Self-templated formation of tremella-like MoS<Subscript>2</Subscript> with expanded spacing of (002) crystal planes for Li-ion batteries

Tremella-like MoS₂ consisting of ultrathin nanosheets (~7 nm in thickness) is prepared via a one-pot hydrothermal reaction without using any surfactants and templates. The reaction involves transforming precursor MoO₃ to polyhedral intermediate (K₂NaMoO₃F₃ and K₃Mo₂O₄F₅) through its reaction with Na⁺, K⁺, and F^? ions in the initial stage of hydrothermal reaction. Then the polyhedral intermediate acting as the sacrifice template reacts with the S^2? released from a hydrolysis process of SCN^? ion and transforms to tremella-like MoS₂. The obtained MoS₂ product exhibits expended spacing of the (002) crystal plane, which can facilitate faster lithium ions intercalation behavior. This tremella-like MoS₂ used as an anode material for lithium-ion batteries shows a very high reversible capacity of 693 mA h g^?1 after 50 cycles, good rate capability, and high cyclic capacity retention. Even cycled at a high current density of 4800 mA g^?1, the tremella-like MoS₂ still can deliver a high capacity of 252 mA h g^?1. The secondary hierarchical microstructures consisting of ultrathin nanosheets are beneficial to greatly improved electrochemical performance of the MoS₂ electrode.     

Improved cycling stability of the capping agent-free nanocrystalline FeS<Subscript>2</Subscript> cathode via an upper cut-off voltage control

Transition metal chalcogenides such as FeS₂ are promising electrode materials for energy storage. However, poor rate performance and low cycling stability hinder the practical application of FeS₂ cathode in secondary batteries. In this study, highly pure pyrite FeS₂ nanocrystals (NCs) with octahedral shape and 200–300 nm size have been synthesized via a facile and environmentally benign approach based on a surfactant-free aqueous reaction. Combined with a compatible ether electrolyte, the prepared FeS₂ NCs, despite their dimension far beyond the quantum confined regime, could achieve high utilization and reversibility as a cathode active material due to the well-defined crystal structure and the uncapped rough surfaces. Furthermore, we find that the last charging voltage step of FeS₂ only contributes a minor capacity but caused severe capacity fading due to the formation of soluble polysulfides. By suppressing this step through setting a proper upper cut-off voltage, the cycle life of the Li/FeS₂ cell is dramatically improved. The Li/FeS₂ cell running over a voltage window of 1.0–2.4 V at 1C delivers an initial capacity of 486.1 mA h g^?1, slightly lower than that running over 1.0–3.0 V (561.1 mA h g^?1), but outperforms the latter substantially after 500 cycles (367 mA h g^?1 vs 315 mA h g^?1), corresponding to a capacity decay rate as low as 0.048% per cycle. Our results provide a meaningful approach for the development of not only the advanced FeS₂ material for long-life rechargeable batteries, but also other transition metal chalcogenide nanomaterials for a variety of potential applications.     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods with secondary plate-like nanostructures; preparation,characterization and application as high performance electrode material in supercapacitors

Mn₃O₄ nanorods with secondary plate-like structures were prepared through precipitation from a 0.005 M manganese chloride bath, under the applying direct current mode (i = 2 mA cm^?2). The structural analysis through XRD and FTIR confirmed that the deposited nanopowder has pure monoclinic phase of Mn₃O₄. Further morphological assessment through SEM proved the product to have the Mn₃O₄ nanorods in large quantity, which constructed the secondary plate-like building blocks. Cyclic voltammetric and charge–discharge experiments on the product indicated the prepared Mn₃O₄ to possess high specific capacitance (SC) values of 298 F g^?1, as well as an outstandingly durable cycling stability (95.1 % of initial capacity after discharging 1000 cycles).     

Mn<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles embedded in 3D reduced graphene oxide network as anode for high-performance lithium ion batteries

Mn₃O₄ nanoparticles were in-situ synthesized in the 3D framework of reduced graphene oxide (RGO) by a facile one-step hydrothermal method. In the reduced graphene-Mn₃O₄ (RGM) composite, the RGO network not only serves as a mechanical support to construct a self-supported and binder-free electrode, but also offers 3D continuous conductive network for effective electron transfer. The Mn₃O₄ nanoparticles anchored uniformly across the RGO framework, which provided high capacity and prevented the restacking of the RGO thin sheets. Based on the unique composite structures, strong synergistic effect was achieved between Mn₃O₄ and RGO, resulting in superior specific capacity, enhanced rate capability, stable cycling performance and nearly 100% Coulombic efficiency in the RGM2 composites. With an optimal Mn₃O₄ composition of 44% by weight (similarly hereinafter), the composite exhibits high specific capacities of 696–795 mAh g¹ based on the overall weight of the electrode in 60 cycles at 200 mA g^?1, with a large coulombic efficiency of around 98%. Even at a high current density of 10,000 mA g^?1, the composite can still deliver a capacity of 383 mAh g^?1, demonstrating its excellent rate performance. The outstanding performances of the composites are attributed to the synergistic effect of both components and the hierarchical structure of the composite.     

Vertically-aligned Mn(OH)<Subscript>2</Subscript> nanosheet films for flexible all-solid-state electrochemical supercapacitors

The arrangement of the electrode materials is a significant contributor for constructing high performance supercapacitor. Here, vertically-aligned Mn(OH)₂ nanosheet thin films were synthesized by cathodic electrodeposition technique on flexible Au coated polyethylene terephthalate substrates. Morphologies, microstructures, chemical compositions and valence state of the nanosheet films were characterized systematically. It shows that the nanosheets arranged vertically to the substrate, forming a porous nanowall structures and creating large open framework, which greatly facilitate the adsorption or diffusion of electrolyte ions for faradaic redox reaction. Electrochemical tests of the films show the specific capacitance as high as 240.2 F g^?1 at 1.0 A g^?1. The films were employed to assemble symmetric all-solid-state supercapacitors with LiCl/PVA gel severed as solid electrolyte. The solid devices exhibit high volumetric capacitance of 39.3 mF?cm^?3 at the current density 0.3 mA cm^?3 with robust cycling stability. The superior performance is attributed to the vertically-aligned configuration.     

Impact of CTAB on morphology and electrochemical performance of MoS<Subscript>2</Subscript> nanoflowers with improved lithium storage properties

The search for high capacity, low-cost electrode materials for lithium-ion batteries is a significant challenge in energy research. Among the numerous potential candidates, layered compounds such as MoS₂ (Molybdenum Disulfide) have attracted increasing attention. A facile hydrothermal reduction process using hexadecyltrimethy ammonium bromide (CTAB) as surfactant was developed for the synthesis of lithium-ion battery anode material MoS₂ nanoflowers. The impact of CTAB on morphology and electrochemical performance of MoS₂ has been investigated. With the increase of CTAB content, MoS₂ ultrathin nanosheets with high specific surface area and more active sites have been successfully synthesized. Electrochemical measurements demonstrated that MoS₂ nanoflowers synthesized with 1% content of CTAB have better electrochemical performance than others as anode materials for Li-ion batteries, which yield a high discharge capacity of 1245 mAh g^?1 at a current density of 50 mA g^?1 and a stable capacity retention of 740 mAh g^?1 until 100 electrochemical cycles.     

Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystal anode materials with improved cyclic stability for lithium ion batteries

The cyclic stability of Cr₂O₃ is very poor due to the large volume change during lithiation/delithiation. In this study, we have found that Cr₂O₃ nanocrystals synthesized by using a simple hydrothermal method can improve its cyclic stability. Sample calcined at 430 °C has uniform size, compact structure and high crystallization degree. These Cr₂O₃ nanocrystals exhibit a stable cyclic performance of 185 mAh g^?1 after 100 cycles at 100 mA g^?1. It is useful in real life, such as providing power consumption for minitype device, etc.     

Construction of point-line-plane (0-1-2 dimensional) Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-SnO<Subscript>2</Subscript>/graphene hybrids as the anodes with excellent lithium storage capability

The assembly of hybrid nanomaterials has opened up a new direction for the construction of high-performance anodes for lithium-ion batteries (LIBs). In this work, we present a straightforward, eco-friendly, one-step hydrothermal protocol for the synthesis of a new type of Fe₂O₃-SnO₂/graphene hybrid, in which zero-dimensional (0D) SnO₂ nanoparticles with an average diameter of 8 nm and one-dimensional (1D) Fe₂O₃ nanorods with a length of ~150 nm are homogeneously attached onto two-dimensional (2D) reduced graphene oxide nanosheets, generating a unique point-line-plane (0D-1D-2D) architecture. The achieved Fe₂O₃-SnO₂/graphene exhibits a well-defined morphology, a uniform size, and good monodispersity. As anode materials for LIBs, the hybrids exhibit a remarkable reversible capacity of 1,530 mA·g^?1 at a current density of 100 mA·g^?1 after 200 cycles, as well as a high rate capability of 615 mAh·g^?1 at 2,000 mA·g^?1. Detailed characterizations reveal that the superior lithium-storage capacity and good cycle stability of the hybrids arise from their peculiar hybrid nanostructure and conductive graphene matrix, as well as the synergistic interaction among the components.

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3D composites of ZnSnO<Subscript>3</Subscript> nanoplates/reduced graphene oxide aerogels as an advanced lithium-ion battery anode

Zinc-based bimetal oxides have received considerable attention as anode for lithium-ion batteries (LIBs). A one-pot self-assembly hydrothermal method is developed for the fabrication of 3D hierarchical structure aerogels from zinc stannate (ZnSnO₃) and reduced graphene oxide (rGO). 3D interconnected porous structure with ZnSnO₃ hexagon nanoplates uniformly dispersed on graphene sheets has been constructed successfully, in which the crystalline hexagon nanoplates ZnSnO₃ are firstly used to prepare ZnSnO₃-based anode materials for LIBs. The as-prepared ZnSnO₃ nanoplates/reduced graphene oxide aerogels (ZnSnO₃–rGAs) electrode demonstrates an excellent reversible capacity (780 mAh g^?1) after 200 cycles at a certain current density (100 mA g^?1) and still delivers a specific capacity of 460 mAh g^?1 even at 1000 mA g^?1. The superior performance of lithium storage is attributed to the 3D porous hierarchical structure and the synergistic effects of uniform hexagon nanoplates ZnSnO₃ and rGO sheets.     

Scalable synthesis of TiO<Subscript>2</Subscript> crystallites embedded in bread-derived carbon matrix with enhanced lithium storage performance

TiO₂/carbon (C/TiO₂) composites have been synthesized via an in-situ pyrolysis method using bread as carbon source and investigated as anodes for lithium-ion batteries. As a cheap and common staple food with a sponge-like structure, bread contains a certain amount of moisture, enabling the hydrolysis of tetrabutyl orthotitanate. It is characterized that TiO₂ nanocrystallites are embedded in bread-derived carbon matrix, and their synergetic effect on improving electrochemical properties is demonstrated as well. Partially surface lithium storage of ultrasmall TiO₂ particles is credited to the unique embedment structure. Meanwhile, the carbon species are of importance in enhancing reversible capacities and accelerating interfacial charge transfer. It delivers a reversible capacity of 231 mAh g^?1 at a specific current of 100 mA g^?1 after 200 cycles for the resultant C/TiO₂ composite with 38.8 wt.% carbon. This work presents a facile strategy toward scalable and eco-friendly preparation of metal oxides compositing with carbonaceous materials.     

Samarium-doped Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles with improved magnetic and supercapacitive performance: a novel preparation strategy and characterization

Sm³⁺-doped magnetite (Fe₃O₄) nanoparticles were synthesized through a one-pot facile electrochemical method. In this method, products were electrodeposited on a stainless steel (316L) cathode from an additive-free 0.005 M Fe(NO₃)₃/FeCl₂/SmCl₃ aqueous electrolyte. The structural characterizations through X-ray diffraction, field-emission electron microscopy, and energy-dispersive X-ray indicated that the deposited material has Sm³⁺-doped magnetite particles with average size of 20 nm. Magnetic analysis by VSM revealed the superparamagnetic nature of the prepared nanoparticles (Ms = 41.89 emu g^?1, Mr = 0.12 emu g^?1, and H _Ci = 2.24 G). The supercapacitive capability evaluation of the prepared magnetite nanoparticles through cyclic voltammetry and galvanostat charge–discharge showed that these materials are capable to deliver specific capacitances as high as 207 F g^?1 (at 0.5 A g^?1) and 145 F g^?1 (at 2 A g^?1), and capacity retentions of 94.5 and 84.6% after 2000 cycling at 0.5 and 1 A g^?1, respectively. The results proved the suitability of the electrosynthesized nanoparticles for use in supercapacitors. Furthermore, this work provides a facile electrochemical route for the synthesis of lanthanide-doped magnetite nanoparticles.     

High-performance flexible supercapacitors based on C/Na<Subscript>2</Subscript>Ti<Subscript>5</Subscript>O<Subscript>11</Subscript> nanocomposite electrode materials

A new solution method to synthesize Na₂Ti₅O₁₁ with titanium powder is presented, and the C/Na₂Ti₅O₁₁ nanocomposite with high specific surface area and tunnel structure as the electrode material has excellent electrochemical performance. The single electrode composed of the C/Na₂Ti₅O₁₁ nanocomposite based on carbon fiber fabric (CFF) has the highest area capacitance of 1066 mF cm^?2 at a current density of 2 mA cm^?2, which is superior to other titanates and Na-ion materials for supercapacitors (SCs). By scan-rate dependence cyclic voltammetry analysis, the capacity value shows both capacitive and faradaic intercalation processes, and the intercalation process contributed 81.7% of the total charge storage at the scan rate of 5 mV s^?1. The flexible symmetric solid-state SCs (C/Na₂Ti₅O₁₁/CFF//C/Na₂Ti₅O₁₁/CFF) based on different C/Na₂Ti₅O₁₁ mass were fabricated, and 7 mg SCs show the best supercapacitive characteristics with an area capacitance of 309 mF cm^?2 and a specific capacitance of 441 F g^?1, it has a maximum energy density of 22 Wh kg^?1 and power density of 1286 W kg^?1. As for practical application, three SCs in series can power 100 green light-emitting diodes (LEDs) to light up for 18 min, which is much longer than our previous work by Wang et al. lighting 100 LEDs for 8 min. Thus, the C/Na₂Ti₅O₁₁ nanocomposite has promising potential application in energy storage devices.     

Template-free synthesis of Ni<Subscript>2</Subscript>P hollow microspheres with great photocatalytic and electrochemical properties

The hollow Ni₂P microspheres were prepared using a facile one-step template-free solvothermal method. The products were characterized and the results showed that they were pure hexagonal Ni₂P microspheres, made up of large amounts of Ni₂P nanoparticles, and had an obvious inner space in the central of the microspheres. After being investigated, it was found that these Ni₂P hollow spheres initially were some solid spheres, but after a specified time, they were converted to a hollow structure by an Ostwald ripening process, some even had a multi-wall hollow structure. Meanwhile, the as-prepared Ni₂P hollow spheres showed a good photocatalytic degradation performance for Methylene Blue in aqueous solution. Electrochemical measurements turned out that the Ni₂P hollow spheres have a great cycling performance. The initial discharge capacity capacity of is Ni₂P hollow spheres up to 660 mAh g^?1 and it always keep in about 300 mAh g^?1 within 100 cycles at the current density of 100 mA g^?1.     

Ordered mesoporous carbon-supported CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> composite with enhanced lithium storage properties

A high and stable reversible specific capacity (1277.7 mAh g^?1) was successfully achieved by the CoFe₂O₄/ordered mesoporous carbon nanohybrids (CFO/CMK-3) composite anode at the current density of 0.1 A g^?1 after 100 cycles. CFO/CMK-3 electrode also exhibited a stable capacity up to 733.2 and 482.6 mAh g^?1 at the current densities of 0.5 and 1 A g^?1 after 500 cycles, respectively. The CFO particles were found to be uniformly distributed inside the pore channels of CMK-3. Structure characterization before and after 100 tests revealed that the specific CMK-3 mesoporous structure and CFO crystallites remained unchanged. The stability of the anode composite stability and the rapid redox capability of CFO gave rise to superior lithium storage capacity and excellent cycling stability. CFO/CMK-3 showed a great promise to serve as anode for high-performance lithium-ion battery.     

Investigation for the synthesis of hierarchical Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@MnO<Subscript>2</Subscript> nanoarrays materials and their application for supercapacitor

We designed and fabricated hierarchical Co₃O₄@MnO₂ nanoarrays directly grown on nickel foam by hydrothermal and calcination methods. After the investigation of growth mechanism, we found that the deposition of MnO₂ was based on the self-decomposition of KMnO₄ and the reducibility of Co₃O₄ during the hydrothermal process. Thanks to the hierarchical structure, the obtained electrode exhibited excellent capacitive performance in supercapacitor. It delivered 21.72 F cm^?2 at a current density of 5 mA cm^?2 and retained ~94 % capacitance of initial value after 5000 cycles.     

Rietveld analysis of CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> thin films obtained by RF-sputtering

Calcium copper titanate, CaCu₃Ti₄O₁₂, CCTO, thin films with polycrystalline nature have been deposited by RF sputtering on Pt/Ti/SiO₂/Si (100) substrates at a room temperature followed by annealing at 600 °C for 2 h in a conventional furnace. The crystalline structure and the surface morphology of the films were markedly affected by the growth conditions. Rietveld analysis reveal a CCTO film with 100 % pure perovskite belonging to a space group Im3 and pseudo-cubic structure. The XPS spectroscopy reveal that the in a reducing N₂ atmosphere a lower Cu/Ca and Ti/Ca ratio were detected, while the O₂ treatment led to an excess of Cu, due to Cu segregation of the surface forming copper oxide crystals. The film present frequency -independent dielectric properties in the temperature range evaluated, which is similar to those properties obtained in single-crystal or epitaxial thin films. The room temperature dielectric constant of the 600-nm-thick CCTO films annealed at 600 °C at 1 kHz was found to be 70. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10^?7 A/cm² at a 1.0 V. The current–voltage measurements on MFS capacitors established good switching characteristics.     

Facile synthesis and characterization of MnO<Subscript>2</Subscript> nanomaterials as supercapacitor electrode materials

MnO₂ nanomaterials are synthesized via calcinations in air at various temperatures. Amorphous MnO₂ masses appear between 100 and 300 °C and nanorods form above 400 °C. Transmission and scanning electron microscopy are used to observe the geometries of each material, with further structural analyses conducted using X-ray photoelectron spectroscopy, X-ray diffraction, and BET method. The electrochemical properties are investigated through galvanostatic charge/discharge cycling, electrochemical impedance spectra, and cyclic voltammetry within a three-electrode test cell filled with 1 mol L^?1 Na₂SO₄ solution. The slightly asymmetric galvanostatic cycling curves suggest that the reversibility of the Faradaic reactions are imperfect, requiring a larger time to charge than discharge. The specific capacitances of each sample are calculated and trends are identified, proving that the samples synthesized at higher temperatures exhibit poorer electrochemical behaviors. The highest calculated specific capacitance is 175 F g^?1 by the sample calcinated at 400 °C. However, the lower temperature samples exhibit more favorable geometric properties and higher overall average specific capacitances. For future research, it is suggested that surface modifications such as a carbon coating could be used in conjunction with the MnO₂ nanorods to reach the electrochemical properties required by contemporary industrial applications.     

Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

Enhanced electrochemical reduction of hydrogen peroxide by Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowire electrode

Crystalline Co₃O₄ nanowire arrays with different morphologies grown on Ni foam were investigated by varying the reaction temperature, the concentration of precursors, and reaction time. The Co₃O₄ nanowires synthesized under typical reaction condition had a diameter range of approximately 500–900 nm with a length of 17 µm. Electrochemical reduction of hydrogen peroxide (H₂O₂) of the optimized Co₃O₄ nanowire electrode was studied by cyclic voltammetry. A high current density of 101.8 mA cm^?2 was obtained at ?0.4 V in a solution of 0.4 M H₂O₂ and 3.0 M NaOH at room temperature compared to 85.8 mA cm^?2 at ?0.35 V of the Co₃O₄ nanoparticle electrode. Results clearly indicated that the Ni foam supported Co₃O₄ nanowire electrode exhibited superior catalytic activity and mass transport kinetics for H₂O₂ electrochemical reduction.     

Graphene oxide-decorated Fe<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> microflowers as a promising anode for lithium and sodium storage

Mixed transition metal oxides (MTMOs) have received intensive attention as promising anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). In this work, we demonstrate a facile one-step water-bath method for the preparation of graphene oxide (GO) decorated Fe₂(MoO₄)₃ (FMO) microflower composite (FMO/GO), in which the FMO is constructed by numerous nanosheets. The resulting FMO/GO exhibits excellent electrochemical performances in both LIBs and SIBs. As the anode material for LIBs, the FMO/GO delivers a high capacity of 1,220 mAh·g^–1 at 200 mA·g^–1 after 50 cycles and a capacity of 685 mAh·g^–1 at a high current density of 10 A·g^–1. As the anode material for SIBs, the FMO/GO shows an initial discharge capacity of 571 mAh·g^–1 at 100 mA·g^–1, maintaining a discharge capacity of 307 mAh·g^–1 after 100 cycles. The promising performance is attributed to the good electrical transport from the intimate contact between FMO and graphene oxide. This work indicates that the FMO/GO composite is a promising anode for high-performance lithium and sodium storage.

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