Design and Fabrication of a Novel Electrode-Supported Honeycomb SOFC

We report the design and fabrication of a novel electrode-supported honeycomb solid oxide fuel cell (SOFC), that can generate high volumetric power density. Among various cell designs, honeycomb SOFCs are suitable for compact SOFC modules because they have a large surface electrode area per unit volume. We have succeeded in fabricating a cathode-supported honeycomb SOFC via extrusion of a LaSrMnO₃ honeycomb monolith and through the use of a new slurry injection method for the channel surface coating using electrolyte/anode bi-layers. The fabricated honeycomb SOFCs exhibited high volumetric power densities of approximately 1.2 W/cm³ at 600°C under a wet H₂ fuel flow.     

Plasma Spraying of Lanthanum Chromite Films for Solid Oxide Fuel Cell Interconnection Application

This paper discusses a novel plasma-spraying process for depositing dense LaCrO₃-based interconnection for solid oxide fuel cells (SOFCs). Calcium aluminate was mixed with LaCrO₃ in a slurry containing PVA binder and spray dried to form free-flowing agglomerates. These free-flowing agglomerates were plasma sprayed onto a porous substrate of doped LaMnO₃ and then heat-treated to form a gas-tight and electrically conducting interconnection. Samples of the plasma-sprayed interconnection were characterized for morphology, phase constituents, and coefficient of thermal expansion, as well as electrical resistivity and oxygen nonstoichiometry at 1000°C in the P O₂ range from 1 to} 1× 10^-16 atm. The calcium aluminate additive was found to facilitate densification of the interconnection, most likely through the formation of low-temperature melting phase(s) in the system Ca–Cr–Al–O. A SOFC with such a plasma-sprayed interconnection was fabricated and electrically tested. This cell exhibited good electrical performance, and the interconnection was stable under fuel cell operation conditions.     

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.     

Preparation of Yttria-Stabilized Zirconia Thin Films on Strontium-Doped LaMnO3 Cathode Substrates via Electrophoretic Deposition for Solid Oxide Fuel Cells

A yttria-stabilized zirconia (YSZ) thin film on an La_0.8Sr_0.2MnO₃ porous cathode substrate was prepared, using electrophoretic deposition (EPD) to fabricate a solid oxide fuel cell (SOFC). The electrical conductivity of an La_0.8Sr_0.2MnO₃ substrate is satisfactorily high at room temperature; therefore, YSZ powder could be deposited electrophoretically onto an La_0.8Sr_0.2MnO₃ substrate without any extra surface treatment, such as a metal coating. Successive repetition of EPD and sintering was required to obtain a film without gas leakage, because of the thermal expansion coefficient mismatch between the YSZ and the La_0.8Sr_0.2MnO₃ substrate. On the other hand, the electromotive force of the oxygen concentration in the cell that used YSZ film prepared via EPD increased and attained the theoretical value when the number of deposition and calcination cycles was increased. Six or more successive repetitions were required to obtain a YSZ film without gas leakage. A planar-type SOFC was fabricated, using nickel as the anode and YSZ film (∼10 μm thick) that had been deposited onto the La_0.8Sr_0.2MnO₃ substrate as the electrolyte and cathode. The cell exhibited an open circuit voltage of 1.0 V and a maximum power density of 1.5 W/cm². Thus, the EPD method could be used as a colloidal process to prepare YSZ thin-film electrolytes for SOFCs.     

Structural Characterization of Lanthanum Chromite Perovskite Coating Deposited by Magnetron Sputtering on an Iron-Based Chromium-Containing Alloy as a Promising Interconnect Material for SOFCs

Chromium-containing stainless steel (SS) is a prospective material for use as an interconnect in solid oxide fuel cells (SOFCs). However, during operations at high temperatures, the growth of oxide scales causes the performance of the interconnect and SOFC as a whole to deteriorate. The coating of SS 446 with a conducting perovskite is a potential method of slowing the growth of oxide scale and, therefore, improving overall SOFC performance. In the present research, the structural characterization of a pure LaCrO₃ thin film on the SS 446 substrates has been performed as a model material that can be used as a barrier coating for the metallic interconnect. The deposition of an amorphous La-Cr-O thin film on SS 446 was performed using radio-frequency (rf) magnetron sputtering. The deposited amorphous film was annealed in air to form the desired perovskite phase. The film underwent an amorphous to LaCrO₄ phase transition during annealing at 500°C with further transformation to LaCrO₃ orthorhombic phase during annealing at 700°C. A self-organized dendritic structure was reported as a result of the perovskite-phase formation. Although formation of various oxides, such as Fe₂O₃ and Fe₃O₄, was observed during the annealing of uncoated SS 446 in air, the coating of SS 446 surface with LaCrO₃ film prevented formation of various oxide phases at the interconnect surface. The structural characterization of the films and SS 446 surfaces was accomplished using scanning electron microscopy with energy-dispersive X-ray analysis, X-ray diffractometry, micro-Raman spectroscopy, and nanoindentation.     

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.     

LSCF Nanopowder from Cellulose–Glycine-Nitrate Process and its Application in Intermediate-Temperature Solid-Oxide Fuel Cells

Nanostructured La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF) oxide powder was synthesized by a facile autocombustion process based on a modified glycine-nitrate process (GNP) using cellulose fiber as micro-reactor. As compared with the normal GNP, this novel process allows the combustion to proceed in a much more environmentally friendly and controllable way. The resulted powder is nanocrystallized with particle size of only 15–20 nm as observed by transmission electron microscopy examination. More importantly, because the metal ions could disperse homogenously in cellulose–GN precursor, SrCO₃ impurity was effectively suppressed. The concentrations of SrCO₃ impurity in LSCF products were determined by carbon dioxide–temperature-programmed desorption technique, which decreased to as low as 1.3 wt% from cellulose–GN process, in contrast to 4.3 wt% from the normal GNP. These features resulted in the attractive improvement of its cathode performance in solid-oxide fuel cells (SOFCs). The interfacial resistances of only ∼0.70 and ∼0.36 Ω·cm² at 600° and 650°C under air, respectively, were observed, which was about two times better than the LSCF cathode derived from the normal GNP. A peak power density of ∼346 mW/cm² was achieved at 600°C with cellulose–GN-derived LSCF cathode based on thin-film Sm_0.2Ce_0.8O_1.9 electrolyte SOFC using 3% humidified H₂ as the fuel.     

The Effect of H2S on the Performance of SOFCs using Methane Containing Fuel

In recent years, the interest for using biogas derived from biomass as fuel in solid oxide fuel cells (SOFCs) has increased. To maximise the biogas to electrical energy output, it is important to study the effects of the main biogas components (CH₄ and CO₂), minor ones and traces (e.g. H₂S) on performance and durability of the SOFC. Single anode‐supported SOFCs with Ni–Yttria‐Stabilised‐Zirconia (YSZ) anodes, YSZ electrolytes and lanthanum‐strontium‐manganite (LSM)–YSZ cathodes have been tested with a CH₄–H₂O–H₂ fuel mixture at open circuit voltage (OCV) and 1 A cm^–2 current load (850 °C). The cell performance was monitored with electric measurements and impedance spectroscopy. At OCV 2–24 ppm H₂S were added to the fuel in 24 h intervals. The reforming activity of the Ni‐containing anode decreased rapidly when H₂S was added to the fuel. This ultimately resulted in a lower production of fuel (H₂ and CO) from CH₄. Applying 1 A cm^–2 current load, a maximum concentration of 7 ppm H₂S was acceptable for a 24 h period.     

Thermodynamic Analysis of Methane-fueled Solid Oxide Fuel Cells Considering CO Electrochemical Oxidation

abstract Thermodynamic analyses in the literature have shown that solid oxide fuel cells (SOFCs) with proton conducting electrolyte (H-SOFC) exhibited higher performance than SOFC with oxygen ion condu...     

PhysicoChemical Characterization of Strontium- and Cobalt-Doped Lanthanum Chromite Powders Produced by Combustion Synthesis

Doped lanthanum chromites are investigated as ceramic interconnect materials to be used in high-temperature solid oxide fuel cells (SOFCs). In this work, a La_0.80Sr_0.20Cr_0.92Co_0.08O₃ powder was produced by combustion synthesis and characterized in terms of phases and crystalline structure, thermal evolution, particle size, and surface behavior. The effects of milling time on the particle size distribution and the agglomeration factor were also studied. The physicochemical characterization was completed with ζ potential measurements in order to establish the isoelectric point and the best pH conditions because slurry-processing techniques are mostly used for the manufacture of the SOFC devices.     

原位浸渍法制备NiO-BZCYYb阳极支撑SOFCs及电化学性能

采用原位浸渍法一步烧结成型制备了NiO-BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ（BZCYYb）/SDC/LSCF管状结构阳极支撑型SDC电解质膜固体氧化物燃料电池（SOFCs）。以加湿H₂（约含有体积分数为3%的水）为燃料,空气为氧化剂,研究了电池的电化学性能、热循环性能和工作电压下运行的稳定性。结果表明：电池在600、650、700、750、800℃的开路电压分别为1.084、1.074、1.067、1.058、1.046 V;最大输出功率密度分别为0.12、0.25、0.38、0.54和0.70 W·cm^-2。单电池在700℃和0.7 V连续放电测试过程中稳定运行,没有明显的下降和衰退。单电池经历了11次热循环,输出功率稳定,能够经受住重复启动考验。     

Doped Perovskite Oxide, PrMnO3, as a New Cathode for Solid-Oxide Fuel Cells that Decreases the Operating Temperature

Cathodic overpotentials of Ln_0.6Sr_0.4MnO₃ (Ln is La, Pr, Nd, Sm, Gd, Yb, and Y) were studied for a new cathode for solid-oxide fuel cells (SOFCs) with low overpotentials in a relatively-low-temperature region. Cathodic overpotentials strongly depended on the rare-earth cations in the A sites of the perovskite oxide. In particular, overpotentials of a Sr-doped PrMnO₃ cathode maintained low values despite decreased operating temperature. Consequently, almost the same power density of a SOFC with Ln_0.6Sr_0.4MnO₃ cathode was obtained at about 100 K lower operating temperature by using Sr-doped PrMnO₃ as the cathode.     

A Simple and Cost-Effective Approach to Fabrication of Dense Ceramic Membranes on Porous Substrates

A simple and elegant approach to fabrication of dense ceramic membranes on porous substrates, a traditional dry pressing of foam powders, has been developed to reduce the cost of fabrication. Gd-doped ceria (GDC, Gd_0.1Ce_0.9O_1.95) electrolyte membranes as thin as 8 μm are obtained by dry-pressing highly porous GDC powders. The membrane thickness can be readily controlled by the amount of powder. The electrolyte membranes are studied in a solid-oxide fuel cell (SOFC) with air as oxidant and humidified hydrogen (3% H₂O) as fuel. Open-circuit voltages of about 1.0 V are observed, implying that the permeability of the membranes to molecular gases is insignificant. Power densities of 140 and 380 mW/cm² are demonstrated at 500° and 600°C, respectively, representing a significant progress in developing low-temperature SOFCs.     

氨燃料固体氧化物燃料电池性能研究进展与展望

氨是一种零碳燃料,也是富氢载体,具有较大储运优势。固体氧化物燃料电池(solid oxide fuel cell, SOFC)是一种清洁高效发电装置,在分布式发电、热电联供、储能调峰等领域有广阔应用前景,氨气可直接用作SOFC阳极燃料以实现高效、清洁、低成本发电。首先简介了质子传导型和氧离子传导型氨SOFC的工作原理,电解质、电极材料的选择以及氨气在阳极的分解过程。其次总结了氨SOFC的实验研究现状,以单电池最大功率密度为评价指标,综述了不同电解质/电极材料、电解质厚度、操作温度等因素下两种传导类型的氨SOFC的性能表现,并分析了造成电池性能差异的原因。之后介绍了氨SOFC当前面临的挑战,最后对氨SOFC未来研究方向、热电联供系统的应用进行了展望。     

Thermal Expansion Behavior of Titanium-Doped La(Sr)CrO3 Solid Oxide Fuel Cell Interconnects

La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite has been designed as an interconnect material in high-temperature solid oxide fuel cells (SOFCs) because of its thermal expansion compatibility in both oxidizing and reducing atmospheres. La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ shows a single phase with a hexagonal unit cell of a = 5.459(1) Å, c = 13.507(2) Å, Z = 6 and a space group of R -3 C . Average linear thermal expansion coefficients of this material in the temperature range from 50° to 1000°C were 10.4 × 10⁻⁶/°C in air, 10.5 × 10⁻⁶/°C under a He–H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁵ atm at 1000°C), and 10.9 × 10⁻⁶/°C in a H₂ atmosphere (oxygen partial pressure of 4 × 10⁻¹⁹ atm at 1000°C). La_0.8Sr_0.2Cr_0.9Ti_0.1O₃ perovskite with a linear thermal expansion in both oxidizing and reducing environments is a promising candidate material for an SOFC interconnect. However, there still remains an air-sintering problem to be solved in using this material as an SOFC interconnect.     

Low-Temperature Pressureless Sintering of Sr- and Mg-Doped Lanthanum Gallate Ceramics by Sintering Atmosphere Control

The present investigation reports a new processing technique that can reduce the sintering temperature of Sr- and Mg-doped lanthanum gallate (LSGM), a good candidate material for the electrolyte of the solid oxide fuel cell (SOFC). When LSGM was sintered at 1623 K for 5 h in N₂ or O₂, the samples were densified over 98% relative density. In contrast, only 93% relative density was achieved after sintering in air, the conventional sintering atmosphere. As a result of better densification in N₂ or O₂, the electrical conductivity of the N₂-sintered and air-annealed or the O₂-sintered sample was higher than that of the air-sintered sample by 30%. This result shows the beneficial effect of N₂ or O₂ sintering of LSGM and provides a high possibility of a low-temperature preparation of an LSGM-based SOFC.     

Three‐Dimensional Computational Fluid Dynamics Modeling of a Planar Solid Oxide Fuel Cell

A three‐dimensional computational fluid dynamics model was developed to study the performance of a planar solid oxide fuel cell (SOFC). The governing equations were solved with the finite volume method. The model was validated by comparing the simulation results with data from literature. Parametric simulations were performed to investigate the coupled heat/mass transfer and electrochemical reactions in a planar SOFC. Different from previous two‐dimensional studies the present three‐dimensional analyses revealed that the current density was higher at the center along the flow channel while lower under the interconnect ribs, due to slower diffusion of gas species under the ribs. The effects of inlet gas flow rate and electrode porosity on SOFC performance were examined as well. The analyses provide a better understanding of the working mechanisms of SOFCs. The model can serve as a useful tool for SOFC design optimization.     

Suppression of Rhombohedral-Phase Appearance and Low-Temperature Sintering of Scandia-Doped Cubic-Zirconia

Inhibition of cubic-rhombohedral phase transformation and low-temperature sintering at 1000°C were achieved for 10-mol%-Sc₂O₃-doped cubic-ZrO₂ by the presence of 1 mol% Bi₂O₃. The powders of 1-mol%-Bi₂O₃–10-mol%-Sc₂O₃-doped ZrO₂ were prepared using a hydrolysis and homogeneous precipitation technique. No trace of rhombohedral-ZrO₂ phase could be detected, even after sintering at 1000°–1400°C. The average grain size of the ZrO₂ sintered at 1200°C was >2 μm because of grain growth in the presence of Bi³⁺. Cubic, stabilized Bi-Sc-doped ZrO₂ sintered at 1200°C had sufficient conductivity at 1000°C (0.33 S/cm) to be used as an electrolyte for a solid-oxide fuel cell (SOFC) and at 800°C (0.12 S/cm) for an intermediate-temperature SOFC.     

固体氧化物燃料电池双钙钛矿阴极材料PrBaCo2O5+δ的掺杂改性

固体氧化物燃料电池(SOFC)是一种清洁、高效的能量转换装置,其性能受制于阴极的氧还原反应,钴基双钙钛矿氧化物PrBaCo₂O_5+δ具有较高的氧表面交换系数和体扩散系数,是近年来备受重视的阴极催化材料。然而,PrBaCo₂O_5+δ在SOFC中的应用受到热膨胀匹配性差等的制约,为此,大量的工作研究了PrBaCo₂O_5+δ的掺杂改性。本文综述了各种掺杂研究,按照掺杂位置分别总结了Pr位、Ba位、Co位和O位的掺杂元素和掺杂量,结合钙钛矿的容忍因子,讨论了掺杂对PrBaCo₂O_5+δ性能的影响,包括晶体结构、氧的非化学计量δ、电导率、热膨胀系数、氧传输性能和电化学性能等。     

Selection of appropriate fuel processor for biogas-fuelled SOFC system

The performance of biogas-fed solid oxide fuel cell (SOFC) systems utilizing different reforming agents (steam, air and combined air/steam) has been investigated via thermodynamic analysis to determine the most suitable feed. The boundary of carbon formation was first calculated to specify the minimum amount of each reforming agent necessary to avoid carbon formation. The SOFC performance (electrical efficiency and power density) was determined at different biogas compositions and reforming agent:biogas ratios. The SOFC performance is better when the methane content in the biogas is higher. Steam is considered to be the most suitable reforming agent in this study as the steam-fed SOFC offers much higher power density than the air-fed SOFC although its electrical efficiency is slightly lower. When steam is added in the air-fed SOFC as in the case of the co-fed SOFC, the power density can be improved but the electrical efficiency becomes lower compared with the case of the air-fed SOFC. Finally, in order to improve the electrical efficiency of the steam-fed SOFC, the biogas split option was proposed. It was found that a higher electrical efficiency can be achieved. In addition, although the power density is lowered by this operation, the value is still higher than the case of the air-fed SOFC.