SOFC单相氧化物MIEC阳极材料的研究进展

综述了近年来国内外固体氧化物燃料电池复合导电性能(MIEC)单相氧化物阳极材料的研究进展。阐述了钙钛矿结构、立方萤石结构以及其它诸如烧绿石结构的单相氧化物阳极材料的导电性能以及应用于电池阳极的发电性能。指出了阳极材料研究亟待解决的问题及发展方向。     

操作条件对固体氧化物燃料电池阳极反应转变的影响

研究了不同电流密度下,甲烷浓度、反应温度对甲烷在SOFC中反应由部分氧化到完全氧化转变的规律;测量了不同电流密度下,阳极出口气体产生速率;确定了甲烷浓度和电池反应温度变化时甲烷电化学反应由部分氧化转变为完全氧化的电流密度门槛值,及该门槛值与甲烷浓度、电池操作温度的变化关系.结果说明甲烷开始发生完全氧化的电流密度门槛值与甲烷浓度成正比;甲烷浓度一定,温度升高,甲烷开始发生完全氧化的电流密度的门槛值也随之提高.     

Scaling up aqueous processing of A-site deficient strontium titanate for SOFC anode supports

All ceramic anode supported half cells of technically relevant scale were fabricated in this study, using a novel strontium titanate anode material. The use of this material would be highly advantageous in solid oxide fuel cells due to its redox tolerance and resistance to coking and sulphur poisoning. Successful fabrication was possible through aqueous tape casting of both anode support and electrolyte layers and subsequent lamination. Screen printing of electrolyte layers onto green anode tapes was also attempted but resulted in cracked electrolyte layers upon firing. Microstructural, electrical and mechanical properties of anode supports and half cells will be discussed. The use of two different commercial titanate powders with nominal identical, but in reality different stoichiometries, strongly affect electrical and mechanical properties. Careful consideration of such variations between powder suppliers, and batches of the same supplier, is critical for the successful implementation of ceramic anode supported solid oxide fuel cells.     

Morphology and electrochemical activity of SOFC composite cathodes: I. experimental analysis

This paper describes the first part of an experimental and theoretical study performed on composite Lanthanum Strontium Manganite (LSM) and Yttria-stabilized Zirconia (YSZ) electrodes. Cathode electrocatalytic activity was investigated using different cell configurations and carrying out potentiodynamic polarisation and electrochemical impedance spectroscopy measurements (EIS). Measurements were carried out at different oxygen partial pressures, overpotentials, temperatures and electrode geometries. In order to identify the main steps involved in cathodic oxygen reduction, the NLLS-Fit procedure was used. The results for different cell geometries agree with each other, suggesting a transition in the overall reaction mechanism, from charge transfer to mass transfer control, at a critical temperature of about 750 °C. The experimental results also show a remarkable effect of electrode thickness on the overall reaction rate, throughout the temperature range tested. A grey level gradient along the thickness of the thicker electrodes were detected by analyzing microscopic images of the cells. These results, together with electrochemical measurements on cathodes with different thickness, confirm that morphology plays a key role in determining the performance of Solid Oxide Fuel Cells (SOFC) composite cathodes.     

A novel concept for improved thermal management of the planar SOFC

A new design for the solid oxide fuel cell (SOFC) planar stack is proposed to minimise the thermal gradients in the cell. This design involves including a secondary air channel with flow in the counter direction to the cathodic air channel. The effectiveness of the new design is tested by means of a tank in series reactor (TSR) model of the SOFC. It is found that the new design is capable of reducing the steady state temperature difference across the cell to less than 2 K over a range of voltages, while satisfying the requirements on fuel utilisation (FU) and cell average temperature. This is achieved by manipulating the primary air channel inlet flow rate and the secondary air channel inlet temperature. More modelling and experimental studies are required to further investigate the proposed design.     

Morphology and electrochemical activity of SOFC composite cathodes: II. Mathematical modelling

This paper presents a mathematical model of mass and charge transport and electrochemical reaction in porous composite cathodes for application in solid oxide fuel cells. The model describes a porous composite cathode as a continuum, and characterises charge and mass transfer and electrochemical kinetics using effective parameters (i.e. conductivity, diffusivity, exchange current) related to morphology and material properties by percolation theory. The model accounts for the distribution of morphological properties (i.e. porosity, tortuosity, density of contacts among particles) along cathode thickness, as experimentally observed on scanning electron microscope images of LSM/YSZ cathodes of varying thickness. This feature allows the model to reproduce the dependence of polarisation resistance on thickness, as determined by impedance spectroscopy on LSM/YSZ cathodes of varying thickness. Polarisation resistance in these cathodes is almost constant for thin cathodes (up to 10 μm thickness), it sharply decreases for intermediate thickness, to reach a minimum value for about 50 μm thickness, then it slightly increases in thicker cathodes.     

固体氧化物燃料电池阳极材料Sr_2Fe_(1.5)Mo_(0.5)O_6(SFM)/Sm_(0.2)Ce_(0.8)O_(1.9)(SDC)的研究

采用机械混合法合成了Sr2Fe1.5Mo0.5O6(SFM)和Sm0.2Ce0.8O1.9(SDC)质量比为7∶3的SFM/SDC复合材料。用X射线衍射(XRD)、扫描电镜(SEM)、H2-TPR、EIS等表征手段对其进行了表征,并以SFM/SDC|La0.8Sr0.2Ga0.83Mg0.17O3(LSGM)|Ba0.5Sr0.5Co0.8Fe0.2O3(BSCF)为单电池片进行电化学测试,对其性能进行评价。结果表明,复合材料取得了较好的放电性能,即以氢气为燃料气,850、800、750℃时分别取得了630.6、548.4、426 mW/cm2最大功率密度;以甲醇为燃料,850、800、750℃时分别取得了551.6、426.8、335.3 mW/cm2最大功率密度。     

Analysis of the oxygen reduction process on SOFC composite electrodes

The electrochemical characteristics of composite cathodes consisting of Lanthanum Strontium Manganite (LSM) and Yttria Stabilised Zirconia (YSZ) have been analysed in order to emphasise the opportunity offered by these electrodes in the attempt to reduce the temperature of solid oxide fuel cells. Impedance analysis and potentiodynamic polarisation have been used as tools to evaluate the main electrochemical parameters and the results show that a volume ratio between LSM and YSZ close to 1 gives the best electrochemical activity because of the extension of the three phase boundary (TPB) in the electrode. Electrodes of this composition were subjected to high current load to verify the stability of the electrochemical performance and the results confirmed good cathode reliability.     

固体氧化物燃料电池CuCoNi/SDC阳极微结构与电性能的研究

本论文采用溶胶-凝胶低温燃烧合成法制作CuxCo0.5-xNi0.5O1.75-0.5x固溶体阳极粉末,并将电解质粉末和阳极合金粉末按1:1的比例制作了CuCoNi/SDC阳极片。采用热重差热仪检测粉末的处理情况,采用x射线衍射仪(XRD)检测了粉末的成相情况。并且采用四端子法检测了不同组成阳极片的电导率值。分析了固体氧化物燃料电池CuCoNi/SDC阳极的显微结构。结果显示,用上述方法合成的粉体成相很好,阳极片的电导率和组成、温度有着极强的联系,氢气还原前后微结构有明显的变化。     

Combustion synthesis of SOFC materials in a continuous reactor

La_0.8Sr_0.2CrO₃ and LaMg_0.2Cr_0.8O₃ materials for use in solid oxide fuel cells (SOFCs) were synthesized in a continuous SHS reactor from powder mixtures of La₂O₃, MgO, SrCO₃, Cr₂O₃, and Cr. Based on XRD data, the degree of conversion was found to grow with increasing combustion temperature and burning velocity. SHS-produced powders were reground in a vibratory mill, pressed into cylindrical pellets (3–4 mm in height and 10 mm in diameter), and sintered. The required level of properties was attained for sintering temperatures above 1600°C. The article is published in the original.     

Modeling of transport, chemical and electrochemical phenomena in a cathode-supported SOFC

This paper investigates the performance of a planar cathode-supported solid oxide fuel cell (SOFC) with composite electrodes using a detailed numerical model. The methane reforming reaction is included in the model and takes place mostly in the porous, thin anode at the high operating temperature of 800-1000^°C. A single computational domain comprises the fuel and air channels and the electrodes-electrolyte assembly eliminating the need for internal boundary conditions. The equations governing transport and chemical and electrochemical processes for mass, momentum, chemical and charged species and energy are solved using Star-CD augmented by subroutines written in-house. The operating cell voltage is determined by the potential difference between the cathode and the anode, whose potentials are fixed. Results of temperature, chemical species, current density and electric potential distribution for a co-flow configuration are shown and discussed. It is found that the sub-cooling effect observed in anode-supported cells is almost ameliorated, making the cathode-supported cell favorable from the viewpoint of material stability.     

A study of thermal stability and methane tolerance of Cu-based SOFC anodes with electrodeposited Co

Cu-based, solid oxide fuel cell (SOFC) electrodes were modified by electrodeposition of Co. The addition of only 5 vol% Co by electrodeposition significantly improved the thermal stability compared to either Cu-ceria-YSZ, Cu-Co-ceria-YSZ, or Co-ceria-YSZ electrodes prepared only by impregnation with much higher metal loadings, demonstrating that electrodeposited metal layers form metal films with better connectivity. In the absence of Co, SEM showed structural changes in the impregnated Cu after heating to 1173 K in humidified H₂ and these changes caused large increases in the ohmic resistance of fuel cells, as measured by impedance spectroscopy. In contrast, the ohmic resistance of a cell with 13 vol% Cu, 9 vol% ceria, and 5 vol% Co increased only slightly after 48 h at 1173 K in humidified H₂. While a Co-ceria-YSZ composite was found to form large amounts of carbon upon exposure to dry CH₄ at 1073 K for 3 h, the Co-Cu-ceria-YSZ composites did not form measurable amounts of carbon for the same conditions. XPS results for a Cu foil with a 250-nm Co film demonstrated that Cu migrates to the surface of the Co upon heating above 873 K, forming a stable Cu layer that appears to be approximately one monolayer thick. The implication of these results for the development of practical SOFC electrodes for the direct utilization of hydrocarbons is discussed.     

Electrochemical characterization of perovskite-based SOFC cathodes

The electrochemical performance of La_0.58Sr_0.4Co_0.2Fe_0.8O_3-δ (L58SCF), La_0.78Sr_0.2Co_0.2Fe_0.8O_3-δ (L78SCF) and composite La_0.65Sr_0.3MnO_3-δ – 8 mol% Y₂O₃ stabilized ZrO₂ (LSM-YSZ, 50:50 wt%) cathode electrodes interfaced to a double-layer electrolyte made of Ce_0.8Gd_0.2O_2-δ (CGO) and YSZ was studied in the temperature range 600–850 °C using impedance spectroscopy and current-overpotential measurements. The experiments were carried out in a single chamber cell using a three electrode set-up with porous Pt films as auxiliary electrodes. The perovskite powders were synthesized using the spray-drying technique starting from nitrate precursors and were deposited on the solid electrolyte via screen-printing. Open circuit impedance measurements on as-prepared electrodes, i.e. before any polarization, and micropolarization measurements have shown that the L78SCF/CGO/YSZ electrode exhibits the lowest area specific polarization resistance R _F (R _F was approximately equal to 0.4 Ω cm² at 800 °C and = 21 kPa) or, equivalently, the highest electrocatalytic activity according to the order: LSM/LSM-YSZ/CGO/YSZ<L58SCF/CGO/YSZ<L78SCF/CGO/YSZ. Current-overpotential data taken over an extended cathodic overpotential (ohmic-drop-free) range (0 to −500 mV) also indicated the aforementioned order of electrocatalytic activity. The Nyquist plots corresponded to at least two overlapping arcs or, equivalently, to at least two rate limiting processes. The relative contribution and degree of overlap of these arcs depended on electrode material, temperature and oxygen partial pressure, the low frequency arc being in general dominant at low temperatures and low oxygen partial pressures. Open circuit impedance experiments carried out at different oxygen partial pressures (0.01–100 kPa) revealed an exponential increase of the open-circuit area specific polarization conductance with increasing .     

Alternative concept for SOFC with direct internal reforming operation: Benefits from inserting catalyst rod

Mathematical models of direct internal reforming solid oxide fuel cell (DIR‐SOFC) fueled by methane are developed using COMSOL® software. The benefits of inserting Ni‐catalyst rod in the middle of tubular‐SOFC are simulated and compared to conventional DIR‐SOFC. It reveals that DIR‐SOFC with inserted catalyst provides smoother temperature gradient along the system and gains higher power density and electrochemical efficiency with less carbon deposition. Sensitivity analyses are performed. By increasing inlet fuel flow rate, the temperature gradient and power density improve, but less electrical efficiency with higher carbon deposition is predicted. The feed with low inlet steam/carbon ratio enhances good system performances but also results in high potential for carbon formation; this gains great benefit of DIR‐SOFC with inserted catalyst because the rate of carbon deposition is remarkably low. Compared between counter‐ and co‐flow patterns, the latter provides smoother temperature distribution with higher efficiency; thus, it is the better option for practical applications. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Evaluation of SOFC anode polarization simulation using three-dimensional microstructures reconstructed by FIB tomography

In order to evaluate the numerical simulation method for solid oxide fuel cell anode polarization, three-dimensional lattice Boltzmann method simulation is carried out using Ni–YSZ microstructures reconstructed by a focused ion beam scanning electron microscope. The effects of reconstructed sample volume size on the three phase boundary length, tortuosity factors and overpotential are first investigated. The YSZ tortuosity factor has remained nearly unchanged when the cross-sectional area exceeds approximately 200 μm², while the pore tortuosity factor is almost independent of the sample volume size. On the other hand, the Ni tortuosity shows very large variation regardless of the sample volume size. The overpotential predicted with the largest volume size sample is slightly larger than those of smaller volume samples. Two exchange current models based on patterned electrodes are assessed presently. Both models give weaker dependence on the steam concentration than the experimental data. From the predicted three-dimensional current stream lines, it is found that the mirrored computational structure gives a thinner reactive layer because of the factitious connection of Ni phase. Thus, it is recommended to use larger volume size samples which can cover whole reactive thickness when discussing the local potential and flux distributions.     

纳/微异构型钙钛矿氧化物电极在固体氧化物燃料电池的研究进展

开发高效、稳定、廉价的钙钛矿氧化物电极材料是固体氧化物燃料电池(SOFC)进一步商业化发展的关键。目前,研究重点仍集中在解决阳极积碳、硫毒化以及阴极氧还原(ORR)低温性能不佳等问题。最近,有研究报道,一些易还原过渡金属元素掺杂的钙钛矿可以在还原气氛中原位析出该金属并以纳米颗粒的形式"镶嵌"在钙钛矿表面形成"纳米金属–钙钛矿"复合结构。该方法制备的材料具有性能高、抗积碳能力强、可再生性好等优点。从钙钛矿氧化物本体的选择、A/B位掺杂、缺陷调整、以及拓扑离子交换、相变诱发等方面,总结了近年来关于构建纳米(析出金属颗粒)微米(钙钛矿氧化物母体)异质结构(统称纳微异构)钙钛矿氧化物纳米纤维复合电极的研究。此外,总结了具有纳米纤维状形貌的钙钛矿氧化物电极及其结构对于SOFC性能、稳定性的影响,最后提出了该类纳微异构材料的优势、不足和展望。     

SOFC中干甲烷在Ni-YSZ阳极上的转化

以氧化钇稳定的氧化锆(YSZ)作电解质、Ni-YSZ为阳极,研究中/低浓度干甲烷在固体氧化物燃料电池(SOFC)中阳极的反应。改变甲烷浓度,测量不同电流密度下,阳极出口气体产生速率,得到不同电流密度下的CH_4转化率(X_(CH_4))与CO选择性(S_(CO))。根据质量平衡以及产物生成速率与不同反应速率之间的关系,分析干甲烷在阳极平行发生的化学和电化学反应,得到X_(CH_4)和S_(CO)与阳极反应的关系。结果表明,低浓度千甲烷,在电流密度小时,发生部分氧化(POM)反应;电流密度大时,在发生POM反应的同时,发生全氧化(DOM)反应。中浓度干甲烷,发生POM反应。当发生DOM反应时,随电流密度的增加,CO选择性降低,甲烷转化率增加的幅度降低。发生POM反应时,两种浓度甲烷的电化学转化速率基本相同。     

Durability test of SOFC cathodes

The durability of solid oxide fuel cell (SOFC) composite cathodes of lanthanum strontium manganite and yttria stabilised zirconia was investigated. The cathodes were kept at constant, realistic operating conditions (–300 mA cm^–2 at 1000 °C in air) for up to 2000 h. After the 2000 h test the increase in electrode overvoltage exceeded 100% of the initial value. Nominally identical cathodes kept for 2000 h at 1000 °C in air without current load for comparison showed little or no degradation. Thus, the current load of –300 mA cm^–2, rather than the operation temperature of 1000 °C, was responsible for the degradation. Structural analysis showed an increase in the porosity at the electrode interfaces, when the electrode had been polarised. No such structural changes were found for electrodes tested without current load. The degradation is primarily ascribed to pore formation in the electrode material induced by an electric field.     

SOFC中低浓度干甲烷在Ni/YSZ阳极上的反应

固体氧化物燃料电池(SOFC)趋向于直接使用甲烷天然气为燃料,确定甲烷在固体氧化物燃料电池阳极发生的化学与电化学反应非常重要.以Ni/YSZ为阳极、YSZ板做电解质、LSM为阴极,用涂浆法制作电解质支撑的电池,研究低浓度干甲烷在固体氧化物燃料电池中的反应.改变甲烷浓度、电池工作温度、电解质厚度,用在线色谱测量不同电流密度下,阳极出口气体产生速率.根据阳极出口气体产生速率变化,分析干甲烷在阳极的反应变化.通过氧消耗计算和转移电子数的分析,说明甲烷在电池阳极发生不同类型的反应.电流密度小时,甲烷发生部分氧化反应.电流密度大时,发生氢氧化和CO氧化,部分甲烷发生总反应为完全氧化的反应.部分甲烷发生完全氧化反应的同时,部分甲烷仍发生部分氧化反应,但其反应速率随电流密度增加逐渐降低.甲烷浓度和试验温度增加,甲烷开始发生完全氧化的电流密度增加.     

Fabrication,characterization, and performance of YbDSB ternary compounds for IT‐SOFC applications

(Yb₂O₃)_x(Dy₂O₃)_y(Bi₂O₃)_1?x?y (0.04≤x+y≤0.20) powders (xYbyDSB) were synthesized by modified sol‐gel Pecchini method. The powders were characterized for structural, surface morphological, thermal, and electrical properties and power density measurements by means of X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis/thermal gravimetry (DTA/TG), and impedance spectroscopy, respectively. Lattice parameters and crystalline size of δ‐phase of Yb₂O₃‐ and Dy₂O₃‐doped Bi₂O₃ samples were calculated from the X‐ray diffraction data. Surface and grain properties of the related phases were determined by SEM analysis. In the investigated system, the maximum electrical conductivity was observed as σ=0.954 S cm^?1 for 6% mol Yb₂O₃ and 6% mol Dy₂O₃ at 800°C among all δ‐YbDSB systems. Cathode supported electrochemical cell was fabricated and 6Yb6DSB was used as the electrolyte. Maximum power density of single cell with an active area of 1.5 cm² is 72.50 mW/cm² at 700°C.