Jianhui Fang

Li3V2(PO4)3/graphene nanocomposites as cathode material for lithium ion batteries

Li(3)V(2)(PO(4))(3)/graphene nanocomposites have been firstly formed on reduced graphene sheets as cathode material for lithium batteries. The nanocomposites synthesized by the sol-gel process exhibit excellent high-rate and cycling stability performance, owing to the nanoparticles connected with a current collector through the conducting graphene network.

Kinetics of conventional carbon coated-Li3V2(PO4)3 and nanocomposite Li3V2(PO4)3/graphene as cathode materials for lithium ion batteries

Recently, improvement on cycling stability and rate performance were reported when the electrode materials were supported by graphene. In this work, we report the approaches for fabricating a nano-structure Li3V2(PO4)3/carbon with conventional carbon-coating and Li3V2(PO4)3/graphene with graphene sheets supporting the composite. The crystal structure and morphology, the lithium diffusion behavior and high rates capacities of pure LVP, composites of LVP with conventional carbon and graphene sheets are studied in detail. The conventional carbon or some LVP particles are separately aggregated without effectively compounding with each other, but there is a more efficient carbon coating by graphene because the LVP nanoparticles are grown on or are enwrapped into a 2D network of graphene layers. Minor graphene contained in the Li3V2(PO4)3/graphene nanocomposite can result in a reduction of crystal size, a large surface area, an increase in conductivity (three orders of magnitude), and great improvement in the rate performance and cycling stability. We proposed an effective carbon coating (ECC) model of microstructure of LVP nanoparticles compounded with carbon or graphene to discuss the key roles of graphene on the great improvement of electrochemical performance. It should offer a new idea in the design and synthesis of battery electrodes based on carbon-coated technology.

Synthesis and photocatalytic properties of highly stable and neutral TiO2/SiO2 hydrosol.

Stable, neutral TiO(2) hydrosols were prepared using TiCl(4) as titanium source, HNO(3) as peptizing agent, and SiO(2) as stabilizer. Based on XRD, TEM, and FTIR measurements, the TiO(2) was rodlike anatase crystallite with a major axis of 15-25 nm and a minor axis of 5 nm. TiOSi bonds were formed, which suppressed the TiO(2) grain growth and stabilized the TiO(2) hydrosols. The isoelectric points (IEP) of the series hydrosols were 3.1-4.7 pH values and the absolute zeta potentials of the SiO(2)-modified TiO(2) hydrosols were much higher than 50.0 mV under neutral conditions. Methylene blue and reactive brilliant red X-3B were taken as the simulated pollutants to study the adsorption and photocatalytic properties of the obtained hydrosols. The results suggested that the prepared hydrosols had strong adsorption capacity for cationic pollutants rather than anionic ones, and high photodegradation rate of both cationic and anionic pollutants.

Preparation, characterization and electrical properties of fluorine-doped tin dioxide nanocrystals

Fluorine-doped tin dioxide (FTO) nanocrystals were prepared with a sol-gel process followed by a hydrothermal treatment using SnCl(4) and NH(4)F as SnO(2) and fluorine dopant, respectively. The nanostructure and composition were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), zeta potential analysis, electrochemical measurement technology and X-ray photoelectron spectroscopy (XPS) respectively. The diameter of the fluorine doped SnO(2) nanocrystal in rutile-type structure is about 10nm. Compared to the pure SnO(2) nanocrystals, the fluorine doped SnO(2) nanocrystals can be dispersed homogeneously in H(2)O, forming transparent sol with high stability. The powder of fluorine doped SnO(2) nanocrystals could be obtained by removing the solvent, and the electrical resistivity properties were measured by a four-point probe measurement. The results show that sheet resistances (Rs) of fluorine doped SnO(2) decrease with the increasing NH(4)F/Sn molar ratio in the range from 0 to 2. However, further increase of NH(4)F/Sn molar ratio from 2 to 5 leads to higher sheet resistance. The F/Sn molar ratio of fluorine doped SnO(2) measured by XPS is about 0.18 when NH(4)F/Sn molar ratio is equal to 2, and the sheet resistance of fluorine doped SnO(2) powder is 110Ω/□.

Nitrogen-doped porous carbon derived from a bimetallic metal–organic framework as highly efficient electrodes for flow-through deionization capacitors

Novel nitrogen-doped porous carbon has been synthesized from a bimetallic zeolitic imidazolate framework (BMZIF) based on ZIF-8 and ZIF-67 using a self-sacrificial template method and explored for application in flow-through deionization capacitors (FTDCs). The BMZIF itself provides the carbon and nitrogen sources as well as the porous structure. After carbonization and acid etching of BMZIF crystals, the obtained BMZIF derived nanoporous carbon (denoted as BNPC) not only maintains the original rhombic dodecahedron shape of the parent BMZIF, but also possesses a large surface area of 813 m2 g−1, a high N content of 8.00%, high graphitization degree, and good wettability. Electrochemical studies demonstrate that the BNPC electrode integrates the advantageous properties of carbons independently from ZIF-8 and ZIF-67, exhibiting high specific capacitance, lower inner resistance and good stability. Furthermore, the desalination performance of the BNPC electrode under different applied voltages, salty concentrations, and flow rates is investigated by the FTDC experiment. The BNPC electrode exhibits a high salt adsorption capacity of 16.63 mg g−1 in a 500 mg L−1 NaCl aqueous solution at a cell voltage of 1.4 V and a flow rate of 40 mL min−1, which is higher than those of pure ZIF-8 carbon (12.25 mg g−1), ZIF-67 carbon (11.38 mg g−1), and commercial activated carbon (6.12 mg g−1) under the same experimental conditions. Moreover, the BNPC electrode exhibits a high salt adsorption rate and good regeneration performance. The enhanced capacitive deionization performance of BNPC is ascribed to synergistic contributions of its unique hybrid structure, large surface area, rich nitrogen doping, and high graphitic degree. The results indicate that BNPC is a promising material for FTDCs.

Morphological Evolution of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Materials for Lithium-Ion Batteries: The Critical Effects of Surface Orientations and Particle Size

An evolution panorama of morphology and surface orientation of high-voltage spinel LiNi(0.5)Mn(1.5)O4 cathode materials synthesized by the combination of the microwave-assisted hydrothermal technique and a postcalcination process is presented. Nanoparticles, octahedral and truncated octahedral particles with different preferential growth of surface orientations are obtained. The structures of different materials are studied by X-ray diffraction (XRD), Raman spectroscopy, X-ray absorption near edge spectroscopy (XANES), and transmission electron microscopy (TEM). The influence of various morphologies (including surface orientations and particle size) on kinetic parameters, such as electronic conductivity and Li(+) diffusion coefficients, are investigated as well. Moreover, electrochemical measurements indicate that the morphological differences result in divergent rate capabilities and cycling performances. They reveal that appropriate surface-tailoring can satisfy simultaneously the compatibility of power capability and long cycle life. The morphology design for optimizing Li(+) transport and interfacial stability is very important for high-voltage spinel material. Overall, the crystal chemistry, kinetics and electrochemical performance of the present study on various morphologies of LiNi(0.5)Mn(1.5)O4 spinel materials have implications for understanding the complex impacts of electrode interface and electrolyte and rational design of rechargeable electrode materials for lithium-ion batteries. The outstanding performance of our truncated octahedral LiNi(0.5)Mn(1.5)O4 materials makes them promising as cathode materials to develop long-life, high energy and high power lithium-ion batteries.

Solvothermal Synthesis of Crystalline Phase and Shape Controlled Sn4+-Doped TiO2 Nanocrystals: Effects of Reaction Solvent

The Sn(4+)-doped TiO(2) nanocrystals with controlled crystalline phase and morphology had been successfully prepared through easily adjusting the solvent system from the peroxo-metal-complex precursor by solvothermal method. The Sn(4+)-doped TiO(2) nanocrystals were characterized by XRD, Raman, TEM, HRTEM, XPS, ICP-AES, BET, and UV-vis. The experimental results indicated that the Sn(4+)-doped TiO(2) nanocrystals prepared in the pure water or predominant water system trend to form rodlike rutile, whereas the cubic-shaped anatase Sn(4+)-doped TiO(2) nanocrystals can be obtained in the alcohol system. The growth mechanism and microstructure evolution of the Sn(4+)-doped TiO(2) nanocrystals prepared in the different solvent systems are discussed. The liquid-phase photocatalytic degradation of phenol was used as a model reaction to test the photocatalytic activity of the synthesized materials. It was found that sample Sn(4+)-doped TiO(2) prepared in 1-butanol showed the maximum photoactivity, which attributed to higher band gap, optimal crystalline phase and surface state modifications.

From anisotropic graphene aerogels to electron- and photo-driven phase change composites

To overcome fatal shortcomings of organic phase change materials (PCMs), such as leakage during work, low thermal conductivity and shortage of multiple driving ways, we propose a novel strategy to synthesize structurally, mechanically, electrically and optically anisotropic graphene aerogels (AN-GAs) by using gaseous hydrogen chloride to in situ solidify ordered graphene oxide liquid crystals followed by chemical reduction, supercritical fluid drying and annealing in an Ar atmosphere in sequence. The confined pore space and aligned wall structure of the resulting AN-GAs have benefited crystallization of organic phase change molecules and thus highly efficient phase change composites (PCCs) are fabricated with long durability and good strength. The resulting PCCs can also be driven either by applying a small voltage (1–3 V) with high electro-heat efficiency (up to 85%) or by irradiating with weak sunlight (0.8–1.0 sun) with high photo-heat efficiency (up to 77%).

Preparation and CO conversion activity of ceria nanotubes by carbon nanotubes templating method

Abstract Ceria nanotubes with high CO conversion activity by means of carbon nanotubes as removable templates in the simple liquid phase process were fabricated under moderate conditions. The pristine CNTs were first pretreated by refluxing in a 30% nitric acid solution at 140 °C for 24 h, then dispersed in an ethanolic Ce(NO 3 ) 3 ·6H 2 O solution with ultrasonic radiation at room temperature for 1 h. Under vigorous stirring, NaOH solution was added drop by drop into the above ethanolic solution until the pH value was 10. The product was collected and repeatedly washed with ethanol and on drying at 60 °C, the CeO 2/ CNT composites were obtained. Then, the as-prepared composites were heated at 450 °C in an air atmosphere for 30 min to remove CNTs. The ceria nanotubes were characterized by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectrum (XPS). The results showed that the ceria nanotubes were polycrystalline face-centered cubic phase and were composed of lots of dense ceria nanoparticles. The diameter of ceria nanotubes was about 40–50 nm. Catalytic activity of the product for CO oxidation was carried out at the region of 30–300 °C in a U-shaped quartz reactor with feeding about 0.15 g of the catalyst, which was loaded on Al 2 O 3 carrier. The inlet gas composition was 1.0% CO and 28% O 2 with N 2 as balance, and the rate of flow was kept at 40 ml/min. The catalytic products were analyzed by gas chromatography. The as-prepared CeO 2 nanotubes showed higher CO oxidation activity, which indicated that the morphology of ceria products affected the catalytic performance. The ceria nanotubes supported on Al 2 O 3 demonstrated that conversion temperature for CO oxidation to CO 2 was lower than that for bulk catalysts.

Biological cell derived N-doped hollow porous carbon microspheres for lithium–sulfur batteries

Lithium–sulfur (Li–S) batteries are appealing for next generation efficient energy power systems due to their high energy density and low cost. Yeast cells, as a natural biotemplate, are self-duplicable, nitrogen-rich, inexpensive and regular in morphology. Yeast cells show promising applications in the synthesis of nitrogen-doped hollow porous carbon materials for energy storage and transition systems. In this work, we have developed a green and facile self-templating route through low-cost and renewable yeast cells with hollow structures to fabricate N-doped hollow porous carbon microspheres (NHPCMs) for encapsulating sulfur. The sulfur-loaded NHPCM (NHPCM@S) composite with 65 wt% sulfur is then used as the cathode material for Li–S batteries. These batteries exhibit a reversible specific capacity of 1202 mA h g−1 and a capacity retention of 725 mA h g−1 over 400 cycles at 0.1C with a capacity decay of 0.09% per cycle, as well as an enhanced rate performance of 587 mA h g−1 at 2C. In the NHPCM@S composite, the stable micro/mesoporous carbon shell acts as an efficient reservoir for soluble polysulfide, and the doped nitrogen in the carbon shell can offer exceptional electronic conductivity and strong adsorption for polysulfide species. This work demonstrates that an environmentally friendly, economical, sustainable, and self-templating route for N-doped hollow porous microspheres with natural and reproducible biological resources can lead to exciting developments in Li–S batteries and their practical applications in portable electronic devices, advanced electric vehicles, and energy storage systems.