Oxygen-Incorporated MoS₂ Nanosheets with Expanded Interlayers for Hydrogen Evolution Reaction and Pseudocapacitor Applications

Two-dimensional transition-metal dichalcogenides (TMDs) nanosheets have attracted tremendous research interest. Engineering the structure of MoS₂ may result in desirable performance for energy applications. In this work, oxygen-incorporated MoS₂ nanosheets with expanded interlayers have been synthesized by a solvothermal reaction. The oxygen-incorporated MoS₂ nanosheets with rich defects demonstrate excellent hydrogen evolution reaction activity with a small Tafel slope of 42 mV decade^–1 as well as excellent long-term stability. Interestingly, a large expanded ∼8.40 Å interlayer of (002) faces can be achieved by controlling the reaction time. This material also shows excellent long-term cycling stability (up to 20 000 cycles) as well as high specific capacitance for pseudocapacitors. We believe that the structural modification strategy can be applied for other TMDs to further optimize the performance for various applications

Additional file 1: of Controllable Preparation of V2O5/Graphene Nanocomposites as Cathode Materials for Lithium-Ion Batteries

XRD patterns of vanadium precursors, CV curves, charge/discharge profiles of the V@GO-II composite. Discharge/charge voltage profiles of the V@GO-I composite. Raman peaks and their assignments of V2O5. Figure S1. XRD patterns of the nanosheet-assembled vanadium precursor/GO composite (blue line) and the nanoparticle-assembled vanadium precursor/GO composite (red line). Figure S2. CV curves of the V/GO-II composite at a scan rate of 0.1 mV s−1. Figure S3. Charge/discharge profiles of the V@GO-II composite at different densities. Figure S4. Discharge/charge voltage profiles of the V@GO-I composite (a) and the V@GO-I composite (b) at a current rate of 2C. (DOC 4760 kb

Ultrathin Na_1.1V₃O_7.9 Nanobelts with Superior Performance as Cathode Materials for Lithium-Ion Batteries

The Na_1.1V₃O_7.9 nanobelts have been synthesized by a facile and scalable hydrothermal reaction with subsequent calcinations. The morphologies and the crystallinity of the nanobelts are largely determined by the calcination temperatures. Ultrathin nanobelts with a thickness around 20 nm can be obtained, and the TEM reveals that the nanobelts are composed of many stacked thinner belts. When evaluated as a cathode material for lithium batteries, the Na_1.1V₃O_7.9 nanobelts exhibit high specific capacity, good rate capability, and superior long-term cyclic stability. A high specific capacity of 204 mA h g^–1 can be delivered at the current density of 100 mA g^–1. It shows excellent capacity retention of 95% after 200 cycles at the current density of 1500 mA g^–1. As demonstrated by the ex situ XRD results, the Na_1.1V₃O_7.9 nanobelts have very good structural stability upon cycling. The superior electrochemical performances can be attributed to the ultra-thin nanobelts and the good structural stability of the Na_1.1V₃O_7.9 nanobelts

Uniform MnCo₂O₄ Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo₂O₄ porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo₂O₄ dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m² g^–1 with a pore size distribution of 2–10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo₂O₄ dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g^–1 can be maintained after 180 cycles at 200 mA g^–1. Even at a high current density of 2000 mA g^–1, the electrode can still deliver a specific capacity of 423.3 mA h g^–1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo₂O₄ porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm^–2 and a Tafel slope of 93 mV dec^–1

Dodecahedron-Shaped Porous Vanadium Oxide and Carbon Composite for High-Rate Lithium Ion Batteries

Carbon-based nanocomposites have been extensively studied in energy storage and conversion systems because of their superior electrochemical performance. However, the majority of metal oxides are grown on the surface of carbonaceous material. Herein, we report a different strategy of constructing V₂O₅ within the metal organic framework derived carbonaceous dodecahedrons. Vanadium precursor is absorbed into the porous dodecahedron-shaped carbon framework first and then <i>in situ</i> converted into V₂O₅ within the carbonaceous framework in the annealing process in air. As cathode materials for lithium ion batteries, the porous V₂O₅@C composites exhibit enhanced electrochemical performance, due to the synergistic effect of V₂O₅ and carbon composite

Nanorod-Nanoflake Interconnected LiMnPO₄·Li₃V₂(PO₄)₃/C Composite for High-Rate and Long-Life Lithium-Ion Batteries

Olivine-type structured LiMnPO₄ has been extensively studied as a high-energy density cathode material for lithium-ion batteries. However, preparation of high-performance LiMnPO₄ is still a large obstacle due to its intrinsically sluggish electrochemical kinetics. Recently, making the composites from both active components has been proven to be a good proposal to improve the electrochemical properties of cathode materials. The composite materials can combine the advantages of each phase and improve the comprehensive properties. Herein, a LiMnPO₄·Li₃V₂(PO₄)₃/C composite with interconnected nanorods and nanoflakes has been synthesized via a one-pot, solid-state reaction in molten hydrocarbon, where the oleic acid functions as a surfactant. With a highly uniform hybrid architecture, conductive carbon coating, and mutual cross-doping, the LiMnPO₄·Li₃V₂(PO₄)₃/C composite manifests high capacity, good rate capability, and excellent cyclic stability in lithium-ion batteries. The composite electrodes deliver a high reversible capacity of 101.3 mAh g^–1 at the rate up to 16 C. After 4000 long-term cycles, the electrodes can still retain 79.39% and 72.74% of its maximum specific discharge capacities at the rates of 4C and 8C, respectively. The results demonstrate that the nanorod-nanoflake interconnected LiMnPO₄·Li₃V₂(PO₄)₃/C composite is a promising cathode material for high-performance lithium ion batteries

Nitrogen-Doped Yolk–Shell-Structured CoSe/C Dodecahedra for High-Performance Sodium Ion Batteries

In this work, nitrogen-doped, yolk–shell-structured CoSe/C mesoporous dodecahedra are successfully prepared by using cobalt-based metal–organic frameworks (ZIF-67) as sacrificial templates. The CoSe nanoparticles are in situ produced by reacting the cobalt species in the metal–organic frameworks with selenium (Se) powder, and the organic species are simultaneously converted into nitrogen-doped carbon material in an inert atmosphere at temperatures between 700 and 900 °C for 4 h. For the composite synthesized at 800 °C, the carbon framework has a relatively higher extent of graphitization, with high nitrogen content (17.65%). Furthermore, the CoSe nanoparticles, with a size of around 15 nm, are coherently confined in the mesoporous carbon framework. When evaluated as novel anode materials for sodium ion batteries, the CoSe/C composites exhibit high capacity and superior rate capability. The composite electrode delivers the specific capacities of 597.2 and 361.9 mA h g^–1 at 0.2 and 16 A g^–1, respectively

Presentation_1_Electrospun Single Crystalline Fork-Like K2V8O21 as High-Performance Cathode Materials for Lithium-Ion Batteries.pdf

<p>Single crystalline fork-like potassium vanadate (K₂V₈O₂₁) has been successfully prepared by electrospinning method with a subsequent annealing process. The as-obtained K₂V₈O₂₁ forks show a unique layer-by-layer stacked structure. When used as cathode materials for lithium-ion batteries, the as-prepared fork-like materials exhibit high specific discharge capacity and excellent cyclic stability. High specific discharge capacities of 200.2 and 131.5 mA h g⁻¹ can be delivered at the current densities of 50 and 500 mA g⁻¹, respectively. Furthermore, the K₂V₈O₂₁ electrode exhibits excellent long-term cycling stability which maintains a capacity of 108.3 mA h g⁻¹ after 300 cycles at 500 mA g⁻¹ with a fading rate of only 0.043% per cycle. The results demonstrate their potential applications in next-generation high-performance lithium-ion batteries.</p

Ni₂P₂O₇ Nanoarrays with Decorated C₃N₄ Nanosheets as Efficient Electrode for Supercapacitors

Ni₂P₂O₇-based composites grown on conductive substrate can efficiently promote the electrical transport during the electrochemical reactions in supercapacitors. However, Ni₂P₂O₇ nanoarrays are easily peeled off from the substrate upon repeated electrochemical reaction. Herein, Ni₂P₂O₇ nanoarrays grown on Ni foam with surficially decorated C₃N₄ thin nanosheets are achieved by a hydrothermal and in situ calcination strategy. The decorated C₃N₄ nanosheet network on the surface fully covers both Ni₂P₂O₇ and Ni foam and efficiently prevents Ni₂P₂O₇ nanoarrays from peeling off during the charge and discharge cycles. The optimized composites exhibit high pseudocapacitance and greatly enhanced cycling stability. The assembled asymmetric supercapacitor shows favorable specific capacitance and stability as energy storage devices. Such a strategy for fabricating C₃N₄-modified Ni₂P₂O₇ nanoarrays is feasible and efficient, and can be therefore extended for constructing other electrodes with high capacitance and excellent stability