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1.
In this study, an ionic complex of V(V) was synthesized by using ultrasonic method, and it was used as a precursor for production of a new catalyst for selective preparation of methylal or dimethoxymethane (DMM). By reaction between an ionic ligand [pyda.H2]2+[pydc]2? (LH2), (pyda.H2 = 2,6-pyridine diammonium and pydc = 2,6-pyridinedicarboxylate) and ammonium vanadate, the five coordinated V(V) complex, [pyda.H][V(pydc)O2], {2,6- diaminopyridinum 2,6-pyridinedicarboxylatodioxovanadate(V)}, VLH2 was synthesized. The prepared complex VLH2 was characterized by SEM, thermal analysis TGA/DTA, FT-IR spectroscopy and X-ray diffraction studies. The results showed that the yield of the reaction was increased up to 64%. The average particle sizes of the obtained complex VLH2 were about 50–60 nm. Also, the nano-catalyst of V2O5/Al2O3 was synthesized by impregnation method and was prepared as a nano-catalyst with average particles sizes of 50–60 nm, and its characterization was performed by XRD, EDX and SEM methods. Finally, the prepared catalyst was used to converting of methanol to methylal at different process conditions.  相似文献   

2.
Nickel zinc ferrite (Ni0.4Zn0.6Fe2O4) films on Si (100) substrate were synthesized using a spin-coating method. The crystallinity of the Ni0.4Zn0.6Fe2O4 films with the thickness of about 386 nm became better as the annealing temperature increased. The films have smooth surface, relatively good packing density and uniform thickness. The volatilization of Zn is serious at 900 °C. With the increase of annealing temperature, the saturation magnetization M s increases in the temperature ranging from 400 to 700 °C, however, decreases above 700 °C, and the coercivity H c increases in the temperature range 400–800 °C, decreases above 800 °C. After annealed at 700 °C for 2 h in air with the heating rate 2 °C/min, the film shows a maximum saturation magnetization M s of 349 emu/cc and low coercivity H c of 66 Oe. The M s is higher than others which prepared by this method, however, the H c is lower. The M s of Ni0.4Zn0.6Fe2O4 films annealed at 700 °C increases with increasing annealing time and the H c changes slightly.  相似文献   

3.
Bi2O2.7/Bi2Ti2O7 composite photocatalyst films are synthesized by sol–gel dip-coating. The ratio of adding Bi and Ti precursors can be controlled during the preparation process. The phase structure is confirmed by X-ray diffraction. The UV–visible diffuse reflectance spectrum shows that the composite catalysts present light absorption in the visible region. The obtained Bi2O2.7/Bi2Ti2O7 composite films possess superior photocatalytic degradation of rhodamine B, owing to the visible light response of Bi2O2.7 and the separation of photogenerated electrons and holes between the two components. As a result, the Bi2O2.7/Bi2Ti2O7 (Bi/Ti = 1:1) displays the highest photocatalytic activity under visible light or UV light irradiation for the degradation of different organic dyes, including methyl blue, methyl orange and acid orange 7.  相似文献   

4.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
  相似文献   

5.
Zn-doped LiNi0.8Co0.2O2 exhibits impressive electrochemical performance but suffers limited cycling stability due to the relative large size of irregular and bare particle which is prepared by conventional solid-state method usually requiring high calcination temperature and prolonged calcination time. Here, submicron LiNi0.8Co0.15Zn0.05O2 as cathode material for lithium-ion batteries is synthesized by a facile sol-gel method, which followed by coating Al2O3 layer of about 15 nm to enhance its electrochemistry performance. The as-prepared Al2O3-coated LiNi0.8Co0.15Zn0.05O2 cathode delivers a highly reversible capacity of 182 mA h g?1 and 94% capacity retention after 100 cycles at a current rate of 0.5 C, which is much superior to that of bare LiNi0.8Co0.15Zn0.05O2 cathode. The enhanced electrochemistry performance can be attributed to the Al2O3-coated protective layer, which prevents the direct contact between the LiNi0.8Co0.15Zn0.05O2 and electrolyte. The escalating trend of Li-ion diffusion coefficient estimated form electrochemical impedance spectroscopic (EIS) also indicate the enhanced structural stability of Al2O3-coated LiNi0.8Co0.15Zn0.05O2, which rationally illuminates the protection mechanism of the Al2O3-coated layer.  相似文献   

6.
We report the synthesis of NiCo2O4/reduced graphene oxide (NiCo2O4/rGO) hybrid hierarchical structures with unique nanonet and microsphere morphologies by organic polar solvent-assisted solvothermal method. The electrocatalytic oxygen evolution reaction (OER) activity of these materials is studied by cyclic voltammetry, linear sweep voltammetry and chronoamperometry methods in O2-saturated 0.1 M KOH solution. The NiCo2O4/rGO hybrid nanocomposite materials are found to be highly active electrocatalysts for OER at lower overpotentials. The nanonet and microsphere-like NiCo2O4/rGO catalysts require overpotentials of 0.450 and 0.530 V at a current density of 10 mA cm?2, and their corresponding Tafel slopes are 53 and 62 mV dec?1, which are much lower than values reported for non-precious electrocatalysts. Further, both NiCo2O4/rGO catalysts show good catalytic stability with current retention more than 92 % over long period of 15,000 s determined by chronoampirometry and at the end of 1000th cycle determined by linear sweep voltammetry. The enhanced OER activity of nanostructured NiCo2O4/rGO hybrid catalysts is attributed to synergistic interaction between rGO and NiCo2O4, which seems to be essential for maintaining the large contact area at the electrode-electrolyte interface, better mass, and charge transport and to minimize the aggregation of NiCo2O4 nanoparticles.  相似文献   

7.
The study of superparamagnetic Fe3O4/Ag nanocomposites have received great research attention due to their wide range of potential applications in biomedicine. In this report, an easy microemulsion reaction was employed to synthesis Fe3O4/Ag nanocomposites with self-aggregated branch like nanostructures. The Fe3O4 nanoparticles were initially prepared and subsequently AgNO3 was reduced as Ag by chemical reduction method. The results showed that the average size of the Fe3O4/Ag nanocomposites were in the range of 10 ± 2 nm. These nanoparticles were self-aggregated as a branch like nanostructure. The optical properties of Fe3O4 nanoparticles were modified with surface plasmon resonance of Ag nanoparticles. The observed saturation magnetization of superparamagnetic Fe3O4/Ag nanocomposites were 40 emu/g.  相似文献   

8.
Monodisperse and porous nonstoichiometric Zn ferrite can be prepared by a solvothermal method. Such non-Zn ferrite was used to be the precursor for synthesis of ZnFe2O4/Fe2O3 composite via calcination at 600°C for 3 h in air. X-ray powder diffractometer (XRD) and Energy Dispersive Spectrometer (EDS) proved the nonstoichiometry of Zn ferrite synthesized by solvothermal method and the formation of ZnFe2O4/Fe2O3 composite via calcination. TEM image showed that non-Zn ferrite spheres with wormlike nanopore structure were made of primary nanocrystals. BET surface area of non-Zn ferrite was much higher than that of ZnFe2O4/Fe2O3 composite. Saturation magnetization of non-Zn ferrites was significantly higher than that of ZnFe2O4/Fe2O3 composites. Calcination of non-Zn ferrite resulted in the formation of large amount of non-magnetic Fe2O3,which caused a low magnetization of composite. Because of higher BET surface area and higher saturation magnetization, non-Zn ferrite presented better Cr6+ adsorption property than ZnFe2O4/Fe2O3 composites.  相似文献   

9.
Fe@Fe2O3 core-shell nanowires were synthesized via the reduction of Fe3+ ions by sodium borohydride in an aqueous solution with a subsequent heat treatment to form Fe2O3 shell and employed as a cathode catalyst for non aqueous Li-air batteries. The synthesized core-shell nanowires with an average diameter of 50–100 nm manifest superior catalytic activity for oxygen evolution reaction (OER) in Li-O2 batteries with the charge voltage plateau reduced to ~3.8 V. An outstanding performance of cycling stability was also achieved with a cutoff specific capacity of 1000 milliampere hour per gram over 40 cycles at a current density of 100 mA g?1. The excellent electrochemical properties of Fe@Fe2O3 as an O2 electrode are ascribed to the high surface area of the nanowires’ structure and high electron conductivity. This study indicates that the resulting iron-containing nanostructures are promising catalyst in Li-O2 batteries.  相似文献   

10.
LiNi0.80Co0.15Al0.05O2 (NCA) is explored to be applied in a hybrid Li+/Na+ battery for the first time. The cell is constructed with NCA as the positive electrode, sodium metal as the negative electrode, and 1 M NaClO4 solution as the electrolyte. It is found that during electrochemical cycling both Na+ and Li+ ions are reversibly intercalated into/de-intercalated from NCA crystal lattice. The detailed electrochemical process is systematically investigated by inductively coupled plasma-optical emission spectrometry, ex situ X-ray diffraction, scanning electron microscopy, cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The NCA cathode can deliver initially a high capacity up to 174 mAh g?1 and 95% coulombic efficiency under 0.1 C (1 C?=?120 mA g?1) current rate between 1.5–4.1 V. It also shows excellent rate capability that reaches 92 mAh g?1 at 10 C. Furthermore, this hybrid battery displays superior long-term cycle life with a capacity retention of 81% after 300 cycles in the voltage range from 2.0 to 4.0 V, offering a promising application in energy storage.  相似文献   

11.
Due to the high specific capacities and environmental benignity, lithium-sulfur (Li-S) batteries have shown fascinating potential to replace the currently dominant Li-ion batteries to power portable electronics and electric vehicles. However, the shuttling effect caused by the dissolution of polysulfides seriously degrades their electrochemical performance. In this paper, Mn2O3 microcubes are fabricated to serve as the sulfur host, on top of which Al2O3 layers of 2 nm in thickness are deposited via atomic layer deposition (ALD) to form Mn2O3/S (MOS) @Al2O3 composite electrodes. The MOS@Al2O3 electrode delivers an excellent initial capacity of 1012.1 mAh g?1 and a capacity retention of 78.6% after 200 cycles at 0.5 C, and its coulombic efficiency reaches nearly 99%, giving rise to much better performance than the neat MOS electrode. These findings demonstrate the double confinement effect of the composite electrode in that both the porous Mn2O3 structure and the atomic Al2O3 layer serve as the spacious host and the protection layer of sulfur active materials, respectively, for significantly improved electrochemical performance of the Li-S battery.  相似文献   

12.
CuGaSe2 and CuGaS2 polycrystalline thin film absorbers were prepared by one-step electrodeposition from an aqueous electrolyte containing CuCl2, GaCl3 and H2SeO3. The pH of the solution was adjusted to 2.3 by adding HCl and KOH. Annealing improved crystallinity of CuGaSe2 and further annealing in sulphur atmosphere was required to obtain CuGaS2 layers. The morphology, topography, chemical composition and crystal structure of the deposited thin films were analysed by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy and X-ray diffraction, respectively. X-Ray diffraction showed that the as-deposited CuGaSe2 film exhibited poor crystallinity, but which improved dramatically when the layers were annealed in forming gas atmosphere for 40 min. Subsequent sulphurization of CuGaSe2 films was performed at 400 °C for 10 min in presence of molecular sulphur and under forming gas atmosphere. The effect of sulphurization was the conversion of CuGaSe2 into CuGaS2. The formation of CuGaS2 thin films was evidenced by the shift observed in the X-ray diffraction pattern and by the blue shift of the optical bandgap. The bandgap of CuGaSe2 was found to be 1.66 eV, while for CuGaS2 it raised up to 2.2 eV. A broad intermediate absorption band associated to Cr and centred at 1.63 eV was observed in Cr-doped CuGaS2 films.  相似文献   

13.
The conductivity of films consisting of a mixture of SnO2 and In2O3 nanocrystals at 200–500°C was studied. Based on the experimental data, it was assumed that in films containing less than 20 wt % In2O3, the current flows along SnO2 nanocrystals. A model of conductivity in these films is presented; it includes an electron transfer from In2O3 to SnO2, which forms positively charged In2O3 nanocrystals that contact the negatively charged SnO2 nanocrystals. In the presence of In2O3 nanocrystals, the activation energy of the electron transfer between SnO2 nanocrystals decreased substantially because of a decrease in the barrier of electron transfer between SnO2 crystals under the action of the negative charge. As a result, a percolation cluster of charged SnO2 crystals formed. At high contents of In2O3 (over 20 wt %), the conductivity increased dramatically. The curve of the temperature dependence of conductivity changed because of the appearance of a percolation cluster of In2O3 nanocrystals, in which the current passed. The conductivity of a mixed film of this kind differed from that of the nanocrystalline film of pure In2O3.  相似文献   

14.
Direct hydrocarbon type solid oxide fuel cells are attractive from simple gas feed process and also high energy conversion efficiency. In this study, La0.5Sr0.5MnO3 (LSM55) perovskite oxide was studied as oxide anode for direct hydrocarbon type solid oxide fuel cell (SOFC). Although reasonable power density like 1 W/cm2 and open circuit voltage (OCV) (1.1 V) at 1273 K was exhibited when H2 was used as fuel, the power density as well as OCV of the cell using LSM55 for anode was significantly decreased when dry C3H8 was used for fuel. After power generation measurement, LSM55 phase was decomposed to MnO and La2MnO4. Effects of various dopants to Mn site in LSM55 were studied and it was found that partial substitution of Mn in LSM55 with other cation, especially transition metal, is effective for increasing maximum power density. In particular, reasonable high power density can be achieved on the cell using Ni-doped LSM55 for anode. On the other hand, Al substitution is effective for increasing stability against reduction and so, dopant effects of Al were studied in more details for dry C3H8 fuel. The power density as well as OCV increased with increasing Al content and the highest power density was achieved at x = 0.4 in La0.5Sr0.5Mn1 ? x Al x O3. Among the examined composition, it was found that the cell using La0.5Sr0.5Mn0.6Al0.4O3 anode shows the largest power density (0.2 W/cm2) at 1173 K and high OCV (1.01 V) against dry C3H8 fuel.  相似文献   

15.
Vanadium pentoxide (V2O5) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V2O5 nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V2O5 nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g?1 (between 2.0 and 4.0 V vs. Li/Li+), good cycling stability (223 mAh g?1 after 50 cycles), and good rate performance (~?150 mAh g?1 at 2 A g?1). This can attribute to the carbon wrapped on the V2O5 nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V2O5 coated by carbon layer and composited with MWCNT NFs (V2O5/C@MWCNT NFs) to ensure the material is more stable.  相似文献   

16.
The metal-ferroelectric-semiconductor (MFS) heterostructure has been fabricated using Bi3.25La0.75Ti3O12 (BLT) as a ferroelectric layer by sol-gel processing. The effect of annealing temperature on phase formation and electrical characteristics of Ag/BLT/p-Si heterostructure were investigated. The BLT thin films annealed at from 500°C to 650°C are polycrystalline, with no pyrochlore or other second phases. The C-V curves of Ag/BLT/p-Si heterostructure annealed at 600°C show a clockwise C-V ferroelectric hysteresis loops and obtain good electrical properties with low current density of below 2×10−8 A/cm2 within ±4 V, a memory window of over 0.7 V for a thickness of 400 nm BLT films. The memory window enlarges and the current density reduces with the increase of annealing temperature, but a annealing temperature over 600°C is disadvantageous for good electrical properties.  相似文献   

17.
Li4Ti5O12/Li2TiO3 composite nanofibers with the mean diameter of ca. 60 nm have been synthesized via facile electrospinning. When the molar ratio of Li to Ti is 4.8:5, the Li4Ti5O12/Li2TiO3 composite nanofibers exhibit initial discharge capacity of 216.07 mAh g?1 at 0.1 C, rate capability of 151 mAh g?1 after being cycled at 20 C, and cycling stability of 122.93 mAh g?1 after 1000 cycles at 20 C. Compared with pure Li4Ti5O12 nanofibers and Li2TiO3 nanofibers, Li4Ti5O12/Li2TiO3 composite nanofibers show better performance when used as anode materials for lithium ion batteries. The enhanced electrochemical performances are explained by the incorporation of appropriate Li2TiO3 which could strengthen the structure stability of the hosted materials and has fast Li+-conductor characteristics, and the nanostructure of nanofibers which could offer high specific area between the active materials and electrolyte and shorten diffusion paths for ionic transport and electronic conduction. Our new findings provide an effective synthetic way to produce high-performance Li4Ti5O12 anodes for lithium rechargeable batteries.  相似文献   

18.
Additives to MgB2 can improve the superconducting functional characteristics, such as critical current density (J c) and irreversibility field (H irr). Recently, we have shown that repagermanium (C6H10Ge2O7) is an effective additive, enhancing both J c and H irr. To look into details of the processes taking place during the reactive sintering, a thermal analysis study (0.167 K s?1, in Ar) is reported. We used differential scanning calorimetry between 298 and 863 K and simultaneous thermogravimetric—differential thermal analysis between 298 and 1233 K. Samples were mixtures of powders with composition 97 mol% MgB2 and 3 mol% C6H10Ge2O7. Up to 863 K, repagermanium decomposes by multiple steps and forms amorphous phases. A reaction with MgB2 is not observed. Above this temperature, partial decomposition of MgB2 occurs. Crystalline Ge and MgO are detected before formation of Mg2Ge and MgB4, when temperature approaches the melting point of Ge (1211 K). Carbon substitution for boron in the crystal lattice of MgB2 is observed for samples heated above 863 K. The amount of substitutional C does not significantly change with temperature.  相似文献   

19.
Kinetics of LiFePO4, LiMn2O4, and LiCoO2 cathodes operating in 1 M LIPF6 solution in a mixture of ethylene carbonate and dimethyl carbonate was deduced from impedance spectra taken at different temperatures. The most striking difference of electrochemical impedance spectroscopy (EIS) curves is the impedance magnitude: tens of ohms in the case of LiFePO4, hundreds of ohms for LiMn2O4, and thousands of ohms for LiCoO2. Charge transfer resistances (R ct) for lithiation/delitiation processes estimated from the deconvolution procedure were 6.0 Ω (LiFePO4), 55.4 Ω (LiCoO2), and 88.5 Ω (LiMn2O4), respectively. Exchange current density for all the three tested cathodes was found to be comparable (0.55–1·10?2 mAcm?2, T = 298 K). Corresponding activation energies for the charge transfer process, \( {E}_{ct}^{\#} \), differed considerably: 66.3, 48.9, and 17.0 kJmol?1 for LiMn2O4, LiCoO2, and LiFePO4, respectively. Consequently, temperature variation may have a substantial influence on exchange current densities (j o) in the case of LiMn2O4 and LiCoO2 cathodes.  相似文献   

20.
Although TiO2 anatase phase has been widely chosen as the main photocatalyst, it presents high electron/hole recombination rate. However, today, what is sought is a semiconductor material with enhanced photocatalytic activity with higher photon to electron conversion efficiency by introduction of electrons trap dopants. In this paper, TiO2 nanotubes arrays obtained by anodization of Ti substrates were decorated with Ru via electrodeposition, and their photo-response was investigated. First, voltammetric experiments were performed to elucidate the route of Ru reduction on the TiO2 surface and to select the range of potentials for Ru deposition. The reduction potentials were used for controlling the amount of Ru distributed all over the surface. Although Ru was electrodeposited at potentials over the range from ??0.025 to ??0.188 V vs. Ag/AgCl, the deposition of 3.7 mC cm?2 at ??0.100 V for 30 min resulted in a tenfold greater photocurrent when compared to the recorded photocurrent for the undecorated TiO2 nanotubes array. Next, Ru-decorated TiO2 nanotubes with a length of 323?±?18 nm and inner and outer diameters of 91 and 104 nm, respectively, were characterized using SEM-WDS, SEM-FEG, XRD, and XPS. UV-Vis-NIR diffuse reflectance spectroscopy and photoluminescence (PL) measurements, which revealed a maximum PL emission at 445 nm, showed that for the array of Ru-decorated TiO2 nanotubes, the electron-hole recombination may be effectively inhibited by the presence of ruthenium electrodeposited, which can make this photocatalyst even more attractive for environmental applications. The performances of the TiO2 and Ru-decorated TiO2 catalysts were compared in heterogeneous photocatalysis experiments for color removal of an azo-dye, which presented a pseudo-first-order rate constant more than twofold greater for the Ru-decorated TiO2 catalysts.  相似文献   

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