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1.
A systematic investigation was conducted on the mechanism and electrocatalytic properties of O2 and Cl2 evolution on mixed oxide electrodes of nominal composition: Ti/[Ru(0.3)Ti(0.6)Ce(0.1−x)]O2[Nb2O5](x) (0 ≤ x ≤ 0.1). For the oxygen evolution, a 30 mV Tafel slope is obtained in the presence of CeO2, while in its absence a 40 mV coefficient is observed. The intrinsic electrocatalytic activity is mainly due to electronic factors, as result of the synergism between Ru and Ce oxides. For chlorine evolution, the Tafel slope (30 mV) is independent on oxide composition. The best global electrocatalytic activity for ClER was observed in the absence of Nb2O5 additive. Variation of the voltammetric charge throughout the experiments confirms high CeO2 content compositions are fragile, due mainly to the porosity caused by CeO2 presence. On the other hand, Nb2O5 addition decreases considerably this instability.  相似文献   

2.
New pyrochlore ceramics have been produced by doping Sm and Nd into the Bi site and Fe into the Nb site in the Bi1.5Zn0.92Nb1.5O6.92 (BZN) pyrochlore. Doped pyrochlore ceramics were produced by conventional solid state mixing of oxides at different doping levels using the compositions of Bi1.5−xSmxZn0.92Nb1.5O6.92, Bi1.5−xNdxZn0.92Nb1.5O6.92 and Bi1.5Zn0.92Nb1.5−xFexO6.92−x. The solubility limit of cations was determined as x = 0.13, 0.18 and 0.15 for Sm, Nd and Fe, respectively. While Sm and Nd increased the dielectric constant (?), Fe doping led a decrease in ?. Dielectric constant of Sm and Nd doped BZN increased to 199 at x = 0.13 (Sm) and to 219 at x = 0.18 (Nd). At low Fe dopings (x = 0.05), the dielectric constant of BZN increased to 242 but decreased to 211 at x = 0.15. The dielectric losses were lower for Sm and Nd dopings than Fe but in all cases it was lower than 0.006. The dielectric constant of Sm, Nd and Fe doped BZN ceramics was nearly independent of frequency within the frequency range between 1 kHz and 2 MHz, but decreased considerably with temperature between 20 and 200 °C. Temperature coefficient of Sm doped BZN (−354 ppm/°C) was lower than Nd and Fe doped BZN ceramics at solubility limits (−538 ppm/°C for Nd and −565 ppm/°C for Fe).  相似文献   

3.
In this study, MgxM2 − xP2O7 (M = Cu, Ni; 0 ≤ x ≤ 2) and Mg3 − yNiy(PO4)2 (0 ≤ y ≤ 3) compositions were synthesized by the chemical coprecipitation method and characterized by X-ray diffraction, UV-vis-NIR spectroscopy and CIE L* a* b* (Commission Internationale de l’Eclairage L* a* b*) parameters measurements.Solid solutions with α-Cu2P2O7 and α-Ni2P2O7 structures and solid solutions with Ni3(PO4)2 structure were obtained from diphosphate and orthophosphate compositions respectively. Isostructurality of α-Ni2P2O7 and α-Mg2P2O7 structures enlarges the compositional range of solid solution formation respect to the MgxCu2 − xP2O7 solid solutions one.The CIE L* a* b* parameters in MgxNi2 − xP2O7 samples were obtained comparable with these parameters in others yellow materials suitable for ceramic pigments. Mg0.5Ni1.5P2O7 composition fired at 800 °C or 1000 °C is the optimal composition to obtain yellow materials with α-diphosphate structure in conditions of this study.  相似文献   

4.
The performances of different promoters (CeO2, ZrO2 and Ce0.5Zr0.5O2 solid solution) modified Pd/SiC catalysts for methane combustion are studied. XRD and XPS results showed that Zr4+ could be incorporated into the CeO2 lattice to form Zr0.5Ce0.5O2 solid solution. The catalytic activities of Pd/CeO2/SiC and Pd/ZrO2/SiC are lower than that of Pd/Zr0.5Ce0.5O2/SiC. The Pd/Zr0.5Ce0.5O2/SiC catalyst can ignite the reaction at 240 °C and obtain a methane conversion of 100% at 340 °C, and keep 100% methane conversion after 10 reaction cycles. These results indicate that active metallic nanoparticles are well stabilized on the SiC surface while the promoters serve as oxygen reservoir and retain good redox properties.  相似文献   

5.
(Nd1−xGdx)2(Ce1−xZrx)2O7 (0 ≤ x ≤ 1.0) powders with an average particle size of 100 nm were synthesized with chemical-coprecipitation and calcination method, and were characterized by X-ray diffractometry and scanning electron microscopy. The sintering behaviour of (Nd1−xGdx)2(Ce1−xZrx)2O7 powders was studied by pressureless sintering at 1600–1700 °C for 10 h in air. The relative densities of (Nd1−xGdx)2(Ce1−xZrx)2O7 solid solutions increase with increasing the sintering temperature, and gradually decrease with increasing the content of neodymium and cerium at identical temperature levels. (Nd1−xGdx)2(Ce1−xZrx)2O7 solid solutions have a single phase of defect fluorite-type structure among all the composition combinations studied. The lattice parameters of (Nd1−xGdx)2(Ce1−xZrx)2O7 solid solutions agree well with the Vegard's rule.  相似文献   

6.
In this work, polycrystalline samples of the substituted n = 3 Ruddlesden-Popper Ca4−xRExMn3O10 phase were prepared by solid-state reaction (RE, rare earth = Ce, Nd, Sm, Eu, Gd, Dy). Single phased samples were synthesized for sintering times larger than 150 h at 1350 °C. Complete thermoelectric characterizations were performed from 5 to 390 K, in terms of electrical resistivity (ρ), Seebeck coefficient (S) and thermal conductivity (κ). As expected, the substitution of Ca by different rare earth elements leads to a significant modification of the thermoelectric properties. With substitution level as low as 1.25 at.%, a remarkable decrease of the electrical resistivity is observed. The influence of this cationic substitution on the thermal conductivity (κ), Seebeck coefficient (S), and the figure of merit ZT is also discussed. In this study, the best one reaches 5.8 × 10−3 at 300 K for the Ca3.95Eu0.05Mn3O10 composition, a value 6 times higher than the ZT exhibited by the beginning Ca4Mn3O10 sample.  相似文献   

7.
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   

8.
Ce2(WO4)3 ceramics have been synthesized by the conventional solid-state ceramic route. Ce2(WO4)3 ceramics sintered at 1000 °C exhibited ?r = 12.4, Qxf = 10,500 GHz (at 4.8 GHz) and τf = −39 ppm/°C. The effects of B2O3, ZnO–B2O3, BaO–B2O3–SiO2, ZnO–B2O3–SiO2 and PbO–B2O3–SiO2 glasses on the sintering temperature and microwave dielectric properties of Ce2(WO4)3 were investigated. The Ce2(WO4)3 + 0.2 wt% ZBS sintered at 900 °C/4 h has ?r = 13.7, Qxf = 20,200 GHz and τf = −25 ppm/°C.  相似文献   

9.
The atomic arrangement of WO3-doped Bi2O3 was found similar to that of the fluorite structure. However, the electrical conductivity of WO3-doped Bi2O3 is significantly lower than that of commonly used Y2O3-doped Bi2O3. The structure and electrical conductivity of samples formulated as (CaxW0.15Bi0.85−x)2O3.45−x (x = 0, 0.1, 0.2 and 0.3) were investigated. The as-sintered (W0.15Bi0.85)2O3.45 and (Ca0.1W0.15Bi0.75)2O3.35 exhibit similar single tetragonal structure that is isostructural with 7Bi2O3·2WO3. Therefore, (W0.15Bi0.85)2O3.45 and (Ca0.1W0.15Bi0.75)2O3.35 formed a superstructure consisting of 10 enlarged cubic fluorite subcells. However, the as-sintered samples consist of a tetragonal structure and tetragonal CaWO4 for x = 0.2 and 0.3 because the oxygen vacancy concentration increases. The conductivities of (CaxW0.15Bi0.85−x)2O3.45−x (x = 0, 0.1, 0.2 and 0.3) did not exhibit linear dependence with x value. The best conductivity is 2.35 × 10−2 S cm−1 at 700 °C for x = 0.1 that is higher than that of Ca-free (W0.15Bi0.85)2O3.45. The higher conductivity of (Ca0.1W0.15Bi0.75)2O3.35 than (W0.15Bi0.85)2O3.45 may result from the higher anion vacancy concentration and more symmetrical structure.  相似文献   

10.
NiFe2−xBixO4 (x = 0, 0.1, 0.15) nanopowders were synthesized via sol-gel method. The precursor gels were calcined at 773 K in air for 1 h to obtain the pure nanostructured NiFe2−xBixO4 spinel phase. The crystal structure and magnetic properties of the substituted spinel series of NiFe2−xBixO4 have been investigated by means of 57Fe Mössbauer spectroscopy, transmission electron microscopy and alternating gradient force magnetometry. Mössbauer spectroscopic measurements revealed that Bi3+ cations tend to occupy octahedral positions in the structure of the substituted ferrite, i.e., the crystal-chemical formula of the as-prepared nanoparticles may be written as: (Fe)[NiFe1−xBix]O4 (x = 0, 0.1, 0.15), where parentheses and square brackets enclose cations on sites of tetrahedral and octahedral coordination, respectively. Selective area electron diffraction studies provided evidence that the samples of the NiFe2−xBixO4 series, independently of x, exhibit the cubic spinel structure. The values of the saturation magnetization and the coercive field of NiFe2−xBixO4 nanoparticles were found to decrease with increasing degree of bismuth substitution.  相似文献   

11.
The reduction of commercial and mechanochemically processed CeO2 powders was studied. Nanostructured CeO2, with the crystallite size of 21 nm and the lattice distortion of 0.37%, was obtained during 60 min of milling in a high-energetic vibratory mill. X-ray diffraction, scanning electron microscopy and Brunauer-Emmett-Teller method were applied to characterize the milled powders. During the thermal treatment at 1200 and 1400 °C in an argon atmosphere the nonstoichiometric CeO2−x oxides with the defect fluorite structure were formed. Compositions of CeO2−x oxides were determined according to its lattice parameter. The results showed that the release of oxygen, as well as the rate of reduction, was more effective in nanocrystalline then in the microcrystalline CeO2, producing at 1200 °C CeO1.80 and CeO1.85 oxides, while at 1400 °C were obtained similarly, CeO1.77 and CeO1.78, compositions.  相似文献   

12.
We report the effect of Cu2+ ion on CaAl2O4 with different molar concentrations of 0.0, 0.4 and 0.8 M prepared by simple combustion method. The materials have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FT-IR) and scanning electron microscopy (SEM). DC electrical conductivity has also been measured to study the electrical behavior of the materials. The XRD patterns confirm the formation of single-phase CaAl2O4 along with some impurity phases like CaAl4O7, CaAl12O19 and Ca12Al14O33. The FT-IR spectra show the stretching and bending vibrations of the synthesized compounds. DC electrical conductivity of the Ca1−xCuxAl2O4 is found to vary from 26.46 × 10−4 to 515.68 × 10−4 S cm−1 for x = 0.0 to x = 0.8 at the measuring temperature of 1000 °C. SEM images show the morphological features of the compounds.  相似文献   

13.
The Li[Li(1/3−x/3)CrxMn(2/3−2x/3)]O2 (0.15 ≤ x ≤ 0.3) cathode materials were synthesized by sol-gel process using aqueous solutions of metal acetates and citric acid as the chelating agent. The precipitate of metal citrate was dried in a vacuum oven for 10 h at 100 °C. After drying, the gel precursor was calcined at 300 °C for about 10 h. The resulted powder was ground and heated at 900 °C. The structural characterization was carried out by fitting the XRD data with Rietveld program. The samples exhibited a well defined layered structure and the unit cell parameters linearly increased with increasing chromium contents in Li[Li(1/3−x/3)CrxMn(2/3−2x/3)]O2 Surface morphology was determined by SEM and HRTEM and it is found that the cathode material consisted of highly ordered single crystalline particles with layered-hexagonal structure. Test cells were assembled and cycled in the voltage range of 2.0-4.9 V with a current density of 7.947 mA/g. Electrode with (x = 0.2) delivered a high reversible capacity of around 280 mA h/g in cycling.  相似文献   

14.
Powders of gadolinium-doped ceria solid solutions, Ce1−xGdxO2−δ (x = 0.05, 0.1, 0.2, 0.3 and 0.4), were prepared by a freeze-drying precursor route. Dense ceramic pellets with average grain sizes in the range of several microns were obtained after sintering at 1600 °C. Cobalt nitrate was added to the powders to obtain dense ceramic samples with grain sizes in the submicrometer range at 1150 °C. The ionic conduction was analysed by impedance spectroscopy in air, to de-convolute the bulk and grain boundary contributions. The bulk conductivity at low temperature clearly decreases with increasing content of Gd whereas the activation energy increases. An alternative method is proposed to analyse the extent of defect interactions on conduction. For samples without addition of Co, the specific grain boundary conductivity increases with increasing Gd content. Addition of cobalt does not alter the bulk properties but produces an important increase in the specific grain boundary conductivity, mainly in samples with lower Gd-concentration (x = 0.05 and 0.1). Segregation of Gd and its strong interaction with charge carriers may explain the blocking effects of grain boundaries.  相似文献   

15.
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   

16.
Values of open-circuit-potentials (OCP) have been determined for pairs of electrodes: Au and Pt, Ni-Ce0.8Sm0.2O1.9 cermet and Au, Pt and Sm0.5Sr0.5CoO3 composite at the YSZ electrolyte, in the uniform atmospheres of xCH4 + yO2 + (1 − x − y)Ar gas mixtures with variable x and y coefficients, at 600 °C. The determined dependencies of OCP values on the initial gas mixture compositions have been compared with the respective dependencies calculated for equilibrium or quasi-equilibrium compositions of these gas mixtures. The OCP values for the pair of Pt and Au electrodes have been measured also in the xH2 + yO2 + (1 − x − y)Ar uniform gas mixtures but no distinct difference of the OCP values has been observed in this atmosphere. For some pairs of electrodes investigated in xCH4 + yO2 + (1 − x − y)Ar atmospheres the measured OCP values have shown differences up to ca 0.9-1.0 V. These differences were stable within large range of compositions of this gas mixture. Within this gas composition range one of the electrodes conserves the potential of oxygen electrode determined by oxygen partial pressure in the initial gas mixture and is insensitive to reaction occurring in the gas phase. These results are discussed on the basis of equilibria or some quasi-equilibria, that establish in the C-H-O gas mixture and the solid carbon deposition is considered. For a given pair of dissimilar electrodes, their selective sensibility to the electrochemical process of oxygen electrode has been confirmed. Within large range of gas mixture concentrations, in the Pt-Au electrode pair Au has shown behavior of the oxygen electrode, whereas the OCP values of the Pt electrode are within the range of hydrogen electrode, also at gas compositions corresponding to the solid carbon stability. With this pair the OCP differences of ca. 600 mV have been obtained. Among three electrodes studied the cermet Ni-Ce0.8Sm0.2O1.9 electrode shows the best electrocatalytic properties resulting in the OCP values following exactly the respective equilibrium dependence. In the pair Ni-Ce0.8Sm0.2O1.9 and Au a stable potential difference of ca. 900 mV have been established. Unexpectedly, Pt electrode in the pair with the Sm0.5Sr0.5CoO3 composite electrode plays role of the oxygen electrode quite insensitive to other components of the equilibrated initial gas mixture. This surprising fact seems indicate that in conditions of the experiments performed the electrocatalytic behavior of the electrode depends not only of the material of this electrode but also on the properties of the second electrode in the given pairs of electrodes.  相似文献   

17.
The microwave dielectric properties of Sm(Mg0.5Ti0.5)O3 incorporated with various amount of Bi2O3 and B2O3 additives have been investigated systematically. In this study, both Bi2O3 and B2O3 additives acting as a sintering aid can effectively lower the sintering temperature from 1550 °C to 1300 °C. The ionic radius of Bi3+ for a coordination number of 6 is 0.103 nm, whereas the ionic radius of B3+ is 0.027 nm. Clearly, the ionic radius of Bi3+ is greatly larger than one of B3+, which resulted in the specimens incorporated with Bi2O3 having larger lattice parameters and cell volume than those incorporated with B2O3. The experimental results show that no second phase was observed throughout the entire experiments. Depending on the interfacial tension, the liquid phase may penetrate the grain boundaries completely, in which case the grains will be separated from one another by a thin layer as shown in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with Bi2O3. Whereas, in Sm(Mg0.5Ti0.5)O3 ceramics incorporated with B2O3, the volume fraction of liquid is high, the grains may dissolve into the liquid phase, and rapidly rearrange, in which case contact points between agglomerates will be dissolved due to their higher solubility in the liquid, leading plate-like shape microstructure.A dielectric constant (?r) of 29.3, a high Q × f value of 26,335 GHz (at 8.84 GHz), and a τf of −32.5 ppm/°C can be obtained for Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 10 mol% Bi2O3 sintered at 1300 °C. While Sm(Mg0.5Ti0.5)O3 ceramics incorporated with 5 mol% B2O3 can effectively lower temperature coefficient of resonant frequency, which value is −21.6 ppm/°C. The Sm(Mg0.5Ti0.5)O3 ceramic incorporated with heavily Bi2O3 and B2O3 additives exhibits a substantial reduction in temperature (∼250 °C) and compatible dielectric properties in comparison with that of an un-doped one. This implied that this ceramic is suitable for miniaturization in the application of dielectric resonators and filters by being appropriately incorporated with a sintering aid.  相似文献   

18.
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   

19.
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   

20.
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   

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