Preparation of MoS2-coated three-dimensional graphene networks for high-performance anode material in lithium-ion batteries

Cysteine-Induced Chirality Evolution of Molybdenum Disulfide Nanodots from a Bottom-Up Strategy

The transfer of chirality from molecules to synthesized nanomaterials has recently attracted significant attention. Although most studies have focused on graphene and plasmonic metal nanostructures, layered transition metal dichalcogenides (TMDs), particularly MoS2, have recently garnered considerable attention due to their semiconducting and electrocatalytic characteristics. Herein, we report a new approach for the synthesis of chiral molybdenum sulfide nanomaterials based on a bottom-up synthesis method in the presence of chiral cysteine enantiomers. In the synthesis process, molybdenum trioxide and sodium hydrosulfide serve as molybdenum and sulfur sources, respectively. In addition, ascorbic acid acts as a reducing agent, resulting in the formation of zero-dimensional MoS2 nanodots. Moreover, the addition of cysteine enantiomers to the growth solutions contributes to the chirality evolution of the MoS2 nanostructures. The chirality is attributed to the cysteine enantiomer-induced preferential folding of the MoS2 planes. The growth mechanism and chiral structure of the nanomaterials are confirmed through a series of characterization techniques. This work combines chirality with the bottom-up synthesis of MoS2 nanodots, thereby expanding the synthetic methods for chiral nanomaterials. This simple synthesis approach provides new insights for the construction of other chiral TMD nanomaterials with emerging structures and properties. More significantly, the as-formed MoS2 nanodots exhibited highly defect-rich structures and chiroptical performance, thereby inspiring a high potential for emerging optical and electronic applications.

Titanium Carbide (Ti3C2Tx) MXene as Efficient Electron/Hole Transport Material for Perovskite Solar Cells and Electrode Material for Electrochemical Biosensors/Non-Biosensors Applications

Recently, two-dimensional (2D) MXenes materials have received enormous attention because of their excellent physiochemical properties such as high carrier mobility, metallic electrical conductivity, mechanical properties, transparency, and tunable work function. MXenes play a significant role as additives, charge transfer layers, and conductive electrodes for optoelectronic applications. Particularly, titanium carbide (Ti3C2Tx) MXene demonstrates excellent optoelectronic features, tunable work function, good electron affinity, and high conductivity. The Ti3C2Tx has been widely used as electron transport (ETL) or hole transport layers (HTL) in the development of perovskite solar cells (PSCs). Additionally, Ti3C2Tx has excellent electrochemical properties and has been widely explored as sensing material for the development of electrochemical biosensors. In this review article, we have summarized the recent advances in the development of the PSCs using Ti3C2Tx MXene as ETL and HTL. We have also compiled the recent progress in the fabrication of biosensors using Ti3C2Tx-based electrode materials. We believed that the present mini review article would be useful to provide a deep understanding, and comprehensive insight into the research status.

Covalently bridged bond assembly of MoS2lamellae onto a graphene sheet: an outstanding electrode for high rate and long-life lithium/sodium-ion batteries

The practical application of Molybdenum sulphide (MoS2) electrodes has been hindered by its structural instability, and poor electrical conductivity. To enhance the cycle stability and rate performance of MoS2in lithium/sodium-ion batteries (LIBs/SIBs), we synthesized a graphene-supported MoS2composite (MoS2@rGO) with affluent covalent bridged bonds through a facile and scalable hydrothermal and annealing process. The covalent bridged bonds of Mo-S-C, Mo-O-C and C-O-S provide an effective charge transfer path between MoS2and graphene, facilitating fast charge hopping and improving rate performance. As anode materials for LIBs, the MoS2@rGO exhibited exceptional long-term cycle life (906 mAh g-1at 1.0 A g-1after 400 cycles) and outstanding rate capability (1267.7/314.7 mAh g-1at 0.1/6.5 A g-1). Additionally, the MoS2@rGO electrode demonstrated a stable reversible capacity of 521.7 mAh g-1at 1.0 A g-1after 700 cycles and excellent rate capabilities of 665.1 and 326.3 mAh g-1at 0.1 and 10.0 A g-1in SIBs. The edge Mo of MoS2is directly coupled with the oxygen of the functional group on rGO, achieved by adjusting the pH value of the solution to tune the surface charge feature, can effectively enhance the structural stability of electrode even under higher current density.

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.

Ex Situ Characterization of 1T/2H MoS2 and Their Carbon Composites for Energy Applications, a Review

The growing interest in the development of next-generation net zero energy systems has led to the expansion of molybdenum disulfide (MoS₂) research in this area. This activity has resulted in a wide range of manufacturing/synthesis methods, controllable morphologies, diverse carbonaceous composite structures, a multitude of applicable characterization techniques, and multiple energy applications for MoS₂. To assess the literature trends, 37,347 MoS₂ research articles from Web of Science were text scanned to classify articles according to energy application research and characterization techniques employed. Within the review, characterization techniques are grouped under the following categories: morphology, crystal structure, composition, and chemistry. The most common characterization techniques identified through text scanning are recommended as the base fingerprint for MoS₂ samples. These include: scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Similarly, XPS and Raman spectroscopy are suggested for 2H or 1T MoS₂ phase confirmation. We provide guidance on the collection and presentation of MoS₂ characterization data. This includes how to effectively combine multiple characterization techniques, considering the sample area probed by each technique and their statistical significance, and the benefit of using reference samples. For ease of access for future experimental comparison, key numeric MoS₂ characterization values are tabulated and major literature discrepancies or currently debated characterization disputes are highlighted.

An interlayer spacing design approach for efficient sodium ion storage in N-doped MoS2

MoS₂ in a graphene-like structure that possesses a large interlayer spacing is a promising anode material for sodium ion batteries (SIBs). However, its poor cycling stability and bad rate performance limit its wide application. In this work, we synthesized an N-doped rGO/MoS₂ (ISE, interlayer spacing enlarged) composite based on an innovative strategy to serve as an anode material for SIBs. By inserting NH₄⁺ into the interlayer of MoS₂, the interlayer spacing of MoS₂ was successfully expanded to 0.98 nm. Further use of N plasma treatment achieved the doping of N element. The results show that N-rGO/MoS₂(ISE) exhibits a high specific capacity of 542 mA h g^-1 after 300 cycles at 200 mA g^-1. It is worth mentioning that the capacity retention rate reaches an ultra-large percentage of 97.13%, and the average decline percentage per cycle is close to 0.01%. Moreover, it also presents an excellent rate performance (477, 432, 377, 334 mA h g^-1 at 200, 500, 1000, 2000 m A g^-1 respectively). This work reveals a unique approach to fabricating promising anode materials and the electrochemical reaction mechanism for SIBs.

Recent Advancement and Structural Engineering in Transition Metal Dichalcogenides for Alkali Metal Ions Batteries

Currently, transition metal dichalcogenides-based alkaline metal ion batteries have been extensively investigated for renewable energy applications to overcome the energy crisis and environmental pollution. The layered morphologys with a large surface area favors high electrochemical properties. Thermal stability, mechanical structural stability, and high conductivity are the primary features of layered transition metal dichalcogenides (L-TMDs). L-TMDs are used as battery materials and as supporters for other active materials. However, these materials still face aggregation, which reduces their applicability in batteries. In this review, a comprehensive study has been undertaken on recent advancements in L-TMDs-based materials, including 0D, 1D, 2D, 3D, and other carbon materials. Types of structural engineering, such as interlayer spacing, surface defects, phase control, heteroatom doping, and alloying, have been summarized. The synthetic strategy of structural engineering and its effects have been deeply discussed. Lithium- and sodium-ion battery applications have been summarized in this study. This is the first review article to summarize different morphology-based TMDs with their intrinsic properties for alkali metal ion batteries (AMIBs), so it is believed that this review article will improve overall knowledge of TMDs for AMIBS applications.

Recent advances in hierarchical MoS2/graphene-based materials for supercapacitor applications

Hierarchical MoS₂/graphene (MoS₂/G) has been widely researched in energy storage via supercapacitors. The combination of MoS₂ with graphene not only provides high conductivity but also enhances the structural stability, which are critical factors determining the electrochemical performance for energy storage. In this review, the recent development of various hierarchical MoS₂/G nanostructures in supercapacitor applications is summarized by classifying the materials into MoS₂/G nanospheres, MoS₂/G nanosheets, and MoS₂/G-based ternary composite. The description of the structural characteristics and electrochemical performance gives a clear and profound understanding of hierarchical MoS₂/G nanostructures as a supercapacitor material. In addition, further research prospects of hierarchical MoS₂/G are suggested.

Two Birds with One Stone: Prelithiated Two-Dimensional Nanohybrids as High-Performance Anode Materials for Lithium-Ion Batteries

As an inexpensive and naturally abundant two-dimensional (2D) material, molybdenum disulfide (MoS₂) exhibits a high Li-ion storage capacity along with a low volume expansion upon lithiation, rendering it an alternative anode material for lithium-ion batteries (LIBs). However, the challenge of using MoS₂-based anodes is their intrinsically low electrical conductivity and unsatisfied cycle stability. To address the above issues, we have exploited a wet chemical technique and integrated MoS₂ with highly conductive titanium carbide (Ti₃C₂) MXene to form a 2D nanohybrid. The binary hybrids were then subjected to an n-butyllithium (n-Buli) treatment to induce both MoS₂ deep phase transition and MXene surface functionality modulation simultaneously. We observed a substantial increase in 1T-phase MoS₂ content and a clear suppression of -F-containing functional groups in MXene due to the prelithiation process enabled by the n-Buli treatment. Such an approach not only increases the overall network conductivity but also improves Li-ion diffusion kinetics. As a result, the MoS₂/Ti₃C₂ composite with n-Buli treatment delivered a high Li-ion storage capacity (540 mA h g^-1 at 100 mA g^-1), outstanding cycle stability (up to 300 cycles), and excellent rate capability. This work provides an effective strategy for the structure-property engineering of 2D materials and sheds light on the rational design of high-performance LIBs using 2D-based anode materials.

High-performance quasi-solid-state flexible supercapacitors based on a flower-like NiCo metal–organic framework

NiCo metal–organic framework (MOF) electrodes were prepared by a simple hydrothermal method. The flower-like NiCo MOF electrode exhibited an exciting potential window of 1.2 V and an excellent specific capacitance of 927.1 F g⁻¹ at 1 A g⁻¹. The flower-like NiCo MOF//activated carbon (AC) device delivered a high energy density of 28.5 W hkg⁻¹ at a power density of 400.5 W kg⁻¹ and good cycle stability (95.4% after 5000 cycles at 10 A g⁻¹). Based on the flower-like NiCo MOF electrode, the asymmetric quasi-solid-state flexible supercapacitor (AFSC) was prepared and exhibited good capacitance retention after bending (79% after 100 bends and 64.4% after 200 bends). Furthermore, two AFSCs in series successfully lit up ten parallel red LED lights, showing great application potential in flexible and wearable energy storage devices.

The flower-like NiCo MOF prepared by a hydrothermal has a specific capacitance of 927.1 F g⁻¹ at 1 A g⁻¹ and a capacitance retention of 69.7% from 1 A g⁻¹ to 10 A g⁻¹, showing excellent electrochemical performance.

Coal-Derived Graphene/MoS2 Heterostructure Electrodes for Li-Ion Batteries: Experiment and Simulation Study

A novel coal-derived graphene-intercalated MoS₂ heterostructure was prepared with a facile in situ hydrothermal approach followed by high-temperature calcination. XRD, FE-SEM, HR-TEM, HR-Raman, and TOC analytical instruments, combined with first-principles simulations, were employed to explore the structural and electrochemical properties of this heterostructure for use as an electrode material. The XRD measurements and simulations confirmed the formation of the MoS₂/graphene (MoS₂-G) heterostructure. The microstructure analysis indicated that a well-defined 3D flower-like structure with tunable interlayer distances was created in the MoS₂ layer. The novel MoS₂-09% G anode exhibits a remarkable initial discharge capacity of ∼929 mAh/g due to its interlayer expansion from the intercalation of graphene between the MoS₂ layers. This anode maintains a capacity of ∼813 mAh/g with a Coulombic efficiency (CE) of ∼99% after 150 cycles at a constant current density of 100 mA/g. This anode also delivers a high-rate capability of ∼579 mAh/g at a current density of 2000 mA/g, significantly higher than that of other comparable structures. The unique flower-like arrangement, sufficient interlayer spacing for Li-ion diffusion, and the increased conductive matrix created using coal-derived graphene enhance the electrode kinetics during electrochemical reactions. Our first-principles calculations revealed that the diffusion barriers are significantly lower in heterostructures compared to that of bare MoS₂. This heterostructure design has significant potential as a new type of anode for Li-ion storage in next-generation batteries.

Effect of porous structural properties on lithium-ion and sodium-ion storage: illustrated by the example of a micro-mesoporous graphene1-x (MoS2) x anode

In this work, we synthesized micro-mesoporous graphene1-x (MoS2) x with different compositional ratios via co-reduction of graphite oxide and exfoliated MoS2 platelets. We systematically studied the performance of the micro-mesoporous graphene1-x (MoS2) x as anodes in lithium-ion batteries and sodium-ion batteries. The results show that the specific surface areas of the composites decrease with introducing MoS2. The irreversible capacitance, which is related to the formation of solid electrolyte interphases, also decreases. Besides specific surface area, we found that micropores can benefit the lithiation and sodiation. We demonstrated that a specific charge capacity of 1319.02 mA h g-1 can be achieved at the 50th cycle for the graphene½(MoS2)½ anode in lithium-ion batteries. Possible relationships between such a high specific capacity and the micro-mesoporous structure of the graphene1-x (MoS2) x anode are discussed. This work may shed light on a general strategy for the structural design of electrode materials in lithium-ion batteries and sodium-ion batteries.

Solid-State Synthesis of Layered MoS2 Nanosheets with Graphene for Sodium-Ion Batteries

Sodium-ion batteries have potential as energy-storage devices owing to an abundant source with low cost. However, most electrode materials still suffer from poor conductivity, sluggish kinetics, and huge volume variation. It is still challenging to explore apt electrode materials for sodium-ion battery applications to avoid the pulverization of electrodes induced by reversible intercalation of large sodium ions. Herein, we report a single-step facile, scalable, low-cost, and high-yield approach to prepare a hybrid material; i.e., MoS2 with graphene (MoS2-G). Due to the space-confined effect, thin-layered MoS2 nanosheets with a loose stacking feature are anchored with the graphene sheets. The semienclosed hybrid architecture of the electrode enhances the integrity and stability during the intercalation of Na+ ions. Particularly, during galvanostatic study the assembled Na-ion cell delivered a specific capacity of 420 mAhg−1 at 50 mAg−1, and 172 mAhg−1 at current density 200 mAg−1 after 200 cycles. The MoS2-G hybrid excels in performance due to residual oxygen groups in graphene, which improves the electronic conductivity and decreases the Na+ diffusion barrier during electrochemical reaction, in comparison with a pristine one.

Glucose-Assisted One-Pot Hydrothermal Synthesis of Hierarchical-Structured MoS2/C Quasi-Hollow Microspheres for High-Performance Lithium Ion Battery

In this work, hierarchical MoS2/C quasi-hollow microspheres are prepared by a one-pot hydrothermal process with the addition of glucose. The glucose is not only inclined to form the roundish sphere in the completion of the synthesis of MoS2, but at the same time the microspheres formed by the glucose can act as the nuclei on which the MoS2 grows. Glucose, acting as a nucleating agent, has the advantages of being low-cost and environmentally friendly, which can simplify the fabrication process. The interiors of the MoS2/C samples are multi-hole and quasi-hollow, which is beneficial for the insertion and extraction of lithium ions. For the first time, we demonstrate that hierarchical-structured MoS2/C quasi-hollow microspheres exhibit an excellent cycling stability and rate capability in lithium ion batteries (LIBs) and are significantly superior to the bulk MoS2. The method presented in this article may provide a simple, clean. and economical strategy for the preparation of MoS2/C microspheres as a feasible and promising anode material for LIBs.

Exfoliated Molybdenum Disulfide-Wrapped CdS Nanoparticles as a Nano-Heterojunction for Photo-Electrochemical Water Splitting

We developed a heterojunction photocathode, MoS₂@CdS, based on the wrapping of CdS nanoparticles by the MoS₂ nanocrystals. The liquid-phase exfoliation method was adopted for preparing few-layer MoS₂ nanocrystals of a layer thickness of ∼7.9 nm, whereas CdS nanoparticles of an average diameter of ∼17 nm were synthesized by the one-step hydrothermal process. The synthesized nanocrystals and nanoparticles were characterized by AFM, FESEM, HRTEM, STEM, XRD, GIXRD, UV-vis absorption, fluorescence emission, and Raman spectroscopy. The difference between two modes in the Raman spectrum of MoS₂ indicates the formation of few-layer MoS₂. The photoelectrochemical performance of the heterojunction photocathode was excellent. The MoS₂@CdS heterostructure photocathode increased the photocurrent density (J_Ph) under 100 mW/cm² illumination. We obtained the maximum applied biased photoconversion efficiency (ABPE) of ∼1.2% of the MoS₂@CdS heterojunction photocathode in optimum device configuration. The production of H₂ was measured as ∼72 μmol/h for the MoS₂@CdS heterostructure with a cyclic stability of up to 7500 s.

Catalyst-free growth of single- to few-layered graphene on ionic liquid surfaces at room temperature

Single- to few-layered graphene is successfully fabricated on ionic liquid surfaces by a modified arc-discharge evaporation method without the assistance of catalysts and at room temperature.

Formation of Coherent 1H-1T Heterostructures in Single-Layer MoS2 on Au(111)

Heterojunctions of semiconductors and metals are the fundamental building blocks of modern electronics. Coherent heterostructures between dissimilar materials can be achieved by composition, doping, or heteroepitaxy of chemically different elements. Here, we report the formation of coherent single-layer 1H-1T MoS₂ heterostructures by mechanical exfoliation on Au(111), which are chemically homogeneous with matched lattices but show electronically distinct semiconducting (1H phase) and metallic (1T phase) character, with the formation of these heterojunctions attributed to a combination of lattice strain and charge transfer. The exfoliation approach employed is free of tape residues usually found in many exfoliation methods and yields single-layer MoS₂ with millimeter (mm) size on the Au surface. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning tunneling microscopy (STM), and scanning tunneling spectroscopy (STS) have collectively been employed to elucidate the structural and electronic properties of MoS₂ monolayers on Au substrates. Bubbles in the MoS₂ formed by the trapping of ambient adsorbates beneath the single layer during deposition, have also been observed and characterized. Our work here provides a basis to produce two-dimensional heterostructures which represent potential candidates for future electronic devices.

State of the Art and Future Perspectives in Advanced CMOS Technology

The international technology roadmap of semiconductors (ITRS) is approaching the historical end point and we observe that the semiconductor industry is driving complementary metal oxide semiconductor (CMOS) further towards unknown zones. Today's transistors with 3D structure and integrated advanced strain engineering differ radically from the original planar 2D ones due to the scaling down of the gate and source/drain regions according to Moore's law. This article presents a review of new architectures, simulation methods, and process technology for nano-scale transistors on the approach to the end of ITRS technology. The discussions cover innovative methods, challenges and difficulties in device processing, as well as new metrology techniques that may appear in the near future.

Atomic Layer Deposition-Assisted Fabrication of Co-Nanoparticle/N-Doped Carbon Nanotube Hybrids as Efficient Electrocatalysts for the Oxygen Evolution Reaction

Transition metal (TM)-based carbon hybrids have numerous applications in the field of regenerative electrochemical energy. The synergetic effects of high conductivity of carbon supports and abundant catalytic active sites in TMs make these hybrids promising oxygen evolution reaction (OER) electrocatalysts. However, strategies for modulating the catalytic active species in the above hybrids are limited despite being highly sought after. Furthermore, the exact roles of chemical species in the hybrids (e.g., N, C, or TM) mainly responsible for this high OER performance remain unknown. Herein, an innovative approach based on atomic layer deposition is developed to tune the true active species in Co nanoparticle/N-doped carbon nanotube (Co/N-CNT) hybrids. Specifically, the configuration predominantly promoting water oxidation in an alkaline medium is identified as pyridinic N-Co-C. Furthermore, a physicochemical intact interface between metallic Co nanoparticles and conductive N-CNTs is demonstrated to induce synergetic effects for accelerating charge transfer and enhancing electrocatalytic activity as well as stability in the hybrid catalysts. The optimized hybrid catalyst is revealed to exhibit outstanding alkaline OER activity and stability, outperforming RuO₂ , a benchmark novel OER electrocatalyst.

Bi-MOF derived micro/meso-porous Bi@C nanoplates for high performance lithium-ion batteries

Micro/meso-porous Bi@C nanoplates are synthesized by pyrolyzing Bi-based metal-organic frameworks (MOFs) prepared by a microwave-assisted hydrothermal method to overcome huge volume expansion and pulverization of anode materials during battery operation. The Bi@C nanoplates are composed of ∼10-50 nm Bi nanoparticles in an amorphous carbon shell. The material shows very high capacity (556 mA h g-1) after 100 cycles at 100 mA g-1 and good cycling performance. Moreover, the Bi@C nanoplates perform well at high current densities and have excellent cyclic stability; their capacity is 308 mA h g-1 after 50 cycles and 200 mA h g-1 after 1000 cycles at 3000 mA g-1. The outstanding performance of this anode is due to the nanosized Bi and amorphous carbon shell. The nanosized Bi reduces the diffusion length of Li ions, while the amorphous carbon shell improves the electrical conductivity of the anode and also restrains the pulverization and aggregation of the metal during cycling. The proposed hierarchical micro/meso-porous materials derived from MOFs are a new type of nanostructures that can aid the development of novel Bi-based anodes for LIBs.

Advanced Matrixes for Binder-Free Nanostructured Electrodes in Lithium-Ion Batteries

Commercial lithium-ion batteries (LIBs), limited by their insufficient reversible capacity, short cyclability, and high cost, are facing ever-growing requirements for further increases in power capability, energy density, lifespan, and flexibility. The presence of insulating and electrochemically inactive binders in commercial LIB electrodes causes uneven active material distribution and poor contact of these materials with substrates, reducing battery performance. Thus, nanostructured electrodes with binder-free designs are developed and have numerous advantages including large surface area, robust adhesion to substrates, high areal/specific capacity, fast electron/ion transfer, and free space for alleviating volume expansion, leading to superior battery performance. Herein, recent progress on different kinds of supporting matrixes including metals, carbonaceous materials, and polymers as well as other substrates for binder-free nanostructured electrodes in LIBs are summarized systematically. Furthermore, the potential applications of these binder-free nanostructured electrodes in practical full-cell-configuration LIBs, in particular fully flexible/stretchable LIBs, are outlined in detail. Finally, the future opportunities and challenges for such full-cell LIBs based on binder-free nanostructured electrodes are discussed.

Engineering Phase Transformation of MoS2/RGO by N-doping as an Excellent Microwave Absorber

As a hot two-dimensional (2D) material, molybdenum disulfide has been attracting extensive attention for electromagnetic wave response applications because of its unique structure. However, the electronic conductivity of nanostructured MoS₂ needs to be optimized urgently. Here, nitrogen-doped 1T@2H-MoS₂/reduced graphene oxide (RGO) composites are effectively constructed by hydrothermal reaction and consecutive calcination under an NH₃ atmosphere. The prepared composites possess great microwave absorption (MA) performance with an expected absorption bandwidth (4.00 GHz) at the Ku band and a maximum reflection loss value (-67.77 dB), which is much better than the performance of conventional 2H-MoS₂ or 2H-MoS₂/RGO. The prominent absorption property is ascribed to the (i) unique self-assemble morphology of rose-like MoS₂ supported on 2D RGO; (ii) controllable crystalline phase switch between 2H and 1T; and (iii) brilliant energy attenuation caused by the intense multipolarization. Furthermore, the dominant MA mechanism is described as the local polarization motivated by the interaction between RGO and MoS₂. Thus, our novel structure design provides a necessary reference to achieve optimized absorption performance based on 2D materials.

Two-Dimensional Materials to Address the Lithium Battery Challenges

Despite the ever-growing demand in safe and high power/energy density of Li⁺ ion and Li metal rechargeable batteries (LIBs), materials-related challenges are responsible for the majority of performance degradation in such batteries. These challenges include electrochemically induced phase transformations, repeated volume expansion and stress concentrations at interfaces, poor electrical and mechanical properties, low ionic conductivity, dendritic growth of Li, oxygen release and transition metal dissolution of cathodes, polysulfide shuttling in Li-sulfur batteries, and poor reversibility of lithium peroxide/superoxide products in Li-O₂ batteries. Owing to compelling physicochemical and structural properties, in recent years two-dimensional (2D) materials have emerged as promising candidates to address the challenges in LIBs. This Review highlights the cutting-edge advances of LIBs by using 2D materials as cathodes, anodes, separators, catalysts, current collectors, and electrolytes. It is shown that 2D materials can protect the electrode materials from pulverization, improve the synergy of Li⁺ ion deposition, facilitate Li⁺ ion flux through electrolyte and electrode/electrolyte interfaces, enhance thermal stability, block the lithium polysulfide species, and facilitate the formation/decomposition of Li-O₂ discharge products. This work facilitates the design of safe Li batteries with high energy and power density by using 2D materials.

Two-Dimensional Materials for High-Energy Solid-State Asymmetric Pseudocapacitors with High Mass Loadings

A porous nanostructure and high mass loading are crucial for a pseudocapacitor to achieve a good electrochemical performance. Although pseudocapacitive materials, such as MnO₂ and MoS₂ , with record capacitances close to their theoretical values have been realized, the achieved capacitances are possible only when the electrode mass loading is less than 1 mg cm^-2 . Increasing the mass loading affects the capacitance as electron conduction and ion diffusion become sluggish. Achieving fast ion and electron transport at high mass loadings through all active sites remains a challenge for high-mass-loading electrodes. In this study, 2D MnO₂ nanosheets supported on carbon fibers (MnO₂ @CF) as well as MoS₂ @CF with high mass loadings (6.6 and 7.2 mg cm^-2 , respectively) were used in a high-energy pseudocapacitor. These hierarchical 2D nanosheets yielded outstanding areal capacitances of 1187 and 495 mF cm^-2 at high current densities with excellent cycling stabilities. A pliable pseudocapacitive solid-state asymmetric supercapacitor was designed using MnO₂ @CF and MoS₂ @CF as the positive and negative electrodes, respectively, with a high mass loading of 14.2 mg cm^-2 . The assembled solid-state asymmetric cell had an energy density of 2.305 mWh cm^-3 at a power density of 50 mW cm^-3 and a capacitance retention of 92.25 % over 11 000 cycles and a very small diffusion resistance (1.72 Ω s^-1/2 ). Thus, it is superior to most state-of-the-art reported pseudocapacitors. The rationally designed nanostructured electrodes with high mass loading are likely to open up new opportunities for the development of a supercapacitor device capable of supplying higher energy and power.

An Ultrafast Conducting Polymer@MXene Positive Electrode with High Volumetric Capacitance for Advanced Asymmetric Supercapacitors

Pseudocapacitors or redox capacitors that synergize the merits of batteries and double-layer capacitors are among the most promising candidates for high-energy and high-power energy storage applications. 2D transition metal carbides (MXenes), an emerging family of pseudocapacitive materials with ultrahigh rate capability and volumetric capacitance, have attracted much interest in recent years. However, MXenes have only been used as negative electrodes as they are easily oxidized at positive (anodic) potential. To construct a high-performance MXene-based asymmetric device, a positive electrode with a compatible performance is highly desired. Herein, an ultrafast polyaniline@MXene cathode prepared by casting a homogenous polyaniline layer onto a 3D porous Ti₃ C₂ T_x MXene is reported, which enables the stable operation of MXene at positive potentials because of the enlarged work function after compositing with polyaniline, according to the first-principle calculations. The resulting flexible polyaniline@MXene positive electrode demonstrates a high volumetric capacitance of 1632 F cm^-3 and an ultrahigh rate capability with 827 F cm^-3 at 5000 mV s^-1 , surpassing all reported positive electrodes. An asymmetric device is further fabricated with MXene as the anode and polyaniline@MXene as the cathode, which delivers a high energy density of 50.6 Wh L^-1 and an ultrahigh power density of 127 kW L^-1 .

Effect of Ni Doping on the MoS2 Structure and Its Hydrogen Evolution Activity in Acid and Alkaline Electrolytes

We have investigated three-dimensional (3D) MoS2 nanoarchitectures doped with different amount of Ni to boost the hydrogen evolution reaction (HER) in alkaline environment, where this reaction is normally hindered. As a comparison, the activity in acidic media was also investigated to determine and compare the role of the Ni sites in both media. The doping of MoS2, especially at high loadings, can modify its structural and/or electronic properties, which can also affect the HER activity. The structural and electronic properties of the Ni doped 3D-MoS2 nanoarchitecture were studied by X-ray diffraction (XRD), Raman spectroscopy, scanning and transmission electronic microscopy (SEM; TEM), and X-ray photoemission Spectroscopy (XPS). XPS also allowed us to determine the Ni-based species formed as a function of the dopant loading. The HER activity of the materials was investigated by linear sweep voltammetry (LSV) in 0.5 M H2SO4 and 1.0 M KOH. By combining the physicochemical and electrochemical results, we concluded that the Ni sites have a different role in the HER mechanism and kinetics in acidic and in alkaline media. Thus, NiSx species are essential to promote HER in alkaline medium, whereas the Ni-Mo-S ones enhance the HER in acid medium.

Few-Layer MoS2 Nanosheets Encapsulated in N-Doped Carbon Hollow Spheres as Long-Life Anode Materials for Lithium-Ion Batteries

Two-dimensional molybdenum disulfide (MoS₂ ) has been recognized as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity, but its rapid capacity decay owing to poor conductivity, structure pulverization, and polysulfide dissolution presents significant challenges in practical applications. Herein, triple-layered hollow spheres in which MoS₂ nanosheets are fully encapsulated between inner carbon and outer nitrogen-doped carbon (NC) were fabricated. Such an architecture provides high conductivity and efficient lithium-ion transfer. Moreover, the NC shell prevents aggregation and exfoliation of MoS₂ nanosheets and thus maintains the integrity of the nanostructure during the charge/discharge process. As anode materials for LIBs, the C@MoS₂ @NC hollow spheres deliver a high reversible capacity (747 mA h g^-1 after 100 cycles at 100 mA g^-1 ) and excellent long-cycle performance (650 mA h g^-1 after 1000 cycles at 1.0 A g^-1 ), which confirm its potential for high-performance LIBs.

Challenges and recent advancements of functionalization of two-dimensional nanostructured molybdenum trioxide and dichalcogenides

Atomically thin two-dimensional (2D) semiconductors are the thinnest functional semiconducting materials available today. Among them, both molybdenum trioxide and chalcogenides (MT&Ds) represent key components within the family of different 2D semiconductors for various electronic, optoelectronic and electrochemical applications due to their unique electronic, optical, mechanical and electrochemical properties. However, despite great progress in research dedicated to the development and fabrication of 2D MT&Ds observed within the last decade, there are significant challenges that affected their charge transport behavior and fabrication on a large scale as well as there is high dependence of the carrier mobility on the thickness. In this article, we review the recent progress in the carrier mobility engineering of 2D MT&Ds and elaborate devised strategies dedicated to the optimization of MT&D properties. Specifically, the latest physical and chemical methods towards the surface functionalization and optimization of the major factors influencing the extrinsic transport at the electrode-2D semiconductor interface are discussed.

Synthesis of Three-Dimensional Graphene-Based Hybrid Materials for Water Purification: A Review

Graphene-based nanostructures and nanomaterials have been widely used for the applications in materials science, biomedicine, tissue engineering, sensors, energy, catalysis, and environmental science due to their unique physical, chemical, and electronic properties. Compared to two-dimensional (2D) graphene materials, three-dimensional (3D) graphene-based hybrid materials (GBHMs) exhibited higher surface area and special porous structure, making them excellent candidates for practical applications in water purification. In this work, we present recent advances in the synthesis and water remediation applications of 3D GBHMs. More details on the synthesis strategies of GBHMs, the water treatment techniques, and the adsorption/removal of various pollutants from water systems with GBHMs are demonstrated and discussed. It is expected that this work will attract wide interests on the structural design and facile synthesis of novel 3D GBHMs, and promote the advanced applications of 3D GBHMs in energy and environmental fields.

Photo-Fenton degradation of amoxicillin via magnetic TiO2-graphene oxide-Fe3O4 composite with a submerged magnetic separation membrane photocatalytic reactor (SMSMPR)

The photo-Fenton process is one of the most important advanced oxidation technologies in environmental remediation. However, the poor recovery of catalysts from treated water impedes the commercialization of this process. Herein, we propose a novel approach for the preparation of TiO₂-graphene oxide (GO)-Fe₃O₄ with high photo-Fenton catalytic performance and capability of magnetic recovery. To realize the recovery of the catalysts, the combination of a submerged magnetic separation membrane photocatalytic reactor (SMSMPR) and TiO₂-GO-Fe₃O₄ was applied to degrade the refractory antibiotic organic compounds in aqueous solution. The results indicate that GO can induce better cycle and catalytic performance of the catalysts. Fe₃O₄ can not only enhance the heterogeneous Fenton degradation of organic compounds but also provide magnetism of the photocatalyst for magnetic separation from treated water. As a result, the TiO₂-GO-Fe₃O₄ composite in the SMSMPR exhibits excellent photo-Fenton catalytic performance and stability for amoxicillin (AMX) degradation. Both backwashing treatment and magnetic separation in the SMSMPR could enhance the photo-Fenton catalytic activity, durability, and separation properties, promoting practical application of this approach for wastewater treatment. Two possible pathways for AMX photodegradation in the SMSMPR were analyzed by means of a Q-TOF LC/MS system, with most of the intermediates finally mineralized to CO₂, water and inorganic ions.

The rational design of hierarchical MoS2 nanosheet hollow spheres sandwiched between carbon and TiO2@graphite as an improved anode for lithium-ion batteries

Molybdenum disulfide (MoS₂) shows high capacity but suffers from poor rate capability and rapid capacity decay, which greatly limit its practical applications in lithium-ion batteries. Herein, we successfully prepared MoS₂ nanosheet hollow spheres encapsulated into carbon and titanium dioxide@graphite, denoted as TiO₂@G@MoS₂@C, via hydrothermal and polymerization approaches. In this hierarchical architecture, the MoS₂ hollow sphere was sandwiched by graphite and an amorphous carbon shell; thus, TiO₂@G@MoS₂@C exhibited effectively enhanced electrical conductivity and withstood the volume changes; moreover, the aggregation and diffusion of the MoS₂ nanosheets were restricted; this advanced TiO₂@G@MoS₂@C fully combined the advantages of a three-dimensional architecture, hollow structure, carbon coating, and a mechanically robust TiO₂@graphite support, achieving improved specific capacity and long-term cycling stability. In addition, it exhibited the high reversible specific capacity of 823 mA h g^-1 at the current density of 0.1 A g^-1 after 100 cycles, retaining almost 88% of the initial reversible capacity with the high coulombic efficiency of 99%.

Self-Assembled Nickel Pyrophosphate-Decorated Amorphous Bimetal Hydroxides 2D-on-2D Nanostructure for High-Energy Solid-State Asymmetric Supercapacitor

To obtain a supercapacitor with a remarkable specific capacitance and rate performance, a cogent design and synthesis of the electrode material containing abundant active sites is necessary. In present work, a scalable strategy is developed for preparing 2D-on-2D nanostructures for high-energy solid-state asymmetric supercapacitors (ASCs). The self-assembled vertically aligned microsheet-structured 2D nickel pyrophosphate (Ni₂ P₂ O₇ ) is decorated with amorphous bimetallic nickel cobalt hydroxide (NiCo-OH) to form a 2D-on-2D nanostructure arrays electrode. The resulting Ni₂ P₂ O₇ /NiCo-OH 2D-on-2D array electrode exhibits peak specific capacity of 281 mA hg^-1 (4.3 F cm^-2 ), excellent rate capacity, and cycling stability over 10 000 charge-discharge cycles in the positive potential range. The excellent electrochemical features can be attributed to the high electrical conductivity and 2D layered structure of Ni₂ P₂ O₇ along with the Faradic capacitance of the amorphous NiCo-OH nanosheets. The constructed Ni₂ P₂ O₇ /NiCo-OH//activated carbon based solid-state ASC cell operates in a high voltage window of 1.8 V with an energy density of 78 Wh kg^-1 (1.065 mWh cm^-3 ) and extraordinary cyclic stability over 10 000 charge-discharge cycles with excellent energy efficiency (75%-80%) over all current densities. The excellent electrochemical performance of the prepared electrode and solid-state ASC device offers a favorable and scalable pathway for developing advanced electrodes.