Modeling of a SOFC fuelled by methane: From direct internal reforming to gradual internal reforming

Natural gas appears to be a fuel of great interest for SOFC systems. The principal component of natural gas is methane, which can be converted into hydrogen by direct or gradual internal reforming (DIR or GIR) within the SOFC anode. However, DIR requires a large amount of steam to produce hydrogen. If the injected mixture contains very small quantities of steam, GIR is then obtained. With GIR, the risk of carbon formation is even greater. This paper proposes a model and simulation, using the CFD-Ace software package, of the behaviour of a tubular SOFC using GIR and a comparison between utilization in DIR and GIR. A thermal study is included in the model and a detailed thermodynamic analysis is carried out to predict the carbon formation boundary for SOFCs fuelled by methane. Thermodynamic equilibrium calculations taking into account Boudouard and methane cracking reactions allowed us to investigate the occurrence of carbon formation. Simulations were used to calculate the distributions of partial pressures for all the gas species (CH₄, H₂, CO, CO₂, H₂O), current densities and potentials in both electronic and ionic phases within the anode part (i.e., gas channel and cermet anode). The simulations indicate that there is no decrease in electrochemical performance if GIR is used rather than DIR. A thermal study appears to confirm that the cooling effect due to the endothermic reforming reaction is eliminated in GIR, but the thermodynamic study indicates that carbon formation can be suspected for x_H2O/x_CH4 ratios lower than one.     

Discrete modelling of the electrochemical performance of SOFC electrodes

The composite anode and cathode of solid oxide fuel cells (SOFC) are modelled as sintered mixtures of electrolyte and electrocatalyst particles. A particle packing is first created numerically by the discrete element method (DEM) from a loose packing of 40 000 spherical, monosized, homogeneously mixed, and randomly positioned particles. Once the microstructure is sintered numerically, the effective electrode conductivity is determined by discretization of the particle packing into a resistance network. Each particle contact is characteristic of a bond resistance that depends on contact geometry and particle properties. The network, which typically consists of 120 000 bond resistances in total, is solved using Kirchhoff's current law. Distributions of local current densities and particle potentials are then performed. We investigate how electrode performance depends on parameters such as electrode composition, thickness, density and intrinsic material conductivities that are temperature dependent. The simulations show that the best electrode performance is obtained for compositions close to the percolation threshold of the electronic conductor. Depending on particle conductivities, the electrode performance is a function of its thickness. Additionally, DEM simulations generate useful microstructural information such as: coordination numbers, triple phase boundary length and percolation thresholds.     

焦化废水电化学处理技术研究进展

介绍了焦化废水的电化学处理技术的现状,并结合近年来环境电化学技术的前沿研究,提出了焦化废水电化学处理技术的发展方向.结合量子力学和结构化学理论,重点分析了采用极端的电化学条件来改变分子的几何结构和电子云结构,从而达到降解焦化废水中难降解有机物的可能性.     

The influence of formation features on SOFC electrochemical performance and long-term stability

Journal of Applied Electrochemistry - The design and production features of a solid oxide fuel cell greatly impact its microstructure and performance; however, these factors are frequently omitted...     

Electrocatalytic reforming of carbon dioxide by methane in SOFC system

The reaction of carbon dioxide catalytic reforming with methane is an attractive route because these greenhouse gases can be converted into variable feedstocks. However this reaction is a highly energy consuming and coke forming process. These problems were improved by the electrocatalytic reforming of CO₂ with CH₄ in a solid oxide fuel cell (SOFC) membrane reactor system, which generates high electrical power and synthesis gases. The single cell consists of catalyst electrode (NiO–MgO), counter electrode ((La,Sr)MnO₃) and Y₂O₃ stabilized ZrO₂ (YSZ) electrolyte. The reaction rates of CO₂ and CH₄, and the electrochemical properties were investigated by an on-line GC and impedance-analyzer under open- and closed-circuit conditions, respectively. It was found that reaction rates of CO₂ and CH₄ under the closed-circuit condition were more stable than those of the open-circuit. The results were interpreted that the stability of catalyst anode was maintained by the reaction of oxygen ion transferred from the cathode with the surface carbon formed in the internal CO₂ reforming by CH₄ in SOFC system.     

平板状固体氧化物燃料电池电化学特性Simlink建模与仿真

在分析平板状固体氧化物燃料电池电化学特性的基础上,建立了Simlink仿真模型,探讨了工作温度和燃料中水蒸气含量对燃料电池理想电势和有效电势的影响。仿真结果表明,低电流密度下,温度的升高会导致有效电势的降低;高电流密度下,有效电势会随着温度升高而增加。水蒸气含量越低,燃料电池的理想电势和有效电势越高。     

电化学氧化及反硝化BAF联用深度处理焦化废水

针对焦化废水二级处理出水含难降解有毒有害有机物,且难以达标排放的问题,研究了BDD电极电化学氧化与反硝化曝气生物滤池联用深度处理焦化废水的效果。结果表明,当电化学氧化的水力停留时间控制在1 h,BAF的停留时间控制在12 h时,系统出水水质稳定,出水平均COD、NH_3~-N、NO_3~--N分别为62.9、2.60、9.9 mg/L,系统平均去除率分别为74.2%、83.6%、59.6%。     

Operation viability and performance of solid oxide fuel cell fuelled by different feeds

The performances of solid oxide fuel cells (SOFCs) fed by different types of feed, i.e. biogas, biogas-reformed feed, methane-reformed feed and pure hydrogen, are simulated in this work. Maximum temperature gradient and maximum cell temperature are regarded as indicators for operation viability investigation whereas power density and electrical efficiency are considered as performance indicators. The change in operating parameters, i.e. excess air, fuel feed rate and operating voltage, affects both the performance and operation viability of SOFC, and therefore, these operating parameters should be carefully selected to obtain best possible power density and reasonable temperature and temperature gradient. Pure hydrogen feed offers the highest SOFC performance among the other feeds. Extremely high excess air is required for SOFC fed by biogas to become operation viable and, in addition, its power density is much lower than those of SOFCs fed by the other feeds. Methane-reformed feed offers higher power density than biogas-reformed feed since H₂ concentration of the former one is higher.     

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.     

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.     

Investigation of a proton-conducting SOFC with internal autothermal reforming of methane

This study presents a performance analysis of a proton-conducting SOFC (SOFC-H⁺) with internal reforming of methane. The autothermal reforming within the SOFC-H⁺ stack is considered to be a potential solution of the carbon formation problem facing in operation of internal steam reforming SOFC-H⁺. A one-dimensional, steady-state model of the SOFC-H⁺ coupled with a detailed electrochemical model is employed to investigate its performance in terms of power density and fuel cell efficiency. The simulation results show that when SOFC-H⁺ is operated under an autothermal reforming environment, the presence of carbon monoxide, which is a major cause of carbon formation, in the fuel cell stack decreases. Effect of key operating parameters, such as temperature, steam-to-carbon and oxygen-to-carbon feed ratios, current density and fuel utilization, on the SOFC-H⁺ performance in terms of electrical efficiencies and energy demand is also investigated. The results indicate that operating temperatures have strong influence on SOFC-H⁺ performance, carbon monoxide production and heat generation.     

SOFC内部重整反应与电化学反应耦合机理

以经过预重整反应的混合气为原料的固体氧化物燃料电池（SOFC）内部,甲烷蒸气重整反应与电化学反应同时发生在阳极多孔介质中,二者受到不同的操作与设计参数的影响,对电池总体性能起着决定性作用。编制了三维数值模拟程序,对由多孔阳极层、气体流动管道、固体支撑平板构成的单个复合管道进行了研究。结果显示：重整反应主要发生在多孔材料靠近流动管道的薄层内,只有靠近管道入口处才能在较深处进行;电化学反应发生在多孔层与电解质的交界面处;重整反应生成的H2、CO扩散到多孔材料底部参加电化学反应;电化学反应生成的热量供重整反应使用。说明研究范围内,SOFC阳极复合通道具有较好的传热、传质性能,化学/电化学反应存在较好的耦合关系。     

电化学氧化耦合絮凝技术深度处理焦化废水影响因素分析

采用了电化学氧化耦合絮凝技术处理焦化废水,研究了电流密度、pH值、水力停留时间(HRT)和絮凝剂投加量对CODCr去除效果的影响。研究结果表明,电化学氧化耦合絮凝技术处理焦化废水有较好的协同效应。当进水中CODCr的质量浓度为99 mg/L,在电流密度为30 mA/cm2,HRT为30 min,pH值为6.5,PAM投加量为600 mg/L时,CODCr去除率达到80%以上,出水水质指标稳定,并能达到GB 8978—1996《污水综合排放标准》一级排放标准。     

Industrial coking of coal batch without bituminous coal

For many years, Kuznetsk-coal batch has always included bituminous coal. Depending on the content of such coal, the batch may be characterized as lean, moderately clinkering, or bituminous. This classification was adopted by specialists of the Eastern Coal-Chemistry Institute (ECCI) in experimental coking at Magnitogorsk Metallurgical Works in 1945 [1]. Lean batch contained 10% Osinovsk bituminous coal (plastic-layer thickness y = 13 mm); moderately coking coal contained 25% bituminous coal (y = 16 mm); and bituminous batch contained 40% of such coal (y = 20 mm).     

基于电化学性能的La-Mg-Ni系储氢合金的成分优化

以La-Mg-Ni系A2B7型储氢合金为研究对象,系统分析了合金A、B侧元素含量对其电化学性能的影响。对La1-m-n-y Pr m Nd n Mg y(Ni1-z Co z)x合金的容量和衰减速率进行了讨论。结果表明,合金容量随B/A值的增大先增大后减小,当x=3.5时,合金的容量最大,衰减速率最小;最佳的合金配比为La0.5Pr0.2Nd0.1Mg0.2(Ni0.8Co0.2)3.5。XRD分析表明,La1-m-n-y Pr m Nd n Mg y(Ni1-z Co z)x的合金主相结构均为Ce2Ni7型La2Ni7相。     

Cell/stack electrochemical performance and stability of cone-shaped tubular SOFCs for direct operation with methane

Cone-shaped tubular anode-supported solid oxide fuel cells (SOFCs) and two-cell-stack based on NiO-YSZ traditional anodes direct utilization methane as fuel were successfully developed in this study. The single cell exhibited maximum power densities of 1.255 W cm⁻² for hydrogen and 1.099 W cm⁻² for methane at 800 °C, respectively. A stability test of the single cell was performed with different constant current densities at 700 °C in methane. The results indicated that the single cell can be operated stable at high current density in methane. And EDX results showed that there is no measurable coking effect of operation in methane at relatively high current density.A two-cell-stack based on the above-mentioned SOFCs was fabricated and tested by direct utilization of methane. Its typical electrochemical performance was investigated. The two-cell-stack provided a maximum power output of about 3.5 W (350 mW cm⁻² calculated using effective cathode area) by directly using methane at 800 °C. The stack experienced 20 h durability testing. The results demonstrated that the stack was kept at around 1 V (J = 0.05 A cm⁻²) at 700 °C. The stack presented basically stably during the whole test, and the performance of the stack is acceptable for application.     

响应曲面法优化电化学耦合体系预处理焦化废水

针对焦化废水有机负荷高、生物抑制性强等特点,采用电化学耦合体系进行预处理研究。以原厂污泥制备污泥活性炭（AC）粒子电极,并表征其表面含有羟基、醚基、羰基、羧基等多种含氧官能团,有利于催化反应。考察阴极曝气对预处理的影响及降解机理分析,结果表明曝气有利于开环反应。基于Central-Composite响应曲面法考察外加电压、初始pH、曝气量、AC填充比等因素对预处理的单独影响及交互作用,并以COD去除率为评价指标。结果表明：各因子的影响显著性顺序为AC填充比 > 初始pH > 曝气量 > 外加电压,其中初始pH和曝气量的交互作用较显著。最佳运行条件为外加电压15 V,初始pH 5.8,曝气量12.4 ml·min^-1,AC填充比50%,反应时间45 min,此时COD去除率达46.8%。废水COD由4700 mg·L^-1降至2500 mg·L^-1,色度去除率为50%,B/C由0.05增至0.37,可生化性明显提高,且能耗较低为0.971 kW·h·（kg COD）^-1。研究表明,采用电化学技术能有效预处理焦化废水,并提高可生化性。     

Fabrication and performance of advanced multi-layer SOFC cathodes

Multilayered cathodes for solid oxide fuel cells are presented. The cathodes are composed of strontium doped lanthanum manganate and yttria stabilised zirconia, the ratio of which is increased with increasing distance from a supporting zirconia electrolyte. Some cathodes additionally carry a number of layers with a graded transition from manganite to cobaltite to add an electronically highly efficient current collector. The cathodes were prepared by spray painting and low temperature sintering. Electrochemical measurements revealed a performance up to 0.2 Ω cm² at 750°C for the first generation of these cathodes. The electrochemical performance was found to be influenced further by the microstructure at the interface close to the solid electrolyte and the quality of electrical contact thorough the sintered electrode.     

电化学法处理焦化废水的研究进展

从微电解法、电解氧化法、电凝聚法、三维电极法等方面讨论了电化学法处理焦化废水的研究进展,并分析了各种方法的优点与不足,提出了电化学法处理焦化废水的发展方向。     

SOFC中不同浓度干甲烷在Ni-YSZ阳极上的反应

引言 天然气是适于固体氧化物燃料电池(SOFC)应用的燃料之一,天然气中主要成分是甲烷.甲烷通过全氧化或部分氧化[1-4]反应,在发电的同时,生成适于发电或其他用途的富含H2、CO的气体.