固-溶法制备中温固体氧化物燃料电池高性能La0.8Sr0.2MnO3-Ba0.5Sr0.5Co0.8Fe0.2O3阴极

研究了新型固溶法合成La_0.8Sr_0.2MnO₃（LSM）包覆Ba_0.5Sr_0.5Co_0.8Fe_0.2O₃（BSCF）复合粉体（LSM-BSCF）,并探讨了其作为中温固体氧化物燃料电池阴极材料的电化学性能。LSM-BSCF阴极结合了LSM和BSCF阴极的优点,不仅增大了三相界面,而且稳定了微观结构。当温度为600-750℃时,其极化阻抗为0.61-0.09 Ω·cm²。与溶液注入法制备的高性能电极相比,极大地提高了性能稳定性。     

La0.6Sr1.4MnO4 layered perovskite anode material for intermediate temperature solid oxide fuel cells

La_0.6Sr_1.4MnO₄ (LSMO₄) layered perovskite with K₂NiF₄ structure was prepared and evaluated as anode material for La_0.8Sr_0.2Ga_0.83Mg_0.17O_3 − δ (LSGM) electrolyte supported intermediate temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction results show that LSMO₄ is redox stability. Thermal expansion coefficient of LSMO₄ is close to that of LSGM electrolyte. By adopting LSMO₄ as anode and La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF) as cathode, maxium power densities of 146.6, 110.9 mW cm^− 2 with H₂ fuel at 850, 800 °C and 47.3 mW cm^− 2 with CH₄ fuel at 800 °C were obtained, respectively. Further, the cell demonstrated a reasonably stable performance under 180 mA cm^− 2 for over 40 h with H₂ fuel at 800 °C.     

有机燃料对合成大比表面积La0．8Sr0．2CoO3性能的影响

采用溶液燃烧合成法(solution com bustion synthesis,简称SCS)制备了La0.8Sr0.2CoO3钙钛矿复合氧化物,考察了丙氨酸、氨基乙酸和丙三醇等有机燃料对催化剂结构和CH4催化燃烧活性的影响,并运用XRD、FI-TR、BET、TPR等技术进行了表征。结果表明,不同有机燃料所制La0.8Sr0.2CoO3复合氧化物均具有较大比表面积,有机燃料对催化剂的结构和性能有较大的影响,其中以丙氨酸有机燃料制备的复合氧化物活性最好,其T50和T100分别为470℃和550℃。该法所制La0.8Sr0.2CoO3复合氧化物的平均晶粒度较小,比表面积和晶格畸变率较大,表面和氧空穴处的化学吸附氧较易移动,表观活化能较低。     

低浓度甲烷甲醇深度氧化Ag/La0.6Sr0.4MnO3催化剂

Ag-modified La0.6Sr0.4MnO3 catalysts were prepared and their catalytic performance for deep oxidation of CH4 and CH3OH at low concentrations were investigated. The results showed that the La0.6Sr0.4MnO3 host catalyst with the perovskite-type nano-crystallite structure displayed considerably high catalytic activity for deep oxidation of CH4 and CH3OH at low concentrations. Ag modification to the La0.6Sr0.4MnO3 host catalyst resulted in significant enhancement of the catalyst activity, making the T95 (the reaction temperature needed for conversion of 95%of CH4 or CH3OH) lowered down to 735K (for CH4) and 421K (for CH3OH) from 813 and 465 K over the Ag-free system under the reaction conditions:0.1MPa,CH4/O2/N2=2/12/86(molar ratio),GHSV=45000 h-1 and CH3OH/O2/N2= 0.2/1.0/98.8 (molar ratio),GHSV=58000 h-1,respectively.The carbon containing product was almost CO2 and the contents of HCHO and CO in the reaction exit gas were both under GC detectable limit in both cases.
The results of spectroscopic characterization indicated that modification by proper amount of Ag-dopant did not change the perovskite structure of the La0.6Sr0.4MnO3 host catalyst as a whole. Interaction of Ag-dopant with the surface of the host catalyst,La0.6Sr0.4MnO3,was in favor of high dispersion of the Ag component at the catalyst surface and led to the oxidation of part of the Mn3+species to Mn4+,resulting in an increase of amounts of the reducible Mnn+ species and a decrease of their reduction temperature. On the other hand, this interaction led also to enhancement of adsorption ability of the catalyst toward O2 at relatively low temperature. High activity of the Ag modified La0.6Sr0.4MnO3 catalyst for CH4 and CH3OH complete oxidation was closely related to high redox-activity of the catalyst and its prominent adsorption-activation ability to O2 at relatively low temperatures.     

负载型La0.8Sr0.2MnO3燃烧催化剂的载体效应

Combustion catalysts La0.8Sr0.2MnO3 supported on γ-Al2O3, α-Al2O3, cordierite (2MgO•2Al2O3•5SiO2) and ZrO2 were compared. Further investigation was focused on LSM/ γ-Al2O3 catalyst. It was observed that LSM/γ－Al2O3 catalyst loaded with 20% (mass fraction) LSM (La0.8Sr0.2MnO3 or corresponding oxides), heated at 750℃ or above, perovskite-type oxides were found by XRD examination, whereas, the same catalyst loaded with 10% or less LSM, perovskite oxides were absent, calcination temperature about 750℃ is necessary for the formation of perovskite structure in LSM/γ-Al2O3 catalysts. High activity of complete oxidation of xylen will be obtained when perovskite-type oxides.
Investigation of TPR showed that neat LSM or LSM/γ-Al2O3(20%) was reduced by H2-N2 mixed gas. Two degradation processes took place. In the first, reduced temperature peak was about 350 - 450℃. If reduction ended at 400℃, perovskite structure was retained, which may be due to the reduction of Mn3+to Mn2+ on the surface of LSM only. In the second process, perovskite structure was destroied, and La2O3, Mn2O3, Mn - Sr - O oxides could be obtained, which took place in the temperature range 685 - 750℃ and ended at 800℃. This was proved by TPR experiments (Fig. 3, 5) and XRD patterns (Fig. 4)
Catalysts LSM/γ-Al2O3(10% or 20%) heated at 500℃ have only one TPR peak, i. e. lower temperature peak. This is due to the absence of perovskite-type oxides in the catalysts. However, neat LSM or LSM/γ-Al2O3(20%) heated 750℃ or above, not only the first low temperature TPR peak but also the second peak, which is contributed by the perovskite-type oxides in these catalysts appeared. Therefore, the second TPR peak, i. e. the higher temperatue peak is a characteristic peak for perovskite-type oxides in the reduced process. When LSM/ γ-Al2O3 (10%) catalys is heated at 750℃, no perovskite-type oxides were detected by XRD, and the second reduction peak was absent also in TPR process. \
The order of the second reduction peak temperature(characteristic peak of perovskite - type ox- ides) is: neat LSM(750℃）> LSM/γ-Al2O3 20% (685-698℃) -deposited LSM/γ-Al2O3 (698℃) > LSM/γ-Al2O3 15% (677 - 680℃) >(LSM/γ-AL2O3 10% 620 - 630℃, for Mn - Al - O medium oxides on surface). It is correleted with the increasing of the effect of support sequentially.
When LSM/γ-Al2O3 catalysts were heated at 900℃, more stable phase, spinel MnAl2O4 appeared, which could be proved by TPR of model catalyst MnAl2O4/γ-Al2O3.     

负载型钙钛矿La0.8Sr0.2MnO3/SBA-15催化燃烧甲苯的研究

采用逐层负载-孔道内氨/水蒸气原位羟化法制备了一系列负载型钙钛矿La_0.8Sr_0.2MnO₃/SBA-15催化剂,用XRD、BET、TG-DTG、XPS、H₂-TPR等手段对催化剂的物性结构等进行了表征,并在常压连续流动固定床反应器上评价了该催化剂对甲苯催化燃烧的催化性能。结果表明,逐层负载-孔道内氨/水蒸气原位羟化法的使用有助于活性组分La_0.8Sr_0.2MnO₃进入SBA-15的孔道,并在SBA-15上形成钙钛矿结构。La_0.8Sr_0.2MnO₃/SBA-15上钙钛矿结构的形成和晶格氧的出现,可为催化剂提供较多的活性中心,有利于其催化燃烧甲苯的活性。     

Kinetic study of methane oxidation over perovskite oxides La1?xSrxCoO3

Methane oxidation over perovskite oxide (La_1−xSr_xCoO₃) were investigated under rich oxygen circumstance. The large x in oxide or the higher temperature will promote the lattice oxygen to participate in the reaction. The relative adsorption properties of catalyst and reaction kinetic were also studied.     

Comparative study of LaNiO3 and La2NiO4 catalysts for partial oxidation of methane

The catalytic activity and stability of LaNiO₃ and La₂NiO₄, prepared using a citric acid complex method, have been investigated for partial oxidation of methane (POM) to synthesis gas. The catalysts were characterized by thermo-gravimetric analysis (TG), temperature-programmed reduction (TPR) and temperature-programmed desorption of ammonia (NH₃-TPD). The results show that the catalytic activity and stability of La₂NiO₄ are higher than those of LaNiO₃, due to the stronger interactions between Ni and La₂O₃ in La₂NiO₄ and to its lower acidity as demonstrated by TPR and NH₃-TPD. TG result indicates that carbon deposition occurs on both catalysts, and the carbon species deposited on La₂NiO₄ are mainly metal carbides, while on LaNiO₃ are mainly graphite.     

The chemical and dielectric properties of epoxy/(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 composites for embedded capacitor application

The characteristics of epoxy/(Ba_0.8Sr_0.2)(Ti_0.9Zr_0.1)O₃ (BSTZ) composites are investigated for the further application in embedded capacitor device. The effects of BSTZ ceramic powder filler ratio on the chemical, physical and dielectric properties of epoxy/BSTZ composites are studied. Differential scanning calorimeter (DSC) thermal analysis is conducted to determine the optimum values of hardener agent, curing temperature, reaction heat, and glass transition temperature (T_g). The hardener reaction process starts at about 115 °C and completes at about 200 °C, for that it is appropriate to process of epoxy/BSTZ composites in the range of temperature. The highest glass transition temperature (T_g) of 155 °C is obtained at one equivalent weight ratio (hardener/epoxy). Only the BSTZ phase can be detected in the XRD patterns of epoxy/BSTZ composites. The more BSTZ ceramic powder is mixed with epoxy, the higher crystalline intensity of tetragonal BSTZ phase are revealed in the XRD patterns. The dielectric constant measured at 1 MHz increases from 5.8 to 23.6 as the content of BSTZ ceramic powder in the epoxy/BSTZ composites increases from 10 to 70 wt%. The loss tangents of the epoxy/BSTZ composites slightly increase with the increase of measurement frequency.     

High performance protonic ceramic membrane fuel cells (PCMFCs) with Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite cathode

Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. BaZr_0.1Ce_0.7Y_0.2O_3−δ (BZCY7) electrolyte based PCMFCs with stable Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) perovskite cathode were investigated. Using thin membrane BZCY7 electrolyte (about 15 μm in thickness) synthesized by a modified Pechini method on NiO-BZCY7 anode support, PCMFCs were assembled and tested by selecting stable BSZF perovskite cathode. An open-circuit potential of 1.015 V, a maximum power density of 486 mW cm⁻², and a low polarization resistance of the electrodes of 0.08 Ω cm² was achieved at 700 °C. The results have indicated that BZCY7 proton-conducting electrolyte with BSZF cathode is a promising material system for the next generation solid oxide fuel cells.     

Structure and properties of a novel cobaltate La0.30CoO2

The layered cobaltate La_0.30CoO₂ was prepared from Na_xCoO₂ precursor by a solid-state ionic exchange and was characterized by means of X-ray and neutron diffraction, magnetic, thermal and electric transport measurements. The compound consists of hexagonal sheets of edge-sharing CoO₆ octahedra interleaved by lanthanum monolayers. Compared to Na⁺ in the parent system, the La³⁺ ions occupy only one-third of available sites, forming a 2-dimensional superstructure. The deviation from the ideal stoichiometry La_1/3CoO₂ introduces extra hole carriers into the diamagnetic LS Co³⁺ matrix making the sample Pauli paramagnetic. The temperature dependence of the electrical conductivity in La_0.30CoO₂ follows Mott's T^−1/3 law up to about 400 K, which is in contrast with the standard metallic behavior in the Na⁺ homolog possessing the same formal doping. The experiments are complemented by electronic structure calculations for La_0.30CoO₂ and related Na_xCoO₂ systems.     

Sol-gel synthesized semiconducting LaCo0.8Fe0.2O3-based powder for thick film NH3 gas sensor

Perovskite type LaCo_xFe_1−xO₃ nanoparticles was synthesized by a sol-gel citrate method. The structural, electrical and sensing characteristics of the LaCo_xFe_1−xO₃ system were investigated. The structural characteristics were performed by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) to examine the phase and morphology of the resultant powder. The XRD pattern shows nanocrystalline solid solution of LaCo_xFe_1−xO₃ with perovskite phase. Electrical properties of synthesized nanoparticles are studied by DC conductivity measurement. The sensor shows high response towards ammonia gas in spite of other reducing gases when x = 0.8. The effect of 0.3 wt.% Pd-doped LaCo_0.8Fe_0.2O₃ on the response and a recovery time was also addressed.     

异质双碳源对LiMn0.8Fe0.2PO4复合材料电化学性能的影响

采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn_0.8Fe_0.2PO₄/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn_0.8Fe_0.2PO₄/C复合材料进行了X射线衍射(XRD)、比表面积测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g^-1,达到其理论比容量的 87%;在 5C 下最大的放电比容量为 133 mAh·g^-1;在 2C 倍率下经过 300 次循环后比容量维持在 127 mAh·g^-1,衰减率仅为1.9%,表现出了优良的循环稳定性。     

异质双碳源对LiMn0.8Fe0.2PO4复合材料电化学性能的影响

采用水基流变相辅助的固相法,以异质碳蔗糖和石墨为碳源,合成了LiMn_0.8Fe_0.2PO₄/C复合材料,研究了不同石墨加入方式对所制复合材料电化学性能的影响,并对所制备的LiMn_0.8Fe_0.2PO₄/C复合材料进行了X射线衍射(XRD)、N₂吸附-脱附测试、扫描电子显微镜(SEM)、透射电子显微镜(TEM)等表征。结果表明,不同石墨包覆工艺对材料结构和电化学性能具有显著影响。前驱体煅烧后再加入石墨获得的样品纯度高,形貌呈均一的椭圆形,在0.1C下的放电比容量为149 mAh·g^-1,达到其理论比容量的87%;在5C下最大的放电比容量为133 mAh·g^-1;在2C倍率下经过300次循环后比容量维持在127 mAh·g^-1,衰减率仅为1.9%,表现出了优良的循环稳定性。     

阴极材料LaFe0.8-xCuxNi0.2O3的合成和烧结性能

LaFe_0.8-xCu_xNi_0.2O₃ (x=0.0~0.2) (LFCN), a new cathode material of solid oxide fuel cell (SOFC), was synthesized by Co-precipitation method using sodium bicarbonate. The lattice structures of samples with different x contents were characterized by XRD. Porosity and density of the porous LaFe_0.8-xCu_xNi_0.2O₃ (x=0.0~0.1) as a function of sintering temperature were investigated. It was found that the orthorhombic structure could be formed after calcination at 900 ℃ for 4 h. The particle size of LFCN was about 350 nm. The density of the porous LFCN increased with sintering temperature, but the opposite was true for the porosity. On the other hand, at the same sintering temperature, the porosity of LaFe_0.8-xCu_xNi_0.2O₃ (x=0.0~0.1) decreased with increasing x contents. It is indicated that the dopant of Cu on LaFe_0.8Ni_0.2O₃ can facilitate the sintering of the materials. After sintering at 1 100 ℃ for 4 h, the porous LaFe_0.7Cu_0.1Ni_0.2O₃ was still with appropriate structure, and its porosity was 29%.     

梯度材料LiNi0.8Co0.2O2的合成与表征

The gradient composite LiNi_0.8Co_0.2O₂ was synthesized using spherical Ni(OH)₂ particle coated by a sol-gel containing cobalt and lithium. The precursor was examined by DSC-TG. The gradient composite was characterized by SEM, EDS, XPS, XRD and ICP-AES. The XPS, EDS and ICP-AES results show that content of cobalt in the surface is higher than in the center of the spherical particle of the gradient composite. The first discharge specific capacity of the gradient composite sintered at 700 ℃ is 187.3 mAh·g^-1.     

La_(1.6)Sr_(0.4)NiO_4-Ag中空纳米纤维的制备与电化学性质研究

采用静电纺丝法制备了La1.6Sr0.4NiO4-Ag中空纳米纤维。利用XRD和SEM对材料物相及形貌进行分析。结果表明,800℃烧结2 h形成平均直径为400 nm的La1.6Sr0.4NiO4-Ag复合空心纤维;850℃烧结1 h,纤维交叉连接形成网格状结构,并与电解质紧密接触。EIS谱测试结果表明,La1.6Sr0.4NiO4-Ag纳米纤维电极在700℃空气气氛的极化电阻为0.32Ω·cm2;氧分压测试结果显示,在600~700℃范围内,电极反应速率控制步骤均为电荷转移反应。     

La1.6Sr0.4NiO4-Ag中空纳米纤维的制备与电化学性质研究

采用静电纺丝法制备了La_1.6Sr_0.4NiO₄-Ag中空纳米纤维。利用XRD和SEM对材料物相及形貌进行分析。结果表明,800℃烧结2h形成平均直径为400nm的La_1.6Sr_0.4NiO₄-Ag复合空心纤维;850℃烧结1h,纤维交叉连接形成网格状结构,并与电解质紧密接触。EIS谱测试结果表明,La_1.6Sr_0.4NiO₄-Ag纳米纤维电极在700℃空气气氛的极化电阻为0.32Ω·cm²;氧分压测试结果显示,在600~700℃范围内,电极反应速率控制步骤均为电荷转移反应。     

LiNi0.8Co0.2O2 / MWNTs复合物超级电容器电极材料的研究

Multiwalled carbon nanotubes (MWNTs) were used as the conductive additive in the electrode materials. The electrochemical properties of supercapacitors based on LiNi_0.8Co_0.2O₂ / MWNTs composite and LiNi_0.8Co_0.2O₂/acetylene black composite and MWNTs in 1.0 mol·L^-1 LiClO₄ / EC+DEC [V(EC)∶V(DEC)=1∶1] electrolyte were investigated by means of constant charge/discharge current tests, respectively. The experimental results show that the LiNi_0.8Co_0.2O₂ / MWNTs composite has better performance than that of others, and the maximum specific capacitance of the supercapacitor can reach 271.6 F·g^-1, while the energy density is up to 339.5 Wh·kg^-1. Furthermore, it is remarkable that the performance of MWNTs is better than that of acetylene black as the conductive additive.     

Application of principal component analysis to gas sensing characteristics of Cr0.8Fe0.2NbO4 thick film array

The transient changes in resistances of Cr_0.8Fe_0.2NbO₄ thick film sensors towards specified concentrations of H₂, NH₃, acetonitrile, acetone, alcohol, cyclohexane and petroleum gas at different operating temperatures were recorded. The analyte-specific characteristics such as slopes of the response and retrace curves, area under the curve and sensitivity deduced from the transient curve of the respective analyte gas have been used to construct a data matrix. Principal component analysis (PCA) was applied to this data and the score plot was obtained. Distinguishing one reducing gas from the other is demonstrated based on this approach, which otherwise is not possible by measuring relative changes in conductivity. This methodology is extended for three Cr_0.8Fe_0.2NbO₄ thick film sensor array operated at different temperatures.