State Key Laboratory of Silicon Materials, School of Materials Science & Engineering, and Cyrus Tang Center for Sensor Materials and Applications, Zhejiang University, Hangzhou, Zhejiang 310027, People's Republic of China.
Nanoscale. 2017 Aug 10;9(31):11077-11084. doi: 10.1039/c7nr02638b.
Bimetallic nanocrystals with a branched shape have received great interest as catalysts due to their unique structures and fascinating properties. However, the conventional synthetic approaches based on the island growth mode often lead to the dendritic nanostructures with inhomogeneous and uncontrolled branches. Here precise control over the number of branches has been realized in the deposition of Pt on Pd seeds through the Stranski-Krastanov growth mechanism. Based on such a growth mode, Pd@Pt core-shell hexapods and octapods have been generated by a seeded growth with Pd octahedra and cubes as the seeds, respectively. We found that Pt atoms are initially deposited on the side faces of Pd seeds through a layer-by-layer epitaxial growth in the presence of oleylamine (OAm), leading to a local strain focused at their corners. These strain-concentrated sites promote the subsequent island growth of Pt atoms at the corners of the Pd seeds, resulting in the Pd@Pt core-shell hexapods or octapods. Both the Pd@Pt core-shell hexapods and octapods exhibit the substantially enhanced catalytic properties in terms of activity and stability towards a methanol oxidation reaction (MOR) relative to the commercial Pt/C. Specifically, the Pd@Pt core-shell hexapods show the highest specific (1.97 mA cm) activity and mass activity (0.52 mA μg) for the MOR, which are 5.8 and 2.6 times higher than those of the commercial Pt/C, respectively. This enhancement can probably be attributed to their unique structures and the synergistic effect between Pt and Pd.
具有支化形状的双金属纳米晶体因其独特的结构和迷人的性质而受到极大关注，作为催化剂。然而，基于岛状生长模式的传统合成方法往往导致枝晶状纳米结构具有不均匀和不可控的分支。在这里，通过 Stranski-Krastanov 生长机制，在 Pd 种子上沉积 Pt 时，实现了对分支数量的精确控制。基于这种生长模式，分别以 Pd 八面体和立方体作为种子，通过种子生长生成了 Pd@Pt 核壳六足和八足。我们发现，在油胺 (OAm) 的存在下，Pt 原子通过逐层外延生长最初沉积在 Pd 种子的侧面上，导致其角部出现局部应变。这些应变集中的位点促进了随后 Pt 原子在 Pd 种子角部的岛状生长，从而形成了 Pd@Pt 核壳六足或八足。与商业 Pt/C 相比，Pd@Pt 核壳六足和八足在甲醇氧化反应 (MOR) 的活性和稳定性方面都表现出显著增强的催化性能。具体而言，Pd@Pt 核壳六足在 MOR 中表现出最高的比活性 (1.97 mA cm) 和质量活性 (0.52 mA μg)，分别比商业 Pt/C 高 5.8 倍和 2.6 倍。这种增强可能归因于它们独特的结构以及 Pt 和 Pd 之间的协同效应。
