Intriguing structures and magic sizes of heavy noble metal nanoclusters around size 55 governed by relativistic effect and covalent bonding

Strain Engineering of a Defect-Free, Single-Layer MoS2 Substrate for Highly Efficient Single-Atom Catalysis of CO Oxidation

Single-atom catalysts (SACs) are of great scientific and technical importance due to their low cost, high site density, and high specificity to enhance chemical reactions. Nevertheless, a major issue that severely limits the practical exploration of SACs is their instability, i.e., the preference of sintering and clustering over a defect-free substrate during operation. Here, we employ first-principles calculations to investigate how substrate engineering can stabilize SACs by strain-tuning the electronic interactions between the metal and the substrate using two Pd adatoms on a defect-free, single-layer MoS₂ as a typical example. It is identified that the Pd₂ dimer is prone to dissociate and form highly efficient SACs for CO oxidation due to the enhanced charge transfer and orbital hybridization with the MoS₂ substrate under a suitable tensile strain. The straining induces a semiconductive-to-metallic phase transition of the substrate. Moreover, low-cost elements, such as Ag, Ni, Cu, and Cr, can also be stabilized into high-performance SACs for CO oxidation with tunable reaction barriers by straining. The present findings offer a new avenue to inhibit the transition metal atoms from clustering into nanoclusters/particles and provide a clear guidance for the development of highly cost-efficient and stable SACs on defect-free substrates.

Relative edge energy in the stability of transition metal nanoclusters of different motifs

When a structure is reduced to a nanometer scale, the proportion of the edge atoms increases significantly, which can play a crucial role in determining both their geometric and electronic properties, as demonstrated by the recently established generalized Wulff construction principle [S. F. Li, et al., Phys. Rev. Lett., 2013, 111, 115501]. Consequently, it is of great interest to clarify quantitatively the role of the edge atoms that dominate the motifs of these nanostructures. In principle, establishing an effective method valid for determining the absolute value of the surface energy and particularly the edge energy for a given nanostructure is expected to resolve such a problem. However, hitherto, it is difficult to obtain the absolute edge energy of transition metal clusters, particularly when their sizes approach the nanometer regime. In this paper, taking Ru nanoclusters as a prototypical example, our first-principles calculations introduce the concept of relative edge energy (REE), reflecting the net edge atom effect over the surface (facet) atom effect, which is fairly powerful to quasi-quantitatively estimate the critical size at which the crossover occurs between different configurations of a given motif, such as from an icosahedron to an fcc nanocrystal. By contrast, the bulk effect should be re-considered to rationalize the power of the REE in predicting the relative stability of larger nanostructures between different motifs, such as fcc-like and hcp-like nanocrystals.