Synthesis of high-performance LiMnPO<Subscript>4</Subscript>/C /rGO composite via a mechanical-activation-assisted polyol process

A mechanical-activation-assisted polyol method for efficient preparation of high-performance rod-like LiMnPO₄ composite is developed. The nanosized [Mn₃(PO₄)₂·8H₂O + Li₃PO₄]/graphene oxide (GO) precursors are prepared via a mechano-chemical liquid-phase activation–assisted technique from LiH₂PO₄ and manganese powder. LiMnPO₄/reduced graphene oxide (rGO) samples are obtained by polyol process in boiling triethylene glycol (TEG) and then followed with pyrolytic carbon coating to prepare the LiMnPO₄/C/rGo nanocomposite. The characterized results prove that well-crystallized LiMnPO₄ nanorods can be successfully synthesized by polyol processing. The LiMnPO₄ nanorods have a large percentage of highly oriented (020) facets, which provide a high pore density for Li-ion insertion/extraction. Both rGO modification and further carbon coating significantly improve the conductivity and reduce the charge-transfer resistance. The optimized LiMnPO₄/C/rGO composite delivers good electrochemical performance.     

Solid state synthesis of nonstoichiometric Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>/Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> composites as visible-light photocatalyst

Nonstoichiometric Bi₂WO₆ photocatalyst with the composition of Bi_2?+?x WO_6?+?1.5x (?0.25 ≤ x ≤ 1) wa synthesized by a facile solid state reaction method. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-vis absorption spectrum. The Bi_2.5WO_6.75 photocatalyst showed excellent visible-light-driven photocatalytic performance; nearly 100 % of RhB (10 ppm, pH?=?3?~?4) was decomposed within 25 min, which demonstrated that nonstoichiometric semiconductors could be an efficient visible-light-driven photocatalyst.     

Pd/WO<Subscript>3</Subscript>/C nanocomposite with APTMS-functionalized tungsten oxide nanosheet for formic acid electrooxidation enhancement

A Pd/WO₃/C nanocomposite with 3-aminopropyltrimethoxysilane (APTMS)-functionalized tungsten oxide nanosheets (Pd/WO₃/C-APTMS) was synthesized and applied as the efficient anode catalyst for direct formic acid fuel cells (DFAFCs). The mechanism for synthesizing the nanocomposite is as follows: initially, [PdCl₄]^2? was assembled onto the tungsten oxide nanosheets modified with APTMS. Following this, Pd nanoparticles were reduced via traditional impregnation reduction of [PdCl₄]^2? with NaBH₄. The transmission electron microscope (TEM) images revealed that the Pd nanoparticles were uniformly dispersed on WO₃ nanosheets and were approximately 2.7 nm in size. The electrochemical test results showed that enhanced electrocatalytic activity for the formic acid oxidation reaction (FAOR) was obtained on the Pd/WO₃/C catalyst compared with Pd/C. The higher electrocatalytic activity might be attributed to the uniform distribution of Pd with smaller particles. Furthermore, it is likely that the improvement in catalytic stability for the Pd/WO₃/C catalyst is due to the hydrogen spillover effect of WO₃ particles. These results indicate that this novel Pd/WO₃/C-APTMS nanocomposite exhibits promising potential for use as an anode electrocatalyst in DFAFCs.     

Fabrication and electrochemical performance of La<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> impregnated porous YSZ cathode

La_0.5Sr_0.5CoO₃-yttria-stabilized zirconia (LSCO-YSZ) composite cathode for solid oxide fuel cell (SOFC) has been fabricated by wet impregnation method. Nitrate precursors of La, Sr, and Co have been impregnated into the pre-sintered porous YSZ matrix, which is converted into LSCO phase after calcination at 850 °C in the presence of glycine as confirmed from X-ray diffraction. LSCO of 5, 7, and 10 wt% impregnated porous YSZ have been electrochemically characterized using 2-probe AC conductivity method. Maximum ionic conductivity of 0.27 S/cm at 800 °C and activation energy of 0.15 eV between 600 and 800 °C have been observed for 10 wt% LSCO-YSZ cathode. Area-specific resistance of 1.01 Ω cm² at 800 °C is estimated for the electrolyte-supported half-cell (10 wt% LSCO-YSZ/YSZ). After testing the LSCO-YSZ cathode matrix, the electrolyte-supported full cell (10 wt% LSCO-YSZ/YSZ/NiO-YSZ) has been tested and produced maximum power density 51.12 mW/cm² (109.38 mA/cm²) at 800 °C. The electrolyte-supported full cell exhibited 6 Ω cm² electrode polarization at 800 °C in H₂, which is in higher side leading to low performance. LSCO-YSZ/YSZ/NiO-YSZ SOFC found to give stable performance up to 2 h and scanning electron microscopy analysis has been carried out before and after cell testing to assess the morphological changes.     

n型有序多孔硅基氧化钨室温气敏性能研究

利用电化学腐蚀方法制备了n型有序多孔硅, 并以此为基底用直流磁控溅射法在其表面溅射不同厚度的氧化钨薄膜. 利用X射线和扫描电子显微镜表征了材料的成分和结构, 结果表明, 多孔硅的孔呈柱形有序分布, 溅射10 min的WO₃薄膜是多晶结构, 比较松散地覆盖在整个多孔硅的表面. 分别测试了多孔硅和多孔硅基氧化钨在室温条件下对二氧化氮的气敏性能, 结果表明, 相对于多孔硅, 多孔硅基氧化钨薄膜对二氧化氮的气敏性能显著提高. 对多孔硅基氧化钨复合结构的气敏机理分析认为, 多孔硅和氧化钨薄膜复合形成的异质结对良好的气敏性能起到主要作用, 氧化钨薄膜表面出现了反型层引起了气敏响应时电阻的异常变化. 关键词： 有序多孔硅 氧化钨薄膜 二氧化氮 室温气敏性能     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

Cu-supported carbon networks containing SnO<Subscript>2</Subscript> as three-dimensional anodes for lithium-ion batteries

Cu-supported SnO₂@C composite coatings constructed by interconnected carbon-based porous branches were fabricated by annealing Cu foils with films formed by knife coating DMF solution containing SnCl₂, polyacrylonitrile (PAN), and poly(methyl methacrylate) (PMMA) on their surface in vacuum. The carbon-based porous branches consist of amorphous carbon matrices, SnO₂ nanoparticles with a size of 30–100 nm mainly encapsulated inside, and many micropores with a size of 1–5 nm. The three-dimensional (3D) porous network structures of the SnO₂@C composite were achieved by volatilization of PMMA and pyrolysis of SnCl₂. The SnO₂@C composite coatings demonstrate good cyclic performance with a high reversible capacity of 642 mA h g^?1 after 100 cycles at a current density of 50 mA g^?1 without apparent capacity fading during cycling and excellent rate performance with a capacity of 276 mA h g^?1 at a high current density up to 10 A g^?1.     

Solution processable reduced graphene oxide decorated ATO electrode for organic solar cells

A novel concept based on the use of solutions containing already qualified crystalline antimony-doped tin oxide SnO₂:Sb (ATO) nanoparticles has been developed. ATO nanoparticles are decorated by reduced graphene oxide (rGO) through a hydrothermal synthesis method. The electrical and optical properties of the graphene oxide films are investigated systematically. The sheet resistance (R _□) of the ATO–rGO films decreases with the increase in the rGO content in the precursor solution. The R _□ can be decreased after the ATO–rGO films annealing in the air for 1 h and can be further decreased by depositing Au on the surface of the films. The optimum property of the ATO–rGO film shows that the R _□ is 80 Ω/□ and the transmittance is about 70 %. The ATO–rGO films are used as the anode of the organic solar cells. The anode film impact on the performance of the devices is studied. Finally, the power conversion efficiency (PCE) of the device based on the poly-(3-hexylthiophene): [6, 6]-phenyl C61-butyric acid methyl ester (PCBM) blended is 1.85 %, and the PCE of the device based on the poly-benzo[1,2-b:4,5-b′] dithio-phene thieno[3,4-b] thiophene:PCBM blended is 3.4 %.     

Synthesis of Li3V2(PO4)3/reduced graphene oxide cathode material with high-rate capability

The Li₃V₂(PO₄)₃/reduced graphene oxide (LVP/rGO) composite is successfully synthesized by a conventional solid-state reaction with a high yield of 10 g, which is suitable for large-scale production. Its structure and physicochemical properties are investigated using X-ray diffraction, Raman spectra, field-emission scanning electron microscopy, transmission electron microscopy, and electrochemical methods. The rGO content is as low as ~3 wt%, and LVP particles are strongly adhered to the surface of the rGO layer and/or enwrapped into the rGO sheets, which can facilitate the fast charge transfer within the whole electrode and to the current collector. The galvanostatic charge–discharge tests show that the LVP/rGO electrode delivers an initial discharge capacity of 177 mAh g^?1 at 0.5 C with capacity retention of 88 % during the 50th cycle in a wide voltage range of 3.0–4.8 V. A superior rate capability is also achieved, e.g., exhibiting discharge capacities of 137 and 117 mAh g^?1 during the 50th cycle at high C rates of 2 and 5 C, respectively.     

Fabrication and capacitive characteristics of conjugated polymer composite p-polyaniline/n-WO3 heterojunction

A nanocrystalline and porous p-polyaniline/n-WO₃ dissimilar heterojunction at ambient temperature is reported. The high-quality and well-reproducible conjugated polymer composite films have been fabricated by oxidative polymerization of anilinium ion on predeposited WO₃ thin film by chemical bath deposition followed by thermal annealing at 573 K for 1 h. Atomic force microscopy (AFM) analyses reveal a homogenous but irregular cluster of faceted spherically shaped grains with pores. The scanning electron microscopy confirms the porous network of grains, which is in good agreement with the AFM result. The optical absorption analysis of polyaniline/WO₃ hybrid films showed that direct optical transition exist in the photon energy range 3.50–4.00 eV with bandgap of 3.70 eV. The refractive index developed peak at 445 nm in the dispersion region while the high-frequency dielectric constant, ? _∞, and the carrier concentration to effective mass ratio, N/m^*, was found to be 1.58 and 1.10 × 10³⁹ cm^?3, respectively. The temperature dependence of electrical resistivity of the deposited films follows the semiconductor behavior while the C–V characteristics (Mott–Schottky plots) show that the flat band potential was ?791 and 830 meV/SCE for WO₃ and polyaniline.     

The transport and thermal properties of glassy LiPO<Subscript>3</Subscript>/crystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) composite electrolytes

Glassy LiPO₃/crystalline Al₂O₃ and glassy LiPO₃/crystalline ZrO₂ (0–12.5 vol.% of oxide fillers) composite solid electrolytes have been prepared by glass matrix softening. Their thermal and transport properties have been investigated by differential scanning calorimetry (DSC) and impedance spectroscopy methods. The addition of ZrO₂ leads to a decrease in the crystallization temperature of LiPO₃ glass. It was found that the conductivity behavior depends on the nature of the dispersed addition. In the case of the Al₂O₃ addition, the increase in the electrical conductivity is observed. The ionic conductivity of the LiPO₃/10% Al₂O₃ composite reaches 5.8 × 10^?8 S/cm at room temperature. In contrast, the conductivity in the LiPO₃/ZrO₂ composite system decreases.     

Metal Oxide Nanomaterials with Nitrogen‐Doped Graphene‐Silk Nanofiber Complexes as Templates

Fabricating electrode materials with superior electrochemical performance remains a challenge. Here, a simple but effective strategy for the formation of metal oxide nanomaterials with superior performance has been developed. Silk protein nanofibers adhered on reduced graphene oxide (rGO) sheets are used as templates to regulate the formation of nanostructured iron oxide composites, achieving porous nanorod structures that could not be attained in control experiments. These porous nanorods demonstrate superior electrochemical performance as electrodes with retention of a capacity of 1495 mAh g^?1 after 180 cycles at 0.2 C and a rate capability of 900 mAh g^?1 at 2 C discharge rate. These new rGO/silk composite templates provide a more controllable environment for Fe₂O₃ fabrication, resulting in improved nanostructures and superior electrical performance. The strategy developed here should also be more broadly applicable in the design of metal oxide nanomaterials with specialized structures and useful performance.     

Photocatalytic ability of Bi<Subscript>6</Subscript>Ti<Subscript>3</Subscript>WO<Subscript>18</Subscript> nanoparticles with a mix-layered Aurivillius structure

Aurivillius phase layered perovskites Bi₆Ti₃WO₁₈ was prepared by the sol-gel citrate-complexation synthesis. The sample developed into the plate-like nanoparticles with the exposed (001) facets. The phase formation and structure have been verified via X-ray polycrystalline powder diffraction (XRD) Rietveld refinements. The nanoparticles were investigated via the measurements such as FE-SEM, TEM, EDS, and the surface analyses. UV–Vis absorption data revealed that the Aurivillius compound has a direct band characteristic with the band energy of 2.214 eV. The band structure of Bi₆Ti₃WO₁₈ nanoparticles was discussed on the base of the experiments and theoretical calculation. Bi³⁺-containing Aurivillius Bi₆Ti₃WO₁₈ shows efficient photocatalytic degradation for rhodamine B dye (RhB) with the visible light irradiation (λ?>?420 nm). Dynamic characteristic of the light-created excitons was measured by the luminescence and decay lifetime. The multivalent properties of W and Ti ions in the Aurivillius-like lattices of Bi₆Ti₃WO₁₈ photocatalyst were discussed.     

Fast electrochromic response of porous-structured cobalt oxide (Co<Subscript>3</Subscript>O<Subscript>4</Subscript>) thin films by novel nebulizer spray pyrolysis technique

Electrochromic effect of cobalt oxide thin films was studied as a function of substrate temperature (573–673 K). Tricobalt tetraoxide (Co₃O₄) thin films were deposited on glass and fluorine-doped tin oxide (FTO) substrates by nebulized spray technique using cobalt nitrate as precursor material. The XRD patterns indicated (311) plane was dominant for all the films irrespective of the deposition temperature. Williamson-Hall (W-H) analysis was made to understand the strain variation in the prepared Co₃O₄ films under different deposition temperature by employing uniform deformation model (UDM). Scanning electron microscopy images revealed porous morphology for the film prepared at 623 K. The optical parameters such as refractive index (n), extinction coefficient (k), and band gap were derived from UV-visible spectra of Co₃O₄ films. The electrochromic performance of the deposited Co₃O₄ films was analyzed through cyclic voltammetry, chronocoulometry, chronoamperometry, and iono-optical studies.     

Structural and optical properties of WO<Subscript>3</Subscript> electrochromic layers prepared by the sol-gel method

Thin layers of tungsten trioxide have been prepared from an aqueous solution of peroxotungstic acid (PTA) using the sol-gel method. Compositional, structural and optical characteristics of WO₃ coated on indium tin oxide (ITO) conductive glass substrates were studied using X-ray diffractometery (XRD), cyclic voltammetery (CV), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Monoclinic and triclinic crystalline structures for thin film and powdered WO₃ were confirmed by XRD analysis. SEM micrograph of annealed samples revealed micro cracks due to a decrease in density and a contraction of layers. EDX analysis showed that 1∶2 ratio of oxygen and tungsten atoms in the prepared films is obtained at heat treatment temperatures higher than 200 °C. Furthermore, the annealed samples showed very good electrochromic behavior in cyclic voltammetery studies. Refractive index “n” and extinction coefficient “k” values were found to be reduced by increasing the wavelength and decreasing the temperature.     

High-performance hierarchical cypress-like CuO/Cu<Subscript>2</Subscript>O/Cu anode for lithium ion battery

Composite CuO/Cu₂O/Cu anode for lithium ion battery was designed and synthesized via facile electrodeposition and the subsequent in situ thermal oxidation in air at 300 °C for 1 h. The as-prepared composite CuO/Cu₂O/Cu anode was studied in terms of scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic charge/discharge, cyclic voltammetry (CV), and AC impedance. As expected, the composite CuO/Cu₂O/Cu with CuO-rich surface displayed hierarchical cypress-like morphology; furthermore, the hierarchical cypress-like CuO/Cu₂O/Cu anode also delivered satisfactory electrochemical performances. For example, the reversible discharge capacity remained at 534.1 mAh/g even after 100 cycles. The enhanced electrochemical performances were attributed to the hierarchical cypress-like porous structure and the synergistic effect among the composite active copper oxides and highly conductive Cu current collector.     

Synthesis of PANI/rGO composite as a cathode material for rechargeable lithium-polymer cells

Graphene oxide (GO) was synthesized by an improved Hummers method and then reduced with NaBH₄; GO became rGO with regular layered structure. Polyaniline (PANI)/rGO composite was prepared by a adsorption double oxidant method with rGO as a template. Some physical characterization methods (Fourier transform infrared spectroscopy analysis, X-ray diffraction, scanning electron microscope, and transmission electron microscope) were used to analyze the morphology and crystallinity of the composite. The electrochemical properties were characterized by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge, and rate capability. The first discharge specific capacity of the rPANI/rGO and PANI/rGO was 181.2 and 147.8 mAh/g. After 100 cycles, the capacity retention rate was still 90.2 and 88.9% separately, and the coulombic efficiency of batteries is close to 100%. These results demonstrate the composite has exciting potentials for the cathode material of lithium-ion battery.     

Electrochromic materials from the visible to the infrared region: an example WO<Subscript>3</Subscript>

Herein, the example of the most typical electrochromic material, namely WO₃, is used to illustrate the potential of electrochromic materials for controlling infrared reflectance and hence, emissivity. Playing with various growth parameters, contrast in reflectance between the inserted H _xWO₃ and deinserted WO₃ states as high as 73% in mid-wavelength band (MW, 3–5 μm) was achieved for 320 nm WO₃ films. The latter electrochromic materials were radio frequency sputtered on Au substrate at ambient temperature in 6 Pa of chamber pressure. In comparison, for long wavelength band (LW, 8–12 μm), the contrast in reflectance did not exceed 30%. The origins of the various electrochromic behaviours are correlated to the film structure, morphology and composition, indicating better properties for porous, nonstoichiometric films. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

Preparation of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> hollow microsphere/graphene/carbon nanotube flexible film as a binder-free anode material for lithium-ion batteries

A flexible Co₃O₄ hollow microsphere/graphene/carbon nanotube hybrid film is successfully prepared through a facile filtration strategy and a subsequent thermally treated process. The composition, morphology, and structure of the as-prepared film are characterized by X-ray diffraction, X-ray photoelectron spectrometer, scanning electron microscopy, and transmission electron microscopy. Based on the morphology characterizations on the hybrid film, the Co₃O₄ hollow microspheres are uniformly and closely attached on three-dimensional (3D) graphene/carbon nanotubes (GR/CNTs) network, which decreases the agglomeration of Co₃O₄ microspheres effectively. In this hybrid film, the 3D GR/CNT network which enhances conductance as well as prevents aggregation is a benefit to help Co₃O₄ to exert its lithium storage capabilities sufficiently. When used as a binder-free anode material for lithium-ion batteries, the hybrid film delivers excellent electrochemical properties involving reversible capacity (863 mAh g^?1 at a current density of 100 mA g^?1) and rate performance (185 mAh g^?1 at a current density of 1600 mA g^?1).