Dynamic phase evolution of MoS3 accompanied by organodiselenide mediation enables enhanced performance rechargeable lithium battery.

Considerable efforts have been devoted to Li-S batteries, typically the soluble polysulfides shuttling effect. As a typical transition metal sulfide, MoS2 is a magic bullet for addressing the issues of Li-S batteries, drawing increasing attention. In this study, we introduce amorphous MoS3 as analogous sulfur cathode material and elucidate the dynamic phase evolution in the electrochemical reaction. The metallic 1T phase incorporated 2H phase MoS2 with sulfur vacancies (SVs-1T/2H-MoS2) decomposed from amorphous MoS3 achieves refined mixing with the "newborn" sulfur at the molecular level and supplies continuous conduction pathways and controllable physical confinement. Meanwhile, the in situ-generated SVs-1T/2H-MoS2 allows lithium intercalation in advance at high discharge voltage (≥1.8 V) and enables fast electron transfer. Moreover, aiming at the unbonded sulfur, diphenyl diselenide (PDSe), as a model redox mediator is applied, which can covalently bond sulfur atoms to form conversion-type organoselenosulfides, changing the original redox pathway of "newborn" sulfur in MoS3, and suppressing the polysulfides shuttling effect. It also significantly lowers the activation energy and thus accelerates the sulfur reduction kinetics. Thus, the in situ-formed intercalation-conversion hybrid electrode of SVs-1T/2H-MoS2 and organoselenosulfides realizes enhanced rate capability and superior cycling stability. This work provides a novel concept for designing high-energy-density electrode materials.

Pressure-Assisted Synthesis of Highly Crystalline 1T''-Lix MoS2.

Lix MoS2 is not only a lithium battery material, but is also an important precursor for the synthesis of MoS2 nanomaterials. Current syntheses of MoS2 , such as in n-butyllithium/LiBH4 or electrochemically, are not satisfying in terms of defined stoichiometry and crystallinity, so an accurate experimental crystal structure determination of this important and widely used material has been long awaited. A high-pressure/high-temperature synthesis yielded highly crystalline 1T''-Lix MoS2 (x=1, 1.333). 1T''-LiMoS2 crystallizes in the space group P 1 ‾ $\bar 1$ with a=6.2482(3) Å, b=6.6336(3) Å, c=6.7480(3) Å, α=119.321(2)°, ß=90.010(2)° and γ=90.077(2)°. The arrangement of Mo atoms within the b-c-plane confirmed a predicted Peierls distortion. A similar atom distribution pattern to that of Mo is also observed for the lithium atoms. Calculation of bond valence site energies gave an activation barrier of 1.244 eV for 2D lithium-ion migration. For x=1.333, a phase-pure synthesis was achieved.

Rapid and large-scale synthesis of MoS2via ultraviolet laser-assisted technology for photodetector applications.

Two-dimensional transition metal dichalcogenide (TMDC) thin films have been extensively employed in microelectronics research. Molybdenum disulfide (MoS2), as one of prominent candidates of this class, has been applied in photodetectors, integrated electronic devices, gas sensing, and electrochemical catalysis, owing to its extraordinary optoelectronic, chemical, and mechanical properties. Synthesis of MoS2crystal film is the key to its application. However, the reported technology revealed several drawbacks, containing limited surface area, prolonged high-temperature environment, and unsatisfying crystallinity. In order to enhance the convenience of MoS2applications, there is a pressing need for optimized fabrication technology, which could be quicker, with a large area, with adequate crystallinity and heat-saving. In this work, we presented an ultraviolet laser-assisted synthesis technology, accomplishing rapid growth (with the growth rate of about 40µm s-1) of centimeter-scale MoS2films at room temperature. To achieve this, we self-assembled a displaceable reaction chamber system, coupled with krypton fluoride ultraviolet pulse laser. The laser motion speed and trajectory could be customized in the software, allowing the maskless patterning of crystal films. As application, we exhibited a photodetector with the integration of synthesized MoS2and lead sulfide colloidal quantum dots (PbS CQDs), displaying broadband photodetection from ultraviolet, visible to near-infrared spectrum (365-1550 nm), with the detectivity of 109-1010Jones, and the rising time of 0.2-0.3 s. This work not only demonstrated a high-process-efficiency synthesis of TMDC materials, but also has opened up new opportunities for ultraviolet laser used in optoelectronics.

Combining Highly Dispersed Amorphous MoS3 with Pt Nanodendrites as Robust Electrocatalysts for Hydrogen Evolution Reaction.

Surface modification of electrocatalysts to obtain new or improved electrocatalytic performance is currently the main strategy for designing advanced nanocatalysts. In this work, highly dispersed amorphous molybdenum trisulfide-anchored Platinum nanodendrites (denoted as Pt-a-MoS3  NDs) are developed as efficient hydrogen evolution electrocatalysts. The formation mechanism of spontaneous in situ polymerization MoS4 2- into a-MoS3 on Pt surface is discussed in detail. It is verified that the highly dispersed a-MoS3 enhances the electrocatalytic activity of Pt catalysts under both acidic and alkaline conditions. The potentials at the current density of 10 mA cm-2 (η10 ) in 0.5 m sulfuric acid (H2 SO4 ) and 1 m potassium hydroxide (KOH) electrolyte are -11.5 and -16.3 mV, respectively, which is significantly lower than that of commercial Pt/C (-20.2 mV and -30.7 mV). This study demonstrates that such high activity benefits from the interface between highly dispersed a-MoS3 and Pt sites, which act as the preferred adsorption sites for the efficient conversion of hydrion (H+ ) to hydrogen (H2 ). Additionally, the anchoring of highly dispersed clusters to Pt substrate greatly enhances the corresponding electrocatalytic stability.

Building hybrid structure of monolayered S-depleted Mo-S nanocrystals and 3D graphene towards promising aqueous supercapacitor applications.

Two-dimensional (2D) 1H molybdenum disulfide (1H-MoS2) is hard to be directly used in energy storage devices due to its inert basal plane and unfavorable 2D stacking. This work demonstrated how the basal plane of 1H MoS2nanocrystals (NCs) can be activated to offer doubled specific capacitance by simple surface S depletions. Building on the expanded graphene with three-dimensional (3D) structures, as-prepared NCs were chemically grafted on the graphene surface to deliver stable energy storage and high capacitance, which overcame above challenges of 1H-MoS2. Aside from the mostly focused metastable phase, this work confirmed that the stable 1H Mo-S material is also promising in energy storage applications.

Molybdenum disulfide co-catalysis boosting nanoscale zero-valent iron based Fenton-like process: Performance and mechanism.

The conventional Fenton process has the drawbacks of low efficiency of Fe3+/Fe2+ conversion, low utilization of H2O2, and narrow range of pH. In this paper, molybdenum sulfide (MoS2) was used as a co-catalyst to boost the nanoscale zero-valent iron (nZVI) based heterogeneous Fenton-like process for the degradation of Rhodamine B (RhB). The catalytic performance, influences of parameters, degradation mechanism, and toxicity of intermediates were explored. Compared with the conventional like-Fenton process, the existence of MoS2 accelerated the decomposition of H2O2 and the RhB degradation rate constant of MoS2/nZVI/H2O2 reached more than six times that of nZVI/H2O2. In addition, the effective pH range of MoS2/nZVI/H2O2 was broadened to 9.0 with 84.9% of RhB being removed within 15 min. The co-catalytic system of MoS2 and nZVI was stable and had high reusability according to the results of four consecutive runs. Quenching tests and electron paramagnetic resonance (EPR) demonstrated that hydroxyl radical (·OH), superoxide anions (·O2-), and singlet oxygen (1O2) were all involved in MoS2/nZVI/H2O2. Compared with nZVI/H2O2 system, MoS2 not only increased the corrosion of nZVI but also accelerated the conversion of Fe3+/Fe2+. ECOSAR analysis suggested that the overall acute and chronic toxicity of the degradation products decreased after treatment. Hence, this MoS2 co-catalytic nZVI based Fenton-like process can be used as a promising alternative for the treatment of organic wastewater.

Atomic-scale evidence for highly selective electrocatalytic N-N coupling on metallic MoS2.

Molybdenum sulfide (MoS2) is the most widely studied transition-metal dichalcogenide (TMDs) and phase engineering can markedly improve its electrocatalytic activity. However, the selectivity toward desired products remains poorly explored, limiting its application in complex chemical reactions. Here we report how phase engineering of MoS2 significantly improves the selectivity for nitrite reduction to nitrous oxide, a critical process in biological denitrification, using continuous-wave and pulsed electron paramagnetic resonance spectroscopy. We reveal that metallic 1T-MoS2 has a protonation site with a pKa of ∼5.5, where the proton is located ∼3.26 Šfrom redox-active Mo site. This protonation site is unique to 1T-MoS2 and induces sequential proton-electron transfer which inhibits ammonium formation while promoting nitrous oxide production, as confirmed by the pH-dependent selectivity and deuterium kinetic isotope effect. This is atomic-scale evidence of phase-dependent selectivity on MoS2, expanding the application of TMDs to selective electrocatalysis.

Quantitative measurement of CA 15-3 cancer biomarker using an electrochemical aptasensor based on the electrodeposition of Au thin film on cauliflower-like rGO-MoS2 nanocomposite.

The present research was conducted to design and construct an electrochemical aptasensor for evaluating carbohydrate antigen 15-3 (CA15-3) as a biomarker for breast cancer. The aptasensor has been fabricated by a gold thin film (AuTF) electrodeposited on a cauliflower-like reduced graphene oxide-molybdenum sulfide nanocomposite (rGO-MoS2). The modified electrode's surface was used to immobilize the thiolated aptamer, which was subsequently treated with CA 15-3 antigen. The aptasensor fabrication process was assessed using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). This research also applied EIS to the quantitative measurement of CA 15-3 antigen by the proposed aptasensor. The interfacial charge transfer resistance (Rct) alteration before and after incubation of CA 15-3 by the immobilized aptamer was considered a signal for the quantitative measurement of CA 15-3. A linear concentration ranging from 5.0 to 200.0 U mL-1 with a detection limit of 3.0 × 10-1 U mL-1 was obtained for CA 15-3 using the EIS method. This designed aptasensor indicates satisfactory repeatability and stability, good selectivity, and high sensitivity. Moreover, clinical samples were assayed by the prepared aptasensor and compared with the ELISA method, yielding acceptable results. The recovery and relative standard deviation (RSD) of CA 15-3 in human serum samples were in the range 95.0 to 107.0% and 3.5 to 7.5%, respectively.

Ligand Modulation of Active Sites to Promote Cobalt-Doped 1T-MoS2 Electrocatalytic Hydrogen Evolution in Alkaline Media.

Highly efficient hydrogen evolution reaction (HER) electrocatalyst will determine the mass distributions of hydrogen-powered clean technologies, while still faces grand challenges. In this work, a synergistic ligand modulation plus Co doping strategy is applied to 1T-MoS2 catalyst via CoMo-metal-organic frameworks precursors, boosting the HER catalytic activity and durability of 1T-MoS2 . Confirmed by Cs corrected transmission electron microscope and X-ray absorption spectroscopy, the polydentate 1,2-bis(4-pyridyl)ethane ligand can stably link with two-dimensional 1T-MoS2 layers through cobalt sites to expand interlayer spacing of MoS2 (Co-1T-MoS2 -bpe), which promotes active site exposure, accelerates water dissociation, and optimizes the adsorption and desorption of H in alkaline HER processes. Theoretical calculations indicate the promotions in the electronic structure of 1T-MoS2 originate in the formation of three-dimensional metal-organic constructs by linking π-conjugated ligand, which weakens the hybridization between Mo-3d and S-2p orbitals, and in turn makes S-2p orbital more suitable for hybridization with H-1s orbital. Therefore, Co-1T-MoS2 -bpe exhibits excellent stability and exceedingly low overpotential for alkaline HER (118 mV at 10 mA cm-2 ). In addition, integrated into an anion-exchange membrane water electrolyzer, Co-1T-MoS2 -bpe is much superior to the Pt/C catalyst at the large current densities. This study provides a feasible ligand modulation strategy for designs of two-dimensional catalysts.

Facile Synthesis of Single Iron Atoms over MoS2 Nanosheets via Spontaneous Reduction for Highly Efficient Selective Oxidation of Alcohols.

The facile creation of high-performance single-atom catalysts (SACs) is intriguing in heterogeneous catalysis, especially on 2D transition-metal dichalcogenides. An efficient spontaneous reduction approach to access atomically dispersed iron atoms supported over defect-containing MoS2 nanosheets is herein reported. Advanced characterization methods demonstrate that the isolated iron atoms situate atop of molybdenum atoms and coordinate with three neighboring sulfur atoms. This Fe SAC delivers exceptional catalytic efficiency (1 atm O2 @ 120 °C) in the selective oxidation of benzyl alcohol to benzaldehyde, with 99% selectivity under almost 100% conversion. The turnover frequency is calculated to be as high as 2105 h-1 . Moreover, it shows admirable recyclability, storage stability, and substrate tolerance. Density functional theory calculations reveal that the high catalytic activity stems from the optimized electronic structure of single iron atoms over the MoS2 support.

Conducting molybdenum sulfide/graphene oxide/polyvinyl alcohol nanocomposite hydrogel for repairing spinal cord injury.

A sort of composite hydrogel with good biocompatibility, suppleness, high conductivity, and anti-inflammatory activity based on polyvinyl alcohol (PVA) and molybdenum sulfide/graphene oxide (MoS2/GO) nanomaterial has been developed for spinal cord injury (SCI) restoration. The developed (MoS2/GO/PVA) hydrogel exhibits excellent mechanical properties, outstanding electronic conductivity, and inflammation attenuation activity. It can promote neural stem cells into neurons differentiation as well as inhibit the astrocytes development in vitro. In addition, the composite hydrogel shows a high anti-inflammatory effect. After implantation of the composite hydrogel in mice, it could activate the endogenous regeneration of the spinal cord and inhibit the activation of glial cells in the injured area, thus resulting in the recovery of locomotor function. Overall, our work provides a new sort of hydrogels for SCI reparation, which shows great promise for improving the dilemma in SCI therapy.

[Mo3 S13 ]2- as a Model System for Hydrogen Evolution Catalysis by MoSx : Probing Protonation Sites in the Gas Phase by Infrared Multiple Photon Dissociation Spectroscopy.

Materials based on molybdenum sulfide are known as efficient hydrogen evolution reaction (HER) catalysts. As the binding site for H atoms on molybdenum sulfides for the catalytic process is under debate, [HMo3 S13 ]- is an interesting molecular model system to address this question. Herein, we probe the [HMo3 S13 ]- cluster in the gas phase by coupling Fourier-transform ion-cyclotron-resonance mass spectrometry (FT-ICR MS) with infrared multiple photon dissociation (IRMPD) spectroscopy. Our investigations show one distinct S-H stretching vibration at 2450 cm-1 . Thermochemical arguments based on DFT calculations strongly suggest a terminal disulfide unit as the H adsorption site.

Zeolite-Stabilized Di- and Tetranuclear Molybdenum Sulfide Clusters Form Stable Catalytic Hydrogenation Sites.

Supercages of faujasite (FAU)-type zeolites serve as a robust scaffold for stabilizing dinuclear (Mo2 S4 ) and tetranuclear (Mo4 S4 ) molybdenum sulfide clusters. The FAU-encaged Mo4 S4 clusters have a distorted cubane structure similar to the FeMo-cofactor in nitrogenase. Both clusters possess unpaired electrons on Mo atoms. Additionally, they show identical catalytic activity per sulfide cluster. Their catalytic activity is stable (>150 h) for ethene hydrogenation, while layered MoS2 structures deactivate significantly under the same reaction conditions.

Fabrication of a Robust PEM Water Electrolyzer Based on Non-Noble Metal Cathode Catalyst: [Mo3 S13 ]2- Clusters Anchored to N-Doped Carbon Nanotubes.

High investment costs and a dependence on noble metal catalysts currently obstruct the large-scale implementation of proton exchange membrane water electrolyzers (PEMWEs) for converting fluctuating green electricity into chemical energy via water splitting. In this context, this work presents a high-performing and stable non-noble metal catalyst for the hydrogen evolution reaction (HER), consisting of [Mo3 S13 ]2- clusters supported on nitrogen doped carbon nanotubes (NCNTs). Strikingly, a significant electrochemically induced activation of the Mo3 S13 -NCNT catalyst at high current densities is observed in full cell configuration, enabling a remarkable current density of 4 A cm-2 at a cell voltage of 2.36 V. To the authors' knowledge, this is the highest reported value to date for a PEMWE full cell using a non-noble metal HER catalyst. Furthermore, only a minor degradation of 83 µV h-1 is observed during a stability test of 100 h constant current at 1 A cm-2 , with a nearly unchanged polarization behavior after the current hold. Catalyst stability and activity are additionally analyzed via online dissolution measurements. X-ray photoelectron spectroscopy examination of the catalyst before and after electrochemical application reveals a correlation between the electrochemical activation occurring via electrodissolution with changes in the molecular structure of the Mo3 S13 -NCNT catalyst.

Significant acceleration of Fe2+/ peroxydisulfate oxidation towards sulfisoxazole by addition of MoS2.

Activation of peroxydisulfate (PDS) by Fe2+ has been considered as an effective activation method to generate reactive oxygen species (ROS). However, the process is limited for the low production yield of ROS owing to the inefficient Fe3+/Fe2+ cycle. Herein, we demonstrated that Fe2+/PDS system in the presence of molybdenum sulfide (MoS2) was significantly efficient for the degradation of sulfisoxazole (SIX). As a co-catalyst in the Fe2+/PDS system, MoS2 could greatly enhance the Fe3+/Fe2+ cycle by the exposed Mo4+ active sites, which could also improve the PDS decomposition efficiency. As a result, the degradation efficiency of SIX in the MoS2/Fe2+/PDS system could reach to as high as 97.1% within 40 min, which was in distinct comparison with the 45.5% achieved by Fe2+/PDS system without MoS2. Besides, effects of various reaction conditions on SIX degradation were also evaluated during the experiments, including the dosages of MoS2, Fe2+, PDS and initial solution pH and the coexisting inorganic anions. In addition, both of sulfate radicals and hydroxyl radicals were identified as the dominant active species for SIX degradation by the radical scavenging experiments and verified by electron paramagnetic resonance (EPR). This study provides a promising idea for the degradation of organic contaminants in water treatment based on Fe2+/PDS process.

Interfacial Charge Transfer in MoS2/TiO2 Heterostructured Photocatalysts: The Impact of Crystal Facets and Defects.

One of the most challenging issues in photocatalytic hydrogen evolution is to efficiently separate photocharge carriers. Although MoS2 loading could effectively improve the photoactivity of TiO2, a fundamental understanding of the charge transfer process between TiO2 and MoS2 is still lacking. Herein, TiO2 photocatalysts with different exposed facets were used to construct MoS2/TiO2 heterostructures. XPS, ESR, together with PL measurements evidenced the Type II electron transfer from MoS2 to {001}-TiO2. Differently, electron-rich characteristic of {101}-faceted TiO2 were beneficial for the direct Z-scheme recombination of electrons in TiO2 with holes in MoS2. This synergetic effect between facet engineering and oxygen vacancies resulted in more than one order of magnitude enhanced hydrogen evolution rate. This finding revealed the elevating mechanism of constructing high-performance MoS2/TiO2 heterojunction based on facet and defect engineering.

Synergistic Doping and Intercalation: Realizing Deep Phase Modulation on MoS2 Arrays for High-Efficiency Hydrogen Evolution Reaction.

A synergistic N doping plus PO4 3- intercalation strategy is used to induce high conversion (ca. 41 %) of 2H-MoS2 into 1T-MoS2 , which is much higher than single N doping (ca. 28 %) or single PO4 3- intercalation (ca. 10 %). A scattering mechanism is proposed to illustrate the synergistic phase transformation from the 2H to the 1T phase, which was confirmed by synchrotron radiation and spherical aberration TEM. To further enhance reaction kinetics, the designed (N,PO4 3- )-MoS2 nanosheets are combined with conductive vertical graphene (VG) skeleton forming binder-free arrays for high-efficiency hydrogen evolution reaction (HER). Owing to the decreased band gap, lower d-band center, and smaller hydrogen adsorption/desorption energy, the designed (N,PO4 3- )-MoS2 /VG electrode shows excellent HER performance with a lower Tafel slope and overpotential than N-MoS2 /VG, PO4 3- -MoS2 /VG counterparts, and other Mo-base catalysts in the literature.

Conductive Molybdenum Sulfide for Efficient Electrocatalytic Hydrogen Evolution.

Molybdenum sulfide (MoS2 ) is a layered material with high activity for electrocatalytic hydrogen evolution reaction (HER). In conventional MoS2 , the high electrical resistance between the layers hampers the bulk charge transfer and therefore greatly limits its performance in electrolysis. Herein, ultrathin MoS2 nanosheets with bent layers on reduced graphene oxide (RGO) are reported. In sharp contrast to the bulk MoS2 , the resulting MoS2 has mostly 1 or 2 layers, and the layer distance is significantly expanded to ≈1 nm. From computational studies, the prepared MoS2 with limited layer numbers and expanded layer distances has similar physical and chemical features with single-layer MoS2 . Importantly, the bent single layer is electrically conductive and is intrinsically more active than a normal flat single layer. In addition, the unusual features of confined sizes and distorted lattices in the prepared MoS2 can bring about plentiful active sites and are beneficial for mass diffusion during electrocatalysis. The hybrid material exhibits high activity for electrocatalytic HER, affording a current density of 10 mA cm-2 at a low overpotential of 66 mV.

An Electrosynthesized 3D Porous Molybdenum Sulfide/Graphene Film with Enhanced Electrochemical Performance for Lithium Storage.

Molybdenum sulfide/graphene composites are promising anode materials for lithium-ion batteries (LIBs). In this work, MoSx /graphene composite film with an ideal 3D porous structure is developed via a facile and straightforward electrochemical route. The MoSx nanoparticles are uniformly anchored on the graphene nanosheets that are randomly arranged, resulting in MoSx /graphene composites with well-developed porous structure. Benefiting from such structure and the synergistic effect from two components, this material shows a high specific capacity over 1200 mA h g-1 , an excellent rate performance, and superior cycling stability. The dominating pseudocapacitive behavior in Li storage contributes to the outstanding rate capacity. Importantly, this kind of novel material can be easily produced as 3D microelectrodes for microscaled LIBs that are highly demanded for autonomous microelectronic systems.

Quasi-Emulsion Confined Synthesis of Edge-Rich Ultrathin MoS2 Nanosheets/Graphene Hybrid for Enhanced Hydrogen Evolution.

High-purity hydrogen produced by water splitting is considered as one of the most promising fuels to replace traditional fossil fuels. Developing highly efficient electrocatalysts toward hydrogen evolution is vital for the realization of large-scale H2 generation. Glycerol is used herein in a facile solvothermal process to synthesize edge-rich ultrathin MoS2 /reduced graphene oxide (RGO) composites. The introduction of glycerol plays an important role in the formation of such interesting structures. The MoS2 /RGO electrocatalyst exhibits excellent hydrogen evolution reaction (HER) activity and remarkable stability, owing to the rich active edges and improved electrical conductivity of the catalyst composites. This work provides new insights to engineer the structures of MoSx -based composites and thus achieves more active and efficient electrocatalysts.