Novel design of nickel cobalt boride nanosheets-decorated molybdenum disulfide hollow spheres as efficient battery-type materials of hybrid supercapacitors

Transition metal borides (TMBs) with high theoretical capacitances and excellent electronic properties have attracted much attention as a promising active material of supercapacitors (SCs). However, TMB nanoparticles are prone to conduct self-aggregation, which significantly deteriorates the electrochemical performance and structural stability. To address the severe self-aggregation in TMBs and improve the active material utilization, it is imperative to provide a conductive substrate that promotes the dispersion of TMB during growths. In this work, sheet-like nickel cobalt boride (NCB) was grown on molybdenum disulfide (MoS2) hollow spheres (H-MoS2) by using simple template growth and chemical reduction methods. The resultant NCB/H-MoS2-50 was observed with uniform NCB nanosheets structure on the surface of the H-MoS2 and stronger MB bonding. After optimizing the loading amount of H-MoS2, the optimal composite (NCB/H-MoS2-50) modified nickel foam (NF) exhibits a superior specific capacity (1302 C/g) than that of the NCB electrode (957 C/g) at 1 A/g. Excellent rate capability of 84.8% (1104 C/g at 40 A/g) is also achieved by the NCB/H-MoS2-50 electrode. The extraordinary electrochemical performance of NCB/H-MoS2-50 is credited to the unique nanosheet-covered hollow spheres structure for facilitating ion diffusion and versatile charge storage mechanisms from the pseudocapacitive behavior of H-MoS2 and the Faradaic redox behavior of NCB. Furthermore, a hybrid SC is assembled with NCB/H-MoS2-50 and activated carbon (AC) electrodes (NCB/H-MoS2-50//AC), which operates in a potential window up to 1.7 V and delivers a high energy density of 76.8 W h kg-1 at a power density of 850 W kg-1. A distinguished cycling stability of 93.2% over 20,000 cycles is also obtained for NCB/H-MoS2-50//AC. These findings disclose the significant potential of NCB/H-MoS2-50 as a highly performed battery-type material of SCs.

Tailored Nanoarchitectures: MoS₂/Graphene and MoS2/Graphene Oxide Thin Films via Liquid-Liquid Interfacial Route

The nanostructured assembly of different two-dimensional (2D) materials in specific organization is crucial for developing materials with synergistic properties. In this study, we present a general methodology to prepare thin, transparent and self-assembled films of 2D/2D composites based on molybdenum sulfide (MoS2)/graphene oxide (GO) or MoS2/reduced graphene oxide (rGO), through the liquid/liquid interfacial route. Different nanoarchitectures are obtained by changing simple experimental parameters during the thin film preparation steps. The films were characterized by UV-Vis and Raman spectroscopy, scanning electron microscopy and cyclic voltammetry, evidencing that the experimental route used plays a role in the organization and properties of the assembled nanoarchitectures. Likewise, nanostructures of MoS2/GO and MoS2/rGO prepared through the same route have different organizations due to the different interactions between the materials. This showcases the potential of the technique to prepare tailored nanoarchitectures with specific properties for various applications, paving the way for innovative nanotechnology and materials science applications.

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.

Synergetic enhancement effect of two-dimensional MoS2 nanosheets and metal organic framework-derived porous ZnO nanorods for photodegradation performance

Two-dimensional transition metal dichalcogenides and semiconductor metal oxides have shown great potential in photocatalysis. However, their stability and efficiency need to be further improved. In this paper, porous ZnO nanorods with high specific surface area were prepared from metal-organic framework ZIF-8 by a simple hydrothermal method. A MoS2/ZnO composite was constructed by loading MoS2 onto the surface of porous ZnO nanorods. Compared with ZnO materials prepared by other methods, MoS2/ZnO prepared in this paper exhibits superior photocatalytic performance. The enhanced photocatalytic activity of the MoS2/ZnO composite can be attributed to the formation of heterojunctions and strong interaction between them, which greatly facilitate the separation of electrons and holes at the contact interface. In addition, due to the wide absorption region of the visible spectrum, MoS2 can greatly broaden the light absorption range of the material after the formation of the composite material, increase the utilization rate of visible light, and reduce the combination of electrons and holes. This study provides a new way to prepare cheap and efficient photocatalysts.

Nanoarchitected graphene/copper oxide nanoparticles/MoS2 ternary thin films as highly efficient electrodes for aqueous sodium-ion batteries

Sodium-ion batteries (SIBs) operating in aqueous electrolyte are an emerging technology that promises to be safer, cheaper, more sustainable and more efficient than their lithium-based counterparts. One of the great challenges associated with this technology is the development of advanced materials with high specific capacity to be used as electrodes. Herein, we describe an ingenious strategy to prepare unprecedented tri-component nanoarchitected thin films with superior performance when applied as anodes in aqueous SIBs. Taking advantage of the broadness and versatility of the liquid-liquid interfacial route, three transparent nanocomposite films comprising graphene, molybdenum sulphide and copper oxide nanoparticles have been prepared. The samples were characterized using several techniques, and the results demonstrated that depending on the specific experimental strategy, different nanoarchitectures are achieved, resulting in different and improved properties. An astonishing capacity of 1377 mA h g-1 at 0.1 A g-1 and a degree of recovery of 100% were observed for the film in which the interactions among the components were optimized. This is among the highest capacity values reported in the literature and demonstrates the potential of these tri-component materials to be used as anodes in aqueous sodium-ion batteries.

Molybdenum disulfide (MoS2) along with graphene nanoplatelets (GNPs) utilized to enhance the capacitance of conducting polymers (PANI and PPy)

Hybrid composites of molybdenum disulfide (MoS2), graphene nanoplatelets (GNPs) and polyaniline (PANI)/polypyrrole (PPy) have been synthesized as cost-effective electrode materials for supercapacitors. We have produced MoS2 from molybdenum dithiocarbamate by a melt method in an inert environment and then used a liquid exfoliation method to form its composite with graphene nanoplatelets (GNPs) and polymers (PANI and PPy). The MoS2 melt/GNP ratio in the resultant composites was 1 : 3 and the polymer was 10% by wt. of the original composite. XRD (X-ray diffraction analysis) confirmed the formation of MoS2 and SEM (scanning electron microscopy) revealed the morphology of the synthesized materials. The electrochemical charge storage performance of the synthesized composite materials was assessed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge (GCCD) measurements. Resultant composites showed enhanced electrochemical performances (specific capacitance = 236.23 F g-1, energy density = 64.31 W h kg-1 and power density = 3858.42 W kg-1 for MoS2 melt 5 mPP at a current density of 0.57 A g-1 and had 91.87% capacitance retention after 10 000 charge-discharge cycles) as compared to the produced MoS2; thus, they can be utilized as electrode materials for supercapacitors.

A graphitic nano-onion/molybdenum disulfide nanosheet composite as a platform for HPV-associated cancer-detecting DNA biosensors

An electrochemical DNA sensor that can detect human papillomavirus (HPV)-16 and HPV-18 for the early diagnosis of cervical cancer was developed by using a graphitic nano-onion/molybdenum disulfide (MoS₂) nanosheet composite. The electrode surface for probing DNA chemisorption was prepared via chemical conjugation between acyl bonds on the surfaces of functionalized nanoonions and the amine groups on functionalized MoS₂ nanosheets. The cyclic voltammetry profile of an 1:1 nanoonion/MoS₂ nanosheet composite electrode had an improved rectangular shape compared to that of an MoS₂ nanosheet elecrode, thereby indicating the amorphous nature of the nano-onions with sp₂ distancing curved carbon layers that provide enhanced electronic conductivity, compared to MoS₂ nanosheet only. The nanoonion/MoS₂ sensor for the DNA detection of HPV-16 and HPV-18, respectively, was measured at high sensitivity through differential pulse voltammetry (DPV) in the presence of methylene blue (MB) as a redox indicator. The DPV current peak was lowered after probe DNA chemisorption and target DNA hybridization because the hybridized DNA induced less effective MB electrostatic intercalation due to it being double-stranded, resulting in a lower oxidation peak. The nanoonion/MoS₂ nanosheet composite electrodes attained higher current peaks than the MoS₂ nanosheet electrode, thereby indicating a greater change in the differential peak probably because the nanoonions enhanced conductive electron transfer. Notably, both of the target DNAs produced from HPV-18 and HPV-16 Siha and Hela cancer cell lines were effectively detected with high specificity. The conductivity of MoS₂ improved by complexation with nano-onions provides a suitable platform for electrochemical biosensors for the early diagnosis of many ailments in humans.

Morphology-controlled synthesis of MoS2 using citric acid as a complexing agent and self-assembly inducer for high electrochemical performance

Two-dimensional MoS2 with a controllable morphology was prepared via a simple one-step hydrothermal method. Citric acid was used as a complexing agent and self-assembly inducer. The morphology of MoS2 changed from clusters to nanosheets, and, eventually, to stacked nanorods. A formation mechanism is proposed for the observed evolution of the morphology. The nanosheet structure presents a relatively large specific surface area, more exposed active sites and greater 1T phase content compared to the other morphologies. The electrochemical performance tests show that the MoS2 nanosheets exhibit excellent electrochemical behavior. Their specific capacitance is 320.5 F g-1, and their capacitance retention is up to 95% after 5000 cycles at 5 mA cm-2. This work provides a feasible approach for changing the morphology of MoS2 for high efficiency electrode materials for supercapacitors.

The Enhanced Energy Density of rGO/TiO2 Based Nanocomposite as Electrode Material for Supercapacitor

TiO2 electrode material is a poor choice for supercapacitor electrodes because it has low conductivity, poor cyclic stability, and a low capacitance value. It is inevitable to enhance electrode materials of this kind by increasing the surface area and combining high electronic conductivity materials. In the current research work, it was proposed to combine reduced graphene oxide (rGO) as it might provide a large surface area for intercalation and deintercalation, and also, it could establish the shorter paths to ion transfer, leading to a reduction in ionic resistance. The size, surface morphology, and crystalline structure of as-prepared rGO/TiO2 nanocomposites were studied using HRTEM, FESEM, and XRD, respectively. Using an electrochemical workstation, the capacitive behaviors of the rGO/TiO2 electrode materials were assessed with respect to scan rate and current density. The capacitances obtained through cyclic voltammetry and galvanostatic charge-discharge techniques were found to be higher when compared to TiO2 alone. Furthermore, the as-synthesized nanocomposites were able to achieve a higher energy density and better cycle stability.

High-Performance MnO2 Nanowire/MoS2 Nanosheet Composite for a Symmetrical Solid-State Supercapacitor

To improve the production rate of MoS₂ nanosheets as an excellent supercapacitor (SC) material and enhance the performance of the MoS₂-based solid-state SC, a liquid phase exfoliation method is used to prepare MoS₂ nanosheets on a large scale. Then, the MnO₂ nanowire sample is synthesized by a one-step hydrothermal method to make a composite with the as-synthesized MoS₂ nanosheets to achieve a better performance of the solid-state SC. The interaction between the MoS₂ nanosheets and MnO₂ nanowires produces a synergistic effect, resulting in a decent energy storage performance. For practical applications, all-solid-state SC devices are fabricated with different molar ratios of MoS₂ nanosheets and MnO₂ nanowires. From the experimental results, it can be seen that the synthesized nanocomposite with a 1:4 M ratio of MoS₂ nanosheets and MnO₂ nanowires exhibits a high Brunauer-Emmett-Teller surface area (∼118 m²/g), optimum pore size distribution, a specific capacitance value of 212 F/g at 0.8 A/g, an energy density of 29.5 W h/kg, and a power density of 1316 W/kg. Besides, cyclic charging-discharging and retention tests manifest significant cycling stability with 84.1% capacitive retention after completing 5000 rapid charge-discharge cycles. It is believed that this unique, symmetric, lightweight, solid-state SC device may help accomplish a scalable approach toward powering forthcoming portable energy storage applications.

Recent progress of hierarchical MoS2 nanostructures for electrochemical energy storage

Hierarchical MoS2 nanostructures are of increasing importance in energy storage via batteries or supercapacitors. Herein, the various hierarchical MoS2 materials as electrochemical electrode are reviewed in detail by classifying the...

Synergistically modified WS2@PANI binary nanocomposite-based all-solid-state symmetric supercapacitor with high energy density

WS2@PANI nanocomposite prepared by hydrothermal and physical blending method shows remarkably high specific capacitance and energy density while retaining excellent cyclic stability.

A 2H-MoS2/carbon cloth composite for high-performance all-solid-state supercapacitors derived from a molybdenum dithiocarbamate complex

A molecular complex Mo₂O₂(μ-S)₂(Et₂dtc)₂ (dtc = dithiocarbamate) is prepared and loaded onto carbon cloth (CC) through facile solvothermal treatment, followed by subsequent single-source pyrolysis. This results in a highly porous 2H-MoS₂/CC composite with a sponge-like stacked lamellar morphology. Due to its high porosity and unique nano/microstructure, the MoS₂/CC composite exhibits a specific capacitance of 550.0 F g^-1 at 1 A g^-1, outperforming some 1T-MoS₂ based electrodes. The composite is further assembled into a symmetric all-solid-state supercapacitor, which can be operated stably at a wide potential window and shows a specific capacitance of 127.5 F g^-1 at 1 A g^-1. In addition, the device delivers a high energy density of 70.8 W h kg^-1 at 1 kW kg^-1, which still remains 15.0 W h kg^-1 at 18.0 kW kg^-1. 75% of the performance of the device can be retained after 8000 cycles. Such remarkable electrochemical performance is attributed to its novel nano/microstructures with a large surface area, convenient ion transport pathways, enhanced conductivity, and improved structural stability. Thus, this work demonstrates a highly promising dithiocarbamate-based single-precursor pyrolysis route towards the fabrication of metal sulfides/carbon composites for energy storage applications.

Oxygen Nucleation of MoS2 Nanosheet Thin Film Supercapacitor Electrodes for Enhanced Electrochemical Energy Storage

A direct thin film approach to fabricate large-surface MoS₂ nanosheet thin film supercapacitors using the solution-based diffusion of thiourea into an anodized MoO₃ thin film was investigated. A dense MoS₂ nanosheet thin film electrode (D-MoS₂ ) was obtained when the anodized MoO₃ thin film was processed in a low thiourea solution concentration, whereas a highly porous MoS₂ nanosheet thin film electrode (P-MoS₂ ) was formed at a higher thiourea solution concentration. The charge storage performances of the D-MoS₂ and P-MoS₂ thin films displayed an unusual increase in capacitance on extended cycling, leading to a capacitance as high as around 5-8 mF cm^-2 . X-ray diffraction and cross-sectional microscopy revealed the capacitance enhancements of the MoS₂ supercapacitors are attributable to the nucleation of a new MoS_2-x O_x phase upon cycling. For the D-MoS₂ nanosheet thin film, the formation and growth of the MoS_2-x O_x phase during cycling was accompanied by a volumetric expansion of the MoS₂ layer. For the P-MoS₂ thin film, the nucleation and growth of the MoS_2-x O_x phase occurred in the pores of the MoS₂ layer. The propagation of the MoS_2-x O_x phase also shifted the charge storage process in both films from a diffusion-limited process to a capacitive-dominant process.

Construction of magnetic MgFe2O4/CdS/MoS2 ternary nanocomposite supported on NaY zeolite and highly efficient sonocatalytic degradation of organic pollutants

In this work, the novel magnetically separable NaY zeolite/MgFe₂O₄/CdS nanorods/MoS₂ nanoflowers nanocomposite was successfully synthesized through the ultrasonic-assisted solvothermal approach. FESEM, EDAX, XRD, FTIR, TEM, AFM, VSM, N₂-BET, UV-vis DRS and PL were utilized to identify the as-synthesized nanocomposite. Subsequently, the sonocatalytic activity of this nanocomposite was assessed in the degradation of organic dyes, including methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) from water solutions for the first time. Several analytical parameters like irradiation time, process type, initial MB concentration, H₂O₂ concentration, catalyst dosage, organic dye type, and US power have been systematically investigated to attain the maximum sonocatalytic yield. Regarding the acquired data, the NaY/MgFe₂O₄/CdS NRs/MoS₂ NFs sonocatalyst was incredibly able to completely eliminate the MB via engaging the US/H₂O₂ system. The kinetic evaluates demonstrated the sonodegradation reactions of the MB followed a first-order model. The apparent rate constant (k _app) and half-life time (t _1/2) acquired for the sonodegradation process of MB utilizing the US/H₂O₂/NaY/MgFe₂O₄/CdS NRs/MoS₂ NFs system were measured to be 1.162 min and 0.596 min^-1, respectively. The free ˙OH radicals were also recognized as the main reactive oxygen species in the MB sonodegradation process under US irradiation. In addition, the outcomes of the recyclability study of the NaY/MgFe₂O₄/CdS NRs/MoS₂ NFs sonocatalytic clearly displayed a less than 6% drop of the catalytic activity in up to four sequential runs. Lastly, a plausible mechanism for the sonodegradation reaction of organic dyes was suggested and discussed.

Lichen-like anchoring of MoSe2 on functionalized multiwalled carbon nanotubes: an efficient electrode for asymmetric supercapacitors

In the present study, we have developed a composite electrode of MSNT using a simple and scalable two-step scheme to synthesize a composite electrode material comprising MoSe₂/multiwalled carbon nanotubes (MoSe₂/MWCNTs) for supercapacitor applications. First, a MWCNT thin film was deposited on a stainless steel substrate by using a “dip and dry” coating technique. Subsequently, MoSe₂ was deposited onto the MWCNT thin film using the successive ionic layer adsorption and reaction method. The lichen-like growth of MoSe₂ on the MWCNT network provided dual charge storage and an effective ion transfer path. The composite electrode of MSNT has been studied systematically with different electrolytes and concentrations of electrolyte. As a result, the MoSe₂/MWCNT (MSNT) electrode exhibited excellent electrochemical properties such as a specific capacity of 192 mA h g⁻¹ and a capacitance retention of 88% after 2000 cycles in 1 M LiCl electrolyte. The results demonstrated the huge potential of the MSNT composite electrode for practical application in supercapacitors. The aqueous symmetric cell fabricated using the MSNT composite as both the anode and cathode showed an energy density of 17.9 W h kg⁻¹. Additionally, the energy density improved by designing an asymmetric device of MSNT//MnO₂ and notably, it reveals two-fold improvement in the energy density compared to a symmetric MSNT cell. The MSNT//MnO₂-based asymmetric cell exhibited a maximum specific capacitance of 112 F g⁻¹ with a high energy density of 35.6 W h kg⁻¹.

Simple and scalable chemical synthesis approach to develop a MoSe₂/MWCNTs composite thin film electrode for a highly efficient asymmetric supercapacitor cell.

Current Research of Graphene-Based Nanocomposites and Their Application for Supercapacitors

This review acmes the latest developments of composites of metal oxides/sulfide comprising of graphene and its analogues as electrode materials in the construction of the next generation of supercapacitors (SCs). SCs have become an indispensable device of energy-storage modes. A prompt increase in the number of scientific accomplishments in this field, including publications, patents, and device fabrication, has evidenced the immense attention they have attracted from scientific communities. These efforts have resulted in rapid advancements in the field of SCs, focusing on the development of electrode materials with features of high performance, economic viability, and robustness. It has been demonstrated that carbon-based electrode materials mixed with metal oxides and sulfoxides can perform extremely well in terms of energy density, durability, and exceptional cyclic stability. Herein, the state-of-the-art technologies relevant to the fabrication, characterization, and property assessment of graphene-based SCs are discussed in detail, especially for the composite forms when mixing with metal sulfide, metal oxides, metal foams, and nanohybrids. Effective synthetic methodologies for the nanocomposite fabrications via intercalation, coating, wrapping, and covalent interactions will be reviewed. We will first introduce some fundamental aspects of SCs, and briefly highlight the impact of graphene-based nanostructures on the basic principle of SCs, and then the recent progress in graphene-based electrodes, electrolytes, and all-solid-state SCs will be covered. The important surface properties of the metal oxides/sulfides electrode materials (nickel oxide, nickel sulfide, molybdenum oxide, ruthenium oxides, stannous oxide, nickel-cobalt sulfide manganese oxides, multiferroic materials like BaMnF, core-shell materials, etc.) will be described in each section as per requirement. Finally, we will show that composites of graphene-based electrodes are promising for the construction of the next generation of high performance, robust SCs that hold the prospects for practical applications.

Three-Dimensional MoS2 Nanodot-Impregnated Nickel Foam Electrodes for High-Performance Supercapacitor Applications

An economical and binder-free electrode was fabricated by impregnation of sub-5 nm MoS₂ nanodots (MoS₂ NDs) onto a three-dimensional (3D) nickel substrate using the facile dip-coating method. The MoS₂ NDs were successfully synthesized by controlled bath sonication of highly crystalline MoS₂ nanosheets. The as-fabricated high-surface area electrode demonstrated promising electrochemical properties. It was observed that the as-synthesized NDs outperformed the layered MoS₂ peers as the electrode for supercapacitors. MoS₂ NDs exhibited an excellent specific capacitance (C _sp) of 395 F/g at a current load of 1.5 A/g in a three-electrode configuration. In addition, the fabricated symmetric supercapacitor demonstrated a C _sp value of 122 F/g at 1 A/g and a cyclic performance of 86% over 1000 cycles with a gravimetric power and energy density of 10,000 W/kg and 22 W h/kg, respectively. Owing to its simple and efficient fabrication and high surface area, such 3D electrodes show high promise for various energy storage devices.

Synergistic effect of Bi-doped exfoliated MoS2 nanosheets on their bactericidal and dye degradation potential

Nanosheets incorporated with biological reducing agents are widely used to minimize the toxic effects of chemicals. Biologically amalgamated metal oxide nanomaterials have crucial importance in nanotechnology. In this study, bare and bismuth (Bi)-doped molybdenum disulfide (MoS2) nanosheets were synthesized via a hydrothermal method. Different Bi weight ratios of 2.5, 5, 7.5 and 10% were incorporated in a fixed amount of MoS2 to evaluate its catalytic and antimicrobial activities. Doped nanosheets were characterized using XRD, FTIR and UV-vis spectroscopy, FESEM, HRTEM, Raman, PL, DSC/TGA, EDX, XRF and XPS analysis. The XRD spectra confirmed that the doped nanosheets exhibit a hexagonal structure and their crystallite size increases gradually upon doping. The morphology and interlayer d-spacing of doped MoS2 were determined by FESEM and HRTEM. The presence of functional groups in the doped nanosheets was confirmed using FTIR, PL and Raman analysis. The absorption intensity increased and the corresponding measured band gap energy decreased with doping. The thermal stability and weight loss behaviour of the prepared samples were studied using DSC/TGA. The doped MoS2 nanosheets showed a higher catalytic potential compared to undoped MoS2. The doped Bi nanosheets exhibited higher antimicrobial activity against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) at different concentrations of Bi (0.075 and 0.1), showing a tendency to counter the emerging drug resistance against pathogenic bacterial diseases. Consequently, significant inhibition zones were recorded against (MDR) S. aureus ranging from 2.25 to 3.3 mm and 3.25 to 5.05 mm at low and high concentrations of doped-Bi nanosheets and against Gram-negative E. coli ranging from 1 to 1.45 mm at high concentrations. In conclusion, the Bi-doped MoS2 nanocomposite has exhibited significant potential for use in industrial dye degradation applications. Its antibacterial properties can also mitigate health risks associated with the presence of several well-known pathogens in the environment.

Molybdenum-based two-dimensional materials: Synthesis, dispersion, exfoliation and thin film deposition

We report a simple and effective route to synthesize, disperse, exfoliate and process different molybdenum-based 2-dimensional (2D) materials. Starting from a reaction between ammonium molybdate and ammonium sulfide solutions, a powder consisting of a mixture between amorphous molybdenum oxide and sulfide is obtained. By tuning the atmosphere and the temperature, different compositions can be prepared by thermal treatment of this sample: heat treatments in ambient atmosphere produce MoO₃ with different morphologies, controllable according to the chosen temperature. On the other hand, heat treatments in inert atmosphere produce mixtures between crystalline 2D MoS₂ and MoO₃. Further handling of these mixtures with acetonitrile separates the components due to the different solvent/solid affinities, with the layered MoS₂ becoming homogeneously dispersed, and the MoO₃ agglomerating as a solid easily removed by centrifugation. The resulting sulfide dispersions in acetonitrile present high stability, and they are constituted by exfoliated MoS₂, which means that acetonitrile is a tri-functional agent, separating the sulfide/oxide mixture, exfoliating the sulfide and stabilizing the dispersion. The MoS₂ dispersions were used to produce homogeneous, freestanding and transparent thin films through the liquid-liquid interfacial route, which were easily deposited over different substrates and characterized by different techniques.

Nanocomposite Synthesis of Nanodiamond and Molybdenum Disulfide

A chemically conjugated nanodiamond (ND)/MoS2 nanocomposite was synthesized with amine-functionalized MoS2 and acyl chloride-coordinated ND. The chemical structure and morphology of the nanocomposite were characterized to examine the dispersion of MoS2 on the ND platform. The results revealed that the degree of dispersion was enhanced with increasing ratio of MoS2 nanosheets to ND. Moreover, the nanosheets consisted of several molecular interlayers that were well-dispersed on the ND platform, thereby forming a nanophase. The efficient electrocapacity of the ND/MoS2 nanocomposite was considerably greater than that of the MoS2 electrode alone. Furthermore, the nanophase distribution of MoS2 on ND with a graphitic shell provided a large surface area and reduced the diffusion distance of ions and electrons. Therefore, the nanophase electrode showed higher electrochemical capacitance than that of the MoS2 electrode alone.

Heterostructure of two different 2D materials based on MoS2 nanoflowers@rGO: an electrode material for sodium-ion capacitors

Sodium ion capacitors are under extensive investigation as companionable pre-existing lithium ion batteries and sodium ion batteries. Finding a suitable host for sodium ion storage is still a major challenge. In this context, here we report a MoS₂ nanoflowers@rGO composite produced via a hydrothermal method followed by an ultra sonication process as a sodium ion symmetric hybrid supercapacitor. The structural and electrochemical performances of the electrode material were investigated to establish its applicability in sodium ion capacitors. The electrochemical performance was evaluated using metallic sodium in a half cell configuration which delivered a maximum specific capacitance of 226 F g^-1 at 0.03 A g^-1. When examined as a symmetric hybrid electrode (full cell) it delivered a maximum capacitance of 55 F g^-1 at 0.03 A g^-1. This combination may be a new gateway for upcoming research work which deals with sodium ion storage applications. The results confirmed that the as-synthesized MoS₂ nanoflowers@rGO heterostructure electrode exhibited notable electrochemical behaviour.

Engineering 2D Architectures toward High-Performance Micro-Supercapacitors

The rise of micro-supercapacitors is satisfying the demand for power storage in portable devices and wireless gadgets. But the miniaturization of the energy-storage components is significantly limited by their energy density. Electrode materials with adequate electrochemical active surfaces are therefore required for improving performance. 2D materials with ultralarge specific surface areas offer a broad portfolio of the development of high-performance micro-supercapacitors in spite of their several critical drawbacks. An architecture engineering strategy is therefore developed to break these natural limits and maximize the significant advantages of these materials. Based on the approaches of phase transformation, intercalation, surface modification, material hybridization, and hierarchical structuration, 2D architectures with improved conductivity, enlarged specific surface, enhanced redox activity, as well as the unique synergetic effect exhibit great promise in the application of miniaturized supercapacitors with highly enhanced performance. Herein, the architecture engineering of emerging 2D materials beyond graphene toward optimizing the performance of micro-supercapacitors is discussed, in order to promote the application of 2D architectures in miniaturized energy-storage devices.

Using light, X-rays and electrons for evaluation of the nanostructure of layered materials

As a case study for the evaluation of the nanostructure of layered materials, we report on results of the comprehensive characterization of high-energy ball-milled layered molybdenum disulfide (2H-MoS₂) on different length scales. Analysis of X-ray powder diffraction patterns (XRPDs) including the Debye background at low scattering angles caused by uncorrelated single or few-layer MoS₂ slabs (full scattering model), yield much more precise data about the average stacking degree than routine XRPD evaluation, and an estimation of the amount of single layer material is possible. Reflections with super Lorentzian line shape can be satisfactorily modeled assuming different stacking sequences induced by the mechanical forces exerted during the high-energy ball-mill process. An advanced analysis of UV-Vis spectra to determine layer number and lateral crystallite size, which was recently developed for liquid exfoliation materials, is used for the first time, and the results demonstrate the universal applicability of the approach. The data obtained with this analysis support the main findings of evaluation of the XRPD data. Both methods clearly evidence that increasing the duration of high-energy ball-mill treatment leads to an increase of material with decreasing average stacking and a reduction of the lateral size of the slabs. Finally, high-resolution transmission electron microscopy enabled identification of defects which can hardly be detected in XRPDs or in UV-Vis spectra.

Unveiling the Effect of the Structure of Carbon Material on the Charge Storage Mechanism in MoS2-Based Supercapacitors

MoS₂ is a 2D material that has been widely used in supercapacitor applications because of its layered structure that provides a large surface area and allows for high electric double-layer charge storage. To enhance the cycling stability and capacitance of MoS₂, it is usually mixed with carbon materials. However, the dependence of the charge storage mechanism on the structure of the carbon material is still unclear in literature. Herein, the effect of the structure of the carbon material on the charge storage mechanism in 2H flower-shaped MoS₂ is investigated in detail. Specifically, 2H MoS₂ was mixed with either 8 nm-diameter carbon nanotubes (CNTs) or graphene nanoflakes (GNFs) in different weight ratios. Also, a composite of MoS₂, CNTs, and GNFs (1:1:1) was also studied. The charge storage mechanism was found to depend on the structure and content of the carbon material. Insights into the possible storage mechanism(s) were discussed. The MoS₂/CNT/GNF composite showed a predominant pseudocapacitive charge storage mechanism where the diffusion current was ∼89%, with 88.31% of the resulted capacitance being due to faradic processes.

Fabrication of a 3D Hierarchical Sandwich Co9 S8 /α-MnS@N-C@MoS2 Nanowire Architectures as Advanced Electrode Material for High Performance Hybrid Supercapacitors

Supercapacitors suffer from lack of energy density and impulse the energy density limit, so a new class of hybrid electrode materials with promising architectures is strongly desirable. Here, the rational design of a 3D hierarchical sandwich Co₉ S₈ /α-MnS@N-C@MoS₂ nanowire architecture is achieved during the hydrothermal sulphurization reaction by the conversion of binary mesoporous metal oxide core to corresponding individual metal sulphides core along with the formation of outer metal sulphide shell at the same time. Benefiting from the 3D hierarchical sandwich architecture, Co₉ S₈ /α-MnS@N-C@MoS₂ electrode exhibits enhanced electrochemical performance with high specific capacity/capacitance of 306 mA h g^-1 /1938 F g^-1 at 1 A g^-1 , and excellent cycling stability with a specific capacity retention of 86.9% after 10 000 cycles at 10 A g^-1 . Moreover, the fabricated asymmetric supercapacitor device using Co₉ S₈ /α-MnS@N-C@MoS₂ as the positive electrode and nitrogen doped graphene as the negative electrode demonstrates high energy density of 64.2 Wh kg^-1 at 729.2 W kg^-1 , and a promising energy density of 23.5 Wh kg^-1 is still attained at a high power density of 11 300 W kg^-1 . The hybrid electrode with 3D hierarchical sandwich architecture promotes enhanced energy density with excellent cyclic stability for energy storage.

Recent Advances in Metal Chalcogenides (MX; X = S, Se) Nanostructures for Electrochemical Supercapacitor Applications: A Brief Review

Supercapacitors (SCs) have received a great deal of attention and play an important role for future self-powered devices, mainly owing to their higher power density. Among all types of electrical energy storage devices, electrochemical supercapacitors are considered to be the most promising because of their superior performance characteristics, including short charging time, high power density, safety, easy fabrication procedures, and long operational life. An SC consists of two foremost components, namely electrode materials, and electrolyte. The selection of appropriate electrode materials with rational nanostructured designs has resulted in improved electrochemical properties for high performance and has reduced the cost of SCs. In this review, we mainly spotlight the non-metallic oxide, especially metal chalcogenides (MX; X = S, Se) based nanostructured electrode materials for electrochemical SCs. Different non-metallic oxide materials are highlighted in various categories, such as transition metal sulfides and selenides materials. Finally, the designing strategy and future improvements on metal chalcogenide materials for the application of electrochemical SCs are also discussed.

Synthesis, structure and applications of graphene-based 2D heterostructures

With the profuse amount of two-dimensional (2D) materials discovered and the improvements in their synthesis and handling, the field of 2D heterostructures has gained increased interest in recent years. Such heterostructures not only overcome the inherent limitations of each of the materials, but also allow the realization of novel properties by their proper combination. The physical and mechanical properties of graphene mean it has a prominent place in the area of 2D heterostructures. In this review, we will discuss the evolution and current state in the synthesis and applications of graphene-based 2D heterostructures. In addition to stacked and in-plane heterostructures with other 2D materials and their potential applications, we will also cover heterostructures realized with lower dimensionality materials, along with intercalation in few-layer graphene as a special case of a heterostructure. Finally, graphene heterostructures produced using liquid phase exfoliation techniques and their applications to energy storage will be reviewed.

V2O5 nanorod electrode material for enhanced electrochemical properties by a facile hydrothermal method for supercapacitor applications

Metal oxides have attracted considerable interest due to their distinguished electrochemical properties and applications in multiple fields such as supercapacitors and solar cells.

Hierarchical nanostructures of nitrogen-doped molybdenum sulphide for supercapacitors

Flower-like nanostructures of molybdenum disulphide (MoS₂) have been effectively synthesised by the hydrothermal method and further doped with nitrogen using varying concentrations of urea. The formed hierarchical nanostructures are characterised by spectroscopy as well as electrochemical techniques. The structural analysis confirms the formation of a hexagonal MoS₂ crystal structure. The existence of MoO₂/MoO₃/MoS₂ composites is also observed after heating MoS₂ with a lower urea concentration. Surface morphological analysis of all the prepared compositions shows the appearance of flower-like nanostructures formed by the stacking of 20–80 nanosheets to create individual flower petals. Nitrogen doping shows enhancement in the specific capacitance of MoS₂ due to an increase in the electronic conductivity. Furthermore, the specific capacitance is enhanced due to the formation of an MoO₂/MoO₃/MoS₂ composite. The highest specific capacitance calculated from the charge–discharge curve for nitrogen-doped MoS₂ prepared using 1 : 1 (MoS₂ : urea) weight ratio is observed at around 129 (F g⁻¹) at 2 (A g⁻¹) specific current. The nitrogen-doped MoS₂ demonstrates almost four-fold enhancement in specific capacitance than pristine nano-shaped MoS₂.

The specific capacitance values describe the effect of urea concentration for nitrogen-doped molybdenum sulphide.

Highly Uniform Atomic Layer-Deposited MoS2@3D-Ni-Foam: A Novel Approach To Prepare an Electrode for Supercapacitors

This article takes an effort to establish the potential of atomic layer deposition (ALD) technique toward the field of supercapacitors by preparing molybdenum disulfide (MoS₂) as its electrode. While molybdenum hexacarbonyl [Mo(CO)₆] serves as a novel precursor toward the low-temperature synthesis of ALD-grown MoS₂, H₂S plasma helps to deposit its polycrystalline phase at 200 °C. Several ex situ characterizations such as X-ray diffractometry (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and so forth are performed in detail to study the as-grown MoS₂ film on a Si/SiO₂ substrate. While stoichiometric MoS₂ with very negligible amount of C and O impurities was evident from XPS, the XRD and high-resolution transmission electron microscopy analyses confirmed the (002)-oriented polycrystalline h-MoS₂ phase of the as-grown film. A comparative study of ALD-grown MoS₂ as a supercapacitor electrode on 2-dimensional stainless steel and on 3-dimensional (3D) Ni-foam substrates clearly reflects the advantage and the potential of ALD for growing a uniform and conformal electrode material on a 3D-scaffold layer. Cyclic voltammetry measurements showed both double-layer capacitance and capacitance contributed by the faradic reaction at the MoS₂ electrode surface. The optimum number of ALD cycles was also found out for achieving maximum capacitance for such a MoS₂@3D-Ni-foam electrode. A record high areal capacitance of 3400 mF/cm² was achieved for MoS₂@3D-Ni-foam grown by 400 ALD cycles at a current density of 3 mA/cm². Moreover, the ALD-grown MoS₂@3D-Ni-foam composite also retains high areal capacitance, even up to a high current density of 50 mA/cm². Finally, this directly grown MoS₂ electrode on 3D-Ni-foam by ALD shows high cyclic stability (>80%) over 4500 charge-discharge cycles which must invoke the research community to further explore the potential of ALD for such applications.