Atomic Structure and Dynamics of Single Platinum Atom Interactions with Monolayer MoS₂

Abstract

We have studied atomic level interactions between single Pt atoms and the surface of monolayer MoS 2 using aberration-corrected annular dark field scanning transmission electron microscopy at an accelerating voltage of 60 kV. Strong contrast from single Pt atoms on the atomically resolved monolayer MoS 2 lattice enables their exact position to be determined with respect to the MoS 2 lattice, revealing stable binding sites. In regions of MoS 2 free from surface contamination, the Pt atoms are localized in S vacancy sites and exhibit dynamic hopping to nearby vacancy sites driven by the energy supplied by the electron beam. However, in areas of MoS 2 contaminated with carbon surface layers, the Pt atoms appear at various positions with respect to the underlying MoS 2 lattice, including on top of Mo and in off-axis positions. These variations are due to the Pt bonding with the surrounding amorphous carbon layer, which disrupts the intrinsic Pt−MoS 2 interactions, leading to more varied positions. Density functional theory (DFT) calculations reveal that Pt atoms on the surface of MoS 2 have a small barrier for migration and are stabilized when bound to either a single or double sulfur vacancies. DFT calculations have been used to understand how the catalytic activity of the MoS 2 basal plane for hydrogen evolution reaction is influenced by Pt dopants by variation of the hydrogen adsorption free energy. This strong dependence of catalytic effect on interfacial configurations is shown to be common for a series of dopants, which may provide a means to create and optimize reaction centers. KEYWORDS: Pt dopants, MoS 2 , ADF-STEM, 2D materials, catalysts, dopants T he presence of single isolated atom impurities and dopants either on the surface or directly bonded within the lattice structure of 2D materials influences the properties.1−10 Understanding the atomic structure that defines the bonding between single foreign atoms and the host 2D crystal is critical for developing accurate models that can predict the impacts of doping. Single metal atom doping of materials has also found significant recent interest in the development of catalysts by reducing the mass content of precious metals such as Pt, while maintaining high performance.11−13 A key aspect to single metal atom catalysts is preventing aggregation of the active species into clusters, reducing the loss of metal atoms by detachment, and providing the optimum bonding configuration for catalytic activity. Recent work has shown that doping 2D layered MoS 2 can lead to higher activities in the hydrogen evolution reaction, utilizing Co, Ni, and Pt single-metal dopants.14,15 MoS 2 is normally active only at edge sites, but the incorporation of isolated metal substitutional or surface dopants can activate the basal plane and lead to a large increase in the number of active catalytic sites. Therefore, resolving the atomic structure of single metal atoms and their structural interaction with MoS 2 helps reveal the stable configurations that dictate the catalytic...

Defect‐Based Single‐Atom Electrocatalysts

“…In addition to cation vacancies, anion vacancies of metal oxides,[19b,59] metal sulfides,[14a,60] metal nitrides[14b,61] can be well anchor sites to stabilize isolated metal atoms. Oxygen vacancy is considered as the most common defects in metal oxides, and its formation energy has great effects on the redox performance of metal oxides.…”

“…When compared with traditionally prepared CoMoS 2 catalysts, MoS 2 monolayer sheets attached by single Co atoms have exhibited superior activity, stability, and selectivity without sulfur loss and deactivation. Recently, Li et al reported that the Pt single‐atom sites were anchored on monolayer MoS 2 through bond connections with S vacancies . The exact position of Pt could be determined at the MoS 2 lattice by the strong contrast between single Pt atoms and MoS 2 at the atomic level, which indicated the stable binding sites.…”

Single Metal Atom Photocatalysis

“…S vacancies, which often appear in metal dichalcogenides, can also serve as anchoring sites to bound single metal atoms. By using aberration‐corrected annular dark‐field scanning transmission electron microscopy, Li et al revealed that isolated Pt atoms on defective MoS 2 were stabilized by bonding within S vacancies ( Figure ) . It was found by Liu et al that S vacancies can trap single Co metal atoms on S‐deficient MoS 2…”

“…d) DFT relaxed atomic model showing a Pt atom in a 2S vacancy site. Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…These high‐energy surface sites thus can anchor and bond strongly with foreign atoms to reduce the total system energy. Therefore, utilizing the surface defects, which are induced by controlling the synthesis process, has been applied to synthesize various single metal atoms, such as Pt 1 /Ni(OH) x , Au 1 /CeO 2 , M 1 (M = Ni, Co, Mn, Ti and Zr)/Fe 3 O 4 , Rh 1 /CoO, and Pt 1 /MoS 2 . In addition, the surface defects can modulate the physiochemical properties of semiconductor support.…”