Molybdenum Selenide Research Articles

Tribological properties of biocompatible molybdenum selenide nanoparticles as water lubrication additives for ultra-high molecular weight polyethylene/304 stainless steel contact

A hydrothermal method was adopted to synthesize molybdenum selenide (MoSe2) nanoparticles, which exhibited excellent dispersibility and biocompatibility in water. The morphology and structures of the MoSe2 nanoparticles were analyzed using scanning electron microscopy and transmission electron microscopy and were found to be flower-like. Furthermore, ball-on-disk tribological experiments were conducted using a UMT-2 tribometer to evaluate the lubrication effects of MoSe2 nanoparticles as an additive for water. The results indicated that the addition of MoSe2 nanoparticles in water could decrease the friction coefficient by 55.4 %, and the wear rate also decreased by 65.8 %. The good anti-friction and anti-wear properties of MoSe2 nanoparticles were ascribed to the layered structure that easily slipped and the filling and patching effect on the disk surface caused by these nanoparticles. MoSe2 water lubricants are expected to be used in real-life applications.

Regulating electronic structure and adsorptivity in molybdenum selenide for boosting electrocatalytic water splitting

Rationally designing highly efficient, cost-effective electrocatalysts towards overall water splitting to substitute noble-metal-based catalysts currently is still an outstanding challenge for renewable energy conversion. Herein, we demonstrate multiscale regulation of MoSe2 by CoSe tailoring for achieving significantly increased activity as a bifunctional electrocatalyst for highly efficient overall water splitting. X-ray absorption near-edge structure (XANES) and ultraviolet photoelectron spectroscopy (UPS) measurements unravel electron transfer from CoSe to MoSe2 as well as the increase of atomic disorder degree and the decrease of coordination number for MoSe2, thus facilitating efficient and fast interfacial charge transport and meanwhile providing more electrocatalytic active sites. Moreover, the introduced CoSe species not only improves the water adsorption/dissociation capability of MoSe2 by providing additional water adsorption sites, which is crucial for subsequent fast H2 generation, but also promotes MoSe2 to realize bifunctional behavior. Besides, density functional theory (DFT) calculations further reveal that CoSe modification for MoSe2 could evidently tailor d-band center of MoSe2 and accordingly significantly reduce hydrogen-adsorption Gibbs free energy (ΔGH*) of MoSe2 from 0.78 to 0.16 eV, along with an enhanced electronic conductivity owing to the increased electronic states near the Fermi level based on density of states (DOSs). This work gives a deeper insight for the relationship between multiscale regulation strategy and intrinsic activity of materials.

Molecular-level insights into the immobilization of vapor-phase mercury on Fe/Co/Ni-doped hierarchical molybdenum selenide

A novel and efficient adsorbent (TM-MoSe2, TM = Fe, Co, Ni) for mercury removal was developed and studied. The adsorption of mercury species (Hg0, HgCl, and HgCl2) and the oxidation of Hg0 by HCl on TM-MoSe2 (001) surface were explored at molecular level by density functional theory (DFT). The results shown that the Hg0 adsorption capacity of MoSe2 was improved by the doping of Fe/Co/Ni, which was also confirmed by experiments. The initial Hg0 removal efficiency of MoSe2-based adsorbents reached 96.4–100.0%. In addition, HgCl was mainly adsorbed on TM-MoSe2 (001) surface in the form of dissociation. The escape of Hg atom from HgCl resulted in the release of Hg0 again. However, HgCl2 could be fixed well on the surface of adsorbent through molecular adsorption or dissociative adsorption. For the oxidation process of Hg0 by HCl, it abided with the Langmuir–Hinshelwood mechanism. In comparison with direct oxidation (Hg → HgCl2), two-step pathway (Hg → HgCl → HgCl2) was an achievable reaction route with lower energy. Furthermore, the Hg → HgCl process was the rate-limiting step of the two-step pathway. The proposed adsorption and oxidation mechanism of mercury species on TM-MoSe2 (001) provide advanced strategies on the development of adsorbents for industrial mercury removal.

Iron molybdenum selenide supported on reduced graphene oxide as an efficient hydrogen electrocatalyst in acidic and alkaline media

It is of great significance to develop inexpensive and high-efficiency electrocatalysts for the hydrogen evolution reaction (HER). In this work, we synthesized iron molybdenum selenide (FeSe2-MoSe2) loaded on reduced graphene oxide (FeSe2-MoSe2/rGO) by a one-step hydrothermal method. We further optimized the Fe/Mo ratio and determined the best ratio to be 1-1. In acidic (or alkaline) solution, the optimized FeSe2-MoSe2(1-1)/rGO has a small Tafel slope of 55 (or 80) mV dec−1 and needs an overpotential of 101 (or 178) mV to achieve 10 mA cm−2. These good properties are mainly due to the structure of bimetallic selenides combining rGO. Moreover, rGO enhances the electrical conductivity. Furthermore, the synergistic effect between FeSe2-MoSe2(1-1) and rGO results in better HER performance. Density functional theory (DFT) calculation proves that FeSe2-MoSe2(1-1)/rGO has a small work function. Based on our reasonable design and analysis, FeSe2-MoSe2(1-1)/rGO is expected to be an efficient and robust catalyst for large-scale applications.

Tungsten-Modulated Molybdenum Selenide/Graphene Heterostructure as an Advanced Electrode for All-Solid-State Supercapacitors.

Transition metal dichalcogenides (TMDs) have attracted widespread attention due to their excellent electrochemical and catalytic properties. In this work, a tungsten (W)-modulated molybdenum selenide (MoSe2)/graphene heterostructure was investigated for application in electrochemistry. MoSe2/graphene heterojunctions with low-doped W compositions were synthesized by a one-step hydrothermal catalysis approach. Based on the conducted density functional theory (DFT) calculations, it was determined that inserting a small amount of W (≈5%) into the MoSe2/graphene heterostructure resulted in the modification of its lattice structure. Additionally, an increase in the distance between layers (≈8%) and a decrease in the adsorption energy of the potassium ions (K+) (≈−1.08 eV) were observed following W doping. Overall, the electrochemical performance of the MoSe2/graphene hybrid was enhanced by the presence of W. An all-solid-state supercapacitor device prepared using electrodes based on the W-doped MoSe2/graphene composite achieved excellent capacitance of 444.4 mF cm−2 at 1 mV s−1. The results obtained herein revealed that the MoSe2/graphene hybrid exhibiting low W composition could be valuable in the field of energy storage and isoelectronic doping of TMDs.

A robust 3D self-powered photoelectrochemical type photodetector based on MoSe2 nanoflower

Molybdenum selenide (MoSe2) has been extensively studied in recent years due to its strong absorption for sunlight and unique band structure. Herein, a self-assembly three-dimensional (3D) MoSe2 nanoflowers were prepared by a two-step process. Significantly, the photodetection device based on MoSe2 nanoflowers exhibited a maximum responsivity about 12.39 µA W−1 and a rapid photo-response time about 0.15 s at 0 V bias under simulated sunlight exposure benefiting from its large specific surface area and unique morphologic structure. Meanwhile, we demonstrated the outstanding stability after 2 weeks of the photodetection device. In this way, the MoSe2 nanoflower-based photodetectors enriched the basic research of molybdenum selenide and provided some reference for the following researches based on molybdenum selenide.

Superoxide radicals dominated visible light driven peroxymonosulfate activation using molybdenum selenide (MoSe2) for boosting catalytic degradation of pharmaceuticals and personal care products

In recent years, molybdenum disulfides (MoS2) have been widely recognized as a promising catalyst or cocatalyst in Advanced Oxidation Processes (AOPs); however, the discharge of hydrogen sulfide (H2S) after catalytic process is still a key issue that needs to be addressed. Hence, in this study, a superoxide radical (O2−) dominated visible-light-driven peroxymonosulfate activation process has been established by adopting molybdenum selenide (MoSe2) to replace MoS2 in order to dramatically enhance the catalytic degradation efficiency of three types of pharmaceuticals and personal care products (PPCPs) (e.g., ibuprofen, benzophenone-3 and carbamazepine). This enhancement is due to its exposed surface metallic Mo4+ ions, accompanied with the oxidization to Mo5+ and Mo6+ for further participating in the decomposing of PMS, as well as the photo-generated electrons playing a prominent role in reducing the Mo5+ and Mo6+ back to Mo4+. Scavenger tests and electron paramagnetic resonance (EPR) identify the O2− as the primary reactive oxygen species (ROS) in the MoSe2/PMS system, and singlet oxygen (1O2) is mainly derived from the transformation of O2−. Density Functional Theory (DFT) is used to explain the elongation of OO bond in the PMS molecule that would facilitate the generation of sulfate radicals and hydroxyl radicals in both of MoSe2 catalyzed PMS system and cocatalyzed Fe(II) or Fe(III)/PMS systems. Ultimately, the MoSe2/PMS system is also applicable for the treatment of actual sewage. This work highlights the important role of photo-generated electrons and molybdenum ions in PMS reduction and oxidation, and establishes theoretical support for further relevant studies.

Facile preparation of metallic 1T phase molybdenum selenide as cocatalyst coupled with graphitic carbon nitride for enhanced photocatalytic H2 production

Low-cost, highly active and efficient alternative co-catalysts that can replace precious metals such as Au and Pt are urgently needed for photocatalytic hydrogen evolution reaction (HER). Herein, we show that 1T phase MoSe2 can act as the co-catalyst in the 1T-MoSe2/g-C3N4 composites and we synthesize this composite by a one-step hydrothermal method to promote photocatalytic H2 generation. Our prepared 1T-MoSe2/g-C3N4 composite exhibits highly enhanced photocatalytic H2 production compared to that of g-C3N4 nanosheets (NSs) only. The 7 wt%-1T-MoSe2/g-C3N4 composite presents a considerably improved photocatalytic HER rate (6.95 mmol·h−1·g−1), approximately 90 times greater than that of pure g-C3N4 (0.07 mmol·h−1 g−1). Moreover, under illumination at λ = 370 nm, the apparent quantum efficiency (AQE) of the 7 wt%-1T-MoSe2/g-C3N4 composite reaches 14.0%. Furthermore, the 1T-MoSe2/g-C3N4 composites still maintain outstanding photocatalytic HER stability.

2D gallium molybdenum selenide grown on a hollow carbon nanofibrous aerogel for high-efficiency electroreduction of nitrogen: Optimized basal plane activity via selenium vacancy modulation

Herein, a novel, Se-vacancy-modulable Ga–Mo–Se layered compound (GayMo1–ySe2–x) is synthesized by rational incorporation of two different kinds of 2D chalcogenides, i.e., transition metal dichalcogenide (MoSe2) and post-transition metal monochalcogenide (GaSe). The strained effect originating from their lattice misfit (∼13 %) and the electron nonequilibrium between Mo4+ and Ga2+ induce abundant Se vacancies, whose concentration can be arbitrarily modulated to optimize the basal plane activity. Moreover, a highly porous and conductive hollow carbon nanofibrous aerogel is synthesized for the first time, which serves as an ideal matrix for the in-situ growth of 2D GayMo1–ySe2–x due to integrated 3D percolation network and sufficient electrode–electrolyte contact. The unique architecture and optimized activity contribute to an advanced catalyst towards high-efficiency N2 fixation, delivering an NH3 yield of 2.57 × 10–10 mol s–1 cm–2 and a Faradaic efficiency of 26.5 % at –0.3 V vs. RHE in 0.1 M Na2SO4.

Adsorption-improved MoSe2 nanosheet by heteroatom doping and its application for simultaneous detection and removal of mercury (II)

Water pollution arising from heavy metal ions continues to be a major environmental problem, which represents a serious threat to human beings and animals worldwide. New materials that can simultaneously detect and remove these toxic ions are urgently required. Herein, nitrogen and sulfur co-doped molybdenum selenide nanosheets (N, S-MoSe2) were prepared and found to be fluorescently responsive to mercury (II) with an improved adsorption capacity (208.33 mg g−1), thereby providing the possibility for the simultaneous detection and removal of mercury (II) in water samples. The great affinity was the result of the complexation of mercury (II) with Se and S atoms in N, S-MoSe2 as well as the electrostatic adsorption of cation mercury (II) on negatively charged N, S-MoSe2. Besides good sensitivity and selectivity toward mercury (II), N, S-MoSe2 displayed a relatively consistent performance under a wide pH range from 3 to 10. The removal efficiency reached 87.5% with fast adsorption kinetics, and N, S-MoSe2 could be reused after simple treatment. Thus, this work is expected to provide new material for the detection and removal of mercury (II) in an aqueous solution and offer an insight into the interaction between heavy metal ions and inorganic nanomaterials.

Hollow Co–Mo–Se nanosheet arrays derived from metal-organic framework for high-performance supercapacitors

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices.

Engineering MoSe2/WS2 Hybrids to Replace the Scarce Platinum Electrode for Hydrogen Evolution Reactions and Dye-Sensitized Solar Cells.

In recent times, two-dimensional transition-metal dichalcogenides (TMDs) have become extremely attractive and proficient electrodes for dye-sensitized solar cells (DSSCs) and water electrolysis hydrogen evolution as alternatives to the scarce metal platinum (Pt). The active TMD molybdenum selenide (MoSe2) and tungsten disulfide (WS2) are inspiring systems owing to their abundance of active sulfur and selenium sites, but their outputs are lacking due to their inactive basal planes and ineffective transport behavior. In this work, van der Waals interrelated MoSe2/WS2 hybrid structures were constructed on conducting glass substrates by chemicophysical methodologies. For the first time, the constructed MoSe2/WS2 structures were effectively used as a counter electrode for DSSCs and an active electrode for hydrogen evolution to replace the nonabundant Pt. The assembled DSSCs using the designed MoSe2/WS2 heterostructure counter electrode provided a superior power-conversion efficiency of 9.92% and a photocurrent density of 23.10 mA·cm-2, unmatchable by most of the TMD-based structures. The MoSe2/WS2 heterostructure displayed excellent electrocatalytic hydrogen evolution behavior with a 75 mV overpotential to drive a 10 mA·cm-2 current density, a 60 mV·dec-1 Tafel slope, and an over 20 h durable process in an acidic medium. The results demonstrated the advantages of the MoSe2/WS2 hybrid development for generating interfacial transport and active facet distribution and enriching the electrocatalytic activity for DSSCs and the water-splitting hydrogen evolution process.

Engineered MoSe2/WSe2 based heterostructures for efficient hydrogen evolution reaction

Electrocatalytic water splitting into hydrogen and oxygen using semiconducting heterogeneous nanostructures is a promising and emerging technology. Semiconductor materials based heterogeneous nanostructures have attracted much attention to be used as catalysts, co-catalysts, photocatalysts and photo absorbers. The present work deals with the investigation of heterostructures of molybdenum selenide (MoSe2) and tungsten selenide (WSe2) nanosheets prepared through liquid exfoliation method as electrocatalysts for the hydrogen evolution reaction (HER). Our experimental studies reveal that MoSe2/WSe2 heterostructures synthesized using hydrogen peroxide (H2O2) exhibits superior HER performance. These novel structures leads to the exposure of more catalytically active sites and maintains effective electron transport, resulting in a small Tafel slope of 80 mV/decay and large electrochemical surface area (ECSA) of 87. This low-cost method finds application in high-performance HER electrocatalyst.

Modeling the ternary chalcogenide Na2MoSe4 from first-principles

In the ongoing pursuit of inorganic compounds suitable for solid-state devices, transition metal chalcogenides have received heightened attention due to their physical and chemical properties. Recently, alkali-ion transition metal chalcogenides have been explored as promising candidates to be applied in optoelectronics, photovoltaics and energy storage devices. In this work, we present a theoretical study of sodium molybdenum selenide (Na2MoSe4). First-principles computations were performed on a set of hypothetical crystal structures to determine the ground state and electronic properties of Na2MoSe4. We find that the equilibrium structure of Na2MoSe4 is a simple orthorhombic (oP) lattice, with space group Pnma, as evidenced by thermodynamics. Finally, meta-GGA computations were performed to model the band structure of oP Na2MoSe4 at a predictive level. We employ the Tran–Blaha modified Becke–Johnson potential to demonstrate that oP Na2MoSe4 has a direct bandgap at the Γ point that is suitable for optoelectronics. Our results provide a foundation for future studies concerned with the modeling of inorganic and hybrid organic–inorganic materials chemically analogous to Na2MoSe4.

Enhanced optical response of InSe nanosheet devices decorated with CsPbX3 (X = I, Br) perovskite nanocrystals

The combination of several two-dimensional materials opens the door for the creation of cooperative nanodevices with functionalities that complement to each other and even compensate the weaknesses of the individual components. Two-dimensional indium selenide (InSe) shows one of the largest tunability bandgap found in two-dimensional materials with application in optoelectronics. However, the intrinsic out-of-plane luminescent dipolar nature limits its implementation in devices operating in vertical configuration. All-inorganic CsPbX3 (X = Br, I) cubic nanoparticles offer high absorption and emission quantum yields and great integrability with two-dimensional materials. Combining these two compounds, it is found that InSe-perovskite nano-heterostructures enhances the photoluminescence of the InSe side of the device, as compared to the bare InSe nanosheet, due to the multi-oriented down-shift light conversion mediated by the perovskite-nanocrystals. Similar nanostructures have been prepared by using Molybdenum Selenide (MoSe2), but a reduction of its photoluminescence is observed in this case due to its well-known in-plane dipole orientation.

Raman Tensor of van der Waals MoSe2.

Molybdenum selenide (MoSe2) is a van der Waals layered crystal with both the anisotropic light absorption and light scattering outside its surface. At present, the study of the Raman tensor of MoSe2, which affects and even determines the inelastic light scattering's anisotropy, is not sufficient. In this research, with the aim of studying the out-of-plane anisotropy, we performed systematic angle-resolved polarized Raman (APR) spectroscopy and abstracted complete Raman tensors both experimentally and theoretically. In addition, according to first-principles calculations, in different conditions of laser excitation, MoSe2 has various Raman tensor forms, of which the phase difference between Raman tensor elements of the A1g mode is a particular one. By studying the anisotropic optical absorption properties, we confirmed that it is the dispersion and absorption of MoSe2 under different pump light that lead to the photon-energy-dependent phase differences.

Increasing wear resistance of the hinge guide compressor in aircraft engine

The article is devoted to the problem of increasing reliability and a service life of the cylindrical hinge for turning the blades of a guide axial compressor of aircraft engines under sliding friction without lubrication. The prospects of using nanostructured crystals of zirconium dioxide partially stabilized by yttrium oxide are justified. High anti-friction properties of the hinge are provided by the selection of the counterface material. Particular attention is paid to the resistance to scoring of the studied friction pairs. It has been established that the most promising counterfaces for the crystals of zirconium dioxide are molybdenum selenide coatings and alpha-titanium alloys. A post-publication change was made to this article on 11 Jun 2020 to correct the pdf so that it matched the webpage.

Molybdenum Selenide nanosheets Surrounding nickel Selenides Sub-microislands on nickel foam as high-performance bifunctional electrocatalysts for water Splitting

Transition metal selenides supported on three-dimensional metal foams have attracted extensive attention as promising electrocatalysts for water splitting. Herein, the direct growth of misaligned and intertwined molybdenum selenide nanosheets surrounding nickel selenide sub-microislands on nickel foam (denoted as Mo–Ni–Se@NF) was demonstrated via a simple one-step hydrothermal approach. The as-prepared Mo–Ni–Se@NF demonstrates excellent electrocatalytic activity for hydrogen evolution reaction (HER) in alkaline electrolyte, demanding a low overpotential of 113 mV to achieve the current density of 10 mA cm−2, and a small Tafel slope of 85.7 mV dec−1. It also displays good catalytic performance towards oxygen evolution reaction (OER) with an overpotential of 397 mV at the current density of 100 mA cm−2, and a Tafel slope of 44.9 mV dec−1. Moreover, when applied as both anode and cathode in a two-electrode electrolyzer for overall water splitting, low voltages of 1.583 and 2.098 V are allowed to reach the current densities of 20 and 100 mA cm−2, respectively. Large electrochemical surface area, low electron-transfer resistance, and good stability were demonstrated during the test. The superior activity of Mo–Ni–Se@NF is largely attributed to the seamless integration of the three-dimensional and conductive Ni foam substrate, the direct growth of molybdenum selenide nanosheets on Ni foam with sufficient active sites, and the metallic nickel selenide sub-microislands with good activity and electronic conductivity for the electrons transfer from the substrate to the active sites on molybdenum selenide nanosheets during electrocatalytic process. This work can inspire the optimal design of bimetal selenides on metal foam as efficient and low-cost electrocatalysts for overall water splitting.

Hierarchical 3D Oxygenated Cobalt Molybdenum Selenide Nanosheets as Robust Trifunctional Catalyst for Water Splitting and Zinc-Air Batteries.

The development of hierarchical nanostructures with highly active and durable multifunctional catalysts has a new significance in the context of new energy technologies of water splitting and metal-air batteries. Herein, a strategy is demonstrated to construct a 3D hierarchical oxygenated cobalt molybdenum selenide (O-Co1- x Mox Se2 ) series with attractive nanoarchitectures, which are fabricated by a simple and cost-effective hydrothermal process followed by an exclusive ion-exchange process. Owing to its highly electroactive sites with numerous nanoporous networks and plentiful oxygen vacancies, the optimal O-Co0.5 Mo0.5 Se2 could catalyze the hydrogen evolution reaction and oxygen evolution reaction effectively with a low overpotential of ≈102 and 189 mV, at a current density of 10 mA cm-2 , respectively, and exceptional durability. Most importantly, the O-Co0.5 Mo0.5 Se2 ||O-Co0.5 Mo0.5 Se2 water splitting device only entails a voltage of ≈1.53 V at a current density of 10 mA cm-2 , which is much better than benchmark Pt/C||RuO2 (≈1.56 V). Furthermore, O-Co0.5 Mo0.5 Se2 air cathode-based zinc-air batteries exhibit an excellent power density of 120.28 mW cm-2 and exceptional cycling stability for 60 h, superior to those of state-of-art Pt/C+RuO2 pair-based zinc-air batteries. The present study provides a strategy to design hierarchical 3D oxygenated bimetallic selenide-based multifunctional catalysts for energy conversion and storage systems.

Few Layer Molybdenum Selenide Saturable Absorber using Optical Deposition Technique for Q-switched Ytterbium Pulses Laser Generation

We have successfully generated a Q-switched ytterbium-doped fiber laser pulses using few layers of Molybdenum Selenide (MoSe2) as saturable absorber (SA). The setup was a ring fiber laser cavity with few-layer MoSe2, deposited onto a fiber ferrule using an optical deposition technique. A stable pulses started at input power of 68.8 mW with repetition rate ranging from 14.2 kHz to 34.0 kHz was achieved with highest pulse energy, shortest pulse width and highest output power of 3.6 nJ, 4.4 µs and 0.12 mW were observed, respectively.