Quantum Dots of 1T Phase Transitional Metal Dichalcogenides Generated via Electrochemical Li Intercalation

Abstract

We prepare group VI transitional metal dichalcogenides (TMDs, or MX) from the 1T phase with quantum-sized and monolayer features via a quasi-full electrochemical process. The resulting two-dimensional (2D) MX (M = W, Mo; X = S, Se) quantum dots (QDs) are ca. 3.0-5.4 nm in size with a high 1T phase fraction of ca. 92%-97%. We attribute this to the high Li content intercalated in the 1T-MX lattice (mole ratio of Li:M is over 2:1), which is achieved by an increased lithiation driving force and a reduced electrochemical lithiation rate (0.001 A/g). The high Li content not only promotes the 2H → 1T phase transition but also generates significant inner stress that facilitates lattice breaking for MX crystals. Because of their high proportion of metallic 1T phase and sufficient active sites induced by the small lateral size, the 2D 1T-MoS QDs show excellent hydrogen evolution reactivity (with a typical η of 92 mV, Tafel slope of 44 mV/dec, and J of 4.16 × 10 A/cm). This electrochemical route toward 2D QDs might help boost the development of 2D materials in energy-related areas.

Metastable MoS2: Crystal Structure, Electronic Band Structure, Synthetic Approach and Intriguing Physical Properties

“…Recently,Z hang et al reported the preparation of 1T MoS 2 quantum dots via an modifiede lectrochemical lithium intercalation. [45] They enhanced the driving force for lithium intercalation and decreased the intercalation rate. Li 2 MoS 2 was obtained under ad ischarging current density of 0.001 Ag À1 .T he enough lithium ions in the interlayers promoted the complete phase transition from 2H to 1T and generated large inner stress to facilitate crystal lattice breaking.…”

Differentiating Polymorphs in Molybdenum Disulfide via Electron Microscopy

“…The S/N ratio of the STEM image can be degraded by random Poisson noise and scanning noise during the image capture. In addition, surface contamination as well as any underlying thin carbon film reduce the S/N ratio. In many reports, the assignment of 1T‐MoS 2 has been made on the basis of the absence of the S dimer, however, the S dimer in 1H‐MoS 2 is sometimes obscured by contamination or an underlying carbon film.…”

Strategies on Phase Control in Transition Metal Dichalcogenides

“…Understanding the mechanism and the conditions under which the phase transition is triggered could lead to better utilization of TMDs in the future. Moreover, it could also lead to improving current applications, especially those involving phase transition processes . For example, a recent work on the study of alkali metal ion–intercalated MoS 2 showed that prelithiation‐treated MoS 2 demonstrated an improved cycle stability and rate capability compared with the bulk or exfoliated–restacked MoS 2 ( Figure a).…”