Fangli Yuan

A new synthetic route to hollow Co3O4 octahedra for supercapacitor applications

Co3O4 hollow octahedra were successfully synthesized via a facile one-step solvothermal route. Time-resolved electron microscopy and X-ray diffraction analyses revealed that the Co3O4 hollow octahedra were formed through the self-assembly of primary nanocrystals followed by subsequent Ostwald ripening. Subtle control over the reaction conditions led to different morphologies (hexagonal plates and nanocubes) and crystal structures (β-Co(OH)2–Co3O4 composite). The unique hollow nanostructure rendered our Co3O4 potentially useful for charge-storage applications. To prove its usefulness, the pseudocapacitive performance of the Co3O4 hollow octahedra as a supercapacitor electrode was evaluated and exhibited a charge storage capacity of 192 F g−1 with good long-term cyclability.

“Protrusions” or “holes” in graphene: which is the better choice for sodium ion storage?

The main challenge associated with sodium-ion battery (SIB) anodes is a search for novel candidate materials with high capacity and excellent rate capability. The most commonly used and effective route for graphene-based anode design is the introduction of in-plane “hole” defects via nitrogen-doping; this creates a spacious reservoir for storing more energy. Inspired by mountains in nature, herein, we propose another way – the introduction of blistering in graphene instead of making “holes”; this facilitates adsorbing/inserting more Na+ ions. In order to properly answer the key question: ““protrusions” or “holes” in graphene, which is better for sodium ion storage?”, two types of anode materials with a similar doping level were designed: a phosphorus-doped graphene (GP, with protrusions) and a nitrogen-doped graphene (GN, with holes). As compared with GN, the GP anode perfectly satisfies all the desired criteria: it reveals an ultrahigh capacity (374 mA h g−1 after 120 cycles at 25 mA g−1) comparable to the best graphite anodes in a standard Li-ion battery (∼372 mA h g−1), and exhibits an excellent rate capability (210 mA h g−1 at 500 mA g−1). In situ transmission electron microscopy (TEM) experiments and density functional theory (DFT) calculations were utilized to uncover the origin of the enhanced electrochemical activity of “protrusions” compared to “holes” in SIBs, down to the atomic scale. The introduction of protrusions through P-doping into graphene is envisaged to be a novel effective way to enhance the capacity and rate performance of SIBs.

Fabrication of ZnO nanorod-assembled multishelled hollow spheres and enhanced performance in gas sensor

In this work, ZnO multishelled hollow spheres with an average diameter of 5 μm were prepared by a facile solvothermal process in a ternary solvent system including water, ethanol and ethylene, and as-synthesized products were constructed by highly directional interactions of anisotropic single-crystalline ZnO nanorods. A two-step assembly process followed symmetric Ostwald ripening process is proposed to explain the formation mechanism of obtained products, which highlights the driving force of the solvents in promoting the nanorod aggregation and the solid evacuation of final products. Scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy were used to characterize the structure of synthesized products. The investigation of the gas-sensing properties indicated that control of the shape-defined building units and their assembled structure provides ZnO with high performance in gas sensing, and the double-wall hollow structures exhibit the highest sensitivity to formaldehyde gas than the nanorods and hollow spheres, which is contributed to their high donor-related and the low acceptor-related intrinsic defects in ZnO crystals.

Synthesis of uniform octahedral tungsten trioxide by RF induction thermal plasma and its application in gas sensing

Well-defined uniform octahedral WO3 are prepared via a simple one-step thermal plasma technique. The detailed structures of the synthesized materials are characterized by XRD, EDX, FESEM, SAED and HRTEM. Each octahedron is nearly perfect with a highly symmetric, regular shape containing 8 facets, 6 vertices, and 12 edges, which exhibit sharp edges and corners as well as smooth surfaces. Processing parameters dependent experiments are performed to control its shape and size distribution. The regular octahedral WO3 shows good sensing properties to benzene gas, which might mainly be due to its highly exposed {111} faces and the regular octahedral shape.

Fabrication of Porous TiO2 Hollow Spheres and Their Application in Gas Sensing

In this work, porous TiO2 hollow spheres with an average diameter of 100 nm and shell thickness of 20 nm were synthesized by a facile hydrothermal method with NH4HCO3 as the structure-directing agent, and the formation mechanism for this porous hollow structure was proved to be the Ostwald ripening process by tracking the morphology of the products at different reaction stages. The product was characterized by SEM, TEM, XRD and BET analyses, and the results show that the as-synthesized products are anatase phase with a high surface area up to 132.5 m2/g. Gas-sensing investigation reveals that the product possesses sensitive response to methanal gas at 200°C due to its high surface area.

Dopant-Controlled Morphology Evolution of WO3 Polyhedra Synthesized by RF Thermal Plasma and Their Sensing Properties

In this paper, a simple way is developed for the synthesis of Cr-doped WO3 polyhedra controlled by tailoring intrinsic thermodynamic properties in RF thermal plasma. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy are used to characterize the detail structures and surface/near-surface chemical compositions of the as-prepared products. Kinetic factors showed little effects on the equilibrium morphology of Cr-doped WO3 polyhedra, while equilibrium morphologies of WO3 polyhedra can be controlled by the thermodynamic factor (Cr doping). Set crystal growth habits of pure WO3 as an initial condition, coeffects of distortions introduced by Cr into the WO3 matrix, and a chromate layer on the crystal surface could reduce the growth rates along [001], [010], and [100] directions. The morphology evolution was turning out as the following order with increasing Cr dopants: octahedron-truncated octahedron-cuboid. 2.5 at. % Cr-doped WO3 polyhedra exhibit the highest sensing response due to coeffects of exposed crystal facets, activation energy, catalytic effects of Cr, and particle size on the surface reaction and electron transport units. By simply decorating Au on Cr-doped WO3 polyhedra, the sensing responses, detection limit, and response-recovery properties were significantly improved.

Synthesis of uniform α-Si3N4 nanospheres by RF induction thermal plasma and their application in high thermal conductive nanocomposites.

In this paper, single-crystalline α-Si3N4 nanospheres with uniform size of ∼50 nm are successfully synthesized by using a radio frequency (RF) thermal plasma system in a one-step and continuous way. All Si3N4 nanoparticles present nearly perfect spherical shape with a narrow size distribution, and the diameter is well-controlled by changing the feeding rate. Compact Si3N4/PR (PR = phenolic resin) composites with high thermal conductivity, excellent temperature stability, low dielectric loss tangent, and enhanced breakdown strength are obtained by incorporating the as-synthesized Si3N4 nanospheres. These enhanced properties are the results of good compatibility and strong interfacial adhesion between compact Si3N4 nanospheres and polymer matrix, as large amount of Si3N4 nanospheres can uniformly disperse in the polymer matrix and form thermal conductive networks for diffusion of heat flow.

In Situ Electrochemistry of Rechargeable Battery Materials: Status Report and Perspectives

The development of rechargeable batteries with high performance is considered to be a feasible way to satisfy the increasing needs of electric vehicles and portable devices. It is of vital importance to design electrodes with high electrochemical performance and to understand the nature of the electrode/electrolyte interfaces during battery operation, which allows a direct observation of the complicated chemical and physical processes within the electrodes and electrolyte, and thus provides real-time information for further design and optimization of the battery performance. Here, the recent progress in in situ techniques employed for the investigations of material structural evolutions is described, including characterization using neutrons, X-ray diffraction, and nuclear magnetic resonance. In situ techniques utilized for in-depth uncovering the electrode/electrolyte phase/interface change mechanisms are then highlighted, including transmission electron microscopy, atomic force microscopy, X-ray spectroscopy, and Raman spectroscopy. The real-time monitoring of lithium dendrite growth and in situ detection of gas evolution during charge/discharge processes are also discussed. Finally, the major challenges and opportunities of in situ characterization techniques are outlined toward new developments of rechargeable batteries, including innovation in the design of compatible in situ cells, applications of dynamic analysis, and in situ electrochemistry under multi-stimuli. A clear and in-depth understanding of in situ technique applications and the mechanisms of structural evolutions, surface/interface changes, and gas generations within rechargeable batteries is given here.

Formation of cubic Cu mesocrystals by a solvothermal reaction

Cubic Cu mesocrystals were prepared via a facile solvothermal reaction in a mixed solvent of glycerol–water. The microstructure of synthesized mesocrystals can be successfully controlled by adjusting the volume ratio of glycerol/water. The evolution of these cubic Cu mesocrystals was investigated and the mechanism was discussed. The oriented attachment process controls the initial stage in the formation of scabbled cubic Cu mesocrystals and then Ostwald ripening process contributes to the formation of the final Cu mesocrystals by shearing the scabbled mesocrystals. The influences of reaction temperature and NaOH concentration on the morphology of the synthesized mesocrystals were also investigated. Isotropic conductive adhesives (ICA), filled with cubic Cu mesocrystals, exhibit a low bulk resistivity, of about 5.21 × 10−4 Ω cm.

Shape-controlled synthesis and luminescence properties of yttria phosphors

Y(OH)3 hexagonal tubes with embedded polyhedrons (HTEPs) were successfully prepared by a facile hydrothermal method using sodium citrate as the crystal modifier, and as-synthesized products exhibit uniform diameter and length of about 2 μm and 2–3 μm, respectively. An oriented aggregation and subsequent dissolution-recrystallization process was proposed to explain the growth mechanism of obtained products. Y2O3 : Eu3+ microstructures with similar morphologies were obtained after thermal treatment of the as-prepared Y(OH)3 : Eu3+ microstructures at 1000 °C for 2 h. X-Ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and fluorescence spectrometer were used to characterize the samples. The photoluminescence properties investigation reveals that Y2O3 : Eu3+ HTEPs show a strong red emission with the strongest peak centered at 614 nm under the excitation of 259 nm ultraviolet light.