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Solid oxide fuel cell (SOFC) is highly efficient and is a promising candidate for future power systems. Among the many types of SOFCs which have been reported, the micro tubular design offers improved thermal robustness, with the possibility of rapid start-up/shut-down. In this study, a new stack structure for anode-supported micro tubular SOFCs was developed in which porous MgO matrices were used to position the micro tubular cell elements. This arrangement allowed for electrical interconnection of each cell in a series, using a silver paste and a connecting LSCF paste for the anode and the cathode, respectively, in the MgO support structure. With this technique, the bundle size could be easily increased towards the kW class module design.

Fabrication technology of multi-layered electrolyte for micro tubular SOFCs has been developed. Sc2O3 stabilized ZrO2(ScSZ) and Gd2O3-doped CeO2 (GDC) was selected for the electrolyte materials and a GDC-ScSZ-GDC multi-layered electrolyte was successfully prepared using multiple dip coating and co-firing technique. The thickness of each layer for the electrolyte was about 3, 3, and 12 micron, respectively. The cell performance test showed the open circuit voltage (OCV) of over 1 V at 600oC or higher, while a SOFC with 10 micron thick GDC electrolyte showed the OCV of 0.78 V at 600oC. The cell performance of 0.35 Wcm-2 @ 0.7 V was obtained at the operating temperature of 650 oC.

Porous Anodes for Solid Oxide Fuel Cells Fuel cells that use ion-conducting oxides as the electrolyte can be highly efficient and use hydrocarbon fuels directly. However, their very high operating temperatures (usually above 700°C) can lead to unwanted reactions with their electrode materials and premature degradation of their performance. In order to improve fuel-cell electrochemical performance, Suzuki et al. (p. 852 ) describe a route for increasing the porosity of the anode material, which contains nickel oxide and zirconia doped with scandium and cerium and is fabricated as a cylinder. Subsequent coating and firing steps added a layer of a zirconia-based electrolyte and the (La,Sr)(Co,Fe)O 3 cathode. The resulting fuel-cell power density exceeded 1 watt per square centimeter at 600°C, and its performance improved as hydrogen fuel velocities were increased through the cell.

Here we report the effect of anode microstructure on the SOFC performance using two types of micro tubular SOFCs, 0.8 and 1.6mm in diameter with different anode microstructure (Cells A and B). The cells consisted of NiO-Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and (La, Sr)(Fe, Co)O 3 (LSCF)-GDC as a cathode. The anode tube for Cell A was prepared using NiO (d g ~ 5µm) and GDC (d g ~ 0.2µm) powders without using a pore former, while the anode tube for Cell B was prepared using NiO (d g ~ 0.5µm)and GDC(d g ~ 0.2µm) powders using a pore former. The peak power density of these cells were shown to be 203, 400 and 857mW cm − 2 for Cell A and 273, 628 and 1017mW cm − 2 for Cell B, respectively at 450, 500, and 550°C operating temperature. Both cells showed outstanding performance, and furthermore the anode microstructure of Cell B was shown to be more optimized for better cell performance.

A wet atomising system has been employed as a novel method to prepare ultrafine Gd-doped CeO2 (GDC) electrolyte slurries. By changing the fluid flow pressure and repeating the atomisation process several times for the same atomised slurries, we have obtained optimised ultrafine GDC slurry with high-dispersed and homogeneous distribution. The sizes of the particles of GDC were in the range of tens of nanometres. A highly dense electrolyte layer (membrane) was prepared using the ultrafine GDC slurries for intermediate temperatures microtubular solid oxide fuel cell (SOFC) applications. The SOFC was fabricated by using supporting porous anode tubes of NiO and GDC, and the cathode consisted of La0.6Sr0.4Co0.2Fe0.8O3–y and GDC. A dense 10 μm GDC electrolyte layer was obtained at a lower sintering temperature of 1,250 °C for 1 h. The SOFC was tested with humidified (3% H2O) hydrogen as a fuel and the static air as an oxidant, and the tubular cell maintained its high performance even at 500 °C.

A fundamental issue with micro-tubular solid oxide fuel cells (SOFCs) is improvement of the mechanical strength of the cell. Fabricated using extrusion and co-firing techniques, the approximately 1.7 mm diameter SOFC tubes examined in this work are composed of a 50:50 NiO and Gd 0.2 Ce 0.8 O 2− x Gd-doped ceria (GDC) cermet anode (support tube), GDC as an electrolyte and La 0.8 Sr 0.2 Co 0.6 Fe 0.4 O 3 (LSCF)–GDC as a cathode. The mechanical properties of SOFCs are analyzed through internal burst testing and micro- and nano-indentation testing; the burst test is an especially important parameter because of improved power efficiency at increased fuel pressures. Results from micro- and nano-indentation tests performed on electrolyte-coated Ni–GDC anode pellets indicate that the hardness of GDC is comparable or greater than that of YSZ. In order to develop a trend for the mechanical behavior of micro-tubes in relation to variations in fabrication techniques, several parameters were varied. The standard anodes, used as a baseline, have four key design parameters as follows: they are not reduced, contain 40 vol% pore former, are sintered at 1400 °C and have a wall thickness of approximately 315 μm. An independent variation on each of the four parameters is performed. The four variations are (1) to reduce the standard tube, (2) to increase the percent pore former to 50% then to 60%, (3) to decrease sintering temperature to 1350 °C, and (4) to decrease the wall thickness to approximately 230 μm. An average burst strength of 22.4 ± 1.5 MPa is observed for the standard tubes, 34.2 ± 16.5 MPa for the reduced tubes, 16.5 ± 4.2 MPa for 50 vol% pore former and 11.7 ± 7.5 for 60 vol% pore former, 29.3 ± 9.6 MPa for the decreased sintering temperature and 34.3 ± 6.9 MPa for the thinner-walled tubes.

Steam electrolysis was carried out using a microtubular ceramic reactor with the following cell configuration: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3− δ (LSCF)–Ce 0.8 Gd 0.2 O 1.9 (CGO) electrode/CGO buffer layer/(ZrO 2 ) 0.89 (Sc 2 O 3 ) 0.1 (CeO 2 ) 0.01 (ScSZ) electrolyte/Ni-ScSZ electrode supporting tube. 10% H 2 /Ar gas was used as steam carrier gas, and 18% steam was supplied to the ceramic reactors. The cell performance was as follows: 1.43 V at 0.1 A cm −2 and 650 °C (Area specific resistance: 4.7 Ω cm 2 ) or 1.37 V at 0.1 A cm −2 and 700 °C (4.3 Ω cm 2 ). During steam electrolysis, hydrogen production proportionally increased with current density according to Faraday's law, and heat generation at a low current density was observed by an electrochemical technique. Voids and Zr diffusion from the ScSZ electrolyte were confirmed in the CGO buffer layer. Such factors near the surface probably influenced the increase in ohmic loss and electrode polarization.

Micro-tubular solid oxide fuel cells (SOFCs) have high thermal stability and higher volumetric power density, which are considered to be ideal features for portable power sources and auxiliary power units for automobile. Here, we report a new stack design using anode supported micro-tubular SOFCs with 2 mm diameter using Gd doped CeO2 (GDC) electrolyte, NiO-GDC anode and (La, Sr)(Co, Fe)O3 (LSCF)-GDC cathode. The new stack consists of three bundles with five tubular cells, sealing layers and interconnects and fuel manifolds. The performance of the stack whose volume is 1 cm3 was shown to be 2.8 V OCV and maximum power output of 1.5 W at 500 °C, applying air only by natural convection. The results also showed strong dependence of the fuel flow rates on the stack performance, which was correlated to the gas diffusion limitation.

In this study, glass–ceramic composites as sealing materials for solid oxide fuel cells (SOFCs) were investigated. A commercially available magnesium boro-silicate glass with soften temperature of about 700 °C, and MgO powder were used for the composites in order to control and improve the thermal property as the sealing materials for low temperature SOFC. MgO was added 0–30 vol% into the glass matrix to prepare the glass–ceramic composites and the properties of each composite was investigated. An increase of the coefficient of thermal expansion (CTE) for the glass–ceramic composites and an improvement of thermal stability were observed as the amount of the MgO additive increased, while the electrical and sealing performances were degraded. As a result, the composite with 10 vol% MgO additive was shown to have high thermal stability with reasonable sealing performance.

We report the world smallest tubular solid oxide fuel cell – needle-type micro SOFCs applicable to micro power devices. The anode-supported cell was prepared using cost effective, conventional extrusion and dip-coating techniques. The diameter of the needle-type cell is 0.4 mm, consisting of NiO-Gd doped Ceria (GDC) for anode (under 100 μm thick), GDC for electrolyte (8 μm thick), and (La, Sr) (Co, Fe)O3 – GDC for cathode. The cell performances of 80, 160 and 300 mW cm−2 at 450 °C, 500 °C, and 550 °C, respectively, were obtained using a simple current collection method with wet H2 fuel. Impedance analysis indicated that the SOFC has a potential to be improved by optimizing the current collection method. Bundle concept using the SOFCs with the packing density of 100 cells in 1 cm3 was also proposed. Keywords: SOFC, Micro-tubular, Low temperature, Ceria, Anode-supported

Fabrication and characterization of tubular SOFCs under sub-millimeter (0.8 mm), bundles and stacks for low temperature operation were shown. The materials used in this study were Gd doped CeO 2 (GDC) for electrolyte, NiO–GDC for anode and (La, Sr)(Co, Fe)O 3 (LSCF)–GDC for cathode, respectively, and LSCF for supports of the tubular cells for bundle fabrication. After applying a sealing layer and current collector for each bundle of five micro tubular SOFCs, each bundle was stacked vertically, to build a four-storey cube-type stack with volume of about 0.8 cm 3 . The performance of the stack was shown to be 3.6 V OCV and 2 W maximum output power under 500 °C operating temperature. Preliminary quick start-up test was also conducted at the condition of 3 min start-up time from 150 to 400 °C for 5 times, and the results showed no degradation of the performance during the test.

In this study, new temperature monitoring method for solid oxide fuel cells (SOFCs) was proposed, and the demonstration using micro-tubular SOFCs has done. The fabricated micro-tubular SOFCs were operated under the two different conditions, and polarization during the power generation was measured. The cell resistance as a function temperature was also measured. Based on the temperature dependence of cell resistance and the measured ohmic drop during the power generation, the cell temperature was estimated. The estimated cell temperature clearly depended on operation condition and increased with increasing of the current density. The estimated cell temperature was also in nearly proportion to the temperature which was measured by a thermocouple, and it was conformed that this temperature monitoring method by electrochemical technique certainly functioned.

Tubular SOFCs have shown many desirable characteristics such as high thermal stability during rapid heat cycling and large electrode area per unit volume, which can accelerate to realize SOFC systems applicable to portable devices and auxiliary power units for automobile. So far, we have developed anode-supported tubular SOFCs with 0.8–2 mm diameter using Gd-doped CeO 2 (GDC) electrolyte, NiO-GDC anode and (La, Sr)(Co, Fe)O 3 (LSCF)-GDC cathode. In this study, a newly developed cube-type SOFC stack which consists of three SOFC bundles was designed and examined. The bundle consists of three 2 mm diameter tubular SOFCs and a rectangular shaped cathode support where these tubular cells are arranged in parallel. The performance of the stack whose volume is less than 1 cm 3 was shown to be 2.8 V OCV and over 1 W at 1.6 V under 500 °C. Cathode loss factor due to current collection from cathode matrix was also estimated using a proposed model.

We report the fabrication and characterization of a micro-tubular cathode-supported cell consisting of a Ce0.9Gd0.1O1.95 electrolyte with a Ni–cermet anode on a porous La0.6Sr0.4Co0.2Fe0.8O3−δ/Ce0.9Gd0.1O1.95 (60:40 volume) tube (460 μm wall thickness and 2.26 mm diameter). The cells were fabricated by a cost-effective technique involving extrusion molding and slurry coating through a co-firing process. Densification of the ceria film (thickness

In this study, micro tubular SOFCs under 1 mm diameter have been fabricated and investigated at 450–550 °C operating temperature with H 2 fuel. The performance of the 0.8 mm diameter tubular SOFC was 110–350 mW cm −2 at 450–550 °C operating temperatures. To maximize the performance of the cell as well as to optimize the geometry of tubular cells, a current collecting method used in the experiment was examined. A model was proposed to estimate the loss of performance for single cell due to the current collecting method as functions of anode tube length and thickness. The results showed that the losses of performance were calculated to be 0.8, 2.0, and 4.6% at 450, 500, and 550 °C operating temperatures, respectively, for the 0.8 mm diameter tubular SOFC with the length of 1.2 cm.

Micro-tubular solid-oxide fuel cell consisting of a 10-μm thick (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (ScSZ) electrolyte on a support NiO/(ScSZ) anode (1.8 mm diameter, 200 μm wall thickness) with a Ce0.8Gd0.2O1.9 (GDC) buffer-layer and a La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)/GDC functional cathode has been developed for intermediate temperature operation. The functional cathode was in situ formed by impregnating the well-dispersed nano-Ag particles into the porous LSCF/GDC layer using a citrate method. The cells yielded maximum power densities of 1.06 W cm−2 (1.43 A cm−2, 0.74 V), 0.98 W cm−2 (1.78 A cm−2, 0.55 V) and 0.49 W cm−2 (1.44 A cm−2, 0.34 V), at 650, 600 and 550 °C, respectively. Keywords: Solid-oxide fuel cells, Micro-tubular, Impregnation, Electrochemically catalytic Ag, Power performance

It is known that a small tubular design enables SOFCs to have high thermal shock resistance and rapid startability. In this study, we fabricated anode-supported micro-tubular SOFCs which were introduced a Sc-doped ZrO2 electrolyte. The cell dimensions were 1.8 mm in diameter and 500 mm in length. And the cell configuration was (La,Sr) (Fe,Co)O3 - Gd doped CeO2 (CGO) cathode /CGO buffer layer /Sc-doped ZrO2 electrolyte (ScSZ) / Ni-ScSZ anode. The power generating test and the polarization measurement of this micro tubular cell have done at 650oC. The maximum power density of this cell was ca. 0.7Wcm-2 (2.6Acm-2, 0.26V) at 650oC, and the polarization resistance was higher than the ohmic resistance.

Solid oxide fuel cells (SOFCs) have serious problems under heating cycle. As a solution for this problem, use of micro- tubular SOFCs is considered for robustness under rapid changes of operating temperature. We fabricated cube-shaped SOFC bundles with following method; Micro-tubular Gd-CeO2(GDC)-NiO anode was fabricated by extrusion, and then was co-fired with GDC electrolyte coated on the surface of the anode tube. La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF) cathode matrices with grooves were also prepared by extruding of a mass with LSCF powder and pore-former. Then, the tubes were arranged in the grooves of LSCF cathode matrices, where the tubes and the matrices were jointed with LSCF pastes. Optimization of the micro tubular cell configuration in cube-shaped SOFC bundles and microstructure of cathode is important to achieve our target power density (2W/cm3). In this study, we considered the configuration of cube-shaped SOFC bundles and investigated the character of single tubular cell and cathode porous matrices.

n this study, we fabricated anode-supported solid oxide fuel cell (SOFC) tubes of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) - Ce0.8Gd0.2O1.9 (CGO) cathode / CGO buffer layer / (ZrO2)0.89 (Sc2O3)0.1(CeO2)0.01 (ScSZ) electrolyte / Ni-ScSZ anode. The power generation test of the SOFC was carried out at 0.1 - 0.7 MPa at 650{degree sign}C. Using wet H2-N2 mixture gas and air, the maximum power density at 0.1 MPa was 0.68 W cm-2 (@2.6 A cm-2, Uf = 78%). With increase operating pressure, the performance has been improved, and the power density finally became over 1.48 W cm-2 (@2.8 A cm-2, Uf = 86%). It was conformed by current interruption method that both of the polarization resistance and ohmic resistance reduced under the pressurized condition.

The Ni-cermet anode-supported micro-tubular SOFC based on La0.6Sr0.4Co0.2Fe0.8O3-d cathode shows high power density below 650{degree sign}C. Current collecting appears to a major obstacle towards the integration of these single cells in a cube-shaped cell bundle, which can finally lead to a higher volumetric power density. This study aims to develop and modify for high performance current collectors for the compact and high power SOFC bundles. Feasibility of the La0.6Sr0.4Co0.2Fe0.8O3-d based oxides was then investigated. The well-dispersed Ag particles were introduced to give an enhanced electron path and a lowed interfacial resistance.

Micro tubular SOFCs have been expected to overcome shown many desirable characteristics over conventional (planar) SOFCs such as high thermal stability during rapid heat cycling and high packing density of the cells, which enables to realize micro SOFC systems applicable to portable devices and auxiliary power units for automobile. Our research project Advance Ceramic Reactors aims to develop innovative processing method to fabricate such new micro tubular SOFCs and their stacks. In this study, new micro tubular SOFC stacks was fabricated and the performance of the stack was investigated.

Solid oxide fuel cells (SOFCs) have the highest energy efficiency among various power generators. However, SOFCs generally have problems regarding to heat stress due to the heating cycle during cell operation, especially quick start-up/shut-down and the size of SOFC systems, which limit their application use. Micro tubular SOFCs are expected to be a solution to these problems because they are considered to be robust for repeated cycling under rapid changes in cell operating temperatures. If highly dense micro tubular SOFC stacks become available, it will accelerate development of SOFC systems, as well as increase a variety of applications. Our study aims to fabricate compact and high power SOFC bundles, which are composed of tubular SOFCs with the diameter of sub-millimeters. In this study, as the first stage of the development, processing technologies of tubular SOFCs and cube shaped cathode matrices were examined. Micro tubular SOFCs were fabricated using extrusion and co-firing techniques. The tubular SOFCs were then, arranged in the cathode matrices, which were piled up to be a cube shaped bundle. Each component of the cube shaped micro tubular SOFC bundle (cube) will be discussed in detail.

The catalytic activity of the La 0.6 Sr 0.4 Co x Fe 1− x O 3−δ ( x = 0.2) perovskite cathode was significantly improved by introducing Ag. This strongly depends on the particle size of Ag that relates to the synthesis route. The Ag particles in nano-range were in situ incorporated into the La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ based cathode using a novel infiltration. The functional cathode was successfully operated on the anode-supported cell with a ceria thin-electrolyte resulting in a higher cell output at 500 °C. Durability of the cell was evaluated within a short-term period.

In this study, we proposed the non-combined cycle pressurized IT-SOFC system for efficient use of compression hydrogen energy in a gas cylinder, and the possibility of the system was discussed by comparison of the SOFC power gain by pressurization and power consumption gain of an air compressor. Oxygen partial pressure pO2 management on cathode side is also important because pO2 directly influences to the polarization resistances. For estimation of the power densities as functions of air utilization Uair and pressurized air remaining factor χ(=(pO2,cathode−0.021Uair)/(0.21(pair−0.1))), the ac impedance data of a micro tubular single cell, which was developed in ceramic reactor project, was measured under the several pO2 conditions on cathode side at atmospheric pressure (0.1MPa) and 0.3MPa. Area specific activation polarization resistance Rpol.act and concentration polarization resistance Rpol.conc. were obtained from the the ac impedance data, and the power generation curves of SOFC bundle under the several Uair and χ conditions were simulated using the Rpol.act and Rpol.conc. These simulations suggested that if χ is high enough, i.e. over 0.5, pressurization could dramatically reduce Rpol.act and Rpol.conc. even at Uair = 0.95. Based on these simulated power generation curves of the SOFC bundle, the preconditions of SOFC system were expanded up to 10kW class for practical comparison between SOFC power and power loss by the air compressor. This comparison is suggested that the maximum actual power Wact. of pressurized SOFC at 0.3MPa can be higher than that of atmospheric pressure SOFC if χ is over c.a. 0.5. The χ and Uair must be kept high enough for the high performance operation. It is found out that effective exhaust of low pO2 gas from system is important for holding the high χ.Copyright © 2012 by ASME

A microtubular solid oxide fuel cell (SOFC) bundle was developed based on a new design. Anode-supported microtubular SOFCs with the cell configuration, La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF)-Ce 0.9 Gd 0.1 O 1.95 (CGO) cathode/CGO electrolyte/Ni-CGO anode were fabricated and bundled in a porous LSCF current-collecting cube with sides of 1 cm. The power generation of the fabricated SOFC bundle was measured under pressurized conditions. Using humidified 30% H 2 /N 2 mixture gas and air, the cubic power density of the bundle at 500°C under atmospheric pressure (0.1 MPa) was 0.47 W cm ―3 at 0.4 A cm ―2 . With increasing operating pressure, the performance increased, and the cubic power density reached 0.66 W cm ―3 at 0.6 MPa. The power enhancement brought about by pressurization was due to increased open circuit voltage and reduced polarization resistance. After comparing the power gain of the pressurized SOFC and the power consumption gain of the air compressor used for pressurization, it was found that pressurized cell operation exhibited the highest actual power gain at around 0.3 MPa.

Microtubular solid oxide fuel cells (SOFCs) are considered to be ideal for application such as auxiliary power units due to their high thermal shock resistance and their compactness (high volumetric power density). Thus, it is of importance to understand the performance of the cell under actual fuel-fed condition. In this study, we demonstrate the performance of the microtubular SOFCs using a forming gas and a gas reformed from ethanol-water mixture.

In this work, a microtubular cell consisting of a thin Ce0.9Gd0.1O1.95 (GDC) electrolyte (thickness: below 10 μm) on a support NiO/GDC anode (1.8 mm outer diameter, 200 μm wall thickness) with a La0.6Sr0.4Co0.2Fe0.8O3−δ/GDC functional cathode has been developed for intermediate/low temperature operation. The functional cathode was prepared by in situ infiltrating the electrochemically catalytic nano-Ag particles into the as-established 20 μm thick cathode. The as-proposed Ag-impregnation route ensures a very homogeneous particle dispersion and a good adhesion of Ag to the ceramic matrices. The cells were successfully operated to produce the maximum power densities of 0.41 W cm−2 (1.27 A cm−2, 0.32 V), 0.83 W cm−2 (2.23 A cm−2, 0.37 V), and 1.05 W cm−2 (2.39 A cm−2, 0.44 V) at 450°C, 500°C, and 550°C, respectively.

Solid oxide fuel cells (SOFCs) have the highest energy conversion efficiency among various power generators and expected to be earlier commercialization. Our study aims to develop fabrication techniques of microtubular SOFC bundles and establish realistic bundle structure for kilowatt class module. So far, we have succeeded to establish fabrication technology of the microtubular SOFC bundles using porous supporting matrices. In this study, the simulation study of the microtubular SOFC bundle was carried out to understand Joule heat and temperature distribution in the microtubular SOFC bundle during operation. The results indicated that the method of current collection had to be carefully considered, since the total output power loss of the bundle was estimated to be 27.8%. The temperature distribution of the bundle using porous MgO matrices turned out to be moderate compared with that in the previous bundle using porous (La,Sr)(Co,Fe)O3 matrices due to the difference in the thermal conductivity of each matrix constitute.

Ceramic reactors, which convert materials and energy electrochemically, are expected to solve various environmental problems, and the use of a microreactor design was shown to realize a high performance reactor with high thermal durability, operable at lower temperatures. Our research project, “Advanced Ceramic Reactor,” supported by the New Energy and Industrial Technology Development Organization, targets to develop new fabrication technology for such microreactors and modules using conventional, commercially available materials. In this study, fabrication technology of microtubular ceramic reactors have been investigated for aiming solid oxide fuel cell (SOFC) applications such as small distributed power generators, auxiliary power units for vehicles, and portable power sources. So far, microtubular SOFCs under a diameter of 1 mm using doped ceria electrolyte, and Ni–ceria based cermet for tubular support has been successfully developed and evaluated. The single microtubular SOFC showed a cell performance of 0.46 W/cm2 (at 0.7 V) at 550°C with H2 fuel. The bundle design for such tubular cell was also proposed and fabricated. The discussion will cover the fabrication technology of a single tubular SOFC and bundle, and the optimization of the cell and bundle design by considering gas pressure loss and current collecting loss.

Currently, microtubular solid oxide fuel cells (SOFC) bundles are under development, which consist of microtubular SOFCs (diameter=0.8–2 mm) and porous cathode matrix where the SOFCs are integrated. In this study, a new fabrication process of the sealing layer for the microtubular SOFC bundles was examined using MgO-magnesium boro-silicate glass composites. A sheet and paste of these composites were prepared, and the microstructure and shrinkage behavior of the composite glass layers were investigated to minimize the deformation of the layer during fabrication process. The results indicated that using 100% glass sheet with the composite glass pastes appeared to be effective in reducing the shrinkage of the glass layer. In addition, the effect of sheet thickness on the shrinkage behavior was investigated and showed that the shrinkage ratio reduced as the sheet thickness decreased, and the shrinkage of about 0.2% was achieved at the sheet thickness of about 200 μm without defects or shape deformations. Thus, this fabrication method turned out to be effective for constructing a sealing layer for the microtubular SOFC bundles.

Microtubular solid oxide fuel cells (SOFCs) are shown to be robust under rapid temperature changes and have large electrode area per volume (high volumetric power density). Such features are believed to increase a variety of application. Our study aims to establish a fabrication technique for microtubular SOFC bundles with the volumetric power density of 2 W cm−3 at 0.7 V. So far, we have succeeded to develop a fabrication technology for microtubular SOFC bundles using anode supported tubular SOFCs and cathode matrices with well-controlled microstructures. A key to improve the performance of the microtubular SOFC bundles is to optimize the microstructure of the cathode matrices because it influences a pressure loss for air and electric current collection. In this paper, a simulation study of an air flow, temperature, and potential distributions in the microtubular SOFC bundle was conducted in order to understand the characteristics of the present bundle design. In addition, operating conditions of the microtubular SOFC bundles was discussed for realizing the target power density of 2 W cm−3.

Publisher Summary A typical Solid oxide fuel cell (SOFC) consists of doped zirconia for an electrolyte, Ni cermet for an anode and doped lanthanum manganite for a cathode, and it has shown its long-term stability over 20,000 h operation as well as high power output up to 2 W/cm2 at 800°C. SOFCs have been recognized as a keystone of the future energy economy, and the development of SOFC systems has been an important issue in recent years. This chapter discusses development of micro tubular SOFCs, summarizes recent development of fabrication/integration technology for micro tubular SOFCs, and examines characteristics of micro tubular SOFCs. High-performance SOFCs lies in the design of the cell/bundle/stack and novel fabrication technology that can realize optimized electrode structures. By using recent development of fabrication/integration technology for micro tubular SOFCs with diameters of 0.8–2.0 mm in diameter operable at at/under 550°C are fabricated. Characterization of micro tubular SOFC is discussed in detail, including current collecting loss due to the dimension of the cell. For practical realization of the micro tubular SOFC system, further investigations of the tubular cells and the bundles are necessary to gain the knowledge necessary for understanding the following issues: stack design (manifold design); thermal distribution in the stack and thermal management (simulation); gas pressure loss in the stack/system and optimization of gas flow; fuel utilization; current collecting loss from the cathode matrix; and sealing technology.

We developed evaluation technologies for microtubular solid oxide fuel cells under pressurized conditions. The pressurized cell evaluation system for the single cell was produced. The chamber temperature of the evaluation system can be controlled up to 750°C, and the maximum chamber pressure is 0.8MPa. It was possible to manually control the pressure difference between air and fuel gas within ±3kPa during the pressure increase. The hard sealing technique was introduced for the evaluation under pressurized conditions. Using two different types of commercial inorganic ceramic adhesives, the gas leakage was controlled at approximately 2%. Differential pressure control between fuel and air is effective for the stable open circuit voltage and power generation. The power generation under pressurized conditions was successful at 650°C, and the pressurized effect was clearly confirmed.

In this study, a single-step cofiring through the extrusion molding and wet-ceramic coating technique was developed to fabricate a cathode-supported microtubular cell. The cell is consisting of a Ce0.9Gd0.1O1.95 (GDC) electrolyte with a NiO–GDC anode on a porous La0.6Sr0.4Co0.2Fe0.8O3−δ∕GDC tube (460μm wall thickness and 2.26mm diameter). Densification of the ceria membrane (thickness

Microtubular solid oxide fuel cells (SOFCs) have successfully demonstrated their advantages over conventional (planar) SOFCs, such as high thermal stability during rapid heat cycling and large electrode area per volume, which enables one to realize SOFC systems applicable to portable devices and auxiliary power units for automobile. In this study, the fabrication method of the microtubular SOFCs was examined. Shrinkage behavior and the microstructure of electrolyte/anode as a function of sintering temperature were shown and correlated with densification of the electrolyte during cosintering process.

Ceramic reactors, which convert materials and energy electrochemically, are expected to solve various environmental problems, and use of micro reactor design was shown to realize high performance reactor with high thermal durability operable at lower temperatures. Our research project “Advanced Ceramic Reactor” supported by NEDO targets to develop new fabrication technology for such micro reactors and modules using conventional, commercially available materials. In this study, fabrication technology of micro tubular ceramic reactors have been investigated for aiming solid oxide fuel cells (SOFCs) application, such as small distributed power generators, APU for vehicles, and portable power sources. So far, micro tubular SOFCs under 1 mm diam. using doped ceria electrolyte and Ni-ceria based cermet for tubular support has been successfully developed and evaluated. The single micro tubular SOFC showed cell performance of 0.46 W/cm2 (@0.7 V) at 550 °C with H2 fuel. Bundle design for such tubular cell was also proposed and fabricated. Discussion will cover fabrication technology of single tubular SOFC and bundle, and optimization of the cell and bundle design by considering gas pressure loss and current collecting loss.

A micro tubular solid oxide fuel cell (SOFC) bundle was developed based on new concept. The anode-supported micro tubular SOFCs with the cell configuration, La0.6 Sr0.4 Co0.2 Fe0.8 O3−δ (LSCF) – Ce0.9 Gd0.1 O2−δ (CGO) cathode / CGO electrolyte / Ni – CGO anode were fabricated and were bundled by a porous LSCF current collecting cube 1 cm on a side. The power generation test of the fabricated SOFC bundle was carried out under pressurized conditions. Using wet 30%H2 / N2 mixture gas and air, the cubic power density of the bundle at 500°C was 0.47 Wcm−3 at 0.4Acm−2 , atmospheric pressure (0.1MPa). With increasing operating pressure, the performance has been improved, and the cubic power density finally reached to 0.66 Wcm−3 at 0.6MPa. Pressurization effect for the power improvement was brought about by the open circuit voltage enhancement and reduction of the polarization resistance.Copyright © 2008 by ASME

Solid oxide fuel cells (SOFCs) have several problems regarding to rapid heat cycle. In order to solve these problems, we utilized micro tubular SOFCs and developed a micro tubular SOFC bundle with the performance over 3 Wcm-3. In this study, we focused on the establishment of fabrication technique of 15 cm3 stack-bundle and assembling technique of a few-hundred-W class module. The micro tubular cells in the stack-bundle were connected by using a conducting paste in series and parallel. The stack-bundle has current terminals on the top and bottom of the stack-bundle, which allows easy assembling of a module (consisting of eight stack-modules, a pair of current collectors and a pair of fuel manifolds) only by fastening several bolts. The power of this module was designed to generate 200 W from the output power of single micro tubular SOFCs.

The 30W-class SOFC module using 54 anode supported micro tubular cells were successfully fabricated. The performance of the module was high even at low ambient temperatures. This module could start up within an hour. After several rapid start-up operation tests, no degradation was observed.

A micromodule, the size of 0.2 X 1 X 3 cm (-0.6 cm 3 ) was fabricated using three micro-solid oxide fuel cell (SOFC) bundles which consist of anode-supported microtubular SOFCs of 0.8 mm diameter and porous cathode matrices. The module was designed to apply to small-sized power sources at a low operating temperature under 600°C. The open-circuit voltage of the module depended upon the operating temperatures, the lower for higher temperature due to the use of a ceria-based electrolyte. Maximum power outputs of the module were 0.5, 0.9, and 1.4 W at 450, 500, and 550°C operating temperatures, respectively, where the air was applied only by natural convection. As a result, the performance of the module turned out to be over 2 W per cm 3 at 550°C operating temperature. The results also showed a strong influence of the fuel flow rate; the higher rate led to an increased performance due to improved gas transport.

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