Preparation and electrochemical properties of carbon-coated LiFePO4 hollow nanofibers

Carbon-coated LiFePO₄ hollow nanofibers as cathode materials for Li-ion batteries were obtained by coaxial electrospinning. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller specific surface area analysis, galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) were employed to investigate the crystalline structure, morphology, and electrochemical performance of the as-prepared hollow nanofibers. The results indicate that the carbon-coated LiFePO₄ hollow nanofibers have good long-term cycling performance and good rate capability: at a current density of 0.2C (1.0C = 170 mA·g-1) in the voltage range of 2.5–4.2 V, the cathode materials achieve an initial discharge specific capacity of 153.16 mAh·g-1 with a first charge–discharge coulombic efficiency of more than 97%, as well as a high capacity retention of 99% after 10 cycles; moreover, the materials can retain a specific capacity of 135.68 mAh·g-1, even at 2C.     

Synthesis and characterization of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> magnetic composite nanoparticles by a one-pot process

Fe₃O₄@SiO₂ core–shell composite nanoparticles were successfully prepared by a one-pot process. Tetraethyl-orthosilicate was used as a surfactant to synthesize Fe₃O₄@SiO₂ core–shell structures from prepared Fe₃O₄ nanoparticles. The properties of the Fe₃O₄ and Fe₃O₄@SiO₂ composite nanoparticles were studied by X-ray diffraction, transmission electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. The prepared Fe₃O₄ particles were approximately 12 nm in size, and the thickness of the SiO₂ coating was approximately 4 nm. The magnetic properties were studied by vibrating sample magnetometry. The results show that the maximum saturation magnetization of the Fe₃O₄@SiO₂ powder (34.85 A·m2·kg–1) was markedly lower than that of the Fe₃O₄ powder (79.55 A·m2·kg–1), which demonstrates that Fe₃O₄ was successfully wrapped by SiO₂. The Fe₃O₄@SiO₂ composite nanoparticles have broad prospects in biomedical applications; thus, our next study will apply them in magnetic resonance imaging.     

Preparation and electrochemical properties of carbon-coated LiFePO4 hollow nanofibers

Carbon-coated LiFePO4 hollow nanofibers as cathode materials for Li-ion batteries were obtained by coaxial electrospinning. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller specific surface area analysis, galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) were employed to investigate the crystalline structure, morphology, and electrochemical performance of the as-prepared hollow nanofibers. The results indicate that the carbon-coated LiFePO4 hollow nanofibers have good long-term cycling performance and good rate capability:at a current density of 0.2C (1.0C=170 mA·g?1) in the voltage range of 2.5–4.2 V, the cathode materials achieve an initial discharge specific capacity of 153.16 mAh·g?1 with a first charge–discharge coulombic efficiency of more than 97%, as well as a high capacity retention of 99%after 10 cycles;moreover, the materi-als can retain a specific capacity of 135.68 mAh·g?1, even at 2C.     

Synthesis and characterization of wormhole-like mesoporous Ce0.6Zr0.35Y0.05O2 solid solutions

Nanoparticles of Ce0.6Zr0.35Y0.05O2 (CZY) solid solution have been prepared by the CTAB (hexadecyl-trimethyl ammonium bromide), CTAB-EG (ethylene glycol) templating, and CTAB-EG-NaCl (in which the pores of the precursor synthesized by the CTAB-EG method is filled by a certain amount of NaCl) method, respectively. The physical properties of these materials were characterized by means of tech-niques such as X-ray diffraction (XRD), high resolution scanning electron microscopy (HRSEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and N2 adsorp-tion-desorption measurements. The CZY samples synthesized by the above three methods display wormhole-like mesoporous morphology and cubic crystal structures. The materials are narrow in pore size distribution (averaged pore diameter = 5.3―7.1 nm), high in surface areas (95―119 m2/g), and large in pore volumes (0.16―0.18 cm3/g). It has been demonstrated that the introduction of NaCl is capable of retaining the pore structures of solid nanomaterials at high-temperature calcination.     

石墨烯包覆SnO2空心球的制备及其锂离子电池负极性能

以K2SnO3为原料,采用简单的水热反应,通过基于静电引力的自组装机制,制得石墨烯包覆SnO2空心球的复合材料.采用SEM、TEM、XRD、N2吸附等温线研究了复合材料的形貌和结构;采用电化学方法研究了复合材料的锂离子电池负极性能.结果表明,复合材料为石墨烯包覆的直径约200～300nm的SnO2空心球,比表面积为140.1 m2·g-1.当放电电流密度为158m A·g-1时,充电比容量为425 mAh·g-1,库伦效率保持为92%以上,复合材料具有良好的循环性能.     

石墨烯/二氧化锰复合材料的制备及其电化学性能

通过水热法在160℃条件下成功制备了手风琴状石墨烯/MnO2复合材料.通过场发射扫描电镜、透射电镜、X射线衍射、X射线能量色散谱、BET法以及拉曼光谱对材料进行表征.结果表明,手风琴状二氧化锰与层状石墨烯之间具有十分高效的贴合,这种创新性设计有效地利用了石墨烯的高电导率、大比表面积以及二氧化锰的优秀赝电容行为.电化学测试结果给出在0.2 A·g-1时,样品的比电容高达138 F·g-1,数倍增强于单独的二氧化锰或石墨烯样品.     

碱处理对剑麻基活性炭电化学性能的影响

采用剑麻制得生物质碳材料,取部分所得碳材料进行碱处理．借助X射线衍射（XRD）、扫描电子显微镜（SEM）等对材料的结构和形貌进行了表征,并采用三电极体系,通过恒流充放电、循环伏安等方法,对该碳材料的充放电特性和比电容进行考察．恒流充放电测试结果表明,在电流密度为1A·g-1时,未经碱处理样品的电极放电比电容为231．85F·g-1,而经碱处理的样品则增至290．35F·g-1;在其它电流密度下,经碱处理样品的电极放电比电容总是大于未经碱处理的样品,经1000次循环后,样品比电容有所增加,经碱处理的样品具有更好的循环稳定性,且碳碱质量比为7：1时,比电容达到最大．     

Preparation of nanocrystalline Co<Subscript>3</Subscript>O<Subscript>4</Subscript> and its properties as supercapacitors

Electrochemical capacitors store the capacitance through faradic reaction, which is generally named psue-docapacitance or supercapacitance. They are currently extensively studied as novel energy storage devices. Due to their superb characteristics of high power density and long cycle life compared to the conventional batteries, their high pulse-power capability is very excellent. Inter-ests in supercapacitor energy-storage systems have arisen in recent years on account of possible applications…     

Graphene-immobilized flower-like Ni<Subscript>3</Subscript>S<Subscript>2</Subscript> nanoflakes as a stable binder-free anode material for sodium-ion batteries

A binder-free Ni₃S₂ electrode was prepared directly on a graphene-coated Ni foam (G/Ni) substrate through surface sulfiding of substrate using thiourea as the sulfur source in this work. The Ni₃S₂ showed a flower-like morphology and was uniformly distributed on the G/Ni surface. The flower-like Ni₃S₂ was composed of cross-arrayed nanoflakes with a diameter and a thickness of 1-2 μm and~50 nm, respectively. The free space in the flowers and the thin feature of Ni₃S₂ buffered the volume changes and relieved mechanical strain during repeated cycling. The intimate contact with the Ni substrate and the fixing effect of graphene maintained the structural stability of the Ni₃S₂ electrode during cycling. The G/Ni-supported Ni₃S₂ maintained a reversible capacity of 250 mAh·g-1 after 100 cycles at 50 mA·g-1, demonstrating the good cycling stability as a result of the unique microstructure of this electrode material.     

气体扩散层集流体对Ni(OH)2纳米结构电化学性能的影响

We report the electrochemical performance of Ni(OH)₂ on a gas diffusion layer (GDL). The Ni(OH)₂ working electrode was successfully prepared via a simple method, and its electrochemical performance in 1 M NaOH electrolyte was investigated. The electrochemical results showed that the Ni(OH)₂/GDL provided the maximum specific capacitance value (418.11 F·g?1) at 1 A·g?1. Furthermore, the Ni(OH)₂ electrode delivered a high specific energy of 17.25 Wh·kg?1 at a specific power of 272.5 W·kg?1 and retained about 81% of the capacitance after 1000 cycles of galvanostatic charge–discharge (GCD) measurements. The results of scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed the occurrence of sodium deposition after long-time cycling, which caused the reduction in the specific capacitance. This study results suggest that the light-weight GDL, which can help overcome the problem of the oxide layer on metal–foam substrates, is a promising current collector to be used with Ni-based electroactive materials for energy storage applications.     

镍钴硫化物的制备及其反应温度对形貌和超级电容器性能的影响

采用一步溶剂热合成法制备了镍钴硫化物纳米微球,利用 X 射线衍射光谱（XRD）、扫描电子显微镜（SEM）和 X 光电子能谱（XPS）对制备的材料进行了表征。采用循环伏安和恒电流充放电等电化学方法考察了镍钴硫化物用作超级电容器的电极材料的性能。160℃制备的材料在2 mA／cm2的电流密度下,测得的质量比电容和面积比电容分别为1298 F／g 和1．13 F／cm2。在电流密度为10 mA／cm2下,经过10000圈的循环稳定性测试后,比电容保持了原来的70．8％。此外,通过对反应温度的控制,研究了反应温度对其超级电容器性能的影响。结果表明,反应温度对生成物的形貌几乎没有什么影响,对其电化学性能有一定的影响。     

纳米层状二氧化锰的制备及电化学性能研究

以KMnO₄、NaOH和MnCl₂为原料,在室温下采用液相氧化还原法制备了层状二氧化锰电极材料.分别采用X-射线衍射、扫描电子显微镜和N₂吸附-脱附等方法对材料试样的晶型结构、表观形貌和比表面积等物理性能进行了表征; 采用循环伏安、恒流充放电和交流阻抗等电化学方法研究了材料试样的电化学性能.研究结果表明:所制备的层状二氧化锰为纳米材料,比表面积为89 m·g,在0.5 mol·LLi₂SO₄水系电解液中比电容为96.7 F·g,等效串联电阻为1 Ω,漏电流为0.24 mA,800次循环前后具有良好的循环稳定可逆性.     

Effect of the synthesis route on the structural and dielectric properties of SrBi<Subscript>1.8</Subscript>Y<Subscript>0.2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

This work is devoted to the synthesis and characterization of yttrium-doped SrBi₂Nb₂O₉ ceramics prepared by three methods: solid state reaction, co-precipitation, and hydrothermal. Multiple characterizations, specifically scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR), were used to validate the structural feature. The crystallite size was estimated by Scherrer’s formula and the Williamson–Hall plot. The effect of the process on the band intensities of the FTIR spectra was investigated. The crystallite size and microstructure of ceramics prepared from different synthesis processes were strongly influenced by the sinterability. SEM images revealed nanograin ceramics for materials prepared by co-precipitation and hydrothermal methods and micrograin ceramics prepared by the solid state method. The synthesized compounds underwent phase transitions at 480–465°C. The dielectric and electrical properties of these Y-doped SrBi₂Nb₂O₉ ceramics appear to be dependent on the grain size.     

Synthesis and characterization of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> prepared from atmospheric pressure acid leach liquors of nickel laterite ores

A chemical precipitation-thermal decomposition method was developed to synthesize Co₃O₄ nanoparticles using cobalt liquor obtained from the atmospheric pressure acid leaching process of nickel laterite ores. The effects of the precursor reaction temperature, the concentration of Co2+, and the calcination temperature on the specific surface area, morphology, and the electrochemical behavior of the obtained Co₃O₄ particles were investigated. The precursor basic cobaltous carbonate and cobaltosic oxide products were characterized and analyzed by Fourier transform infrared spectroscopy, thermogravimetric differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy, specific surface area analysis, and electrochemical analysis. The results indicate that the specific surface area of the Co₃O₄ particles with a diameter of 30 nm, which were obtained under the optimum conditions of a precursor reaction temperature of 30℃, 0.25 mol/L Co2+, and a calcination temperature of 350℃, was 48.89 m2/g. Electrodes fabricated using Co₃O₄ nanoparticles exhibited good electrochemical properties, with a specific capacitance of 216.3 F/g at a scan rate of 100 mV/s.     

球形氧化镍粉末对乙醇的电催化性能的研究

通过水热-热分解法制备球形介孔氧化镍粉末,并采用X射线衍射、扫描电镜、透射电镜和比表面积仪对氧化镍粉末的形貌和结构进行表征;通过循环伏安法、计时电流法和电化学阻抗谱的测试,系统研究该种粉末在碱性介质中对乙醇的电催化氧化活性.结果表明：所得到的氧化镍粉末为球形,比表面积为35 m2·g-1,平均孔径为15.88 nm;该粉末对乙醇具有良好的催化活性,氧化电流随乙醇浓度和扫描速率的增大而增大,在0.60 V电位下保持1000 s,球形多孔氧化镍对乙醇氧化催化的电流衰减率为0.075%,稳定性比较好.循环伏安法、计时电流法和电化学阻抗谱测试表明,球形介孔NiO/玻碳电极( NiO/GCE)对乙醇的催化氧化反应机理为扩散控制.     

Hydrothermal synthesized porous Co(OH)2 nanoflake film for supercapacitor application

Porous Co(OH)2 film directly grown on nickel foam is prepared by a facile hydrothermal method.The as-prepared Co(OH)2 film possesses a structure consisting of randomly porous nanoflakes with thicknesses of 20-30 nm.The capacitive behavior of the Co(OH)2 film is investigated by cyclic voltammograms and galvanostatic charge-discharge tests in 2 mol/L KOH.The porous Co(OH)2 film exhibits a high discharge capacitance of 935 F g-1 at a current density of 2 A g-1 and excellent rate capability.The specific capacitance keeps a capacitance of 589 F g-1 when the current density increases to 40 A g-1.The specific capacitance of 82.6% is maintained after 1500 cycles at 2 A g-1.     

La<Subscript>2</Subscript>Zr<Subscript>2</Subscript>O<Subscript>7</Subscript> TBCs toughened by Pt particles prepared by cathode plasma electrolytic deposition

La₂Zr₂O₇ thermal barrier coatings (TBCs) with dispersed Pt particles were prepared by cathode plasma electrolytic deposition (CPED) with ceramic balls added to the cathode region. Compared with the conventional CPED, when ceramic balls are used in the cathode region, the plasma discharge ignition current density decreases approximately 62-fold and the stable plasma discharges occur at the whole cathode surface. Such TBCs with a thickness of 100 μm exhibit a crack-free surface and are composed of pyrochlore-structured La₂Zr₂O₇. Cyclic oxidation, scratching, and thermal insulation capability tests show that such TBCs not only exhibit high resistance to oxidation and spallation but also provide good thermal insulation. These beneficial effects are attributed to the excellent properties of TBCs, such as good thermal insulation because of low thermal conductivity, high-temperature oxidation resistance because of low-oxygen diffusion rate, and good mechanical properties because of the toughening effect of Pt particles.     

Preparation and radar-absorbing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powder

Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al₂O₃ particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.     

Phase transformation and crystal growth behavior of 8mol% (SmO<Subscript>1.5</Subscript>, GdO<Subscript>1.5</Subscript>, and YO<Subscript>1.5</Subscript>) stabilized ZrO<Subscript>2</Subscript> powders

Nanocrystalline powders of ZrO₂-8mol%SmO_1.5(8SmSZ), ZrO₂-8mol%GdO_1.5 (8GdSZ), and ZrO₂-8mol%YO_1.5(8YSZ) were prepared by a simple reverse-coprecipitation technique. Differential thermal analysis/thermogravimetry (DTA/TG), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to study the phase transformation and crystal growth behavior. The DTA results showed that the ZrO₂ freeze-dried precipitates crystallized at 529, 465, and 467℃ in the case of 8SmSZ, 8GdSZ, and 8YSZ, respectively. The XRD and Raman results confirmed the presence of tetragonal ZrO₂ when the dried precipitates were calcined in the temperature range from 600 to 1000℃ for 2 h. The crystallite size increased with increasing calcination temperature. The activation energies were calculated as 12.39, 12.45, and 16.59 kJ/mol for 8SmSZ, 8GdSZ, and 8YSZ respectively.     

Photocatalytic oxidation of gaseous benzene over nanosized TiO2 prepared by solvothermal method

Nanosized TiO2 particles were prepared by solvothermal method using tetrabutyl titanate as precursor,ethanol and water as solvents,and a facile immobilization method of nanosized TiO2 particles on woven glass fabric was developed. The samples obtained under various preparation conditions were charac-terized by means of thermo gravimetric analysis(TG) and differential scanning calorimetry(DSC) ,X-ray diffraction(XRD) ,transmission electron microscopy(TEM) ,high resolution-transmission electron mi-croscopy(HR-TEM) ,and Brunauer-Emmett-Teller(BET) . The results show that the cube-shape of TiO2 prepared by solvothermal method has good crystallinity of(101) surface,higher thermal stability and large specific surface area. Scanning electron microscopy(SEM) images confirmed that the immobi-lized TiO2 film was uniformly distributed and clung to the substrate firmly. The photocatalytic activity of the catalysts was tested using photocatalytic oxidation of gaseous benzene. The results show that the TiO2 calcined after solvothermal treatment suffers from lower specific surface area,and hence de-creases its photocatalytic activity. The photocatalytic activities of the TiO2 by solvothermal treatment with or without calcination in degradation 400 mg/m3 benzene are 3.7 and 4.1 times as high as catalyst without solvothermal treatment,respectively.