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1.
LiCoPO4 nanoparticles were precipitated from polyethylene glycol solution of lithium acetate, cobalt acetate, and ammonium dihydrogen phosphate by refluxing at 250 °C for 35 h. The resultant powder samples were heated at 800 °C for different time periods of 2 and 4 h to study the effect of annealing time on the growth of samples. The X-ray diffraction pattern of the obtained samples exhibited olivine phase. The scanning electron microscopic images of dried powder sample and samples heated at 800 °C for 2 and 4 h showed a homogenous orthorhombic morphology with a particle size of few nanometers range. For the first time, orthorhombic olivine was introduced as positive electrode for a hybrid electrochemical supercapacitor cell with carbon nanofoam as negative electrode in 1 M LiClO4 in ethylene carbonate and propylene carbonate (1:1 in volume) solution. A sloping voltage profile of 2 to 0 V is observed for all the three hybrid cells. From the impedance results, we inferred that LiCoPO4 nanoparticles synthesized by polyol process offers less resistance than lithium titanium oxide. According to the results of electrochemical testing for the first time, maximum power density of 192 W/kg at 11 Wh/kg energy density was obtained for LiCoPO4 nanoparticles annealed at 800 °C for 2 h. The dried sample and the sample heated at 800 °C for 2 and 4 h exhibited high capacitances of 5, 19, and 4 F/g, respectively, with an excellent rate capability over 1,000 cycles.  相似文献   

2.
LiCr0.2Ni0.4Mn1.4O4 was synthesized by a sol–gel technique in which tartaric acid was used as oxide precursor. The synthesized powder was annealed at five different temperatures from 600 to 1,000 °C and tested as a 5-V cathode material in Li-ion batteries. The study shows that annealing at higher temperatures resulted in improved electrochemical performance, increased particle size, and a differentiated surface composition. Spinel powders synthesized at 900 °C had initial discharge capacities close to 130 mAh g?1 at C and C/2 discharge rates. Powders synthesized at 1,000 °C showed capacity retention values higher than 85 % at C/2, C, and 2C rates at 25 °C after 50 cycles. Annealing at 600–800 °C resulted in formation of spinel particles smaller than 200 nm, while almost micron-sized particles were obtained at 900–1,000 °C. Chromium deficiency was detected at the surface of the active materials annealed at low temperatures. The XPS results indicate presence of Cr6+ impurity when the annealing temperature was not high enough. The study revealed that increased annealing temperature is beneficial for both improved electrochemical performance of LiCr0.2Ni0.4Mn1.4O4 and for avoiding formation of Cr6+ impurity on its surface.  相似文献   

3.
Bismuth titanate (Bi4Ti3O12) was developed by means of titanium oxide (TiO2) suspension in auto-combustion process at 220 °C to get nanosized (20 ± 5 nm) bismuth titanate (Bi4Ti3O12) powder. Complete piezoelectric phase (tetragonal) was obtained after calcination at 700 °C. Dilatometery of compacts was performed to find out sintering temperature. On the basis of shrinkage results, compacts were sintered at 750, 800, and 850 °C for 2 h. After sintering single phase was obtained with orthorhombic structure analyzed by X-ray diffraction and also investigated by Rietveld method. High-resolution scanning electron microscopy revealed that fine plate-like structure which is a characteristic of BIT powder can be obtained at 850 °C. Sintering results indicate that density and average grain size increase with the increasing temperature. A maximum of about 90 % of the theoretical density was achieved for the sintered product at 850 °C.  相似文献   

4.
LiFePO4/carbon complexes were prepared by electrospinning to improve rate performance at high C-rate and their electrochemical properties were investigated to be used as a cathode active material for lithium ion battery. The LiFePO4/carbon complexes were prepared by the electrospinning method. The prepared samples were characterized by SEM, EDS, XRD, TGA, electrometer, and electrochemical analysis. The LiFePO4/carbon complexes prepared have a continuous structure with carbon-coated LiFePO4 and the LiFePO4 in LiFePO4/carbon complex has improved thermal stability from carbon coating. The conductivity of LiFePO4/carbon complex heat-treated at 800 °C is measured as 2.23 × 10?2 S cm?1, which is about 106–107 times more than that of raw LiFePO4. The capacity ratio of coin cell manufactured from raw LiFePO4 is 40%, whereas the capacity ratio of coin cell manufactured from LiFePO4/carbon complex heat-treated at 800 °C is 61% (10 C/0.1 C). The improved rate performance of LiFePO4/carbon complex heat-treated at 800 °C is due to the carbon coating and good electrical connection.  相似文献   

5.
Nickel-substituted layered perovskite PrBaCo2 ? x Ni x O5 + δ (PBCN) powders with various proportions of nickel (x?=?0, 0.1, 0.2, and 0.3, abbreviated as PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively) are investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) based on the yttria-stabilized zirconia (YSZ) electrolyte. It is found that PBCN-1 has the highest electrical conductivity of 1,397 S cm?1 at 400 °C. Substitution of Co by Ni decreases the thermal expansion coefficient (TEC) clearly. The average TEC at the temperature range of 35–900 °C decreases from 22.8?×?10?6 K?1 for PBCN-0 to 18.9?×?10?6 K?1 for PBCN-3. The polarization resistances of PBCN samples on YSZ electrolyte at 800 °C are 0.053, 0.048, 0.052, and 0.042 Ω cm2 for PBCN-0, PBCN-1, PBCN-2, and PBCN-3, respectively. The single fuel cell with the configuration of PBCN-3/YSZ/Pt delivers the highest power densities of 100, 185, 360, 495, and 660 mW cm?2 at 600, 650, 700, 750, and 800 °C, respectively.  相似文献   

6.
0.65CaTiO3–0.35Sm0.9Nd0.1AlO3 (CTSA) ceramic nanopowders were synthesized via sol–gel method using the ethylene diamine tetraacetic acid as a chelating agent. Thermal analysis, Fourier transform infrared spectroscopy and X-ray diffraction were used to character the decomposition of precursor and phase transformation process of derived oxide powders. Single phase and well-crystallized 0.65CaTiO3–0.35Sm0.9Nd0.1AlO3 powders with particle size of 30–40 nm were obtained by calcination at 800 °C. Dense ceramic was successfully obtained from the ultrafine powders sintered at 1,325 °C, almost 100 °C lower than 1,415 °C required for conventional powders. Compared with those prepared by conventional solid-state method, the CTSA ceramics derived from sol to gel process sintered at a lower temperature showed better microwave dielectric properties of εr ~ 39, Q × f over 50,000 GHz and small τf ~ ?7.1 ppm/K.  相似文献   

7.
La4Ni3O10 oxide was synthesized as a cathode material for intermediate-temperature solid oxide fuel cells by a facile sol–gel method using a nonionic surfactant (EO)106(PO)70(EO)106 tri-block copolymer (F127) as the chelating agent. The crystal structure, electrical conductivity, and electrochemical properties of La4Ni3O10 were investigated by X-ray diffraction, DC four-probe method, electrochemical impedance spectra, and I–V measurements. The La4Ni3O10 cathode showed a significantly low polarization resistance (0.26 Ω cm2) and cathodic overpotential value (0.037 V at the current density of 0.1 A cm?2) at 750 °C. The results measured suggest that the diffusion process was the rate-limiting step for the oxygen reduction reaction. The La4Ni3O10 cathode revealed a high exchange current density value of 62.4 mA cm?2 at 750 °C. Furthermore, an anode-supported single cell with La4Ni3O10 cathode was fabricated and tested from 650 to 800 °C with humidified hydrogen (~3 vol% H2O) as the fuel and the static air as the oxidant. The maximum power density of 900 mW cm?2 was achieved at 750 °C.  相似文献   

8.
CaCu3Ti4O12 (CCTO) powders were prepared via a non-hydrolytic sol–gel (NHSG) method by using acetylacetone as chelating agent and ethylene glycol as solvent. The samples were characterized by TG–DSC, Fourier transform infrared spectroscopy, X-ray diffraction and scanning electron microscope. The dielectric properties of ceramics were also measured. The pure perovskite-like CCTO powders were obtained by heat treatment at 800 °C for 2 h. The average particle sizes of CCTO powders calcined at 800 °C were approximately 350–450 nm. The samples sintered at 1,000 °C showed the mean grain size of 2.5–4 μm. Specially, the ceramics exhibited high dielectric constant (1.19 × 105–1.40 × 105) and low dielectric loss (0.051–0.1) in the temperature range of 30–110 °C. Moreover, with the NHSG method the period of synthesis process was greatly shortened.  相似文献   

9.
Micro- and mesoporous carbide-derived carbons (CDCs) were synthesised from TiC powder via a gas-phase reaction using HCl and Cl2 within the temperature range of 700–1,100 °C. Analysis of X-ray diffraction results show that TiC-CDCs consist mainly of graphitic crystallites. The first-order Raman spectra showed the graphite-like absorption peaks at ~1,577 cm?1 and the disorder-induced peaks at ~1,338 cm?1. The low-temperature N2 sorption experiments were performed, and specific surface areas up to 1,214 and 1,544 m2?g?1 were obtained for TiC-CDC (HCl) synthesised at T?=?800 °C and TiC-CDC (Cl2) synthesised at T?=?900 °C, respectively. For the TiC-CDC powders synthesised, a bimodal pore size distribution has been established with the first maximum in the region up to 1.5 nm and the second maximum from 2 to 4 nm. The energy-related properties of supercapacitors based on 1 M (C2H5)3CH3NBF4 in acetonitrile and TiC-CDC (Cl2) and TiC-CDC (HCl) as electrode materials were also investigated by cyclic voltammetry, impedance spectroscopy, galvanostatic charge/discharge and constant power methods. The specific energy, calculated at U?=?3.0 V, are maximal for TiC-CDC (Cl2 800 °C) and TiC-CDC (HCl 900 °C), which are 43.1 and 31.1 W?h?kg?1, respectively. The specific power, calculated at cell potential U?=?3.0 V, are maximal for TiC-CDC (Cl2 1,000 °C) and TiC-CDC (HCl 1,000 °C), which are 805.2 and 847.5 kW?kg?1, respectively. The Ragone plots for CDCs prepared by using Cl2 or HCl are quite similar, and at high power loads, the TiC-CDC material synthesised using Cl2 at 900 °C, i.e. the material with optimal pore structure, delivers the highest power at constant energy.  相似文献   

10.
Novel environment-friendly yellow mixed oxide inorganic pigment from Bi2O3–ZnO–CeO2 system with the composition 23 mol% Bi2O3, 15 mol% ZnO and 62 mol% CeO2 was successfully synthesized by a conventional solid-state reaction method. Comprehensive analyses were carried out to characterize the develop pigment powder including simultaneous TG–DTA thermal analysis, colour properties and particle size distribution. The results demonstrated that the optimum calcination for pigment synthesis was located at a range 800–950 °C. The colour of the studied mixed oxide pigment is connected with the calcination condition. The substitution of Zn2+ changes the colour from orange to yellow. The colour of the obtained samples was dependent on the calcination condition and the particle size distribution. The most saturated yellow hue was obtained at the calcination temperature of 950 °C for 2 h in a furnace of pure air and after its application into organic binder in mass tone. The value C of this sample was approx. 65. The mixed oxide pigments were also evaluated from the standpoint of their particle size distribution. Bi2Ce2O7 is considered to be a non-toxic compound, and the other component (Zn2+ ions) is also the safe element. Therefore, the present mixed oxide could be an attractive candidate as a novel environment-friendly inorganic yellow pigment.  相似文献   

11.
It was established that heating to 90 °C of nitrate solutions of U, Np and Pu in the presence of hydrazine hydrate results in the formation of hydrated dioxides of these elements. On ignition under inert or reducing conditions in the temperature range of 280–800 °C hydrated uranium dioxide transmogrify into crystalline UO2. On ignition in air atmosphere UO2·nH2O turns into UO3 at 440 °C and into U3O8 at 570–800 °C. It was shown that thermolysis of the solution containing a mixture of uranium, neptunium and plutonium nitrates at 90 °C in the presence of hydrazine hydrate allows one to prepare hydrated dioxides (U, Np, Pu)O2·nH2O which on heating to ~300 °C transmogrify into crystalline product of UO2, NpO2 and PuO2 solid solution. The technique of preparation of solid solutions of U and Pu dioxides is very promising as simple and effective method of production of MOX-fuel for.  相似文献   

12.
Electrochemical characteristics of single cell performances at various humidity conditions and constant temperatures of 40?100 °C using membrane electrode assemblies (MEAs) were studied. The MEAs consist of alternative proton-conducting hybrid membrane electrolyte and noble Pt/C catalyst for the H2/O2 proton exchange membrane fuel cells (PEMFCs). The function of humidity on the cell performances was investigated at larger current density values of 501 mA cm?2 and constant cell temperatures of 80 and 90 °C and the relative humidity of 100 %. The power density value of 400 mW cm?2 was obtained when the same MEA at similar operating conditions was used. The effects of temperature on the single cell performances were investigated at various temperature ranges of 40–100 °C and constant relative humidity of 50, 70, and 100 %. The maximum current density and power density values of about 600 mA cm?2 and 160 mW cm?2, respectively, were obtained at 90 °C with 100 % RH. The results were compared with the reported results of Nafion membrane and similar hybrid membranes operating at low temperatures for H2/O2 fuel cells. Finally, the results provided an alternative proton-conducting electrolyte as promising candidate for low/intermediate temperature operating H2/O2 fuel cells.  相似文献   

13.
The effect of the aggregation state of Pluronic copolymer (PEO100–PPO65–PEO100, F127) and the concentration of hydrophilic modified ibuprofen (Ibuprofen–PEG800, IP800) on the interaction between F127 and IP800 was systematically investigated by nuclear magnetic resonance, dynamic light scatter (DLS), surface tension, and freeze-fractured transmission electron microscopy. In the solution of F127 unimers (5 °C), F127 unimers tended to wrap around IP800 micelles, and the binding model of F127 unimers to IP800 micelles transferred from wrapping around to partly threading through with increasing IP800 concentration. The latter binding model was straightly confirmed by nuclear Overhauser enhancement spectroscopy. As the aggregation state of F127 is in the beginning of the micellization (20 °C), the addition of IP800 significantly promoted the micellization of F127 to form the F127/IP800 complex with F127 micelles as the skeleton called the F127–micelle complex. The sudden decrease of the size obtained from DLS stemmed from the disruption of the F127–micelle complex and accompanying rehydration of PPO which is weaker compared with refs. The amount of IP800 to disintegrate the F127–micelle complex increased in the F127–micelle-dominated solution (40 °C) compared to that at 20 °C.  相似文献   

14.
The Co–Mg–Al mixed metal oxides were prepared by calcination of co-precipitated hydrotalcite-like precursors at various temperatures (600–800 °C), characterised with respect to chemical (AAS) and phase (XRD) composition, textural parameters (BET), form and aggregation of cobalt species (UV–vis-DRS) and their redox properties (H2-TPR, cyclic voltammetry). Moreover, the process of thermal decomposition of hydrotalcite-like materials to mixed metal oxide systems was studied by thermogravimetric method combined with the analysis of gaseous decomposition products by mass spectrometry. Calcined hydrotalcite-like materials were tested as catalysts for methanol incineration. Catalytic performance of the oxides depended on cobalt content, Mg/Al ratio and calcination temperature. The catalysts with lower cobalt content, higher Mg/Al ratio and calcined at lower temperatures (600 or 700 °C) were less effective in the process of methanol incineration. In a series of the studied catalysts, the best results, with respect to high catalytic activity and selectivity to CO2, were obtained for the mixed oxide with Co:Mg:Al molar ratio of 10:57:33 calcined at 800 °C. High activity of this catalyst was likely connected with the presence of a Co–Mg–Al spinel-type phases, containing easy reducible Co3+ cations, formed during high-temperature treatment of the hydrotalcite-like precursor.  相似文献   

15.
We demonstrate a rational template carbonization method to produce nitrogen-containing nanoporous carbons at 800 °C, using 1, 10-phenanthroline (or benzimidazole) as carbon/nitrogen source and magnesium citrate as template. The mass ratio of 1, 10-phenanthroline (or benzimidazole) and magnesium citrate has exerted the vital role in the determination of pore structures and the resulting electrochemical performances. It reveals that the carbon-P:Mg-1:1 (obtained by heating 1, 10-phenanthroline and magnesium citrate at 800 °C with the mass ratio of 1:1) and carbon-B:Mg-1:1 (obtained by heating benzimidazole and magnesium citrate at 800 °C with the mass ratio of 1:1) samples both are amorphous, nitrogen-containing, and highly nanoporous in nature. The carbon-P:Mg-1:1 sample has a large BET surface area of 1,657.4 m2 g?1 and high pore volume of 1.83 cm3 g?1, and those of carbon-B:Mg-1:1 sample are of 1,105.4 m2 g?1 and 1.67 cm3 g?1, respectively. Based on a three-electrode system using a 6-mol L?1 KOH aqueous solution as electrolyte, the carbon-P:Mg-1:1 and carbon-B:Mg-1:1 samples can deliver large specific capacitances of 289.0 and 255.6 F g?1 at a current density of 0.5 A g?1. They can also exhibit high energy densities of 40.1 and 35.5 Wh kg?1 when designated the power density as 0.25 kW kg?1 as well as highly long-term cycling durabilities.  相似文献   

16.
Single crystals of melaminium bis (hydrogen oxalate) (MOX) single crystals have been grown from aqueous solution by slow solvent evaporation method at room temperature. X-ray powder diffraction analysis confirms that MOX crystallises in monoclinic system with space group C2/c. The calculated lattice parameters are a = 20.075 ± 0.123 Å b = 8.477 ± 0.045 Å, c = 6.983 ± 0.015 Å, α = 90°, β = 102.6 ± 0.33°, γ = 90° and V = 1,159.73 (Å)3. Thermogravimetric analysis at three different heating rates 10, 15 and 20 °C min?1 has been done to study the thermal decomposition behaviour of the crystal. Non-isothermal studies on MOX reveal that the decomposition occurs in two stages. Kinetic parameters [effective activation energy (E a), pre-exponential factor (ln A)] of each stage were calculated by model-free method: Kissinger, Kim–Park and Flynn–Wall method and the results are discussed. A significant variation in effective activation energy (E a) with conversion progress (α) indicates that the process is kinetically complex. The linear relationship between the ln A and E a was established (compensation effect). DTA analyses were conducted at different heating rates and the activation energy was determined graphically from Kissinger and Ozawa equation. The average effective activation energy is calculated as 276 kJ mol?1 for the crystallization peak. The Avrami exponent for the crystallization peak temperature determined by Augis and Bennett method is found to be 1.95. This result indicates that the surface crystallization dominates overall crystallization. Dielectric study has also been done, and it is found that both dielectric constant and dielectric loss decreases with increase in frequency and is almost a constant at high frequency region.  相似文献   

17.
A tubular anode-supported solid oxide fuel cell with a double-layer anode for the direct conversion of CH4 has been prepared and operated at 800 °C successfully. The double-layer anode was composed of NiO–YSZ and CoO–NiO–SDC acting as supporting layer and active reforming layer, respectively. At 800 °C, a maximum power density of 350 mW cm−2 was obtained with CH4 as fuel and air as oxidant. The time-dependent impedance spectra of the tubular cell were examined and discussed. No carbon deposition was observed on the surface of the anode when the cell was operated at a constant current density of 250 mA cm−2.  相似文献   

18.
Low temperature lithium titanate compounds (i.e., Li4Ti5O12 and Li2TiO3) with nanocrystalline and mesoporous structure were prepared by a straightforward aqueous particulate sol–gel route. The effect of Li:Ti molar ratio was studied on crystallisation behaviour of lithium titanates. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that the powders were crystallised at the low temperature of 500 °C and the short annealing time of 1 h. Moreover, it was found that Li:Ti molar ratio and annealing temperature influence the preferable orientation growth of the lithium titanate compounds. Transmission electron microscope (TEM) images showed that the average crystallite size of the powders annealed at 400 °C was in the range 2–4 nm and a gradual increase occurred up to 10 nm by heat treatment at 800 °C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had mesoporous and nanocrystalline structure with the average grain size of 21–28 nm at 600 °C and 49–62 nm at 800 °C depending upon the Li:Ti molar ratio. Moreover, atomic force microscope (AFM) images confirmed that the lithium titanate films had columnar like morphology at 600 °C, whereas they showed hill-valley like morphology at 800 °C. Based on Brunauer–Emmett–Taylor (BET) analysis, the synthesized powders showed mesoporous structure containing pores with needle and plate shapes. The surface area of the powders was enhanced by increasing Li:Ti molar ratio and reached as high as 77 m2/g for the ratio of Li:Ti = 75:25 at 500 °C. This is one of the smallest crystallite size and the highest surface areas reported in the literature, and the materials could be used in many applications such as rechargeable lithium batteries and tritium breeding materials.  相似文献   

19.
This work reports the study the structure, optical and magnetic properties of LaFeO3 nanoparticles synthesized by the polymerized complex method. The LaFeO3 nanoparticles were successfully obtained from calcination of the precursor at different temperatures from 750 to 1,050 °C in air for 2 h. The calcined LaFeO3 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and vibrating sample magnetometry. The XRD and TEM results showed that all LaFeO3 samples had a single phase nature with the orthorhombic structure. The estimated crystallite sizes were in the range of 44.5 ± 2.4–74.1 ± 4.9 nm. UV–Vis spectra showed strong UV and Vis absorption with small band gap energy. The valence states of Fe ions were in the Fe3+ and Fe4+ state, as confirmed by XPS and XANES results. The weak ferromagnetic behavior with specific saturation magnetization of 0.1 emu/g at 10 kOe was obtained for the small particle of 44.5 ± 2.4 nm. The uncompensated spins at the surface was proposed as playing a part in the magnetic properties of small sized LaFeO3.  相似文献   

20.
Powders of (Pb0.8Ca0.2)(Ti0.99Mn0.01)O3 have been prepared by sol-gel processing. A tetragonal phase is formed after heat treatment at as low as 800°C. The tetragonality was found to be 1.053±0.005 and Curie temperature 315°C. Composite films with 0–3 connectivity were prepared from 800°C heat treated powders and P(VDF-TrFE) by the solvent casting technique. Composites poled at 20 MV/m, exhibited a pyroelectric coefficient of 17.4 μC/m2K and a pyroelectric figure of merit (FOMp=p/ε) of 0.51 μC/m2K.  相似文献   

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