以干甲烷为燃料的SOFC阳极反应及材料的研究进展

描述了在固体氧化物燃料电池 (SOFC) 阳极上可能发生的化学反应及电化学反应,以及以干甲烷为燃料气时阳极上的反应机制.介绍了目前主要的 SOFC 阳极材料,即Ni基材料、Cu基材料及CeO2基氧化物的特点及研究进展.     

IT-SOFC阳极表面催化反应机理与传递过程的数值模拟与分析

固体氧化物燃料电池(SOFC)具有效率高、污染低、对燃料适应性好、功率大等特点。其性能与工作状态受发生在多孔阳极的化学反应与多种传递过程耦合的影响。基于流体力学方程组和多步基元化学反应模型,建立了描述上述耦合特性的三维数学模型,并自编程序求解分析。结果显示:重整反应主要发生在靠近通道进口的多孔阳极,表面成分Ni_s的覆盖率占70%～80%,其他主要表面成分为CO_s占20%～25%,H_s占6%,O_s占1.5%; Ni_s随工作温度升高而增加;加强吸附基元反应会提高燃料利用率和工作温度;渗透率增加会提高反应气体在多孔介质内的传递效果,但催化反应会因接触不充分而减弱。通过考虑基元反应机理研究表明,在微观层面,催化剂Ni利用率不高,催化反应受温度、化学反应速率常数、孔隙率等参数影响较大。     

固体氧化物燃料电池中CH4与CO2重整反应的研究

概述了有关CH4和CO2重整反应在固体氧化物燃料电池(SOFC)中的研究进展.对该反应在SOFC阳极活化及重整的反应机理进行了探讨;讨论了反应温度、压力等因素对阳极表面产生积碳的影响,分析了有利于消除积碳、促进反应进行的压力及温度范围;介绍了开发新型、高效、抗积碳的阳极材料来改善SOFC阳极积碳状况的方法,如:在阳极材料中添加不同的活化成分、助剂及选择不同载体等.     

固体氧化物燃料电池Cu/Ni-LSCM阳极中n(Cu)/n(Ni)对碳沉积影响数值模拟研究

固体氧化物燃料电池(SOFC)使用碳氢化合物为燃料时,多孔阳极易出现严重的积碳的现象,导致阳极催化活性降低,电池功率密度下降以及电池寿命急剧衰减。铬酸镧基钙钛矿材料在高温氧化和还原气氛下具有较好的稳定性、电催化活性和抗积碳性能。建立LSCM以及Cu/Ni-LSCM中CH₄与CO₂干重整动力学模型,模型耦合了动量传递、质量传递、化学反应动力学、域微分方程以及气体在多孔介质中的传质模型,并利用该模型研究了Cu/Ni-LSCM阳极材料的抗积碳性能、催化活性以及孔隙率随时间的变化情况。得出结论:Cu的引入可以明显降低碳沉积速率,在一定基础上增加燃料转化率。其中CH₄热分解是形成积碳的主要原因。与此同时,模拟结果显示阳极燃料入口处为碳沉积最为严重的区域。     

天然气内重整和外重整下SOFC多场耦合三维模拟分析

内重整(IR)和外重整(ER)是固体氧化物燃料电池(SOFC)以天然气(NG)为燃料时的两种工作方式,不同重整方式下的电池性能、效率也不尽相同。借助有限元分析软件COMSOL Multiphysics?5.2,以天然气为燃料,建立了电池组成为Ni-YSZ//YSZ//LSCF-GDC的ER-SOFC和IR-SOFC两种三维单电池模型。模拟结果表明:相同条件下,IR-SOFC具有比ER-SOFC更高的功率密度、燃料利用率和能量利用率;阳极重整反应主要发生在靠近燃料入口的区域内;H_2和CO含量在IR-SOFC中先升高后降低,在ER-SOFC中则一直降低;IR-SOFC的温度变化更剧烈,燃料入口处温度梯度最大;越靠近集流体的区域,电解质表面的离子电流密度越大;ER-SOFC阳极不会发生热力学上的积炭现象,对于IR-SOFC,CH4热分解反应是整个阳极发生积炭的主要原因,其在燃料入口处的积炭活性高达270。     

使用丙烷燃料的便携式固体氧化物燃料电池研究进展

阐述了丙烷燃料应用于固体氧化物燃料电池(solid oxide fuel cell,SOFC)的工艺及其原理,其中包括重整、部分氧化;综述了使用丙烷燃料SOFC阳极材料研究进展,现有的研究工作主要围绕着如何阻止积炭进行,主要途径是改善阳极性能和选用合适的阳极催化剂等;介绍了当今世界上针对便携式应用的各式SOFC的研究发展现状,特别介绍了单气室SOFC;对便携式SOFC的发展前景进行了展望。     

阳极孔隙率对固体氧化物燃料电池性能影响的数值分析

基于商用计算流体动力学软件及开发的燃料电池多孔介质内多组分流动和扩散、传热传质、电化学反应、电流场等复杂的物理过程的计算程序,对采用不同孔隙率阳极的平板式阳极支撑固体氧化物燃料电池(planar-electrode-support solid oxide fuel cell,PES-SOFC)的性能进行数值计算,得到不同阳极孔隙率下单电池内部各气体组分浓度、温度、电势、电流、电流密度等参数的分布。由计算结果可知,在阳极孔隙率为0.3～0.4之间时,以氢气为燃料的该类型SOFC单电池表现出较好的气体扩散和电流传导特性,相应输出电压也较高。     

天然气内重整和外重整下SOFC多场耦合三维模拟分析

内重整（IR）和外重整（ER）是固体氧化物燃料电池（SOFC）以天然气（NG）为燃料时的两种工作方式,不同重整方式下的电池性能、效率也不尽相同。借助有限元分析软件COMSOL Multiphysics^? 5.2,以天然气为燃料,建立了电池组成为Ni-YSZ//YSZ//LSCF-GDC的ER-SOFC和IR-SOFC两种三维单电池模型。模拟结果表明：相同条件下,IR-SOFC具有比ER-SOFC更高的功率密度、燃料利用率和能量利用率;阳极重整反应主要发生在靠近燃料入口的区域内;H₂和CO含量在IR-SOFC中先升高后降低,在ER-SOFC中则一直降低;IR-SOFC的温度变化更剧烈,燃料入口处温度梯度最大;越靠近集流体的区域,电解质表面的离子电流密度越大;ER-SOFC阳极不会发生热力学上的积炭现象,对于IR-SOFC,CH₄热分解反应是整个阳极发生积炭的主要原因,其在燃料入口处的积炭活性高达270。     

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。     

金属支撑固体氧化物燃料电池研究进展

与传统全陶瓷结构的燃料电池不同,金属支撑固体氧化物燃料电池利用多孔金属来支撑功能阳极层–电解质层–阴极层,具有结构稳定性高、抗热快速热循环能力强,电堆组装简单,材料成本低等优势。本文分析了金属支撑固体氧化物燃料电池(SOFC)材料的选择和电池制备过程中的关键问题,并概述了金属支撑SOFC技术的研究进展。     

SOFC fuelled by methane without coking: optimization of electrochemical performance

In recent years, fuel cell technology has attracted considerable attention from several fields of scientific research as fuel cells produce electric energy with high efficiency, emit little noise, and are non-polluting. Solid oxide fuel cells (SOFCs) are particularly important for stationary applications due to their high operating temperature (1,073–1,273 K). Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by direct internal reforming (DIR) within the SOFC anode. Unfortunately, internal steam reforming in SOFC leads to inhomogeneous temperature distributions which can result in mechanical failure of the cermet anode. Moreover this concept requires a large amount of steam in the fed gas. To avoid these problems, gradual internal reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However, with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell configuration of SOFC electrolyte support was studied. This configuration combined a catalyst layer (0.1%Ir–CeO₂) with a classical anode, allowing GIR without coking. In order to optimise the process a SOFC model has been developed, using the CFD-Ace+ software package, and including a thin electrolyte. The impact of a thin electrolyte on previous conclusions has been assessed. As predicted, electrochemical performances are higher and carbon formation is always avoided. However a sharp decrease in the electrochemical performances appears at high current densities due to steam clogging.     

Modeling of a Tubular‐SOFC: The Effect of the Thermal Radiation of Fuel Components and CO Participating in the Electrochemical Process

A mathematical model based on first principles is developed to study the effect of heat and electrochemical phenomena on a tubul solid oxide fuel cell (SOFC). The model accounts fordiffusion, inherent impedance, transport (momentum, heat and mass transfer) processes, internal reforming/shifting reaction, electrochemical processes, and potential losses (activation, concentration, and ohmic losses). Thermal radiation of fuel gaseous components is considered in detail in this work in contrast to other reported work in the literature. The effect of thermal radiation on SOFC performance is shown by comparing with a model without this factor. Simulation results indicate that at higher inlet fuel flow pressures and also larger SOFC lengths the effect of thermal radiation on SOFC temperature becomes more significant. In this study, the H₂ and CO oxidation is also studied and the effect of CO oxidation on SOFC performance is reported. The results show that the model which accounts for the electrochemical reaction ofCO results in better SOFC performance than other reported models. This work also reveals that at low inlet fuel flow pressures the CO and H₂ electrochemical reactions are competitive and significantly dependent on the CO/H₂ ratio inside the triple phase boundary.     

Effect of methane slippage on an indirect internal reforming solid oxide fuel cell

Creation of an autothermal system by coupling an endothermic to an exothermic reaction demands matching the thermal requirements of the two reactions. The application studied here is the operation of a solid oxide fuel cell (SOFC) with both direct (DIR) and indirect (IIR) internal reforming of methane. Such internal reforming within a high-temperature fuel cell module can lead to an overall autothermal operation which simplifies the system design and increases efficiency. However, such coupling is not easy to achieve because of the mismatch between the thermal load associated with the rate of steam reforming at typical SOFC temperatures and the local amount of heat available from the fuel cell reactions. Previous results have shown that the use of typical metal-based (e.g. Ni) IIR catalysts leads to full methane consumption but undesirable local cooling at the reformer entrance and the use of less active IIR catalysts (e.g. non-metals or diffusion limited nickel) leads to methane being carried-over into the SOFC anode (methane slippage). In order to evaluate performance in the latter case, a combined DIR and IIR SOFC steady-state model has been developed. Simulation results have shown that, lowering the IIR catalyst activity to prevent local cooling effects at the reformer entrance is not adequate, as the fast kinetics of the direct reforming reaction then lead to full methane conversion and steep temperature gradients in the first 10% of the fuel channel length. It is shown that the simultaneous reduction of the anode DIR reaction rate improves performance considerably. The system behaviour towards changes in current density, operating pressure, and flow configuration (counter-flow vs. co-flow) has been studied. Reduction of both DIR and IIR catalyst activity combined with a counter-flow operation leads to the best performance. System performance with an IIR oxide-based catalyst is also evaluated.     

Catalytic aspects of the steam reforming of hydrocarbons in internal reforming fuel cells

Steam reforming of hydrocarbons such as natural gas is an attractive method of producing the hydrogen fuel gas required by fuel cells. It may be carried out external to the fuel cell or internally. The two types of fuel cell in which internal reforming is most appropriate are the molten carbonate (MCFC), operating at ca. 650°C and the solid oxide (SOFC) which currently operates above 800°C. At such temperatures, the heat liberated by the electrochemical reactions within the cell can be utilised by the endothermic steam reforming reaction. This paper reviews some of the catalytic aspects of internal reforming in these two types of cell. In the MCFC the major catalyst issue is that of long term activity in the presence of a corrosive alkaline environment produced by the cell's electrolyte. In Europe, this is being addressed by British Gas and others, in a programme part-funded by the European Commission. In this programme, potential catalysts for the direct internal reforming MCFC were evaluated in ‘out-of-cell’ tests. This has led to the demonstration of a 1 kW proof-of-concept DIR-MCFC stack and the start of a European ‘Advanced DIR-MCFC’ project. For the SOFC, it has been shown that state-of-the-art nickel cermet anodes can provide sufficient activity for steam reforming without the need for additional catalyst. However, anode degradation may occur when steam reforming is carried out for long periods. New anode materials could therefore offer significant benefits.     

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.     

Effect of methane concentration on reaction behavior in direct-methane solid oxide fuel cells with (Ce,Gd)O2−x-impregnated FeCr layer for fuel processing

A solid oxide fuel cell (SOFC) with a Ni-yttria-stabilized zirconia anode of 1 cm² area was set up with a porous disk of gadolinia-doped ceria-impregnated FeCr as a gas diffusion layer (GDL) under direct-methane feeding. In this setup of SOFC plus GDL, the tests at 800 °C and ambient pressure show that the current density, the methane conversion rate, the product formation rates, and the CO₂ selectivity increased with increasing methane concentration. The major reaction in the GDL is CO₂ reforming of methane to produce the syngas (CO plus H₂). The anodic electrochemical oxidation of CO from GDL results in an overall rate of CO₂ formation being much larger than that of CO formation. There is a synergy between the rate of reaction in the GDL and that over the anode.     

Effect of precious metal addition to Ni-YSZ cermet on reforming of CH4 and electrochemical activity as SOFC anode

Various kinds of precious metals were added to the Ni-Y₂O₃-stabilized zirconia (Ni-YSZ) cermets, and the relation between steam reforming of CH₄ and the electrochemical activity as a solid oxide fuel cell (SOFC) anode was investigated. Ru and Pt additions promoted the reforming and suppressed the coke depositions. The electrochemical activity of the SOFC anode was enhanced by the addition of Ru and Pt, indicating that these precious metals effectively functioned as the anode catalysts. The impedance related to gas diffusion was greatly reduced, indicating that stability of the anode catalyst of SOFC was considerably improved since coke was hardly deposited.     

Modelling of an indirect internal reforming solid oxide fuel cell

Creation of an autothermal system by coupling an endothermic to an exothermic reaction demands the matching of the thermal requirements of the two reactions. The application under study is a solid oxide fuel cell (SOFC) with indirect internal reforming (IIR) of methane, whereby the endothermic steam reforming reaction is thermally coupled to the exothermic oxidation reactions. A steady-state model of an IIR-SOFC has been developed to study the mismatch between the thermal load associated with the rate of steam reforming at typical SOFC temperatures and the local amount of heat available from the fuel cell reactions. Results have shown a local cooling effect, undesirable for ceramic fuel cells, close to the reformer entrance. The system behaviour towards changes in catalyst activity, fuel inlet temperature, current density, and operating pressure has been studied. Increasing the operating pressure is shown to be an effective way of reducing both the local cooling caused by the reforming reactions and the overall temperature increase across the cell. Simulations for both counter-flow and co-flow configurations have been performed and compared.     

Development of a novel test system for in situ catalytic, electrocatalytic and electrochemical studies of internal fuel reforming in solid oxide fuel cells

A test system based around a thin‐walled extruded solid electrolyte tubular reactor has been developed, which enables the fuel reforming catalysis and surface chemistry occurring within solid oxide fuel cells and the electrochemical performance of the fuel cell to be studied under genuine operating conditions. It permits simultaneous monitoring of the catalytic chemistry and the cell performance, allowing direct correlation between the fuel cell performance and the reforming characteristics of the anode, as well as enabling the influence of drawing current on the catalysis and surface reaction pathways to be studied. Temperature‐programmed reaction measurements can be carried out on anodes in an actual SOFC, and have been used to investigate the reduction characteristics of different anode formulations, methane activation and methane steam reforming, and to evaluate the nature and level of carbon deposition on the anode during reforming. This revised version was published online in July 2006 with corrections to the Cover Date.