NiSe2 Nanooctahedra as an Anode Material for High-Rate and Long-Life Sodium-Ion Battery

Construction of Sugar-Gourd-Shaped Carbon Nanofibers Embedded with Heterostructured Zinc-Cobalt Selenide Nanocages for Superior Potassium-Ion Storage

Transition metal selenides are considered as promising anode materials for potassium-ion batteries (PIBs) due to their high theoretical capacities. However, their applications are limited by low conductivity and large volume expansion. Herein, sugar-gourd-shaped carbon nanofibers embedded with heterostructured ZnCo-Se nanocages are prepared via a facile template-engaged method combined with electrospinning and selenization process. In this hierarchical ZnCo-Se@NC/CNF, abundant phase boundaries of CoSe2/ZnSe heterostructure can promote interfacial electron transfer and chemical reactivity. The interior porous ZnCo-Se@NC nanocage structure relieves volume expansion and maintains structural integrity during K+ intercalation and deintercalation. The exterior spinning carbon nanofibers connect the granular nanocages in series, which prevents the agglomeration, shortens the electron transport distance and enhances the reaction kinetics. As a self-supporting anode material, ZnCo-Se@NC/CNF delivers a high capacity (362 mA h g-1 at 0.1 A g-1 after 100 cycles) with long-term stability (95.9% capacity retention after 1000 cycles) and shows superior reaction kinetics with high-rate K-storage. Energy level analysis and DFT calculations illustrate heterostructure facilitates the adsorption of K+ and interfacial electron transfer. The K+ storage mechanism is revealed by ex situ XRD and EIS analyses. This work opens a novel avenue in designing high-performance heterostructured anode materials with ingenious structure for PIBs.

Metal-injection and interface density engineering induced nickel diselenide with rapid kinetics for high-energy sodium storage

The key to the innovation of sodium-ion batteries (SIBs) is to find efficient sodium-storage electrode. Here, metal Mo doping of NiSe2 is proposed by modified electrospinning strategy followed by in situ conversion process. The Mo-NiSe2 anchoring on hollow carbon nanofibers (HCNFs) would make full use of the multi-channel HCNFs in the inner layer and the active sites of Mo-NiSe2 in the outer layer, which plays an important role in buffering the volume stress of Na+ (de)insertion and reducing the adsorption energy barrier of Na+. Innovatively, it is proposed to jointly regulate the SIBs performance of NiSe2 by both metal atom doping and interface effects, thereby adjusting the sodium ion adsorption barrier of NiSe2. The Mo-NiSe2@HCNFs exhibits remarkable performance in SIBs, demonstrating a high specific capacity of 396 mAh/g after 100 cycles at 1 A/g. Moreover, it maintains outstanding cycling stability, retaining 77.6 % of its capacity (211 mAh/g) even after 1000 cycles at 10 A/g. This comprehensive electrochemical performances are due to the structural stability and outstanding electronic conductance of the Mo-NiSe2@HCNFs, as evidenced by the diffusion analysis and ex situ charge-discharge process characterization. Furthermore, coupled with the Na3V2(PO4)2O2F cathodes, the full cell also achieves a high energy density of 123 Wh kg-1. The theoretical calculation of the hypervalent Mo doing further proves the benefit of its Na+ adsorption and denser conduction band distribution. This study provides a reference for the construction of transition metal selenide via doping and interface engineering in sodium storage.

Hybrid Membrane Composed of Nickel Diselenide Nanosheets with Carbon Nanotubes for Catalytic Conversion of Polysulfides in Lithium-Sulfur Batteries

Lithium-sulfur batteries demonstrate enormous energy density are promising forms of energy storage. Unfortunately, the slow redox kinetics and polysulfides shuttle effect are some of the factors that prevent the its development. To address these issues, the hybrid membrane with combination of nickel diselenide nanosheets modified carbon nanotubes (NSN@CNTs) and utilized Li2 S6 catholyte for lithium sulfur battery. The conductive CNTs facilitates fast electronic/ionic transport, while the polarity of NSN as a strong affinity to lithium polysulfides, effectively anchoring them, facilitating the redox conversion of polysulfide species, and effectively diminishing reaction barriers. The cell with NSN@CNTs delivers the first discharge capacity of 1123.8 mAh g-1 and maintains 786.5 mAh g-1 after 300 cycles (0.2 C) at the sulfur loading 5.4 mg. Its rate capability is commendable, enabling it to sustain a capacity of 559.8 mAh g-1 even at a high discharge rate of 2 C. In addition, its initial discharge capacity can remain 8.33 mAh even at 10.8 mg for duration of 100 cycles. This research indicates the potential application of NSN@CNTs hybrid materials in lithium-sulfur batteries.

Alleviating the competitive adsorption of hydrogen and hydroxyl intermediates on Ru by d-p orbital hybridization for hydrogen electrooxidation

Strengthening the hydroxyl binding energy (OHBE) on Ru surfaces for efficient hydrogen oxidation reaction (HOR) in alkaline electrolytes at the expense of narrowing the effective potential window (EPW) increases the risk of passivation under transient conditions for the alkaline exchange membrane fuel cell technique. Herein, an effective Ru/NiSe2 catalyst was reported which exhibits a gradually enhanced intrinsic activity and slightly enlarged EPW with the increased degree of coupling between Ru and NiSe2. This promotion could be attributed to the optimized electron distribution and d-band structures of Ru surfaces weakening the hydrogen binding energy and especially the OHBE through the strong d-p orbital hybridization between Ru and NiSe2. Unlike the conventional way of strengthened OHBE enhancing the oxidative desorption of hydrogen intermediates (Had) via the bi-functional mechanism, the weakened OHBE on this Ru/NiSe2 model catalyst alleviates the competitive adsorption between Had and the hydroxyl intermediates (OHad), thereby accelerating the HOR kinetics at low overpotentials and hindering the full poisoning of the catalytic surfaces by strongly adsorbed OHad spectators at high overpotentials. The work reveals a missed but important approach for Ru-based catalyst development for the fuel cell technique.

Metal Selenides Find Plenty of Space in Architecting Advanced Sodium/Potassium Ion Batteries

The rapid evolution of smart grid system urges researchers on exploiting systems with properties of high-energy, low-cost, and eco-friendly beyond lithium-ion batteries. Under the circumstances, sodium- and potassium-ion batteries with the semblable work mechanism to commercial lithium-ion batteries, hold the merits of cost-effective and earth-abundant. As a result, it is deemed a promising candidate for large-scale energy storage devices. Exploiting appropriate active electrode materials is in the center of the spotlight for the development of batteries. Metal selenides with special structures and relatively high theoretical capacity have aroused broad interest and achieved great achievements. To push the smooth development of metal selenides and enhancement of the electrochemical performance of sodium- and potassium-ion batteries, it is vital to grasp the inherent properties and electrochemical mechanisms of these materials. Herein, the state-of-the-art development and challenges of metal selenides are summarized and discussed. Meanwhile, the corresponding electrochemical mechanism and future development directions are also highlighted.

Multiphase Interfacial Regulation Based on Hierarchical Porous Molybdenum Selenide to Build Anticorrosive and Multiband Tailorable Absorbers

Electromagnetic wave (EMW) absorbing materials have an irreplaceable position in the field of military stealth as well as in the field of electromagnetic pollution control. And in order to cope with the complex electromagnetic environment, the design of multifunctional and multiband high efficiency EMW absorbers remains a tremendous challenge. In this work, we designed a three-dimensional porous structure via the salt melt synthesis strategy to optimize the impedance matching of the absorber. Also, through interfacial engineering, a molybdenum carbide transition layer was introduced between the molybdenum selenide nanoparticles and the three-dimensional porous carbon matrix to improve the absorption behavior of the absorber. The analysis indicates that the number and components of the heterogeneous interfaces have a significant impact on the EMW absorption performance of the absorber due to mechanisms such as interfacial polarization and conduction loss introduced by interfacial engineering. Wherein, the prepared MoSe2/MoC/PNC composites showed excellent EMW absorption performance in C, X, and Ku bands, especially exhibiting a reflection loss of - 59.09 dB and an effective absorption bandwidth of 6.96 GHz at 1.9 mm. The coordination between structure and components endows the absorber with strong absorption, broad bandwidth, thin thickness, and multi-frequency absorption characteristics. Remarkably, it can effectively reinforce the marine anticorrosion property of the epoxy resin coating on Q235 steel substrate. This study contributes to a deeper understanding of the relationship between interfacial engineering and the performance of EMW absorbers, and provides a reference for the design of multifunctional, multiband EMW absorption materials.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg²⁺ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe₂ micro-octahedra was modulated by nitrogen doping (N-NiSe₂) through hydrothermal method followed by a pyrolysis process and this N-NiSe₂ micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe₂ micro-octahedra shows more redox active sites and faster Mg²⁺ diffusion kinetics compared with NiSe₂ micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg²⁺ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg²⁺ adsorption sites. As a result, the N-NiSe₂ micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g^-1 at the current density of 50 mA g^-1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g^-1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Preparation and Evaluation of Co-Doped Fe7S8/C Composites for Lithium Storage

Fe₇S₈ has a high theoretical capacity (663 mAh g^-1) and can be prepared at a low cost, making it advantageous for production. However, Fe₇S₈ has two disadvantages as a lithium-ion battery anode material. The first is that the conductivity of Fe₇S₈ is not good. The second is that when the lithium ion is embedded, the volume expansion of the Fe₇S₈ electrode is serious. That is why Fe₇S₈ has not been used in real life yet. In this paper, Co-Fe₇S₈/C composites were prepared by doping Co into Fe₇S₈ through a one-pot simple hydrothermal method. In situ Co is doped into Fe₇S₈ to produce a more disordered microstructure to improve ion and electron transport performance, thereby reducing the activation barrier of the main material. The Co-Fe₇S₈/C electrode presents a high specific discharge capacity of 1586 mAh g^-1 and a Coulombic efficiency (CE) of 71.34% at an initial cycle at 0.1 A g^-1. After 1500 cycles, the specific discharge capacity remains at 436 mAh g^-1 (5 A g^-1). When the current density returns to 0.1 A g^-1, the capacity almost returns to the initial level, showing excellent rate performance.

CoSe2 nanoparticles anchored on porous carbon network structure for efficient Na-ion storage

Cobalt selenide, as a star material in battery industry, has attracted much attention. However, when it is applied solely in sodium ion batteries, it will cause large volume expansion and material agglomeration, which will seriously affect the overall performance of batteries. In this work, we use ice bath impregnation to combine CoSe₂ nanoparticles with porous nitrogen-doped carbon networks (NC) as advanced anodes for ultra-long cycle life sodium ion batteries (SIBs). CoSe₂ nanoparticles are evenly attached to NC with strong interfacial contacts in CoSe₂@NC. The strong contact of CoSe₂ on the porous carbon network, along with the carbon network's unique network cross-linking structure, results in rapid electron transfer and Na ion diffusion kinetics of CoSe₂@NC, resulting in superior electrochemical performance. Besides, we have synthesized CoSe₂@NC with different loading by changing Co²⁺ concentration. The results show that CoSe₂@NC anode thus provides a high reversible capacity of 406 mAh/g. In addition, at high current 5 A/g, it can keep a reversible capacity of 300 mAh/g after 4500 cycles with an average capacity loss of less than 0.01 % per cycle. The excellent anchoring structure enables it to form stable solid electrolyte film (SEI) and reduce the amount of dead sodium in the first charge-discharge process, showing high Initial Coulombic Efficiency (ICE) (89.2 %). Finally, CoSe₂@NC and Na₃V₂(PO₄)₃ (NVP) are assembled into a full cell and the results shows an ultra-long cycle stability at 0.1 A/g. This strategy will facilitate the application of transition metal selenides in next-generation energy storage systems.

Metal Selenides Anode Materials for Sodium Ion Batteries: Synthesis, Modification, and Application

The powerful and rapid development of lithium-ion batteries (LIBs) in secondary batteries field makes lithium resources in short supply, leading to rising battery costs. Under the circumstances, sodium-ion batteries (SIBs) with low cost, inexhaustible sodium reserves, and analogous work principle to LIBs, have evolved as one of the most anticipated candidates for large-scale energy storage devices. Thereinto, the applicable electrode is a core element for the smooth development of SIBs. Among various anode materials, metal selenides (MSe_x ) with relatively high theoretical capacity and unique structures have aroused extensive interest. Regrettably, MSe_x suffers from large volume expansion and unwished side reactions, which result in poor electrochemistry performance. Thus, strategies such as carbon modification, structural design, voltage control as well as electrolyte and binder optimization are adopted to alleviate these issues. In this review, the synthesis methods and main reaction mechanisms of MSe_x are systematically summarized. Meanwhile, the major challenges of MSe_x and the corresponding available strategies are proposed. Furthermore, the recent research progress on layered and nonlayered MSe_x for application in SIBs is presented and discussed in detail. Finally, the future development focuses of MSe_x in the field of rechargeable ion batteries are highlighted.

Metal-Organic Framework-Based Photocatalysis for Solar Fuel Production

Metal-organic frameworks (MOFs) represent a novel class of crystalline inorganic-organic hybrid materials with tunable semiconducting behavior. MOFs have potential for application in photocatalysis to produce sustainable solar fuels, owing to their unique structural advantages (such as clarity and modifiability) that can facilitate a deeper understanding of the structure-activity relationship in photocatalysis. This review takes the photocatalytic active sites as a particular perspective, summarizing the progress of MOF-based photocatalysis for solar fuel production; mainly including three categories of solar-chemical conversions, photocatalytic water splitting to hydrogen fuel, photocatalytic carbon dioxide reduction to hydrocarbon fuels, and photocatalytic nitrogen fixation to high-energy fuel carriers such as ammonia. This review focuses on the types of active sites in MOF-based photocatalysts and discusses their enhanced activity based on the well-defined structure of MOFs, offering deep insights into MOF-based photocatalysis.

A unique two-phase heterostructure with cubic NiSe2 and orthorhombic NiSe2 for enhanced lithium ion storage and electrocatalysis

Two-phase heterostructures have received tremendous attention in energy-related fields as high-performance electrode materials. However, heterogeneous interfaces are usually constructed by introducing foreign elements, which disturbs the investigation of the intrinsic effect of the two-phase heterostructure. Herein, unique heterostructures constructed with orthorhombic NiSe₂ and cubic NiSe₂ phases are developed, which are embedded in in situ formed porous carbon from metal-organic frameworks (MOFs) (O/C-NiSe₂@C). Precisely-controlled selenylation of MOFs is crucial for the formation of the O/C-NiSe₂ heterostructure. The heterogeneous interfaces with lattice dislocations and charge distribution are conducive to the high-speed transfer of electrons and ions during electrochemical processes, so as to improve the electrochemical reaction kinetics for lithium-ion storage and the hydrogen evolution reaction (HER). When used as the anode of lithium-ion batteries (LIBs), O/C-NiSe₂@C shows a superior electrochemical performance to the counterparts with only the cubic phase (C-NiSe₂@C), in view of the cycling performance (719.3 mA h g^-1 at 0.1 A g^-1 for 100 cycles; 456.3 mA h g^-1 at 1 A g^-1 for 1000 cycles) and rate capabilities (344.8 mA h g^-1 at 4 A g^-1). Furthermore, O/C-NiSe₂@C also exhibits better HER properties than C-NiSe₂@C, that is, much lower overpotentials of 154 mV and 205 mV in 0.5 M H₂SO₄ and 1 M KOH, respectively, at 10 mA cm^-2, a smaller Tafel slope as well as stable electrocatalytic activities for 2000 cycles/10 h. Preliminary observations indicate that the unique orthorhombic/cubic two-phase heterostructure could significantly improve the electrochemical performance of NiSe₂ without additional modifications such as doping, suggesting the O/C-NiSe₂ heterostructure as a promising bifunctional electrode for energy conversion and storage applications.

Sponge-like hierarchical porous carbon decorated by Fe atoms for high-efficiency sodium storage and diffusion

Hierarchical pores with accessible active sites in carbon are highly desired for enhancing sodium storage in sodium ion batteries (SIBs). However, it is still challenging to construct such materials with tunable architectures. Herein, a sponge-like 3D hierarchical porous Fe-doped carbon (Fe@NCS) was successfully assembled from an energetic framework. The continuous distribution of micro/meso/macro-pores in the range of 5 nm-2 μm and homogenously decorated Fe atoms were achieved, which greatly enhanced the storage and diffusion of Na⁺ ions and displayed brilliant high-rate capability and cycling stability.

Bimetallic Selenide Decorated Nanoreactor Synergizing Confinement and Electrocatalysis of Se Species for 3D-Printed High-Loading K-Se Batteries

The potassium-selenium (K-Se) battery has been considered an appealing candidate for next-generation energy storage systems owing to the high energy and low cost. Nonetheless, its development is plagued by the tremendous volume expansion and sluggish reaction kinetics of the Se cathode. Moreover, implementing favorable areal capacity and longevous cycling of a high-loading K-Se battery remains a daunting challenge facing commercial applications. Herein, we devise a Se and CoNiSe₂ coembedded nanoreactor (Se/CoNiSe₂-NR) affording low carbon content as an advanced cathode for K-Se batteries. We systematically uncover the enhanced K₂Se₂/K₂Se adsorption and promoted K⁺ diffusion behavior with the incorporation of Co throughout theoretical simulation and electrokinetic analysis. As a result, Se/CoNiSe₂-NR harvests high cycling stability with a capacity decay rate of 0.038% per cycle over 950 cycles at 1.0 C. More encouragingly, equipped with a 3D-printed Se/CoNiSe₂-NR electrode with tunable Se loadings, K-Se full batteries enable steady cycling at an elevated Se loading of 3.8 mg cm^-2. Our endeavor ameliorates the capacity and lifetime performance of the emerging K-Se device, thereby offering a meaningful tactic in pursuing its practical application.

The rational design of nickel-cobalt selenides@selenium nanostructures by adjusting the synthesis environment for high-performance sodium-ion batteries

Different selenization products (from the perspectives of micromorphology and sodium storage performance) can be obtained via regulating the selenization environment.

General metal-organic framework-derived strategy to synthesize yolk-shell carbon-encapsulated nickelic spheres for sodium-ion batteries

Transition-metal compounds have attracted enormous attention as potential energy storage materials for their high theoretical capacity and energy density. However, the most present transition-metal compounds still suffer from severe capacity decay and limited rate capability due to the lack of robust architectures. Herein, a general metal-organic framework-derived route is reported to fabricate hierarchical carbon-encapsulated yolk-shell nickelic spheres as anode materials for sodium-ion batteries. The nickelic metal-organic framework (Ni-MOF) precursors can be in situ converted into hierarchical carbon-encapsulated Ni₂P (Ni₂P/C), NiS₂ (NiS₂/C) and NiSe₂ (NiSe₂/C) by phosphorization, sulfuration, and selenation reaction, respectively, and maintain their yolk-shell sphere-like morphology. The as-synthesized Ni₂P/C sample can deliver much lower polarization and discharge platform, smaller voltage gap, and faster kinetics in comparison with that of the other two counterparts, and thus achieve higher initial specific capacity (3222.1/1979.3 mAh g^-1) and reversible capacity of 765.4 mAh g^-1 after 110 cycles. This work should provide new insights into the phase and structure engineering of carbon-encapsulated transition-metal compound electrodes via MOFs template for advanced battery systems.

Two-dimensional ZnS@N-doped carbon nanoplates for complete lithium ion batteries

Metal sulfides are promising anode materials for lithium ion batteries because of the high specific capacities and better electrochemical kinetics comparing to their oxide counterparts. In this paper, novel monocrystalline wurtzite ZnS@N-doped carbon (ZnS@N-C) nanoplates, whose morphology and phase are different from the common ZnS particles with cubic phase, are successfully synthesized. The ZnS@N-C nanoplates exhibit long cycle life with a high reversible specific capacity of 536.8 mAh · g^-1after 500 cycles at a current density of 500 mA · g^-1, which is superior to the pure ZnS nanoplates, illustrating the obvious effect of the N-doped carbon coating for mitigating volume change of the ZnS nanoplates and enhancing the electronic conductivity during charge/discharge processes. Furthermore, it is revealed that the ZnS single crystals with wurtzite phase in the ZnS@N-C nanoplates are transformed to the polycrystalline cubic phase ZnS after charge/discharge processes. In particular, the ZnS@N-C nanoplates are combined with the commercial LiNi_0.6Co_0.2Mn_0.2O₂cathode to fabricate a new type of LiNi_0.6Co_0.2Mn_0.2O₂/ZnS@N-C complete battery, which exhibits good cycling durability up to 120 cycles at a charge/discharge rate of 1 C after the prelithiation treatment on the ZnS@N-C anode, highlighting the potential of the ZnS@N-C nanoplates anode material applied in lithium ion battery.

Impact of Annealing Temperature on the Morphological, Optical and Photoelectrochemical Properties of Cauliflower-like CdSe0.6Te0.4 Photoelectrodes; Enhanced Solar Cell Performance

We are reporting on the impact of air annealing temperatures on the physicochemical properties of electrochemically synthesized cadmium selenium telluride (CdSe0.6Te0.4) samples for their application in a photoelectrochemical (PEC) solar cell. The CdSe0.6Te0.4 samples were characterized with several sophisticated techniques to understand their characteristic properties. The XRD results presented the pure phase formation of the ternary CdSe0.6Te0.4 nanocompound with a hexagonal crystal structure, indicating that the annealing temperature influences the XRD peak intensity. The XPS study confirmed the existence of Cd, Se, and Te elements, indicating the formation of ternary CdSe0.6Te0.4 compounds. The FE-SEM results showed that the morphological engineering of the CdSe0.6Te0.4 samples can be achieved simply by changing the annealing temperatures from 300 to 400 °C with intervals of 50 °C. The efficiencies (ƞ) of the CdSe0.6Te0.4 photoelectrodes were found to be 2.0% for the non-annealed and 3.1, 3.6, and 2.5% for the annealed at 300, 350, and 400 °C, respectively. Most interestingly, the PEC cell analysis indicated that the annealing temperatures played an important role in boosting the performance of the photoelectrochemical properties of the solar cells.

Emergence of Ni-Based Chalcogenides (S and Se) for Clean Energy Conversion and Storage

Nickel chalcogenide (S and Se) based nanostructures intrigued scientists for some time as materials for energy conversion and storage systems. Interest in these materials is due to their good electrochemical stability, eco-friendly nature, and low cost. The present review compiles recent progress in the area of nickel-(S and Se)-based materials by providing a comprehensive summary of their structural and chemical features and performance. Improving properties of the materials, such as electrical conductivity and surface characteristics (surface area and morphology), through strategies like nano-structuring and hybridization, are systematically discussed. The interaction of the materials with electrolytes, other electro-active materials, and inactive components are analyzed to understand their effects on the performance of energy conversion and storage devices. Finally, outstanding challenges and possible solutions are briefly presented with some perspectives toward the future development of these materials for energy-oriented devices with high performance.

Three-dimensional microspheres constructed with MoS2 nanosheets supported on multiwalled carbon nanotubes for optimized sodium storage

Molybdenum disulfide (MoS2) has been regarded as a promising anode material in the field of sodium-ion batteries (SIBs), with the advantages of high theoretical capacity and large interlayer spacings. Unfortunately, its intrinsic poor electrical conductivity and large volume changes during the sodiation/desodiation reactions still limit its practical application. To deal with this shortcoming, we built MoS2 nanosheet/multiwalled carbon nanotube (denoted as MoS2-MSs/MWCNTs) composites with a three-dimensional (3D) micro-spherical structure, assembled in situ from MoS2 nanosheets. These nanosheets are connected to each other by the MWCNTs network, which provides a highly conductive pathway for electrons/ions through interparticle and intraparticle interfaces, accelerating charge transfer and ion diffusion capabilities. More importantly, the carbon network can boost electrical conductivity and relieve structural strain. Consequently, the as-prepared MoS2-MSs/MWCNTs composite presents a high reversible specific capacity of 519 mA h g-1 at 0.1 A g-1 after 100 cycles with a capacity retention of 94.4% and excellent rate performance (227 mA h g-1 at 10 A g-1). Outstanding cycling stability was also achieved (327.1 mA h g-1 over 1000 cycles at 2 A g-1) and was characterized by scanning electron microscopy (SEM) analysis. Our findings provide a simple and effective strategy to explore anode materials with advanced sodium storage properties.

Advanced Carbon-Nickel Sulfide Hybrid Nanostructures: Extending the Limits of Battery-Type Electrodes for Redox-Based Supercapacitor Applications

Transition-metal sulfides combined with conductive carbon nanostructures are considered promising electrode materials for redox-based supercapacitors due to their high specific capacity. However, the low rate capability of these electrodes, still considered "battery-type" electrodes, presents an obstacle for general use. In this work, we demonstrate a successful and fast fabrication process of metal sulfide-carbon nanostructures ideal for charge-storage electrodes with ultra-high capacity and outstanding rate capability. The novel hybrid binder-free electrode material consists of a vertically aligned carbon nanotube (VCN), terminated by a nanosized single-crystal metallic Ni grain; Ni is covered by a nickel nitride (Ni₃N) interlayer and topped by trinickel disulfide (Ni₃S₂, heazlewoodite). Thus, the electrode is formed by a Ni₃S₂/Ni₃N/Ni@NVCN architecture with a unique broccoli-like morphology. Electrochemical measurements show that these hybrid binder-free electrodes exhibit one of the best electrochemical performances compared to the other reported Ni₃S₂-based electrodes, evidencing an ultra-high specific capacity (856.3 C g^-1 at 3 A g^-1), outstanding rate capability (77.2% retention at 13 A g^-1), and excellent cycling stability (83% retention after 4000 cycles at 13 A g^-1). The remarkable electrochemical performance of the binder-free Ni₃S₂/Ni₃N/Ni@NVCN electrodes is a significant step forward, improving rate capability and capacity for redox-based supercapacitor applications.

Highly conductive Co3Se4 embedded in N-doped 3D interconnected carbonaceous network for enhanced lithium and sodium storage

Traditional cobalt selenides as active materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) would suffer from drastic volume expansions and large stacking effects, leading to a low cycling stability. In this work, we utilized a facile template method for preparing Co₃Se₄@N-CN (CSNC) that encapsulated Co₃Se₄ nanoparticles into 3D interconnected nitrogen-doped carbon network (N-CN). Satisfactorily, it possesses excellent cycling stability with enhanced lithium and sodium energy storage capacity. As an anode material in LIBs, CSNC exhibited a prominent reversible discharge performance of 1313.5 mAh g^-1 after 100 cycles at 0.1 A g^-1 and 835.6 mAh g^-1 after 500 cycles at 1.0 A g^-1. Interestingly, according to the analysis from cyclic voltammetry, the in-situ generated Se might provide extra capacity that leaded to a rising trend of capacity. When utilized as an anode in SIBs, CSNC delivered an outstanding capacity of 448.7 mAh g^-1 after 100 cycles at 0.1 A g^-1 and could retain 328.9 mAh g^-1 (77.2% of that of 0.1 A g^-1) even at a high current density of 5.0 A g^-1. The results demonstrate that CSNC is a superior anode material in LIBs and SIBs with great promise. More importantly, this strategy opens up an effective avenue for the design of transition metal selenide/carbonaceous composites for advanced battery storage systems.

Electronic and topological properties of group-10 transition metal dichalcogenides

The group 10 transition metal dichalcogenides (TMDs) (MX ₂: M = Ni, Pd, Pt; X = S, Se, Te) have attracted much attention in the last few decades because of observation of exotic phases and phenomena such as superconductivity (SC), topological surface states (TSSs), type II Dirac fermions, helical spin texture, Rashba effect, 3D Dirac plasmons, metal-insulator transitions, charge density waves (CDW) etc. In this review, we cover the experimental and theoretical progress on the physical phenomena influenced by the strong electron-electron correlation of the group-10 TMDs from the past to the present. We have especially emphasized on the SC and topological phases in the bulk as well as in atomically thin materials.

Highly Efficient Sodium-Ion Storage Enabled by an rGO-Wrapped FeSe2 Composite

Exploitation of superior anode materials is a key step to realize the pursuit of high-performance sodium-ion batteries. In this work, a reduced graphene oxide-wrapped FeSe₂ (FeSe₂ @rGO) composite derived from a metal-organic framework (MOF) was synthesized to act as the anode material of sodium-ion batteries. The MOF-derived carbon framework with high specific surface area could relieve the large volumetric change during cycling and ensure the structural stability of electrode materials. Besides, the rGO conductive network allowed to promote the electron transfer and accelerate reaction kinetics as well as to provide a protection role for the internal FeSe₂ . As a result, the FeSe₂ @rGO composite exhibited a high capacity of 350 mAh g^-1 after 600 cycles at 5 A g^-1 . Moreover, in situ XRD was conducted to explore the reaction mechanism of the FeSe₂ @rGO composite upon sodiation/de-sodiation. Importantly, the presented method for the synthesis of MOF-derived materials wrapped by rGO could not only be used for FeSe₂ @rGO-based sodium-ion batteries but also for the different transition metal-based composite materials for electrochemical devices, such as water splitting and sensors.

Synergizing Phase and Cavity in CoMoOx Sy Yolk-Shell Anodes to Co-Enhance Capacity and Rate Capability in Sodium Storage

Sodium-ion batteries (SIBs) have been recognized as the promising alternatives to lithium-ion batteries for large-scale applications owing to their abundant sodium resource. Currently, one significant challenge for SIBs is to explore feasible anodes with high specific capacity and reversible pulverization-free Na⁺ insertion/extraction. Herein, a facile co-engineering on polymorph phases and cavity structures is developed based on CoMo-glycerate by scalable solvothermal sulfidation. The optimized strategy enables the construction of CoMoO_x S_y with synergized partially sulfidized amorphous phase and yolk-shell confined cavity. When developed as anodes for SIBs, such CoMoO_x S_y electrodes deliver a high reversible capacity of 479.4 mA h g^-1 at 200 mA g^-1 after 100 cycles and a high rate capacity of 435.2 mA h g^-1 even at 2000 mA g^-1 , demonstrating superior capacity and rate capability. These are attributed to the unique dual merits of the anodes, that is, the elastic bountiful reaction pathways favored by the sulfidation-induced amorphous phase and the sodiation/desodiation accommodatable space benefits from the yolk-shell cavity. Such yolk-shell nano-battery materials are merited with co-tunable phases and structures, facile scalable fabrication, and excellent capacity and rate capability in sodium storage. This provides an opportunity to develop advanced practical electrochemical sodium storage in the future.

Urchin-Like Fe3 Se4 Hierarchitectures: A Novel Pseudocapacitive Sodium-Ion Storage Anode with Prominent Rate and Cycling Properties

Transition metal chalcogenides have received great attention as promising anode candidates for sodium-ion batteries (SIBs). However, the undesirable cyclic life and inferior rate capability still restrict their practical applications. The design of micro-nano hierarchitectures is considered as a possible strategy to facilitate the electrochemical reaction kinetics and strengthen the electrode structure stability upon repeated Na⁺ insertion/extraction. Herein, urchin-like Fe₃ Se₄ hierarchitectures are successfully prepared and developed as a novel anode material for SIBs. Impressively, the as-prepared urchin-like Fe₃ Se₄ can present an ultrahigh rate capacity of 200.2 mAh g^-1 at 30 A g^-1 and a prominent capacity retention of 99.9% over 1000 cycles at 1 A g^-1 , meanwhile, a respectable initial coulombic efficiency of ≈100% is achieved. Through the conjunct study of in situ X-ray diffraction, ex situ X-ray absorption near-edge structure spectroscopy, as well as cyclic voltammetry curves, it is intriguing to reveal that the phase transformation from monoclinic to amorphous structure accompanied by the pseudocapacitive Na⁺ storage behavior accounts for the superior electrochemical performance. When paired with the Na₃ V₂ (PO₄ )₃ cathode materials, the assembled full cell enables high energy density and decent cyclic stability, demonstrating potential practical feasibility of the present urchin-like Fe₃ Se₄ anode.

Highly Porous NiCoSe4 Microspheres as High-Performance Anode Materials for Sodium-Ion Batteries

Binary transition metal selenides have been more promising than single transition metal selenides as anode materials for sodium-ion batteries (SIBs). However, the controlled synthesis of transition metal selenides, especially those derived from metal-organic-frameworks with well-controlled structure and morphology is still challenging. In this paper, highly porous NiCoSe₄ @NC composite microspheres were synthesized by simultaneous carbonization and selenization of a Ni-Co-based metal-organic framework (NiCo-MOF) and characterized by scanning electron microscopy, transition electron microscopy, X-Ray diffraction, X-Ray photoelectron spectroscopy and electrochemical techniques. The rationally engineered NiCoSe₄ @NC composite exhibits a capacity of 325 mAh g^-1 at a current density of 1 A g^-1 , and 277.8 mAh g^-1 at 10 A g^-1 . Most importantly, the NiCoSe₄ @NC retains a capacity of 293 mAh g^-1 at 1 A g^-1 after 1500 cycles, with a capacity decay rate of 0.025 % per cycle.

Construction of Bimetallic Selenides Encapsulated in Nitrogen/Sulfur Co-Doped Hollow Carbon Nanospheres for High-Performance Sodium/Potassium-Ion Half/Full Batteries

Metallic selenides have been widely investigated as promising electrode materials for metal-ion batteries based on their relatively high theoretical capacity. However, rapid capacity decay and structural collapse resulting from the larger-sized Na⁺ /K⁺ greatly hamper their application. Herein, a bimetallic selenide (MoSe₂ /CoSe₂ ) encapsulated in nitrogen, sulfur-codoped hollow carbon nanospheres interconnected reduced graphene oxide nanosheets (rGO@MCSe) are successfully designed as advanced anode materials for Na/K-ion batteries. As expected, the significant pseudocapacitive charge storage behavior substantially contributes to superior rate capability. Specifically, it achieves a high reversible specific capacity of 311 mAh g^-1 at 10 A g^-1 in NIBs and 310 mAh g^-1 at 5 A g^-1 in KIBs. A combination of ex situ X-ray diffraction, Raman spectroscopy, and transmission electron microscopy tests reveals the phase transition of rGO@MCSe in NIBs/KIBs. Unexpectedly, they show quite different Na⁺ /K⁺ insertion/extraction reaction mechanisms for both cells, maybe due to more sluggish K⁺ diffusion kinetics than that of Na⁺ . More significantly, it shows excellent energy storage properties in Na/K-ion full cells when coupled with Na₃ V₂ (PO₄ )₂ O₂ F and PTCDA@450 °C cathodes. This work offers an advanced electrode construction guidance for the development of high-performance energy storage devices.

Construction of a bimetallic nickel–cobalt selenide pompon used as a superior anode material for high performance sodium storage

Pompon-like NiCo₂Se₄ can effectively promote the penetration of an electrolyte, increase electron and ion diffusion channels, alleviate volume expansion and achieve excellent sodium storage performance.

High-Capacity Interstitial Mn-Incorporated MnxFe3-xO4/Graphene Nanocomposite for Sodium-Ion Battery Anodes

Sodium-ion batteries (SIBs) have attracted wide attention because of their prospects for grid-scale electrical regulation and cost effectiveness of sodium. In this regard, iron oxides (FeO_x) are considered as one of the most promising anode candidates due to their high theoretical capacity and low cost. Unfortunately, the utilization of FeO_x anodes suffers from sluggish reaction kinetics and significant lattice variation, causing insufficient rate performance and fast capacity degradation during the sodiation/desodiation process. In this study, Mn ions are incorporated through interstitial sites into a Fe₃O₄ lattice to form the Mn-incorporated Fe₃O₄/graphene (M-Fe₃O₄/G) composites through a facile hydrothermal method. Confirmed by XRD Rietveld refinement and the first-principles calculation, Mn occupation into the body structure can effectively condense the electron density around the Fermi level and thus contributes to the increased electrical conductivity and improved electrochemical properties. Accordingly, the M_0.1Fe_2.9O₄/G composite demonstrates a high reversible capacity of 439.8 mA h g^-1 at a current density of 100 mA g^-1 over 200 cycles. Even at a high current density of 1 A g^-1, the M-Fe₃O₄/G composites remain stable for over 1200 cycles, delivering a capacity of 210 mA h g^-1. Coupled with a Na₃V₂(PO₄)₃-type cathode, the Mn-incorporated Fe₃O₄/G composites demonstrate good suitability in full SIBs (161.2 mA h g^-1 at the current density of 1 A g^-1 after 100 cycles). The regulation of Mn ions in the Fe₃O₄ lattice provides insights into the optimization of metal oxide anode candidates for their application in SIBs.

Two-Dimensional T-NiSe2 as a Promising Anode Material for Potassium-Ion Batteries with Low Average Voltage, High Ionic Conductivity, and Superior Carrier Mobility

Potassium-ion batteries (KIBs) have attracted great attention due to their unique advantages including abundant resources, low redox potential of K, and feasible usage of cheap aluminum current collector in battery assembly. In the present work, through first-principles calculations, we find that the recently synthesized two-dimensional T-NiSe₂ is a promising anode material of KIBs. It possesses a large capacity (247 mAh/g), small diffusion barrier (0.05 eV), and low average voltage (0.49 V), rendering T-NiSe₂ a high-performance KIB anode candidate. In addition, we analyze the carrier mobility of T-NiSe₂, and the results demonstrate that it possesses a superior carrier mobility of 1685 cm²/(V s), showing the potential for applications in nanoelectronic devices.

Composition Engineering Boosts Voltage Windows for Advanced Sodium-Ion Batteries

Transition-metal selenides have captured sustainable research attention in energy storage and conversion field as promising anodes for sodium-ion batteries. However, for the majority of transition metal selenides, the potential windows have to compress to 0.5-3.0 V for the maintenance of cycling and rate capability, which largely sacrifices the capacity under low voltage and impair energy density for sodium full batteries. Herein, through introducing diverse metal ions, transition-metal selenides consisted of different composition doping (CoM-Se₂@NC, M = Ni, Cu, Zn) are prepared with more stable structures and higher conductivity, which exhibit superior cycling and rate properties than those of CoSe₂@NC even at a wider voltage range for sodium ion batteries. In particular, Zn²⁺ doping demonstrates the most prominent sodium storage performance among series materials, delivering a high capacity of 474 mAh g^-1 after 80 cycles at 500 mA g^-1 and rate capacities of 511.4, 382.7, 372.1, 339.2, 306.8, and 291.4 mAh g^-1 at current densities of 0.1, 0.5, 1.0, 1.4, 1.8, and 2.0 A g^-1, respectively. The composition adjusting strategy based on metal ions doping can optimize electrochemical performances of metal selenides, offer an avenue to expand stable voltage windows, and provide a feasible approach for the construction of high specific energy sodium-ion batteries.

Method for Synthesis of Zeolitic Imidazolate Framework-Derived LiCoO2/CNTs@AlF3 with Enhanced Lithium Storage Capacity

Metal-organic framework-derived lithium cobaltate nanoparticles were fabricated by annealing of the ZIF-67 precursor with Li₂CO₃ under air, followed by homogeneous AlF₃ coating and carbon nanotubes (CNTs) wrapping. The as-prepared AlF₃-coated LiCoO₂/CNTs electrode can act as a potential cathode for enhanced lithium storage at both room temperature and an elevated temperature of 50 °C.

General Approach to Produce Nanostructured Binary Transition Metal Selenides as High-Performance Sodium Ion Battery Anodes

Multiple transition metals containing chalcogenides have recently drawn boosted attraction as anodes for sodium ion batteries (SIBs). Their greatly enhanced electrochemical performances can be attributed to the superior intrinsic conductivities and richer redox reactions, comparative to mono metal chalcogenides. To employ various binary metals comprising selenides (B-TMSs) for SIBs, discovery of a simplistic, scalable and universal synthesis approach is highly desirable. Herein, a simple, facile, and comprehensive strategy to produce various combinations of nanostructured B-TMSs is presented. As a proof of concept, optimized, high surface area bearing, and hierarchical nanosheets of iron-nickel selenide (FNSe), iron-cobalt selenide, and nickel-cobalt selenide are produced and employed in SIBs. These B-TMSs exhibit adequately high energy capacities, excellent rate capabilities, and an extraordinarily stable life of 2600 cycles. As far as it is known, it is the first work to discuss sodium storage of FNSe, so various in situ and ex situ battery analyses are carried out to probe the sodium storage mechanism. When employed in sodium full batteries, these B-TMSs present reasonably high reversible specific capacities even after 100 cycles. Overall, the presented strategy will pave the way for facile synthesis of numerous binary transition metal chalcogenides that are the potential materials for energy storage and conversion systems.

A Flexible Film toward High-Performance Lithium Storage: Designing Nanosheet-Assembled Hollow Single-Hole Ni-Co-Mn-O Spheres with Oxygen Vacancy Embedded in 3D Carbon Nanotube/Graphene Network

Ternary transition metal oxides (TMOs) are highly potential electrode materials for lithium ion batteries (LIBs) due to abundant defects and synergistic effects with various metal elements in a single structure. However, low electronic/ionic conductivity and severe volume change hamper their practical application for lithium storage. Herein, nanosheet-assembled hollow single-hole Ni-Co-Mn oxide (NHSNCM) spheres with oxygen vacancies can be obtained through a facile hydrothermal reaction, which makes both ends of each nanosheet exposed to sufficient free space for volume variation, electrolyte for extra active surface area, and dual ion diffusion paths compared with airtight hollow structures. Furthermore, oxygen vacancies could improve ion/electronic transport and ion insertion/extraction process of NHSNCM spheres. Thus, oxygen-vacancy-rich NHSNCM spheres embedded into a 3D porous carbon nanotube/graphene network as the anode film ensure efficient electrolyte infiltration into both the exterior and interior of porous and open spheres for a high utilization of the active material, showing an excellent electrochemical performance for LIBs (1595 mAh g^-1 over 300 cycles at 2 A g^-1 , 441.6 mAh g^-1 over 4000 cycles at 10 A g^-1 ). Besides, this straightforward synthetic method opens an efficacious avenue for the construction of various nanosheet-assembled hollow single-hole TMO spheres for potential applications.

3D CoMoSe4 Nanosheet Arrays Converted Directly from Hydrothermally Processed CoMoO4 Nanosheet Arrays by Plasma-Assisted Selenization Process Toward Excellent Anode Material in Sodium-Ion Battery

In this work, three-dimensional (3D) CoMoSe4 nanosheet arrays on network fibers of a carbon cloth denoted as CoMoSe4@C converted directly from CoMoO4 nanosheet arrays prepared by a hydrothermal process followed by the plasma-assisted selenization at a low temperature of 450 °C as an anode for sodium-ion battery (SIB) were demonstrated for the first time. With the plasma-assisted treatment on the selenization process, oxygen (O) atoms can be replaced by selenium (Se) atoms without the degradation on morphology at a low selenization temperature of 450 °C. Owing to the high specific surface area from the well-defined 3D structure, high electron conductivity, and bi-metal electrochemical activity, the superior performance with a large sodium-ion storage of 475 mA h g-1 under 0.5-3 V potential range at 0.1 A g-1 was accomplished by using this CoMoSe4@C as the electrode. Additionally, the capacity retention was well maintained over 80 % from the second cycle, exhibiting a satisfied capacity of 301 mA h g-1 even after 50 cycles. The work delivered a new approach to prepare a binary transition metallic selenide and definitely enriches the possibilities for promising anode materials in SIBs with high performances.

MoP hollow nanospheres encapsulated in 3D reduced graphene oxide networks as high rate and ultralong cycle performance anodes for sodium-ion batteries

Molybdenum phosphide (MoP), regarded as a promising anode material for sodium-ion batteries due to its superior conductivity and high theoretical specific capacity, still suffers from rapid capacity decay because of a large volume change and weak diffusion kinetics. Hollow nano-structures will be an effective solution to alleviate structural strain and improve cycling stability. Yet the preparation of MoP needs a high temperature phosphorization procedure which would cause agglomeration and structure collapse, making it difficult to achieve hollow nano-structures. Herein, caged by 3D graphene networks, MoP hollow nanospheres encapsulated in 3D reduced graphene oxide networks (H-MoP@rGO) were prepared successfully, and benefiting from the merits of the hollow nano-structure and flexibility of rGO, H-MoP@rGO demonstrates a superior cycle performance of 353.8 mA h g-1 at 1 A g-1 after 600 cycles and an extraordinary rate performance of 183.4 mA h g-1 at an ultrahigh current density of 10 A g-1 even after 3000 cycles.

Ultrathin Ti3C2Tx (MXene) Nanosheet-Wrapped NiSe2 Octahedral Crystal for Enhanced Supercapacitor Performance and Synergetic Electrocatalytic Water Splitting

Metal selenides, such as NiSe₂, have exhibited great potentials as multifunctional materials for energy storage and conversation. However, the utilization of pure NiSe₂ as electrode materials is limited by its poor cycling stability, low electrical conductivity, and insufficient electrochemically active sites. To remedy these defects, herein, a novel NiSe₂/Ti₃C₂T_x hybrid with strong interfacial interaction and electrical properties is fabricated, by wrapping NiSe₂ octahedral crystal with ultrathin Ti₃C₂T_x MXene nanosheet. The NiSe₂/Ti₃C₂T_x hybrid exhibits excellent electrochemical performance, with a high specific capacitance of 531.2 F g^-1 at 1 A g^-1 for supercapacitor, low overpotential of 200 mV at 10 mA g^-1, and small Tafel slope of 37.7 mV dec^-1 for hydrogen evolution reaction (HER). Furthermore, greater cycling stabilities for NiSe₂/Ti₃C₂T_x hybrid in both supercapacitor and HER have also been achieved. These significant improvements compared with unmodified NiSe₂ should be owing to the strong interfacial interaction between NiSe₂ octahedral crystal and Ti₃C₂T_x MXene, which provides enhanced conductivity, fast charge transfer as well as abundant active sites, and highlight the promising potentials in combinations of MXene with metal selenides for multifunctional applications such as energy storage and conversion.

A metal-organic-framework approach to engineer hollow bimetal oxide microspheres towards enhanced electrochemical performances of lithium storage

Nanosized electrode materials with a hollow structure, larger specific surface area, and lower energy density as well as more void space are widely adopted for high-performance lithium-ion batteries. In this work, we obtained bimetal-organic frameworks of Fe/Mn-MOF-74 with a hollow microsphere morphology via a facile one-step microwave method and further used it to fabricate hollow Fe-Mn-O/C microspheres. Endowed with the metal-organic-framework-derived carbon-coated nanoparticle-assembled hollow structure with hierarchical porous characteristics and synergistic effects between two different metal species, the Fe-Mn-O/C electrode exhibits outstanding electrochemical performances as the anode of lithium-ion batteries. It achieves improved cycling performance (1294 mA h g-1 after 200 cycles at 0.1 A g-1) and good rate capability (722, 604, and 521 mA h g-1 at 0.2, 0.5 and 1 A g-1). The smart design of a hollow morphology with uniform two metal species can promote the synthesis of multimetal oxides and their carbon composites, as well as their further potential application for energy-storage.