Zhongfu Zhou

SnS2@reduced graphene oxide nanocomposites as anode materials with high capacity for rechargeable lithium ion batteries

Nanostructured electrode materials have been studied extensively with the aim of enhancing lithium ion and electron transport, lowering the stress caused by their volume changes during the charge/discharge processes of electrodes, and decreasing overpotential of the electrode reactions in lithium ion batteries. In this work, we develop a new synthetic route to high capacity “double-sandwich-like” SnS2-based nanocomposites (i.e., SnS2-reduced graphene oxide, termed as SSG) which can be used as an anode material in LIBs with improved electrochemical properties, such as large initial discharge capacity (1032 mA h g−1), high reversible discharge capacity (738 mA h g−1, or 1421 mA h cm−3 at 2nd cycle), and excellent cyclability (564 mA h g−1, or 1087 mA h cm−3 after 60 cycles, corresponding to ∼76.5% of the initial reversible capacity), with an excellent coulombic efficiency of ∼96.9%. The electrochemical reaction mechanism of SnS2 with lithium has been suggested to be the alloy-type storage lithium mechanism.

In situstudy of self-ion irradiation damage in W and W–5Re at 500 °C

In situ self-ion irradiations (150 keV W+) have been carried out on W and W–5Re at 500 °C, with doses ranging from 1016 to 1018 W+m−2 (∼1.0 dpa). Early damage formation (1016W+m−2) was observed in both materials. Black–white contrast experiments and image simulations using the TEMACI software suggested that vacancy loops were formed within individual cascades, and thus, the loop nucleation mechanism is likely to be ‘cascade collapse’. Dynamic observations showed the nucleation and growth of interstitial loops at higher doses, and that elastic loop interactions may involve changes in loop Burgers vector. Elastic interactions may also promote loop reactions such as absorption or coalescence or loop string formation. Loops in both W and W–5Re remained stable after annealing at 500 °C. One-dimensional hopping of loops (b = 1/2 ⟨111>) was only seen in W. At the final dose (1018W+m−2), a slightly denser damage microstructure was seen in W–5Re. Both materials had about 3–4 × 1015 loops m−2. Detailed post-irradiation analyses were carried out for loops of size ⩾ 4 nm. Both b = 1/2 ⟨111⟩ (∼75%) and b = ⟨100> (∼25%) loops were present. Inside–outside contrast experiments were performed under safe orientations to determine the nature of loops. The interstitial-to-vacancy loop ratio turned out close to unity for 1/2 ⟨111⟩ loops in W, and for both 1/2 ⟨111⟩ and ⟨100⟩ loops in W–5Re. However, interstitial loops were dominant for ⟨100⟩ loops in W. Re seemed to restrict loop mobility, leading to a smaller average loop size and a higher number density in the W-Re alloy.

Hydrothermal Fabrication of MnCO3@rGO Composite as an Anode Material for High-Performance Lithium Ion Batteries

The layer structure of graphene or reduced graphene oxide (rGO) opens an avenue for the development of advanced functional materials. In this paper, a MnCO3@rGO composite (MGC) was fabricated by anchoring MnCO3 nanoparticles (NPs) on rGO sheets in the hydrothermal reduction process of graphene oxide by using NaBH4. MnCO3 NPs with an average diameter of 8-20 nm were anchored onto the surface of rGO. The layer structure of rGO was maintained in MGC. The MGC was employed as an anode active material for lithium ion batteries. Excellent performances were obtained with a high specific capacity up to 857 mA·h·g(-1) after 100 cycles. The various charging-discharging current rates of 0.2-5.0 C exhibited no clear negative effect on the recycling stability of the MGC. The enhanced structure stability and ion and electron conductivity of the MGC are responsible for the superior electrochemical properties.

Electrochemical extraction of Ti5Si3 silicide from multicomponent Ti/Si-containing metal oxide compounds in molten salt

Ti5Si3 silicide has been extracted directly from complex multicomponent Ti/Si-containing metal oxide compounds by electro-deoxidation in molten calcium chloride using an inert solid oxide oxygen-ion-conducting membrane (SOM) based anode. Studies on the microstructure evolution and electrochemical extraction mechanism show that the formation of Ti5Si3 and the removal of impurity elements happened simultaneously during the electro-deoxidation process. It is found that the electro-deoxidation generated Ti5Si3 micro-particles typically possess a smooth surface, which could contribute to create a continuous anti-oxidation surface layer with excellent high-temperature oxidation resistance property. Consideration is also given to the parameters of electrolysis and the electrochemical characteristics including chemical and/or electrochemical reactions during the electro-deoxidation process, and then a relevant kinetic model is proposed.

Simulations of weak-beam diffraction contrast images of dislocation loops by the many-beam Howie–Basinski equations

A computer program has been developed to solve numerically the Howie–Basinski equations of electron diffraction theory, which avoid the so-called column approximation. In this paper we describe the basis of the numerical approach, and apply it to simulate images of small loops in copper under a variety of weak-beam imaging conditions. Simulations were carried out for faulted Frank loops of size 2–10 nm with systematic variations in imaging parameters (the loop orientation, the diffraction vector, the deviation parameter, the loop depth, the foil thickness and beam convergence). Comparisons are made with experiments in ion-irradiated copper. The simulated images were found to be in good qualitative agreement with experimental TEM micrographs. We are able to reach conclusions on the likely visibility of very small clusters, and we discuss the implications of the simulations for experimental measurements of loop number densities and sizes.

Synthesis, characterization, and catalytic performance of La0.6Sr0.4NixCo1−xO3 perovskite catalysts in dry reforming of coke oven gas

Abstract The dry reforming of coke oven gas (COG) to produce syngas was performed over La 0.6 Sr 0.4 Ni x Co 1– x O 3 catalysts in a fixed-bed reactor at 800 °C. These perovskite-type oxides were synthesized using a sol-gel method and characterized using X-ray diffraction (XRD), N 2 adsorption-desorption, temperature-programmed reduction of H 2 , scanning electron microscopy, transmission electron microscopy, and thermogravimetry-differential scanning calorimetry. XRD results showed that the La 0.6 Sr 0.4 Ni x Co 1– x O 3 perovskite-type oxides formed quaternary solid solutions. The effects of the degree of Ni substitution ( x ) and the catalyst calcination temperature on the dry reforming of COG were investigated. XRD analysis of the tested catalysts showed the formation of Ni 0 , Co 0 , and La 2 O 2 CO 3 , of which the latter is the main active phase responsible for the high activity and stability, and the suppression of coke formation under severe reaction conditions. COG rich in H 2 can also reduce the formation of carbon deposits by inhibiting CH 4 decomposition.

Graphene oxide based BCNO hybrid nanostructures: tunable band gaps for full colour white emission

The emission of BCNO phosphors has been easily tuned from the violet to the near red regions by varying the carbon content. Here we report the optimal conversion of graphene oxide (GO) into BCNO hybrid nanostructures by one-step air oxidation with boric acid and urea. White lighting phosphor was obtained in which the doped porous graphene acts as an interconnecting framework generating and transferring electrons under excitation light. Various carbon-related levels in the BN band structures play an essential role in emitting full colour white light. The quantum confinement in the various kinds of GQDs and GO are also beneficial to widen the emission spectrum.

Magnetic catalysts as nanoactuators to achieve simultaneous momentum-transfer and continuous-flow hydrogen production

It will be very interesting for many important reactions to endow highly active catalysts with momentum-transfer efficiency. However, the intrinsic magnetism of ferromagnetic catalysts is difficult to exploit due to the interaction between the catalyst and stirring devices. Herein, a catalytically active and super paramagnetic Co–carbon–rGO composite (CCGC) was synthesized and used as a nanoactuator to simultaneously achieve momentum-transfer and hydrolysis of NaBH4 or H3NBH3 for hydrogen production. The CCGC magnetically transferred momentum in a batch or continuous flow reactor. The external magnetic field can drive the catalyst to transfer momentum for excellent agitation. The catalyst can be fixed at an appointed position in the continuous flow for efficient separation. The separation of the catalyst from the reaction mixture also becomes facile. The CCGC showed superior retention as a pollutant adsorbent for the removal of Rhodamine B (Rh-B) from water in the absence of magnetic or mechanical stirring apparatus. The unique momentum-transfer properties, as well as excellent catalysis and adsorption, warrant its promising application in the corresponding fields.

ADF STEM imaging of screw dislocations viewed end-on

This paper presents annular dark-field scanning transmission electron microscope image simulations of a screw dislocation viewed end-on in a thin single crystal of Mo, taking into account surface relaxation (the Eshelby twist). The image contrast can be understood in terms of the effects of the displacements normal to the dislocation arising from the Eshelby twist on the channelling behaviour and interband scattering of the incident beam. With the beam focussed at the entrance surface, the image peak positions reflect the positions of the atoms at the entrance surface. For atomic columns at distances from the core less than the foil thickness, the image peak positions are predicted to lie between the perfect crystal and actual surface atom positions. The predicted intensity distribution of the image is qualitatively similar to that of a published experimental image of a screw dislocation in GaN [Phys. Rev. Lett. 91 (2003) p. 165501]. An assessment is made of the possibility of imaging core displacements by focussing near the foil centre, where surface relaxation effects should be minimised.

Percolation channels: a universal idea to describe the atomic structure and dynamics of glasses and melts

Understanding the links between chemical composition, nano-structure and the dynamic properties of silicate melts and glasses is fundamental to both Earth and Materials Sciences. Central to this is whether the distribution of mobile metallic ions is random or not. In silicate systems, such as window glass, it is well-established that the short-range structure is not random but metal ions cluster, forming percolation channels through a partly broken network of corner-sharing SiO4 tetrahedra. In alumino-silicate glasses and melts, extensively used in industry and representing most of the Earth magmas, metal ions compensate the electrical charge deficit of AlO4− tetrahedra, but until now clustering has not been confirmed. Here we report how major changes in melt viscosity, together with glass Raman and Nuclear Magnetic Resonance measurements and Molecular Dynamics simulations, demonstrate that metal ions nano-segregate into percolation channels, making this a universal phenomenon of oxide glasses and melts. Furthermore, we can explain how, in both single and mixed alkali compositions, metal ion clustering and percolation radically affect melt mobility, central to understanding industrial and geological processes.