Effect of Cathode and Anode Voltage on an Ion Sheath Thickness in a Magnetically Confined Diffusion Plasma

This article reports about the ion sheath thickness variation occurring in front of a negatively biased plate immersed in the target plasma region of a double plasma device. The target plasma is produced due to the local ionization of neutral gas by the high energetic electrons coming from the source region (main discharge region). It is observed that for an increase in cathode voltage (filament bias voltage) in the source region, the ion flux into the plate increases. As a result, the sheath at the plate contracts. Again, for an increase in source anode voltage (magnetic cage bias), the ion flux to the plate decreases. As a result, the sheath expands at the plate. The ion sheath formed at the separation grid of the device is found to expand for an increase in cathode voltage and it contracts for an increase in the anode voltage of the main discharge region. One important observation is that the applied anode bias can control the Bohm speed of the ions towards the separation grid. Furthermore, it is observed that the ion current collected by the separation grid is independent of changes in plasma density in the diffusion region but is highly dependent on the source plasma parameters. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Mathematical modeling of the operation of SOFC Nickel-cermet anodes

A surface diffusion–reaction model is developed and solved to describe the steady-state operation of Nickel-cermet anodes in solid oxide fuel cells. The model accounts for the migration (backspillover) and diffusion of oxygen ions from the solid electrolyte onto the nickel surface and the concomitant reaction with the fuel over a finite reaction zone extending from the three-phase boundaries onto the Ni–gas interface. The model is developed for various nickel particle geometries and is compared with existing anode model predictions for flat geometries. The performance of the anode, expressed by an anodic effectiveness factor, is found to depend on two dimensionless numbers, which contain all the operational and structural information of the anode. The model is validated with literature experimental data regarding the dependence of the anode performance on the fuel partial pressure and predicts correctly the observed deviation from linearity of the dependence of cell current on fuel partial pressure.     

Structural study and magnetoresistance effect of epitaxial La0.67Sr0.33MnO3–δ and Pr0.7Ca0.3MnO3−δ multilayer films

La_0.67Sr_0.33MnO_3−δ (LSMO) and Pr_0.7Ca_0.3MnO_3−δ (PCMO) multilayer epitaxial films, which were fabricated with different LSMO and PCMO layer thickness on LaAlO₃ single crystal substrates of (0 0 1) orientation by a direct current magnetron sputtering technique, were studied further, after the structure, magnetoresistance effect and magnetic properties of LSMO/PCMO/LSMO (LPL) trilayer epitaxial films were systemically studied. The superlattice structures of multilayer films were observed according to the diffraction peaks of X-ray diffraction patterns at small angles. The metal–insulator transition temperature (T_P) and peak resistivity (ρ_max) obviously changed when we altered the thickness of PCMO middle layer and the intra-field related with the thickness of those layers and their interaction. Considering the effect of the distribution of electrical field and current, and the interaction among the layers of LSMO and PCMO, an effective fact n* was introduced to replace n (the number of layer). All the calculated values of ρ (the resistivity of multilayer films) accorded with the experimental values.     

Carbon paste electrodes electrochemically modified with cyclodextrins

Cyclic voltammetry was used in order to obtain carbon paste electrodes (CPEs) modified with α- and β-cyclodextrins (CPE_α-CD, CPE_β-CD) in HClO₄ media as electrolyte. The modified CPEs were obtained by applying 30 potential cycles, thus forming on the substrate a film with electroactive characteristics; a rise in current for the anodic and cathodic peaks became apparent as the number of cycles increased. Such behaviour confirmed the CPE modification by the species mentioned. The CPE_α-CD and CPE_β-CD exhibited significant stability before various electrolytes. In order to evaluate the sort of modification attained on the CPEs, a study was conducted, varying the potential scan rate, that confirmed the CD's presence. The modified electrodes were used to determine Pb(II) ions in solution within the range from 1×10^–5 M up to 1×10^–3 M. The CPE_α-CD and CPE_β-CD electrochemical response was studied by means of anodic stripping voltammetry of the Pb(II) ions, thereby giving a linear relation between the current for the anodic peak as a function of Pb(II) concentration with r ²=0.996 for the CPE_β-CD and 0.992 for the CPE_α-CD. Electronic Publication     

LaxSr1-xMnO3氧化物的导电和吸收特性

对LaxSr1 -xMnO3氧化物的导电和吸收特性进行了研究。x =0 5时 ,其电阻率随着温度升高而上升 ,呈现金属导电特性 ,室温电阻率很低 ,为 3× 10 - 5Ω·cm。在 8～ 12GHz频率范围的微波电磁场中 ,它的吸收特性最佳 ,在涂层厚度 2 2 1mm时 ,吸收峰高 2 5dB ,峰宽 3GHz ,这是由于La0 .5Sr0 .5MnO3氧化物是一种铁磁材料 ,在上述频率范围内具有较大的磁损耗和介电损耗。     

稻壳制备锂离子电池炭材料的研究

本主要研究了炭化温度、升温速率以及碱处理浓度对稻壳制备锂离子电池负极材料结构及充放电性能的影响．通过差-热热重分析曲线(DT-TGA)、元素分析、X射线粉末衍射(XRD)以及电化学性能测试手段对材料进行了表征．结果表明：在最佳实验条件下，材料的首次充电容量为678mA h／g，首次放电容量为239mA h／g，循环10次的容量保持率为86．2％．     

Critical assessment of a new in situ spectroelectrochemical cell designed for the study of interfacial reactions between a porous graphite anode and alkyl carbonate solution

This article critically evaluates the characteristics of a new in situ spectroelectrochemical cell with an optimized path of the IR beam, designed in our laboratory for study of the solid electrolyte interphase (SEI) layer formed between a porous graphite anode and alkyl carbonate solution for lithium-ion batteries. The cell was designed in view of the optical principles underlying the way the in situ cell works, to give depth of penetration of the evanescent IR beam through the attenuated total internal reflectance crystal into the electrolyte at such a small value, ranging from 0.277 to 2.77 μm, that it was possible to minimize the "masking effect" of the ethylene carbonate/diethyl carbonate solvent. Moreover, the "local compositional change" which may arise significantly from the "thin layer electrolyte configuration" cell also could be fairly avoided, since only the electrolyte in the vicinity of the electrode composed of graphite particles is reduced to form the SEI layer to a thickness of at most 0.1 μm during the application of potentials. Thus, it was possible to measure the in situ FT-IR spectra in the cell, which represents the real chemical composition and structure of the SEI layer. Taking the application of the designed in situ cell as an example, this article reports the effect of salt type and electrolyte temperature on the chemical composition and structure of the SEI layer between graphite particles and alkyl carbonate solution with the help of various measured in situ FT-IR spectra. Electronic Publication     

锂离子电池锡基复合氧化物负极材料的研究

采用共沉淀法制备了SnSbO2.5和SnGeO3两种锡基复合氧化物粉末.XRD分析表明,这两种锡基复合氧化物的共同特点是在27°～28°处有波峰,属无定型结构.将其分别作为锂离子电池负极材料的活性物质,利用恒电流电池测试仪研究它们的电化学性能.实验表明,这两种锡基复合氧化物都有较高的电化学容量,SnSbO2.5的可逆容量为1200mA·h/g,SnGeO3的可逆容量为750mA·h/g.这两种锡基复合氧化物的电化学容量远高于碳材料(石墨的理论容量为372mA·h/g),因此,这两种锡基复合氧化物可以作为锂离子电池负极材料的候选材料.     

CoO填充多壁碳纳米管作为锂离子电池负极材料

碳纳米管自1990年被日本科学家Iijima发现以来[1],由于其独特的结构组成而具有良好的强度和弹性模量、高比表面积、良好的耐腐蚀性和导电性等特点受到了广泛的关注,并已在催化剂载体、纳米电子器件、储能材料、复合功能材料等诸多领域得到应用。多壁碳纳米管(MWCNT)是由多层石墨卷绕而成的同心圆筒,石墨层间距约为0.034nm,管径一般为几十纳米,管长可达数微米,因此多壁碳纳米管具有较高的长径比,可以被看作一维纳米线。由于多壁碳纳米管在管壁之间和管腔之中存在大量空间,为锂离子的嵌入提供了可能,因此近年来关于多壁碳纳米管储锂的研究…     

钙掺杂的氧化铈用于中温SOFCs阳极材料研究

作为一种混合的离子-电子导体材料,掺杂的氧化铈已逐渐被用来作为SOFCs阳极材料或其组成部分之一加以研究,但主要以稀土掺杂剂为主,为了进一步降低采用阳极支撑构型的SOFCs的成本,研究了钙掺杂的氧化铈(CCO)。结果表明,掺杂20%钙的材料(20CCO)的电导率最高,850℃时在氢气气氛下的电导率可以达到0.209S·cm-1,远大于在空气气氛中的电导率。800℃时在空气中的电导率为0.041S·cm-1,比同样温度下阳极中经常采用的钐掺杂的氧化铈(SDC)的电导率低了约0.04S·cm-1。但这并不影响单电池的输出性能,分别以Ni-20CCO作为阳极,Sm0.5Sr0.5Co-SDC作为阴极,SDC作为电解质(厚约35μm)的单电池在650℃,氢气气氛下的最大输出功率可以达到623mW·cm-2。