Metallic MoS2 Research Articles

The modified liquid | liquid interface: An electrochemical route for the electrode-less synthesis of MoS2 metal composite thin films

An interfacial route is described to form composites of molybdenum disulfide with metals. Metal deposition occurs at the liquid| liquid interface, on to the pre-adsorbed MoS2 film. The method is exemplified via the interfacial deposition of Cu and Pd at the MoS2-modified water/1,2,-dichlorobenzene interface, under electrochemical control (interface between two immiscible electrolyte solutions). Differences in morphology between the two metals are related to their differing modes of growth. The voltammetric measurements were analysed to elucidate the effect of the interfacial MoS2 film on the reduction and growth of the metals. Overall, the MoS2 film was found to impact the metallic deposition reaction, and the effect depends on the nature of the metallic precursor.

Molecularly imprinted sensor based on 1T/2H MoS2 and MWCNTs for voltammetric detection of acetaminophen

1T phase molybdenum disulfide (MoS2) possesses excellent electrical conductivity, 107 times higher than that of 2H phase MoS2. Thus, metallic 1T MoS2 is highly desirable for electrochemical analysis and catalysis. In this study, hybrid 1T/2H MoS2/multi-walled carbon nanotubes (MoS2/MWCNTs) composite was prepared by a facile and simple hydrothermal approach. Powder X-ray diffraction, field emission scanning and transmission electron microscopes, Fourier transform infrared spectroscopy, Raman spectroscopy, cyclic voltammetry (CV), and electrochemical impedance spectroscopy were used to characterize the composites. The results show that metallic 1T phase MoS2 was formed by the inductive effect of MWCNTs. The high conductivity and large specific surface area of hybrid 1T/2H MoS2/MWCNTs composite endow great catalysis activity in electrochemical analysis. Polypyrrole molecularly imprinted polymer (MIP) film imprinted with acetaminophen (AP) template was electrochemically deposited on glassy carbon electrode (GCE) modified by 1T/2H MoS2/MWCNTs (MoS2/CNTs/GCE) to construct MIP based sensor. The prepared MIP/MoS2/CNTs/GCE sensor shows a sensitive current response towards AP. Through the optimization of the ratio of monomer and template, CV electropolymerization cycles, CV elution cycles, incubation time, and pH, the accessible linear range of 0.01–300 μM was obtained with the limit of detection of 0.003 μM (S/N = 3) by differential pulse voltammetry. In addition, the prepared sensor shows great detecting robustness with excellent selectivity, anti-interference property, reproducibility, and stability. In the urine sample tests, the sensor shows desirable reliability with the recovery rate of 88.1–95.9%.

All‐Solid‐State Li–S Batteries Enhanced by Interface Stabilization and Reaction Kinetics Promotion through 2D Transition Metal Sulfides

AbstractAll‐solid‐state lithium‐sulfur batteries (ASSLSBs) based on sulfide solid‐state electrolytes (SSEs) provide prospectively high energy density and safety. However, the low conductivity and sluggish reaction kinetic of sulfur cathode limit its commercialization. The use of carbon additives can improve the electrical conductivity but accelerates the decomposition of SSEs. Herein, a highly conductive carbon fiber decorated with hybrid 1T/2H MoS2 nanosheets is designed. The high chemical and electrochemical compatibility among MoS2 and sulfide SSE can greatly improve the stability of the cathode and therefore maintain pristine interfaces. The uniform distribution of electrical‐conductive metallic 1T MoS2 on carbon fiber benefits the electron transfer between carbon and sulfur. Meanwhile, the layered structure of MoS2 can be intercalated by a large amount of Li ions facilitating ionic and electronic conductivity. In consequence, the charge transfer and reaction kinetics are greatly enhanced, and the decomposition of SSEs is successfully relieved. As a result, the ASSLSB delivers an ultrahigh initial discharge and charge capacity of 1456 and 1470 mAh g−1 at 0.05 C individually with ultrahigh coulombic efficiency and maintains high capacity retention of 78% after 220 cycles. The batteries also obtain a remarkable rate performance of 1069 mAh g−1 at 1 C.

Metallic MoS2 enhances the performance of water-based drilling fluids

In this work, the metal phase MoS2 was prepared by a simple one-step hydrothermal method, and it was systematically studied by XRD, Raman, SEM, TEM, and other characterization methods. In addition, the tribological behavior of M-MoS2 in water-based drilling fluids has been extensively studied with a ball-disk tribometer. In addition, the influence of applied load and speed on friction performance is also studied. The experimental results show that the introduction of M-MoS2 significantly reduces the friction and wear of the material. Among them, M-MoS2-5-water-based drilling fluid has the lowest friction coefficient (~0.11).

Gold nanodots-decoration stabilizes and activates metastable metallic phase MoS2 nanosheets for efficient hydrogen evolution reaction

Hydrogen evolution reaction (HER), an efficient and sustainable method for clean hydrogen energy producing, has been impeded by scarcity and costly of precious metals electrocatalysts. Two-dimensional (2D) metallic phase MoS2 (M-MoS2) nanosheets (NSs) have been identified as cost-effective and efficient alternative electrocatalysts for HER. However, the practical applications of M-MoS2 NSs are often limited by the metastable property of their metallic phase. Here, we demonstrate both the metallic phase stability and the electrocatalytic activity of the M-MoS2 NSs can be dramatically improved by gold (Au) nanodots (NDs) decoration. The obtained Au NDs decorated M-MoS2 NSs (namely, Au NDs@M-MoS2 NSs) maintain well their metallic phase even after about 100 days storage, while the M-MoS2 NSs have already transferred to dominant 2H phase one for about 2 weeks. The results of first-principles density functional theory (DFT) calculation also indicate that the Au NDs modification can stabilize the metastable metallic phase of M-MoS2 NSs. Moreover, the as-prepared Au NDs@M-MoS2 NSs also show remarkable enhanced electrocatalytic activity toward HER. These findings may open up an ideal approach to stabilize and activate the metastable metallic phase 2D transition metal dichalcogenides-based electrocatalysts for various promising applications.

A study of metal-MoS2 contacts by using an in-house developed ab-initio transport simulator

By combining DFT calculations and an in-house developed, ab-initio transport simulator, we investigate the transport properties of n-type contacts between 3D metallic conductors and monolayer MoS2. Moreover, the impact of buffer layers between the metal and the MoS2 is also analyzed in order to reduce the Schottky barrier and approach the Ohmic behavior of contacts.

Dual-phase MoS2/MXene/CNT ternary nanohybrids for efficient electrocatalytic hydrogen evolution

Two-dimensional (2D) molybdenum disulfide (MoS2) has been recognized as a potential substitution of platinum (Pt) for electrochemical hydrogen evolution reaction (HER). However, the broad adoption of MoS2 is hindered by its limited number of active sites and low inherent electrical conductivity. In this work, we employed a one-step solvothermal synthesis technique to construct a ternary hybrid structure consisting of dual-phase MoS2, titanium carbide (Ti3C2) MXene, and carbon nanotubes (CNTs), and demonstrated synergistic effects for active site exposure, surface area enlargement, and electrical conductivity improvement of the catalyst. The dual-phase MoS2 (DP-MoS2) is directly formed on the MXene with CNTs acting as crosslinks between 2D islands. The existence of edge-enriched metallic phase MoS2, the conductive backbone of MXene along with the crosslink function of CNTs clearly improves the overall HER performance of the ternary nanocomposite. Moreover, the integration of MoS2 with MXene not only increases the interlayer distance of the 2D layers but also partially suppresses the MXene oxidation and the 2D layer restacking, leading to good catalytic stability. As a result, an overpotential of 169 mV and a low Tafel slope of 51 mV/dec was successfully achieved. This work paves a way for 2D-based electrocatalyst engineering and sheds light on the development of the next-generation noble metal-free HER electrocatalysts.

Hydrazine Hydrate Intercalated 1T-Dominant MoS2 with Superior Ambient Stability for Highly Efficient Electrocatalytic Applications.

Metallic 1T-phase MoS2 exhibits superior hydrogen evolution reaction (HER) performance than natural 2H-phase MoS2 owing to its higher electrical conductivity and abundance of active sites. However, the reported 1T-MoS2 catalysts usually suffer from extreme instability, which results in quick phase transformation at ambient conditions. Herein, we present a facile approach to engineer the phase of MoS2 by introducing intercalated hydrazine. Interestingly, the as-synthesized 1T-dominant MoS2 sample demonstrates excellent ambient stability without noticeable degradation for 3 months. Additionally, the 1T-dominant MoS2 exhibits superior electrical conductivity (∼700 times higher than that of 2H-MoS2) and improved electrochemical catalytic performance (current density ∼12 times larger than that of 2H-MoS2 at an overpotential of 300 mV vs the reversible hydrogen electrode, RHE). Through experimental characterizations and density functional theory (DFT) calculation, we conclude that the stabilization of the metallic phase could be attributed to the electron donation from hydrazine molecules to the adjacent Mo atoms. The phase control strategy in this work provides a guideline to develop other highly efficient and stable two-dimensional (2D) electrocatalysts.

High-performance monolayer or bilayer SiC short channel transistors with metallic 1T-phase MoS2 contact

In this paper, high-performance monolayer or bilayer SiC short channel transistors with metallic 1T-Phase MoS2 contact have been proposed and investigated by using ab initio simulations. The results show that monolayer or bilayer SiC Schottky-barrier field-effect transistors (SBFET) could conquer the short channel effect, even if the channel length is reduced to 4.1 nm. The p-type ON-currents of monolayer SiC-SBFET, bilayer AB-stacked SiC-SBFET, and bilayer AA-stacked SiC-SBFET are 1132 μA/μm, 980 μA/μm, and 1457 μA/μm, respectively. The all could satisfy the requirement of the high-performance transistor outlined by International Technology Roadmap for Semiconductors (ITRS, 2013 version) for production year 2028. However, the n-type ON-currents of above SiC-SBFETs are 35 μA/μm, 21 μA/μm, and 229 μA/μm, which are much lower than that of p-type ON-currents. Comparing spectral current and spatial local density of states are used to explore the great differences between the p-type and n-type ON-currents.

Temperature Dependence of the Indirect Gap and the Direct Optical Transitions at the High-Symmetry Point of the Brillouin Zone and Band Nesting in MoS2, MoSe2, MoTe2, WS2, and WSe2 Crystals.

Following the rise of interest in the properties of transition metal dichalcogenides, many experimental techniques were employed to research them. However, the temperature dependencies of optical transitions, especially those related to band nesting, were not analyzed in detail for many of them. Here, we present successful studies utilizing the photoreflectance method, which, due to its derivative and absorption-like character, allows investigating direct optical transitions at the high-symmetry point of the Brillouin zone and band nesting. By studying the mentioned optical transitions with temperature from 20 to 300 K, we tracked changes in the electronic band structure for the common transition metal dichalcogenides (TMDs), namely, MoS2, MoSe2, MoTe2, WS2, and WSe2. Moreover, transmission and photoacoustic spectroscopies were also employed to investigate the indirect gap in these crystals. For all observed optical transitions assigned to specific k-points of the Brillouin zone, their temperature dependencies were analyzed using the Varshni relation and Bose–Einstein expression. It was shown that the temperature energy shift for the transition associated with band nesting is smaller when compared with the one at high-symmetry point, revealing reduced average electron–phonon interaction strength.

Direct Synthesis of Stable 1T-MoS2 Doped with Ni Single Atoms for Water Splitting in Alkaline Media.

Metallic MoS2 (i.e., 1T-MoS2 ) is considered as the most promising precious-metal-free electrocatalyst with outstanding hydrogen evolution reaction (HER) performance in acidic media comparable to Pt. However, sluggish kinematics of HER in alkaline media and its inability for the oxygen evolution reaction (OER), hamper its development as bifunctional catalysts. The instability of 1T-MoS2 further impedes its applications for scaling up, calling an urgent need for simple synthesis to produce stable 1T-MoS2 . In this work, the challenge of 1T-MoS2 synthesis is first addressed using a direct one-step hydrothermal method by adopting ascorbic acid. 1T-MoS2 with flower-like morphology is obtained, and transition metals (Ni, Co, Fe) are simultaneously doped into 1T-MoS2 . Ni-1T-MoS2 achieves an enhanced bifunctional catalytic activity for both HER and OER in alkaline media, where the key role of Ni doping as single atom is proved to be essential for boosting HER/OER activity. Finally, a Ni-1T-MoS2 ||Ni-1T-MoS2 electrolyzer is fabricated, reaching a current density of 10mA cm-2 at an applied cell voltage of only 1.54V for overall water splitting.

Metallic phase enabling MoS2 nanosheets as an efficient sonosensitizer for photothermal-enhanced sonodynamic antibacterial therapy

Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets (e.g., MoS2) with metallic phase (1T or 1T´ phase) have been proven to exhibit superior performances in various applications as compared to their semiconducting 2H-phase counterparts. However, it remains unclear how the crystal phase of 2D TMD nanosheets affects their sonodynamic property. In this work, we report the preparation of MoS2 nanosheets with different phases (metallic 1T/1T´ or semiconducting 2H) and exploration of its crystal-phase effect on photothermal-enhanced sonodynamic antibacterial therapy. Interestingly, the defective 2D MoS2 nanosheets with high-percentage metallic 1T/1T´ phase (denoted as M-MoS2) present much higher activity towards the ultrasound-induced generation of reactive oxygen species (ROS) as compared to the semiconducting 2H-phase MoS2 nanosheets. More interestingly, owing to its metallic phase-enabled strong absorption in the near-infrared-II (NIR-II) regime, the ultrasound-induced ROS generation performance of the M-MoS2 nanosheets can be further enhanced by the photothermal effect under a 1064 nm laser irradiation. Thus, after modifying with polyvinylpyrrolidone, the M-MoS2 nanosheets can be used as an efficient sonosensitizer for photothermal-enhanced sonodynamic bacterial elimination under ultrasound treatment combining with NIR-II laser irradiation. This study demonstrates that metallic MoS2 nanosheets can be used as a promising sonosensitizer for antibacterial therapy, which might be also promising for cancer therapies.Graphical

Defect-Rich Monolayer MoS2 as a Universally Enhanced Substrate for Surface-Enhanced Raman Scattering.

Monolayer 2H-MoS2 has been widely noticed as a typical transition metal dichalcogenides (TMDC) for surface-enhanced Raman scattering (SERS). However, monolayer MoS2 is limited to a narrow range of applications due to poor detection sensitivity caused by the combination of a lower density of states (DOS) near the Fermi energy level as well as a rich fluorescence background. Here, surfaced S and Mo atomic defects are fabricated on a monolayer MoS2 with a perfect lattice. Defects exhibit metallic properties. The presence of defects enhances the interaction between MoS2 and the detection molecule, and it increases the probability of photoinduced charge transfer (PICT), resulting in a significant improvement of Raman enhancement. Defect-containing monolayer MoS2 enables the fluorescence signal of many dyes to be effectively burst, making the SERS spectrum clearer and making the limits of detection (LODs) below 10−8 M. In conclusion, metallic defect-containing monolayer MoS2 becomes a promising and versatile substrate capable of detecting a wide range of dye molecules due to its abundant DOS and effective PICT resonance. In addition, the synergistic effect of surface defects and of the MoS2 main body presents a new perspective for plasma-free SERS based on the chemical mechanism (CM), which provides promising theoretical support for other TMDC studies.

Low-Cost, High-Gain MoS2 FETs from Amorphous Low-Mobility Film Precursors

With the aggressive invasion of thin film transistors (TFTs) in the rapidly altering/disposable portable electronics, displays, smartphones, and wearable market, cost reduction has evolved into a challenge as much as electrical properties’ improvement. Therefore, it is not surprising that processes requiring expensive equipment and energy-intensive processes are abandoned in favor of room-temperature (RT) approaches, liquid-phase deposition, and colloids. Despite being cheaper, the latter suffer from controllability, performance, and large contact resistance issues, deteriorating the quality of the final product. To meet the trends while not compromising the performance, we fabricate a MoS2-based ionic liquid-gated TFT with an ON-current of 1.5 × 104 A for holes and a field-effect mobility of 64.3 cm2·V–1·s–1 at RT in a hybrid liquid–solid-state three-dimensional (3D) topology utilizing low-energy expenditure impurity-tolerant processes. The device addresses the weakness of unattainability of P-type conduction in MoS2, thereby extending its pertinency to PN diodes and complementary integration logic. In addition, photoenabled switching and memory functionality are demonstrated and detailed material and electrical properties are investigated. The herein presented advanced architecture is, to the best of our knowledge, the first low-cost, high-gain MoS2 metal–oxide–semiconductor field-effect transistor (MOSFET) based on amorphous low-mobility film precursors that enables high-performance multifunctional stackable MOSFETs on any kind of processing-sensitive, plastic, and/or flexible substrate.

MoS2 nanoflowers decorated natural fiber-derived hollow carbon microtubes for boosting perfluorooctanoic acid degradation

Calotropis gigantea fiber (CGF) is a natural cellulose fiber with thin-walled large lumen. Benefitted from its unique structure, CGF was utilized here as a bio-template for the fabrication of hollow carbon microtubes using a facile hydrothermal method, and simultaneously, nano-sized MoS2 flowers were in-situ generated along the inner and outside surfaces of carbonized fiber microtubes, forming MoS2 nanoflowers decorated biochar MoS2/CGB. Coupled with dual active centers from non-metallic biochar and metallic MoS2, MoS2/CGB was then used for activating peroxymonosulfate (PMS) to degrade perfluorooctanoic acid (PFOA), one emerging pollutant that had received wide attention in recent years. The experimental results indicated that at room temperature and pH 3.0, MoS2/CGB exhibited the degradation efficiency of 79.6% for PFOA, and removal percentage of 50.7% for total organic carbon. During the degradation process, the free radical (SO4•−/•OH) and non-radical (1O2) routes coexisted, and the amount of SO4•− was about 9 times that of •OH. Combined with mass spectrometry, the possible degradation pathway of PFOA was proposed as transforming into short chained C2- to C5-containing carboxylic acids. With Vibrio fischeri as an indicator, the acute toxicity of PFOA solution and intermediates was evaluated, with the inhibition rate decreased from 27.6% to 4.5%. Finally, MoS2/CGB had the ability not only for removing perfluorinated compounds with different carbon chain lengths, but also for catalytically degrading PFOA in tap water and Yellow River water. This work provides plant fiber-based sustainable catalyst for potential application in PMS-based system for boosting PFOA degradation.

Flatten the Li‐ion Activation in Perfectly Lattice‐Matched MXene and 1T‐MoS2 Heterostructures via Chemical Functionalization

AbstractThe complexity of the ionic and electronic dynamics in MXene based hybrids, which are normally involved for device integration, triggers both challenges and opportunities for its application. Herein, as a prototype of metallic hybrids of MXene, heterostructures consisting of Ti3C2T2 (T = None, O and F atoms) and metallic MoS2 (1T phase) are investigated for lithium‐ion battery (LIB) applications. It is found that different surface atomic groups in MXene significantly alter the affinity, redox reaction and kinetics of Li atoms in the interface of the Ti3C2T2 and 1T‐MoS2. Through examining the three possible pathways of Li by first‐principles calculations and ab‐initio molecular dynamics, the diffusion curve becomes significantly flattened from the naked to O‐ and F‐terminated Ti3C2 MXene with activation barriers reducing dramatically from 0.80 to 0.22 and 0.29 eV, respectively, and accordingly promoted diffusion coefficients. The functionalization with O or F eliminates the steric hindrance of Li intercalation by breaking the strong interaction between two layers and provides additional adsorption sites for Li diffusion in the meantime. The work suggests that surface functional groups play a significant role in Ti3C2T2/1T‐MoS2 modification and similar strategy via chemical modification of metallic hybrids provides hints for designing high performance anode material for LIBs.

Interfacial ferroelectricity in rhombohedral-stacked bilayer transition metal dichalcogenides.

van der Waals materials have greatly expanded our design space of heterostructures by allowing individual layers to be stacked at non-equilibrium configurations, for example via control of the twist angle. Such heterostructures not only combine characteristics of the individual building blocks, but can also exhibit physical properties absent in the parent compounds through interlayer interactions1. Here we report on a new family of nanometre-thick, two-dimensional (2D) ferroelectric semiconductors, where the individual constituents are well-studied non-ferroelectric monolayer transition metal dichalcogenides (TMDs), namely WSe2, MoSe2, WS2 and MoS2. By stacking two identical monolayer TMDs in parallel, we obtain electrically switchable rhombohedral-stacking configurations, with out-of-plane polarization that is flipped by in-plane sliding motion. Fabricating nearly parallel-stacked bilayers enables the visualization of moiré ferroelectric domains as well as electric field-induced domain wall motion with piezoelectric force microscopy. Furthermore, by using a nearby graphene electronic sensor in a ferroelectric field transistor geometry, we quantify the ferroelectric built-in interlayer potential, in good agreement with first-principles calculations. The new semiconducting ferroelectric properties of these four new TMDs opens up the possibility of studying the interplay between ferroelectricity and their rich electric and optical properties2-5.

Ultrathin metallic phase MoS2 nanosheets decorated hollow carbon spheres for sodium and potassium ions storage

Molybdenum disulfide (MoS2) has become a very promising anode material due to its expandable interlayer spacing and high theoretical capacity. Herein, metallic phase MoS2 ultrathin nanosheets in-situ grown on chemically activated hollow carbon spheres (HCS) are synthesized. The 3D conductive structures not only improve the conductivity and shorten the ion diffusion path, but also buffer the volume expansion and avoid the agglomeration of the MoS2 nanosheets. Due to the above advantages, this composite electrode shows considerable storage characteristics. When used as the anode for SIBs, the discharge capacity is 296.2 mA h g−1 at a current density of 0.1 A g−1 after 50 cycles. When used as the anode for PIBs, the discharge capacity reaches 287.8 mA h g−1 after 50 cycles at a current density of 0.1 A g−1. The current synthesis strategy provides an alternative route to develop high performance electrodes for sodium and potassium ions storage.

Metallic 1T-MoS2 coupled with MXene towards ultra-high rate-capabilities for supercapacitors

A schematic diagram showing the synthesis of the 1T-MoS2/Ti3C2Tx heterostructure and the fast charge–discharge networks in the heterostructure.

The Effect of Proton Ion Exchange Reaction on the Stability of Metallic Mos2

The Effect of Proton Ion Exchange Reaction on the Stability of Metallic Mos2