Preparation and hydrogen permeation properties of BaCe_(0.95)Nd_(0.05)O_(3-δ) membranes

Dense mixed proton and electron conducting membrane made of BaCe_(0.95)Nd_(0.05)O_(3-δ)(BCNd5)was prepared by pressing followed by sintering.X-ray diffraction(XRD)was used to characterize the phase structure of both the powder and the sintered membranes.The microstructure of the sintered membranes was studied by scanning electron microscopy(SEM).Hydrogen permeation through the BCNd5 membrane was studied using a high temperature permeator.The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions,which is due to H~ hopping via surface OH groups.At 925℃,a hydrogen permeation flux of 0.02 mL/min cm~2 was obtained under wet condition,which recommends BCNd5 as a potential material for hydrogen-selective membranes.     

SrCe_(0.95)Y_(0.05)O_3-δ在中温区的电化学性质及其在常压合成氨中的应用

SrCe0.95Y0.05O3-δ是一种高温质子导体，本研究采用溶胶—凝胶法合成了 SrCe0.95Y0.05O3-δ纳米粉体，并以该粉体烧制得固体复合氧化物电解质陶瓷，测 定了其在中温区间(400-600℃)的电导率，结果表明不同气氛对其电导率有很大影 响．用该陶瓷在固态质子传导电他中常压下以氮气和氢气为原料合成了氨，并研究 了影响氨合成的关键因素，确定了合适的工作温度，在常压下480℃时氨的产率可 达10^-9mol/(s.cm^-2)以上．     

Novel Ba_(0.5)Sr_(0.5)Fe_(0.8)Zn_(0.2)O_(3-δ) membranes for POM

A novel cobalt-free perovskite based on Ba_(0.5)Sr_(0.5)Fe_(0.8)Zn_(0.2)O_(3-δ)(BSFZ)were prepared by EDTA-citric acid method.The lattice constants of the BSFZ perovskite were characterized by in situ high-temperature X-ray diffraction(HTXRD).The thermal expansion coefficient of BSFZ is 10.5×10~(-6)K~(-1),which is lower than that of cobalt-based perovskite materials.The BSFZ membrane was also used to construct reactors for the partial oxidation of methane(POM)to syngas.Results show that the BSFZ membrane...     

Ce_(0.8)Nd_(0.2)O_(1.9)-La_(0.95)Sr_(0.05)Ga_(0.9)Mg_(0.1)O_(3-δ)固体复合电解质的结构和电性能

采用溶胶-凝胶法分别制备La0.95Sr0.05Ga0.9Mg0.1O3-δ(LSGM)和Ce0.8Nd0.2O1.9(NDC)电解质,并在NDC溶胶中加入0-15%(w,质量分数)的LSGM预烧粉体制得NDC-LSGM复合电解质,研究不同质量比复合电解质的结构和电性能.采用X射线衍射(XRD)、场发射扫描电子显微镜(FE-SEM)和X能量色散谱仪(EDS)对样品进行结构表征,交流(AC)阻抗谱测试样品导电性能.结果表明:NDC-LSGM复合体系主要由立方萤石结构相、钙钛矿结构相和杂质相组成;LSGM的添加可促进晶粒的生长,产生大量相界面,清除或降低SiO2有害影响,明显提高晶界导电性;LSGM质量分数为10%的样品NL10具有最高晶界电导率和总电导率,400°C时NL10的晶界电导率σgb和总电导率σt分别为12.15×10-4和3.49×10-4S cm-1,与NDC的σgb(1.41×10-4S cm-1)和σt(1.20×10-4S cm-1)相比分别提高了7.62和1.91倍,总电导率的提高主要归因于晶界电导率的影响.     

Perovskite Sr_(0.9)Fe_(0.9)Zr_(0.1)O_(3-δ):Redox-stable Structure,Oxygen Vacancy,Electrical Properties and Steam Electrolysis Performance

Many researchers have studied on perovskite oxide for its unique structure.Perovskite oxides,ABO_(3-δ),with different A and B metals have shown wide applications in many fields,in particular solid oxide electrolysers.SrFeO_(3-δ),typical perovskite oxides,in which iron is the mixed-valence cation with the capacity to change the chemical valence,have a wide range of oxygen nonstoichiometry.In this study,Sr_(0.9)Fe_(0.9)Zr_(0.1)O_(3-δ)(SFZO) is synthesized and then treated in 5%H_2/Ar and air at high temperature,exhibiting excellent redox stability.Redox-stable structure,oxygen vacancy and electrical properties of SFZO are investigated.Steam electrolysis is then performed with SFZO cathode under 5%H_2O/5%H_2/Ar and 5%H_2O/Ar atmospheres,respectively.The present results indicate that the SFZO is a novel promising cathode material for solid oxide steam electrolyser.     

BaCe_(0.8)Zr_(0.1)La_(0.1)O_(3-α)陶瓷的制备和电性能研究

以高温固相反应法制备了BaCe0.8Zr0.1La0.1O3-α陶瓷,用粉末X-射线衍射(XRD)和扫描电镜(SEM)对其晶体结构和断面形貌进行了表征。以陶瓷材料为固体电解质、多孔性铂为电极,用交流阻抗谱技术测定了材料在500～900℃下不同气体气氛中的电导率;用气体浓差电池方法测定了材料在干燥空气和湿润空气中的离子迁移数;研究了材料的离子导电特性。结果表明,该陶瓷材料为单一钙钛矿型BaCeO3斜方晶结构。在500～900℃下,干燥和湿润的氧气、空气和氮气中,材料的电导率随着温度升高和氧分压增大而增大。在干燥的空气中,材料的氧离子迁移数为0.06～0.17,表现为氧离子与电子空穴的混合导电性,其中,电子空穴导电为主导。在湿润的空气中,材料的质子迁移数为0.52～0.01,氧离子迁移数为0.14～0.27,表现为质子、氧离子和电子空穴的混合导电性,其中,在500～550℃下,质子导电为主导;高于550℃,电子空穴导电为主导。     

Efficient CO_2 Electrolysis with Fluorite Structure Nanoparticles Modified Perovskite Structure La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) Cathode

Perovskite structure La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ)(LSCM) cathode with unique structure can electrolyze CO_2 to CO in solid oxide electrolysers(SOEs).However,the cell performance is restricted by its electro-catalysis activity.In this work,fluorite structure nanoparticles(CeO_(2-δ)) are impregnated on LSCM cathode to improve the electro-catalysis activity.X-ray diffraction(XRD),scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS) together approve that the fluorite structure nanoparticles are uniformly distributed on the perovskite structure LSCM scaffold.Electrochemical measurements illustrate that direct CO_2 electrolysis with 10%mol CeO_(2-δ) impregnated LSCM cathode exhibits excellent performance for current density(0.5 A×cm~(-2)) and current efficiency(～95%) at 800 ℃ under 1.6 V.It is believed that the enhanced performance of directed CO_2 electrolysis may be due to the synergetic effect of fluorite structure CeO_(2-δ) nanoparticles and perovskite structure LSCM ceramic electrode.     

Ni/Ce_(0.75)Zr_(0.25)O_2界面催化CO_2甲烷化密度泛函理论研究

将温室气体CO_2催化加氢转化为CH_4,有利于碳资源化利用和减轻环境污染,是具有一定现实意义的模型化反应.实验发现,氧化物负载型催化剂对CO_2甲烷化过程展现出较高的催化活性和稳定性,但其催化机理和界面作用机制并未得到清楚认识.基于DFT+U计算方法,本文系统研究了复合氧化物Ce_(0.75)Zr_(0.25)O_2负载Ni体系催化CO_2甲烷化复杂基元过程.结果表明,在Ni/Ce_(0.75)Zr_(0.25)O_2(110)体系中,CO_2甲烷化反应涉及CO_2分解和甲酸盐两条途径,且CO_2的分解途径占主导地位,整个反应的控制步骤为CO_2吸附过程.产物甲烷是由界面上CO_2解离加氢产生的CH基团进一步在金属Ni活性位上加氢生成,揭示了该催化体系中载体与负载物之间存在协同催化作用,即载体界面主要发生碳氧化物的脱氧加氢,碳氢中间物种的加氢反应在Ni上发生.     

Nd_(1 x)Ba_(2-x)Cu_3O_(7-δ)超导体的热处理

通过对Nd1 xBa2 -xCu3O7-δ的两种样品 (烧结样品和区域熔炼样品 )的XRD谱图分析 ,研究了高温氩气氛下热处理对样品中Nd对Ba的取代值x的影响 ,同时比较了不同样品的Tc 和Jc 值。研究表明 ,氩气下 95 0℃热处理可以减少Nd对Ba的取代 ,Tc 和Jc 都有不同程度的提高。对不同固溶度x值的Nd1 xBa2 -xCu3O7-δ进行吸氧热处理 ,样品在热处理前后分别作XRD分析。从XRD谱图可以看出 :当x <0 4时 ,样品经吸氧后可以从四方相转变为正交相 ,而当x >0 4时 ,样品虽经长时间吸氧也不能使其从四方相转变为正交相     

Hydrogen Permeation Properties of Perovskite-type BaCe_(0.9)Mn_(0.1)O_(3-δ)Dense Ceramic Membrane

In recent years, mixed-conducting oxides, in which both protonic and electronic charge carriers exist, have received increasing attentions1. Ceramic membranes made of such materials are semipermeable to hydrogen at elevated temperatures. In the early 1980s, Iwahara et al. first reported protonic conduction in SrCeO3-based materials2. Later, BaCeO3 system was extensively studied because of its higher conductivities. However, the electronic conductivity of rare earth doped-BaCeO3 ceramic…     

Preparation and hydrogen permeation of BaCe0.95Nd0.05O3−δ membranes

A mixed proton–electron conducting perovskite made of BaCe_0.95Nd_0.05O_3−δ (BCN) was prepared by EDTA/citric acid complexing method. The precursor was characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction (XRD). In order to learn the perovskite formation process during the calcination, the intermediate, i.e. the sample calcined at 750 °C for 5 h, was investigated by scanning (STEM), energy-filtered (EFTEM), and high-resolution transmission electron microscopy (HRTEM) as well as electron energy-loss spectroscopy (EELS). The results revealed that the perovskite structure was formed via a solid-state reaction between barium–cerium mixed carbonate and cerium–neodymium mixed oxide particles. Dense mixed proton–electron conducting BCN membranes were made by pressing BCN powder followed by sintering. The microstructure of the sintered membranes was investigated by scanning electron microscopy (SEM). Hydrogen permeation through the BCN membrane was studied using a high-temperature permeator. The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions, which is due to increased proton concentrations in the H⁺ hopping via OH groups. The hydrogen permeation increased with increasing hydrogen and steam concentrations in the feed. For a steam concentration of 15 vol.%, the hydrogen permeation flux reaches 0.026 ml/min cm².     

A dense oxygen separation membrane with a layered morphologic structure

A configuration of dense mixed ionic and electronic conducting (MIEC) membrane with layered morphological structure for oxygen separation, which combines the benefits of high oxygen permeation flux of cobalt-based membrane, high chemical stability of iron-based perovskite and high mechanical strength of thick membrane, was studied. The membrane is normally composed of two layers; each layer is a dense MIEC oxide. The substrate layer is a thick dense membrane with high oxygen permeability but relatively lower chemical stability. The feasibility of dense thick Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF5582) membrane as the substrate layer and Ba_0.5Sr_0.5Co_0.2Fe_0.8O_3−δ (BSCF5528) as the thin-film layer was mainly experimentally investigated. Both the BSCF5582 and the BSCF5528 show the same cubic perovskite structure and the similar lattice constant with no detrimental reaction products formed. By optimizing fabrication parameters of a simple dry pressing process, dual-layered membrane, free of cracks, was successfully fabricated. The oxygen permeation flux of a dual-layered membrane with the thin-film BSCF5528 layer facing to the sweep gas reached 2.1 mL cm⁻² min⁻¹ [STP] (1.56 × 10⁻⁶ mol cm⁻² s⁻¹) at 900 °C, which is about 3.5 times higher than that of the BSCF5528 membrane (0.6 mL cm⁻² min⁻¹, [STP] (4.46 × 10⁻⁷ mol cm⁻² s⁻¹) under the same conditions.     

Mechanical stability and transport properties of the Sn-promoted SrCo0.8Fe0.2O3−δ ceramic membrane

In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo_0.8Fe_0.2O_3−δ (SCF) and the SrCo_0.8Fe_0.1Sn_0.1O_3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10⁻⁶ mol cm⁻² s⁻¹ was obtained at 1000 °C and under the oxygen partial pressure gradient of P_O2 (h)/P_O2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10⁻⁶ mol cm⁻² s⁻¹ for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity (σ_e) for SSCF sample appeared with increasing temperature. The second peak value of σ_e for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice.     

Oxygen permeation through a Ce0.8Sm0.2O2−δ–La0.8Sr0.2CrO3−δ dual-phase composite membrane

A composite of oxygen ion conducting oxide Ce_0.8Sm_0.2O_2−δ (60 vol.%) and electron conducting oxide La_0.8Sr_0.2CrO_3−δ was prepared by sintering a powder compact at a temperature of 1550 °C. No significant reaction between the two constituent oxides was observed under preparation and oxygen permeation conditions. Appreciable oxygen permeation fluxes through the composite membrane were measured at elevated temperatures with one side of it exposed to the ambient air and the other side to a flowing helium gas stream. The oxygen flux initially increased with time, and took a long time to reach a steady value. A steady oxygen permeation flux as high as 1.4 × 10⁻⁷ mol cm⁻² s⁻¹ was obtained with a 0.3 mm thick membrane at 950 °C under a relatively small oxygen partial pressure difference of 0.21 bar/0.0092 bar. It was revealed that the overall oxygen permeation process was mainly limited by the transport in the bulk of the membrane in the range of the membrane thickness greater than 1.0 mm, and the limitation by the surface oxygen exchange came into play at reduced thickness of 0.6 mm.     

Hollow fiber membrane of yttrium-stabilized zirconia and strontium-doped lanthanum manganite dual-phase composite for oxygen separation

The hollow fiber composite membrane involving Zr_0.84Y_0.16O_1.92 (YSZ) as an oxygen ionic conductor and La_0.8Sr_0.2MnO_3−δ (LSM) as an electronic conductor was explored for oxygen separation application. The hollow fiber precursor was prepared by the phase-inversion process, and transformed to a gas-tight ceramic by sintering at 1350 °C. The as-prepared fiber exhibited a thermal expansion coefficient of 11.1 × 10⁻⁶ K⁻¹ and a three-point bending strength of 152 ± 12 MPa. An oxygen permeation flux of 2.1 × 10⁻⁷ mol cm⁻² s⁻¹ was obtained under air/He gradient at 950 °C for a hollow fiber of length 57.00 mm and wall thickness 0.16 mm. The oxygen permeation flux remained unchanged when the sweeping gas was changed from helium to high concentration of CO₂. Considering the satisfactory trade-off between the permeability and stability, the YSZ–LSM hollow fiber is promising for oxygen production applications.     

Preparation and hydrogen permeation of SrCe0.95Y0.05O3−δ asymmetrical membranes

Asymmetrical thin membranes of SrCe_0.95Y_0.05O_3−δ (SCY) were prepared by a conventional and cost-effective dry pressing method. The substrate consisted of SCY, NiO and soluble starch (SS), and the top layer was the SCY. NiO was used as a pore former and soluble starch was used to control the shrinkage of the substrate to match that of the top layer. Crack-free asymmetrical thin membranes with thicknesses of about 50 μm and grain sizes of 5–10 μm were successfully pressed on to the substrates. Hydrogen permeation fluxes (J_H2) of these thin membranes were measured under different operating conditions. At 950 °C, J_H2 of the 50 μm SCY asymmetrical membrane towards a mixture of 80% H₂/He was as high as 7.6 × 10⁻⁸ mol/cm² s, which was about 7 times higher than that of the symmetrical membranes with a thickness of about 620 μm. The hydrogen permeation properties of SCY asymmetrical membranes were investigated and activation energies for hydrogen permeation fluxes were calculated. The slope of the relationship between the hydrogen permeation fluxes and the thickness of the membranes was −0.72, indicating that permeation in SCY asymmetric membranes was controlled by both bulk diffusion and surface reaction in the range investigated.     

SrFe0.6Cu0.3Ti0.1O3-δ混合导体透氧材料的稳定性

利用柠檬酸络合法制备了SrFe(Cu,Ti)O_3-δ混合导体透氧材料。 采用XRD、O₂-TPD、H₂-TPR、SEM等测试技术考察了材料的稳定性。 结果表明,SrFe_0.7Cu_0.3O_3-δ在低氧压下会发生相分解,产生SrCuO₂杂相,而掺杂Ti后的SrFe_0.6Cu_0.3Ti_0.1O_3-δ在低氧压下保持单一的钙钛矿结构。 H₂-TPR和O₂-TPD的测试表明,Ti⁴⁺的掺杂提高了材料的氧脱附起始温度和其它金属离子的还原温度。 SrFe_0.6Cu_0.3Ti_0.1O_3-δ膜在透氧过程中,会有Cu²⁺和Sr²⁺从钙钛矿结构中析出,在原晶粒边界形成新的小晶粒,但这种轻微的组分偏析没有影响到材料的透氧量,此透氧膜在66 h的操作过程中显示了良好的稳定性。     

氢分离与CO催化甲烷化双功能型钯复合膜

以多孔Al₂O₃陶瓷为基体材料, 采用浸渍法担载NiO后用2B铅笔修饰NiO/Al₂O₃表面, 通过化学镀法沉积约5 μm厚的金属钯, 还原后成功制得Pd/Pencil/Ni/Al₂O₃膜. 为进行对比, 还制备了未担载镍的Pd/Pencil/Al₂O₃膜. 膜的表面和断面形貌分别采用扫描电镜和金相显微镜观测, 膜的透氢动力学通过H₂/N₂单气体法测试, 并以成分为H₂ 77.8%, CO 5.2%, CO₂ 13.5%和CH₄ 3.5%的原料氢测定了膜的氢分离效果. 结果表明, 未载镍的Pd/Pencil/Al₂O₃膜只具有氢分离作用, 而Pd/Pencil/Ni/Al₂O₃膜还可以有效地将钯膜泄漏的CO和CO₂转化为甲烷, 因而成为双功能型钯膜. 这种双功能膜尤其适用于面向质子交换膜燃料电池(PEMFC)的氢气分离, 既有效解决了PEMFC对氢燃料中CO格外敏感的难题, 又提高了对钯膜缺陷的容忍度, 因而延长了钯膜的使用寿命.     

O/O and H/D separation factors for liquid/vapor permeation of water through an hydrophobic membrane

Liquid/vapor permeation of water through commercial grade hydrophobic PTFE membranes at 323<P(Torr)<160, shows enhancements in logarithmic separation factors, ln[(i'/i)] = In [(χ'/χ) _downstream/ (χ'/χ) _upstream], which differ markedly for isotope separation of oxygen and hydrogen. The prime refers to the lighter isotope and χ is the mole fraction. Thus ln[(16/18)] is found to be as large as 6 times the ratio of the vapor pressure isotope effect, ln(_o = ln (P^o'/P^o), but ln[(H/D)]/ln[_o(H/D)] is only as large as 1.3. The difference in enhancement factors indicates that membrane transport mechanisms must be different for the two separations. The unusually large separation factor for ¹⁶O/¹⁸O may be of practical interest.     

Determination of parameters in surface limited hydrogen permeation through metal membrane

Hydrogen permeation through metal membranes at low upstream pressures is considered in the regime where the permeation rate is limited by the surface processes and not by diffusion in the bulk. The mathematical model for the hydrogen permeation through asymmetric membrane in the surface limited regime (SLR) is briefly introduced. For this model, we show that it is not possible to determine the unknown hydrogen-related membrane parameters by measuring the permeation flux through the membrane only in one direction. As an alternative to experiments on permeation in both directions, we describe an innovative and simple experimental technique that enables measurement of the permeation and outgassing rates of the membrane. All fluxes are determined from the upstream pressure change. For the proposed technique, we give a mathematical model and procedure that allows to extract all hydrogen-related membrane parameters from the experimental data without any fitting, solving of differential equations and without relying on the published parameters. The error of the obtained parameters introduced by the calculational procedure is only a few percents.