Na2 Ti6 O13 Nanorods with Dominant Large Interlayer Spacing Exposed Facet for High-Performance Na-Ion Batteries.

As the delegate of tunnel structure sodium titanates, Na2 Ti6 O13 nanorods with dominant large interlayer spacing exposed facet are prepared. The exposed large interlayers provide facile channels for Na(+) insertion and extraction when this material is used as anode for Na-ion batteries (NIBs). After an activation process, this NIB anode achieves a high specific capacity (a capacity of 172 mAh g(-1) at 0.1 A g(-1) ) and outstanding cycling stability (a capacity of 109 mAh g(-1) after 2800 cycles at 1 A g(-1) ), showing its promising application on large-scale energy storage systems. Furthermore, the electrochemical and structural characterization reveals that the expanded interlayer spacings should be in charge of the activation process, including the enhanced kinetics, the lowered apparent activation energy, and the increased capacity.

Synthesis of triple-layered Ag@Co@Ni core-shell nanoparticles for the catalytic dehydrogenation of ammonia borane.

Triple-layered Ag@Co@Ni core-shell nanoparticles (NPs) containing a silver core, a cobalt inner shell, and a nickel outer shell were formed by an in situ chemical reduction method. The thickness of the double shells varied with different cobalt and nickel contents. Ag0.04 @Co0.48 @Ni0.48 showed the most distinct core-shell structure. Compared with its bimetallic core-shell counterparts, this catalyst showed higher catalytic activity for the hydrolysis of NH3 BH3 (AB). The synergetic interaction between Co and Ni in Ag0.04 @Co0.48 @Ni0.48 NPs may play a critical role in the enhanced catalytic activity. Furthermore, cobalt-nickel double shells surrounding the silver core in the special triple-layered core-shell structure provided increasing amounts of active sites on the surface to facilitate the catalytic reaction. These promising catalysts may lead to applications for AB in the field of fuel cells.

Recovered LiCoO2 as anode materials for Ni/Co power batteries.

LiCoO(2) material is recovered from spent lithium-ion batteries and investigated as anode materials for Ni/Co power batteries for the first time. LiCoO(2) electrodes with a small amount of S-doping display excellent electrochemical properties. The electrochemical reactions occurring on M0 electrodes during the first several cycles and after being activated are proposed, respectively. A function mechanism of S powder on M10 electrode is also proposed.

Hierarchical Ti3C2@TiO2 MXene hybrids with tunable interlayer distance for highly durable lithium-ion batteries.

To realize high-rate and long-term performance of rechargeable batteries, the most effective approach is to develop an advanced hybrid material with a stable structure and more reaction active sites. Recently, 2D MXenes have become an up-and-coming electrode owing to their high conductivity and large redox-active surface area. In this work, we firstly prepared Ti3C2 MXenes through the selective etching of silicon from Ti3SiC2 (MAX) using HF and an oxidant for highly durable lithium-ion batteries (LIBs). The interlayer distance of Ti3C2 MXenes can be controlled with the oxidizability of the oxidant and etching temperature. In addition, Ti3C2@TiO2 MXene hybrids with further expanded interlayer spacing were purposefully fabricated by a simple hydrothermal method. The hierarchical N-doped Ti3C2@TiO2 MXene hybrids show that the in situ synthesized nanoscale TiO2 particles are loaded homogeneously on the layered N-doped Ti3C2 surface. The interlayer distance of N-doped Ti3C2@TiO2 MXene can reach 12.77 Å when using HNO3 as the oxidant at room temperature. As an anode material, the N-doped Ti3C2@TiO2(HNO3-RT) hybrid displays a high reversible capacity of 302 mA h g-1 at 200 mA g-1 after 500 cycles and 154 mA h g-1 at 2000 mA g-1 after 1500 cycles, which indicates its long cycle lifetime and excellent stability in LIBs. This highly durable LIB anode performance is ascribed to synergetic contributions from the high capacitive contribution, high electrical conductivity, high-capacity of in situ formed nanoscale TiO2 and interlayer-expanded architecture of the N-doped Ti3C2@TiO2(HNO3-RT). This study provides a theoretical basis for the application of MXenes as high capacity anodes for advanced LIBs.

In Situ Synthesis of 3D Flower-Like Nanocrystalline Ni/C and its Effect on Hydrogen Storage Properties of LiAlH4.

Lithium alanate (LiAlH4 ) is of particular interest as one of the most promising candidates for solid-state hydrogen storage. Unfortunately, high dehydrogenation temperatures and relatively slow kinetics limit its practical applications. Herein, 3D flower-like nanocrystalline Ni/C, composed of highly dispersed Ni nanoparticles and interlaced carbon flakes, was synthesized in situ. The as-synthesized nanocrystalline Ni/C significantly decreased the dehydrogenation temperature and dramatically improved the dehydrogenation kinetics of LiAlH4 . It was found that the LiAlH4 sample with 10 wt % Ni/C (LiAlH4 -10 wt %Ni/C) began hydrogen desorption at approximately 48 °C, which is very close to ambient temperature. Approximately 6.3 wt % H2 was released from LiAlH4 -10 wt %Ni/C within 60 min at 140 °C, whereas pristine LiAlH4 only released 0.52 wt % H2 under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C under 4 MPa H2 . The synergetic effect of the flower-like carbon substrate and Ni active species contributes to the significantly reduced dehydrogenation temperatures and improved kinetics.

Improved Dehydrogenation Properties of LiBH4 Using Catalytic Nickel- and Cobalt-based Mesoporous Oxide Nanorods.

Lithium borohydride (LiBH4 ) with a theoretical hydrogen storage capacity of 18.5 wt % has attracted intense interest as a high-density hydrogen storage material. However, high dehydrogenation temperatures and limited kinetics restrict its practical applications. In this study, mesoporous nickel- and cobalt-based oxide nanorods (NiCo2 O4 , Co3 O4 and NiO) were synthesized in a controlled manner by using a hydrothermal method and then mixed with LiBH4 by ball milling. It is found that the dehydrogenation properties of LiBH4 are remarkably enhanced by doping the as-synthesized metal oxide nanorods. When the mass ratio of LiBH4 and oxides is 1:1, the NiCo2 O4 nanorods display the best catalytic performance owing to the mesoporous rod-like structure and synergistic effect of nickel and cobalt active species. The initial hydrogen desorption temperature of the LiBH4 -NiCo2 O4 composite decreases to 80 °C, which is 220 °C lower than that of pure LiBH4 , and 16.1 wt % H2 is released at 500 °C for the LiBH4 -NiCo2 O4 composite. Meanwhile, the composite also exhibits superior dehydrogenation kinetics, which liberates 5.7 wt % H2 within 60 s and a total of 12 wt % H2 after 5 h at 400 °C. In comparison, pure LiBH4 releases only 5.3 wt % H2 under the same conditions.

Enhanced Hydrogen Storage Properties and Reversibility of LiBH4 Confined in Two-Dimensional Ti3C2.

LiBH4 is of particular interest as one of the most promising materials for solid-state hydrogen storage. Herein, LiBH4 is confined into a novel two-dimensional layered Ti3C2 MXene through a facile impregnation method for the first time to improve its hydrogen storage performance. The initial desorption temperature of LiBH4 is significantly reduced, and the de-/rehydrogenation kinetics are remarkably enhanced. It is found that the initial desorption temperature of LiBH4@2Ti3C2 hybrid decreases to 172.6 °C and releases 9.6 wt % hydrogen at 380 °C within 1 h, whereas pristine LiBH4 only releases 3.2 wt % hydrogen under identical conditions. More importantly, the dehydrogenated products can partially rehydrogenate at 300 °C and under 95 bar H2. The nanoconfined effect caused by unique layered structure of Ti3C2 can hinder the particles growth and agglomeration of LiBH4. Meanwhile, Ti3C2 could possess superior effect to destabilize LiBH4. The synergetic effect of destabilization and nanoconfinement contributes to the remarkably lowered desorption temperature and improved de-/rehydrogenation kinetics.

Reconstruction of Mini-Hollow Polyhedron Mn2O3 Derived from MOFs as a High-Performance Lithium Anode Material.

A mini-hollow polyhedron Mn2O3is used as the anode material for lithium-ion batteries. Benefiting from the small interior cavity and intrinsic nanosize effect, a stable reconstructed hierarchical nanostructure is formed. It has excellent energy storage properties, exhibiting a capacity of 760 mAh g-1 at 2 A g-1 after 1000 cycles. This finding offers a new perspective for the design of electrodes with large energy storage.

Hierarchical Co@C Nanoflowers: Synthesis and Electrochemical Properties as an Advanced Negative Material for Alkaline Secondary Batteries.

Hierarchical Co@C nanoflowers have been facilely synthesized via a simple route based on a low-temperature solid-phase reaction. The obtained hierarchical Co@C nanoflowers, each constructed of a number of nanosheets, display a three-dimensional architecture with an average grain size of about 300 nm. The electrochemical properties of the Co@C nanoflowers as the negative material for Ni/Co cells have been systemically researched. In particular, Co@C material exhibits high discharge-specific capacity and good cycling stability. The discharge-specific capacity of our Co@C-3 electrode can reach 612.1 mA h g(-1), and the specific capacity of 415.3 mA h g(-1) is retained at a current density of 500 mA g(-1) after 120 cycles, indicating its great potential for high-performance Ni/Co batteries. Interestingly, the as-synthesized Co@C electrode also exhibits favorable rate capability. These desirable properties can be attributed to porous pathways, which allow fast transportation of ions and electrons and easy accessibility to the electrolyte. The dominant electrochemical mechanism of Co@C can be attributed to the reduction-oxidation reaction between metallic cobalt and cobalt hydroxide in alkaline solution.

Exfoliated-SnS2 restacked on graphene as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries.

Designed as a high-capacity, high-rate, and long-cycle life anode for sodium ion batteries, exfoliated-SnS2 restacked on graphene is prepared by the hydrolysis of lithiated SnS2 followed by a facile hydrothermal method. Structural and morphological characterizations demonstrate that ultrasmall SnS2 nanoplates (with a typical size of 20-50 nm) composed of 2-5 layers are homogeneously decorated on the surface of graphene, while the hybrid structure self-assembles into a three-dimensional (3D) network architecture. The obtained SnS2/graphene nanocomposite delivers a remarkable capacity as high as 650 mA h g(-1) at a current density of 200 mA g(-1). More impressively, the capacity can reach 326 mA h g(-1) even at 4000 mA g(-1) and remains stable at ∼610 mA h g(-1) without fading up to 300 cycles when the rate is brought back to 200 mA g(-1). The excellent electrochemical performance is attributed to the synergetic effects between the ultrasmall SnS2 and the highly conductive graphene network. The unique structure can simultaneously facilitate Na(+) ion diffusion, provide more reaction sites, and suppress aggregation and volume fluctuation of the active materials during prolonged cycling.

Copper-doped dual phase Li4Ti5O12-TiO2 nanosheets as high-rate and long cycle life anodes for high-power lithium-ion batteries.

Cu-doped Li4 Ti5 O12 -TiO2 nanosheets were synthesized by a facile, cheap, and environmentally friendly solution-based method. These nanostructures were investigated as an anode material for lithium-ion batteries. Cu doping was found to enhance the electron conductivity of the materials, and the amount of Cu doped controlled the crystal structure and content of TiO2 . In addition, the samples, which benefit from multiphases and doping, exhibited much improved capacity, cycle performance, and high rate capability over Cu-free Li4 Ti5 O12 -TiO2 . The discharge capacity of the 0.05 Cu-doped sample was 190 mAh g(-1) at 1C, and even 144 mAh g(-1) was obtained at 30C after 100 cycles. Moreover, after 500 cycles at 30C, the discharge capacity remained at approximately 130 mAh g(-1) . The excellent electrochemical performance of the cell demonstrated that Cu-doping was able to adjust and control the Li4 Ti5 O12 -TiO2 system appropriately.

Ultrasmall TiO2 Nanoparticles in Situ Growth on Graphene Hybrid as Superior Anode Material for Sodium/Lithium Ion Batteries.

To inhibit the aggregation of TiO2 nanoparticles and to improve the electrochemical kinetics of TiO2 electrode, a hybrid material of ultrasmall TiO2 nanoparticles in situ grown on rGO nanosheets was obtained by ultraphonic and reflux methods. The size of the TiO2 particles was controlled about 10 nm, and these particles were evenly distributed across the rGO nanosheets. When used for the anode of a sodium ion battery, the electrochemical performance of this hybrid TiO2@rGO was much improved. A capacity of 186.6 mAh g(-1) was obtained after 100 cycles at 0.1 A g(-1), and 112.2 mAh g(-1) could be maintained at 1.0 A g(-1), showing a high capacity and good rate capability. On the basis of the analysis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the achieved excellent electrochemical performance was mainly attributed to the synergetic effect of well-dispersed ultrasmall TiO2 nanoparticles and conductive graphene network and the improved electrochemical kinetics. The superior electrochemical performance of this hybrid material on lithium storage further confirmed the positive effect of rGO.

TiS2 nanotubes as the cathode materials of Mg-ion batteries.

Titanium disulfide (TiS2) nanotubes were used as the cathode materials of rechargeable magnesium-ion batteries, showing potential low-cost, high-capacity, and good-reversibility properties.

Understanding the role of few-layer graphene nanosheets in enhancing the hydrogen sorption kinetics of magnesium hydride.

The catalytic effects of few-layer, highly wrinkled graphene nanosheet (GNS) addition on the dehydrogenation/rehydrogenation performance of MgH2 were investigated. It was found that MgH2-5 wt %GNSs nanocomposites prepared by ball milling exhibit relatively lower sorption temperature, faster sorption kinetics, and more stable cycling performance than that of pure-milled MgH2. The dehydrogenation step confirms that the Avrami exponent n increases from 1.22 to 2.20 by the Johnson-Mehl-Avrami (JMA) formalism when the desorption temperature is reduced from 350 °C to 320 °C and 300 °C, implying that a change in the decomposition temperature can alter the mechanism during the dehydrogenation process. For rehydrogenation, the Avrami value n is close to 1; further study by several models coincident with n = 1 reveals that the absorption process of the MgH2-5 wt %GNSs sample conforms to the Mampel equation formulated through the random nucleation approach and that the nature of the absorption mechanism does not change within the temperature range studied. Furthermore, microstructure analysis demonstrated that the defective GNSs are distributed uniformly among the MgH2 particles and that the grain size of the MgH2-5 wt %GNSs nanocomposite is approximately 5-9 nm. The efficient metal-free catalytic dehydrogenation/rehydrogenation of MgH2 can be attributed to the coupling of the nanosize effect and defective GNSs.

NbN nanoparticles as additive for the high dehydrogenation properties of LiAlH4.

The effects of NbN nanoparticles synthesized via a simple "urea glass" route on the dehydrogenation properties of LiAlH4 have been systematically investigated. The particle size of the as-synthesized NbN nanoparticles is determined to be about 10 nm. The surface configuration and dehydrogenation behaviors of the 2 mol% NbN-doped LiAlH4 (2% NbN-LiAlH4) system are also discussed. It is found that the 2% NbN-LiAlH4 sample starts to decompose at about 95 °C and releases a total of 7.10 wt% hydrogen, which is 55 °C lower than that of as-milled LiAlH4. The isothermal dehydrogenation kinetics shows that the 2% NbN-LiAlH4 sample could release approximately 6.10 wt% hydrogen in 150 min at 130 °C, whereas as-received LiAlH4 only releases about 0.63 wt% hydrogen under the same conditions, revealing that the enhancements arising upon adding NbN nanoparticles are almost 8-9 times that of as-milled LiAlH4. The activation energy (Ea) is calculated to be 71.91 and 90.87 kJ mol(-1) for the first and second hydrogen desorption of the NbN-LiAlH4 sample, a 38% and 32% reduction relative to as-received LiAlH4, respectively. A detailed modeling study shows that the first dehydrogenation step can be sufficiently interpreted with the nucleation and growth in a one-dimensional model based on the first-order reaction. More interestingly, the dehydrogenated LiAlH4 sample can recharge H2 under a 5.5 MPa hydrogen pressure. An SEM image of the dehydrogenated 8% NbN-LiAlH4 sample after HP-DSC under 5.5 MPa H2 shows that some nanorods appear.

In situ preparation of 1D Co@C composite nanorods as negative materials for alkaline secondary batteries.

Cobalt-based coordination compounds were successfully prepared via employing nitrilotriacetic acid (NTA) as a complexing agent through a mild surfactant-free solvothermal process. Cobalt ions are linked with the amino group or carboxyl groups of NTA to become one-dimensional nanorods that can be proved by Fourier transform infrared measurement findings. The morphologies of the precursor Co-NTA highly depend on the solvent composition, the reaction time and temperature. The probable growth mechanism has been proposed. After heat treatment, the Co-NTA precursor can be completely converted into Co@C nanorods assembled by numerous core-shell-like Co@C nanoparticles, which preserved the rodlike morphology. The as-prepared Co@C composites display a rodlike morphology with 4 µm length and 100 nm diameter. The electrochemical performances of this novel Co@C material as the alkaline secondary Ni/Co battery negative electrode have been systematically researched. The discharge capacity of the Co@C-1 composite electrode can attain 609 mAh g(-1) and retains about 383.3 mAh g(-1) after 120 cycles (the discharge current density of 500 mA g(-1)). The novel material exhibits a high discharge capacity of 610 and 470 mAh g(-1) at discharge currents of 100 and 1000 mA g(-1), respectively. This suggests that approximately 77% of the discharge capacity is kept when the discharge current density is increased to 1000 mA g(-1) (10 times the initial current density of 100 mA g(-1)). The excellent electrochemical properties could be ascribed to the porous channels of the novel Co@C materials, which is beneficial to electrolyte diffusion and electrons and ions transportation.

Bimetallic NiCo functional graphene: an efficient catalyst for hydrogen-storage properties of MgH2.

Bimetallic NiCo functional graphene (NiCo/rGO) was synthesized by a facile one-pot method. During the coreduction process, the as-synthesized ultrafine NiCo nanoparticles (NPs), with a typical size of 4-6 nm, were uniformly anchored onto the surface of reduced graphene oxide (rGO). The NiCo bimetal-supported graphene was found to be more efficient than their single metals. Synergetic catalysis of NiCo NPs and rGO was confirmed, which can significantly improve the hydrogen-storage properties of MgH2. The apparent activation energy (E(a)) of the MgH2-NiCo/rGO sample decreases to 105 kJ mol(-1), which is 40.7% lower than that of pure MgH2. More importantly, the as-prepared MgH2-NiCo/rGO sample can absorb 5.5 and 6.1 wt% hydrogen within 100 and 350 s, respectively, at 300 °C under 0.9 MPa H2 pressure. Further cyclic kinetics investigation indicates that MgH2-NiCo/rGO nanocomposites have excellent cycle stability.

In situ synthesized one-dimensional porous Ni@C nanorods as catalysts for hydrogen storage properties of MgH2.

We have demonstrated an extremely facile procedure for the preparation of 1D porous Ni@C nanostructures by pyrolysis of Ni-based coordination polymer nanorods. The highly aligned Ni-based polymer nanorods were prepared using nitrilotriacetic acid (NTA) as a chelating agent by a one-step solvothermal approach. The obtained precursors are demonstrated to have a well-designed 1D nanostructure and a 3D interconnected mesoporous texture. After thermal treatment, 1D porous Ni@C nanorods were obtained, which basically preserved the morphology of the precursors. In addition, the carbon in the porous Ni@C nanorods is in both crystalline and amorphous states. The as-prepared Ni@C sample displays nanorod-like morphology with about 3 µm length and about 200 nm diameter. With a large surface area of 161.4 m(2) g(-1), this novel material had a good catalytic effect on de/hydrogenation of MgH2. The desorption peak temperature of MgH2-5 wt% Ni@C composites can be lowered more than 57 °C than the pure as-milled MgH2. The MgH2-5 wt% Ni@C composite could desorb 6.4 wt% H2 within 10 min at 300 °C, in contrast, only 2.3 wt% H2 was desorbed even after 100 min for pure MgH2. In addition, an activation energy of 108 kJ mol(-1) for the as-milled MgH2-5 wt% Ni@C composites has been obtained, which exhibit an enhanced kinetics.

Facile synthesis of TiN decorated graphene and its enhanced catalytic effects on dehydrogenation performance of magnesium hydride.

TiN@rGO nanohybrids were successfully synthesized by a simple "urea glass" technique. Experimental results demonstrated that TiN nanocrystals, with an average particle size of 20 nm, were uniformly anchored onto highly reduced graphene nanosheets. The as-synthesized TiN@rGO nanohybrids showed a porous planar-like structure, which had a large surface area of 177 m(2) g(-1). More importantly, the as-prepared TiN@rGO hybrids showed enhanced catalytic effects on the dehydrogenation of MgH2. The dehydrogenation thermodynamics and kinetics of the MgH2-TiN@rGO composites were systematically investigated and some significant improvements were confirmed. It was found that the 10 wt% TiN@rGO doped MgH2 sample started to release hydrogen at about 167 °C, and roughly 6.0 wt% hydrogen was released within 18 min when isothermally heated to 300 °C. In contrast, the onset dehydrogenation temperature of the pure MgH2 sample was about 307 °C, and only 3.5 wt% hydrogen was released even after 120 min of heating under identical conditions. In addition, the catalytic mechanism of TiN@rGO on the dehydrogenation of MgH2 was discussed using the Johnson-Mehl-Avrami (JMA) model and X-ray diffraction equipment.

Synthesis of size-controlled Ag@Co@Ni/graphene core-shell nanoparticles for the catalytic hydrolysis of ammonia borane.

Size-controlled Ag0.04@Co0.48@Ni0.48 core-shell nanoparticles (NPs) were synthesized by employing graphene (rGO) with different reduction degrees as supports. The number of C=O and C=O functional groups on the surface of rGO might play a major role in controlling the particle size. The strong steric-hindrance effect of C=O resulted in the growth of large particles, whereas C=O contributed to the formation of small particles. The particle size of Ag0.04@Co0.48@Ni0.48 NPs supported on rGO with different reduction degrees decreased as the number of C=O functional groups decreased. The decrease in the particle size probably led to the increase in the catalytic activity towards the hydrolysis of ammonia borane (AB). The enhanced catalytic activity largely stemmed from the increasing active sites on the surface of catalysts owing to the decreasing particle size.