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1.
CHEN Cheng  WANG Wenbao  MA Guilin 《中国化学》2009,27(12):2329-2334
A series of La0.90Ba0.10Ga1?xMgxO3?α (x=0.20, 0.25 and 0.30) ceramics with a perovskite‐type orthorhombic structure were prepared by the conventional solid‐state reaction. Their conduction was studied in wet hydrogen, wet air and dry air atmospheres by various electrochemical methods including AC impedance spectroscopy, isotope effect, electrochemical hydrogen pumping, steam concentration cells and oxygen concentration cells from 873 to1273 K. Proton conduction was confirmed directly by an electrochemical hydrogen‐pumping experiment. The hydrogen evolution rates coincided with theoretical ones calculated from Faraday's law, indicating that in hydrogen atmosphere the charge carriers were predominantly protons. Isotope effect confirmed the ceramic samples possessed proton conduction under water vapor‐containing atmosphere. In wet air atmosphere, the samples were found to be mixed (proton+oxide ion+hole) conductors, and in dry air atmosphere to be mixed (oxide ion+hole) conductors. These results were different from the reports that BaO‐ and MgO‐doped LaGaO3 ceramics were mixed conductors of oxide ion and electron hole in O2 and air; whereas they were oxide ion conductors in N2 and H2 atmospheres.  相似文献   

2.
Ceramic BaCe0.8Ho0.2O3-α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600-1000 ℃ in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600-1000 ℃ was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600-900 ℃ in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 ℃. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01-0.09, and the oxide-ionic transport numbers were 0.27-0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 ℃, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 ℃, the maximum short-circuit current density and power output density were 346 mA/cm^2 and 80 mW/cm^2, respectively.  相似文献   

3.
Ba0.95Ce0.8Ho0.2O3-a was prepared by high temperature solid-state reaction. X-ray diffraction (XRD) pattern showed that the material was of a single perovskite-type orthorhombic phase. Using the material as solid electrolyte and porous platinum as electrodes, the measurements of ionic transport number and conductivity of Ba0.95Ce0.8Ho0.2O3-a were performed by gas concentration cell and ac impedance spectroscopy methods in the temperature range of 600---1000 ℃in wet hydrogen, dry and wet air respectively. Ionic conduction of the material was investigated and compared with that of BaCe0.8Ho0.2O3-a. The results indicated that Ba0.95Ce0.8Ho0.2O3-a was a pure protonic conductor with the protonic transport number of 1 during 600---700℃ in wet hydrogen, a mixed conductor of protons and electrons with the protonic transport number of 0.97--0.93 in 800---1000 ℃. But BaCe0.8Ho0.2O3-a was almost a pure protonic conductor with the protonic transport number of 1 in 600---900 ℃ and 0.99 at 1000 ℃ in wet hydrogen. In dry air and in the temperature range of 600---1000 ℃, they were both mixed conductors of oxide ions and electronic holes, and the oxide-ionic transport numbers were 0.24--0.33 and 0.17--0.30 respectively. In wet air and in the temperature range of 600---1000 ℃, they were both mixed conductors of protons, oxide ions and electronic holes, the protonic transport numbers were 0.11--0.00 and 0.09--0.01 respectively, and the oxide-ionic transport numbers were 0.41--0.33 and 0.27--0.30 respectively. Protonic conductivity of Ba0.95Ce0.8Ho0.2O3-a in both wet hydrogen and wet air was higher than that of BaCe0.8Ho0.2O3-a in 600--- 800 ℃, but lower in 900--1000 ℃. Oxide-ionic conductivity of the material was higher than that of BaCe0.8Ho0.2O3-a in both dry air and wet air in 600---1000 ℃.  相似文献   

4.
Ba1.03Ce0.8Tm0.2O3?α ceramic with orthorhombic perovskite structure was prepared by conventional solid‐state reaction. The conductivity and ionic transport number of Ba1.03Ce0.8Tm0.2O3?α were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen‐air fuel cell was constructed, and the cell performance was examined at 500–900°C. The results indicate that the specimen is a pure ionic conductor with the ionic transport number of 1 at 500–900°C in wet hydrogen. In wet air, the specimen is a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers are 0.071–0.018, and the oxide ionic transport numbers are 0.273–0.365. The conductivities of Ba1.03Ce0.8Tm0.2O3?α under wet hydrogen, wet air or fuel cell atmosphere are higher than those of Ba1.03Ce0.8RE0.2O3?α (RE?Y, Eu, Ho) reported previously by us. The fuel cell can work stably. At 900°C, the maximum power output density is 122.7 mW·cm?2, which is higher than that of our previous cell using Ba1.03Ce0.8RE0.2O3?α (RE?Y, Eu, Ho) as electrolyte.  相似文献   

5.
BaCe0.8Pr0.2O3-α ceramic was synthesized by high temperature solid-state reaction. The structural characteristics and the phase purity of the crystal were determined using powder X-ray diffraction analysis. By using the methods of AC impedance spectroscopy, gas concentration cell and electrochemical pumping of hydrogen, the conductivity and ionic transport number of BaCe0.8Pr0.2O3-α were measured, and the electrical conduction behavior of the material was investigated in different gases in the temperature range of 500-900 ffiC. The results indicate that the material was of a single perovskite-type orthorhombic phase. From 500 ffiC to 900 ffiC, electronic-hole conduction was dominant in dry and wet oxygen, air or nitrogen, and the total conductivity of the material increased slightly with increasing oxygen partial pressure in the oxygen partial pressure range studied. Ionic conduction was dominant in wet hydrogen, and the total conductivity was about one or two orders of magnitude higher than that in hydrogen-free atmosphere (oxygen, air or nitrogen).  相似文献   

6.
A new series of Zr1?xInxP2O7 (x=0.03, 0.06, 0.09, 0.12) samples were prepared by a solid state reaction method. XRD patterns indicated that the samples of x=0.03–0.09 exhibited a single cubic phase structure, and the doping limit of In3+ in ZrP2O7 was x=0.09. The conduction behavior was investigated in wet hydrogen using various electrochemical methods including AC impedance spectroscopy, isotope effect, gas concentration cells at intermediate temperatures (373–573 K). The conductivities were affected by the doping levels, and increased in the order: σ (x=0.03)<σ (x=0.12)<σ (x=0.06)<σ (x=0.09). The highest conductivity was observed for the sample Zr0.91In0.09P2O7 to be 1.59×10?2 S·cm?1 in wet hydrogen at 573 K. The isotope effect also confirmed the proton conduction of the sample under water vapor‐containing atmosphere. It was found that in wet hydrogen atmosphere Zr0.91In0.09P2O7 was almost pure ionic conductor, the ionic conduction was contributed mainly to proton and partially to oxide ionic. The H2/air fuel cell using x=0.09 sample as electrolyte (thickness: 1.73 mm) generated a maximum power density of 13.5 mW·cm?2 at 423 K and 16.9 mW·cm?2 at 448 K, respectively.  相似文献   

7.
采用高温固相反应法制备了非化学计量组成的Ba1.03Ce0.8 Ho0.2O3-α 固体电解质,用XRD和SEM对其相组成和表面及断面形貌进行了表征。用气体浓差电池方法测定了材料在600~1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中的离子迁移数;用交流阻抗谱技术测定了它们在各实验气氛中的电导率。研究了材料的离子导电特性,并与BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α 的性能进行了比较。结果表明:该材料为单相钙钛矿型斜方晶结构。在600~1000 ℃温度范围内、干燥空气中,是氧离子与电子空穴的混合导体,氧离子迁移数为0.10~0.36;在湿润空气中,是质子、氧离子与电子空穴的混合导体,质子迁移数为0.11~0.01,氧离子迁移数为0.34~0.30;在湿润氢气气氛中,是纯质子导体,质子迁移数为1。在600~1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中,非化学计量组成材料(x = 1.03,0.97)的电导率高于化学计量组成材料(x = 1)的电导率,其中,Ba1.03Ce0.8 Ho0.2O3-α的电导率最高 (1000 ℃时、在干燥空气气氛中:3.92×10-2 S·cm-1;在湿润空气气氛中:3.46×10-2 S·cm-1;在湿润氢气气氛中:2.10×10-2 S·cm-1)。Ba1.03Ce0.8 Ho0.2O3-α材料的离子导电性优于BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α。  相似文献   

8.
Dense ceramic samples BaCe0.9?xZrxSm0.10O3?α (x=0.10, 0.15, 0.20, 0.30) were obtained by heat‐treating the precursors prepared from a coprecipitation route. The phase structure, chemical stability and conduction behaviors of the ceramic samples have been investigated by X‐ray powder diffraction and alternating current impedance spectroscopy methods. All the ceramic samples displayed a single phase of orthorhombic perovskite. The samples with x≧0.20 were relatively stable after exposed to the flowing mixed gases: CO2 +H2O+N2 at 873 K for 12 h. Among the samples tested, the sample with x=0.20 exhibited both adequate conductivity and better chemical stability. The contribution of different charged species for x=0.20 sample to the conduction in wet hydrogen atmosphere was investigated by means of gas concentration cells. It was found that the sample of x=0.20 was almost a pure ionic conductor, and the ionic conduction was contributed mainly by proton and partially by oxide ion in wet hydrogen atmosphere at 773–1073 K. The ammonia synthesis at atmospheric pressure in an electrolytic cell based on the sample of x=0.20 was successfully conducted and the peak ammonia formation rate achieved 2.67×10?9 mol·s?1·cm?2 with direct current of 0.80 mA at 773 K.  相似文献   

9.
BaCe0.7Zr0.2Nd0.1O3?α ceramic was prepared by solid state reaction. Phase composition, surface and fracture morphologies of the material were characterized by using XRD and SEM, respectively. Chemical stability against carbon dioxide and water steam at the high temperature was tested. The conductivity and ionic transport number of the material were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 500–900°C in wet hydrogen and wet air, respectively. Using the ceramic as solid electrolyte and porous platinum as electrodes, the hydrogen‐air fuel cell was constructed, and the cell performance at the temperature from 500 to 900°C was examined. The results indicate that BaCe0.7Zr0.2Nd0.1O3?α was a single phase perovskite‐type orthorhombic system, with high density and good chemical stability in carbon dioxide and water steam atmospheres at the high temperature. The conductivity of the material in wet hydrogen and wet air was increased as the temperature rises. In wet hydrogen, the material was a pure protonic conductor with the protonic transport number of 1 from 500 to 600°C, a mixed conductor of proton and electron with the protonic transport number of 0.973–0.955 from 700 to 900°C. In wet air, the material was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.002–0.003, and the oxide ionic transport numbers were 0.124–0.179. The fuel cell could work stably. At 900°C, the maximum short‐circuit current density and power output density were 156 mA·cm?2 and 40 mW·cm?2, respectively.  相似文献   

10.
Ce1‐xNdxO2‐δ (x = 0.05–0.55) solid solutions prepared by sol‐gel route were crystallized in a cubic fluorite structure. The solid limit was determined to be as high as x = 0.45. Raman spectra of the solid solutions with lower composition exhibited only one band, which was assigned to F2g mode. Increasing composition produced broad and asymmetric F2g mode with an appearance of low frequency tail. The new broad peak observed at higher frequency side of the F2g mode associated with the oxygen vacancy in the lattice. The impedance spectra of the solid solutions showed definitely ionic conduction, and Ce0.80Nd0.20O2‐δ solid solution possessed a maximum conductivity. At 500 °C, the conductivity and activation energy were 2.65 × 10?3S/cm and 0.82 eV, respectively.  相似文献   

11.
A bifunctional oxygen electrocatalyst composed of iron carbide (Fe3C) nanoparticles encapsulated by nitrogen doped carbon sheets is reported. X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure revealed the presence of several kinds of active sites (Fe?Nx sites, N doping sites) and the modulated electron structure of nitrogen doped carbon sheets. Fe3C@N‐CSs shows excellent oxygen evolution and oxygen reduction catalytic activity owing to the modulated electron structure by encapsulated Fe3C core via biphasic interfaces electron interaction, which can lower the free energy of intermediate, strengthen the bonding strength and enhance conductivity. Meanwhile, the contribution of the Fe?Nx sites, N doping sites and the effect of Fe3C core for the electrocatalytic oxygen reaction is originally revealed. The Fe3C@N‐CSs air electrode‐based zinc‐air battery demonstrates a high open circuit potential of 1.47 V, superior charge‐discharge performance and long lifetime, which outperforms the noble metal‐based zinc‐air battery.  相似文献   

12.
Two types of templates, an active metal salt and silica nanoparticles, are used concurrently to achieve the facile synthesis of hierarchical meso/microporous FeCo‐Nx‐carbon nanosheets (meso/micro‐FeCo‐Nx‐CN) with highly dispersed metal sites. The resulting meso/micro‐FeCo‐Nx‐CN shows high and reversible oxygen electrocatalytic performances for both ORR and OER, thus having potential for applications in rechargeable Zn–air battery. Our approach creates a new pathway to fabricate 2D meso/microporous structured carbon architectures for bifunctional oxygen electrodes in rechargeable Zn–air battery as well as opens avenues to the scale‐up production of rationally designed heteroatom‐doped catalytic materials for a broad range of applications.  相似文献   

13.
The preparation, structures, and magnetic properties of a series of metal formate perovskites [CH3NH3][MnxZn1?x(HCOO)3] were investigated. The isostructural solid solution can be prepared in the complete range of x=0–1. The metal–organic perovskite structures consist of an anionic NaCl type [MnxZn1?x(HCOO)3?] framework with CH3NH3+ templates located in the nearly cubic cavities and forming hydrogen bonds to the framework. When the proportion of Mn increased (i.e., x changed from 0 to 1), the lattice dimensions and metal–oxygen and metal–metal distances show a slight, nonlinear increase because of the increased averaged metal ionic radius and the local structure distortion. Through the series, the magnetism changes from the long‐range ordering of spin‐canted antiferromagnetism for x≥0.40 to paramagnetism when x≤0.30, and the percolation limit was estimated to be xP=0.31(2) for this simple cubic lattice. In the low‐temperature region, enhancement of magnetization and the gradual decrease and final disappearance of coercive field, remnant magnetization, and spin‐flop field upon dilution were observed through this isotropic Heisenberg magnetic series. IR spectroscopic and thermal properties were also investigated.  相似文献   

14.
Surface states of polydimethylsiloxane (PDMS) treated by plasma were investigated by x‐ray photoelectron spectroscopy and surface voltage decay. X‐ray photoelectron spectroscopy confirmed the formation of a silica‐like (SiOx, x = 3–4) oxidative surface layer. This layer increased in thickness with increasing exposure duration of plasma. Plasma exposure lowers the surface resistivity from 1.78 × 1014 to 1.09 × 1013 Ω □?1 with increasing plasma treatment time. By measuring the decay time constant of surface voltage, the calculated surface resistivity was compared with the value measured directly by a voltage–current method; good agreement between the two methods was obtained. It was observed that plasma treatment led to a decrease in the thermal activation energy of the surface conduction from 31.0 kJ mol?1 for an untreated specimen to 21.8 kJ mol?1 for a plasma‐treated specimen for 1 h. Our results allow the examination of effects of plasma on the electrical properties of PDMS. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

15.
A series of Ag‐enhanced TiO2–x/C composites (Ag/TiO2–x/C composites) with metal‐organic frameworks (MOFs) as precursors were prepared, and their photocatalytic activities were evaluated by the UV‐light driven photodegradation behaviors of methyl blue (MB). The as‐obtained samples were characterized by several techniques such as SEM, XRD, N2‐adsorption, XPS, UV/Vis spectrophotometry and UV/Vis diffuse‐reflectance spectra. The best photocatalytic performance was achieved in Ag/TiO2–x/C composite pyrolyzed at 1000 °C (ATC‐P10) due to rapid capture of electrons caused by silver doping, higher density of TiO2–x lattice oxygen vacancies for better trapping of electrons, and high surface area due to reduction and evaporation of metallic Zn. No obvious deactivation was observed after 10 cycles of UV‐light degradation of MB under the same experimental conditions. This report reveals a new approach to prepare stable and highly efficient UV‐light‐driven photocatalysts for organic pollutants in water.  相似文献   

16.
The new high‐pressure borate HP‐Cs1?x(H3O)xB3O5 (x=0.5–0.7) was synthesized under high‐pressure/high‐temperature conditions of 6 GPa/900 °C in a Walker‐type multianvil apparatus. The compound crystallizes in the monoclinic space group C2/c (Z=8) with the parameters a=1000.6(2), b=887.8(2), c=926.3(2) pm, β=103.1(1)°, V=0.8016(3) nm3, R1=0.0452, and wR2=0.0721 (all data). The boron–oxygen network is analogous to those of the compounds HP‐MB3O5, (M=K, Rb) and exhibits all three structural motifs of borates—BO3 groups, corner‐sharing BO4 tetrahedra, and edge‐sharing BO4 tetrahedra—at the same time. Channels inside the boron–oxygen framework contain the cesium and oxonium ions, which are disordered on a specific site. Estimating the amount of hydrogen by solid‐state NMR spectroscopy and X‐ray diffraction led to the composition HP‐Cs1?x(H3O)xB3O5 (x=0.5–0.7), which implies a nonzero phase width.  相似文献   

17.
Vanadium‐containing heteropoly acid solutions of Keggin H3+xPMo12–xVxO40 and modified HaPzMoyVxOb types (P‐Mo‐V HPAs) are promising nanosized inorganic metal‐oxygen cluster compounds with the property of reversible oxidability (VV ↔ VIV). The oxidation of reduced P‐Mo‐V HPAs at a temperature of 130–170 °C and an oxygen pressure of 4 atm is a convenient method for their regeneration, but results in regeneration degree of only 75–88 %. Various materials with electron transfer or oxidative properties, such as nitrogen doped carbon nanofibers (N‐CNFs), Sibunit‐4, HNO3, and MoO2, were investigated as additives to facilitate and accelerate the regeneration of HPA solutions. Among the studied additives HNO3 was found to show the best efficiency, resulting in regeneration degree of higher 95 %. Rapid and efficient regeneration of spent HPA catalysts is an important criterion for achieving high productivity and sustainability of oxidative processes on their basis.  相似文献   

18.
The novel nitrides (R1–xCa3+xN1–x/3)Bi2 (with R = La, Ce, Pr) crystallize in the K2[NiF4] structure type (I4/mmm, No. 139, Z = 2). Samples (La1–xCa3+xN1–x/3)Bi2 with x = 0.10, 0.05, 0.00, (Ce1–xCa3+xN1–x/3)Bi2 with x = 0.30, and (PrCa3N)Bi2 were obtained as single phase microcrystalline powders according to X‐ray diffraction and the crystal structure details were derived from Rietveld refinements based on X‐ray and neutron diffraction powder patterns. A partial order of R3+/Ca2+ on two crystallographic sites is governed by different ionic radii and charges. (La1–xCa3+xN1–x/3)Bi2 and (Ce1–xCa3+xN1–x/3)Bi2 exhibit small homogeneity ranges and typically a nitrogen deficiency. In contrast, for (PrCa3N)Bi2 no indications for a significant homogeneity range or deficiency of nitrogen was observed. (La1–xCa3+xN1–x/3)Bi2 with x = 0.05 is a diamagnet. X‐ray absorption spectroscopy at the CeL3‐edge as well as magnetic susceptibility measurements evidence that (Ce1–xCa3+xN1–x/3)Bi2 with x = 0.30 contains Ce3+ in the 4f1 configuration. According to electrical resistivity data, samples from all three systems are heavily doped semiconductors.  相似文献   

19.
Aluminum–vanadium bimetallic oxide cluster anions (BMOCAs) have been prepared by laser ablation and reacted with ethane and n‐butane in a fast‐flow reactor. A time‐of‐flight mass spectrometer was used to detect the cluster distribution before and after the reactions. The observation of hydrogen‐containing products AlVO5H? and AlxV4?xO11?xH? (x=1–3) strongly suggests that AlVO5? and AlxV4?xO11?x? (x=1–3) can react with ethane and n‐butane by means of an oxidative dehydrogenation process at room temperature. Density functional theory studies have been carried out to investigate the structural, bonding, electronic, and reactive properties of these BMOCAs. Terminal‐oxygen‐centered radicals (Ot.) were found in all of the reactive clusters, and the Ot. atoms, which prefer to be bonded with Al rather than V atoms, are the active sites of these clusters. All the hydrogen‐abstraction reactions are favorable both thermodynamically and kinetically. To the best of our knowledge, this is the first example of hydrogen‐atom abstraction by BMOCAs and may shed light on understanding the mechanisms of C? H activation on the surface of alumina‐supported vanadia catalysts.  相似文献   

20.
The ceramic powders of BaCe1?xYxO3?α (x = 0.05, 0.10, 0.15, 0.20) have been prepared via a microemulsion method. Green compacts of the powders were sintered to densities higher than 95% of theoretical at the lower temperature (1500 °C). The obtained ceramics showed a single-phase of orthorhombic perovskite. The proton conduction was investigated by employing the techniques of AC impedance and electrochemical hydrogen permeation (hydrogen pumping) at 300–600 °C. It was found that the ceramics were almost pure proton conductors in wet hydrogen, and the highest proton conductivity was observed for x = 0.15 at 600 °C. Ammonia was synthesized successfully from nitrogen and hydrogen at atmospheric pressure in the electrolytic cell using BaCe0.85Y0.15O3?α. The maximum rate of NH3 formation was found to be 2.1 × 10?9 mol s?1 cm?2 at 500 °C with an applied current of 0.75 mA.  相似文献   

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