钙钛矿SrFe1-xMnxO3催化剂:共沉淀法制备及催化甲烷燃烧的性能

通过共沉淀法制备了SrFe1-xMnxO3钙钛矿催化剂。用XRD、TPR和TG-DSC技术对催化剂进行了物理性能表征,以甲烷催化燃烧为目标反应表征其催化性能,通过BET模型计算了其比表面积,通过阿伦尼乌斯方程计算了反应的表观活化能。结果表明用共沉淀法制备钙钛矿催化剂经700℃焙烧4 h后可以形成完整的钙钛矿晶型,样品都具有高的催化性能,但随着锰离子的掺杂,催化剂活性明显提高,其中SrMnO3催化剂具有较高甲烷催化燃烧活性,起燃温度T10%为435℃,至457℃甲烷完全转化。     

双相致密透氧膜

混合导体透氧材料由于在高温下具有氧离子导电特性,在纯氧制备、膜反应器及富氧燃烧等方面显示出广阔的应用前景。单相混合导体材料用作透氧材料时存在稳定性不足、机械性能差等问题,限制了其在生产中的实际应用。在离子导体相中掺入电子导体相形成双相导体膜可以提高透氧材料在高温下和高氧浓度梯度下的工作稳定性和化学稳定性。本文详细论述了双相透氧材料的透氧机理和研究进展,包括氧离子导体/贵金属电子导体和氧离子导体/氧化物电子导体和氧离子导体/混合导体等的复合形式。重点分析了材料的组成、结构以及两相之间的化学相容性和混合比例对材料透氧率和工作稳定性的影响。介绍了双相材料在甲烷部分氧化制合成气(POM)膜反应过程及富氧燃烧中的应用,分析了目前有待解决的问题并提出了今后的研究方向。     

SrCe0.95 Yb0.05 O3-α的制备及其质子导电特性

利用固相反应法制备出固态质子导体SrCe0.95Yb0.05O3-α,并使用X射线衍射分析法及低频阻抗测量法对其电子结构和导电特性进行了研究.X射线分析结果表明,该物质为钙钛矿晶体结构,具有p型电子空穴和氧离子空穴.在低温下主要为电子导电,且电子导电率随温度的升高而增大.在含氢气环境中,当温度高于550 K时, SrCe0.95Yb0.05O3-α具有明显的质子导电性,随着温度的升高,质子导电性增强.当温度高于800 K时,质子是导体中的主要载流子,质子电导率可达4.5 mS/cm.     

镧钴镍复合氧化物催化剂的制备及催化甲烷燃烧活性研究

采用共沉淀法制备LaNi_(1-x)Co_xO_3系列催化剂(x=0,0.2,0.4,0.6,0.8,1.0),研究B位离子Co的掺杂对钙钛矿LaNiO_3催化甲烷燃烧性能的影响。通过X射线衍射、比表面积测定、程序升温还原、扫描电镜、热重分析等对催化剂的结构和性能进行考察。以催化甲烷燃烧为目标,考察了催化剂的性能。研究结果表明,Co离子的掺杂会改变钙钛矿的晶型结构,改善催化活性,当x=0.8时,LaNi_(0.2)Co_(0.8)O_3的催化甲烷燃烧活性最高,其比表面积为22.4 m~2·g~(-1),T_(10%)(起燃温度)为475℃,T_(90%)(完全转化温度)为610℃。     

Ba_xCe_(0.8)Y_(0.2)O_(3-α)固体电解质的氧离子导电性

固体电解质是指固体状态下具有较高电导率的离子导体,根据其传导离子所带电荷分为阳离子导体(如:Na+,Li+,H+等)和阴离子导体(如:F-,Cl-,O2-等)。固体电解质与液体电解质不同之处为:(1)是固态;(2)电荷载流子通常只有一种;(3)由于晶格能较大,通常在较高温度下离子才能迁移。具有实用价值的固体电解质的电导率一般在10-3S·cm-1以上,同时要求其离子迁移数要足够大。至今,已发现和合成了上百种固体电解质材料。在加速研制绿色化学电源、寻找高离子电导率、高化学稳定性、低成本的固体氧化物燃料电池(SOFC)固体电解质的研究中,ABO3钙钛矿型…     

Ba0.5Sr0.5Co0.8Fe0.2O3-δ透氧膜反应器在丙烷氧化脱氢反应中的应用

工业上一般采用丙烷热裂解脱氢反应生产丙烯. 该反应通常在高温(＞700 ℃)下进行,催化剂容易积碳. 而且,由于反应受到热力学平衡的限制,丙烯的选择性也不很高. 近年来,以廉价空气和丙烷为原料的丙烷氧化脱氢(PODH)反应为丙烯的生产提供了另外一条途径,且已引起广泛的关注. 在PODH反应中,一般认为晶格氧(O2-)参与丙烷的选择氧化,而其它氧物种(O-,O-2等)导致丙烷的完全氧化[1]. 钙钛矿结构的混合导体透氧膜是同时具有氧离子导电性和电子导电性的一类材料. 在高温下,当膜两侧存在氧浓度梯度时,氧以氧离子的形式通过氧缺陷进行传导,同时以电子的反向传输来完成传输回路[2]. 这种透氧机理使得混合导体透氧膜在理论上对烷烃氧化反应具有一定的催化活性. 作为膜反应器材料,这类混合导体透氧膜已成功地应用于甲烷部分氧化(POM)反应[3]. 但迄今为止,还没有文献报道这种膜反应器在PODH反应中的应用. 组成为Ba0.5Sr0.5Co0.8Fe0.2O3-δ的钙钛矿膜材料是本研究组开发的一类具有高透氧量、高稳定性的新型透氧膜材料. 本文尝试将该材料制备的膜反应器用于PODH反应,同时研究了PODH反应对膜透氧量的影响.     

BaCe0.5Zr0.4La0.1O3－α陶瓷的制备及其电性能

以高温固相反应法合成了BaCe0.5Zr0.4La0.1O3－α陶瓷. 粉末XRD结果表明, 该陶瓷材料为单一钙钛矿型BaCeO3斜方晶结构, 在高温下、CO2或水蒸气气氛中具有较高的稳定性. 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、湿润空气和湿润氢气气氛中的离子迁移数, 研究了材料的离子导电特性. 结果表明, 在500～900 ℃下, 干燥或湿润的气体气氛中, 随着温度升高和氧分压增大, 材料的电导率均增大. 在干燥空气中, 陶瓷材料的氧离子迁移数为0.685～0.147, 是一个氧离子与电子空穴的混合导体. 在湿润空气中, 陶瓷材料的质子迁移数为0.001～0.006, 氧离子迁移数为0.618～0.164, 是一个质子、氧离子和电子空穴的混合导体. 在湿润氢气中, 500～700 ℃温度范围内, 陶瓷材料的质子迁移数为1, 是一个纯的质子导体; 而在800～900 ℃温度范围内, 陶瓷材料的质子迁移数为0.957～0.954, 是一个质子与电子的混合导体, 质子电导占主导.     

固体电解质质子导体的研究进展

介绍了固体电解质质子导体的应用、结构、质子传输机理以及国内外的最新研究进展,详细地综述了钙钛矿型和非钙钛矿型固体电解质质子导体的多种结构类型以及其质子传导机理的最新理论研究,同时分别介绍了两种质子导体的发展概况和面临问题,展望了未来质子导体的发展前景.     

模板法制备钙钛矿型复合氧化物催化剂的研究进展

钙钛矿型复合氧化物由于其组成和结构的特殊性以及优秀的热稳定性、氧化还原性能、氧迁移率和电子离子导电性,近年来在催化剂领域引起人们的广泛关注。将纳米多孔设计策略应用于钙钛矿型氧化物,可以在各种应用中带来新的和优异的性能。制备多孔金属氧化物材料主要采用模板法,本文综述了钙钛矿型复合氧化物的结构特征以及使用硬模板法、软模板法、生物模板法、其他模板法制备其的基本原理和操作步骤,讨论了各种模板剂的优缺点,简要介绍了钙钛矿型复合氧化物催化剂的几种应用领域,最后展望了钙钛矿型复合氧化物催化剂的未来研究方向。     

Ba0.9La0.1Ce0.9Nd0.1O3-α陶瓷的离子导电性

用高温固相反应法制备了Ba0.9La0.1Ce0.9Nd0.1O3-α质子导电性陶瓷,粉末X-射线衍射(XRD)分析表明,该陶瓷为单一钙钛矿型斜方晶结构。在500~900℃温度范围内,分别用气体浓差电池方法和交流阻抗谱技术研究了材料在不同气体气氛中的离子导电性,并与Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料的离子导电性进行了比较。结果表明,在500~900℃温度范围内、湿润氢气中,Ba0.9La0.1Ce0.9Nd0.1O3-α材料的质子迁移数为1,是一个纯的质子导体。在干燥空气中,该材料是一个氧离子和电子空穴的混合导体,氧离子迁移数为0.295~0.081,氧离子电导率高于Ba0.9Ca0.1Ce0.9Nd0.1O3-α。在湿润空气中,该材料是一个质子、氧离子和电子空穴的混合导体,质子迁移数为0.151~0.009,氧离子迁移数为0.300~0.107,质子电导率低于Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料。在氢-空气燃料电池条件下,Ba0.9La0.1Ce0.9Nd0.1O3-α材料是一个质子、氧离子和电子的混合导体,离子迁移数为0.964~0.853,离子电导率与Ba0.9Ca0.1Ce0.9Nd0.1O3-α材料相近。     

Research On a Ceramics Membrane Reactor for Natural Gas Conversion

We explore the new concept for a ceramics membrane reactor including the investigation of the nickel-based catalysts for methane conversion into synthesis gas and the exploitation of an oxide ionic and electronic mixed conductor. When Ca_0.8Sr_0.2Ti_1−xFe_xO_3−α exhibiting the ionic and electronic mixed conduction was used as a support material of Ni based catalyst, coke formation over the catalyst under the methane conversion with air or carbon dioxide was strongly depended on the iron (III) ion contents, x. From the relationship between the amount of carbon deposited on the catalyst and the mixed conduction in support oxide materials, it was suggested that the self-migration of lattice oxygen inside the support regulated by the balance between the oxide ionic and electronic conductivities played an important role to prevent from accumulating the deposited carbon over the catalysts. In addition, we demonstrated the methane conversion into synthesis gas at 1173 K with one component ceramics membrane reactor constructed with the same type of perovskite-type oxide for both the catalyst supported and mixed conductor.     

Materials design for perovskite SOFC cathodes

Abstract  

This article focuses on perovskite materials for application as cathode material in solid oxide fuel cells. In order to develop new promising materials it is helpful to classify already known perovskite materials according to their properties and to identify certain tendencies. Thereby, composition-dependent structural data and materials properties are considered. Structural data under consideration are the Goldschmidt tolerance factor, which describes the stability of perovskites with respect to other structures, and the critical radius and lattice free volume, which are used as geometrical measures of ionic conductivity. These calculations are based on the ionic radii of the constituent ions and their applicability is discussed. A potential map of perovskites as a tool to classify simple ABO₃ perovskite materials according to their electrical conduction behavior is critically reviewed as a structured approach to the search for new cathode materials based on more complex perovskites with A and/or B-site substitutions. This article also covers the approaches used to influence electronic and the ionic conductivity. The advantage of mixed ionic electronic conductors in terms of the oxygen exchange reaction is addressed and their important properties, namely the oxygen-exchange coefficient and the oxygen diffusion coefficient, and their effect on the oxygen reduction reaction are presented.     

Materials design for perovskite SOFC cathodes

Abstract  This article focuses on perovskite materials for application as cathode material in solid oxide fuel cells. In order to develop new promising materials it is helpful to classify already known perovskite materials according to their properties and to identify certain tendencies. Thereby, composition-dependent structural data and materials properties are considered. Structural data under consideration are the Goldschmidt tolerance factor, which describes the stability of perovskites with respect to other structures, and the critical radius and lattice free volume, which are used as geometrical measures of ionic conductivity. These calculations are based on the ionic radii of the constituent ions and their applicability is discussed. A potential map of perovskites as a tool to classify simple ABO₃ perovskite materials according to their electrical conduction behavior is critically reviewed as a structured approach to the search for new cathode materials based on more complex perovskites with A and/or B-site substitutions. This article also covers the approaches used to influence electronic and the ionic conductivity. The advantage of mixed ionic electronic conductors in terms of the oxygen exchange reaction is addressed and their important properties, namely the oxygen-exchange coefficient and the oxygen diffusion coefficient, and their effect on the oxygen reduction reaction are presented. Graphical abstract        

A concerted migration mechanism of mixed oxide ion and electron conduction in reduced ceria studied by first-principles density functional theory

Ceria based oxides are regarded as key oxide materials for energy and environmental applications, such as solid oxide fuel cells, oxygen permeation membranes, fuel cell electrodes, oxygen storage, or heterogeneous catalysis. This great versatility in applications is rendered possible by the fact that rare earth-doped ceria is a pure oxygen ion conductor while undoped ceria, CeO(2-δ), is a mixed oxygen ion-electron conductor. To get deeper insight into the mixed conduction mechanism of oxygen ions and electrons from atomistic and electronic level viewpoints we have applied first-principles density functional theory (DFT + U method). The calculation results show that oxygen vacancies strongly attract localized electrons, forming associates between them. The migration energy of an oxygen vacancy in such an associate is substantially lowered compared to the unassociated case due to the simultaneous positional rearrangement of localized electrons during the ionic jump process. Accordingly, we propose a concerted migration mechanism of oxygen vacancies and localized electrons in reduced ceria; this mechanism results in an increased diffusivity of oxygen vacancies supported by localized electrons compared with that in pure oxide ion conductors.     

Electrical conductivity of CaMoO4

The electrical conductivity and ionic transport number of CaMoO₄ has been measured as a function of the partial pressure of oxygen (1–10^?18 atm) at 750, 800, and 850°C. Two sets of samples were studied: (1) CaMoO₄ annealed at 1100°C in the presence of CaO, and (2) CaMoO₄ annealed in MoO₃ vapor at 1100°C. Sample 1 is a mixed ionic/electronic conductor while Sample 2 is essentially an electronic conductor. A defect structure model is proposed to explain the results.     

BaCe0.9Y0.1O3-α固体电解质的离子导电性

用交流复阴抗谱法测定了混合离子(质子+氧离子)导电性固体电解质BaCe0.9Y0.1O3-α在600～1000℃下不同气氛(干燥空气、湿润空气及湿润氢气)中的电导率;通过测定总电导率(离子电导率+电子电导率)随气氛中氧分压po2变化,求得离子电导率和离子迁移数;用氢浓差电池方法测得氢气中的质子迁移数。结果表明,BaCe0.9Y0.1O3-α固体电解质在氧分压<10Pa的气氛(如氢气)中几乎为纯离子导体,而在氧分压为10～10^5Pa的气氛(如空气)中为离子和电子空穴混合导体;样品在各气氛中的离子电导率均高于10^-2S·cm^-1。     

Partial Oxidation of Methane into Syngas with Oxygen Permeating Ceramic Membrane Reactors

Partial oxidation of methane (CH₄ +1/2O₂ CO + 2H₂) is considered as an alternative reforming reaction to steam reforming for production of syngas. This reaction is a slightly exothermic reaction and produces syngas of H₂/CO = 2, which is suitable for the synthesis of hydrocarbon or methanol. In this paper, the catalytic partial oxidation of CH₄ with a membrane reactor using oxygen permeating ceramic, in particular, LaGaO₃-based oxide, is reported. Supported Ni or Rh catalysts are active and selective for this reaction. On the other hand, a mixed ionic and electronic conducting (MIEC) ceramic membrane is useful for obtaining pure oxygen from air when the gradient in oxygen partial pressure is obtained. As for a MIEC membrane, mixed electronic–oxide ionic conductors of Fe- or Co-based perovskite oxides are widely investigated. However, the improvement in stability in a reducing atmosphere is critically required for the MIEC membrane for the application to the membrane reactor for CH₄ partial oxidation. Perovskite oxides of LaGaO₃ doped with Sr for a La site and a Fe, Co, or Ni for a Ga site, respectively, are promising as the oxygen-separating membrane for CH₄ partial oxidation because of high stability in a reducing atmosphere as well as high permeability of oxygen. The partial oxidation of CH₄ with solid oxide fuel cells (SOFCs) is also described. Simultaneous generation of electrical power and syngas is demonstrated by the fabricated fuel cell type reactor using a LaGaO₃-based oxide electrolyte.     

BaCe0.8Ho0.2O3-a陶瓷的性质与应用

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.     

Coupled Electrical Conduction in Coordination Polymers: From Electrons/Ions to Mixed Charge Carriers

The coupled transport of ions and electrons is of great potential for next‐generation sensors, energy storage and conversion devices, optoelectronics, etc. Coordination polymers (CPs) intrinsically have both transport pathways for electrons and ions, however, the practical conductivities are usually low. In recent years, significant advances have been made in electronic or ionic conductive coordination polymers, which also results in progress in mixed ionic‐electronic conductive coordination polymers. Here we start from electronic and ionic conductive CPs to mixed ionic‐electronic conductive CPs. Recent advances in the design of mixed ionic‐electronic conductive CPs are summarized. In addition, devices based on mixed conduction are selected.     

Properties of oxygen permeation and partial oxidation of methane in La0.6Sr0.4CoO3−δ (LSC)–La0.7Sr0.3Ga0.6Fe0.4O3−δ (LSGF) membrane

The oxygen separation membrane having perovskite structure for the partial oxidation of methane to synthesis gas was prepared. La_0.7Sr_0.3Ga_0.6Fe_0.4O_3−δ (LSGF) perovskite membrane coated with La_0.6Sr_0.4CoO_3−δ (LSC) (M1), and the one side of M1 membrane coated with NiO (M2) was prepared to examine the partial oxidation of methane. The single oxygen permeations of the LSC + LSGF (M1) membrane and NiO coated membrane (M2) were measured. The oxygen permeation flux in M1 membrane was higher than that of M1 membrane at 850 °C.

The partial oxidation experiment of methane using the prepared membranes was examined at 850 °C. The value of CH₄ conversion and CO selectivity of M2 membrane was higher than that of M1 membrane.

NiO/NiAl₂O₄ catalyst was used to improve the methane conversion, and the partial oxidation experiment of methane with M1 membrane was examined at 850 °C. The CH₄ conversion was 88%, and CO selectivity was 100%.