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1.
Li4AlxTi5−xFyO12−y compounds were prepared by a solid-state reaction method. Phase analyses demonstrated that both Al3+ and F ions entered the structure of spinel-type Li4Ti5O12. Charge-discharge cycling results at a constant current density of 0.15 mA cm−2 between the cut-off voltages of 2.5 and 0.5 V showed that the Al3+ and F substitutions improved the first total discharge capacity of Li4Ti5O12. However, Al3+ substitution greatly increased the reversible capacity and cycling stability of Li4Ti5O12 while F substitution decreased its reversible capacity and cycling stability slightly. The electrochemical performance of the Al3+-F-co-substituted specimen was better than the F-substituted one but worse than the Al3+-substituted one.  相似文献   

2.
The oxygen reduction reaction (ORR) was studied at carbon supported MoOx-Pt/C and TiOx-Pt nanocatalysts in 0.5 mol dm−3 HClO4 solution, at 25 °C. The MoOx-Pt/C and TiOx-Pt/C catalysts were prepared by the polyole method combined by MoOx or TiOx post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoOx and TiOx post-deposition did not lead to a significant growth of the Pt nanoparticles.The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E − log j regions, usually observed with polycrystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoOx-Pt/C and TiOx-Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoOx-Pt/C and TiOx-Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates.  相似文献   

3.
Several compositions of NdYb1−xGdxZr2O7 (0 ≤ x ≤ 1.0) ceramics were prepared by pressureless-sintering method at 1973 K for 10 h in air. The relative density, microstructure and electrical conductivity of NdYb1−xGdxZr2O7 ceramics were analyzed by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance plots measurements. NdYb1−xGdxZr2O7 (0 ≤ x ≤ 0.3) ceramics have a single phase of defect fluorite-type structure, and NdYb1−xGdxZr2O7 (0.7 ≤ x ≤ 1.0) ceramics exhibit a single phase of pyrochlore-type structure; however, the NdYb0.5Gd0.5Zr2O7 composition shows mixed phases of both defect fluorite-type and pyrochlore-type structures. The measured values of the grain conductivity obey the Arrhenius relation. The grain conductivity of each composition in NdYb1−xGdxZr2O7 ceramics gradually increases with increasing temperature from 673 to 1173 K. NdYb1−xGdxZr2O7 ceramics are oxide-ion conductor in the oxygen partial pressure range of 1.0 × 10−4 to 1.0 atm at all test temperature levels. The highest grain conductivity value obtained in this work is 1.79 × 10−2 S cm−1 at 1173 K for NdYb0.3Gd0.7Zr2O7 composition.  相似文献   

4.
LiNi1−xCoxO2 (x = 0, 0.1, 0.2) cathode materials were successfully synthesized by a rheological phase reaction method with calcination time of 0.5 h at 800 °C. All obtained powders are pure phase with α-NaFeO2 structure (R-3m space group). The samples deliver an initial discharge capacity of 182, 199 and 189 mAh g−1 (25 mA g−1, 4.35-3.0 V), respectively. The reaction mechanism was also discussed, which consists of a series of defect reactions. As a result of these defect reactions, the reaction of forming LiNi1−xCoxO2 takes place in high speed.  相似文献   

5.
A series of Ni substituted spinel LiNixMn2−xO4 (0 ≤ x ≤ 0.5) have been synthesized to study the evolution of the local structure and their electrochemical properties. X-ray diffraction showed a few Ni cations moved to the 8a sites in heavily substituted LiNixMn2−xO4 (x ≥ 0.3). X-ray photoelectron spectroscopy confirmed Ni2+ cations were partially oxidized to Ni3+. The local structures of LiNixMn2−xO4 were studied by analyzing the and A1g Raman bands. The most compact [Mn(Ni)O6] octahedron with the highest bond energy of Mn(Ni)O was found for LiNi0.2Mn1.8O4, which showed a Mn(Ni)O average bond length of 1.790 Å, and a force constant of 2.966 N cm−1. Electrolyte decomposition during the electrochemical charging processes increased with Ni substitution. The discharge capacities at the 4.1 and 4.7 V plateaus obeyed the linear relationships with respect to the Ni substitution with the slopes of −1.9 and +1.9, which were smaller than the theoretical values of −2 and +2, respectively. The smaller slopes could be attributed to the electrochemical hysteresis and the presence of Ni3+ in the materials.  相似文献   

6.
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   

7.
Layered Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) have been prepared by the mixed hydroxide and molten-salt synthesis method. The individual particles of synthesized materials have a sub-microsize range of 200-500 nm, and LiNi0.475Mn0.475Zr0.05O2 has a rougher surface than that of LiNi0.5Mn0.5O2. The Li/Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) electrodes were cycled between 4.5 and 2.0 V at a current density of 15 mA/g, the discharge capacity of both cells increased during the first ten cycles. The discharge capacity of the Li/LiNi0.475Mn0.475Zr0.05O2 cell increased from 150 to 220 mAh/g, which is 50 mAh/g larger than that of the Li/LiNi0.5Mn0.5O2 cell. We found that the oxidation of oxygen and the Mn3+ ion concerned this phenomenon from the cyclic voltammetry (CV). Thermal stability of the charged Li[Ni0.5−xMn0.5−xZr2x]O2 (x = 0, 0.025) cathode was improved by Zr doping.  相似文献   

8.
La(1−x)SrxFeO3 (x = 0.2,0.4) powders were prepared by a stearic acid combustion method, and their phase structure and electrochemical properties were investigated systematically. X-ray diffraction (XRD) analysis shows that La(1−x)SrxFeO3 perovskite-type oxides consist of single-phase orthorhombic structure (x = 0.2) and rhombohedral one (x = 0.4), respectively. The electrochemical test shows that the reaction at La(1−x)SrxFeO3 oxide electrodes are reversible. The discharge capacities of La(1−x)SrxFeO3 oxide electrodes increase as the temperature rises. With the increase of the temperature from 298 K to 333 K, their initial discharge capacity mounts up from 324.4 mA h g−1 to 543.0 mA h g−1 (when x = 0.2) and from 147.0 mA h g−1 to 501.5 mA h g−1 (when x = 0.4) at the current density of 31.25 mA g−1, respectively. After 20 charge-discharge cycles, they still remain perovskite-type structure. Being similar to the relationship between the discharge capacity and the temperature, the electrochemical kinetic analysis indicates that the exchange current density and proton diffusion coefficient of La(1−x)SrxFeO3 oxide electrodes increase with the increase of the temperature. Compared with La0.8Sr0.2FeO3, La0.6Sr0.4FeO3 electrode is a more promising candidate for electrochemical hydrogen storage because of its higher cycle capacity at various temperatures.  相似文献   

9.
A new method for studying surface reaction of LaNi5 absorbing alloy in KOH solution (pH 12) was established. It is based on tip-substrate voltammetry of scanning electrochemical microscopy (SECM) where the tip faradic current is recorded while scanning the substrate potential. The Pt electrode is selected as tip electrode, and the Pt oxide formation-reduction is used as a pH-dependent reaction while the tip potential is held at a constant value. As substrate surface reactions proceed, the pH of solution can be changed, and then the tip faradic current is recorded. The mechanism of discharge process of LaNi5 alloy was analyzed by comparing the tip current (Itip) versus substrate potential (Esub) curve, which reflects the exchange of H+ or OH between the alloy surface and the solution, with the substrate current (Isub) versus substrate potential (Esub) curve, which reflects the exchange of electron on the LaNi5 alloy surface. The results showed that the OH adsorption process is occurred before the electron transfer process during discharge process, and the adsorptive OH helps the oxidation of adsorbed hydrogen atom on the alloy surface. A quantitative assessment for the maximum changes of pH during discharge process is also proposed, and the variation as large as 2.65 pH unit was detected.  相似文献   

10.
The electrochemical behaviors of Bi(III), Te(IV), Sb(III) and their mixtures in DMSO solutions were investigated using cyclic voltammetry and linear sweep voltammetry measurements. On this basis, BixSb2−xTey film thermoelectric materials were prepared by potentiodynamic electrodeposition technique from mixed DMSO solution, and the compositions, structures, morphologies as well as the thermoelectric properties of the deposited films were also analyzed. The results show that BixSb2−xTey compound can be prepared in a very wide potential range by potentiodynamic electrodeposition technique in the mixed DMSO solutions. After anneal treatment, the deposited film prepared in the potential range of −200 to −400 mV shows the highest Seebeck coefficient (185 μV/K), the lowest resistivity (3.34 × 10−5 Ω m), the smoothest surface, the most compact structure and processes the stoichiometry (Bi0.49Sb1.53Te2.98) approaching to the Bi0.5Sb1.5Te3 ideal material most. This Bi0.49Sb1.53Te2.98 film is a kind of nanocrystalline material and (0 1 5) crystal plane is its preferred orientation.  相似文献   

11.
A novel nanostructured mesoporous CoxNi1−x layered double hydroxides (CoxNi1−x LDHs), which both Co(OH)2 and Ni(OH)2 exhibit, has been successfully synthesized by a chemical co-precipitation route using polyethylene glycol as the structure-directing reagent. Structural and morphological characterizations were performed using powder X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM). The component and thermal stability of the sample were measured by energy dispersed X-ray spectrometry (EDS), FT-IR and thermal analyses, including thermogravimetry (TG) and differential thermal analysis (DTA). Cyclic voltammogram and galvanostatic charge-discharge testified that the CoxNi1−x LDH has a specific capacitance of 1809 F g−1 at a current density of 1 A g−1 and remains at about 90.2% of the initial value after 1000 cycles at a current density of 10 A g−1. The relationship between the chemical composition and the capacitance is discussed.  相似文献   

12.
J. Jiang 《Electrochimica acta》2005,50(24):4778-4783
Samples of the layered cathode materials, Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/12, 1/4, 5/12, and 1/2), were synthesized at 900 °C. Electrodes of these samples were charged in Li-ion coin cells to remove lithium. The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with EC/DEC solvent or 1 M LiPF6 EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were then welded closed. The reactivity of the samples with electrolyte was probed at two states of charge. First, for samples charged to near 4.45 V and second, for samples charged to 4.8 V, corresponding to removal of all mobile lithium from the samples and also concomitant release of oxygen in a plateau near 4.5 V. Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples with x = 1/4, 5/12 and 1/2 charged to 4.45 V do not react appreciably till 190 °C in EC/DEC. Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples charged to 4.8 V versus Li, across the oxygen release plateau, start to significantly react with EC/DEC at about 130 °C. However, their high reactivity is similar to that of Li0.5CoO2 (4.2 V) with 1 μm particle size. Therefore, Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 samples showing specific capacity of up to 225 mAh/g may be acceptable for replacing LiCoO2 (145 mAh/g to 4.2 V) from a safety point of view, if their particle size is increased.  相似文献   

13.
Electrodeposition of Ni1−xFex (x = 0.1-0.9) films was carried out from a chloride plating solution containing saccharin as an organic additive at a constant current density (5 mA/cm2) and a controlled pH of 2.5. X-ray diffraction studies revealed the existence of an fcc, or γ phase, in the range of 10-58 wt.% Fe, a mixed fcc/bcc phase in the range of 59-60 wt.% Fe, and a bcc, or α phase in the range of 64-90 wt.% Fe. The saturation magnetization, Bs, of electrodeposited Ni1−xFex alloys at the room temperature was found to increase with the increase of Fe-content and follows the Slater-Pauling curve, but deviates from as-cast bulk NiFe alloys. The coefficient of thermal expansion, CTE, of electrodeposited alloys at room temperature also deviates from as-cast bulk NiFe alloys. Annealing of α-Ni36Fe64 alloy results in a martensitic α → γ phase transformation, which takes place between 300 and 400 °C. It was demonstrated that thermal treatment above 400 °C was necessary to obtain magnetic and mechanical properties similar to those to conventional Invar alloy. Annealing of α-Ni36Fe64 alloy at 700 °C brings about a decrease of Bs from 1.75 to 0.45 T. By controlling the annealing conditions of α → γ martensitic transformation, it is possible to adjust the CTE of Ni36Fe64 alloy over the broad limits from 2.7 to 8.7 × 10−6/°C.  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.
Isomerization of n-hexane and n-pentane were studied using equivalent 5 monolayers of MoO3 deposited on TiO2. Addition of 2.5% Pt by weight of MoO3 on the Mo catalyst resulted in an increase in the catalytic activity of the system in favor of hydrocracking products. Surface characterization by XPS-UPS and ISS reveal that the sample surface contains Oxygen, Molybdenum, Platinum and Titanium. Apparently, the metallic properties of the deposited Pt favors the hydrocracking reactions and becomes dominant at reaction temperatures higher than 623 K. Balanced metal-acid functions in MoO2 − x(OH)y phase seems to be in optimized condition toward the hydroisomerization process. The contribution of Platinum addition to this catalytic reaction is not obvious. Combination of surface XPS-UPS, ISS and catalytic reactions carried out at similar experimental conditions enabled us to have better insight concerning the catalytic activities of the different chemical species present on the sample surface.  相似文献   

16.
Preparation of the (Ti1−xNbx)2AlC solid solution (formed from the Mn+1AXn or MAX carbides, where n = 1, 2, or 3, M is an early transition metal, A is an A-group element, and X is C) with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS). Nearly single-phase (Ti,Nb)2AlC was produced through direct combustion of constituent elements. Due to the decrease of reaction exothermicity, the combustion temperature and reaction front velocity decreased with increasing Nb content of (Ti1−xNbx)2AlC formed from the elemental powder compacts. In addition, the samples composed of Ti, Al, Nb2O5, and Al4C3 were adopted for the in situ formation of Al2O3-added (Ti,Nb)2AlC. The SHS process of the Nb2O5/Al4C3-containing sample involved aluminothermic reduction of Nb2O5, which not only enhanced the reaction exothermicity but also facilitated the evolution of (Ti,Nb)2AlC. Based upon the XRD analysis, two intermediates, TiC and Nb2Al, were detected in the (Ti,Nb)2AlC/Al2O3 composite and their amounts were reduced by increasing the extent of thermite reduction involved in the SHS process. The laminated microstructure characteristic of the MAX carbide was observed for both monolithic and Al2O3-added (Ti,Nb)2AlC solid solutions synthesized in this study.  相似文献   

17.
This paper reports the characterization of ternary II-VI semiconductor nanocrystals, deposited by the electrochemical atomic layer epitaxy (ECALE) technique.In particular, morphological and structural properties of the ternary compounds of formula CdxZn1−xSe deposited on Ag (1 1 1) have been characterized as a function of composition. The number of the attainable x values is limited by the necessity of using well-defined ZnSe/CdSe deposition sequences. However, the quantitative analysis carried out on the basis of both electrochemical and extended X-ray absorption fine structure (EXAFS) experiments indicates that the ECALE method is a successful way of controlling the composition of CdxZn1−xSe. In addition, the electrochemical measurements show that the amount of deposition is minimum in correspondence to the compound with x = 0.5, thus corroborating the hypothesis of a higher degree of disorder suggested both by morphological and structural investigation. The morphology was studied by atomic force microscopy (AFM). The structure of the films is estimated by EXAFS which is a powerful technique for the analysis of the local structure around chosen atoms.  相似文献   

18.
This study reports on the synthesis of ternary semiconductor (BixSb1−x)2Te3 thin films on Au(1 1 1) using a practical electrochemical method, based on the simultaneous underpotential deposition (UPD) of Bi, Sb and Te from the same solution containing Bi3+, SbO+, and HTeO2+ at a constant potential. The thin films are characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and reflection absorption-FTIR (RA-FTIR) to determine structural, morphological, compositional and optic properties. The ternary thin films of (BixSb1−x)2Te3 with various compositions (0.0 ≤ x ≤ 1.0) are highly crystalline and have a kinetically preferred orientation at (0 1 5) for hexagonal crystal structure. AFM images show uniform morphology with hexagonal-shaped crystals deposited over the entire gold substrate. The structure and composition analyses reveal that the thin films are pure phase with corresponding atomic ratios. The optical studies show that the band gap of (BixSb1−x)2Te3 thin films could be tuned from 0.17 eV to 0.29 eV as a function of composition.  相似文献   

19.
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   

20.
Amorphous LiCoO2 thin films were deposited on the NASICON-type glass ceramics, Li1+x+yAlxTi2−xSiyP3−yO12 (LATSP), by radio frequency (RF) magnetron sputtering below 180 °C. The as-deposited LiCoO2 thin films were characterized by X-ray diffraction, scanning electron microscopy and atomic force microscope. All-solid-state Li/PEO18-Li (CF3SO2)2N/LATSP/LiCoO2/Au cells were fabricated using the amorphous film. The electrochemical performance of the cells was investigated by galvanostatic cycling, cyclic voltammetry, potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. It was found that the amorphous LiCoO2 thin film shows a promising electrochemical performance, making it a potential application in microbatteries for microelectronic devices.  相似文献   

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