固体氧化物燃料电池阳极材料的抗积炭方法

传统的固体氧化物燃料电池(SOFC)阳极采用镍基金属陶瓷材料,在CH4等碳氢化合物为燃料的阳极反应中,会出现积炭。分析以碳氢化合物为燃料的SOFC阳极材料的积炭机理,阐述反应温度、水蒸汽等因素对阳极积炭的影响,介绍Ni基陶瓷阳极性能优化和解决积炭的方法,对SOFC其他阳极材料以及未来阳极材料的发展方向进行研究展望。     

甲烷为燃料的固体氧化物燃料电池阳极催化剂研究进展

综述了以甲烷为燃料的固体氧化物燃料电池(SOFC)阳极催化剂研究进展,介绍了传统的镍基复合催化剂,添加其它过渡金属Cu、Co、Fe等的复合催化剂和新型的钙钛矿型离子电子混合导体阳极材料体系的性能,提出了阳极极化、催化活性、积碳等存在的问题,展望了以甲烷为燃料的SOFC应用前景.     

甲烷为燃料的中温固体氧化物燃料电池阳极材料研究进展

中温化和直接采用天然气作为燃料是固体氧化物燃料电池的两大发展趋势,作为固体氧化物燃料电池(SOFC)关键材料之一,阳极材料的性能对整个SOFC的性能有着十分重要的影响。综述了以甲烷为燃料的IT-SOFC阳极材料的研究进展,并指出了存在的问题及解决问题的途径。     

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.     

甲烷为燃料的固体氧化物燃料电池阳极反应的研究进展

介绍了甲烷为燃料的固体氧化物燃料电池中不同类型的阳极反应,对直接电化学氧化、蒸汽重整、部分氧化、氧化耦合等阳极过程的反应特点、电性能和材料要求进行了重点评述,并指出了阳极积碳、反应机理、阳极过程热平衡等有待进一步探索的问题.     

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.     

SOFC中干甲烷流量对Ni-YSZ阳极上反应的影响

为为探讨SOFC中干甲烷流量对反应的影响,采用色谱在线检测阳极尾气,总结阳极尾气的变化规律,在此基础上,分析干甲烷在固体氧化物燃料电池Ni-YSZ阳极上的反应,寻找干甲烷流量与电流对电池阳极反应影响的数学关系。依据甲烷基元反应的活化能分析反应的途径,结果表明,随电流密度以及氧离子流量的增加,干甲烷与不同电流密度下的氧离子依次发生电化学反应。这些电化学反应分别是甲烷部分氧化反应生成CO、H2并产生电子,或生成CO、H2O、H2和产生电子的反应,或产生CO、H2O和产生电子的反应,或甲烷完全氧化的电化学反应。高流量甲烷只发生消耗氧离子最少的部分氧化反应,中流量甲烷发生前两个或前三个反应。依据法拉第第一定律及反应物之间的关系,确定甲烷的低、中、高流量的判定依据分别为:v(CH4)小于等于I/(4F),v(CH4)大于等于I/(4F)以及小于等于I/(2F),v(CH4)大于等于I/(2F)。     

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。     

SOFC中干甲烷在Ni-ScSZ阳极上的氧化行为

以氧化钇稳定的氧化锆(YSZ)做电解质,氧化钪稳定的氧化锆(Ni-ScSZ)为阳极,研究了不同浓度干甲烷在固体氧化物燃料电池阳极上的氧化行为.改变甲烷浓度,利用色谱在线测量不同电流密度下阳极出口气体产生的种类与速率.通过氧的分析与反应发生时的电子数分析,研究了干甲烷在Ni-ScSZ阳极的氧化行为,并对比研究了相同浓度的干甲烷在Ni-YSZ阳极上的氧化行为.结果表明,在Ni-ScSZ阳极上,高浓度干甲烷与在Ni-YSZ阳极上类似,由甲烷裂解反应生成的碳发生氧化反应生成CO;低浓度干甲烷在电流密度较低的情况下,在1 000 ℃可发生CO氧化反应,生成CO2.在Ni-YSZ阳极上,低浓度干甲烷在较高电流密度下,在生成CO2的同时甲烷发生完全氧化反应.     

二氧化碳重整甲烷催化剂抗积炭性能的研究进展

概述了二氧化碳重整甲烷催化剂的抗积炭性能的研究进展,介绍了催化剂的活性组分、载体的选择,重点讲述了稀土金属和贵重金属对催化剂的改性,以及采用溶胶-凝胶法制备纳米级催化剂的有关研究状况,并介绍了微波场下甲烷重整的抗积炭性能。     

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。     

Durability and thermal cycling of Ni/YSZ cermet anodes for solid oxide fuel cells

The long-term properties of Ni/yttria stabilized zirconia (YSZ) cermet anodes for solid oxide fuel cells were evaluated experimentally. A total of 13 anodes of three types based on two commercial NiO powders were examined. The durability was evaluated at temperatures of 850 C, 1000 C and 1050 C over 1300 to 2000h at an anodic d.c. load of 300mA cm^–2 in hydrogen with 1 to 3% water. The anode-related polarization resistance, R _P, was measured by impedance spectroscopy and found to be in the range of 0.05 to 0.7 cm². After an initial stabilization period of up to 300h, R _P varied linearly with time within the experimental uncertainty. At 1050 C no degradation was observed. At 1000 C a degradation rate of 10 m cm² per 1000 h was found. The degradation rate was possibly higher at 850 C. A single anode was exposed to nine thermal cycles from 1000 to below 100 C at 100 C h^–1. An increase in R _P of about 30m cm² was observed over the first two cycles. For the following thermal cycles R _P was stable within the experimental uncertainty.     

Micro‐modeling of porous composite anodes for solid oxide fuel cells

A new anode micromodel for solid oxide fuel cells to predict the electrochemical performance of hydrocarbon‐fuelled porous composite anodes with various microstructures is developed. In this model, the random packing sphere method is used to estimate the anode microstructural properties, and the complex interdependency among the multicomponent mass transport, electron and ion transports, and electrochemical and chemical reactions is taken into account. As a case study, a porous Ni–YSZ composite anode operated with biogas fuel is simulated numerically and distributions of the current density, polarization, and mole fraction and rate of flux of the fuel components along the thickness of the anode are determined. The effect of the anode microstructural variables including the porosity, thickness, particle‐size ratio, and particle size and volume fraction of Ni particles on the anode electrochemical performance is also studied. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1893–1906, 2012     

Dependencies of the open-circuit voltage of Au|YSZ|Pt single-chamber fuel cell on the composition of the uniform CH4 + O2 gas mixture with solid carbon deposition

Single-chamber solid oxide fuel cell is a device where two electrodes of different materials contacting a solid oxide ionic conductor, may generate a considerable potential difference and electrical power, when supplied by a common fuel + oxidant gas mixture. The Au|YSZ|Pt system in the CH₄ + O₂ gas mixture is one of the simplest examples of such a cell. In this article the open-circuit voltage (OCV) of this cell, supplied with the gas mixture xO₂ + aCH₄ + (1 − x − a)Ar (where a = 0.01, 0.1 or 0.5), is investigated. On the basis of the obtained results, as well as those for the xCH₄ + (1 − x)(0.2O₂ + 0.8Ar) (0 ≤ x ≤ 1) gas mixture, reported in our previous work [Electrochim. Acta, 50 (2005) 2771], we postulate that the OCV of the above system arises as a result of electrode modification resulting from solid carbon deposition in the cell. After oxidation of the carbon deposit, the system, once treated by the gas mixture enabling the formation of the carbon phase, shows more and more tendency to generate the OCV. The open-circuit potential of the Au electrode depends only on the O₂ concentration in the initial gas mixture, whereas in the case of the Pt electrode it becomes dependent on chemical equilibria determining the O₂ content in the converted gas mixture. Our results reveal that the OCV achieves a reproducible limiting value of ∼650 mV, which is lower by ∼400 mV than the calculated equilibrium value.     

Robust and reliable solid oxide fuel cells with modified thin film YSZ electrolyte

Reduce electrolyte thickness can improve solid oxide fuel cell (SOFC) performance. However, thinner electrolyte often contains prominent defects and flaws, which may decrease the yield and increase operation risk. This work proposes a method to modify the thin film YSZ electrolyte, to improve cell reliability and durability. The as-sintered anode supported half-cell with screen printed YSZ electrolyte was immersed in precursor solution of Y(NO₃)₃·6H₂O and Zr(NO₃)₄·5H₂O, and being treated under hydrothermal condition of 150°C for 12 h. As a result, the modified cells show slight increase in the OCV values. Furthermore, the hydrothermal modification effectively promotes interface sintering between YSZ electrolyte and GDC barrier layer, yielding a smaller ohmic resistance of .142 Ω·cm² (a decrease of ∼11%) and a higher peak power density of .964 W/cm² (an increase of ∼18%) at 750°C, than pristine cell. Moreover, the modified cell operates stably over 300 h, while the pristine cell presents large and irregular voltage fluctuations. This work suggests that the hydrothermal modification is an effective and promisingly industrial applicable method for thin film electrolyte recovery in SOFCs.     

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.     

Modeling of CO2 gasification of carbon for integration with solid oxide fuel cells

This modeling study focuses on gasification of carbon by CO₂ in a minimally fluidized bed containing a solid oxide fuel cell (SOFC). Kinetic parameters for a five‐step reaction mechanism characterizing the Boudouard reaction (C + CO₂ → 2CO) were determined thermogravimetrically at 1 atm from 973 to 1273 K. Experimentally determined kinetic parameters are employed in a transport model that predicts velocities and gas concentration profiles established in the carbon bed as a consequence of convection, diffusion, and heterogeneous reaction. The model is used to simulate the effect of an imbedded SOFC, in contact with the carbon bed. Although the model does not assume particular I‐V characteristics for the fuel cell, it indicates that current densities in the practical range of 100–1000 mA/cm² can be supported. Results show that temperature strongly affects the current density, whereas CO₂ flow rate has only a weak effect. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Calculation of the metal-carbon bond strength of surface carbon deposited on solid oxide fuel cell nickel/zirconia fuel reforming anodes

The activation energy for the removal of surface carbon formed by methane decomposition following high-temperature reforming, from a nickel/zirconia solid oxide fuel cell (SOFC) anode has been calculated using two methods based on temperature-programmed oxidation. It is found that there is a fairly good agreement between the two methods. In addition, it was observed that the addition of small quantities of lithium to the anode resulted in a significant lowering of the activation energy for surface carbon removal by about 50 kJ mol^-1. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development of LSM/YSZ composite cathode for anode-supported solid oxide fuel cells

This paper presents the effect of (La,Sr)MnO₃ (LSM) stoichiometry on the polarization behaviour of LSM/Y₂O₃-ZrO₂ (YSZ) composite cathodes. The composite cathode made of A-site deficient (La_0.85Sr_0.15)_0.9MnO₃ (LSM-B) showed much lower electrode interfacial resistance and overpotential losses than that made of stoichiometric (La_0.85Sr_0.15)_1.0MnO₃ (LSM-A). The much poorer performance of the latter is believed to be due to the formation of resistive substances such as La₂Zr₂O₇/SrZrO₃ between LSM and YSZ phases in the composite electrode. A slight A-site deficiency (∼0.1) was effective in inhibiting the formation of these resistive substances. A power density of ∼1 W cm⁻² at 800 °C was achieved with an anode-supported cell using an LSM-B/YSZ composite cathode. In addition, the effects of cathodic current treatment and electrolyte surface grinding on the performance of composite cathodes were also studied.     

Polarization effects in electrolyte/electrode-supported solid oxide fuel cells

The effects of activation, ohmic and concentration polarization on the overall polarization in solid oxide fuel cells are presented. A complete analysis was conducted based on thermodynamic principles for the calculation of cell voltage. Treating the fuel cell as a control volume, the irreversibility term in a steady flow thermodynamic system was related to the overall polarization. The entropy production was calculated and related to the lost work of the fuel cell, while the heat loss from the cell was determined from the entropy balance. To generalize the cell voltage–current density expression, the Butler–Volmer model was used in the calculation of activation polarization and both ordinary and Knudsen diffusions were considered in the calculation of concentration polarization. The overall cell resistance was deduced from the generalized cell voltage–current density expression. The concentration resistance at the anode can be minimized by humidifying the hydrogen with an appropriate amount of water, depending on the thickness of the anode used. Comparison of polarization effects on the cell performance between the electrolyte-supported and anode-supported cells showed that the latter would give a better cell performance.