Hui-Yuan Wang

Fabrication of TiC particulate reinforced magnesium matrix composites

Abstract A TiC particulate reinforced magnesium matrix composite (PRMMC) was fabricated by adding a TiC–Al master alloy processed via self-propagating high-temperature synthesis reaction into molten magnesium and using the semi-solid slurry stirring technique. The properties of the PRMMC are higher than those of the unreinforced magnesium alloy.

One-pot formation of ultra-thin Ni/Co hydroxides with a sheet-like structure for enhanced asymmetric supercapacitors

In our work, ultra-thin Ni/Co hydroxides (Ni1Co2) with a sheet-like structure are successfully grown on the surface of conductive nickel foam via a one-pot hydrothermal reaction, avoiding the need for binders and conducting agents. In the reaction, NO3− ions from reactants release OH− ions partially with Co2+ ions turning into Co3+ ions and then OH− ions can react with Ni2+, Co2+ or Co3+ in a mixed solvent of water and ethanol, without the necessary addition of an extra alkali source. When used for supercapacitors, the resulting free-standing Ni1Co2 composites exhibit an impressive specific capacitance of 2654.9 F g−1 at a current density of 1 A g−1 and a favorable cycling stability with 77% retention even at a high current density of 10 A g−1 after 1500 cycles. In order to do research into the electrochemical properties of Ni1Co2 composites, a simple asymmetric supercapacitor (ASC) is constructed, using the Ni1Co2 nanosheets as the positive electrode and activated carbon (AC) as the negative electrode. This ASC with an extended voltage window of 0–1.6 V presents an outstanding energy density of 42.4 W h kg−1 (at a power density of 823.2 W kg−1) and still retains 24.8 W h kg−1 (at 10 170.8 W kg−1). Meanwhile, the excellent cycling stability of this ASC device has been revealed via a great specific capacitance retention of 94% after 3000 cycles (at a current density of 5 A g−1). So the Ni1Co2-based composites could be one of the potential materials for high-performance energy storage.

Hierarchical TiO2 spheres as highly efficient polysulfide host for lithium-sulfur batteries

Hierarchical TiO2 micron spheres assembled by nano-plates were prepared through a facile hydrothermal route. Chemical tuning of the TiO2 through hydrogen reduction (H-TiO2) is shown to increase oxygen-vacancy density and thereby modifies the electronic properties. H-TiO2 spheres with a polar surface serve as the surface-bound intermediates for strong polysulfides binding. Under the restricting and recapturing effect, the sulfur cathode could deliver a high reversible capacity of 928.1 mA h g−1 after 50 charge-discharge cycles at a current density of 200 mA g−1. The H-TiO2 additive developed here is practical for restricting and recapturing the polysulfide from the electrolyte.

Synthesis of octahedron and truncated octahedron primary Mg2Si by controlling the Sb contents

Octahedron and truncated octahedron primary Mg2Si were prepared by increasing the contents of Sb in an Al–Mg–Si melt. The structure and morphologies of primary Mg2Si were characterized by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM). The modifier Sb plays an important role in determining their morphologies, which can transform from equiaxed-dendrite to octahedron and finally to truncated octahedron (tetrakaidecahedron) with an increase in Sb content. An adsorption model demonstrates that Sb atoms preferentially adsorb on {100} facets of the Mg2Si crystal, which is the key reason for the morphology evolution. Moreover, the growth processes of octahedron and truncated octahedron primary Mg2Si modified by Sb element have been revealed for the first time. Our study suggests that it is feasible to control the morphologies of primary Mg2Si crystals in metallic melts by a simple method modification, which is critical to the development of advanced structural alloys with high strength and toughness.

Facile shape design and fabrication of ZnFe2O4 as an anode material for Li-ion batteries

Functional materials with exposed highly reactive planes have attracted considerable attention with respect to their enhanced electrochemical energy storage. However, highly active facets of ZnFe2O4 nanocrystals usually have high surface energy, and thus are hard to prepare in the equilibrium state or via traditional methods. In this regard, we propose a novel strategy to fabricate cubic, truncated octahedral, and octahedral ZnFe2O4 by a convenient hydrothermal method and subsequent thermal treatment for the first time. The ZnFe2O4 octahedra exhibit a reversible capacity of 450 mA h g−1 at a current density of 60 mA g−1 after 50 cycles, while the reversible capacity of ZnFe2O4 cubes is 367 mA h g−1. The electrochemical performance of the three types of ZnFe2O4 can be ranked as “octahedron > truncated octahedron > cube”. The exposed planes, which are filled with a high density of atoms, lead to the better electrochemical performance.

Morphology and size control of octahedral and cubic primary Mg2Si in an Mg–Si system by regulating Sr contents

In the present study, primary Mg2Si with different morphologies and sizes over a regime of 5–70 μm have been prepared. By precisely controlling the content of Sr in Mg–4Si alloys, we have obtained octahedral and cubic primary Mg2Si of different average size. Morphologies of primary Mg2Si were identified though field-emission scanning electron microscopy (FESEM) in three-dimensional space. The modifier Sr plays an important role in determining the morphologies of primary Mg2Si, which can be transformed from equiaxed-dendrite to octahedron and finally to a cube shape with increasing Sr content. The 2D nucleation growth pattern of primary Mg2Si modified by Sr element has been revealed for the first time. An adsorption model has been applied to explain the influence of Sr on the growth kinetics of Mg2Si. It is proposed that Sr atoms preferentially adsorbing on {100} facets of Mg2Si crystal is the key reason for the morphology evolution. Our study demonstrates an effective, one-step and cheap method to control the morphologies and sizes of primary Mg2Si crystals in metallic melts, which is critical to achieve industrial application of light alloys with high strength and toughness.

Design and synthesis of ZnO–NiO–Co3O4 hybrid nanoflakes as high-performance anode materials for Li-ion batteries

ZnO–NiO–Co3O4 hybrid nanoflakes are fabricated via a simple hydrothermal method followed by a subsequent annealing process. In these hybrid electrode materials, ZnO and NiO are the main active materials while a small amount of Co3O4 is introduced as a catalyzing and performance-enhancing agent. The obtained hybrid materials possess a novel 2D nanoflake structure which is mainly constructed by firmly interconnected ZnO and NiO nanoparticles. The particle size of ZnO and NiO is reduced to about 47 nm and 12 nm, respectively, through the hybridization process. When applied as anode materials, the ZnO–NiO–Co3O4 hybrid nanoflakes exhibit a high reversible capacity of 1060 mA h g−1 after 300 cycles at 500 mA g−1. The successful alleviation of the capacity fading problem and excellent electrochemical performance can be ascribed to the unique 2D nano-morphology, strong cobalt catalysis, improved electronic conductivity, uniform dispersity and porous surface. The results demonstrate that the ZnO–NiO–Co3O4 hybrid nanoflakes are promising anode materials for high-performance lithium-ion batteries.

A Novel Approach of Using Ground CNTs as the Carbon Source to Fabricate Uniformly Distributed Nano-Sized TiCx/2009Al Composites

Nano-sized TiCx/2009Al composites (with 5, 7, and 9 vol% TiCx) were fabricated via the combustion synthesis of the 2009Al-Ti-CNTs system combined with vacuum hot pressing followed by hot extrusion. In the present study, CNTs were used as the carbon source to synthesize nano-sized TiCx particles. An attempt was made to correlate the effect of ground CNTs by milling and the distribution of synthesized nano-sized TiCx particles in 2009Al as well as the tensile properties of nano-sized TiCx/2009Al composites. Microstructure analysis showed that when ground CNTs were used, the synthesized nano-sized TiCx particles dispersed more uniformly in the 2009Al matrix. Moreover, when 2 h-milled CNTs were used, the 5, 7, and 9 vol% nano-sized TiCx/2009Al composites had the highest tensile properties, especially, the 9 vol% nano-sized TiCx/2009Al composites. The results offered a new approach to improve the distribution of in situ nano-sized TiCx particles and tensile properties of composites.

One-step synthesis of Co-doped Zn2SnO4–graphene–carbon nanocomposites with improved lithium storage performances

Co-doped Zn2SnO4–graphene–carbon nanocomposites have been prepared for the first time through a convenient one-step hydrothermal method. The size of Co-doped Zn2SnO4 nanoparticles is about 3–5 nm and they are well dispersed on graphene nanosheets and carbon layer. L-Ascorbic acid is introduced to serve as a reductant for GO and carbon sources. The doping of Co can enhance the crystalline degree of Zn2SnO4 nanoparticles. When evaluated as anode materials for lithium ion batteries, the Co–ZTO–G–C nanocomposites exhibited a significantly higher reversible capacity of 699 mA h g−1 after 50 cycles at 100 mA g−1 and an improved cycling stability of 461 mA h g−1 after 200 cycles at 500 mA g−1 compared with Co–ZTO–G and ZTO–G–C nanocomposites. Moreover, even at a high current density of 1000 mA g−1, the reversible capacity of 418 mA h g−1 still remained. The improved electrochemical performance can be attributed to the synergy of the graphene substrate, the protective carbon layer, the uniform ultrafine Zn2SnO4 nanoparticles and Co doping. Therefore, Co–ZTO–G–C nanocomposites show great prospect as anodes for lithium-ion batteries.

Facile synthesis of hierarchical worm-like MoS2 structures assembled with nanosheets as anode for lithium ion batteries

Hierarchical worm-like MoS2 structures directionally assembled with nanosheets are successfully synthesized via a simple hydrothermal route using potassium sodium tartrate as a structure-directing agent. The possible growth mechanism of worm-like MoS2 structures is proposed through controlling hydrothermal temperature, time and the amount of potassium sodium tartrate. The results indicate that potassium sodium tartrate plays important roles in formation of worm-like structures. The unique hierarchical structures as anodes for lithium-ion batteries display high specific capacity of 845 mA h g−1 after 50 cycles at 100 mA g−1 and good cyclic stability of 698 mA h g−1 even at high rate of 500 mA g−1 after 100 cycles. The excellent electrochemical performance can be attributed to the hierarchical surface, sufficient void space between neighboring nanosheets and unique worm-like structures. Besides, this work also provides a simple strategy to design and construct other structural materials, such as layered metal sulfides and oxides.