Pure and stable metallic phase molybdenum disulfide nanosheets for hydrogen evolution reaction

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Abstract

Metallic-phase MoS ₂ (M-MoS ₂) is metastable and does not exist in nature. Pure and stable M-MoS ₂ has not been previously prepared by chemical synthesis, to the best of our knowledge. Here we report a hydrothermal process for synthesizing stable two-dimensional M-MoS ₂ nanosheets in water. The metal–metal Raman stretching mode at 146 cm ⁻¹ in the M-MoS ₂ structure, as predicted by theoretical calculations, is experimentally observed. The stability of the M-MoS ₂ is associated with the adsorption of a monolayer of water molecules on both sides of the nanosheets, which reduce restacking and prevent aggregation in water. The obtained M-MoS ₂ exhibits excellent stability in water and superior activity for the hydrogen evolution reaction, with a current density of 10 mA cm ⁻² at a low potential of −175 mV and a Tafel slope of 41 mV per decade.

Abstract

Metallic molybdenum disulfide is a metastable phase of the material. Here, the authors synthesize two-dimensional metallic molybdenum disulfide nanosheets, stabilized by adsorbed aqueous monolayers, and evaluate their catalytic hydrogen evolution activity.

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Atomically thin MoS2: A new direct-gap semiconductor

Tony F Heinz, Jie Shan, James Hone … (2010)

The electronic properties of ultrathin crystals of molybdenum disulfide consisting of N = 1, 2, ... 6 S-Mo-S monolayers have been investigated by optical spectroscopy. Through characterization by absorption, photoluminescence, and photoconductivity spectroscopy, we trace the effect of quantum confinement on the material's electronic structure. With decreasing thickness, the indirect band gap, which lies below the direct gap in the bulk material, shifts upwards in energy by more than 0.6 eV. This leads to a crossover to a direct-gap material in the limit of the single monolayer. Unlike the bulk material, the MoS2 monolayer emits light strongly. The freestanding monolayer exhibits an increase in luminescence quantum efficiency by more than a factor of 1000 compared with the bulk material.

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Phase-engineered low-resistance contacts for ultrathin MoS2 transistors.

Rajesh Kappera, Damien Voiry, Sibel Yalcin … (2014)

Ultrathin molybdenum disulphide (MoS2) has emerged as an interesting layered semiconductor because of its finite energy bandgap and the absence of dangling bonds. However, metals deposited on the semiconducting 2H phase usually form high-resistance (0.7 kΩ μm-10 kΩ μm) contacts, leading to Schottky-limited transport. In this study, we demonstrate that the metallic 1T phase of MoS2 can be locally induced on semiconducting 2H phase nanosheets, thus decreasing contact resistances to 200-300 Ω μm at zero gate bias. Field-effect transistors (FETs) with 1T phase electrodes fabricated and tested in air exhibit mobility values of ~50 cm(2) V(-1) s(-1), subthreshold swing values below 100 mV per decade, on/off ratios of >10(7), drive currents approaching ~100 μA μm(-1), and excellent current saturation. The deposition of different metals has limited influence on the FET performance, suggesting that the 1T/2H interface controls carrier injection into the channel. An increased reproducibility of the electrical characteristics is also obtained with our strategy based on phase engineering of MoS2.

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Atomic mechanism of the semiconducting-to-metallic phase transition in single-layered MoS2.

Yung-Chang Lin, Dumitru Dumcenco, Ying-Sheng Huang … (2014)

Phase transitions can be used to alter the properties of a material without adding any additional atoms and are therefore of significant technological value. In a solid, phase transitions involve collective atomic displacements, but such atomic processes have so far only been investigated using macroscopic approaches. Here, we show that in situ scanning transmission electron microscopy can be used to follow the structural transformation between semiconducting (2H) and metallic (1T) phases in single-layered MoS2, with atomic resolution. The 2H/1T phase transition involves gliding atomic planes of sulphur and/or molybdenum and requires an intermediate phase (α-phase) as a precursor. The migration of two kinds of boundaries (β- and γ-boundaries) is also found to be responsible for the growth of the second phase. Furthermore, we show that areas of the 1T phase can be controllably grown in a layer of the 2H phase using an electron beam.

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Journal

Journal ID (nlm-ta): Nat Commun

Journal ID (iso-abbrev): Nat Commun

Title: Nature Communications

Publisher: Nature Publishing Group

ISSN (Electronic): 2041-1723

Publication date (Electronic): 10 February 2016

Publication date Collection: 2016

Volume: 7

Electronic Location Identifier: 10672

Affiliations

[1 ]Department of Physics and Astronomy, University of Arkansas at Little Rock , 2801 South University Avenue, Little Rock, Arkansas 72204, USA

[2 ]Department of Physics, University at Buffalo , Buffalo, New York 14260, USA

[3 ]Institute for Nanoscale Materials Science and Engineering, University of Arkansas , Fayetteville, Arkansas 72701, USA

[4 ]Department of Mechanical and Industrial Engineering, Northeastern University , Boston, Massachusetts 02115, USA

[5 ]Department of Physics and Materials Science, University of Memphis , Memphis, Tennessee 38152, USA

Author notes

[a ] gengxiu0758@ 123456gmail.com

[b ] jcui@ 123456memphis.edu

[c ] txchen@ 123456ualr.edu

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Publisher Item ID: ncomms10672

DOI: 10.1038/ncomms10672

PMC ID: 4749985

PubMed ID: 26861766

SO-VID: 1050339b-4df0-4b88-9cc7-7d0f16f36445

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Pure and stable metallic phase molybdenum disulfide nanosheets for hydrogen evolution reaction

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Most cited references 11

Atomically thin MoS2: A new direct-gap semiconductor

Phase-engineered low-resistance contacts for ultrathin MoS2 transistors.

Atomic mechanism of the semiconducting-to-metallic phase transition in single-layered MoS2.

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