In-situ Grown of MoS 2 /RGO/MoS 2 @Mo Nanocomposite and Its supercapacitor Performance

Synthesis of Binder-Free, Low-Resistant Randomly Orientated Nanorod/Sheet ZnS-MoS2 as Electrode Materials for Portable Energy Storage Applications

The scientific community needs to conduct research on novel electrodes for portable energy storage (PES) devices like supercapacitors (S-Cs) and lithium-ion batteries (Li-ion-Bs) to overcome energy crises, especially in rural areas where no electrical poles are available. Herein, the nanostructured MoS2 and ZnS-MoS2 E-Ms consisting of nanoparticles/rods/sheets (N-Ps-Rs-Ss) are deposited on hierarchical nickel foam by a homemade chemical vapor deposition (H-M CVD) route. The X-ray diffraction patterns confirm the formation of polycrystalline films growing along various orientations, whereas the field-emission scanning electron microscope analysis confirms the formation of N-Ps-Rs-Ss. The change in structural and microstructural parameters indicates the existence of defects improving the energy storage ability of the deposited ZnS-MoS2@Ni-F electrodes. The specific capacitances of MoS2@Ni-F and ZnS-MoS2@Ni-F electrodes are found to be 1763 and 3565 F/g at 0.5 mV/s and 1451 and 3032 F/g at 1 A/g, respectively. The growing behavior of impedance graphs indicates their capacitive nature; however, the shifting of impedance curves toward y-axis indicates that the increasing diffusion rates due to the formation of nanostructures of ZnS-MoS2 results in low impedance. An excellent energy storage performance, minimum capacity fading, and improved electrical conductivity of the deposited E-Ms are due to the combined contributions of the electrical double layer and pseudocapacitor nature, which is again confirmed by theoretical Dunn's model. The absence of charge transfer resistance and good capacitance retention (95%) even after 10,000 cycles indicates that the deposited E-Ms are better for PES devices like S-Cs and Li-ion-Bs than MoS2 E-Ms. The assembled asymmetric supercapacitor device exhibited the maximum specific capacitance = 996 F/g, energy density = 354-285 W h/kg, power density = 2400-24,000 W/kg, capacitance retention = 95% and Coulombic efficiency = 100% even after a long charging-discharging of 10,000 cycles.

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.

Detection of Cd2+ based on Nano-Fe3O4/MoS2/Nafion/GCE sensor

It is necessary to detect cadmium ions in seawater with high sensitivity because the pollution of cadmium ions seriously endangers the health and life of human beings. Nano-Fe3O4/MoS2/Nafion modified glassy carbon electrode was prepared by a drop coating method. The electrocatalytic properties of Nano-Fe3O4/MoS2/Nafion were measured by Cyclic Voltammetry (CV). Differential Pulse Voltammetry (DPV) was used to study the stripping Voltammetry response of the modified electrode to Cd2+. The optimal conditions were determined: In 0.1 mol/L HAc-NaAc solution, the solution pH was 4.2, the deposition potential was - 1.0 V, and the deposition time was 720 s, the membrane thickness was 8 μL. Under the optimum condition, the linear relation of Cd2+ concentration was found in the range of 5-300 μg/L, and the detection limit was 0.053 μg/L. The recovery of Cd2+ in seawater ranged from 99.2 to 102.9%. A composite material with simple operation, rapid response and high sensitivity was constructed for the determination of Cd2+ in seawater.

Microstructural tailoring of porous few-layer graphene-like biochar from kitchen waste hydrolysis residue in molten carbonate medium: Structural evolution and conductive additive-free supercapacitor application

Biomass-derived graphene-like material is a promising candidate for supercapacitor electrodes, while it is critical to controllably convert biomass into structure-tunable graphene. Herein, few-layer graphene-like biochar (FLGBS) was successfully fabricated from waste biomass in molten carbonate medium. Molten carbonate acted as the effective catalyst for graphitizing and the liquid medium for microcrystal relinking to achieve the rearrangement of carbon structure. It was found that the stacking of graphene layer and formation of porous structure were influenced by the volume of reaction medium and biomass pre‑carbonation. Namely, increasing the dosage of molten K₂CO₃ was in favor to form few layer-type graphene structure, but excess dosage could destroy the nanopore structure to expand the aperture. In addition, pre‑carbonation at high temperature impeded the exfoliation of graphene layers. When FLGBSs were applied to fabricate conductive additive-free electrode, they displayed a superior supercapacitor performance (up to 237.4 F g^-1 at 0.5 Ag^-1). This excellent performance should be attributed to the large specific surface area, hierarchical pore structure and graphene-like structure. In short, this work could help to get insights into the structural evolution of biomass carbon to graphene-like biochar in molten carbonate medium and achieve the tailoring of microstructure for further application in energy storage.

Omnidirectionally irradiated three-dimensional molybdenum disulfide decorated hydrothermal pinecone evaporator for solar-thermal evaporation and photocatalytic degradation of wastewaters

Although most solar steam generation devices are effective in desalinating seawater and purifying wastewaters with heavy metal ions, they are ineffective in degrading organic pollutants from wastewaters. Herein, we design novel solar-driven water purification devices by decoration of three-dimensional pinecones with MoS₂ nanoflowers via a one-step hydrothermal synthesis for generating clean water. The vertically arrayed channels in the central rachis and the unique helically arranged scales of the hydrothermal pinecone can not only transfer bulk water upward to the evaporation surface, but also absorb more solar light from different incident angles for solar-thermal evaporation and photodegradation of wastewaters under omnidirectional irradiations. The decorated MoS₂ nanoflowers can not only enhance the solar-thermal energy conversion efficiency, but also decompose organic pollutants in the bulk water by their photocatalytic degradation effects. The resultant hydrothermal pinecone with in situ decorated MoS₂ (HPM) evaporator exhibits a high evaporation rate of 1.85 kg m^-2 h^-1 under 1-sun irradiation with a high energy efficiency of 96 %. During the solar-driven water purification processes, the powdery HPM can also photodegrade organic pollutants of methylene blue and rhodamine B with high removal efficiencies of 96 % and 95 %, respectively. For practical demonstration, by floating in the methylene blue solution under 1-sun irradiation, the bulky HPM can generate clean water by simultaneous solar-thermal evaporation and photocatalytic degradation. The integration of solar steam generation and photocatalytic degradation mechanisms makes the HPM evaporator highly promising for practical high-yield purification of wastewaters.

One-Step Hydrothermal Synthesis of MoO2/MoS2 Nanocomposites as High-Performance Electrode Material for Supercapacitors

By only changing the ratio of Mo to S source, a distinctive single phase MoO2 or MoS2 and MoO2/MoS2 nanocomposites (NCs) are obtained through a simple one-step hydrothermal method based on CH4N2S as a sulfur source and (NH4)6Mo7O24·4H2O as a source of Mo in oxalic acid. The effect of ratio of Mo to S source on the composition, structure, and electrochemical performance are systematically researched. Due to its unique design, abundant macropores active sites in MoO2/MoS2 NCs induce superior rate property (55.30% capacitance retention to 20 from 1 A g-1) and larger specific capacitance (1667.3 F g-1 at 1 A g-1) and longer cycle life (94.75% after 5000 cycles) as used directly as an electrode. Furthermore, at a power density of 225 W kg-1, a maximal energy density of 21.85 Wh kg-1 is provided by the asymmetric supercapacitor (MoO2/MoS2//AC). The capacitance of asymmetric supercapacitor (ASC) is remarkably enhanced by 129.02% under 5000 cycles at a current density of 1.5 A g-1, demonstrating outstanding cycle property. These results imply the prepared MoO2/MoS2 NCs have promising applications in advanced energy storages. It is important and should be noted that NCs of oxide and sulfide are prepared with only a simple one-step process.

Rhenium Sulfide Incorporated in Molybdenum Sulfide Nanosheets for High-Performance Symmetric Supercapacitors with Enhanced Capacitance

Supercapacitors are considered potential energy storage devices and have drawn significant attention due to their superior intrinsic advantages. Herein, we report the synthesis of ReS₂ embedded in MoS₂ nanosheets (RMS-31) by a hydrothermal technique. The prepared RMS-31 electrode material demonstrated superior pseudocapacitive behavior in 1 M KOH electrolyte solution, which is confirmed by the heterostructure of RMS-31 nanosheet architectures. RMS-31 has a specific capacitance of 244 F g^-1 at a current density of 1 A g^-1 and a greater areal capacitance of 540 mF cm^-2 at a current density of 5 mA cm^-2. The symmetric supercapacitor device with the RMS-31 electrode delivers an energy density of 28 W h cm^-2 with a power density of 1 W cm^-2 and reveals long-term stability at a constant current density of 5 mA cm^-2 for 10,000 cycles while accomplishing a retention of 66.5%. The high performance of this symmetric device is attributed to the synergistic effect of ReS₂ and MoS₂ and the presence of the metallic 1T-MoS₂ phase in the RMS-31 electrode. To the best of our knowledge, this is the first report of increasing the interlayer spacing of 2H-MoS₂ by incorporating ReS₂ for symmetric supercapacitor applications.

Microstructure and Mechanical Properties of Zinc Matrix Biodegradable Composites Reinforced by Graphene

This work used spark plasma sintering (SPS) to prepare graphene nanosheets (GNS) reinforced zinc matrix composites. The influence of GNS on the microstructure and mechanical properties of zinc matrix composites was studied. The results show that the GNS/Zn composites prepared by SPS have a dense structure and good interface bonding, and GNS are uniformly distributed in the zinc matrix. Adding GNS can significantly improve the mechanical properties of the zinc matrix. When 0.7 wt% GNS are added, the comprehensive mechanical properties of the composite material are improved. The ultimate tensile strength is 254 MPa, and the Vickers hardness is 65 HV, which are 126 and 20.3% higher than those of pure zinc (112 MPa and 54 HV), respectively. The strengthening mechanisms of GNS/Zn composites are mainly load transfer of GNS and dislocation strengthening caused by coefficient of thermal expansion (CTE) mismatch. In addition, the biodegradability of GNS/Zn composites was evaluated by electrochemical measurement and immersion test. The results show that adding GNS to the zinc matrix will accelerate the degradation rate of the composite material. But the degradation rate can be controlled by the content of GNS. Its degradation rate is in the range of 69–301 μm/a, an ideal degradation rate as an orthopedic implant material.

MoO2 nanoparticles confined in N,P-codoped graphene aerogels with excellent pseudocapacitance performance

In this work, MoO2@NPGA nanocomposites were successfully prepared via a simple hydrothermal and calcination route. The as-prepared MoO2@NPGA composites exhibit a synergistic effect between MoO2 and N,P-codoped graphene aerogels, which can significantly improve the electrochemical performance of the MoO2@NPGA electrodes. Moreover, the results also proved that the mass loading of MoO2 has a huge effect on the electrochemical properties of MoO2@NPGA composites. With an appropriate amount of MoO2, the MoO2@NPGA composite shows a high specific capacitance (335 F g−1 at 1 A g−1) and excellent cycle stability (capacitance remains at 88% after 6000 cycles). Furthermore, the assembled symmetric supercapacitor displays a high energy density of 23.75 W h kg−1 at a power density of 300 W kg−1 and can maintain an energy density of 17.1 W h kg−1 when the power density reaches up to 6005 W kg−1.

Synergistic effect of MoS2 and Fe3O4 decorated reduced graphene oxide as a ternary hybrid for high-performance and stable asymmetric supercapacitors

Today, two-dimensional materials for use in energy devices have attracted the attention of researchers. Molybdenum disulfide is promising as an electrode material with unique physical properties and a high exposed surface area. However, there are still problems that need to be addressed. In this study, we prepared a hybrid containing MoS₂, Fe₃O₄, and reduced graphene oxide (rGO) by a two-step hydrothermal method. This nanocomposite is well structurally and morphologically identified, and its electrochemical performance is then evaluated for use in supercapacitors. According to the galvanostatic charge-discharge results, this nanocomposite shows a good specific capacity, equivalent to 527 F g^-1 at 0.5 mA cm^-2. The results of the multi-cycle stability test (5000 cycles) indicate a significant stability rate capability, with 93% of the electrode capacity remaining after 5000 cycles. The reason for this could be the synergistic effect between rGO and MoS₂ as well as between molybdenum and iron in the faradic reaction in the charge storage process. Fe₃O₄ and MoS₂ provide electroactive sites for the faradic process and electrolyte accessibility and rGO supply conductivity.

One-Pot Synthesis of W2C/WS2 Hybrid Nanostructures for Improved Hydrogen Evolution Reactions and Supercapacitors

Tungsten sulfide (WS2) and tungsten carbide (W2C) are materialized as the auspicious candidates for various electrochemical applications, owing to their plentiful active edge sites and better conductivity. In this work, the integration of W2C and WS2 was performed by using a simple chemical reaction to form W2C/WS2 hybrid as a proficient electrode for hydrogen evolution and supercapacitors. For the first time, a W2C/WS2 hybrid was engaged as a supercapacitor electrode and explored an incredible specific capacitance of ~1018 F g-1 at 1 A g-1 with the outstanding robustness. Furthermore, the constructed symmetric supercapacitor using W2C/WS2 possessed an energy density of 45.5 Wh kg-1 at 0.5 kW kg-1 power density. For hydrogen evolution, the W2C/WS2 hybrid produced the low overpotentials of 133 and 105 mV at 10 mA cm-2 with the small Tafel slopes of 70 and 84 mV dec-1 in acidic and alkaline media, respectively, proving their outstanding interfaced electrocatalytic characteristics. The engineered W2C/WS2-based electrode offered the high-performance for electrochemical energy applications.

Hybrid phase 1T/2H-MoS2 with controllable 1T concentration and its promoted hydrogen evolution reaction

MoS2 has been investigated as a low-cost alternative to Pt in the electrochemical hydrogen evolution reaction. One of the promising methods to further activate MoS2 is phase engineering. MoS2 generally exhibits two kinds of crystalline phases: hexagonal 2H phase and octahedral 1T phase. 1T-MoS2 exhibits much better chemical/physical properties than natural semiconductor 2H-MoS2. However, 1T-MoS2 is metastable and its synthesis is still a challenge. Hybrid 1T/2H-MoS2 has been synthesized under relatively mild conditions, but controlling the 1T/2H ratio is still an issue which has not been discussed in detail. In this study, the synthesis methods of hybrid phase 1T/2H-MoS2 with controllable 1T concentration are investigated. The electrochemical hydrogen evolution reaction is then evaluated for 1T/2H-MoS2 with different 1T concentrations by performing both experiments and theoretical calculations.

Synthesis of Double-Layer Nitrogen-Doped Microporous Hollow Carbon@MoS2/MoO2 Nanospheres for Supercapacitors

In this work, a double-layer nitrogen-doped microporous hollow carbon@MoS₂/MoO₂ nanosphere (NCs@MoS₂/MoO₂) is prepared via a facile method utilizing Mo-mediated in situ growth on polyaniline-coated polystyrene spheres and carbonization process. Because of its unique structure, the as-obtained NCs@MoS₂/MoO₂ exhibits a high specific capacitance (569 F g^-1 at 1 A g^-1) and excellent rate performance (54.8% capacitance retention) from 1 A g^-1 (569 F g^-1) to 20 A g^-1 (312 F g^-1) when directly used as a supercapacitor electrode. In a two-electrode system, it exhibits 81% capacitance retention and 91.4% Coulombic efficiency even after 5000 cycles at 5 A g^-1. Therefore, the prepared NCs@MoS₂/MoO₂ shows to be an outstanding material for supercapacitor electrodes.

Layer-structured nanohybrid MoS2@rGO on 3D nickel foam for high performance energy storage applications

MoS₂@reduced graphene oxide on 3D nickel foam was synthesized using an inexpensive room-temperature two-step method composed of the layer-by-layer method and solution-based successive ionic layer adsorption and reaction.