MoSe2 Embedded CNT-Reduced Graphene Oxide Composite Microsphere with Superior Sodium Ion Storage and Electrocatalytic Hydrogen Evolution Performances

Honeycomb-Structured MoSe2 /rGO Composites as High-Performance Anode Materials for Sodium-Ion Batteries

Sodium-ion batteries are a promising substitute for lithium batteries due to the abundant resources and low cost of sodium. Herein, honeycomb-shaped MoSe2 /reduced graphene oxide (rGO) composite materials are synthesized from graphene oxide (GO) and MoSe2 through a one-step solvothermal process. Experiments show that the 3D honeycomb structure provides excellent electrolyte penetration while alleviating the volume change during electrochemical cycling. An anode prepared with MoSe2 /rGO composites exhibits significantly improved sodium-ion storage properties, where a large reversible capacity of 215 mAh g-1 is obtained after 2700 cycles at the current density of 30.0 A g-1 or after 5900 cycles at 8.0 A g-1 . When such an anode is paired with Na3 V2 (PO4 )3 to form a full cell, a reversible specific capacity of 107.5 mAh g-1 can be retained after 1000 cycles at the current of 1.0 A g-1 . Transmission electron microscopy, X-ray photoelectron spectroscopy and in situ X-ray diffraction (XRD) characterization reveal the reversible storage reaction of Na ions in the MoSe2 /rGO composites. The significantly enhanced sodium storage capacity is attributed to the unique honeycomb microstructure and the use of ether-based electrolytes. This study illustrates that combining rGO with ether-based electrolytes has tremendous potential in constructing high-performance sodium-ion batteries.

Structural regulation enabled stable hollow molybdenum diselenide nanosheet anode for ultrahigh energy density sodium ion pouch cell

For the continued use of sodium-ion batteries (SIBs), which require matching anode materials, it is crucial to create high energy density energy storage devices. Here, hollow nanoboxes shaped carbon supported sulfur-doped MoSe2 nanosheets (S-MoSe2@NC) are fabricated by in situ growth and heterodoping strategy. This ensures that the MoSe2 nanosheets are tightly anchored to the nanoboxes carbon, and the structure can effectively buffer the volume stress caused by sodium ion (de)intercalation, as well as providing abundant ion/electron migration transportations. As anode for SIBs, the S-MoSe2@NC shows a higher rate capability and excellent cycling stability (431.1 mAh/g after 1100 cycles at 10 A/g). This excellent cycle life and high rate ability are due to the structural stability and outstanding electronic conductance with reduced band gap of the S-MoSe2@NC, as evidenced by the diffusion analysis and theoretical calculation. In order to promote the application of SIBs, the S-MoSe2@NC and NaNi1/3Fe1/3Mn1/3O2 were assembled into a pouch cell, and the test found that besides the excellent cycle rate performance, the ultrahigh energy density of 256 Wh kg-1 and flexible characteristics can be achieved. This study has proven that building a structure with a rock-steady foundation and quick ion migration may efficiently control sodium storage and pave the way for novel applications of high-performance transition metal dichalcogenides in sodium storage.

Recent Advances in Engineering of 2D Materials-Based Heterostructures for Electrochemical Energy Conversion

2D materials, such as graphene, transition metal dichalcogenides, black phosphorus, layered double hydroxides, and MXene, have exhibited broad application prospects in electrochemical energy conversion due to their unique structures and electronic properties. Recently, the engineering of heterostructures based on 2D materials, including 2D/0D, 2D/1D, 2D/2D, and 2D/3D, has shown the potential to produce synergistic and heterointerface effects, overcoming the inherent restrictions of 2D materials and thus elevating the electrocatalytic performance to the next level. In this review, recent studies are systematically summarized on heterostructures based on 2D materials for advanced electrochemical energy conversion, including water splitting, CO2 reduction reaction, N2 reduction reaction, etc. Additionally, preparation methods are introduced and novel properties of various types of heterostructures based on 2D materials are discussed. Furthermore, the reaction principles and intrinsic mechanisms behind the excellent performance of these heterostructures are evaluated. Finally, insights are provided into the challenges and perspectives regarding the future engineering of heterostructures based on 2D materials for further advancements in electrochemical energy conversion.

Metal-Organic Framework-Derived NiSe Embedded into a Porous Multi-Heteroatom Self-Doped Carbon Matrix as a Promising Anode for Sodium-Ion Battery

A self-doping strategy is applied to prepare a multi-heteroatom-doped carbonaceous nickel selenide NiSe@C composite by introducing N and P-containing ligand hexa(4-carboxyl-phenoxy)-cyclotriphosphazene (HCTP-COOH) into a Ni-based MOF precursor. The MOF-derived NiSe@C composite is characterized as NiSe particles nested in a multi-heteroatom-doped carbon matrix. The multi-heteroatom-doped NiSe@C composite with a unique structure shows an excellent sodium-ion storage property. The Na-ion battery from the NiSe@C electrode exhibits a capacity of 447.8 mA h g^-1 at 0.1 A g^-1, a good rate capability (240.3 mA h g^-1 at 5.0 A g^-1), and excellent cycling life (227.8 mAh g^-1 at 5.0 A g^-1 for 1200). The prospects of the synthesis methodology and application of NiSe@C in sodium-ion batteries (SIBs) devices are presented.

Moss-like Hierarchical Architecture Self-Assembled by Ultrathin Na2Ti3O7 Nanotubes: Synthesis, Electrical Conductivity, and Electrochemical Performance in Sodium-Ion Batteries

Nanocrystalline layer-structured monoclinic Na₂Ti₃O₇ is currently under consideration for usage in solid state electrolyte applications or electrochemical devices, including sodium-ion batteries, fuel cells, and sensors. Herein, a facile one-pot hydrothermal synthetic procedure is developed to prepare self-assembled moss-like hierarchical porous structure constructed by ultrathin Na₂Ti₃O₇ nanotubes with an outer diameter of 6–9 nm, a wall thickness of 2–3 nm, and a length of several hundred nanometers. The phase and chemical transformations, optoelectronic, conductive, and electrochemical properties of as-prepared hierarchically-organized Na₂Ti₃O₇ nanotubes have been studied. It is established that the obtained substance possesses an electrical conductivity of 3.34 × 10⁻⁴ S/cm at room temperature allowing faster motion of charge carriers. Besides, the unique hierarchical Na₂Ti₃O₇ architecture exhibits promising cycling and rate performance as an anode material for sodium-ion batteries. In particular, after 50 charge/discharge cycles at the current loads of 50, 150, 350, and 800 mA/g, the reversible capacities of about 145, 120, 100, and 80 mA∙h/g, respectively, were achieved. Upon prolonged cycling at 350 mA/g, the capacity of approximately 95 mA∙h/g at the 200th cycle was observed with a Coulombic efficiency of almost 100% showing the retention as high as 95.0% initial storage. At last, it is found that residual water in the un-annealed nanotubular Na₂Ti₃O₇ affects its electrochemical properties.

Recent Advancements in Chalcogenides for Electrochemical Energy Storage Applications

Energy storage has become increasingly important as a study area in recent decades. A growing number of academics are focusing their attention on developing and researching innovative materials for use in energy storage systems to promote sustainable development goals. This is due to the finite supply of traditional energy sources, such as oil, coal, and natural gas, and escalating regional tensions. Because of these issues, sustainable renewable energy sources have been touted as an alternative to nonrenewable fuels. Deployment of renewable energy sources requires efficient and reliable energy storage devices due to their intermittent nature. High-performance electrochemical energy storage technologies with high power and energy densities are heralded to be the next-generation storage devices. Transition metal chalcogenides (TMCs) have sparked interest among electrode materials because of their intriguing electrochemical properties. Researchers have revealed a variety of modifications to improve their electrochemical performance in energy storage. However, a stronger link between the type of change and the resulting electrochemical performance is still desired. This review examines the synthesis of chalcogenides for electrochemical energy storage devices, their limitations, and the importance of the modification method, followed by a detailed discussion of several modification procedures and how they have helped to improve their electrochemical performance. We also discussed chalcogenides and their composites in batteries and supercapacitors applications. Furthermore, this review discusses the subject’s current challenges as well as potential future opportunities.

Preparation of Polyvinylidene Fluoride Nano-Filtration Membranes Modified with Functionalized Graphene Oxide for Textile Dye Removal

Water scarcity has become one of the most significant problems globally. Membrane technology has gained considerable attention in water treatment technologies. Polymeric nanocomposite membranes are based on several properties, with enhanced water flux, high hydrophilicity and anti-biofouling behavior, improving the membrane performance, flexibility, cost-effectiveness and excellent separation properties. In this study, aminated graphene oxide (NH₂-GO)-based PVDF membranes were fabricated using a phase-inversion method for textile dye removal. These fabricated membranes showed the highest water flux at about 170.2 (J/L.h⁻¹.m⁻²) and 98.2% BSA rejection. Moreover, these membranes removed about 96.6% and 88.5% of methylene blue and methyl orange, respectively. Aminated graphene oxide-based polyvinylidene fluoride (PVDF) membranes emerge as a good membrane material that enhances the membrane performance.

Topological transformation construction of CoSe2/N-doped carbon heterojunction with three-dimensional porous structure for high-performance sodium-ion half/full batteries

Transition metal selenides have been widely used as anode materials for sodium-ion batteries (SIBs) because of their considerable theoretical capacity and good conductivity. Nevertheless, the volume expansion is a serious...

Hierarchical MXene/transition metal chalcogenide heterostructures for electrochemical energy storage and conversion

MXenes have gained rapidly increasing attention owing to their two-dimensional (2D) layered structures and unique mechanical and physicochemical properties. However, MXenes have some intrinsic limitations (e.g., the restacking tendency of the 2D structure) that hinder their practical applications. Transition metal chalcogenide (TMC) materials such as SnS, NiS, MoS₂, FeS₂, and NiSe₂ have attracted much interest for energy storage and conversion by virture of their earth-abundance, low costs, moderate overpotentials, and unique layered structures. Nonetheless, the intrinsic poor electronic conductivity and huge volume change of TMC materials during the alkali metal-ion intercalation/deintercalation process cause fast capacity fading and poor-rate and poor-cycling performances. Constructing heterostructures based on metallic conductive MXenes and highly electrochemically active TMCs is a promising and effective strategy to solve these problems and enhance the electrochemical performances. This review highlights and discusses the recent research development of MXenes and hierarchical MXene/TMC heterostructures, with a focus on the synthesis strategies, surface/heterointerface engineering, and potential applications for lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, electrocatalysis, and photocatalysis. The critical challenges and perspectives of the future development of MXenes and hierarchical MXene/TMC heterostructures for electrochemical energy storage and conversion are forecasted.

Carbon-Free Crystal-like Fe1-xS as an Anode for Potassium-Ion Batteries

Potassium-ion batteries (PIBs) as a new electrochemical energy storage system have been considered as a desirable candidate in the post-lithium-ion battery era. Nevertheless, the study on this realm is in its infancy; it is urgent to develop electrode materials with high electrochemical performance and low cost. Iron sulfides as anode materials have aroused wide attention by virtue of their merits of high theoretical capacities, environmental benignity, and cost competitiveness. Herein, we constructed carbon-free crystal-like Fe_1-xS and demonstrated its feasibility as a PIB anode. The unique structural feature endows the prepared Fe_1-xS with plentiful active sites for electrochemical reactions and short transmission pathways for ions/electrons. The Fe_1-xS electrode retained capacities of 420.8 mAh g^-1 after 100 cycles at 0.1 A g^-1 and 212.9 mAh g^-1 after 250 cycles at 1.0 A g^-1. Even at a high rate of 5.0 A g^-1, an average capacity of 167.6 mAh g^-1 was achieved. In addition, a potassium-ion full cell is assembled by employing Fe_1-xS as an anode and potassium Prussian blue as a cathode; it delivered a discharge capacity of 127.6 mAh g^-1 at 100 mA g^-1 after 50 cycles.

Vapor-phase production of nanomaterials

The synthesis of nanomaterials, with characteristic dimensions of 1 to 100 nm, is a key component of nanotechnology. Vapor-phase synthesis of nanomaterials has numerous advantages such as high product purity, high-throughput continuous operation, and scalability that have made it the dominant approach for the commercial synthesis of nanomaterials. At the same time, this class of methods has great potential for expanded use in research and development. Here, we present a broad review of progress in vapor-phase nanomaterial synthesis. We describe physically-based vapor-phase synthesis methods including inert gas condensation, spark discharge generation, and pulsed laser ablation; plasma processing methods including thermal- and non-thermal plasma processing; and chemically-based vapor-phase synthesis methods including chemical vapor condensation, flame-based aerosol synthesis, spray pyrolysis, and laser pyrolysis. In addition, we summarize the nanomaterials produced by each method, along with representative applications, and describe the synthesis of the most important materials produced by each method in greater detail.

Expanded MoSe2 Nanosheets Vertically Bonded on Reduced Graphene Oxide for Sodium and Potassium-Ion Storage

The cost-efficient and plentiful Na and K resources motivate the research on ideal electrodes for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Here, MoSe₂ nanosheets perpendicularly anchored on reduced graphene oxide (rGO) are studied as an electrode for SIBs and PIBs. Not only does the graphene network serves as a nucleation substrate for suppressing the agglomeration of MoSe₂ nanosheets to eliminate the electrode fracture but also facilitates the electrochemical kinetics process and provides a buffer zone to tolerate the large strain. An expanded interplanar spacing of 7.9 Å is conducive to fast alkaline ion diffusion, and the formed chemical bondings (C-Mo and C-O-Mo) promote the structure integrity and the charge transfer kinetics. Consequently, MoSe₂@5%rGO exhibits a reversible specific capacity of 458.3 mAh·g^-1 at 100 mA·g^-1, great cyclability with a retention of 383.6 mAh·g^-1 over 50 cycles, and excellent rate capability (251.3 mAh·g^-1 at 5 A·g^-1) for SIBs. For PIBs, a high first specific capacity of 365.5 mAh·g^-1 at 100 mA·g^-1 with a low capacity fading of 51.5 mAh·g^-1 upon 50 cycles and satisfactory rate property are acquired for MoSe₂@10%rGO composite. Ex situ measurements validate that the discharge products are Na₂Se for SIBs and K₅Se₃ for PIBs, and robust chemical bonds boost the structure stability for Na- and K-ion storage. The full batteries are successfully fabricated to verify the practical feasibility of MoSe₂@5%rGO composite.

Co-construction of sulfur vacancies and carbon confinement in V5S8/CNFs to induce an ultra-stable performance for half/full sodium-ion and potassium-ion batteries

The construction of anode materials for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) with a high energy and a long lifespan is significant and still challenging. Here, sulfur-defective vanadium sulfide/carbon fiber composites (D-V5S8/CNFs) are designed and fabricated by a facile electrospinning method, followed by sulfuration treatment. The unique architecture, in which V5S8 nanoparticles are confined inside the carbon fiber, provides a short-range channel and abundant adsorption sites for ion storage. Moreover, enlarged interlayer spacings could also alleviate the volume changes, and offer small vdW interactions and ionic diffusion resistance to store more Na and K ions reversibly and simultaneously. The DFT calculations further demonstrate that sulfur defects can effectively facilitate the adsorption behavior of Na+ and K+ and offer low energy barriers for ion intercalation. Taking advantage of the functional integration of these merits, the D-V5S8/CNF anode exhibits excellent storage performance and long-term cycling stability. It reveals a high capacity of 462 mA h g-1 at a current density of 0.2 A g-1 in SIBs, while it is 350 mA h g-1 at 0.1 A g-1 in PIBs, as well as admirable long-term cycling characteristics (190 mA h g-1/17 000 cycles/5 A g-1 for SIBs and 165 mA h g-1/3000 cycles/1 A g-1 for PIBs). Practically, full SIBs upon pairing with a Na3V2(PO4)3 cathode also exhibit superior performance.

Two Grapes Short of a Fruit Salad: Raspberry-, Strawberry-, and Seedpod-Like Organic Microspheres via Colloidal Nanotemplating

The morphology of surfaces critically influences their interaction with the surrounding phase. Herein, we report a modular approach for the synthesis of organic-inorganic raspberry-, strawberry-, and seedpod-like particles to template the porosity of superficially porous particles. Divinylbenzene (DVB) microspheres were employed as core particles, which were modified with polar and nonpolar polymer shells. Subsequently, silica nanoparticle templates were covalently tethered to said particles. Further grafting of polymer shells and subsequent template removal yielded superficially porous core-shell particles. In addition, we introduce a facile procedure for the synthesis of superficially porous particles without distinguishable core-shell morphology. Organic seedpod-like particles were prepared from DVB and silica templates, yielding superficially porous particles after template removal. The surface morphology of the templated particles was investigated via scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) was performed to prove the chemical modification of the particle surfaces.

2D Sandwiched Nano Heterostructures Endow MoSe2 /TiO2- x /Graphene with High Rate and Durability for Sodium Ion Capacitor and Its Solid Electrolyte Interphase Dependent Sodiation/Desodiation Mechanism

Nano heterostructures relying on their versatile construction and the breadth of combined functionality have shown great potential in energy storage fields. Herein, 2D sandwiched MoSe₂ /TiO_{2- x} /graphene nano heterostructures are designed by integrating structural and functional effects of each component, aiming to address the rate capability and cyclic stability of MoSe₂ for sodium ion capacitors (SICs). These 2D nano heterostructures based on graphene platform can facilitate the interfacial electron transport, giving rise to fast reaction kinetics. Meanwhile, the 2D open structure induces a large extent of surface capacitive contribution, eventually leading to a high rate capability (415.2 mAh g^-1 @ 5 A g^-1 ). An ultrathin oxygen deficient TiO_{2- x} layer sandwiched in these nano heterostructures provides a strong chemical-anchoring regarding the products generated during the sodiation/desodiation process, securing the entire cyclic stability. The associated sodiation/desodiation mechanism is revealed by operando and ex situ characterizations, which exhibits a strong solid electrolyte interphase (SEI) dependence. The simulations verify the dependent sodiation products and enhanced heterostructural chemical-anchoring. Assembled SICs based on these nano heterostructures anode exhibit high initial Coulombic efficiency, energy/power densities, and long cycle life, shedding new light on the design of nano heterostructure electrodes for high performance energy storage application.

Carbon nanotube spiderweb promoted growth of hierarchical transition metal dichalcogenide nanostructures for seamless devices

Hierarchical transition metal dichalcogenide (h-TMDC) nanostructures with abundant active edge sites and good electrical conductivity hold great promise for numerous applications. Here, we report a general method for the chemical synthesis of a series of large-area, free-standing h-TMDC films and their devices by using carbon nanotube (CNT) spiderwebs as both growth promoters and electrical/mechanical reinforcement networks. Our approach allows the seamless integration of h-TMDC nanostructures with abundant active edge sites and CNT networks with good electrical conductivity and mechanical flexibility. As a proof of concept, h-MoSe₂/CNT hybrid films with CNT contacts have been chemically synthesized and applied as flexible electrocatalytic devices for hydrogen evolution reaction (HER). Owing to the seamless connection between the CNT contacts and the electroactive h-TMDC/CNT nanostructures, the flexible electrocatalytic devices exhibited excellent mechanical stability and maintained stable electrocatalytic performance under cyclic bendings. Our method can be readily extended to the large-scale production of various h-TMDC/CNT hybrid films and their seamless devices.

Golden Bristlegrass-Like Hierarchical Graphene Nanofibers Entangled with N-Doped CNTs Containing CoSe2 Nanocrystals at Each Node as Anodes for High-Rate Sodium-Ion Batteries

Golden bristlegrass-like unique nanostructures comprising reduced graphene oxide (rGO) matrixed nanofibers entangled with bamboo-like N-doped carbon nanotubes (CNTs) containing CoSe₂ nanocrystals at each node (denoted as N-CNT/rGO/CoSe₂ NF) are designed as anodes for high-rate sodium-ion batteries (SIBs). Bamboo-like N-doped CNTs (N-CNTs) are successfully generated on the rGO matrixed nanofiber surface, between rGO sheets and mesopores, and interconnected chemically with homogeneously distributed rGO sheets. The defects in the N-CNTs formed by a simple etching process allow the complete phase conversion of Co into CoSe₂ through the efficient penetration of H₂ Se gas inside the CNT walls. The N-CNTs bridge the vertical defects for electron transfer in the rGO sheet layers and increase the distance between the rGO sheets during cycles. The discharge capacity of N-CNT/rGO/CoSe₂ NF after the 10 000th cycle at an extremely high current density of 10 A g^-1 is 264 mA h g^-1 , and the capacity retention measured at the 100th cycle is 89%. N-CNT/rGO/CoSe₂ NF has final discharge capacities of 395, 363, 328, 304, 283, 263, 246, 223, 197, 171, and 151 mA h g^-1 at current densities of 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 A g^-1 , respectively.

Facile fabrication of a vanadium nitride/carbon fiber composite for half/full sodium-ion and potassium-ion batteries with long-term cycling performance

Vanadium-based composite anodes have been designed for applications in alkali metal ion batteries, including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). However, the problems of inferior long-term cycling stability caused by the large volume change and dissolution of vanadium-based active materials during cycles and slow diffusion for large radii of Na⁺ and K⁺ still limit their underlying capability and need to be addressed. In the present work, we initially designed and fabricated a vanadium nitride/carbon fiber (VN/CNF) composite via a facile electrospinning method followed by the ammonization process. The obtained VN/CNF composite anode exhibited excellent half/full sodium and potassium storage performance. When used as an anode material for SIBs, it delivered a high capacity of 403 mA h g^-1 at 0.1 A g^-1 after 100 cycles and as large as 237 mA h g^-1 at 2 A g^-1 even after 4000 cycles with negligible capacity fading. More importantly, the VN/CNFs//Na₃V₂(PO₄)₃ full cell by coupling the VN/CNF composite anode with the Na₃V₂(PO₄)₃ (NVP) cathode also exhibited a desirable capacity of 257 mA h g^-1 at 500 mA g^-1 after 50 cycles. Besides, when further evaluated as an anode for PIBs, the VN/CNF composite anode achieved a large capacity of 266 mA h g^-1 after 200 cycles at 0.1 A g^-1 and maintained a stable capacity of 152 mA h g^-1 at 1 A g^-1 even after 1000 cycles, showing significant long-term cycling stability. This is one of the best performances of vanadium-based anode materials for SIBs and PIBs reported so far.

Simultaneously formed and embedding-type ternary MoSe2/MoO2/nitrogen-doped carbon for fast and stable Na-ion storage

To obtain an electrode material that is capable of manifesting high Na-ion storage capacity during long-term cycling at a rapid discharge/charge rate, ternary heterophases MoSe2/MoO2/carbon are rationally designed and synthesized through a supermolecule-assisted strategy. Through using supermolecules that are constructed from MoO4 2- and polydopamine as the precursor and sulfonated polystyrene microspheres as the sacrificial template, the in situ formed ternary phases MoSe2/MoO2/carbon are fabricated into a hollow microspherical structure, which is assembled from ultrathin nanosheets with MoSe2 and MoO2 nanocrystallites strongly embedded in a nitrogen-doped carbon matrix. In the ternary phases, the MoSe2 phase contributes to a high Na-ion storage capacity by virtue of its layered crystalline structure with a wide interlayer space, while the surrounding MoO2 and porous nitrogen-doped carbon phases are conducive to rate behaviour and cycling stability of the ternary hybrids since both the two phases are beneficial for electronic transport and structural stability of MoSe2 during repeated sodiation/desodiation reaction. The as-prepared MoSe2/MoO2/carbon manifests excellent rate behaviour (a Na-ion storage capacity of 461 mA h g-1 at an extremely high current density of 70 A g-1) and outstanding cycle performance (610 mA h g-1 after 1000 cycles).

Layered transition metal dichalcogenide/carbon nanocomposites for electrochemical energy storage and conversion applications

Layered transition metal dichalcogenide (LTMD)/carbon nanocomposites obtained by incorporating conductive carbons such as graphene, carbon nanotubes (CNT), carbon nanofibers (CF), hybrid carbons, hollow carbons, and porous carbons exhibit superior electrochemical properties for energy storage and conversion. Due to the incorporation of carbon into composites, the LTMD/carbon nanocomposites have the following advantages: (1) highly efficient ion/electron transport properties that promote electrochemical performance; (2) suppressed agglomeration and restacking of active materials that improve the cycling performance and electrocatalytic stability; and (3) unique structures such as network, hollow, porous, and vertically aligned nanocomposites that facilitate the shortening of the ion and electrolyte diffusion pathway. In this context, this review introduces and summarizes the recent advances in LTMD/carbon nanocomposites for electrochemical energy-related applications. First, we briefly summarize the reported synthesis strategies for the preparation of LTMD/carbon nanocomposites with various carbon materials. Following this, previous studies using rationally synthesized nanocomposites are discussed based on a variety of applications related to electrochemical energy storage and conversion including Li/Na-ion batteries (LIBs/SIBs), Li-S batteries, supercapacitors, and the hydrogen evolution reaction (HER). In particular, the sections on LIBs and the HER as representative applications of LTMD/carbon nanocomposites are described in detail by classifying them with different carbon materials containing graphene, carbon nanotubes, carbon nanofibers, hybrid carbons, hollow carbons, and porous carbons. In addition, we suggest a new material design of LTMD/carbon nanocomposites based on theoretical calculations. At the end of this review, we provide an outlook on the challenges and future developments in LTMD/carbon nanocomposite research.

Hierarchical Tubular-Structured MoSe2 Nanosheets/N-Doped Carbon Nanocomposite with Enhanced Sodium Storage Properties

Intimately coupled carbon/molybdenum-based hierarchical nanostructures are promising anodes for high-performance sodium-ion batteries owing to the combined effects of the two components and their robust structural stability. Mo-polydopamine (PDA) complexes are appealing precursors for the preparation of various Mo-based nanostructures containing N-doped carbon (NC). A facile method for the fabrication of hierarchical tubular nanocomposites with intimately coupled MoSe₂ and NC nanosheets has been developed, which involves the preparation of Mo-PDA hybrid nanotubes through a chemical route followed by two heat treatments. The strong coupling between Mo anions and the catechol groups in dopamine not only restricts the crystallite size but also inhibits agglomeration during selenization, resulting in few-layered MoSe₂ nanosheets embedded in hierarchical NC substrates. The as-synthesized nanotube composites are constructed by assembling primary MoSe₂ /NC nanosheets. This unique structure not only increases the number of active sites but also shortens the diffusion length of ions and enhances the electronic conductivity of electrode materials. The as-synthesized hierarchical MoSe₂ /NC nanotubes deliver a high capacity of 429 mAh g^-1 at 1 A g^-1 after the 150th cycle when used as anodes in sodium-ion batteries. Furthermore, at a high current density of 10 A g^-1 , a high discharge capacity of 236 mAh g^-1 is achieved.

Dual-Functional Template-Directed Synthesis of MoSe2/Carbon Hybrid Nanotubes with Highly Disordered Layer Structures as Efficient Alkali-Ion Storage Anodes beyond Lithium

Sodium/Potassium-ion batteries (SIBs/PIBs) have recently received tremendous attention because of their particular features of cost-effectiveness and promising energy density, which hold great potential for large-scale applications. Nevertheless, it still has a common bottleneck issue that is the sluggish kinetics of Na⁺/K⁺ intercalation, which raises more rigorous requirement on the electrode candidates regarding the morphology, dimension, and architecture. Herein, we have constructed unique MoSe₂-based hybrid nanotubes with wall structures composed of highly disordered MoSe₂ layers embedded in phosphorus and nitrogen co-doped carbon matrix (denoted MoSe₂⊂PNC-HNTs), by a facile two-step strategy using Se nanorods as the dual-functional template, i.e., shape-directed agent and in situ selenization resources. Benefitting from the combined features of the one-dimensional (1D) hollow interior, hybrid wall structure with high disorder, and the phosphorus and nitrogen co-doping-induced abundant defect sites in the carbon matrix, the MoSe₂⊂PNC-HNT anode exhibits high specific capacities of 280 and 262 mA h g^-1 over 200 cycles at the current density of 0.1 A g^-1 for Na⁺ and K⁺ storage, respectively, and achieves remarkable capacity retention rates of 87.0% at 2 A g^-1 over 3500 cycles for Na-ion storage and 80.1% at 1 A g^-1 after 500 cycles for K-ion storage.

One-Step Construction of MoS0.74Se1.26/N-Doped Carbon Flower-like Hierarchical Microspheres with Enhanced Sodium Storage

Despite the fulfilling advancement in preparing two-dimensional (2D) layered transition-metal dichalcogenide (TMD)-based hybrid architectures, most methods lie on additional template-based procedures for obtaining the expected structure. Here, we present a self-template and in situ synchronous selenization/vulcanization strategy for the synthesis of flower-like hierarchical MoS_0.74Se_1.26/N-doped carbon (MoS_0.74Se_1.26/NC) microspheres by morphology-preserved thermal transformation of a Mo-polydopamine precursor. Introducing element S into the MoSe₂ crystal structure can enhance the electron and ion transportation and lift the ability of MoSe₂ to store Na⁺; the presence of Se can expand the interlayer spacing in contrast to MoS₂. Moreover, carbon composition can also favor the electrical conductivity, and the rigid micro/nanostructure is better for preventing the stacking of MoS_0.74Se_1.26 nanoflakes. The Mo-polydopamine-derived MoS_0.74Se_1.26/NC hybrid exhibits much better performance as the sodium-ion battery (SIB) anode than MoS₂/NC and MoSe₂/NC counterparts, confirming that the advanced electrode material can be attained via the rationalization of the synthetic method. The work provides a new design configuration for novel 2D layered TMDs in the promising application of SIBs as anode materials.

Advances in the synthesis and design of nanostructured materials by aerosol spray processes for efficient energy storage

The increasing demand for energy storage has motivated the search for highly efficient electrode materials for use in rechargeable batteries with enhanced energy density and longer cycle life. One of the most promising strategies for achieving improved battery performance is altering the architecture of nanostructured materials employed as electrode materials in the energy storage field. Among numerous synthetic methods suggested for the fabrication of nanostructured materials, aerosol spray techniques such as spray pyrolysis, spray drying, and flame spray pyrolysis are reliable, as they are facile, cost-effective, and continuous processes that enable the synthesis of nanostructured electrode materials with desired morphologies and compositions with controlled stoichiometry. The post-treatment of spray-processed powders enables the fabrication of oxide, sulfide, and selenide nanostructures hybridized with carbonaceous materials including amorphous carbon, reduced graphene oxide, carbon nanotubes, etc. In this article, recent progress in the synthesis of nanostructured electrode materials by spray processes and their general formation mechanisms are discussed in detail. A brief introduction to the working principles of each spray process is given first, and synthetic strategies for the design of electrode materials for lithium-ion, sodium-ion, lithium-sulfur, lithium-selenium, and lithium-oxygen batteries are discussed along with some examples. This analysis sheds light on the synthesis of nanostructured materials by spray processes and paves the way toward the design of other novel and advanced nanostructured materials for high performance electrodes in rechargeable batteries of the future.

Interfacial engineering of Ag nanodots/MoSe2 nanoflakes/Cu(OH)2 hybrid-electrode for lithium-ion battery

Although the Lithium ion batteries (LIBs) have attracted remarkable attentions, their practical development is hindered by the low rate performance and poor unit area capacity, which is significantly caused by the low conductivity of the active electrode materials. Herein, a three-dimensional (3D) architecture consisting of Ag nanodots embedded MoSe₂ sheets wrapping Cu(OH)₂ nanorods (Cu(OH)₂/MoSe₂/Ag) hybrids were in-situ synthesized on self-standing Cu- foam collector for LIBs application. The 2D MoSe₂ nanoflakes supported on 1D highly conductive Cu nanowires provides efficient pathways for both electrons and ions. The embedded Ag nanodots in the MoSe₂ as the internal-plane active sites not only improves the intrinsic conductivity but also allows the reversible formation and decompose of Ag-Li alloy, and thus leading to the promotion of Li⁺ ion storage. As a result, the Cu(OH)₂/MoSe₂/Ag electrode exhibits a high reversible discharge capacity of 1285.5 mAh g^-1 (current density of 0.2 C), good rate performance (discharge-specific capacity remained 544.8 mAh g^-1 at 5.0C), and excellent cycling stability (with almost no decay after 500 cycles). Significantly, the 3D Cu(OH)₂/MoSe₂/Ag electrode exhibits a high areal capacity of 2.50 mAh cm^-2 at a high current density of 1.82 mA cm^-2. This work provides the new insight into interfaces engineering for 3D architecture toward advanced self-standing LIB electrodes.

Rational design of few-layer MoSe2 confined within ZnSe-C hollow porous spheres for high-performance lithium-ion and sodium-ion batteries

Rechargeable battery systems, including Li-ion batteries and Na-ion batteries, have attracted great interest in energy storage because of their high energy density, low cost, efficient energy storage and suitable redox potential. Nevertheless, their rapid development is still greatly hampered by some typical constraints including low coulombic efficiency, large volume changes and severe particle agglomeration and pulverization during the charge-discharge process. Here, we fabricate a few-layer MoSe2 confined within a ZnSe-C hollow porous sphere nanocomposite through a simple self-assembly strategy followed by selenization, which efficiently circumvents these problems. The fabricated ZnSe/MoSe2@C electrode demonstrates diverse advantages, including the existence of a few-layer structure, an in situ porous carbon matrix, multicomponent coordination and excellent pseudocapacitive behavior. When used as an anode material, it displays extraordinarily attractive electrochemical performance for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). The reversible capacity of ZnSe/MoSe2@C for LIBs reaches as high as 1051 mA h g-1 at 0.2 A g-1 (150 cycles). A long-term high-rate cycling test reveals an excellent stability of 524 mA h g-1 at 4 A g-1 after 600 cycles. In addition, for SIBs, ZnSe/MoSe2@C also manifests a high initial coulombic efficiency of 89% at 0.2 A g-1 and a remarkable reversible capacity of 381 mA h g-1 at a high current density of 4 A g-1 even after 250 cycles with negligible capacity loss. This is one of the best performances of ZnSe-based anode materials for SIBs reported so far. The regulation strategy reported in the present work is expected to offer new insights into the fabrication of high performance anode materials for SIBs.

Large Scale Process for Low Crystalline MoO₃-Carbon Composite Microspheres Prepared by One-Step Spray Pyrolysis for Anodes in Lithium-Ion Batteries

This paper introduces a large-scale and facile method for synthesizing low crystalline MoO₃/carbon composite microspheres, in which MoO₃ nanocrystals are distributed homogeneously in the amorphous carbon matrix, directly by a one-step spray pyrolysis. The MoO₃/carbon composite microspheres with mean diameters of 0.7 µm were directly formed from one droplet by a series of drying, decomposition, and crystalizing inside the hot-wall reactor within six seconds. The MoO₃/carbon composite microspheres had high specific discharge capacities of 811 mA h g-1 after 100 cycles, even at a high current density of 1.0 A g-1 when applied as anode materials for lithium-ion batteries. The MoO₃/carbon composite microspheres had final discharge capacities of 999, 875, 716, and 467 mA h g-1 at current densities of 0.5, 1.5, 3.0, and 5.0 A g-1, respectively. MoO₃/carbon composite microspheres provide better Li-ion storage than do bare MoO₃ powders because of their high structural stability and electrical conductivity.

Novel Cobalt-Doped Ni0.85Se Chalcogenides (Co xNi0.85- xSe) as High Active and Stable Electrocatalysts for Hydrogen Evolution Reaction in Electrolysis Water Splitting

In this paper, novel cobalt-doped Ni_0.85Se chalcogenides (Co _xNi_{0.85- x}Se, x = 0.05, 0.1, 0.2, 0.3, and 0.4) are successfully synthesized and studied as high active and stable electrocatalysts for hydrogen evolution reaction (HER) in electrolysis water splitting. The morphologies, structures, and composition of these as-prepared catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy. The electrochemical tests, such as linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry testing, are performed to evaluate these catalysts' HER catalytic performance including activity and stability. The results indicate that a suitable doping can result in synergetic effect for increasing the catalytic performance. Among different catalysts, Co_0.1Ni_0.75Se shows the highest HER performance. After introducing the reduced graphene oxide (rGO) into this catalyst as the support, the resulted Co_0.1Ni_0.75Se/rGO shows even better performance than unsupported Co_0.1Ni_0.75Se, which are confirmed by the reduction of HER overpotential of Co_0.1Ni_0.75Se/rGO to 103 mV compared to 153 mV of Co_0.1Ni_0.75Se at a current density of 10 mA/cm², and the smaller Tafel slope (43 mV/dec) and kinetic resistance (21.34 Ω) than those of Co_0.1Ni_0.75Se (47 mV/dec, 30.23 Ω). Furthermore, the large electrochemical active surface area and high conductivity of such a Co_0.1Ni_0.75Se/rGO catalyst, induced by rGO introduction, are confirmed to be responsible for the high HER performance.

MoSe₂-GO/rGO Composite Catalyst for Hydrogen Evolution Reaction

There has been considerable research to engineer composites of transition metal dichalcogenides with other materials to improve their catalytic performance. In this work, we present a modified solution-processed method for the formation of molybdenum selenide (MoSe₂) nanosheets and a facile method of structuring composites with graphene oxide (GO) or reduced graphene oxide (rGO) at different ratios to prevent aggregation of the MoSe₂ nanosheets and hence improve their electrocatalytic hydrogen evolution reaction performance. The prepared GO, rGO, and MoSe₂ nanosheets were characterized by X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and scanning electron microscopy. The electrocatalytic performance results showed that the pure MoSe₂ nanosheets exhibited a somewhat high Tafel slope of 80 mV/dec, whereas the MoSe₂-GO and MoSe₂-rGO composites showed lower Tafel slopes of 57 and 67 mV/dec at ratios of 6:4 and 4:6, respectively. We attribute the improved catalytic effects to the better contact and faster carrier transfer between the edge of MoSe₂ and the electrode due to the addition of GO or rGO.