Type Solid Oxide Fuel Cell Research Articles

Performance of solid-oxide fuel cells operating with different sustainable fuel reformates

Solid oxide fuel cells (SOFCs) are recognized for their outstanding fuel flexibility and high efficiency in converting chemical energy into electrical energy. This research presents experiments on SOFCs fed with humidified hydrogen and hydrogen-rich gaseous reformates derived from methanol and ammonia: methanol steam reforming (MSR), methanol decomposition (MD), and ammonia decomposition (AD), at 700–850 °C. Results of SOFCs operating with MD reformate on different types of SOFCs, which to the best of our knowledge aren't available in the literature, are presented and compared with other reformate types for the first time. MD-reformate yielded the highest cell performance, with the least disparity in power density from humidified hydrogen, followed by AD-, and MSR-reformates. The study compares the direct internal reforming method, and the innovative Combined Electro-Thermo-Chemical cycle's potential. Introducing the concept of critical power density, the research evaluates fuel utilization across SOFC types. Scanning Electron Microscopy imaging and Energy-Dispersive X-ray Spectroscopy analyses confirm the viability of CO as a fuel, with no carbon deposits on the anodes when using MD-reformate. The findings demonstrate the suitability of using methanol- and ammonia-decomposition products in SOFCs and their compatibility with hybrid power generation cycles.

Performance of solid-oxide fuel cells fed with pure hydrogen and methanol steam reforming products – experimental study

A solid-oxide fuel cell (SOFC) can be fed by fuels other than pure hydrogen, making it suitable for methanol-based economy power cycles. In the reported article, we carried out for the first-time experiments on different types of SOFCs fueled with methanol steam reforming (MSR) products to evaluate and compare the SOFC performance with pure hydrogen. Through this novel comparison, the study provides new insights into the potential of using methanol as a fuel source for SOFCs. Experimental investigation was conducted to evaluate a button SOFC performance operating with MSR products and pure hydrogen under 700, 750, 800, and 850 °C. Two types of SOFC were tested: 1) NiO-YSZ anode-supported cell and 2) the Next-Cell-HP Hionic™ electrolyte-supported cell. The results indicate that the fuel cell fed with MSR products exhibits slight reduction (less than 5%) in power density compared to pure hydrogen. The results were compared with the theoretical values using zero-dimensional simulations. It was found that the change in effective diffusivity causes the main disparity in the SOFC performance when fed with MSR products and hydrogen. Based on the obtained results, we suggest that the SOFC has the potential to be successfully integrated into methanol-based power generating cycles with thermochemical recovery of a waste heat.

Performance Analysis of Anode-Supported Solid Oxide Fuel Cells: A Machine Learning Approach.

Prior to the long-term utilization of solid oxide fuel cell (SOFC), one of the most remarkable electrochemical energy conversion devices, a variety of difficult experimental validation procedures is required, so it would be time-consuming and steep to predict the applicability of these devices in the future. For numerous years, extensive efforts have been made to develop mathematical models to predict the effects of various characteristics of solid oxide fuel cells (SOFCs) components on their performance (e.g., voltage). Taking advantage of the machine learning (ML) method, however, some issues caused by assumptions and calculation costs in mathematical modeling could be alleviated. This paper presents a machine learning approach to predict the anode-supported SOFCs performance as one of the most promising types of SOFCs based on architectural and operational variables. Accordingly, a dataset was collected from a study about the effects of cell parameters on the output voltage of a Ni-YSZ anode-supported cell. Convolutional machine learning models and multilayer perceptron neural networks were implemented to predict the current-voltage dependency. The resulting neural network model could properly predict, with more than 0.998 R2 score, a mean squared error of 9.6 × 10-5, and mean absolute error of 6 × 10-3 (V). Conventional models such as the Gaussian process as one of the most powerful models exhibits a prediction accuracy of 0.996 R2 score, 10-4 mean squared, and 6 × 10-3 (V) absolute error. The results showed that the built neural network could predict the effect of cell parameters on current-voltage dependency more accurately than previous mathematical and artificial neural network models. It is noteworthy that this procedure used in this study is general and can be easily applied to other materials datasets.

Classification of Solid Oxide Fuel Cells.

Solid oxide fuel cells (SOFC) are promising, environmentally friendly energy sources. Many works are devoted to the study of materials, individual aspects of SOFC operation, and the development of devices based on them. However, there is no work covering the entire spectrum of SOFC concepts and designs. In the present review, an attempt is made to collect and structure all types of SOFC that exist today. Structural features of each type of SOFC have been described, and their advantages and disadvantages have been identified. A comparison of the designs showed that among the well-studied dual-chamber SOFC with oxygen-ion conducting electrolyte, the anode-supported design is the most suitable for operation at temperatures below 800 °C. Other SOFC types that are promising for low-temperature operation are SOFC with proton-conducting electrolyte and electrolyte-free fuel cells. However, these recently developed technologies are still far from commercialization and require further research and development.

Performance Investigation on Mono-Block-Layer Build Type Solid Oxide Fuel Cells with a Vertical Rib Design

Compared with planar-type solid oxide fuel cells (SOFCs), mono-block-layer build (MOLB)-type SOFCs have additional three-phase boundaries per unit volume, and their performance is severely limited by their longer current path. To resolve this issue, a vertical rib design, which was evaluated using a numerical method, was proposed. Compared with the conventional design, the power density for the vertical rib design increased by 12.32%. This is because the vertical rib design provides another short path for current, which not only reduces the ohmic loss in the cathode, but also decreases the ohmic polarization caused by the contact resistance. However, the vertical rib design hinders the transport of oxygen in the cathode and increases the concentration loss. Therefore, the vertical rib size design is crucial. Based on the influence of the vertical rib width, the vertical rib widths on the cathode and anode sides of 0.7 and 1 mm are recommended for different contact resistances, respectively.

Short review on global trends in SOFC scenario and future perspective

Solid oxide fuel cells (SOFCs) are high-efficiency cogeneration devices that can improve the efficiency and cost-effectiveness of various fuels: hydrocarbon, coal gas, biomass, hydrogen, and other renewable fuels. Several types of SOFCs have been used in a variety of applications, including grid-scale, stationary, and portable power generation. Ceramic materials with high chemical stability, good mechanical strength, and low activation energy are used in SOFC technology. However, the high cost of the catalyst and its operating conditions are significant barriers to commercialization. This review summarises current progress in SOFC development, focusing on; (i) current trends and publication patterns and (ii) challenges and opportunities in the SOFC advancements.

Aerosol Deposition of Thin-Film Single- and Bi-layered Solid Electrolytes for Intermediate Temperature Planar Solid Oxide Fuel Cells

One of the main limiting factors determining an increase in the specific power and efficiency of solid oxide fuel cells (SOFCs) is the development of deposition technique for thin-film gas-tight electrolytes. Hence, the development of inexpensive and scalable technologies to form thin-film electrolytes is the key direction of SOFC improvement. Despite existence of well-developed techniques, such as chemical vapor/solution deposition (CVD/CSD), electrochemical deposition (ED), thermal spray (TS), physical vapor deposition (PVD), all of them have a trend in rising deposition temperatures or establishing high vacuum that causes an increase in cost. The aerosol deposition (AD) also known as vacuum kinetic spraying (VKS) is a technique for deposition of thin and thick, gas-tight and porous layers. The deposition occurs due to the impact of high-energy particles to substrate and their consequent fragmentation and consolidation, this phenomenon is called room temperature impact consolidation (RTIC). The AD method is distinguished by the ability to lower the formation temperatures of a gas-tight electrolyte layer down to room temperatures by using a high-energy aerosol jet under conditions of low vacuum (1 – 1000 Pa) and room temperature. In addition, the method is characterized by low equipment cost and easy scaling. The possibility to deposit gas-tight films and films with controlled porosity in a wild range of thickness makes it possible to create all functional SOFCs layers without intermediate sintering steps. In the present work, the aerosol deposition technique was used to deposit thin-film electrolytes for anode-supported SOFCs. Two types of anode-supported SOFCs were manufactured. Type-1: thin-film electrolyte with the composition 8 mol.% yttria-stabilized zirconia (8YSZ) deposited on a bilayered anode substrate (current-collecting and functional sublayers) using the AD method followed by the screen-printing of a composite cathode with the composition of (La0.8Sr0.2)0.95MnO3-δ (LSM) and zirconia co-stabilized with 10 mol.% of scandia and 1 mol.% of yttria (10Sc1YSZ). Type-2: bilayered thin electrolyte made of 8YSZ and 10 mol% gadolinia doped ceria (GDC) protective layer deposited on a bilayered anode substrate using the AD method, followed by the screen printing of an active cathode with the composition of (La0.80Sr0.20)0.95CoO3–δ (LSC). The high quality of electrolyte layers of both types of SOFCs was confirmed by scanning electron microscopy, as well as electrochemical measurements, including the measurements of current-voltage characteristics and impedance spectroscopy. At 800 °C the anode-supported cells with humidified hydrogen as a fuel, and air as an oxidant demonstrated the open-circuit voltage of more than 1.04 V for both types of SOFCs, as well as specific power of more than 420 mW/cm2 and 780 mW/cm2 for type-1 and type-2 of SOFCs, respectively. Based on the studies carried out, further steps were determined to improve the electrochemical parameters of the cells, as well as to scale up to deposition on substrates with an area of 100x100 mm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Effect of Gas Leakage on the Performance of Planar Solid Oxide Fuel Cells

Solid oxide fuel cell (SOFC) is a promising power source with its strong advantage being the use of solid oxide electrolyte. This allows long time operation of the cell without electrolyte depletion. Due to the solid nature of SOFCs, sealing of the cell to the peripheral attachments becomes an issue, especially in planar SOFC type. This defect in gas sealing causes gas-leakage to the outside, as well as, gas-crossover through the peripheral areas of the cell. These leakages lead to a reduction in the open-circuit voltage (OCV) and the overall cell performance. Most previous reports made on gas crossover were only based on H2 crossover through the thin electrolyte membrane. In this work, the performance of a gas-leaked cell was compared with one with a gas-tight sealing. Both cells were 100 cm2 planar SOFCs operated at 750 and supplied with H2 and air gases at the anode and cathode respectively. The cells were supplied by a commercial SOFC producer in South Korea. Electrochemical Impedance Spectroscopy (EIS) and steady-state polarization (SSP) techniques were used in comparing the performance of the cells. An inert gas step addition (ISA) method [1] was also employed in determining quantitatively the partial pressure of water formed at the anode and its resulting internal short current. The ISA was first used to investigate the flow and partial pressure effect on the performance of a molten carbonate fuel cell (MCFC). The method adds nitrogen gas to the anode gas flow and the addition simultaneously increases the reactant gas flow until the added nitrogen arrives at the cell. The nitrogen addition port is placed ca. 5 m ahead of the anode electrode and is supplied through a 1/4-inch stainless tube, thus several seconds are required by the N2 gas to reach the cell. The SSP behavior showed that the OCV and the polarization voltages recorded were higher in the gas-tight cell than in the gas-leaked cell. The impedance spectra, on the other hand, showed a remarkable decrease in the gas-leaked cell and was attributed to the decrease in the water-induced mass transfer resistance of the cell. Through the ISA method, the partial pressure of water formed at the anode as a result of the gas leak was quantitatively determined and was observed to be significantly higher in the case of the gas-leaked cell. Similarly, the computed internal short current was greater in the case of the gas-leaked cell.[1] C.-G. Lee, B.-S. Kang, H.-K. Seo, H.-C. Lim, J. Electroanal. Chem., 540, 169–188 (2003).

Crack propagation of planar and corrugated solid oxide fuel cells during cooling process

The corrugated solid oxide fuel cell (SOFC) can effectively improve energy density and transformation efficiency compared with conventional planar SOFC, but its stability and durability have not been systematically analyzed. The residual stress of SOFC may lead to crack initiation and propagation during cooling process, so stress distributions of planar and corrugated SOFCs are simulated to analyze the location of crack initiation. The materials of electrolyte, anode, and cathode in this paper are yttria-stabilization zirconia (YSZ), Ni-YSZ, and strontium-doped lanthanum manganite (LSM), respectively. The result shows that the edge of cell is more prone to cracking. Therefore, precracks including edge crack and middle crack are introduced into anode-electrolyte interfaces to investigate crack propagation of two types of SOFCs during cooling process. For corrugated SOFC, the cracks propagate more slowly, and the cell is less prone to interfacial delamination compared with planar SOFC. In addition, the interface energy release rates are obtained to further analyze crack propagation of two types of SOFCs, and the corrugated SOFC has lower energy release rate. The research in this paper provides guidance for stability analysis and lays a foundation for future mechanical analysis of corrugated SOFC.

Modeling of all-porous solid oxide fuel cells with a focus on the electrolyte porosity design

Conventional solid oxide fuel cells (SOFCs) could suffer from carbon deposition when fueled with hydrocarbons. For comparison, a new type of SOFC with porous electrolyte can resist carbon deposition because it allows oxygen molecules to transport from the cathode to the anode. As the transport of O2 to the anode lowers the fuel cell performance and causes the risk of explosion, the rate of O2 transport must be well controlled to ensure efficient and safe operation. Following our previous model, this paper focuses on electrolyte porosity optimization under various inlet methane mole fractions, inlet oxygen mole fractions and inlet gas flow rates. Furthermore, a new design with a partial porous electrolyte is proposed and numerically evaluated. The new design significantly improves the electrochemical performance compared with all-porous one. A conversion rate >90% from methane to syngas is achieved at the 0.33 inlet CH4 mole fraction with the new design. The results enhance the understanding of all porous solid oxide fuel cells and the mechanism underlying, inspiring novel designs of solid oxide fuel cells.

Analysis of the Effect of Anode Porosity on Temperature Distribution on Planar Radial Type SOFC

Solid Oxide Fuel Cell (SOFC) is an electrochemical equipment that converts gas into electricity directly. The waste products resulting from SOFC are water vapor and heat when using hydrogen gas. The electrode of the SOFC is the anode, electrolyte and cathode. The performance of SOFC is influenced porosity of the electrode. This study explained the relationship between porosity of the anode and temperature distribution using computational fluid dynamics modeling approach (CFD). In this study, CFD modeling was done by using Fluent software. The geometry model of computational modeling is a planar radial-type SOFC. The assumptions of some boundary conditions used from the study of literature and the object of study. The standard deviation and the different of temperature of the anode-electrolyte surface used to analyse the result. Non-homogenous temperature distribution rise if the anode porosity and gas flow rate is increasing. This indicates the gradient of temperature is bigger in the higher porosity, which may cause thermal stress and degrades the materials of electrode.

Fabrication of Lanthanum Strontium Cobalt Ferrite-Gadolinium-Doped Ceria Composite Cathodes Using a Low-Price Inkjet Printer.

In this work, we have successfully fabricated lanthanum strontium cobalt ferrite (LSCF)-gadolinium-doped ceria (GDC) composite cathodes by inkjet printing and demonstrated their functioning in solid oxide fuel cells (SOFCs). The cathodes are printed using a low-cost HP inkjet printer, and the LSCF and GDC source inks are synthesized with fluidic properties optimum for inkjet printing. The composition and microstructure of the LSCF and GDC layers are successfully controlled by controlling the color level in the printed images and the number of printing cycles, respectively. Anode-support type SOFCs with optimized LSCF-GDC composite cathodes synthesized by our inkjet printing method have achieved a power output of over 570 mW cm-2 at 650 °C, which is comparable to the performance of a commercial SOFC stack. Electrochemical impedance analysis is carried out to establish a relationship between the cell performance and the compositional and structural characteristics of the printed LSCF-GDC composite cathodes.

Simultaneous Function of Gd2O3 As Solid Dopant and Sintering Aid for Anode Support Type Solid Oxide Fuel Cells

For anode support-type solid oxide fuel cell (SOFC), the mechanical strength of anode layer is important factor for commercialization and scale-up. The high sinterability of anode support increase the strength of the cell. NiO/Gd-doped ceria(GDC) cermet is commonly used material for anode support. However, in this study NiO/undoped-ceria(CeO2) was employed as starting material due to the purpose of adopting Gd2O3 as a sintering aid and a dopant. Gd2O3 was uniformly formed on the surface of NiO/CeO2 anode particles. During the sintering procedure, the Gd-ion migrate from Gd2O3 which was formed on the pre-sintered anode support to CeO2 due to similar atomic radius between Gd and Ce. In addition, sinterability of anode support was improved since Gd2O3 functioned as sintering aids. Finally, open-circuit voltage (OCV) was enhanced by less electrical loss and gas separation in soild electrolyte.

Anodic Performance of La0.5Sr0.5Mn0.9Al0.1O3 Perovskite Oxide for Solid Oxide Fuel Cells Using Dry C3H8 Fuel

Direct utilization of hydrocarbon for Solid Oxide Fuel Cells (SOFCs) using oxide ion conductor have the advantage of cost, high energy conversion efficiency and expanding the application area of SOFC. By eliminating the initial external reforming process of hydrocarbon fuels to syngas, significant advantages in cost and simplicity of gas handling process can be expected. Theoretically, direct utilisation of hydrocarbon for fuel is possible in SOFC using oxide ion conducting electrolyte, however, this is usually not easy when the conventional Ni base metal is used for anode because the formation of carbon is significantly occurred resulting in the deactivation of anode, or in the most serious case, permanent failure of the cell is occurred. Even methane as fuel, thermodynamic calculations predict that carbon will form at 1073 K unless steam is co-fed. In this study, Co and Al co-doping to La0.5Sr0.5MnO3 (LSM55) for anode were studied and it was found that doping Co is effective for decreasing anodic IR loss and the power density could be much increased by doping Co for Mn site of LSM doped with Al. XRD measurement suggests that Co was substituted Mn site over wide composition range and up to 40 mol%, partial substitution of Co to Mn in LaMnO3 structure was successfully performed. It was found that the maximum power density was increased by doping Co for LSM doped with 10 mol% Al for both H2 and C3H8 fuel. In particular, the smallest IR loss and anodic overpotential were achieved when 20 mol% Co was doped. The maximum power density of the cell using La0.5Sr0.5Mn0.7Al0.1Co0.2O3 was achieved 953 and 246 mW/cm2 for H2 and C3H8 fuel at 1273 and 1173 K, respectively. Increase in power density can be assigned to the increased surface activity to the electrochemical oxidation by doping Co. Although stability of LSM perovskite structure is still insufficient in dry C3H8 atmosphere, doping Al is effective for increasing stability and so co-doping Al and Co to Mn site of LaMnO3 is effective for decreasing anodic overpotential for direct C3H8 type SOFC. Mixing oxide ion conductor to Co and Al doped LaMnO3 anode was further studied for increasing power density. Among the examined mixed conductor, it was found that mixing Sm doped CeO2 is effective for increasing power density and the MPD of 850 mW/cm2 was achieved at 1173 K on 20 wt% SDC mixed with Co and Al doped LSM anode.

Reversible Operation of Tubular Type Solid Oxide Fuel Cells Using LaGaO3 Electrolyte Porous Layer on Dense Film Prepared by Dip-Coating Method

A micro-tubular type solid oxide fuel cell was prepared by using a NiO-YSZ anode support tube and La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte film which was prepared by dip-coating and co-sintering process. Since a large electric resistance loss (IR loss) was observed at the cathode side, LSGM porous layer was inserted between electrolyte and cathode resulting in much increased power density. The prepared cell using Sm0.5Sr0.5CoO3-δ (SSC) cathode layer on the porous LSGM layer exhibited almost theoretical open circuit voltage (OCV) of ca.1.1 V and a maximum power density (MPD) of ca. 0.782 and 0.1 W/cm2 at 973 and 773 K, respectively, in fuel cell operation. The increased MPD by an inserting the porous LSGM layer can be explained by an increase in mechanical contact and cathodic reaction area. In addition, the electrolysis operation of the prepared LSGM tubular cell with an atmosphere of 20% steam and 30% H2 was examined and it was found that the prepared tubular type LSGM cell showed a reasonably large electrolysis current. The current density of the cell with and without LSGM porous layer was 1.47 and 1.11 A/cm2 at the applied potential of 1.5 V, 973 K. As a result, it was found that the prepared LSGM electrolyte cell can be used as a reversible type cell with reasonable power density in SOFC operation and high H2 formation rate in electrolysis operation by deposition of an LSGM porous layer on the Air electrode side.

Sr(La)TiO3 Anode Substrate for Low Ni Diffusion in Sr- and Mg-Doped LaGaO3 Film Prepared with Co-Sintering Method for Intermediate Temperature Tubular Type Solid Oxide Fuel Cells

Tubular type Solid Oxide Fuel Cells (SOFCs) using La0.9Sr0.1Ga0.8Mg0.2O3−δ film was prepared by dip coating and co-sintering method. Although it is known that LaGaO3 doped with Sr and Mg denoted as LSGM has reactivity with NiO in substrate and nickel diffusion into LSGM film was occurred during co-sintering. Nickel diffusion can be decreased by using Ce0.6La0.4O2-TiO2 (Ti-LDC) and Ce0.6Mn0.3Fe0.1O2 (CMF) buffer bilayer. In this study, LSGM/Ti-LDC/CMF film was prepared on NiO-Sr0.55La0.3TiO3 (SLT) substrate. Since nickel is reacted with Ti4+ in substrate, nickel diffusion was significantly suppressed by using SLT for anode substrate and the cell using LSGM film with suppressed amount of Ni diffusion shows reasonable high open circuit potential and power density. The single SOFC using NiO-SLT substrate shows the maximum power density of 0.412, 0.165 and 0.065 W/cm2 at 973, 873, and 773 K, respectively. Although anodic overpotential is almost the same with that of the cell prepared on NiO-Ce0.8Gd0.2O2 (GDC) substrate, anodic IR loss became much smaller on NiO-GDC at low temperature and this may be assigned to the high conductivity of GDC at low temperature. However, at high temperature, because of small overpotential, the cell using LSGM film on NiO-SLT anode substrate shows higher power density than that of NiO-GDC cell.

Study on Internal Reforming Characteristic of Planar Type Solid Oxide Fuel Cell Stack

Study on Internal Reforming Characteristic of Planar Type Solid Oxide Fuel Cell Stack

Study on Solid Oxide Fuel Cell with Porous Scaffold Electrode Manufactured By Tape Casting Process

Solid oxide fuel cell (SOFC) is energy conversion device which can converts chemical energy of hydrogen and oxygen to electrical energy. Conventional SOFC is fabricated by preparing anode support and coating electrolyte and cathode by spin coating or screen printing. One alternative way to fabricating SOFC is making porous scaffold on electrolyte support by same material with electrolyte and infiltrating electrode catalyst in porous scaffold. By this procedure, nano-sized catalyst network can be distributed in electrode and microstructure of electrode become easy to control and gas diffusion in electrode can be enhanced. However, conventional scaffold type SOFC has high ohmic resistance because of thick electrolyte support. To enhancing the performance of scaffold type SOFC, electrolyte thickness should be reduced. Moreover, there is problem that connectivity of electrolyte support and porous backbones is increased but porosity of scaffold is decreased as sintering temperature is increased. For solving these problems, tape casting process was applied to fabricate SOFC. By laminating tapes of each layers and co-sintering process, both connectivity and porosity can be obtained in high temperature sintering process. In this study, performance of scaffold electrode was compared with thick film electrode and SOFC single cell with porous scaffold electrode was fabricated by tape casting process. First, performance of scaffold electrode was compared with thick film electrode by electrochemical impedance spectroscopy analysis. La0.4Sr0.6Ti0.4Mn0.6O3-δ was infiltrated to porous scaffold as electrode catalyst and symmetric cells of scaffold electrode and thick film electrode were prepared. Area specific resistance (ASR) of scaffold electrode was 0.6 Ω·cm2 and ASR of thick film electrode was 3.4 Ω·cm2 at 800℃. SOFC single cell with porous scaffold electrode was fabricated by tape casting process. 8 mol % Yttria-stabilized Zirnocia (8YSZ) was used as electrolyte material. Electrolyte slurry and porous scaffold slurry with pore former were prepared and sequentially casted to make thin electrolyte and anode support. Cathode backbone tape was laminated on the sample by hot pressing. By sintering at 1400℃, thin electrolyte and porous scaffold were fabricated. La0.4Sr0.6Ti0.4Mn0.6O3-δ and La0.8Sr0.2MnO3 were infiltrated as anode catalyst and cathode catalyst, respectively. Open circuit voltage of the sample was 1.09V at 800℃, indicating that thin and dense electrolyte was formed. And the effects of porous scaffold were also investigated with respect to different porosity and different catalyst loading amount. Figure 1

円筒横縞形SOFCの動作解析

A solid oxide fuel cell (SOFC) system and a SOFC and a gas turbine (GT) hybrid system are expected for high efficient power generators in the thermal power generations. Thermal power generators have been playing an important role in load following due to increase of renewable energy installations such as solar power and wind power generations. It is needed to find dynamic characteristic of SOFC for load following operations because the cells may not have enough strength for rapid change of thermal stress. A dynamic simulator of tubular type SOFC has been developed as a first step to complete a dynamic simulator of a SOFC/GT hybrid system in this study. To confirm the calculation validity of the simulator, a fundamental characteristic of current density and voltage which is known as an I-V curve is shown first. Secondly, temperature distributions along the cell are shown to check the influence of thermal conductivity in the cell. Finally, to show the dynamic characteristics for condition changes of the operation, calculation results are compared with existing experimental data which were obtained by a plate type SOFC. These three kinds of calculations show that the simulator has basic capability to calculate dynamic changes of SOFC.

Electrical Conducting Properties of LSF-Based Composites as an Interconnection of Tubular Type of Solid Oxide Fuel Cells

Tubular type of solid oxide fuel cells (SOFCs) is durable under high temperature operation compared to planar type SOFCs where the use of metallic interconnect is inevitable, which deteriorate electrochemical performance by Cr evaporation. On the contrary, development of ceramic interconnection has been a hurdle to fabricate tubular type SOFCs. The ceramic interconnection material must have high electronic conductivity both in oxidizing and reducing atmosphere. A gas-tight microstructure should also be obtained mostly by co-firing with anode or cathode substrates. We have been developing flat-tubular SOFCs from extruded NiO-YSZ tubular substrates. In this study we investigated (La,Sr)FeO3 (LSF)-based composite materials as the interconnection for tubular SOFCs. La0.8Sr0.2FeO3-δ, a mixed ionic and electronic conductor, was mixed with Gd- or La-doped ceria (GDC or LDC). LSF is a mixed ionic and electronic (hole) conducting material and thus shows low electrical conductivity in reducing (H2) atmosphere. However, composite materials with LSF and ceria showed moderate electrical conductivity by electronic leakage current through doped ceria in reducing atmosphere. LSF-ceria composite and LSF layers were also successfully deposited on NiO-YSZ anode substrate by conventional co-firing process. The area specific resistance of LSF/LSF-GDC bilayer on Ni-YSZ measured in air//H2 condition was initially ~50 mΩ cm2.