference Received: October 24, 2014 Revised: December 3, 2014 Published: December 10, 2014 Article pubs.acs.org/JPCC © 2014 American Chemical Society 10888 dx.doi.org/10.1021/jp5107108 | J. Phys. Chem. C 2015, 119, 10888-10895