1T Phase Research Articles

2D/2D heterojunction interface: Engineering of 1T/2H MoS2 coupled with Ti3C2Tx heterostructured electrocatalysts for pH-universal hydrogen evolution

Two-dimensional (2D) materials have come to light due to their unique thickness that owns abundant exposed edges with enhanced electrocatalytic properties. 2D molybdenum disulfide (MoS2) nanosheet has aroused considerable attention due to its tunable surface chemistry and high electrochemical surface area. Nonetheless, several shortcomings associated with MoS2, such as its naturally existing semiconducting 2H phase, which has limited active sites due to the inert basal plane, restrict its application in water electrocatalysis. Taking into account the benefits of the 1T/2H phase of MoS2, as well as the importance of engineering 2D/2D heterojunction interface for boosted electrocatalysis, metallic Ti3C2Tx was integrated with 1T/2H MoS2 to develop 2D/2D 1T/2H MoS2/Ti3C2Tx heterostructured nanocomposites. Herein, with only 25 % of the intercalating agent, 1T/2H MoS2 with the highest 1T phase content of ∼82 % was successfully synthesized. It was further incorporated with 1 wt% of Ti3C2Tx through a combination of ultrasonication and mechanical stirring process. The 1T/2H MoS2 (25D)/ Ti3C2Tx-1 (MTC-1) manifested outstanding electrocatalytic performance with an overpotential and Tafel slope of 280 mV (83.80 mV dec–1) and 300 mV (117.2 mV dec–1), for catalyzing acidic and alkaline medium HER, respectively. Pivotally, the as-prepared catalysts also illustrated long-term stability for more than 40 h. The coupling method for the 2D nanosheets is crucial to suppress the oxidation of Ti3C2Tx and the restacking issue of 2D nanosheets. The superior HER activity is ascribed to the synergistic effect between the heterostructure, enhancing the electronic structure and charge separation capability. The intrinsic property of the catalyst further confirms by turnover frequency (TOF) calculation. As such, this research paves the way for designing high-efficiency 2D electrocatalysts and sheds light on the further advancement of tunable 2D electrocatalysts for robust water splitting and beyond.

Engineering Single-Layer Hollow Structure of Transition Metal Dichalcogenides with High 1T-Phase Purity for Hydrogen Evolution Reaction.

Rational design and controllable synthesis of hollow structures based on transition metal dichalcogenides (TMDs) have gained tremendous attention in the field of clean energy. However, the general synthetic strategies to fabricate single-layer hollow structures of TMDs, especially with unconventional phases (e.g., 1T or 1T'), still pose significant challenges. Herein, a scalable method is reported for the synthesis of single-layer hollow spheres (SLHS) of TMDs with high 1T-phase purity by etching bismuth (Bi) cores from pre-synthesized Bi@TMDs core-shell heterostructures including SLHS-1T-MoS2 , SLHS-1T-MoSe2 , SLHS-1T-WS2 , and SLHS-1T-WSe2 . Additionally, the etched Bi ions can be adsorbed on the single-layer TMDs shells in the form of single atoms (SAs) via the Bi─S bond. Due to the benefits of the single-layer hollow structure, high conductivity of 1T phase, and synergistic effect of Bi SAs and TMDs supports, the fabricated SLHS-1T-MoS2 exhibits superior electrocatalytic performance for hydrogen production. This work provides a way to manufacture advanced functional materials based on the single-layer hollow structures of 1T-TMDs and to expand their applications.

Rotation angle dependent Li intercalation and the induced phase transition in bilayer MoTe2

In this work, taking twisted bilayer MoTe2 (tb-MoTe2) as an example, density functional theory (DFT) calculations are done to investigate the interlayer rotation angle dependent lithium intercalation as well as the induced 2H → 1T phase transition in two-dimensional layered materials. Both static equipotential energy diagrams and dynamic ab initio molecular dynamics simulations (AIMD) are utilized to obtain the reliable lithium diffusion pathways and barriers. The results reveal that the interlayer rotation leads to increased interlayer separation in tb-MoTe2, and provides a stable environment for Li insertion. Moreover, the diffusion barrier is substantially reduced with increasing twist angle, promoting the fast Li diffusion. At room temperature, the mobility of Li in tb-MoTe2 with the twist angle of θ = 21.79˚ and θ = 60˚ is increased by a factor of 10 and 105, respectively. The energy barrier for the 2H → 1T phase transition is lowered from 1.23 eV in the non-twisted MoTe2 to 0.88 eV in the tb-MoTe2 with a twist angle θ = 21.79˚ for a given concentration of inserted Li. Above all, the enhanced diffusion and lower critical electron concentration facilitate the 2H-1T phase transition in tb-MoTe2. The results provide valuable insights into the non-uniform intercalation and present an opportunity to modulate the phase transition of twisted 2D systems.

Unusual Defect-Related Room-Temperature Emission from WS2 Monolayers Synthesized through a Potassium-Based Precursor.

Alkali-metal-based synthesis of transition metal dichalcogenide (TMD) monolayers is an established strategy for both ultralarge lateral growth and promoting the metastable 1T phase. However, whether this can also lead to modified optical properties is underexplored, with reported photoluminescence (PL) spectra from semiconducting systems showing little difference from more traditional syntheses. Here, we show that the growth of WS2 monolayers from a potassium-salt precursor can lead to a pronounced low-energy emission in the PL spectrum. This is seen 200-300 meV below the A exciton and can dominate the signal at room temperature. The emission is spatially heterogeneous, and its presence is attributed to defects in the layer due to sublinear intensity power dependence, a noticeable aging effect, and insensitivity to washing in water and acetone. Interestingly, statistical analysis links the band to an increase in the width of the A1g Raman band. The emission can be controlled by altering when hydrogen is introduced into the growth process. This work demonstrates intrinsic and intense defect-related emission at room temperature and establishes further opportunities for tuning TMD properties through alkali-metal precursors.

Supercapacitor electrodes based on single crystal layered ZrX2 (X = S, Se) using chemical vapor transport method

We synthesized single crystals of layered zirconium disulfide/diselenide (ZrX2, X = S, Se) using the chemical vapor transport method. Our aim was to explore their potential as energy storage devices, specifically supercapacitors. To confirm the structures of our growth samples, we conducted various characterization tests. The semiconducting nature of ZrX2, particularly in the 1T phase, limits its electrochemical performance. However, the 1T-ZrX2 nanoflakes serve as highly stable conductive electrodes for high-performance supercapacitors. At a scan rate of 10 mV/s, ZrS2 and ZrSe2 exhibited specific capacitance values of 18.8 and 18 F/g, respectively. Notably, the metallic 1T-ZrSe2 electrode outperformed 1T-ZrS2 due to its greater conductive space observed from layer spacing, as confirmed by HRTEM analysis. The ZrSe2 devices demonstrated exceptional stability, exceeding 90%. These findings highlight the promising potential of these 2D materials as supercapacitor electrodes, offering excellent specific capacitance values, conductivity and cycling stability.

Prediction of novel 2D metallic ferroelastic ferromagnet: Monoclinic CrTe2

By combining the USPEX evolutionary algorithm and density functional theory at the HSE06 level, we identified a new CrTe2 monolayer crystallizing in monoclinic phase with C2h symmetry, which is different from the well-known 1T-CrTe2 monolayer. The monoclinic phase is energetically favored over that in 1T phase, is thermodynamically, dynamically, and mechanically stable. The monoclinic phase is an intrinsically ferromagnetic metal with a relatively high Curie temperature of 215 K showing an out-of-plane easy axis with 25° off the z-axis. In particular, the predicted Curie temperature and out-of-plane ferromagnetic order are in agreement with the experimental evidence. In addition, a uniaxial strain can induce a ferroelastic switching together with the magnetic easy axis, resulting in a strong intrinsic magnetoelasticity. Our results open up a new possibility for the realization of novel two-dimensional ferromagnets and provide a platform for understanding the underlying physical mechanism.

Fabrication of 1T VS2 Electrode‐Based In‐Plane Micro‐Supercapacitor Using a Cost‐Effective Mask‐Assisted Printing Technique

Vanadium disulfide (VS2) is an important member of the transition‐metal dichalcogenides (TMDs) family, which offers high conductivity. In nature, it can exist in two phases, i.e., 1T and 2H. Herein, the metallic 1T VS2‐based in‐plane micro‐supercapacitor (MSC) is fabricated by a facile‐mask‐assisted printing technique. Initially, the 1T VS2 nanosheets are synthesized using a simple one‐pot hydrothermal route. The material characterizations have claimed the formation of a 1T phase and the density of states (DOS) reveal that the 1T phase of VS2 is metallic in nature. After experimental and theoretical investigations of synthesized nanosheets, a VS2 electrode‐based in‐plane MSC is fabricated using a simple mask‐assisted printing technique. The fabricated device demonstrates excellent capacitance retention of 97.6% after 1000 cycles of cyclic voltammetry measurement at a 100 mV s−1 scan rate. The device also shows an excellent areal capacitance of 212.7 mF cm−2 and a high areal energy density of 10.63 μWh cm−2 at a high‐power density of 4.45 mW cm−2. This low‐cost and simple fabrication process can produce high‐performance in‐plane MSC devices.

Defect engineered Janus MoXTe (X=S, Se) monolayers for hydrogen evolution reaction: A first principles study

Given the elevated expense and constrained accessibility of platinum, the primary catalyst employed in electrocatalytic hydrogen evolution, it becomes essential to pinpoint an alternative catalyst demonstrating exceptional catalytic efficacy and broader scalability potential. In this study, we undertook an exhaustive inquiry into the electrocatalytic activity concerning hydrogen evolution of the monolayer Janus MoXTe (where X represents S and Se) utilizing first-principle calculation. Furthermore, an evaluation of the performance of defective MoXTe structures was conducted. Our findings illuminate that the incorporation of non-metallic elements like B, C, N, and P into MoXTe can be employed to finely adjust the Gibbs free energy (ΔGH) to approximately 0 eV. Particularly, the doping of B and P into the 1T phase of MoSTe (1T-MoSTe-B@ represents 1T phase of MoSTe-B@ and 1T-MoSTe-P@ represents 1T phase of MoSTe-P@), the doping of P into the 1T′ phase of MoSTe (1T′ phase of MoSTe-P@), and the doping of P into the 1T′ phase of MoSeTe (1T′ phase of MoSeTe-P@) exhibit ΔGH values that are in close proximity to zero (ΔGH = 0.02, −0.03, 0.06, and −0.14 eV, respectively). Through further analysis, we found that the pristine and defective structures all exhibit metallic properties. And the doping of P improved HER performance more effectively among four nonmetallic dopants. In details, H get 0.21, 0.29, 0.43 and 0.28 e on doping of B and P into 1T phase MoSTe (1T phase of MoSTe-B@ and 1T phase of MoSTe-P@) and the doping of P into 1T′ phase MoSeTe (1T’ phase of MoSeTe-P@). This study provides strategies for the design of MoXTe monolayer electrocatalysts, and it is expected to be applied to HER catalysts in affordable and efficient manner.

Well-ordered single-atomic cobalt-1T-MoS2/C superlattice heterostructure toward durable overall water splitting

Van der Waals superlattice heterostructure with different two-dimensional (2D) nanosheets provides a promising way to exploit the intrinsic properties of both 2D components. However, developing efficient methods for precisely constructing ordered/controlled layer sequence superlattice heterostructures has always been challenging. Here, we report a facile strategy for the preparation of single-atomic cobalt anchored 1T-MoS2/carbon (Co-1T-MoS2/C) heterostructure with a well-ordered superlattice of alternating Co-1T-MoS2 and C nanosheets at a molecular level. The coordination of Co atoms on the 1T-MoS2 matrix and its effect on the phase transformation of MoS2 has been systematically investigated. Importantly, the Co atoms can efficiently improve the metastable 1T phase stability of MoS2. As a proof-of-concept application, the obtained Co-1T-MoS2/C is employed as an electrocatalyst for overall water splitting in alkaline conditions. The rapid interfacial charge transfer and abundant active catalytic sites, coupled with the contribution of the single-atomic Co sites enable the Co-1T-MoS2/C superlattice heterostructure to exhibit excellent performance. The assembled Pt/C||Co-1T-MoS2/C cell needs only 1.57 V to reach the current density of 10 mA/cm2. Our research strategy provides a feasible path for the design of 2D-2D van der Waals superlattice heterostructures and further broadens their applications.

Enhanced photocatalytic hydrogen production utilizing few-layered 1T-WS2/g-C3N4 heterostructures prepared with one-step calcination route

Two-dimensional sulfide is considered as one of the best alternative for noble metal cocatalyst, whereas few-layered 1T WS2 structure is very helpful to promote the photocatalytical activity for hydrogen generation. Herein, few-layered 1T-WS2/g-C3N4 composites have been prepared via a facile one-step calcination route and used as a noble metal-free catalyst for H2 evolution. The results showed that the optimized 1T-WS2/g-C3N4 has a H2 evolution rate of 10.08 mmol∙g−1 h−1, which is 180 and 2.44 times larger than that of pure pristine g-C3N4 and g-C3N4 (Pt), respectively. The enhanced photocatalytic activity can be explained as the optimized 1T-WS2/g-C3N4 sample has an increased light absorption (from visible to infrared region), better electrical conductivity and high density of active sites. The studies will be helpful for constructing high efficient heterostructured catalysts by loading 1T phase metal dichalcogenides 2D of material onto a two-dimensional material surface.

High efficient PMS activation by synergistic effects of bimetallic sulfide FeS2@MoS2 for rapid OFX degradation

Antibiotics have been widely used to treat bacterial diseases. Their wide spread in ecological environment will induce generation of antibiotic-resistant bacteria Therefore, it is critical to create an eco-friendly and effective approach for their removal. Herein, a bimetallic sulfide FeS2@MoS2 with rich sulfur vacancies (SVs) and high percentage of metallic 1T phase MoS2 was prepared by one-step solvothermal method to degrade ofloxacin (OFX) by activated peroxymonosulfate (PMS). FeS2@MoS2-1 (the mass ratio of Fe/Mo is 1) exhibited excellent performance for PMS activation, with 99.26% OFX removed in 20 min (0.2 g/L FeS2@MoS2-1, 0.2 mM PMS, initial pH). The degradation rate constant of kobs was 0.21 min−1 with FeS2@MoS2-1 system, which was about 4.88 and 22.91 times of FeS2/PMS and MoS2/PMS systems under the same experimental conditions respectively. In FeS2@MoS2-1, besides S2−, SVs would also accelerate Fe(III)/Fe(II) circulation through increasing the exposure of Mo(IV) active sites. Additionally, MoS2 transferred from the semi-conductive 2H phase to the metallic 1T phase, which could speed up electron transfer rate significantly. Quenching experiment and EPR test showed that SO4− and O2− were the main active oxygen species. Degradation pathway was proposed through the active sites identification by DFT calculations and intermediates detection by HPLC-MS analyzation. The results showed that OFX were vulnerable to be attacked and broke to form small molecular compounds through hydrogen loss, oxidative cracking, decarboxylation and demethylation four ways. In addition, their bio-toxicity was investigated and results showed that the toxic was diminished. This work indicated that the satisfactory universality, recyclability and stability enabled FeS2@MoS2-1 could be used as an efficient catalyst to activate PMS to degrade refractory organic pollutants in water.

1T-2H Mixed-Phase MoS2 Stabilized with a Hyperbranched Polyethylene Ionomer for Mg2+ /Li+ Co-Intercalation Toward High-Capacity Dual-Salt Batteries.

Dual-salt magnesium/lithium-ion batteries (MLIBs) benefit from fast lithium ion diffusion on the cathode side while providing safety due to the dendrite-free Mg2+ stripping/plating mechanism on the anode side. Bulk MoS2 (B-MoS2 ), as a cathode for magnesium-ion batteries (MIBs), suffers from low conductivity and relatively van der Waals gaps and, consequently, resists against divalent Mg2+ insertion due to the high Coulombic interactions. In MLIBs, it exhibits a Daniell-cell type mechanism with the sole accommodation of Li+ . In this paper, the synthesis of a 1T/2H mixed-phase MoS2 (MP-MoS2 ) modified with a hyperbranched polyethylene ionomer, I@MP-MoS2 , for high-capacity MLIBs with a distinct Mg2+ /Li+ co-intercalation mechanism is reported. Benefiting from the enhanced conductivity (due to 53% metallic 1T phase), expanded van der Waals gaps (79% expansion compared to B-MoS2 , 1.11 vs 0.62 nm), and enhanced interactions with THF-based electrolytes following the modification, I@MP-MoS2 shows a dramatically increased Mg2+ storage compared to its parent analogue (144 mAh g-1 vs ≈2 mAh g-1 at 20 mA g-1 ). In MLIBs, I@MP-MoS2 is demonstrated to exhibit remarkable specific capacities up to ≈270 mAh g-1 at 20 mA g-1 through a Mg2+ /Li+ co-intercalation mechanism with 87% of capacity retention over 200 cycles at 100 mA g-1 .

High phase purity of stable 1T-phase Co-doped WS2 for full pH hydrogen evolution reaction in water and seawater

Metallic 1T phase transition metal dichloride (TMDs) shows excellent catalytic activity for the hydrogen evolution reaction (HER), but stabilization of 1T phase TMDs is still challenging. Herein, the Finke-type POMs K10[Co4(H2O)2(PW9O34)2] [Co4(PW9)2] was used for the first time as a precursor to obtaining size ∼ 4 nm, highly dispersed 1T-WS2 in the hollow mesoporous carbon sphere (HMCS) by the effect of confinement, named 1T-CoWS/HMCS. 1T-WS2 was obtained based on the natural Co-W atomic interface of POMs and further enhanced dispersion at the molecular and nano scales. 1T-CoWS/HMCS only requires ultralow overpotential with high electrocatalytic surface area and robust stability in water and seawater. According to DFT calculations, the Co-S-edge site of 1T-CoWS significantly reduced the rate-limiting step of HER as the predominant active site. This work provides a worthy reference for the synthesis of high-quality metastable TMDs.

(Digital Presentation) Hydrothermal Electrodeposition of Molybdenum Sulfide Toward Electrochemical CO2 Reduction Catalysts

The search and development of efficient carbon dioxide (CO2) reduction reaction electrocatalysts is a hot topic in this era of global warming. Among material candidates for sustainable and cost−effective applications, metal sulfides have attracted attention as promising nature-inspired materials due to multiple adsorption sites which are enhanced by the covalent character of sulfur.Molybdenum sulfides (MoS2) is one of the trandition metal dichalcogenides (TMDs) and possesses three kinds of struture; namely, metastable octahedral structure with high electronic conductivity (1T), stable triangular prism structure with low electronic conductivity (2H) and insulating rhombohedral structure (3R). Among them, 1T phase has been widely applied as catalysts for various reactions such as electrochemical nitrogen reduction reaction and electro/photochemical hydrogen evolution reaction. Since the structure of MoS2 largely affect its catalytic and other material property, synthetic process to control their bulk and even local structure should be explored to expand their availability as functional materials. Especially, our previous work (J. Phys. Chem.C, 126, 2772, 2022) demonstrated that metal-sufur bonding length is one of the key parameter to control carbon monoxide production selectivity from electrochemical CO2 reduction.Here in this work, hydrothermal electrodeposition was applied to MoS2 synthesis to control their local structure. Recently, our group developed hydrothermal electrochemical flow reactor which enables the electrochemistry under hydrothermal condition with separate control of temperature and pressure. Using this reactor, hydrothermal electrodeposition of manganese oxides (MnO2) was conducted and samples exhibited higher electrochemical oxygen evolution activity than ones prepared with conventional methods. Also, the characterization results of electrodeposited MnO2 under hydrothermal condition showed the possiblity that morphology and lattice spacing can be controled by changing deposition temperature and pressure, respectively. Thus, we predicted our hydrothermal electrodeposition technique is useful to control the local structure of materials.The hydrothermal electrodeposition of MoS2 were conducted under various temperature and pressure conditions and those samples were characterized with X-ray diffraction (XRD). Also, the effect of the deposition temperature and pressure on sample local structure was examined with Pair Disribution Function analysis of XRD and Extended X-ray Absorption Fine Structure analysis using synchrotron radiation. The electrochemical CO2 reduction experiments using hydrothermally depositted MoS2 samples revealed that the product selectivity for CO2 reduction was changed with deposition pressure. Thus, we confirmed that our hydrothermal electrochemical deposition can be applicable to the synthesis of metal sulfide-based CO2 reduction electrocatalysts, whose local structures are tuned.

An embedded ReS2@MAPbBr3 heterostructure with downhill interfacial charge transfer for photocatalytic upgrading of biomass-derived alcohols to aldehydes and H2

Solar-driven selective upgrading of lignocellulosic biomass-derived alcohols to value-added chemicals and clean fuel hydrogen (H2) shows great potential for tackling the energy crisis and environmental pollution issues. Here, we construct a MAPbBr3/ReS2 heterostructure by embedding distorted tetragonal (1T) phase ReS2 nanoflowers into large-sized MAPbBr3 for green value-added utilization of biomass-derived alcohols. The embedded structure effectively enlarges the contact interface between the ReS2 and the MAPbBr3, and importantly, induces a strong built-in electric field aligned between the spatially well-defined MAPbBr3 and ReS2 nanoflowers. Moreover, the distorted 1T phase ReS2 with low work function well matches the energy band of MAPbBr3, forming a heterostructure with a downward band bending at the interface. These features empower the MAPbBr3/ReS2 photocatalyst with high capability to promote charge separation and expedite the surface redox reaction. Consequently, optimal BAD and H2 production rates of about 1220 μmol h−1 g−1 are realized over a MAPbBr3/ReS2 2% sample, which are approximately 9 times greater than those of blank MAPbBr3. This work demonstrates the great potential of constructing an embedded transition metal dichalcogenide@metal halide perovskites heterostructure with downhill interfacial charge transfer for photocatalytic upgrading of biomass-derived alcohols.

Phase-Dependent Dual Discrimination of MoSe2/MoO3 Composites Toward N,N-Dimethylformamide and Triethylamine at Room Temperature.

Herein, we present, a chemiresistive-type gas sensor composed of two-dimensional 1T-2H phase MoSe2 and MoO3. Mixed phase MoSe2 and MoSe2/MoO3 composites were synthesized via a facile hydrothermal method. The structure analysis using X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the formation of different phases of MoSe2 at different temperatures. With increase in synthesis temperature from 180 to 200 °C, the relative percentage of 1T and 2H-MoSe2 phases changed from 80 to 48%. On the other hand, at 220 °C, 2H-MoSe2 was obtained as a major component. The gas sensing properties of individual MoSe2 and composites were investigated at room temperature toward various analytes. The obtained results revealed that composites possess improved sensing features as compared with individual MoSe2 or MoO3. Data also revealed that the composite with dominating 1T-phase exhibits relatively higher response (10%, at 10 ppm) for dimethylformamide (DMF) compared to triethylamine (TEA) (3%, at 10 ppm). In contrast, the composite with larger 2H-phase exhibited affinity toward TEA and had a relative response of about 2%. Therefore, selectivity of a sensor device can be tuned by an appropriately designed MoSe2/MoO3 composite. These results signify the importance of MoO3-based composites with dual-phase MoSe2 for successfully discriminating between DMF and TEA at room-temperature.

A doping strategy to achieve synergistically tuned magnetic and dielectric properties in MoSe2 for broadband electromagnetic wave absorption

Advanced electromagnetic (EM) wave absorbing materials are essential to tackle the even-increasing EM interference and pollution. Conventional methods usually combine magnetic and dielectric components for optimized impedance matching and attenuation. It is, however, challenging to simultaneously tune magnetic and dielectric properties with one wane and the other wax by adjusting the ratio between the corresponding components. Here, simultaneous modulation of both magnetic and dielectric properties has been achieved via a doping strategy in MoSe2. On the one hand, significant room-temperature ferromagnetism could be induced through the generation and coupling of local magnetic moments of Mn2+. On the other hand, Mn doping also enhances the dielectric properties by promoting the formation of amorphous and 1T phase of doped MoSe2. The synergistic magnetic and dielectric effects give rise to optimal absorption performance with a minimum reflection loss (RLmin) of −54.57 dB and a wide effective absorption bandwidth (EAB) of 8.24 GHz at 2.00 mm. Such comprehensive performance surpasses the majority of the transition metal dichalcogenide (TMD)-based composites and is the best among all the single-component TMD absorbers. Consequently, the study sheds light on synergistic modulation of EM properties in single-component materials, providing prospective solutions in the design of magnetic and dielectric devices for EM wave absorption and other fields, such as sensing, information storing, and quantum computing.

Phase Engineering of W-Doped MoS2 by Magneto-Hydrothermal Synthesis for Hydrogen Evolution Reaction.

Molybdenum disulfide (MoS2 ) has been proved as an excellent potential hydrogen evolution reaction (HER) catalyst. Compared with thermodynamically stable 2H-MoS2 , 1T-MoS2 exhibits higher conductivity and catalytic activity, whereas it is usually difficult to prepare since of thermodynamically metastable. Herein, a feasible method is reported to fabricate ambient-stable MoS2 with high concentration 1T phase through magnetic free energy synergistic microstrain induced by W doping under low magnetic field. The 1T phase proportion in MoS2 can be as high as 80% and is ambient-stable for more than one year. The catalyst prepared under a magnetic field of 3 T delivers an overpotential of 195mV at a current density of 10mA cm-2 and has a long-term stability over 50h. This work provides a novel strategy for preparation of MoS2 with high 1T concentration and high stability.

Facile hydrothermal process achieving 1T/2H phase tailoring of MoS2 nanosheets for efficient microwave absorption

Electromagnetic pollution is becoming a serious concern. Electromagnetic wave absorbers with light weight, high efficiency and broadband are desirable for electromagnetic protection. Recently, 1T/2H hybrid molybdenum disulfide nanosheets attracted great attention due to the enhanced microwave attenuation driven from fabrication of 1T/2H metal-semiconductor heterojunctions. However, the easy and controllable 1T/2H phase tailoring remains a challenge because of the difficulty in accurately controlling the two-phase ratio and the complicated process. In this study, a facile hydrothermal process is proposed to acquire the 1T/2H MoS2 nanosheets with different 1T contents. The high-resolution TEM images reveal the MoS2 nanosheets are composed of 1T/2H nano-heterojunctions with the 1T and 2H nanodomains arranged alternatively. Without compositing with conductive matters, the MoS2 nanosheets exhibit excellent microwave absorption performance with a maximum reflection loss of −27 dB and an effective absorption bandwidth of ∼4.16 GHz (at 2.3 mm thickness). It benefits from the increased conductivity of the MoS2 nanosheets, abundant 1T/2H phase boundaries and lattice defects, and improved impedance matching induced by the embedding of the 1T phase in the 2H matrix. This work demonstrates the feasibility of the proposed facile hydrothermal process in achieving 1T/2H phase regulation, providing an effective method to tailor the properties of MoS2 nanosheets for various applications.

On the excitonic effects of the 1T and 1O[formula omitted] phases of PdS2, PdSe2, and PdSSe monolayers

We report the excitonic effects in the 1T and 1OT phases of PdS2, PdSe2, and PdSSe monolayers. Using fully relativistic norm-conserving non-local PBE pseudopotentials and including the spin–orbit (SOC) coupling, the 1T geometries are indirect band gap semiconductors; conversely, the 1OT structures are semimetallic. The band gaps were corrected using the HSE06 hybrid functional, making all structures semiconductors. Maximally localized Wannier functions were utilized to fit the bands of all six structures. The excitonic band structures were obtained using the Bethe–Salpeter equation (BSE), and the absorption coefficients were estimated at both the BSE and the independent particle approximation (IPA) levels. While the 1OT monolayers are more inclined to absorb light polarized in the y-direction, the 1T structures absorb light equally, independent of the polarization direction. We perceive that the 1T phase is the most promising candidate for photovoltaic devices; in particular, the 1T PdSSe system possesses a maximum power conversion efficiency (PCE) of 29.31% if light trapping techniques are used to enhance absorbance. Amongst the 1OT materials, PdS2 features the highest PCE of 8.38%. Our results constitute the first step to encourage experimental studies towards the fabrication of Pd-based regular and Janus transition metal dichalcogenides photoabsorbers and give hints of how to increase the PCE of such materials.