Sequential Tape Casting of Anode‐Supported Solid Oxide Fuel Cells

A novel route was developed to fabricate anode‐supported solid oxide fuel cells with a high throughput and low manufacturing costs. In contrast to classical manufacturing routes, this novel route starts with the tape casting of the thin electrolyte followed by the tape casting of the anode and anode support. All three layers were cast green‐on‐green and finally sintered to yield a gas‐tight electrolyte. By carefully selecting the raw materials for all three layers, it is possible to manufacture near‐net‐shape half‐cells. The half‐cells were characterized with respect to thickness, microstructure, bending behavior, electrolyte gas leakage, shrinkage, electrolyte residual stresses, and mechanical strength. Finally, the cathode was screen‐printed and fired, and the full cell characteristics were obtained in single‐cell and stack tests. Additionally, a scale‐up to cell sizes of 200 × 200 mm² was verified. Electrolyte and anode thickness were around 20 μm, and the support was cast to 300–500 μm. The helium leak rates were better than the necessary internal threshold, and the characteristic bending strength obtained was in the range of 150–200 MPa. The single‐cell tests revealed current densities of 1.0 A cm^–2 at 700 mV and 800 °C (H₂/air). A first stack test proved their stackability and operational functionality.     

Overview of the Development of Solid Oxide Fuel Cells at Forschungszentrum Juelich

The SOFC group at Forschungszentrum Juelich has assembled and tested more than 220 SOFC stacks during the last 10 years, rated between 100 W and 15 kW. The topics of high-performance materials, corrosion, materials compatibility, and cost-effectiveness, including manufacturing processes, etc., are being continuously addressed. Large stacks of 5 kW and above have been operated since 2002 and have also been successfully delivered to other institutions. In parallel, lightweight stacks have been developed in the "cassette" design line for SOFC-APU. Several 1–20 kW SOFC laboratory systems are in preparation.     

Sintering and Deformation of Solid Oxide Fuel Cells Produced by Sequential Tape Casting

Anode-supported solid oxide fuel cells have been produced by water base sequential tape casting and cosintering. The curvature developed upon cosintering was monitored in situ. By tailoring the green microstructure, it was possible to reduce the curvature rate and to produce flat cells avoiding the need for a creep-flattening treatment. The power density at 800°C and 0.7 V was 751.7 mW/cm².     

固体氧化物燃料电池阳极研究

作为固体氧化物燃料电池(SOFC)的关键部件之一,阳极性能对SOFC性能有着十分重要的影响.本文主要对阳极研究进展进行综述,重点对阳极组织和性能方面的研究情况进行了阐述,合理选择阳极材料和制备工艺条件,优化阳极微观组织结构是获得高性能阳极的重要方面.对阳极材料选择和制备方法进行了简单的介绍.     

多层水系流延和共烧法制备具有阳极功能层固体氧化物燃料电池

采用多层水系流延和共烧方法制备具有阳极功能层的单电池。阳极基底、阳极功能层、电解质层和阴极层分别为Ni-YSZ、Ni-ScSZ、YSZ和LSM-ScSZ。在H2/空气气氛中,分别在700、750、800℃测试具有阳极功能层的单电池,其最大功率密度分别为：0.30、0.55W/cm2和0.8W/cm2;其对应的电池欧姆电阻（R0）分别为0.39、0.30cm2和0.19cm2。电池的极化电阻则分别为1.28、0.91cm2和0.62cm2。采用相同工艺制备无阳极功能层的单电池,其在700、750、800℃的最大功率密度分别为0.21、0.31W/cm2和0.56W/cm2,对应的R0为0.41、0.39cm2和0.28cm2。电池的极化电阻为1.40、1.27cm2和0.91cm2。这说明采用的多层水系流延和共烧法制备的固体氧化物燃料电池的阳极功能层能有效减小电池的活化极化,从而提高单电池的电化学性能。     

Planar Solid Oxide Fuel Cells Using PSZ,Processed by Sequential Aqueous Tape Casting and Constrained Sintering

A process for obtaining planar anode‐supported solid oxide fuel cells was developed. Aqueous‐based slurries were prepared and sequentially deposited via tape casting to form half cell tapes consisting of the electrolyte, functional, and structural anode. Sintering of the three‐layered tapes was done in two stages: presintering circular samples of 25 mm diameter in free conditions first, and then sintering them using zirconium disks as light loads (90 Pa), to obtain half cells having 20 mm and 3.8 m^?1 in diameter and curvature, respectively. Active materials for the electrolyte, anode, and cathode were partially stabilized zirconia (PSZ), Ni and LSM, respectively. Finally, thicknesses of complete cells were 400, 30, 30, and 80 μm for the structural anode, functional anode, electrolyte, and cathode, respectively. The cells were tested in a no‐chamber (direct‐flame) setup evaluating electrochemical performance and shock thermal resistance. Open circuit voltage was 830 mV at 560°C using methanol as fuel in a burner with porous media to modify the shape of the flame. Cells were also strong enough to resist the rapid temperature changes during several no‐chamber tests.     

Alumina Doped Ni/YSZ Anode Materials for Solid Oxide Fuel Cells

The Al₂O₃–Ni–YSZ (Y₂O₃ stabilised ZrO₂) anode materials with 0–6 wt% Al₂O₃ were prepared by tape casting method after being ball‐milled for 48 h. The influence of Al₂O₃ content on flexural strength, electrical conductivity, open porosity, relative density and thermal expansion coefficient (TEC) of Al₂O₃–Ni–YSZ anode was investigated. The introduction of Al₂O₃ significantly enhances the flexural strength of Al₂O₃–Ni–YSZ anode. The flexural strengths of 430 and 299 MPa are achieved for the specimen containing 0.25 wt% Al₂O₃ before and after reduction, respectively, while the flexural strengths are 201 and 237 MPa for the Ni–YSZ samples. The density decreases with increasing Al₂O₃ content and the open porosity increases correspondingly, after being sintered at 1350 °C for 4 h. The electrical conductivity at ambient temperature does not fall off when Al₂O₃ content is less than 1 wt%, but decreases rapidly when the content is above 3 wt% due to the formation of NiAl₂O₄. A maximum electrical conductivity of 1418 S cm^–1 is obtained in the sample containing 0.5 wt% Al₂O₃. The TEC of the samples decreases with the introduction of Al₂O₃ in the temperature range of 20–850 °C.     

Anode Supported Protonic Solid Oxide Fuel Cells Fabricated Using Electrophoretic Deposition

Intermediate temperature solid oxide fuel cells (IT‐SOFCs) were fabricated depositing proton conducting BaCe_0.9Y_0.1O_3–x (BCY10) thick films on cermet substrates made of nickel oxide–yttrium doped barium cerate (NiO–BCY10) using electrophoretic deposition (EPD) technique. The influence of the EPD parameters on the microstructure and electrical properties of BCY10 thick films was investigated. Deposited BCY10 thick films together with green anode substrates were co‐sintered in a single heating treatment at 1,550 °C for 2 h to obtain dense electrolyte and suitably porous anodes. The half‐cells were characterised by field emission scanning electron microscopy (FE‐SEM) and by X‐ray diffraction (XRD) analysis. A composite cathode specifically developed for BCY electrolytes, made of La_0.8Sr_0.2Co_0.8Fe_0.2O₃(LSCF, mixed oxygen‐ion/electronic conductor) and BaCe_0.9Yb_0.1O_3–δ (10YbBC, mixed protonic/electronic conductor), was used. Fuel cells were prepared by slurry coating the composite cathode on the co‐sintered half‐cells. Fuel cell tests and electrochemical impedance spectroscopy (EIS) were performed in the 550–700 °C temperature range. A maximum power density of 296 mW cm^–2 was achieved at 700 °C for electrolyte deposited at 60 V for 1 min.     

Anode Current Collecting Efficiency of Tubular Anode‐supported Solid Oxide Fuel Cells

Anode current collection points (ACCPs) were fabricated on the outside surface of a tubular anode‐supported solid oxide fuel cell (SOFC). The ACCPs were distributed axially along the SOFC tube with the distance between every adjacent two ACCPs the same. The effect of collecting current with different number of ACCPs on the performance of the SOFC was studied. It was found that with the same effective area, using more ACCPs to collect the current leads to better performance, while with a SOFC with a determined total surface area, there is an optimum number of ACCPs to be made and used considering the area occupied by the ACCPs themselves.     

Foaming of Filled Polyurethanes for Fabrication of Porous Anode Supports for Intermediate Temperature-Solid Oxide Fuel Cells

The development of a tailored microstructure is considered essential for the development of anode-supported intermediate temperature-solid oxide fuel cells (IT-SOFCs) as it is expected to enhance kinetics at the triple phase boundary. In this study, the application of an in situ foaming technique for the preparation of Ni-yttria-stabilized zirconia (YSZ) cellular solids as an anode support for IT-SOFCs is presented. The cermet microstructure is dependent on the preparative route followed. The presence of contaminants in the commercial template precursor was found to be detrimental for electrical properties. A high-purity polyurethane was then formulated, and tailored Ni–YSZ foams were obtained with 87% porosity. The foam microstructure is characterized by a hierarchical architecture, with interconnected networks of Ni and YSZ particles, large pores related to the open cell structure, and a submicron porosity of the structural trabecular network, with a conductivity value of 80 S/cm at 700°C.     

Preparation of BaZr0.1Ce0.7Y0.2O3–δ Based Solid Oxide Fuel Cells with Anode Functional Layers by Tape Casting

Solid oxide fuel cells (SOFCs) based on the proton conducting BaZr_0.1Ce_0.7Y_0.2O_3–δ (BZCY) electrolyte were prepared and tested in 500–700 °C using humidified H₂ as fuel (100 cm³ min^–1 with 3% H₂O) and dry O₂ (50 cm³ min^–1) as oxidant. Thin NiO‐BZCY anode functional layers (AFL) with 0, 5, 10 and 15 wt.% carbon pore former were inserted between the NiO‐BZCY anode and BZCY electrolyte to enhance the cell performance. The anode/AFL/BZCY half cells were prepared by tape casting and co‐sintering (1,300 °C/8 h), while the Sm_0.5Sr_0.5CoO_3–δ (SSC) cathodes were prepared by thermal spray deposition. Well adhered planar SOFCs were obtained and the test results indicated that the SOFC with an AFL containing 10 wt.% pore former content showed the best performance: area specific resistance as low as 0.39 Ω cm² and peak power density as high as 0.863 W cm^–2 were obtained at 700 °C. High open circuit voltages ranging from 1.00 to 1.12 V in 700–500 °C also indicated negligible leakage of fuel gas through the electrolyte.     

Thin Yttrium-Stabilized Zirconia Electrolyte Solid Oxide Fuel Cells by Centrifugal Casting

A centrifugal casting technique was developed for depositing thin 8-mol%-yttrium-stabilized zirconia (YSZ) electrolyte layers on porous NiO-YSZ anode substrates. After the bilayers were cosintered at 1400°C, dense pinhole-free YSZ coatings with thicknesses of ∼25 μm were obtained, while the Ni-YSZ retained porosity. After La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF)-Ce_0.9Gd_0.1O_1.95 (GDC) or La_0.8Sr_0.2MnO₃ (LSM)-YSZ cathodes were deposited, single SOFCs produced near-theoretical open-circuit voltages and power densities of ∼1 W/cm² at 800°C. Impedance spectra measured during cell tests showed that polarization resistances accounted for ∼70%–80% of the total cell resistance.     

Phenomenological Theory of Solid Oxide Fuel Cell Anode

We develop a phenomenological theory of oxygen‐ion‐conducting porous cermet anode for solid oxide fuel cells utilizing hydrogen, based on a simple picture of macro‐ and microkinetics of charge and gas transport in the cermet. Its basic equations account for the transport of hydrogen molecules and oxygen anions to the reaction spots, the hydrogen oxidation reaction (whose various mechanisms, including different adsorption stages, are considered) and the water‐product removal. Simple analytical results are obtained for a linear current‐voltage regime, which demonstrate the interplay of these three processes. The nonlinear behavior is analyzed and classified. Various mechanisms of reaction kinetics are considered, subject to three possible mechanisms of water adsorption, in order to specify the law of conversion of ionic current into electronic one. Revealed is the nature of the intermediate quasi‐Tafel regime, in which the anode is usually employed, and of two possible large current regimes: the saturation regime and the blocking regime (due to oxidation of the anode). The study rationalizes principles of anode functioning and builds a basis for a systematic analysis of the effects due to composite structure, that enter through the basic parameters of the theory.     

Tape Casting and Sintering of Strontium-Doped Lanthanum Chromite for a Planar Solid Oxide Fuel Cell Bipolar Plate

Nonagglomerated strontium-doped lanthanum chromite powders were prepared by a modified Pechini resinintermediate process and tape cast to form bipolar plates for a planar solid oxide fuel cell. An air-sintering technique for the strontium-doped lanthanum chromite was developed, which involved placing the green tape between Cr₂O₃-fired plates. The sintering process was found to be diffusion controlled, with densification beginning at the surface and proceeding to the interior. A bipolar plate of 2-mm thickness was fired to more than 93.5% theoretical density when fired at 1670°C for 7 h.     

Experimental Study of Internal Reforming on Large‐area Anode Supported Solid Oxide Fuel Cells

The effect of endothermic internal steam reformation of methane and exothermic fuel cell reaction on the temperature of a planar‐type anode‐supported solid oxide fuel cell was experimentally investigated as a function of current density and fuel utilization. We fabricated a large‐area (22 × 33 cm²) cell and compared temperature profiles along the cell using 30 thermocouples inserted through the cathode end plate at 750 °C under various conditions (Uf ∼50% at 0.4 A cm⁻²; Uf ∼70% at 0.4 A cm⁻²; Uf ∼50% at 0.2 A cm⁻²) with hydrogen fuel and methane‐steam internal reforming. The endothermic effect due to internal reforming mainly occurs at the gas inlet region, so this process is not very effective to cool down the hot spot created by the exothermic fuel cell reaction. This eventually results in a larger temperature difference on the cell. The most moderate condition with regards to thermal gradient on the cell corresponds to high fuel utilization (Uf ∼70%) and low current density (∼0.2 A cm⁻²). The electrochemical performance was also measured, and it was found that the current–voltage characteristics are comparable for the cell operated under hydrogen fuel and internal steam reforming of methane because of lower polarization resistance with high partial pressure of water vapor.     

固体氧化物燃料电池阳极的硫毒化与再生活化

固体氧化物燃料电池(SOFC)的阳极在使用含硫廉价燃料时极易发生硫中毒现象,导致电池性能迅速衰退。本综述在介绍SOFC电极反应机制的基础上,结合近些年的文献,对不同材料的阳极硫中毒现象进行了汇总,分析了阳极硫毒化和活化规律,深入探究了硫中毒物理与化学机制,总结了硫中毒阳极的再生及活化新方法,并分析了相关再生机制。     

固体氧化物燃料电池阳极材料研究进展

主要对SOFC阳极材料的最新研究进展进行综述。首先介绍了SOFC对阳极材料的基本要求,而后对目前各种阳极材料在性能方面的优势和不足进行了比较,其中较为详细地介绍了传统的金属陶瓷阳极和新型的钙钛矿型阳极的研究进展情况,最后对阳极材料的未来发展方向进行了展望。     

固体氧化物燃料电池双钙钛矿陶瓷阳极缺陷结构设计与性能调控

研究了固体氧化物燃料电池Sr₂Fe Mo_0.6Mg_0.25Al_0.15O₆ (SFMMA)双钙钛矿阳极的晶体缺陷结构、热膨胀性能、电荷传输特性、氧化还原稳定性以及电化学性能。结果表明:SFMMA室温下为I 4/m四方结构,400℃时材料转变为F m 3 m立方结构。SFMMA材料的实际晶体结构式为Sr₂(Fe_0.75Mg_0.25)(Mo_0.6Fe_0.25Al_0.15)O6-δ,材料晶格中含有大量反位缺陷FeB’以及—Fe_B—O—Fe_B’—键,有利于氧空位的形成及氧离子的迁移扩散。SFMMA的热膨胀系数在25~400℃和400~900℃范围内分别为13.0×10^–6K^–1和17.6×10^–6K^–1,在氢气气氛下600~900℃温度范围内电导率超过35 S·cm^–1,并且具有较快的氧表面交换特性以及非常优异的氧化还原循环结构稳定性。在900,850,800℃和750℃时,湿润H₂(3%H₂O,50 m L/min)气氛中,SFMMA/La_0.4Ce_0.6O₂(LDC)/La_0.8Sr_0.2Ga_0.8Mg_0.2O₃(LSGM)/LDC/SFMMA对称半电池面比电阻分别为0.096,0.142,0.239Ω·cm²和0.447Ω·cm²。以SFMMA为阳极组装电解质支撑型单电池SFMMA/LDC/LSGM (300μm)/Pr Ba_0.5Sr_0.5Co_1.5Fe_0.5O₅+δ,850℃时电池最大功率密度可达886 m W·cm^–2。     

Effects of Anode Microstructure on Mechanical and Electrochemical Properties for Anode‐Supported Microtubular Solid Oxide Fuel Cells

The effects of anode microstructure on mechanical and electrochemical properties were investigated for anode‐supported microtubular solid oxide fuel cells (SOFCs). The anode microstructures can be varied by the change in pore formers. For example, the acrylic resin pore former was burnt more rapidly at lower temperature than the graphite pore former during sintering. The acrylic resin pore former can introduce macropores with a diameter of several micrometers in nickel–yttria‐stabilized zirconia (Ni–YSZ) anode. The walls of the macropores were packed with the nickel and YSZ particles. Although the Ni–YSZ anode microtube using the 10 wt% acrylic resin pore former was compatible with high porosity and mechanical strength, the maximum fuel utilization was limited to 72%. On the other hand, the graphite pore former can produce a relatively uniform distribution of micropores with a diameter of several hundred nanometers. The mechanical strength was reduced with a rise in porosity for the Ni–YSZ microtube using the graphite pore former in comparison with the acrylic resin. However, a high fuel utilization of 93% was realized for the microtubular SOFCs using the 10 wt% graphite pore former in spite of lower porosity than the acrylic resin. The selection of a pore former is important to obtain higher power generation efficiency for anode‐supported microtubular SOFCs.     

固体氧化物燃料电池的制备工艺

介绍了不同形状和类型的固体氧化物燃料电池的各结构部件的常用制备工艺方法,包括:用于平板式支撑体制备的干压法和流延成型法,制备平板膜的涂刷、丝网印刷、离心沉积和旋涂法,管式支撑体制备的注浆成型、挤出成型、热压注、浸涂、凝胶铸模和相转换法,以及用于管式膜制备的涂刷、浸涂、料浆喷涂、电化学气相沉积和热喷涂法。针对每种工艺方法,介绍了其原理和基本工艺操作流程及其在固体氧化物燃料电池制备中的应用,讨论了工艺影响因素。