Influence of Atmospheric Plasma-Sprayed Composite Cathode on the Performance of Solid Oxide Fuel Cells

Ni-Al2O3 cermet supported tubular solid oxide fuel cells(SOFCs)with different cathodes were fabricated by thermal spraying.The anode,electrolyte and cathode were deposited by atmospheric plasma spraying(APS)aimed at reducing the manufacturing cost of SOFCs.Three porous composite cathodes of lanthanum strontium manganite(LSM)and yttria-stabilized zirconia(YSZ),lanthanum strontium cobalt oxide(LSC)and YSZ,LSC and scandia-stabilized zirconia(ScSZ)were prepared to investigate influence of cathode constitutions on the cell’s performance.The electrode polarization can be improved through using a composite cathode.The maximum power density of the cell with APS YSZ electrolyte and LSC/ScSZ composite cathode is increased about 12%than pure LSM cathode.The maximum output power density of the cell with APS ScSZ electrolyte and LSC/ScSZ composite cathode reaches 1.0 W/cm 2 at 1000 o C.The further optimization of the performance of plasma-sprayed composite cathode can be made through improving the interface contact between YSZ electrolyte and composite cathode.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1-x)La0.8Sr0.2MnO3/xYSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1-x)La0.8Sr0.2MnO3/xYSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm2) was the highest and that of the monolayer cathode (0.13 A/cm2) was the lowest. The polarization resistance (Rp) of the triple-layer graded composite cathode was only 0.182Ω·cm2 and that of the monolayer composite cathode was 0.323Ω·cm2. The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Fabrication and performance of La0.8Sr0.2MnO3/YSZ graded composite cathodes for SOFC

The performance of multi-layer (1 − x) La_0.8Sr_0.2MnO₃/x YSZ graded composite cathodes was studied as electrode materials for intermediate solid oxide fuel cells (SOFC). The thermal expansion coefficient, electrical conductivity, and electrochemical performance of multi-layer composite cathodes were investigated. The thermal expansion coefficient and electrical conductivity decreased with the increase in YSZ content. The (1 -x)La_0.8Sr_0.2MnO₃/x YSZ composite cathode greatly increased the length of the active triple phase boundary line (TPBL) among electrode, electrolyte, and gas phase, leading to a decrease in polarization resistance and an increase in polarization current density. The polarization current density of the triple-layer graded composite cathode (0.77 A/cm²) was the highest and that of the monolayer cathode (0.13 A/cm²) was the lowest. The polarization resistance (R_p) of the triple-layer graded composite cathode was only 0.182 ω·cm² and that of the monolayer composite cathode was 0.323 ω·cm². The power density of the triple-layer graded composite cathode was the highest and that of the monolayer composite cathode was the lowest. The triple-layer graded composite cathode had superior performance.     

Einfluß von Phasengrenzreaktionen bei der Oxidation von Metallen Untersuchungen zur Sulfidierung von Silber in Schwefeldampf

Influence of phase boundary reactions during metal oxidation. Investigation into the sulfidation of silver in sulphur vapour The present paper is concerned with theoretical and experimental investigations into the simultaneous influence of two phase boundary reactions on the kinetics of the sulfidation of silver in sulphur vapour. The two phase boundary reactions involved are

• a diffusion of silver through the phase boundary between solid silver and solid silver sulfide, and
• b absorption by silver sulfide of sulphur from the gas phase.

With either Phase boundary reaction there are inhibiting effects, i.e. there are deviations from the thermodynamical equilibrium at either phase boundary. The Phase boundary reactions can be studied independently from each other by electrochemical methods using silver iodide as a solid auxiliary electrolyte with practically pure ionic conductance. The particular reaction rates can be measured as functions of the chemical Potential of silver in silver sulfide. If the phase boundary reaction is known it is possible to calculate rates of sulfidation of silver in sulphur vapour. The calculated values are in good agreement with the values determined gravimetrically.     

氧化锆材料的掺杂机理探讨

氧化锆基陶瓷材料具有良好的物理性能和化学性能，在很多高新技术产业方面得到广泛的应用。但纯氧化锆与氧化锆陶瓷随温度的升高产生由单料→四方→立方的转变，这种相结构的变化导致性能不稳定，并伴随着体积发生变化使材料遭到破坏。作者综述了近年来对氧化锆掺杂稳定机理的研究，主要包括：低价阳离子掺杂机理，同价阳离子掺杂机理和多相掺杂机理。其中心思想认为空穴是影响氧化锆结构稳定性的最重要因素。并着重叙述了不同价态对结构稳定性的影响。     

先进陶瓷涂层结构调控及其在固体氧化物燃料电池中的应用

等离子喷涂技术可以对陶瓷涂层的微观结构进行调控设计,因此在制备固体氧化物燃料电池方面具有独特的优势。基于等离子喷涂方法,可以直接制备或经过后处理获得致密的电解质涂层。采用等离子喷涂技术也可以制备高性能的多孔阳极和阴极,并可对钙钛矿结构阴极材料的成分和晶体结构进行调控。文中介绍了目前国内外采用涂层制备电池的方法,主要探讨了热喷涂方法制备电解质涂层的特点,对存在的问题和可行思路进行了讨论,并探讨了基于提高三相反应界面长度来制备高性能电极的方法。由于固体氧化物燃料全电池各功能层都有可能通过热喷涂方法制备,因此该方法在固体氧化物燃料电池结构设计具有巨大的潜力。     

Microstructure and Electrochemical Behavior of a Structured Electrolyte/LSM-Cathode Interface Modified by Flame Spraying for Solid Oxide Fuel Cell Application

Plasma-sprayed yttria-stabilized zirconia (YSZ) can be potentially employed as electrolyte layers in solid oxide fuel cells (SOFCs). The formation of a structured electrolyte surface characterized by convex micro deposits generated by only partially molten particles at spraying will increase the specific surface area and subsequently improve the output performance of SOFCs. However, using completely molten YSZ particles during plasma spraying leads to the formation of locally flat surface. In this study, flame spraying was employed to deposit YSZ particles on YSZ substrate using surface-melted particles. The deposition was carried out at different spray distances on YSZ substrate preheated to 650 °C. The surface and cross-section morphology of YSZ particles were characterized by SEM. The electrochemical behavior of single cell with the structured cathode was characterized by the electrochemical impedance spectroscopy. The results show that spray distance exhibits significant influence on the morphology of deposited YSZ particles. The cathode polarization of a structured cathode was decreased by about 30-43% compared to a flat cathode at different temperatures.     

一种无污染脱氧方法

将脱氧剂装入氧离子传导的固体电解质ＺｒＯ２（ＭｇＯ）管中,并用高温电子导电材料封堵料口。利用固体电解质电池短路脱氧的原理。金属液中的氧在氧化锆管外表面获取电子转变为氧离子,并通过固体电解质进入氧化锆管。在内表面与脱氧剂结合生成脱氧产物,产生的自由电子通过电子导电材料传递到外表面与其积累的正电荷中知,从而消除了阻碍氧离子继续迁移的电场,使该过程能够持续下去,直至达到脱氧平衡。由于脱氧产物保留在氧化锆     

Small angle x-ray scattering studies of Cu-Cd alloys obtained using electrodeposition

Small angle X-ray scattering (SAXS) studies have been performed on Cu-Cd alloys obtained using electrodeposition from an ethylenediamine electrolyte in the cathode potential range from -500 mV to -800 mV. SAXS results confirm the existence of at least two phases in these alloys (a solid solution of cadmium in copper and a phase enriched in cadmium) and also indicate that the phase enriched in cadmium has a complex structure which is independent of cathode potential.     

Effect of Gas Pressure on Polarization of SOFC Cathode Prepared by Plasma Spray

A cermet-supported tubular SOFC was fabricated using thermal spray. The cell performance was investigated at temperatures from 750 to 900 °C and pressures from 0.1 to 0.5 MPa to examine the effect of operating gas pressure on the cell performance. The influence of gas pressure on the cathodic polarization was studied through the electrochemical impedance approach to examine the controlling electrochemical processes during cell operation. Results show that increasing the operating gas pressure improves the power output performance significantly. When the gas pressure is increased from 0.1 to 0.3 MPa, the maximum power density is increased by a factor of 32% at a temperature of 800 °C. The cathode polarization decreases significantly with the increase of the gas pressure. The electrochemical analysis shows that the main control processes of the cathode reaction are the oxygen species transfer at the three-phase boundary and oxygen diffusion on the surface or in the bulk of the cathode, which are enhanced with increasing gas pressure.     

Corrosion-inhibiting properties of red lead—I. Pigment suspensions in aqueous solutions

It has been shown by means of a potentiostatic technique that both the anodic and the cathodic behaviour of steel are inhibited in an aqueous red lead slurry with 0.1 M sodium perchlorate as supporting electrolyte. The oxygen reduction on the cathode takes place at a slower rate in the slurry than in the pure electrolyte solution. According to scanning electron microscopy with microprobe analysis and Guinier X-ray diffraction phase analysis, the layer formed on the cathode at about ?1100 mV consisted of metallic lead deposited from solute lead species. At more negative potentials and unidentified phase appeared.     

Current density limitation and diffusion boundary layer calculation using CFD method

The knowledge of limiting current density and thickness of diffusion boundary layer is particularly important in improving space-time-yield of electrolysis and especially of high current-density electrolysis. Both natural and forced convection of electrolyte flow are considered in the presented computational fluid dynamics model for calculation of these values. Natural convection is modeled by implementation of a source term at the cathode surface for copper concentration according to Faraday’s law, which allows calculation of electrolyte density for each volume cell of the grid. Forced convection is considered as flow of electrolyte through the cell generated by electrolyte inlet and outlet. By variation of current density, the limiting current density can be calculated with a copperion concentration of zero at the cathode surface after reaching the steady-state conditions in electrolyte. Time dependency of diffusion boundary layer thickness is shown for a chosen cell geometry. Literature data and measured and calculated values of both quantities are in good agreement.     

High-temperature grain boundary sliding behavior and grain boundary energy in cubic zirconia bicrystals

Misorientation dependence of grain boundary energy and grain boundary sliding at high temperature were examined in cubic zirconia bicrystals with [1 1 0] symmetric tilt boundaries, which were fabricated by diffusion bonding method from two cubic zirconia single crystals. High-resolution transmission electron microscopy observation revealed that the grain boundary in cubic zirconia bicrystals was clean and atomically sharp without any void or grain boundary amorphous layer. Grain boundary energy of the tilt boundaries was estimated from the dihedral angles on thermal grooved surface measured with atomic force microscope techniques. The misorientation dependence of the grain boundary energy in cubic zirconia bicrystals shows similar tendency to that of fcc metal such as aluminum and copper. Grain boundary sliding associated with intragranular dislocation slip in cubic zirconia bicrystals was observed for all specimens. The amount of the grain boundary sliding showed a good correlation with the misorientation factor of each boundary. Grain boundary migration also took place accompanying with the grain boundary sliding. The observed grain boundary sliding and migration can be explained based on a dislocation mechanism for sliding which is based on the movement of lattice dislocations along the grain boundary by a combination of climb and glide.     

基于渐变孔隙正极和叉指型流道主动式锂空气液流电池电化学性能理论研究

提出了具有渐变孔隙正极结构的主动式锂空气液流电池,利用溶液泵驱动电解液循环,结合渐变孔隙正极结构,强化电极内部Li^+和O2扩散和结合能力,减弱电极钝化。基于COMSOL Multiphysics 5.3,建立二维电化学模型,用Darcy定律、Butler-Volmer方程和组分输运公式描述在渐变孔隙正极结构(ε=0.55+αX等)下电极内部电解液流动、正负极电化学反应及电解液中Li^+和O2浓度场分布。由于Li2O2积聚在正极孔隙内,电极比表面积下降,采用Carman-Kozeny方程修正渗透率K。研究渐变孔隙率、压强差、氧气参数、正极厚度及动力学速率系数对该电池放电性能影响。结果表明:在放电电流密度0.1 mA/cm^2,电池比电容量是被动式结构的2.5倍;与ε=0.85-0.1X相比,采用ε=0.55+αX结构的电化学性能较佳;在放电电流密度0.1 mA/cm^2下,正极厚度为500^750μm,电池放电性能较好。     

固体电解质用于熔盐电解析氧过程的研究

将氧化物固体电解质制成析氧阳极,研究了在以析氧阳极和碳阴极构成的电解槽中氧化铝熔盐电解过程,测得分解电压约为1.67V,并定性地研究了固体电解质在冰晶石熔盐中的腐蚀问题,实验结果表明,电解条件下固体电解质管内外两表面间的电势差使固体电解质在冰晶石熔盐中存在溶解阻碍,有很好的耐腐蚀性能。     

A facile and environment-friendly method to fabricate thin electrolyte films for solid oxide fuel cells

A facile and environment-friendly method, the so-called vertical deposition (abbreviated as VD) method, is used to prepare thin yttria-stabilized zirconia (YSZ) films (≤5 μm) for solid oxide fuel cells (SOFCs). The YSZ films are self-assembled by VD process based on capillary force. The influence of experimental conditions (e.g. concentration of YSZ dispersion, deposition times, and sintering procedure) on the morphology of the films produced and thereby on the performance of SOFC devices is investigated. The single cell utilizing a 5 μm dense YSZ film as solid electrolyte achieves a high open circuit voltage of 1.05 V which remains stable at 700 °C for 4 h. The peak power density is 0.4 W cm⁻² at 800 °C for the phase inversion anode-supported fuel cell composed of an YSZ electrolyte film of 5 μm thick. The VD method developed herein is promising for preparing ultra-thin electrolyte films for SOFCs.     

Sodium-beta alumina batteries: Status and challenges

This paper provides a review of materials and designs for sodium-beta alumina battery technology and discusses the challenges ahead for further technology improvement. Sodium-beta alumina batteries have been extensively developed in recent years and encouraging progress in performance and cycle life has been achieved. The battery is composed of an anode, typically molten sodium, and a cathode that can be molten sulfur (Na-S battery) or a transition metal halide incorporated with a liquid phase secondary electrolyte (e.g., ZEBRA battery). In most cases the electrolyte is a dense solid β″-Al₂O₃ sodium ion-conducting membrane. The issues prohibiting widespread commercialization of sodium-beta alumina technology are related to the materials and methods of manufacturing that impact cost, safety, and performance characteristics.     

Permeability and Microstructure of Suspension Plasma-Sprayed YSZ Electrolytes for SOFCs on Various Substrates

Yttria-stabilized zirconia electrolyte coatings for solid oxide fuel cells were deposited by suspension plasma spraying using a range of spray conditions and a variety of substrates, including finely structured porous stainless steel disks and cathode layers on stainless steel supports. Electrolyte permeability values and trends were found to be highly dependent on which substrate was used. The most gas-tight electrolyte coatings were those deposited directly on the porous metal disks. With this substrate, permeability was reduced by increasing the torch power and reducing the stand-off distance to produce dense coating microstructures. On the substrates with cathodes, electrolyte permeability was reduced by increasing the stand-off distance, which reduced the formation of segmentation cracks and regions of aligned and concentrated porosity. The formation mechanisms of the various permeability-related coating features are discussed and strategies for reducing permeability are presented. The dependences of electrolyte deposition efficiency and surface roughness on process conditions and substrate properties are also presented.     

Development of thermal spraying-sintering technology for solid oxide fuel cells

A thermal spraying-sintering process has been developed for an electrolyte and interconnect layer, which results in improved gas tightness, a thinner layer, and higher electric conductivity as required for solid oxide fuel cells (SOFCs). The process is characterized by the heat treatment of composition-controlled plasma-sprayed layers. For the electrolyte, the addition of MnO₂ to zirconia powder is effective for reducing the sintering temperature to obtain gas tightness and for suppressing the reaction between zirconia and air electrode material. An electrolyte layer of 60 μm thickness with sufficient gas tightness and high ionic conductivity was obtained by this process. For the interconnect, chromium-rich lanthanum chromite powder, La_0.8Ca_0.2Cr_1.10O₃, is optimum for both gas tightness and high electric conductivity of the layer. In addition, a single cell with a 60 μm electrolyte was successfully fabricated using the thermal spraying-sintering process. As a result of an operating test using O₂ and humidified H₂ at 1000°C, a power density of 0.73 W/cm² was obtained. It was demonstrated that the thermal spraying-sintering technology is effective for the fabrication of a thin gas tight layer for SOFCs.     

Suspension Plasma Spray and Performance Characterization of Half Cells with NiO/YSZ Anode and YSZ Electrolyte

The use of a liquid feedstock carrier in suspension plasma spray (SPS) permits injection of fine powders, providing the possibility of producing sprayed coatings that are both thin and dense and have fine microstructures. These characteristics make SPS an attractive process for depositing highly efficient electrodes and electrolytes for solid oxide fuel cell (SOFC) applications. In this study, NiO-yttria stabilized zirconia (YSZ) anode and YSZ electrolyte half cells were successfully deposited on porous Hastelloy X substrates by SPS. The NiO-YSZ anode deposition process was optimized by design of experiment. The YSZ electrolyte spray process was examined by changing one parameter at a time. The results from the design-of-experiment trials indicated that the porosity of the as-deposited coatings increased with an increase of suspension feed rate while it decreased with an increase of total plasma gas flow rate and standoff distance. The deposition rate increased with an increase of total plasma gas flow rate, suspension feed rate, and standoff distance. The microstructure examination by SEM showed that the NiO and YSZ phases were homogeneously distributed and that the YSZ phase had a lamellar structure. It was observed that the density of the YSZ electrolyte layer increased as input power of the plasma torch increased. Electrochemical characterization of the fabricated cells indicated that an open cell voltage of 0.989 V at 500 °C and a peak power of 0.610 W/cm² at 750 °C were reached.