共查询到20条相似文献,搜索用时 31 毫秒
1.
Debao Li Cheng YangNing Zhao Huijie QiWenhuai Li Yuhan SunBing Zhong 《Fuel Processing Technology》2007
Ni modified K2CO3/MoS2 catalyst was prepared and the performance of higher alcohol synthesis catalyst was investigated under the conditions: T = 280–340 °C, H2/CO (molar radio) = 2.0, GHSV = 3000 h− 1, and P = 10.0 MPa. Compared with conventional K2CO3/MoS2 catalyst, Ni/K2CO3/MoS2 catalyst showed higher activity and higher selectivity to C2+OH. The optimum temperature range was 320–340 °C and the maximum space-time yield (STY) of alcohol 0.30 g/ml h was obtained at 320 °C. The selectivity to hydrocarbons over Ni/K2CO3/MoS2 was higher, however, it was close to that of K2CO3/MoS2 catalyst as the temperature increased. The results indicated that nickel was an efficient promoter to improve the activity and selectivity of K2CO3/MoS2 catalyst. 相似文献
2.
Ramsdellite Li2Ti3O7 was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li+, respectively. A reversible specific capacity of 150 mA h g−1 at 1C was obtained on Li2Ti3O7 electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C. 相似文献
3.
The electrochemical energy storage and delivery on the electrodes composed of hydrous ruthenium oxide (RuOx·nH2O) or activated carbon-hydrous ruthenium oxide (AC-RuOx) composites are found to strongly depend on the substrate employed. The contact resistance at the active material-graphite interface is much lower than that at the active material-stainless steel (SS) mesh interface. Thin films of gold plus RuOx·nH2O deposited on SS meshes (RuOx/Au/SS) are found to greatly improve the poor contact between SS meshes and electrode materials. The maximum specific capacitance (CS,RuOx) of RuOx·nH2O, 1580 F g−1 (measured at 1 mV s−1), very close to the theoretic value, was obtained from an AC-RuOx/RuOx/Au/SS electrode with 10 wt.% sol-gel-derived RuOx·nH2O annealed in air at 200 °C for 2 h. The highly electrochemical reversibility, high-power characteristics, good stability, and improved frequency response of this AC-RuOx/RuOx/Au/SS electrode demonstrate its promising application potential in supercapacitors. The ultrahigh specific capacitance of RuOx·nH2O probably results from the uniform size distribution of RuOx·nH2O nanoparticles, ranged from 1.5 to 3 nm which is clearly observed from the high-resolution transmission electron microscopy (HRTEM). 相似文献
4.
A series of ZnxMg1 − xGa2O4:Co2+ spinels (x = 0, 0.25, 0.5, 0.75, and 1.0) was successfully produced through low-temperature burning method by using Mg(NO3)2·4H2O, Zn(NO3)2·6H2O, Ga(NO3)3·6H2O, CO(NH2)2, NH4NO3, and Co(NO3)2·6H2O as raw materials. The product was characterized by X-ray diffraction, transmission electron microscopy, and photoluminescence spectroscopy. The product was not merely a simple mixture of MgGa2O4 and ZnGa2O4; rather, it formed a solid solution. The lattice constant of ZnxMg1 − xGa2O4:Co2+ (0 ≤ x ≤ 1.0) crystals has a good linear relationship with the doping density, x. The synthesized products have high crystallinities with neat arrays. Based on an analysis of the form and position of the emission spectrum, the strong emission peak around the visible region (670 nm) can be attributed to the energy level transition [4T1(4P) → 4A2(4F)] of Co2+ in the tetrahedron. The weak emission peak in the near-infrared region can be attributed to the energy level transition [4T1(4P) → 4T2(4F)] of Co2+ in the tetrahedron. 相似文献
5.
The La2−xAxMo2O9−δ (A = Ca2+, Sr2+, Ba2+ and K+) series has been synthesised as nanocrystalline materials via a modification of the freeze-drying method. The resulting materials have been characterised by X-ray diffraction (XRD), thermal analysis (TG/DTA, DSC), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The high-temperature β-polymorph is stabilised for dopant content x > 0.01. The nanocrystalline powders were used to obtain dense ceramic materials with optimised microstructure and relative density >95%. The overall conductivity determined by impedance spectroscopy depends on both the ionic radius and dopant content. The conductivity decreases slightly as the dopant content increases in addition a maximum conductivity value was found for Sr2+ substitution, which show an ionic radii slightly higher than La3+ (e.g. 0.08 S cm−1 for La2Mo2O9 and 0.06 S cm−1 for La1.9Sr0.1Mo2O9−δ at 973 K). The creation of extrinsic vacancies upon substitution results in a wider stability range under reducing conditions and prevents amorphisation, although the stability is not enhanced significantly when compared to samples with higher tungsten content. These materials present high thermal expansion coefficients in the range of (13-16) × 10−6 K−1 between room temperature and 753 K and (18-20) × 10−6 K−1 above 823 K. The ionic transport numbers determined by a modified emf method remain above 0.98 under an oxygen partial pressure gradient of O2/air and decreases substantially under wet 5% H2-Ar/air when approaching to the degradation temperature above 973 K due to an increase of the electronic contribution to the overall conductivity. 相似文献
6.
Au nanoparticles (AuNPs) are good quenchers once they closely contact with luminophore. Here we reported a simple approach to obtain enhanced electrogenerated chemiluminescence (ECL) behavior based on Au/CdS nanocomposite films by adjusting the amount of AuNPs in the nanocomposite. The maximum enhancement factor of about 4 was obtained at an indium tin oxide (ITO) electrode in the presence of co-reactant H2O2. The mechanism of this enhancement was discussed in detail. The strong ECL emission from Au/CdS nanocomposites film was exploited to determine H2O2. The resulting ECL biosensors showed a linear response to the concentration of H2O2 ranging from 1.0 × 10−8 to 6.6 × 10−4 mol L−1 with a detection limit of 5 nmol L−1 (S/N = 3) and good stability and reproducibility. 相似文献
7.
Co-doped Li3V2−xCox(PO4)3/C (x = 0.00, 0.03, 0.05, 0.10, 0.13 or 0.15) compounds were prepared via a solid-state reaction. The Rietveld refinement results indicated that single-phase Li3V2−xCox(PO4)3/C (0 ≤ x ≤ 0.15) with a monoclinic structure was obtained. The X-ray photoelectron spectroscopy (XPS) analysis revealed that the cobalt is present in the +2 oxidation state in Li3V2−xCox(PO4)3. XPS studies also revealed that V4+ and V3+ ions were present in the Co2+-doped system. The initial specific capacity decreased as the Co-doping content increased, increasing monotonically with Co content for x > 0.10. Differential capacity curves of Li3V2−xCox(PO4)3/C compounds showed that the voltage peaks associated with the extraction of three Li+ ions shifted to higher voltages with an increase in Co content, and when the Co2+-doping content reached 0.15, the peak positions returned to those of the unsubstituted Li3V2(PO4)3 phase. For the Li3V1.85Co0.15(PO4)3/C compound, the initial capacity was 163.3 mAh/g (109.4% of the initial capacity of the undoped Li3V2(PO4)3) and 73.4% capacity retention was observed after 50 cycles at a 0.1 C charge/discharge rate. The doping of Co2+into V sites should be favorable for the structural stability of Li3V2−xCox(PO4)3/C compounds and so moderate the volume changes (expansion/contraction) seen during the reversible Li+ extraction/insertion, thus resulting in the improvement of cell cycling ability. 相似文献
8.
Bo Gao 《Electrochimica acta》2010,55(11):3681-11258
Amorphous RuO2·xH2O was well coated on the benzenesulfonic functionalized multi-wall carbon nanotubes (f-MWCNTs) successfully via hydrothermal method. The decorated benzenesulfonic groups served as a bifunctional role both for solubilizing and dispersing MWCNTs into aqueous solution and for tethering Ru3+ precursor to facilitate the following uniform chemical deposition of RuO2·xH2O. The electrochemical performance of RuO2/f-MWCNTs and utilization of RuO2·xH2O were evidenced by cyclic voltammetry and galvanostatic charge/discharge tests. The specific capacitance of 1143 Fg−1 for RuO2·xH2O was obtained from RuO2/f-MWCNTs with 32 wt.% RuO2·xH2O, which was much higher than that of just 798 Fg−1 for the RuO2/p-MWCNTs. Even though the RuO2·xH2O loading increases to 45 wt.%, the utilization of RuO2·xH2O still possesses as high as 844.4 Fg−1, indicating a good energy capacity in the case of high loading. 相似文献
9.
Hydrous ruthenium dioxide (RuO2·xH2O) prepared in a modified sol-gel process was subjected to annealing in air and water at various temperatures for supercapacitor applications. The textural and pseudocapacitive characteristics of RuO2·xH2O annealed in air and water were systematically compared to show the benefits of annealing in water (denoted as hydrothermal annealing). An important concept that hydrothermal annealing effectively restricts condensation of hydroxyl groups within nanoparticles, inhibits crystal growth, and maintains high water content of RuO2·xH2O is demonstrated in this work. The unique textural characteristics of hydrothermally annealed RuO2·xH2O are attributable to the high-pressured, water-enriched surroundings which restrain coalescence of RuO2·xH2O nanocrystallites. The crystalline, hydrous nature of hydrothermally annealed RuO2·xH2O favors the utilization of active species in addition to a merit of minor dependence of specific capacitance on the scan rate of CV for pseudocapacitors. As a result, RuO2·xH2O with hydrothermal annealing at 225 °C for 24 h exhibits 16 wt.% water, an average particle size of about 7 nm, and specific capacitance of ca. 390 F g−1. 相似文献
10.
In this study, single crystal V3O7·H2O nanobelts were successfully synthesized using a simple hydrothermal route, in which templates or catalysts were absent. The synthesized V3O7·H2O nanobelts are highly crystalline and have lengths up to several tens of micrometers. The width and thickness of the nanobelts are found to be about 30-50 and 30 nm, respectively. A lithium battery using V3O7·H2O nanobelts as the positive electrode exhibits a high initial discharge capacity of 409 mAh g−1, corresponding to the formation of LixV3O7·H2O (x = 4.32). Such a high degree of electrochemical performance is attributed to the intrinsic properties of the single-crystalline V3O7·H2O nanobelts. 相似文献
11.
We report the investigation of boron substitution on structural, electrical, thermal, and thermoelectric properties of Ca3−xBxCo4O9 (x=0, 0.5, 0.75, and 1) in the temperature range between 300 K and 5 K. X-ray diffraction studies show that the Ca3Co4O9 phase is successfully preserved as the majority phase in the x=0.5 sample despite the small size of boron ions. Electrical transport measurements confirm that B3+ substitution for Ca2+ causes an increase in resistivity due to the decrease in carrier concentration. x=0.5 sample is found to have a Seebeck coefficient of 181 μV/K at room temperature which is ~1.5 times higher than that of the pure Ca3Co4O9. Our results indicate that the chemical pressure due to the large ionic radii difference between B3+ (0.27 Å) and Ca2+ (1 Å) enhances the thermoelectric properties as long as the unique crystal structure of Ca3Co4O9 is preserved. 相似文献
12.
Composite ceramics based on (1 − x)Mg2TiO4-xCaTiO3-y wt.% ZnNb2O6 (x = 0.12-0.16, y = 0-8) were prepared by a conventional mixed-oxide route. Zn2+ partially replaced Mg2+ in Mg2TiO4 and formed the spinel-structured (Mg1−δZnδ)2TiO4 phase. Nb2+, is known to be solid soluble in CaTiO3, was found to change its shape from cubic to pliable. A bi-phase system (Mg1−δZnδ)2TiO4 and CaTiO3 exhibited in all samples, where a small amount of second phase Mg1−δZnδTiO3 was also detected. The microwave dielectric properties of specimens were strongly related to ZnNb2O6 and CaTiO3 content. As y increased, ?r and τf decreased, however, Q × f decreased to a minimum value and started to increase thereafter. It was also found that ?r and τf increased and Q × f decreased with increasing x. The optimized microwave dielectric properties with ?r = 18.37, Q × f = 31,027 GHz (at 6 GHz), and τf = 0.51 ppm/°C were achieved for (1 − x)Mg2TiO4-xCaTiO3-y wt.% ZnNb2O6 (x = 0.12, y = 4) sintered at 1360 °C for 6 h. 相似文献
13.
Layered metastable lithium manganese oxides, Li2/3[Ni1/3−xMn2/3−yMx+y]O2 (x = y = 1/36 for M = Al, Co, and Fe and x = 2/36, y = 0 for M = Mg) were prepared by the ion exchange of Li for Na in P2-Na2/3[Ni1/3−xMn2/3−yMx+y]O2 precursors. The Al and Co doping produced the T#2 structure with the space group Cmca. On the other hand, the Fe and Mg doped samples had the O6 structure with space group R-3m. Electron diffraction revealed the 1:2 type ordering within the Ni1/3−xMn2/3−yMx+yO2 slab. It was found that the stacking sequence and electrochemical performance of the Li cells containing T#2-Li2/3[Ni1/3Mn2/3]O2 were affected by the doping with small amounts of Al, Co, Fe, and Mg. The discharge capacity of the Al doped sample was around 200 mAh g−1 in the voltage range between 2.0 and 4.7 V at the current density of 14.4 mA g−1 along with a good capacity retention. Moreover, for the Al and Co doped and undoped oxides, the irreversible phase transition of the T#2 into the O2 structure was observed during the initial lithium deintercalation. 相似文献
14.
Br-doped Li4Ti5O12 in the form of Li4Ti5O12−xBrx (0 ≤ x ≤ 0.3) compounds were successfully synthesized via solid state reaction. The structure and electrochemical properties of the spinel Li4Ti5O12−xBrx (0 ≤ x ≤ 0.3) materials were investigated. The Li4Ti5O12−xBrx (x = 0.2) presents the best discharge capacity among all the samples, and shows better reversibility and higher cyclic stability compared with pristine Li4Ti5O12, especially at high current rates. When the discharge rate was 0.5 C, the Li4Ti5O12−xBrx (x = 0.2) sample presented the excellent discharge capacity of 172 mAh g−1, which was very close to its theoretical capacity (175 mAh g−1), while that of the pristine Li4Ti5O12 was 123.2 mAh g−1 only. 相似文献
15.
(BaxPb1−x)(Zn1/3Nb2/3)O3 (BPZN; x = 0.06–0.1) relaxor ferroelectric ceramics produced using a reaction-sintering process were investigated. Without any calcination involved, the mixture of raw materials was pressed and sintered directly. BPZN ceramics of 100% perovskite phase were obtained. Highly dense BPZN ceramics with a density higher than 98.5% of theoretical density could be obtained. Maximum dielectric constant Kmax 13,500 (at 75 °C), 19,600 (at 50 °C) and 14,800 (at 28 °C) at 1 kHz could be obtained in 6BPZN, 8BPZN and 10BPZN, respectively. Dielectric maximum temperature (Tmax) in BPZN ceramics via reaction-sintering process is lower than BPZN ceramics prepared via B-site precursor route. 相似文献
16.
Trang T. Trinh 《Electrochimica acta》2010,56(1):227-234
This paper reports the synthesis, structure, chemical stability and electrical transport properties of Ti substituted Ba3CaNb2O9 (BCN) to develop electrolytes for proton conducting solid oxide fuel cells (H-SOFCs). The powder X-ray diffraction (PXRD) of Ba3CaNb2−xTixO9−δ (x = 0.1, 0.15, 0.2, 0.25 and 0.3) and Ba3Ca1.18Nb1.82−xTixO9−δ (x = 0.15 and 0.25) showed formation of double perovskite-like structure with lattice constant comparable to that of Ba3Ca1.18Nb1.82O9−δ (BCN18). Scanning electron microscopy (SEM) showed dense and pore-free microstructure for Ba3CaNb1.75Ti0.25O8.875. PXRD and Fourier transform infrared (FTIR) spectroscopy data confirmed long-term stability of Ba3CaNb2−xTixO9−δ and Ba3Ca1.18Nb1.82−xTixO9−δ in boiling H2O and in CO2 at elevated temperatures. The AC impedance investigation showed contribution due to bulk, grain-boundary and electrode effect at low temperatures. The electrical conductivity of studied materials were measured in different medium including dry air, dry H2, wet H2, wet N2 and D2O. Increase in conductivity in wet N2 and decrease in conductivity in D2O confirmed the proton conduction in Ba3CaNb1.75Ti0.25O9-δ. Among Ti-substituted compounds investigated in this study, Ba3Ca1.18Nb1.57Ti0.25O8.605 showed the highest conductivity of 3.5 × 10−4 S cm−1 at 400 °C in wet N2 (3%H2O), which is comparable to reported values of Ba2Ca0.79Nb0.66Ta0.55O6−δ and BCN18. 相似文献
17.
Yang Liu 《Electrochimica acta》2008,53(8):3296-3304
Co3O4/RuO2·xH2O composites with various Ru content (molar content of Ru = 5%, 10%, 20%, 50%) were synthesized by one-step co-precipitation method. The precursors were prepared via adjusting pH of the mixed aqueous solutions of Co(NO3)2·6H2O and RuCl3·0.5H2O by using Pluronic123 as a soft template. For the composite with molar ratio of Co:Ru = 1:1 annealed at 200 °C, Brunauer-Emmet-Teller (BET) results indicated that the composite showed mesoporous structure, and the specific surface area of the composite was as high as 107 m2 g−1. The electrochemical performances of these composites were measured in 1 M KOH electrolyte. Compared with the composite prepared without template, the composite with P123 exhibited a higher specific capacitance. When the molar content of Ru was rising, the specific capacitance of the composites increased significantly. It was also observed that the crystalline structures as well as the electrochemical activities were strongly dependent on the annealing temperature. A capacitance of 642 F/g was obtained for the composite (Co:Ru = 1:1) annealed at 150 °C. Meanwhile, the composites also exhibited good cycle stability. Besides, the morphologies and textural characteristic of the samples were also investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM). 相似文献
18.
Electrochromic properties of electrochemically deposited and etched (EDE) WO3−x films have been investigated using voltammetry and nanogravimetry to elucidate the amount of residual stress associated with lattice polarization and deformation in WO3−x nanoparticles. The cathodic WO3−x deposition from pertungstic acid solution and unusual properties of the cathodic electroetching of the oxide in tetraethyl ammonium chloride solution are reported and elucidated on the basis of Electrochemical Quartz Crystal Nanogravimetry (EQCN) measurements. The stress enhanced resonant frequency shift was observed upon WO3−x film coloration. However, the stress enhancement appeared to be much lower (up to 4-6 times) than that measured for films synthesized by other methods. The stress reduction in WO3−x films under study has been attributed to the stress relaxing propensity of EDE film to suppress the compressive stress wave. A considerable isotopic effect has been observed in nanogravimetry of the H+ and D+ ion intercalation into WO3−x films. We have found that the isotopic effect is primarily due to the true mass loading difference between hydrogen and deuterium ions, for the same concentration of color centers (2.65 × 1021 cm−3), since EQCN frequency shifts associated with stress in the film for H+ and D+ are very close to each other. 相似文献
19.
Fernando Pico Teresa A. Centeno Rosa M. Rojas Jose M. Rojo 《Electrochimica acta》2006,51(22):4693-4700
RuO2·xH2O/NiO composites having RuO2 contents in the range 0-100 wt.% have been prepared by a co-precipitation method. Structural, microstructural and textural transformations after heating the as-prepared composites at 200 and 600 °C have been followed by X-ray diffraction, scanning electron microscopy (SEM) and nitrogen adsorption/desorption isotherms. At 200 °C the composites are made of micrometric particles in which nanometric crystallites of the two oxides are aggregated. The composites show microporosity (0.02-0.10 cm3/g), mesoporosity (0.07-0.12 cm3/g) and relatively high specific surface area (62-309 m2/g). At 600 °C the composites are fully dehydrated and RuO2 has crystallized and segregated. Microporosity and mesoporosity as well as specific surface area are strongly decreased. Specific capacitance and specific surface area of the composites heated at 200 and 600 °C have been measured and discussed on the basis of the RuO2 content. For comparison the specific capacitance and specific surface area of mixtures of NiO and RuO2·xH2O (or RuO2) have been taken as references. The higher specific capacitance of the 200 °C-heated composites compared to the 600 °C-heated ones is due to the higher specific surface area of the former and the higher pseudocapacitance of RuO2·xH2O compared to RuO2. The discussion reported in this work can be applied to other composites such as RuO2·xH2O/carbon and RuO2·xH2O/other oxides. 相似文献
20.
Composite G/PPy/PPy(La1−xSrxMnO3)/PPy electrodes made of the perovskite La1−xSrxMnO3 embedded into a polypyrrole (PPy) layer, sandwiched between two pure PPy films, electrodeposited on a graphite support were investigated for electrocatalysis of the oxygen reduction reaction (ORR). PPy and PPy(La1−xSrxMnO3) (0≤ x ≤0.4) successive layers have been obtained on polished and pretreated graphite electrodes following sequential electrodeposition technique. The electrolytes used in the electrodeposition process were Ar saturated 0.1 mol dm−3 pyrrole (Py) plus 0.05 mol dm−3 K2SO4 with and without containing a suspension of 8.33 g L−1 oxide powder. Films were characterized by XRD, SEM, linear sweep voltammetry, cyclic voltammetry (CV) and electrochemical impedance (EI) spectroscopy. Electrochemical investigations were carried out at pH 12 in a 0.5 mol dm−3 K2SO4 plus 5 mmol dm−3 KOH, under both oxygenated and deoxygenated conditions. Results indicate that the porosity of the PPy matrix is considerably enhanced in presence of oxide particles. Sr substitution is found to have little influence on the electrocatalytic activity of the composite electrode towards the ORR. However, the rate of oxygen reduction decreases with decreasing pH of the electrolyte from pH 12 to pH 6. It is noteworthy that in contrast to a non-composite electrode of the same oxide in film form, the composite electrode exhibits much better electrocatalytic activity for the ORR. 相似文献