Yaoming Wu

Facile fabrication of SnO2@TiO2 core–shell structures as anode materials for lithium-ion batteries

A novel strategy to fabricate SnO2@TiO2 composite was developed by combining the glucose-mediated hydrothermal method along with a sol–gel step, followed by a sintering process. Herein, glucose was found to play dual roles of facilitating the rapid precipitation of polycrystalline SnO2 nanocolloids in the hydrothermal process and act as a pore-forming material to leave behind nanopores when it is combusted in the sintering process. Due to the combined superiority of TiO2 as a inert nanoshell and SnO2 as a core with a high theoretical specific capacity, together with the combustion-formed carbon-derived voids with many extra free spaces to buffer the volume change, the obtained SnO2@TiO2 composite has potential for use as an anode material for lithium-ion batteries with enhanced electrochemical performances. A high reversible capacity of 910 mA h g−1 was maintained over 300 cycles at a current density of 100 mA g−1. Even at a high current density of 1000 mA g−1, the substantial discharge capacity could still reach 617 mA h g−1 after 1000 repeated cycles. Such excellent cycling stability and remarkable rate capability of the designed SnO2@TiO2 composite can be attributed to its novel structure and the synergistic effects between the SnO2 core and TiO2 shell.

Enhanced electrochemical performances of FeOx–graphene nanocomposites as anode materials for alkaline nickel–iron batteries

A new type of graphene-based FeOx nanocomposites have been synthesized by high temperature solid-state reaction using FeC2O4·2H2O. The synthesis conditions are optimized by thermogravimetric analysis of the precursor. When evaluated as anode material for the alkaline nickel–iron battery, the FeOx–graphene nanocomposites deliver a high specific capacity of 552.1 mA h g−1 at a current density of 200 mA g−1 and retain 91% of the initial capacity after 100 cycles. Furthermore, the hybridized FeOx–graphene materials undergo only 26% capacity decay when the discharge current density is changed from 200 mA g−1 to 1000 mA g−1. The enhanced cycling and high discharge rate performance derives from the high specific surface area of iron oxide nanoparticles and particular electric conductivity of graphene. This study suggests a safe, inexpensive and powerful rechargeable iron electrode, enabling the promising prospect of large-scale energy storage based on the aqueous iron-based rechargeable battery.

Improved hydrogen production from formic acid under ambient conditions using a PdAu catalyst on a graphene nanosheets–carbon black support

Formic acid (FA) has great potential as a suitable liquid source for hydrogen and hydrogen storage materials, provided highly active and selective dehydrogenation catalysts under ambient conditions are developed. Here, well-dispersed bimetallic gold–palladium (PdAu) nanoparticles (NPs) grown on graphene nanosheets–carbon black (GNs–CB) composite supports are synthesized via a facile co-reduction method, wherein the GNs–CB composite support proved to be a powerful dispersion agent and a distinct support for the PdAu NPs. Interestingly, the resultant PdAu/GNs–CB catalyst manifests high selectivity and exceedingly high activity to complete the decomposition of FA at room temperature.

Nanostructured Carbon/Antimony Composites as Anode Materials for Lithium-Ion Batteries with Long Life.

A series of nanostructured carbon/antimony composites have been successfully synthesized by a simple sol-gel, high-temperature carbon thermal reduction process. In the carbon/antimony composites, antimony nanoparticles are homogeneously dispersed in the pyrolyzed nanoporous carbon matrix. As an anode material for lithium-ion batteries, the C/Sb10 composite displays a high initial discharge capacity of 1214.6 mAh g(-1) and a reversible charge capacity of 595.5 mAh g(-1) with a corresponding coulombic efficiency of 49 % in the first cycle. In addition, it exhibits a high reversible discharge capacity of 466.2 mAh g(-1) at a current density of 100 mA g(-1) after 200 cycles and a high rate discharge capacity of 354.4 mAh g(-1) at a current density of 1000 mA g(-1) . The excellent cycling stability and rate discharge performance of the C/Sb10 composite could be due to the uniform dispersion of antimony nanoparticles in the porous carbon matrix, which can buffer the volume expansion and maintain the integrity of the electrode during the charge-discharge cycles.

Simple preparation of Cu6Sn5/Sn composites as anode materials for lithium-ion batteries

Cu6Sn5/Sn composites are directly fabricated by a high energy mechanical milling technique and subsequent heat treatment. In particular, the effects of the ratios of Sn to Cu6Sn5 (CuxSny, x = 10 − y, y = 4.5, 7 and 9) on the lithium-ion batteries performances are investigated. The results show that the sample with y = 4.5 is a single-phase Cu6Sn5, the sample with y = 7 is slightly Sn rich in the Cu6Sn5 (Sn Cu6Sn5). Furthermore, the Cu6Sn5/Sn composite has an obvious structure of a core–shell, only when y = 7. As an anode material for lithium-ion batteries, the Cu6Sn5/Sn composite with y = 7 exhibits a discharge capacity of 761.6 mA h g−1 after the first cycle, 457.8 mA h g−1 after 20th cycles, and an initial coulombic efficiency of 91.37%, which shows a better electrochemical performance than that of y = 4.5 or 9. In addition, after adding 15 wt% of graphite, the sample with y = 7 maintains a discharge capacity of 605.8 mA h g−1 after 100 repeated cycles, higher than many reported Cu–Sn-based anode materials.

Microstructures and Properties of Melt-Spun and As-Cast Mg-20Gd Binary Alloy

Mg-20Gd(%, mass fraction) samples were prepared using melt-spinning and copper mold casting techniques. Microstructures and properties of the Mg-20Gd were investigated. Results show that the melt-spun ribbon is mainly composed of supersaturated alpha-Mg solid solution phase and the as-east ingot mainly contains alpha-Mg solid solution and Mg5Gd phase. The differential scanning calorimeter (DSC) curve of the ribbon exhibits a small exothermic peak in the temperature range from 630 to 680 K, which indicates that the ribbon contains a metastable phase (amorphous). Tensile strength at room temperature of the melt-spun ribbon and as-cast specimen are 308 and 254 MPa, respectively. The elongations of the two samples are less than 2%. The fracture surfaces demonstrate that the fracture mode of the as-cast Mg-20Gd is a typical cleavage fracture and that of the melt-spun sample is a combination of brittle fracture and ductile fracture.

Investigation and Application of Excellent Performance Mg Rare Earth Alloys as a Structural Material

Magnesium (Mg) alloys are becoming one of the key engineering materials for aerospace and automotive industries because of their low density, high specific strength, excellent machinability and good diecastability, etc. In the meantime, conventional Mg alloys are limited for their low strength and creep resistance. Therefore, special attention is given on its applications at high temperature such as the transmission case and the engine block, In the near decades, much effort have been devoted to improving the properties such as strength, ductility, creep resistance of Mg alloys by adding rare earth (RE) elements, and it has been certified that the addition of RE do improve the performances of the Mg alloys. In this paper, we will review the progresses in the investigations of the Mg-RE alloys as a structural material, and also propose its application prospect in future.

Synthesis of polygonal Co3Sn2 nanostructure with enhanced magnetic properties

A one-pot solvothermal route is employed to fabricate polygonal Co3Sn2 nanostructures. The obtained product exhibits anisotropic structure and morphology, which endow the Co3Sn2 nanostructure with enhanced coercivity of 131.5 Oe, four times as high as the cubic cobalt sample (31.3 Oe).

Structure and mechanical properties of Mg-Zn-RE system alloys

The lightest density of Mg has stimulated renewed interest in Mg based alloys for applications in the automotive, aerospace and communications industries. However, Mg in the pure form has relatively low strength, limited ductility and is susceptible to corrosion. Great efforts have been made to improve the mechanical properties of Mg alloys. Alloying Mg with other elements is one of the most important methods. An important class of Mg alloys is the Mg-Zn-RE system (RE = rare earth elements). In recent few decades, a series of new Mg-Zn-RE system alloys have been obtained, and detailed the structure and mechanical properties of the alloys. In this paper, the structure and mechanical properties of the Mg-Zn-RE alloys have been summarized. It showed that these alloys have high strength and they are prospected to be widely used in the future.

Gd–Sn alloys and Gd–Sn–graphene composites as anode materials for lithium-ion batteries

Due to its high theoretical capacity as high as 990 mA h g−1, Sn is considered as a potential anode material for high-capacity lithium-ion batteries (LIBs). However, the huge volume expansion during the alloying/dealloying process causes poor cycling stability and low rate capability. To address this gap, Gd doped Gd–Sn alloys are introduced in this work. Herein, the Gd–Sn alloys are prepared by arc-melting two different starting bulk metals Gd and Sn with atomic ratios of Gd : Sn = 1 : 3 and 1 : 6. Then, the obtained Gd–Sn powders mixed with graphene at a mass ratio of 1 : 10 are deployed to prepare the Gd–Sn–graphene composites by a ball-milling route. XRD results show that the characteristic peaks of the obtained Gd–Sn–graphene composites are consistent with GdSn3, β-Sn, and graphene phases, where the well-dispersed Gd–Sn alloy particles are distributed with sizes of about hundreds of nanometers. In addition, graphene was homogeneously dispersed with the GdSn3 and Sn particles, when the composite has an atomic ratio of Gd : Sn = 1 : 6 and graphene content of 9 wt% (GdSn6/G composite). The electrochemical characterization shows that the GdSn6/G composite has a higher reversible discharge capacity than that of the Gd–Sn powders. At a current density of 100 mA g−1, the first charge and discharge capacities are 547.1 and 900.2 mA h g−1, and a stable capacity of 455.3 mA h g−1 could be maintained after 30 cycles. Even at a current density of 500 mA g−1 (about 1C rate), a good reversible capacity of 403.9 mA h g−1 could be achieved. The enhanced performance may be attributed to the rare earth metal Gd with good toughness, and graphene with good electrical conductivity and mechanical strength.