MoS2

/Tag: MoS2

Boundary activated hydrogen evolution reaction on monolayer MoS<sub>2</sub>

2019-03-22T18:35:08+00:00March 22nd, 2019|Categories: Publications|Tags: , |

Boundary activated hydrogen evolution reaction on monolayer MoS2Boundary activated hydrogen evolution reaction on monolayer MoS<sub>2</sub>, Published online: 22 March 2019; doi:10.1038/s41467-019-09269-9While water-splitting electrocatalysts enable energy storage in carbon-neutral fuels, a recent challenge has been the discovery and understanding of catalyst active sites. Here, authors find domain boundaries in MoS2 materials to present high-activity, stable, and scalable sites for H2 evolution.

Published in: "Nature Communications".

Indirect bandgap of hBN-encapsulated monolayer MoS2. (arXiv:1903.06427v1 [cond-mat.mes-hall])

2019-03-18T04:30:29+00:00March 18th, 2019|Categories: Publications|Tags: , |

We present measurements of temperature dependence of photoluminescence intensity from monolayer MoS2 encapsulated by hexagonal boron nitride (hBN) flakes. The obtained temperature dependence shows an opposite trend to that of previously observed in a monolayer MoS2 on a SiO2 substrate. Ab-initio bandstructure calculations have revealed that monolayer MoS2 encapsulated by hBN flakes have no longer a direct-gap semiconductor but an indirect-gap semiconductor. This is caused by orbital hybridization between MoS2 and hBN, which leads to upward shift of gamma-valley of MoS2. This work shows an important implication that the hBN-encapsulated structures used to address intrinsic properties of two-dimensional crystals can alter basic properties encapsulated materials.

Published : "arXiv Mesoscale and Nanoscale Physics".

Tuning orbital orientation endows molybdenum disulfide with exceptional alkaline hydrogen evolution capability

2019-03-14T20:35:07+00:00March 14th, 2019|Categories: Publications|Tags: , |

Tuning orbital orientation endows molybdenum disulfide with exceptional alkaline hydrogen evolution capabilityTuning orbital orientation endows molybdenum disulfide with exceptional alkaline hydrogen evolution capability, Published online: 14 March 2019; doi:10.1038/s41467-019-09210-0Technologies allowing for sustainable hydrogen production will contribute to the decarbonization of the future energy supply. Here the authors report that carbon induced orbital modulation can facilitate the otherwise inert MoS2 electrocatalyst superior alkaline hydrogen evolution reactivity.

Published in: "Nature Communications".

Direct Cation Exchange in Monolayer ${mathrm{MoS}}_{2}$ via Recombination-Enhanced Migration

2019-03-14T14:35:57+00:00March 14th, 2019|Categories: Publications|Tags: |

Author(s): Shi-Ze Yang, Weiwei Sun, Yu-Yang Zhang (张余洋), Yongji Gong, Mark P. Oxley, Andrew R. Lupini, Pulickel M. Ajayan, Matthew F. Chisholm, Sokrates T. Pantelides, and Wu Zhou (周武)In addition to their unique optical and electronic properties, two-dimensional materials provide opportunities to directly observe atomic-scale defect dynamics. Here we use scanning transmission electron microscopy to observe substitutional Re impurities in monolayer MoS2 undergo direct exchanges wi…[Phys. Rev. Lett. 122, 106101] Published Mon Mar 11, 2019

Published in: "Physical Review Letters".

Weak localization in boron nitride encapsulated bilayer ${mathrm{MoS}}_{2}$

2019-03-14T14:35:13+00:00March 14th, 2019|Categories: Publications|Tags: , |

Author(s): Nikos Papadopoulos, Kenji Watanabe, Takashi Taniguchi, Herre S. J. van der Zant, and Gary A. SteeleWe present measurements of weak localization on hexagonal boron nitride encapsulated bilayer MoS2. From the analysis we obtain information regarding the phase coherence and the spin diffusion of the electrons. We find that the encapsulation with boron nitride provides higher mobilities in the sample…[Phys. Rev. B 99, 115414] Published Mon Mar 11, 2019

Published in: "Physical Review B".

Designing vertical channels with expanded interlayer for Li-ion batteries

2019-03-14T06:32:53+00:00March 14th, 2019|Categories: Publications|Tags: |

Chem. Commun., 2019, Accepted ManuscriptDOI: 10.1039/C8CC07517D, CommunicationLong Zhang, Yunmei Pan, Yufei Chen, Mengxiong Li, Peiying Liu, Cancan Wang, peng Wang, Hongbin LuThe vertical channels with expanded interlayer spacing based on MoS2/Gr/C composite have been designed. This structure can simultaneously shorten the pathway of Li-ion diffusion across the electrode and enhance the…The content of this RSS Feed (c) The Royal Society of Chemistry

Published in: "Chemical Communications".

Nonlinear dark-field imaging of 1D defects in monolayer dichalcogenides. (arXiv:1903.05139v1 [cond-mat.mes-hall])

2019-03-14T04:30:32+00:00March 14th, 2019|Categories: Publications|Tags: , , |

Extended defects with one dimensionality smaller than that of the host, such as 2D grain boundaries in 3D materials or 1D grain boundaries in 2D materials, can be particularly damaging since they directly impede the transport of charge, spin or heat, and can introduce a metallic character into otherwise semiconducting systems. Unfortunately, a technique to rapidly and non-destructively image 1D defects in 2D materials is lacking. Scanning transmission electron microscopy (STEM), Raman, photoluminescence and nonlinear optical spectroscopies, are all extremely valuable, but current implementations suffer from low throughput and a destructive nature (STEM) or limitations in their unambiguous sensitivity at the nanoscale. Here we demonstrate that dark-field second harmonic generation (SHG) microscopy can rapidly, efficiently, and non-destructively probe grain boundaries and edges in monolayer dichalcogenides (i.e. MoSe2, MoS2 and WS2). Dark-field SHG efficiently separates the spatial components of the emitted light and exploits interference effects from crystal domains of different orientations to localize grain boundaries and edges as very bright 1D patterns through a Cerenkov-type SHG emission. The frequency dependence of this emission in MoSe2 monolayers is explained in terms of plasmon-enhanced SHG related to the defects metallic character. This new technique for nanometer-scale imaging of the grain structure, domain orientation and localized 1D plasmons in 2D different semiconductors, thus enables more rapid progress towards both applications and fundamental materials discoveries.

Published : "arXiv Mesoscale and Nanoscale Physics".

Amorphous phosphorus-doped MoS 2 catalyst for efficient hydrogen evolution reaction

2019-03-13T16:33:53+00:00March 13th, 2019|Categories: Publications|Tags: , |

Splitting water is an important method for producing clean and sustainable hydrogen to replace finite fossil fuels in future energy systems. MoS 2 is reported as a promising catalyst without noble metallic elements to accelerate the rate of the electrocatalytic hydrogen evolution reaction. However, there is a real need and strong demand for further improvement of the MoS 2 -based catalyst. In the present study, a novel amorphous phosphorus-doped MoS 2 nanocomposite (P-MoS 2 ) is prepared by a facile hydrothermal method. Compared with crystalline molybdenum disulfide, the amorphous P-doped MoS 2 catalyst exhibits much better activity with a smaller Tafel slope of 39 mV dec −1 . Moreover, good stability is also demonstrated over the P-MoS 2 catalyst in acidic electrolyte. This highly active amorphous P-doped MoS 2 catalyst is a promising candidate to facilitate the development of economical hydrogen produ…

Published in: "Nanotechnology".

Edge‐Exposed Molybdenum Disulfide with N‐Doped Carbon Hybridization: A Hierarchical Hollow Electrocatalyst for Carbon Dioxide Reduction

2019-03-13T04:33:59+00:00March 13th, 2019|Categories: Publications|Tags: , |

The successful synthesis of a splendid hierarchical catalyst comprised of edge‐exposed 2H MoS2 with N‐doped carbon hybridization for electrochemical CO2 reduction is demonstrated in this work. In situ scanning transmission electron microscopy observation for catalyst growth process is performed at expected temperatures. The hybrid nanostructure paves the way for the desirable construction of MoS2‐based electrocatalysts for energy conversion. Abstract Electrochemical CO2 reduction (CO2RR) is a promising technology to produce value‐added fuels and weaken the greenhouse effect. Plenty of efforts are devoted to exploring high‐efficiency electrocatalysts to tackle the issues that show poor intrinsic activity, low selectivity for target products, and short‐lived durability. Herein, density functional theory calculations are firstly utilized to demonstrate guidelines for design principles of electrocatalyst, maximum exposure of catalytic active sites for MoS2 edges, and electron transfer from N‐doped carbon (NC) to MoS2 edges. Based on the guidelines, a hierarchical hollow electrocatalyst comprised of edge‐exposed 2H MoS2 hybridized with NC for CO2RR is constructed. In situ atomic‐scale observation for catalyst growth is performed by using a specialized Si/SiN x nanochip at a continuous temperature‐rise period, which reveals the growth mechanism. Abundant exposed edges of MoS2 provide a large quantity of active centers, which leads to a low onset potential of ≈40 mV and a remarkable CO production rate of 34.31 mA cm−2 with 92.68% of Faradaic efficiency at an overpotential of 590 mV. The long‐term stability shows negligible degradation for more than 24 h. This work provides fascinating insights into the construction of catalysts for efficient CO2RR.

Published in: "Advanced Energy Materials".

Band Structure Engineering of Interfacial Semiconductors Based on Atomically Thin Lead Iodide Crystals

2019-03-12T22:34:31+00:00March 12th, 2019|Categories: Publications|Tags: , , , |

PbI2 with a unique electronic structure can be synthesized down to the atomic scale by a solution method and used to construct versatile interfacial semiconductors via band alignment engineering. As an illustrative example, the photoluminescence of MoS2 is enhanced due to the type I nature of the MoS2/PbI2 stacks, while dramatic quenching of WS2 and WSe2 occurs in type II WS2/PbI2 and WSe2/PbI2 stacks. Abstract To explore new constituents in two‐dimensional (2D) materials and to combine their best in van der Waals heterostructures is in great demand as being a unique platform to discover new physical phenomena and to design novel functionalities in interface‐based devices. Herein, PbI2 crystals as thin as a few layers are synthesized, particularly through a facile low‐temperature solution approach with crystals of large size, regular shape, different thicknesses, and high yields. As a prototypical demonstration of band engineering of PbI2‐based interfacial semiconductors, PbI2 crystals are assembled with several transition metal dichalcogenide monolayers. The photoluminescence of MoS2 is enhanced in MoS2/PbI2 stacks, while a dramatic photoluminescence quenching of  WS2 and WSe2 is revealed in WS2/PbI2 and WSe2/PbI2 stacks. This is attributed to the effective heterojunction formation between PbI2 and these monolayers; type I band alignment in MoS2/PbI2 stacks, where fast‐transferred charge carriers accumulate in MoS2 with high emission efficiency, results in photoluminescence enhancement, and type II in WS2/PbI2 and WSe2/PbI2 stacks, with separated electrons and holes suitable for light harvesting, results in photoluminescence quenching. The results demonstrate that MoS2, WS2, and WSe2 monolayers with similar electronic structures

Published in: "Advanced Materials".

Edge‐Exposed Molybdenum Disulfide with N‐Doped Carbon Hybridization: A Hierarchical Hollow Electrocatalyst for Carbon Dioxide Reduction

2019-03-12T22:32:59+00:00March 12th, 2019|Categories: Publications|Tags: , |

The successful synthesis of a splendid hierarchical catalyst comprised of edge‐exposed 2H MoS2 with N‐doped carbon hybridization for electrochemical CO2 reduction is demonstrated in this work. In situ scanning transmission electron microscopy observation for catalyst growth process is performed at expected temperatures. The hybrid nanostructure paves the way for the desirable construction of MoS2‐based electrocatalysts for energy conversion. Abstract Electrochemical CO2 reduction (CO2RR) is a promising technology to produce value‐added fuels and weaken the greenhouse effect. Plenty of efforts are devoted to exploring high‐efficiency electrocatalysts to tackle the issues that show poor intrinsic activity, low selectivity for target products, and short‐lived durability. Herein, density functional theory calculations are firstly utilized to demonstrate guidelines for design principles of electrocatalyst, maximum exposure of catalytic active sites for MoS2 edges, and electron transfer from N‐doped carbon (NC) to MoS2 edges. Based on the guidelines, a hierarchical hollow electrocatalyst comprised of edge‐exposed 2H MoS2 hybridized with NC for CO2RR is constructed. In situ atomic‐scale observation for catalyst growth is performed by using a specialized Si/SiN x nanochip at a continuous temperature‐rise period, which reveals the growth mechanism. Abundant exposed edges of MoS2 provide a large quantity of active centers, which leads to a low onset potential of ≈40 mV and a remarkable CO production rate of 34.31 mA cm−2 with 92.68% of Faradaic efficiency at an overpotential of 590 mV. The long‐term stability shows negligible degradation for more than 24 h. This work provides fascinating insights into the construction of catalysts for efficient CO2RR.

Published in: "Advanced Energy Materials".

Engineering 2D Metal–Organic Framework/MoS2 Interface for Enhanced Alkaline Hydrogen Evolution

2019-03-12T10:34:45+00:00March 12th, 2019|Categories: Publications|Tags: |

2D Co‐BDC/MoS2 hybrid nanosheets are synthesized via a facile sonication‐assisted solution strategy. The introduction of Co‐BDC induces the partial phase transfer of MoS2 from semiconducting 2H‐phase to metallic 1T‐phase. The obtained Co‐BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity for alkaline hydrogen evolution due to the generated 1T‐phase MoS2 and well‐designed Co‐BDC/MoS2 interface. Abstract 2D metal–organic frameworks (MOFs) have been widely investigated for electrocatalysis because of their unique characteristics such as large specific surface area, tunable structures, and enhanced conductivity. However, most of the works are focused on oxygen evolution reaction. There are very limited numbers of reports on MOFs for hydrogen evolution reaction (HER), and generally these reported MOFs suffer from unsatisfactory HER activities. In this contribution, novel 2D Co‐BDC/MoS2 (BDC stands for 1,4‐benzenedicarboxylate, C8H4O4) hybrid nanosheets are synthesized via a facile sonication‐assisted solution strategy. The introduction of Co‐BDC induces a partial phase transfer from semiconducting 2H‐MoS2 to metallic 1T‐MoS2. Compared with 2H‐MoS2, 1T‐MoS2 can activate the inert basal plane to provide more catalytic active sites, which contributes significantly to improving HER activity. The well‐designed Co‐BDC/MoS2 interface is vital for alkaline HER, as Co‐BDC makes it possible to speed up the sluggish water dissociation (rate‐limiting step for alkaline HER), and modified MoS2 is favorable for the subsequent hydrogen generation step. As expected, the resultant 2D Co‐BDC/MoS2 hybrid nanosheets demonstrate remarkable catalytic activity and good stability toward alkaline HER, outperforming those of bare Co‐BDC, MoS2, and almost all the previously reported MOF‐based electrocatalysts.

Published in: "Small".

Glucose‐Induced Synthesis of 1T‐MoS2/C Hybrid for High‐Rate Lithium‐Ion Batteries

2019-03-12T10:34:32+00:00March 12th, 2019|Categories: Publications|Tags: |

1T‐MoS2 nanosheets covered by thin carbon layers possess several advantages. Expanded interlayer spacing can effectively release volume variation, high electrical conductivity can accelerate fast transfer of lithium ions and electrons, and the much smaller and fewer‐layer nanosheet structure can shorten the diffusion path of the lithium ions. Benefitting from the synergistic effect of these advantages, a 1T‐MoS2/C hybrid demonstrates excellent electrochemical performance. Abstract 1T phase MoS2 possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T‐MoS2/C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer‐layer 1T‐MoS2 nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T‐MoS2 also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer‐layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g−1 at 1 A g−1 and the capacity can maintain 870 mAh g−1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g−1 at 10 A g−1. These results

Published in: "Small".

Bundled Defect‐Rich MoS2 for a High‐Rate and Long‐Life Sodium‐Ion Battery: Achieving 3D Diffusion of Sodium Ion by Vacancies to Improve Kinetics

2019-03-12T10:34:16+00:00March 12th, 2019|Categories: Publications|Tags: , |

Bundled defect‐rich MoS2 is achieved by quenching MoS2 sheet. Na+ can cross MoS2 layers by vacancies and is not limited to diffusion along the layer, realizing 3D diffusion for high rate capability. The bundled architecture reduces the stack of sheets with a superior cycle life, illustrating the capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles. Abstract Molybdenum disulfide (MoS2), a 2D‐layered compound, is regarded as a promising anode for sodium‐ion batteries (SIBs) due to its attractive theoretical capacity and low cost. The main challenges associated with MoS2 are the low rate capability suffering from the sluggish kinetics of Na+ intercalation and the poor cycling stability owning to the stack of MoS2 sheets. In this work, a unique architecture of bundled defect‐rich MoS2 (BD‐MoS2) that consists of MoS2 with large vacancies bundled by ultrathin MoO3 is achieved via a facile quenching process. When employed as anode for a SIB, the BD‐MoS2 electrode exhibits an ultrafast charge/discharge due to the pseudocapacitive‐controlled Na+ storage mechanism in it. Further experimental and theoretical calculations show that Na+ is able to cross the MoS2 layer by vacancies, not only limited to diffusion along the layer, thus realizing a 3D Na+ diffusion with faster kinetics. Meanwhile, the bundling architecture reduces the stack of sheets with a superior cycle life illustrating the highly reversible capacities of 350 and 272 mAh g−1 at 2 and 5 A g−1 after 1000 cycles.

Published in: "Small".

Revisiting the Buckling Metrology Method to Determine the Young’s Modulus of 2D Materials

2019-03-10T22:34:16+00:00March 10th, 2019|Categories: Publications|Tags: , , , |

Measuring the mechanical properties of atomically thin materials results in a big technical challenge. A method to determine the Young’s modulus of thin polymeric films is revisited. The method is demonstrated to be applicable in the field of 2D materials. Abstract Measuring the mechanical properties of 2D materials is a formidable task. While regular electrical and optical probing techniques are suitable even for atomically thin materials, conventional mechanical tests cannot be directly applied. Therefore, new mechanical testing techniques need to be developed. Up to now, the most widespread approaches require micro‐fabrication to create freely suspended membranes, rendering their implementation complex and costly. Here, a simple yet powerful technique is revisited to measure the mechanical properties of thin films. The buckling metrology method, that does not require the fabrication of freely suspended structures, is used to determine the Young’s modulus of several transition metal dichalcogenides (MoS2, MoSe2, WS2, and WSe2) with thicknesses ranging from 2 to 10 layers. The obtained values for the Young’s modulus and their uncertainty are critically compared with previously published results, finding that this simple technique provides results which are in good agreement with those reported using other highly sophisticated testing methods. By comparing the cost, complexity, and time required for the different methods reported in the literature, the buckling metrology method presents certain advantages that make it an interesting mechanical test tool for 2D materials.

Published in: "Advanced Materials".

Glucose‐Induced Synthesis of 1T‐MoS2/C Hybrid for High‐Rate Lithium‐Ion Batteries

2019-03-10T22:33:42+00:00March 10th, 2019|Categories: Publications|Tags: |

1T‐MoS2 nanosheets covered by thin carbon layers possess several advantages. Expanded interlayer spacing can effectively release volume variation, high electrical conductivity can accelerate fast transfer of lithium ions and electrons, and the much smaller and fewer‐layer nanosheet structure can shorten the diffusion path of the lithium ions. Benefitting from the synergistic effect of these advantages, a 1T‐MoS2/C hybrid demonstrates excellent electrochemical performance. Abstract 1T phase MoS2 possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T‐MoS2/C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer‐layer 1T‐MoS2 nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T‐MoS2 also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer‐layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g−1 at 1 A g−1 and the capacity can maintain 870 mAh g−1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g−1 at 10 A g−1. These results

Published in: "Small".

Glucose‐Induced Synthesis of 1T‐MoS2/C Hybrid for High‐Rate Lithium‐Ion Batteries

2019-03-09T10:33:44+00:00March 9th, 2019|Categories: Publications|Tags: |

1T‐MoS2 nanosheets covered by thin carbon layers possess several advantages. Expanded interlayer spacing can effectively release volume variation, high electrical conductivity can accelerate fast transfer of lithium ions and electrons, and the much smaller and fewer‐layer nanosheet structure can shorten the diffusion path of the lithium ions. Benefitting from the synergistic effect of these advantages, a 1T‐MoS2/C hybrid demonstrates excellent electrochemical performance. Abstract 1T phase MoS2 possesses higher conductivity than the 2H phase, which is a key parameter of electrochemical performance for lithium ion batteries (LIBs). Herein, a 1T‐MoS2/C hybrid is successfully synthesized through facile hydrothermal method with a proper glucose additive. The synthesized hybrid material is composed of smaller and fewer‐layer 1T‐MoS2 nanosheets covered by thin carbon layers with an enlarged interlayer spacing of 0.94 nm. When it is used as an anode material for LIBs, the enlarged interlayer spacing facilitates rapid intercalating and deintercalating of lithium ions and accommodates volume change during cycling. The high intrinsic conductivity of 1T‐MoS2 also contributes to a faster transfer of lithium ions and electrons. Moreover, much smaller and fewer‐layer nanosheets can shorten the diffusion path of lithium ions and accelerate reaction kinetics, leading to an improved electrochemical performance. It delivers a high initial capacity of 920.6 mAh g−1 at 1 A g−1 and the capacity can maintain 870 mAh g−1 even after 300 cycles, showing a superior cycling stability. The electrode presents a high rate performance as well with a reversible capacity of 600 mAh g−1 at 10 A g−1. These results

Published in: "Small".

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