Oxidation studies of anodes layer microstructures in metal supported solid oxide fuel cells

The effect of oxidation on the microstructural and mechanical stability of ceramic layers in metal supported solid oxide fuel cells is reported. Half-cells that are produced with a reduced nickel based anode are oxidized for different times and temperatures in order to assess stability limits. Samples are analyzed in terms of the effective cell curvature and microstructure, where further insight is obtained via the observation of microstructures before and after oxidization. The interpretation is aided by a comparison to the behavior of structures without electrolyte layer. Electrolyte cracking and anode delamination are observed after oxidation, where the latter is absent in case of oxidation experiments without electrolyte layer, highlighting the failure relevance of strain induced by electrolyte deposition.     

Strength of Anode‐Supported Solid Oxide Fuel Cells

Nickel oxide and yttria doped zirconia composite strength is crucial for anode‐supported solid oxide fuel cells, especially during transient operation, but also for the initial stacking process, where cell curvature after sintering can cause problems. This work first compares tensile and ball‐on‐ring strength measurements of as‐sintered anodes support. Secondly, the strength of anode support sintered alone is compared to the strength of a co‐sintered anode support with anode and electrolyte layers. Finally, the orientation of the specimens to the bending axis of a co‐sintered half‐cell is investigated. Even though the electrolyte is to the tensile side, it is found that the anode support fails due to the thermo‐mechanical residual stresses.     

Preparation of Anode/Electrolyte Ceramic Composites by Coextrusion of Pastes

Anode/electrolyte two-layer ceramic composites for tubular solid oxide fuel cells were prepared through coextrusion of multiple pastes containing a water-based binder (an aqueous solution of hydroxypropyl methylcellulose). The multibillet extrusion (MBE) technique was found to be effective in achieving the anode/electrolyte composite pipes. Furthermore, it is possible to reduce the wall thickness of both anode and electrolyte layers by raising the extrusion ratio of each layer. The extrusion pressure and binder content required to obtain sound extrudates decreased with an increase in the fraction of nickel oxide in an anode layer. It is feasible to decrease the difference in the sintering shrinkage between the anode and electrolyte layers by incorporating calcined coarse yttria-stabilized zirconia (YSZ) powder in the electrolyte layer. The incorporation of coarse YSZ powder in an anode is effective in forming a continuous NiO network within the YSZ matrix.     

Five-layer reverse tape casting of IT-SOFC

Tape casting is a well-established method for manufacturing thin ceramic layers with controllable thickness and porosity. This study investigates the potential of 10Sc1CeSZ material for the electrolyte and anode layers for intermediate-temperature solid oxide fuel cells (IT-SOFC) in an anode-supported cell (ASC) geometry. In order to use La_0.6Sr_0.4Co_0.2Fe_0.8 Oxide (LSCF) cathode material, a Gd_0.2Ce_0.8 Oxide (GDC) barrier layer is needed; however, thermal expansion coefficient mismatch results in delamination of the GDC from the electrolyte during high temperature sintering when fabricated by conventional tape casting procedures. For the first time, ASCs have been manufactured by a five-layer tape casting technique; barrier layer, novel composite layer, electrolyte, anode functional layer, and anode substrate. Ni-ScCeSZ composite cells were tested between 650 and 800°C in H₂:N₂ fuel (85% H₂) on the anode and air on the cathode to yield a maximum power density of .46 W/cm². These results demonstrate the feasibility of this new five-layer tape casting technique to produce IT-SOFC.     

Evaluation of solution combustion synthesized NiO/GDC ceramic powders for anode substrate and anode functional layers of intermediate temperature solid oxide fuel cell

Solution combustion (SC) is a versatile technique for the preparation of composite anode powders of solid oxide fuel cell (SOFC). In the present investigation, NiO/GDC ceramic powders, an anode material for intermediate temperature solid oxide fuel cell (IT-SOFC), has been prepared by SC method by using oxalyl di hydrazide (ODH) and hexamethylnetetramine (HMT) as fuels. Reaction with ODH as fuel resulted in the powders consisting of small particle and crystallite size, whereas, powders prepared using HMT as fuel consisted of agglomerated particles which led to the porous structures in the fabricated anode layers. Through combined microstructural analysis, porosity measurements and conductivity measurements, it was inferred that powders prepared using ODH as fuel are ideal for anode functional layers. On the other hand, powders prepared using HMT as fuels are best suited for anode substrate fabrication.     

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.     

In Situ X‐Ray Diffraction and Stress Analysis of Solid Oxide Fuel Cells

To increase the long term stability and performance of solid oxide fuel cell (SOFC) materials, it is important to understand the main degradation processes in their functional layers. In this work, the interface between electrolyte and anode material was investigated by in situ X‐ray diffraction (XRD) stress and phase analysis. It has been found that the determining process for the initial degradation of SOFC is the reduction of the anode material with hydrogen. During this process a tensile strength of 600–700 MPa is measured. These stresses are induced in the electrolyte material and produce crack networks. The reduction from nickel oxide to pure nickel was monitored by in situ phase analysis. This reaction induces tensile stress at the interface between electrolyte and anode. The stress produced in the electrolyte material was also confirmed by the observation of crack networks detected using scanning electron microscopy (SEM). Finally, the reducing process was optimized using different process gases, decreasing the destructive tensile stress level.     

Ni—ZrO2金属陶瓷电极材料的研究

用普通陶瓷工艺制备了固体氧化物燃料电池（SOFCs)阳极用Ni/ZrO2金属陶瓷,用SEM、XRD等手段研究了Ni/ZrO2金属陶瓷的显微结构,并测试了Ni/ZrO2材料的热膨胀和电导率,综合以上三项对Ni/ZrO2金属陶瓷用作固体氧化物燃料电池的阳极材料性能进行评价,筛选了配方,并对制备工艺进行了讨论。     

Scale Up and Anode Development for La‐Doped SrTiO3 Anode‐Supported SOFCs

The possibility of developing large solid oxide fuel cell (SOFC) stacks based upon 25 cm² ceramic oxide anode‐supported cells is investigated. Planar fuel cells comprising strontium titanate‐based anode support impregnated with active catalysts were prepared using a combination of deposition techniques. The fuel cell tests performed in a semisealed rig have shown power densities of 185 mW cm^?2 at 850°C using humidified hydrogen as fuel and air as oxidant. The structure and evolution of the catalytically active impregnated materials‐10 mol% Gd‐doped CeO₂ and nickel‐ are analysed using electron microscopy at the end of the fuel cell test, revealing that a ceria and nickel layer surrounds the titanate backbone grains while ~50–150 nm spherical‐like nickel particles uniformly decorate this top layer.     

提高CeO2基固体电解质电性能的几种方法

CeO2基固体电解质是一种有望用于SOFC上的中温固体电解质，但其在还原气氛下容易发生还原反应而产生电子电导，影响了电池的性能。本文详细地总结了提高、改进CeO2基固体电解质电性能的几种方法，并对其今后的研究提出了自己的看法。     

用于质子交换膜燃料电池的高温无机质子传导材料研究进展

质子交换膜是质子交换膜燃料电池（PEMFC）的核心部件，其主要作用是传导质子。无机质子传导材料作为一种新型的质子传导介质，近年来逐渐引起了人们的关注。本文主要介绍了小分子磷酸、无机沸石材料、固体酸和无机氧化物陶瓷材料等几种高温无机质子传导材料，并对它们的性能和特点进行了评述。主要结论如下：小分子磷酸质子传导率高，但是容易泄露；无机沸石材料化学稳定性好，但质子传导率尚有提高的空间；无机氧化物陶瓷材料力学性能和化学温度性能均很好，但质子传导率相对较低；固体酸质子传导率优异，高温稳定性也好，是最有希望在PEMFC中获得推广应用的材料。     

氧化锆基固体电解质研究

电解质是固体氧化物燃料电池（SOFC）的核心部件,其性能的优良直接决定燃料电池的应用前景。氧化锆基陶瓷具有较高的离子电导率、良好的结构和化学稳定性,是理想的固体电解质材料。本文综合介绍了各种掺杂元素对氧化锆基固体电解质性能的影响,电解质薄膜制备方法和研究现状。并对氧化锆基固体电解质的研究方向进行了展望。     

Cu-Ce-Zr-O／YSZ阳极材料以甲烷为燃料时的抗积炭性能

为研究甲烷在固体氧化物燃料电池中操作稳定性,分别采用共沉淀法和柠檬酸溶胶.凝胶法制备了10%CuO-Ce0.15Zr0.85O2催化剂,并以此为阳极催化剂、LSM为阴极制成了YSZ电解质支撑的SOFC单电池.用XRD对材料进行表征;用SEM对阳极,阴极进行表征.以甲烷为燃料对单电池发电性能进行测试,研究了两种不同方法制备的Cu-Ce-Zr-O阳极催化剂的抗积炭性能.相对于共沉淀法,溶胶-凝胶法制备的阳极结构和发电性能都要优于前者.长期稳定性方面,共沉淀法和溶胶.凝胶法制备的Cu-Ce-Zr-O/YSZ阳极都较传统的Ni-YSZ阳极更能够长期稳定运行.     

Electrochemical properties related to the thickness control of the solid oxide fuel cell component layer using decalcomania paper

We fabricated anode-supported solid oxide fuel cells using decalcomania paper. To investigate the changes in thickness of the component layer and electrical properties in a unit cell, the number of layers of cathodes and the electrolyte decalcomania paper is changed. As a result, the thickness of the electrolyte and cathode layer regularly increases with an increase in the number of decalcomania papers attached. In addition, when only one electrolyte decalcomania paper is attached to an anode support, a tight and dense 8 μm electrolyte layer is obtained. A unit cell with a cathode thickness of 120 μm to which decalcomania paper is attached nine times is shown to have an open circuit voltage (OCV) of 1.08 V and a maximum power density (MPD) of 902 mW cm^?2 at 800 °C.     

Ceramic Fuel Cells

A ceramic fuel cell in an all solid-state energy conversion device that produces electricity by electrochemically combining fuel and oxidant gases across an ionic conducting oxide. Current ceramic fuel cells use an oxygen-ion conductor or a proton conductor as the electrolyte and operate at high temperatures (>600°C). Ceramic fuel cells, commonly referred to as solid-oxide fuel cells (SOFCs), are presently under development for a variety of power generation applications. This paper reviews the science and technology of ceramic fuel cells and discusses the critical issues posed by the development of this type of fuel cell. The emphasis is given to the discussion of component materials (especially, ZrO₂ electrolyte, nickel/ZrO₂ cermet anode, LaMnO₃ cathode, and LaCrO₃ interconnect), gas reactions at the electrodes, stack designs, and processing techniques used in the fabrication of required ceramic structures.     

Effect of Nickel Oxide/Yttria-Stabilized Zirconia Anode Precursor Sintering Temperature on the Properties of Solid Oxide Fuel Cells

An NiO/yttria-stabilized zirconia (YSZ) layer sintered at temperatures between 1100° and 1500°C onto dense YSZ electrolyte foils forms the precursor structure for a porous Ni/YSZ cermet anode for solid oxide fuel cells. Conflicting requirements for the electrochemical performance and mechanical strength of such cells are investigated. A minimum polarization resistance of 0.09 Ω^.cm²at 1000°C in moist hydrogen is obtained for sintering temperatures of 1300°–1400°C. The mechanical strength of the cells decreases with increased sintering temperature because of the formation of channel cracks in the electrode layers, originating in a thermal expansion coefficient mismatch between the layers.     

Solid Oxide Fuel Cells: Technology Status

In its most common configuration, a solid oxide fuel cell (SOFC) uses an oxygen-ion conducting ceramic electrolyte membrane, perovskite cathode, and nickel cermet anode electrode. Cells operate in the 600–1000°C temperature range and utilize metallic or ceramic current collectors for cell-to-cell interconnection. Recent developments in engineered electrode architectures, component materials chemistry, cell and stack designs, and fabrication processes have led to significant improvements in the electrical performance and performance stability as well as reduction in the operating temperature of such cells. Large kW-size power-generation systems have been designed and field demonstrated. This paper reviews the status of SOFC power-generation systems with emphasis on cell and stack component materials, electrode reactions, materials reactions, and corrosion processes.     

Simulation and Validation of Thermo‐mechanical Stresses in Planar SOFCs

To study possible failure modes of the Hexis Galileo solid oxide fuel cell stack, various stack components such as nickel/yttria stabilised zirconia anodes, lanthanum strontium manganese cathodes, 3 mol%‐yttria stabilised zirconia electrolytes and chromium alloy metallic interconnectors have been characterised with respect to their thermo‐mechanical properties. Specifically, coefficients of thermal expansion, Young's moduli, bending strengths, Poisson's ratios and fracture toughnesses have been measured. Furthermore, the temperature‐dependent warpage of complete cells has been investigated by video analysis. All experimental data were taken as input parameters for a set of finite element models to analyse various thermo‐mechanical phenomena on different length scales. The simulations offer an explanation for the often observed ‘saddle‐like‘ deformations of cells at room temperature. They also show that cracks that first develop within the anode induce local tensile stresses within the electrolyte and hence represent a weakening mechanism for the cells. It is shown that the induced electrolyte stresses depend on the anode crack density. The electrolyte stresses decrease as the distances between the anode cracks become smaller.     

Curvature Reversal and Residual Stress in Solid Oxide Fuel Cell Induced by Chemical Shrinkage and Expansion

Structural stability of layered functional ceramic composites is challenged by curvature effects and residual stresses caused by the thermal mismatch and chemical strains. In this study, a phenomenon of curvature reversal is found in the half‐cell structure of solid oxide fuel cell (SOFC) during the reduction of the half‐cell from NiO‐YSZ to Ni‐YSZ. An analytical model is derived to study the curvature and residual stress caused by the chemical shrinkage and expansion of anode. With reducing to Ni‐YSZ, the curvature of the half‐cell changes from the initial direction to an opposite direction, then back to the initial direction. This curvature reversal is inevitable during reduction while the thickness ratio of electrolyte to anode is between 0 and 0.102. The residual stress in electrolyte, calculated by the analytical model, is well agreement with the experiment result using X‐ray stress analysis. The YSZ layer is always subjected to compressive stress in despite of curvature reversal existing in half‐cell. It is impossible to get the residual stress by measuring the curvature unless the half‐cell was reduced completely.     

Intermediate Temperature Anode‐Supported Fuel Cell Based on BaCe0.9Y0.1O3 Electrolyte with Novel Pr2NiO4 Cathode

A proton conducting ceramic fuel cell (PCFC) operating at intermediate temperature has been developed that incorporates electrolyte and electrode materials prepared by flash combustion (yttrium‐doped barium cerate) and auto‐ignition (praseodymium nickelate) methods. The fuel cell components were assembled using an anode‐support approach, with the anode and proton ceramic layers prepared by co‐pressing and co‐firing, and subsequent deposition of the cathode by screen‐printing onto the proton ceramic surface. When the fuel cell was fed with moist hydrogen and air, a high Open Circuit Voltage (OCV > 1.1 V) was observed at T > 550 °C, which was stable for 300 h (end of test), indicating excellent gas‐tightness of the proton ceramic layer. The power density of the fuel cell increased with temperature of operation, providing more than 130 mW cm^–2 at 650 °C. Symmetric cells incorporating Ni‐BCY10 cermet and BCY10 electrolyte on the one hand, and Pr₂NiO_{4 + δ} and BCY10 electrolyte on the other hand, were also characterised and area specific resistances of 0.06 Ω cm² for the anode material and 1–2 Ω cm² for the cathode material were obtained at 600 °C.