Nanocapsule of MnS Nanopolyhedron Core@CoS Nanoparticle/Carbon Shell@Pure Carbon Shell as Anode Material for High-Performance Lithium Storage.

MnS has been explored as an anode material for lithium-ion batteries due to its high theoretical capacity, but low electronic conductivity and severe volume change induce low reversible capacity and poor cycling performance. In this work, the nanocapsule consisting of MnS nanopolyhedrons confined in independent, closed and conductive hollow polyhedral nanospheres is prepared by embedding MnCO3 nanopolyhedrons into ZIF-67, followed by coating of RF resin and gaseous sulfurization/carbonization. Benefiting from the unique nanocapsule structure, especially inner CoS/C shell and outer pure C shell, the MnS@CoS/C@C composite as anode material presents excellent cycling performance (674 mAh g-1 at 1 A g-1 after 300 cycles; 481 mAh g-1 at 5 A g-1 after 300 cycles) and superior rate capability (1133.3 and 650.6 mAh g-1 at 0.1 and 4 A g-1), compared to the control materials (MnS and MnS@CoS/C) and other MnS composites. Kinetics measurements further reveal a high proportion of the capacitive effect and low reaction impedance of MnS@CoS/C@C. SEM and TEM observation on the cycled electrode confirms superior structural stability of MnS@CoS/C@C during long-term cycles. Excellent lithium storage performance and the convenient synthesis strategy demonstrates that the MnS@CoS/C@C nanocapsule is a promising high-performance anode material.

Architecture Design and Catalytic Activity: Non-Noble Bimetallic CoFe/fe3 O4 Core-Shell Structures for CO2 Hydrogenation.

Non-noble metal catalysts now play a key role in promoting efficiently and economically catalytic reduction of CO2 into clean energy, which is an important strategy to ameliorate global warming and resource shortage issues. Here, a non-noble bimetallic catalyst of CoFe/Fe3 O4 nanoparticles is successfully designed with a core-shell structure that is well dispersed on the defect-rich carbon substrate for the hydrogenation of CO2 under mild conditions. The catalysts exhibit a high CO2 conversion activity with the rate of 30% and CO selectivity of 99%, and extremely robust stability without performance decay over 90 h in the reverse water gas shift reaction process. Notably, it is found that the reversible exsolution/dissolution of cobalt in the Fe3 O4 shell will lead to a dynamic and reversible deactivation/regeneration of the catalysts, accompanying by shell thickness breathing during the repeated cycles, via atomic structure study of the catalysts at different reaction stages. Combined with density functional theory calculations, the catalytic activity reversible regeneration mechanism is proposed. This work reveals the structure-property relationship for rational structure design of the advanced non-noble metallic catalyst materials with much improved performance.

Nanowires-Assembled TiO2 Nanorods Anchored on Multilayer Graphene for High-Performance Anodes of Lithium-Ion Batteries.

Multilayer graphene (MLG) prepared via ultrasonic exfoliation has many advantages such as its low-cost and defect-free nature, high electronic conductivity, and large specific surface area, which make it an apt conductive substrate for TiO2 composites. To synthesize graphene/TiO2 hybrids, traditional methods that greatly depend on the chemical bond of oxygen-containing functional groups on graphene with titanium cations are not applicable due to the absence of these functional groups on MLG. In this work, a facile chemical method is developed to directly deposit TiO2 on the MLG surface without the introduction of chemically active groups. With this method, four types of TiO2 materials, that is pure anatase TiO2 nanoparticles, a mixture of anatase TiO2 nanoparticles and rutile TiO2 nanoflowers, pure rutile TiO2 nanoflowers, and pure rutile TiO2 nanorods, are homogeneously anchored on the MLG surface by controlling the amount of HCl in the reactant. Interestingly, the rutile TiO2 nanorods in the TiO2/MLG composite are assembled by many TiO2 nanowires with an ultra-small diameter and ultra-long length, which provides a better synergetic effect for high performances as LIB anodes than other composites. A specific capacity of 631.4 mAh g-1 after 100 cycles at a current density of 100 mA g-1 is delivered, indicating it to be a valuable LIB anode material with low cost and high electrochemical performances.

Synthesis and H2S-Sensing Properties of MOF-Derived Cu-Doped ZnO Nanocages.

Metal-organic framework (MOF)-derived pure ZnO and Cu-doped ZnO nanocages were fabricated by calcining a zeolitic imidazole framework (ZIF-8) and Cu-doped ZIF-8. The morphology and crystal structure of the samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). It was found that Cu doping did not change the crystal structures and morphologies of MOF-derived ZnO nanocages. The H2S-sensing properties of the sensors based on ZnO and Cu-doped ZnO nanocages were investigated. The results indicated that the H2S-sensing properties of MOF-derived ZnO nanocages were effectively improved by Cu doping, and the optimal doping content was 3 at%. Moreover, 3 at% Cu-doped ZnO nanocages showed the highest response of 4733 for 5 ppm H2S at 200 °C, and the detection limit could be as low as 20 ppb. The gas-sensing mechanism was also discussed.

Standing and Lying Ni(OH)2 Nanosheets on Multilayer Graphene for High-Performance Supercapacitors.

For conventional synthesis of Ni(OH)2/graphene hybrids, oxygen-containing functional groups should be firstly introduced on graphene to serve as active sites for the anchoring of Ni(OH)2. In this work, a method for growing Ni(OH)2 nanosheets on multilayer graphene (MLG) with molecular connection is developed which does not need any pre-activation treatments. Moreover, Ni(OH)2 nanosheets can be controlled to stand or lie on the surface of MLG. The prepared hybrids were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The growth processes are suggested according to their morphologies at different growth stages. The enhanced electrochemical performances as supercapacitor electrode materials were confirmed by cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) techniques. Ni(OH)2 nanosheets standing and lying on MLG show specific capacities of 204.4 mAh g-1 and 131.7 mAh g-1, respectively, at 1 A g-1 based on the total mass of the hybrids and 81.5% and 92.8% capacity retention at a high current density of 10 A g-1, respectively. Hybrid supercapacitors with as-prepared hybrids as cathodes and activated carbon as anode were fabricated and tested.

Boosting Lithium-Ion Transport Kinetics by Increasing the Local Lithium-Ion Concentration Gradient in Composite Anodes of Lithium-Ion Batteries.

Constructing composite electrodes is considered to be a feasible way to realize high-specific-capacity Li-ion batteries. The core-double-shell-structured Si@C@TiO2 would be an ideal design for such batteries, considering that carbon (C) can buffer the volume change and TiO2 can constrain the structural deformation of Si. Although the electrochemical performance of the shells themselves is relatively clear, the complexity of the multishell heterointerface always results in an ambiguous understanding about the influence of the heterointerface on the electrochemical properties of the core material. In this work, a multilayer film model that can simplify and simultaneously expand the area of the heterointerface is used to study the heterointerfacial behavior. First, a multilayer film TiO2/C with different numbers of TiO2/C heterointerfaces is studied. It shows that the electrochemical performance is enhanced apparently by increasing the number of TiO2/C heterointerfaces. On the one hand, the TiO2/C heterointerface exhibits a strong lithium-ion storage capacity. On the other hand, the TiO2/C heterointerface appears to effectively promote the local Li-ion concentration gradient and thus boost the Li-ion transport kinetics. Then, TiO2/C is combined with Si to construct a composite anode Si/C/TiO2. An obvious advantage of TiO2/C over single TiO2 and C is observed. The utilization rate of Si is greatly improved in the first cycle and reaches up to 98% in Si/C/TiO2. The results suggest that the electrochemical performance of Si can be greatly manipulated by the heterointerface between the multishells.

Ultrasound sonochemical synthesis of amorphous Sb2S3-graphene composites for sodium-ion batteries.

Different from traditional methods, ultrasound sonochemical synthesis can create very special reaction conditions by virtue of the effects of acoustic cavitation. The localized spots in the medium liquids can reach the temperature of ~5000 K, and the pressure of ~1000 bar with the treatment of ultrasonic irradiation. The extreme conditions make it possible to fabricate a series of nanostructured materials with peculiar properties. Herein, we successfully prepared a unique amorphous composite of Sb2S3-graphene via sonochemical method at room temperature. Thanks to the opening frame of ion diffusion channels and higher reversibility in thermodynamics, the amorphous composite displayed superior electrochemical properties in comparison with the crystalline counterpart for sodium-ion batteries. Specifically, the amorphous Sb2S3-graphene composite delivered a first discharge capacity of 1867.1 mAh g-1 and a high reversible capacity of over 880 mAh g-1 after 50 cycles. The nanostructured materials synthesized by ultrasound sonochemical method with unique properties have well prospect in the field of energy storage.

Supercapacitive Performances of Ternary CuCo2S4 Sulfides.

Currently, ternary CuCo2S4 sulfides are intensively investigated as electrode materials for electrochemical capacitors due to their low cost, high conductivity, and synergistic effect. The research of CuCo2S4 materials for energy storage has gradually grown from 2016. The supercapacitive performances of CuCo2S4 electrodes for electrochemical capacitors are briefly reviewed in this work. The structure, morphology, and particle size of CuCo2S4 are related to the synthesis conditions and electrochemical performances. The thin films of CuCo2S4 nanostructures deposited on conductive substrates and their composites both show better properties than single CuCo2S4. CuCo2S4 and its composites reveal large potential for asymmetric capacitors, delivering high energy densities. However, there is still much new space remaining for future research. The possible development directions, challenges, and opportunities for CuCo2S4 materials are also discussed.

The Synthesis of NiCo2O4-MnO2 Core-Shell Nanowires by Electrodeposition and Its Supercapacitive Properties.

Hierarchical composite films grown on current collectors are popularly reported to be directly used as electrodes for supercapacitors. Highly dense and conductive NiCo2O4 nanowires are ideal backbones to support guest materials. In this work, low crystalline MnO2 nanoflakes are electrodeposited onto the surface of NiCo2O4 nanowire films pre-coated on nickel foam. Each building block in the composite films is a NiCo2O4-MnO2 core-shell nanowire on conductive nickel foam. Due to the co-presence of MnO2 and NiCo2O4, the MnO2@NiCo2O4@Ni electrode exhibits higher specific capacitance and larger working voltage than the NiCo2O4@Ni electrode. It can have a high specific capacitance of 1186 F·g-1 at 1 A·g-1. When the core-shell NiCo2O4-MnO2 composite and activated carbon are assembled as a hybrid capacitor, it has the highest energy density of 29.6 Wh·kg-1 at a power density of 425 W·kg-1 with an operating voltage of 1.7 V. This work shows readers an easy method to synthesize composite films for energy storage.

Research Progress of NiMn Layered Double Hydroxides for Supercapacitors: A Review.

The research on supercapacitors has been attractive due to their large power density, fast charge/discharge speed and long lifespan. The electrode materials for supercapacitors are thus intensively investigated to improve the electrochemical performances. Various transition metal layered double hydroxides (LDHs) with a hydrotalcite-like structure have been developed to be promising electrode materials. Earth-abundant metal hydroxides are very suitable electrode materials due to the low cost and high specific capacity. This is a review paper on NiMn LDHs for supercapacitor application. We focus particularly on the recent published papers using NiMn LDHs as electrode materials for supercapacitors. The preparation methods for NiMn LDHs are introduced first. Then, the structural design and chemical modification of NiMn LDH materials, as well as the composites and films derived from NiMn LDHs are discussed. These approaches are proven to be effective to enhance the performance of supercapacitor. Finally, the reports related to NiMn LDH-based asymmetric supercapacitors are summarized. A brief discussion of the future development of NiMn LDHs is also provided.

Electrochemistry of Selenium with Sodium and Lithium: Kinetics and Reaction Mechanism.

There are economic and environmental advantages by replacing Li with Na in energy storage. However, sluggishness in the charge/discharge reaction and low capacity are among the major obstacles to development of high-power sodium-ion batteries. Among the electrode materials recently developed for sodium-ion batteries, selenium shows considerable promise because of its high capacity and good cycling ability. Herein, we have investigated the mechanism and kinetics of both sodiation and lithiation reactions with selenium nanotubes, using in situ transmission electron microscopy. Sodiation of a selenium nanotube exhibits a three-step reaction mechanism: (1) the selenium single crystal transforms into an amorphous phase Na0.5Se; (2) the Na0.5Se amorphous phase crystallizes to form a polycrystalline Na2Se2 phase; and (3) Na2Se2 transforms into the Na2Se phase. Under similar conditions, the lithiation of Se exhibits a one-step reaction mechanism, with phase transformation from single-crystalline Se to a Li2Se. Intriguingly, sodiation kinetics is generally about 4-5 times faster than that of lithiation, and the kinetics during the different stages of sodiation is different. Na-based intermediate phases are found to have improved electronic and ionic conductivity compared to those of Li compounds by first-principles density functional theory calculations.

Transition metal oxide and graphene nanocomposites for high-performance electrochemical capacitors.

A method for producing nanocomposites of transition metal oxides A(3)O(4) (where A represents Mn, Fe or Co) and graphene nanosheets (GNS) is presented. The reduction of graphene oxide (GO) and the formation of A(3)O(4) nanoparticles (NPs) were carried out simultaneously during the reaction. The electrochemical properties of A(3)O(4)-GNS nanocomposites as electrode materials for supercapacitors are investigated by cyclic voltammetry and galvanostatic charge-discharge tests. The as-prepared Mn(3)O(4)-GNS, Fe(3)O(4)-GNS and Co(3)O(4)-GNS nanocomposites exhibit large specific capacitance (708, 358 and 240 F g(-1), respectively), high energy density (20, 10 and 7 W h kg(-1), respectively) and good electrochemical stability (retention of 73%, 67.8% and 95.8%, respectively, after 1000 charge-discharge cycles). The excellent electrochemical performance of the A(3)O(4)-graphene nanocomposites indicates great potential in the application in commercial supercapacitors.

Nanowires/microfiber hybrid structure multicolor laser.

We demonstrate a compact hybrid structure red-green-ultraviolet three-color laser consisting of three distinct semiconductor nanowires (CdSe, CdS and ZnO) attached to a silica microfiber, which is pumped by 355 nm wavelength laser pulses. The exciting of the nanowires and the collection of the photoluminescence (PL) are implemented by means of evanescent coupling through the same silica microfiber. When pump energy higher than 1.3 microJ, three spatially and spectrally distinct lasing groups can be measured at the same output port simultaneously. The approach can be extended to other materials to produce hybrid lasers that cover ultraviolet to near infrared spectral regions.

Rice hull/MnFe2O4 composite: preparation, characterization and its rapid microwave-assisted COD removal for organic wastewater.

Adsorbent/ferrite composites can adsorb and degrade organics in the organic wastewater treatment. In this study, a rice hull/MnFe(2)O(4) composite (RHM) was prepared via calcination under nitrogen atmosphere and was used to treat organic wastewater with the assistance of microwave radiation. Rice hull was pyrolysed to a porous substrate that consisted of silica and activated carbon under high temperature. Monodisperse spinel MnFe(2)O(4) nanoparticles whose mean diameter is around 59 nm are distributed on the substrate. With the assistance of microwave radiation, RHM was motivated to a hotspot of adsorption and catalysis which could remove more than 70% COD of wastewater within 6 min. The maximum COD removal was 73.5% when the concentration of RHM was 15 mg mL(-1) and the irradiation time of microwave radiation was 6 min. Although the BET surface area and iodine value of RHM are half of rice hull ash (RHA), the COD removal of RHM is 7-20% higher than that of RHA. It is attributed to the presence of MnFe(2)O(4), which enhances the catalytic activity of RHM. RHM can be regenerated via water washing. However, the surface area and the maximum COD removal of RHM decrease for each regeneration cycle. With the advantages of low cost and rapid processing, this novel rice hull/MnFe(2)O(4) composite could gain promising application in wastewater treating-agent.