Pt纳米粒子结构特性和相变规律的分子动力学研究

Molecular Dynamics Study on Phase Transition Properties of Pt Nanoparticles

铂(Pt)具有优良的催化活性,在能源和储能等领域都有广泛应用。研究表明,Pt的催化能力取决于表面活性位点的数量和种类,但其表面活性的调控机制尚不完全清楚。本研究利用分子动力学方法,基于LAMMPS软件,研究了Pt纳米粒子的结构特性和相变规律。结果表明,Pt纳米粒子无序原子占比随粒子半径的增大而减小,Pt纳米粒子的整体熔化温度随着粒子半径的减小而减小。此外,Pt纳米粒子根据配位数可以更深入地划分为核心和壳体2个部分,核心的配位数与块体材料相同为12,壳体的厚度为0.27nm(约为2层原子的厚度),且其配位数随核心距离的增大而减小。这一独特的核壳结构中壳体原子的势能比核心原子低。研究发现,当温度为1300 K时,粒子半径为3 nm Pt壳层原子熔化,而核内原子未熔化。因此,通过相变规律可以调控Pt催化剂的结构特性,为表面活性的调控提供理论依据。

Platinum(Pt) nanoparticles have been widely used in energy and energy storage due to its excellent catalytic activity.The investigation demonstrates that the catalytic capacity of Pt depends on the number and type of active sites on the surface,however,the regulation mechanism of its surface activity is not fully understood.In this paper,the microstructure and phase transformation of Pt nanoparticles were studied based on LAMMPS software.The results show that the proportion of disordered atoms of Pt nanoparticles decreases with the increase of particle radius,and the melting temperature of Pt nanoparticles decreases with the decrease of particle radius.In addition,the particles can be further divided into two parts:the surface shell and the inner core.Like the bulk material,the coordination number of the inner core is also 12.The thickness of the shell is about 0.27 nm with the thickness close to 2 layers of atoms and the coordination number decreases with the increase of the core distance.This unique core-shell structure resulting in that the potential energy of the surface shell atoms is approximately lower than that of the core.In this study,we found that the Pt shell atoms with particle radius of 3 nm can melt at 1300 K,whereas the inner atoms cannot melt.Therefore,the structure characteristics of Pt catalyst can be regulated by the phase transformation law,which provides a theoretical basis for the regulation of surface activity.