Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS<sub>2</sub>

Sun, Lifei; Yan, Xingxu; Zheng, Jingying; Yu, Hongde; Lu, Zhixing; Gao, Shang; Liu, Lina; Pan, Xiaoqing; Wang, Dong; Wang, Zhiguo; Wang, Peng; Jiao, Liying

doi:10.1021/acs.nanolett.8b00452

Cited by 80 publications

(70 citation statements)

References 20 publications

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“…To avoid such unexpected reversion from the as-obtained 1T to the 2H phase [84][85][86][87], a thermal activated hydrogenation method is put forward to substitute LiH for Li [88]. Furthermore, the phase transition induced by intercalation also depends on the thickness of MoS 2 , because the layer number affects both the energy difference between 2Hand 1T'-MoS 2 and the critical injected electron concentrations [89].…”

Section: Intercalationmentioning

confidence: 99%

Phase engineering of two-dimensional transition metal dichalcogenides

et al. 2019

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Two-dimensional (2D) transition metal dichalcogenides (TMDs) have gained much attention in virtue of their various atomic configurations and band structures. Apart from those thermodynamically stable phases, plenty of metastable phases exhibit interesting properties. To obtain 2D TMDs with specific phases, it is important to develop phase engineering strategies including phase transition and phaseselective synthesis. Phase transition is a conventional method to transform one phase to another, while phase-selective synthesis means the direct fabrication of the target phases for 2D TMDs. In this review, we introduce the structures and stability of 2D TMDs with different phases. Then, we summarize the detailed processes and mechanism of the traditional phase transition strategies. Moreover, in view of the increasing demand of high-phase purity TMDs, we present the advanced phase-selective synthesis strategies. Finally, we underline the challenges and outlooks of phase engineering of 2D TMDs in two aspects-high phase purity and excellent controllability. This review may promote the development of controllable phase engineering for 2D TMDs and even other 2D materials toward both fundamental studies and practical applications.

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Section: Intercalationmentioning

confidence: 99%

Phase engineering of two-dimensional transition metal dichalcogenides

et al. 2019

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“…Therefore, the phase transition (2H → 1T) has also been reported to be an efficient approach to promote the electrocatalytic performance of MoS 2 . [ 25–29 ] Recently, Luxa et al [ 29 ] utilizing alkali metals (Li, Na, K, Rb, and Cs) as additives successfully increased 1T ratio on the prepared MoS 2 samples (41.9% for Li‐MoS 2 ), which thereby significantly improved the related HER activities. The sizes of intercalated cations were reported to strongly affect the final 1T ratio on MoS 2 .…”

Section: Introductionmentioning

confidence: 99%

H₂‐Directing Strategy on In Situ Synthesis of Co‐MoS₂ with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism

Jin

Liu

Dai

et al. 2020

Advanced Energy Materials

103

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MoS2 has drawn great attention as a promising Pt‐substituting catalyst for the hydrogen evolution reaction (HER). This work utilizes H2 as the structure directing agent (SDA) to in situ synthesize a range of Co‐MoS2‐n (n = 0, 0.5, 1.0, 1.4, 2.0) with expanded interlayer spacings (d = 9.2 – 11.1 Å), which significantly boost their HER activities. The Co‐MoS2‐1.4 with an interlayer spacing of 10.3 Å presents an extremely low overpotential of 56 mV (at 10 mA cm−2) and a Tafel slope of 32 mV dec−1, which is superior than most reported MoS2‐based catalysts. Density function theory calculations are used to gain insights that i) the H2 can be dissociatively adsorbed on MoS2 and greatly affect the related surface free energy by regulating the interlayer spacing; ii) the expanded interlayer spacing can significantly decrease the absolute value of ΔGH, thereby leading to greatly promoted HER activity. Additionally, the large amounts of 1T phase (73.9–79.2%) and Co‐Mo‐S active sites (40.9–91.3%) also contribute to the enhanced HER activity of the synthesized samples. Overall, a simple new strategy for in situ synthesis of Co‐MoS2 with an expanded interlayer spacing is proposed, which sheds light on other 2D energy material designs.

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“…Apart from alkali metals, several attempts have been made on the covalent functionalization of 2H and 1T phases by organic functional groups . Sarkar et al decorated the 2D layers with metal nanoparticles which changed the transfer characteristics of the 2D devices and demonstrated its capability as a gas sensor .…”

mentioning

confidence: 99%

An Insight into the Phase Transformation of WS₂ upon Fluorination

et al. 2018

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reduces the TMDs and the gliding of the S planes results in the transformation from 2H to 1T. Functionalization by other electron donating species such as Re, Tc, and Mn can also induce the transformation. [7][8][9][10][11] The electron donated by the alkali metals alters the d electron count of the metal (Mo or W), and it splits in the octahedral coordination to have three unpaired electrons in the valence band d orbitals. However, the 1T phase is highly unstable and converts back into 2H phase with time and temperature. [12] Apart from alkali metals, several attempts have been made on the covalent functionalization of 2H and 1T phases by organic functional groups. [13][14][15][16] Sarkar et al. decorated the 2D layers with metal nanoparticles which changed the transfer characteristics of the 2D devices and demonstrated its capability as a gas sensor. [17] Theoretically, hydrogenation also converts the 2H semiconducting phase into the metallic phase. [18] A transformation from an n-type to a p-type semiconductor, a nonmagnetic to a magnetic material and a boost in the catalytic activity was achieved through controlled and selective doping of TMDs by transition metals. [19] An interesting deviation from extrinsic doping was intrinsic doping by the incorporation of islands of 1T in a lattice of 2H semiconducting nanosheets, where the The transformation from semiconducting to metallic phase, accompanied by a structural transition in 2D transition metal dichalcogenides has attracted the attention of the researchers worldwide. The unconventional structural transformation of fluorinated WS 2 (FWS 2 ) into the 1T phase is described. The energy difference between the two phases debugs this transition, as fluorination enhances the stability of 1T FWS 2 and makes it energetically favorable at higher F concentration. Investigation of the electronic and optical nature of FWS 2 is supplemented by possible band structures and bandgap calculations. Magnetic centers in the 1T phase appear in FWS 2 possibly due to the introduction of defect sites. A direct consequence of the phase transition and associated increase in interlayer spacing is a change in friction behavior. Friction force microscopy is used to determine this effect of functionalization accompanied phase transformation. FluorinationThe unique properties found in graphene and later in monolayers of other materials thrust the research on transition metal dichalcogenides (TMDs) as evidenced from the publications on TMDs in the past decade. [1][2][3][4][5] A distinctive property of TMDs is their polymorphic structural and electronic characteristics. For instance, in group 6 chalcogenides such as MoS 2 and WS 2 , when the sulfur (S) atoms occur on top of each other, it results in trigonal prismatic symmetry in the commonly called 2H semiconducting phase and the displaced S atoms results in octahedral symmetry in the 1T metallic phase. [6] Li or K functionalization

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Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS₂

Cited by 80 publications

References 20 publications

Phase engineering of two-dimensional transition metal dichalcogenides

Phase engineering of two-dimensional transition metal dichalcogenides

H₂‐Directing Strategy on In Situ Synthesis of Co‐MoS₂ with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism

An Insight into the Phase Transformation of WS₂ upon Fluorination

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Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS2

Cited by 80 publications

References 20 publications

Phase engineering of two-dimensional transition metal dichalcogenides

Phase engineering of two-dimensional transition metal dichalcogenides

H2‐Directing Strategy on In Situ Synthesis of Co‐MoS2 with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism

An Insight into the Phase Transformation of WS2 upon Fluorination

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Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS₂

H₂‐Directing Strategy on In Situ Synthesis of Co‐MoS₂ with Highly Expanded Interlayer for Elegant HER Activity and its Mechanism

An Insight into the Phase Transformation of WS₂ upon Fluorination