Yang Yang, Yu Haiyan, Cai Yushun, Ferrando Riccardo, Cheng Daojian
Beijing Key Laboratory of Energy Environmental Catalysis, State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, People's Republic of China.
J Phys Condens Matter. 2018 Jul 18;30(28):285503. doi: 10.1088/1361-648X/aaca09. Epub 2018 Jun 4.
Understanding the stability and adsorption properties of O atom can be considered as the first step to understand the mechanism of the oxygen reduction reaction on Pt-Ni nanoclusters. In this work, the equilibrium structures, stability, adsorption properties and deformation energies of medium-sized Pt-Ni nanoclusters are studied by global optimization method and density functional theory calculations. It is found that Pt-Ni nanoclusters are of more stable structure and larger oxygen adsorption energy than Pt nanoclusters, and the enhanced stability and oxygen adsorption capacity of Pt-Ni nanoclusters originate from both the strain and electronic factors. Based on the strain effect, the local pressures are on average much better equilibrated on Pt-Ni nanoclusters, bringing about the more stable structure. The elongation of the metal-metal bond distances results in the increase of adsorption energy of the O atom on Pt-Ni nanoclusters. Considering the electronic effect, the charge interaction between the LDOS (d orbital) of metal atoms adjacent to the adsorbed O atom and the DOS (p orbital) of the O atom gives rise to the increase of oxygen adsorption capacity on Pt-Ni nanoclusters. Simultaneously, the charge density difference analysis shows that the Ni atoms doping is conducive for O atom adsorption. In addition, the diffusion of O atom from surface to interior is difficult due to the high diffusion energy barriers. Our results show that both strain and electronic factors are of important effects on the stability and adsorption properties of nanoalloys.
理解O原子的稳定性和吸附特性可被视为理解Pt-Ni纳米团簇上氧还原反应机理的第一步。在这项工作中，通过全局优化方法和密度泛函理论计算研究了中等尺寸Pt-Ni纳米团簇的平衡结构、稳定性、吸附特性和形变能。研究发现，Pt-Ni纳米团簇比Pt纳米团簇具有更稳定的结构和更大的氧吸附能，Pt-Ni纳米团簇稳定性和氧吸附能力的增强源于应变和电子因素。基于应变效应，Pt-Ni纳米团簇上的局部压力平均而言得到更好的平衡，从而产生更稳定的结构。金属-金属键距的伸长导致O原子在Pt-Ni纳米团簇上的吸附能增加。考虑电子效应，与吸附的O原子相邻的金属原子的LDOS（d轨道）与O原子的DOS（p轨道）之间的电荷相互作用导致Pt-Ni纳米团簇上氧吸附能力的增加。同时，电荷密度差分析表明Ni原子掺杂有利于O原子吸附。此外，由于高扩散能垒，O原子从表面扩散到内部很困难。我们的结果表明，应变和电子因素对纳米合金的稳定性和吸附特性都有重要影响。
