Performance improvement by metal deposition at the cathode active site in solid oxide fuel cells

In this study, the performance improvement of the SOFC single cell and its underlying mechanism was investigated. Furthermore, an application of the identified electrochemical mechanism is proposed and tested experimentally. The deposition of Platinum (Pt) at electrochemically active sites for the oxygen reduction reaction is determined to be responsible for the improved performance. Pt migration from a current collector to the cathode active sites originates from the oxygen partial pressure difference between current collector and triple phase boundary, and the electrochemical reduction reaction. It is supported by the confirmation of Pt particles at the cathode active sites by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and calculations of the thermodynamic equilibrium partial pressure values. In addition, correlation of the initial performance change and the quantities of Pt deposition are investigated. This selective Pt deposition mechanism at the active sites is applied to the LSCF cathode, as well.     

La-doped supported Ni catalysts for steam reforming of methane

Ni-La/α-Al₂O₃ catalysts at different Ni/La ratio of respectively 7/3, 8/2 and 9/1 to obtain a material with total loading of 10 wt% as used in industrial methane steam reforming field are prepared with incipient wetness impregnation method. Various techniques including TGA-DTA, XRF, XRD, particles size, H₂-RTP and BET are used to characterize materials and their catalytic performance is evaluated during the steam reforming reaction at different temperatures ranging from 500 to 800 °C. Only NiO and α-Al₂O₃ phases are evidenced by DRX indicating probably the presence of small lanthanum crystallites in high dispersion state. Addition of La may cause strong change at the surface of NiO sites. Substitute Ni by La leads to smaller and well dispersed NiO particles sizes with strong metal support interaction (SMSI). TPR analysis reveals the reduction of Ni species with high Ni-La-Al interactions particularly well observed with 3 wt%La catalyst. The small Ni particles sizes highly dispersed on the support enhance the dissociative adsorption of CH_x species. The highest H₂ yield is obtained with 7Ni-3La/Al catalyst reaching 94% at 800 °C.     

Low-temperature electrochemical characterization of dense ultra-thin lanthanum strontium cobalt ferrite (La0.6Sr0.4Co0.8Fe0.2O3) cathodes synthesized by RF-sputtering on nanoporous alumina-supported Y-doped zirconia membranes

Dense ultra-thin nanocrystalline La_0.6Sr_0.4Co_0.8Fe_0.2O₃ (LSCF) films with thickness of ∼50 nm, have been sputtered on nanoporous anodic alumina-supported nanocrystalline thin film yttria-stabilized zirconia and patterned by photolithography into microelectrodes. This approach enables low-temperature (425-550 °C) electrochemical properties of dense ultra-thin nanocrystalline LSCF to be characterized. The results reveal that the electrochemical resistance of nanocrystalline ultra-thin LSCF is dominated by the oxygen surface exchange reaction at the electrode surface with an activation energy of 1.1 eV. Area-specific resistance of LSCF was obtained and the results are of potential relevance to utilizing nanostructured oxide cathodes for micro-SOFCs operated at low temperatures.     

Activity of perovskite La1−xSrxMnO3 catalysts towards oxygen reduction in alkaline electrolytes

The behaviour of the perovskite-based series of compounds La_1−xSr_xMnO₃ (where x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) towards oxygen reduction in an ambient temperature alkaline 1 M KOH electrolyte is presented. Within this series, the intermediate compound La_0.4Sr_0.6MnO₃ exhibits the greatest catalytic activity, approaching that of the considerably more expensive fuel cell grade Pt-black examined under the same conditions. The origin of this activity is discussed in terms of material structure and morphology, which exists in the structural transition region between cubic LaMnO₃ and hexagonal SrMnO₃. The small crystallite size and relatively large BET surface area of this material reflect this high level of structural disorder. Furthermore, these features enable this compound to exhibit the greatest proportion of direct four-electron oxygen reduction (preferred) compared to the less efficient two-electron reduction to peroxide.     

Secondary ketonization of primary alcohol over LaMn-based mixed oxides with perovskite-like structure

LaMnO₃-based mixed oxides with perovskite-like structure both bulk and supported on La–Al₂O₃, show high catalytic activity in dehydrogenation of n-butanol to an aldehyde, which then undergoes a secondary reaction to produce a symmetrical ketone. Partial substitution of Cu, V or Sr into LaMnO₃ structure does not destroy the perovskite-like structure and enables to control the acid–base surface properties. It allows linking up these qualitative and quantitative features with activity and selectivity of these materials. The degree of n-butanol conversion depends on the total concentration of basic and acidic sites. Selectivity to butyraldehyde can be related with the share of basic sites. Selectivity to dipropyl ketone is affected both by the acidity and concentration of acidic sites. LaMnO₃/La–Al₂O₃ seems to posses an optimum set of surface characteristics for the examined ketonization of a primary alcohol.     

Models for the release from fuel of Ce, La, Sr, and Eu in accident conditions

During a hypothetical severe nuclear accident involving a pressurised water reactor, it is of primary importance to assess the potential radionuclide releases into the environment. With that view in mind, analytical models have been developed for the release kinetics from fuel of four low-volatile fission products (namely cerium, lanthanum, strontium, and europium) in severe accident conditions. The vaporisation of those fission products from fuel has been evaluated by means of thermodynamic equilibrium calculations. The effects of the fuel temperature and the oxygen potential on the chemical form and volatility of the fission products have been determined. Finally, these models have been integrated in the ASTEC and have been subsequently validated against annealing experiments with various oxidizing and reducing conditions.     

La2O3/LDPE复合材料非等温结晶性能研究

利用差示扫描量热仪(DSC)考察了氧化镧(La2O3)/低密度聚乙烯(LDPE)复合材料的非等温结晶行为。通过Jeziorny法、Ozawa法及莫志深法研究了复合材料的非等温结晶动力学。结果表明:在添加La2O3后,LDPE成核速率降低,结晶度下降,晶体粒径分布变宽。在非等温结晶动力学分析中,Jeziorny法lg[-ln(1-Xt)]～lgt关系曲线在结晶前期和中期具有较好的线性关系,结晶后期产生较大偏离;Ozawa法并不适用;而莫志深法适用于该体系的研究,表明La2O3的加入使LDPE结晶速率增大。     

Transport Behaviour of La~（3＋） with Flat－Sheet－Sandwich Supported Liquid Membrane Extraction System

ＴｒａｎｓｐｏｒｔＢｅｈａｖｉｏｕｒｏｆ Ｌａ~（３＋） ｗｉｔｈ Ｆｌａｔ－Ｓｈｅｅｔ－ＳａｎｄｗｉｃｈＳｕｐｐｏｒｔｅｄ ＬｉｑｕｉｄＭｅｍｂｒａｎｅＥｘｔｒａｃｔｉｏｎＳｙｓｔｅｍＹｉＴａｏ（易涛）；ＹａｎＣｈｕｎｈｕａ（严纯华）；ＬｉＢｉａｏｇｕ?..     

中子活化分析研究长期摄入氯化镧对大鼠脑中部分常量和微量元素含量的影响

利用中子活化分析技术,初步研究了长期从饮水中摄入不同剂量的稀土元素镧对大鼠脑中12种常量和微量元素含量的影响。结果发现,镧的剂量越高,实验大鼠脑组织中含量发生变化的元素种类越多。1000mg/L组大鼠脑组织中有5种元素的含量与对照组相比发生了明显改变,而且这些元素都与脑功能密切相关。因此,镧的摄入可能会对脑的功能产生不利影响。     

Rare Earth Complexes of Aminopolycarboxylic Acid Ⅱ.Synthesis and Structure of Lanthanum Complex of Dipicolinic Acid

Complexes of the general formula,(Me_4N)_2[(Ln(HDPA)_2(DPA)]·Cl,have been synthesized,whereLn=La,Ce,Pr,Nd,Sm and H_2DPA=dipicolinic acid.Among them,the crystal structure of the La complexhas been determined by a four-circle X-ray diffractometer to a final R value of 0.080.The crystal isorthorhombic,space group Pccn with a=1.0321(1),b=1.4951(2),c=2.0766(6)nm,V=3.2044(9)nm~3,andZ=4.The rare earth ion is nine coordinated to forming a tortuous tricapped trigonal prism.