Search

The microstructural effect of the solid-oxide fuel cell (SOFC) anode on fuel cell performance has been investigated using X-ray absorption spectroscopy (XAS). Anodes were examined after the fuel cell had operated at 600–700 °C using H 2 fuel. The microstructure of micro tubular anodes consisting of conventional Ni–yittria stabilized zirconia (YSZ) has been controlled by altering the co-sintering temperature with the zirconia electrolyte. Impedance analysis has clearly shown that the overpotentials for the gas transport and the electrochemical reactions improve for the anode prepared at lower co-sintering temperatures. Using data from the X-ray absorption near edge structure (XANES) energy region, the metallic Ni fraction as a function of distance from the electrolyte has also been measured for those samples. XANES observation has shown the oxidation status of Ni in the anode is quite sensitive to position relative to the anode/electrolyte interface. These results may be an indication of the positions of the reaction sites for oxide ions and the fuel: assuming the oxidation state of nickel (Ni–O) designates the active triple phase boundary.

We investigated direct butane power generation for microtubular solid oxide fuel cells with a diameter of less than 2 mm. Conventional Ni-stabilized zirconia anodes deteriorated rapidly over a period of 3–4 h at 610 °C and a low steam/carbon (S/C) ratio of 0.044 in butane due to a large amount of carbon deposition. For the Ni–Gd doped ceria (Ni–GDC) anode, the power could be generated continuously for more than 24 h at 610 °C and S/C = 0.044 in butane. The rate of carbon deposition for the Ni–GDC was slower than that for the Ni-stabilized zirconia at 610 °C. Ceria can be reduced from Ce 4+ to Ce 3+ , which causes the suppression of carbon deposition on the Ni–GDC anode in butane at low humidity.

We developed a novel cathode electrode system composed of ultra highly porous structured LiFePO4/carbon composite for lithium ion batteries by a gelation–freezing (GF) method. This unique technique can be used to provide various shaped components by use of specific molds, and varying the freezing temperature could control the micrometer-sized cylindrical pore size and wall thickness in the porous composite. Film shapes of carbons that originate in the gelatin were found in the porous LiFePO4/carbon composite cathodes. The porous composite cathode shows a good electrochemical performance at a low current density, despite the low carbon content. Charge/discharge capacities for the LiFePO4/carbon composites decreased with decreasing gel-freezing temperature. The template-free GF method for fabricating the porous LiFePO4/carbon composite opens up a new route to develop electrodes with controlled morphologies for applications in high power lithium batteries.

Three-dimensionally ordered macroporous cathode was fabricated for a zirconia based micro-tubular solid oxide fuel cells (SOFCs). Three different cathodes (cathode A, no pore former; cathode B, with pore former (1.5 μm in diameter); cathode C, with pore former (0.8 μm in diameter)) were compared to investigate how the microstructure of it affected the cell performance at various operating temperatures. Micro-sized pores were well distributed within cathode B and C. The total porosity of cathode A is 35%, while it respectively reached 42 and 50% for cathodes B and C. At the same time, the specific surface area of them was 28.8 and 52.0% larger than that of the cathode A. As a result, the peak power density of the zirconia based cell, with cathode C, was 0.25 and 0.56 W cm−2 at 550 and 600 °C, while the respective value was just 0.11 and 0.30 W cm−2 for the cell with cathode A. Thus, optimizing microstructure of cathode should be one of the best approaches for lowering the operating temperature for SOFCs.

We developed a fabrication processes of a micro-tubular SOFC stack using a metallic tubular interconnect. The stack was made of the 12 micro-tubular cells, which were connected in series. The open circuit voltage (OCV) was above 13V, thus the single cell showed the OCV value about 1.1V. Fuel utilization of the stack under a wet H2 flow of 20cc/min was above 90%, and the efficiency (LHV) was about 60%. In addition, the stack can be started-up within 5 min, and we succeeded the quick-start/shut down multi-cycles.

The DRT method was applied to analyze the AC impedance spectra for anode-supported microtubular solid oxide fuel cells (SOFCs). The anode microstructure has a more severe effect on the electrochemical properties of the anode-supported microtubular SOFCs because of the small inside diameter and thickness of the anode. For example, the maximum current density and fuel utilization for the cells sintered at 1400 °C were lower than that at 1350 °C due to the low porosity of the anode. However, it is difficult to separate the anode and cathode impedances by the general method of complex non-linear least squares (CNLS) with equivalent circuit models, because several components overlap for the impedance spectra measured between the anode and cathode without a reference electrode. The DRT method can easily separate the impedance spectra into five polarization components for the anode-supported microtubular SOFCs. The activation energy of the anode diffusion resistance was only 24–33 kJ/mol. The walls of the pores in the anode were relatively well-packed with the nickel and YSZ particles for the cells made by the use of acrylic resin as a pore former. The anode diffusion resistance decreased by only a small amount with a rise of operating temperature for the anode-supported microtubular SOFCs.

Iron nanoparticles (Fe2O3) were added to NiO/gadolinium-doped CeO2 (GDC) anode supported solid oxide fuel cell (SOFC) for the direct methane–water fuel operation. The cell was co-sintered at 1400 °C, and the anode porosity is 31.8%. The main size corresponding to peak volume is around 1.5 μm. When steam and methane directly fed to the cell, the power density is about 0.57 W cm−2 at 650 °C. It is the familiar performance for H2 operation (4 times of flow rate) with same fuel utilization. Compare with the testing temperature of 600 and 650 °C, there is almost no carbon fiber deposition at 700 °C with steam/methane (S/C) of 5. At the same time, fuel operation of high value of S/C (=3.3) resulted in fiber-like deposition and degradation of power performance based on loading test results.

A microtubular solid oxide fuel cell (SOFC) consisting of Gd-doped CeO2 (GDC) interlayer–Sc stabilized zirconia (ScSZ) electrolyte has been prepared on an anode supported tube using one step sintering process at 1350 °C. The cell performance under high fuel utilization condition, with H2 flow rate as low as 4.3 mL min−1 per 1 cm2 electrode area is evaluated. The one-step sintering process results in an improvement of open circuit voltage but an increase of ohmic resistance due to possible high resistive layer and voids observed between GDC and ScSZ layers. The performance of the cell shows power densities of 0.35–0.57 W cm−2 with corresponding energy efficiencies of 45–20% (LHV), respectively, at 700 °C. Impedance analyses at different voltages have shown that the overpotential due to gas transport is dominant in the low current density region.

A microtubular solid oxide fuel cell (SOFC) with an anode functional layer (AFL) consisting of NiO–Sc stabilized zirconia (ScSZ) between the electrolyte (ScSZ) and the anode (NiO–Y stabilized zirconia) has been fabricated and evaluated at low fuel supplement condition of H2, 6 mL min−1 per electrode area of 1 cm2, in order to discuss the effect of the AFL on the fuel cell energy efficiency. The effect of the AFL has clearly seen in the improvement of the power density as well as fuel utilization, resulting in the improvement of the energy efficiency. The performance of the cell simply improves from 0.27 to 0.45 W cm−2, and 0.35 to 0.52 W cm−2 when the anode functional layer is introduced, and the energy efficiency reached 41 and 47% (LHV) at 650 and 700 °C, respectively using diluted hydrogen as a fuel. Keywords: Anode, Functional layer, SOFC, Fuel cell

Low temperature processed composite cathodes for solid-state fuel cell (SOFC) have been developed, consisting of La0.6Sr0.4Ti0.1Fe0.9O3 and Ag, as low as 800 °C process temperature. Using micro-tubular design, the performances of the cathodes have been investigated at the operating temperatures of 650 and 700 °C. The cell consists of NiO–Y stabilized zirconia (YSZ) as an anode (support tube), Sc stabilized zirconia (ScSZ) as an electrolyte, Gd doped ceria (GDC) for an inter-layer between the electrolyte and the cathodes. The single performance has varied depending upon the types of cathodes, and the composite cathode with 50 wt% La0.6Sr0.4Ti0.1Fe0.9O3 and 50 wt% Ag has shown comparable performance to the cell with standard LSCF–GDC cathode.

NiO-Fe{sub 2}O{sub 3}/Gadolinium-doped CeO{sub 2} (GDC), NiO/GDC anode-supported fuel cells were compared at intermediate temperature to investigate the effect of ferrum (Fe) on anode microstructure and the cell performance. The porosity of Fe{sub 2}O{sub 3}-containing anode tubes are 36.3% (those sintered at 1350 C) and 31.8% (those sintered at 1400 C), which are respectively 1.1% and 5.9% higher than that of the tubes without Fe{sub 2}O{sub 3}. The effect of Fe on microstructure of anode has also been indicated by analyzing the volume fraction of the different-size pores. At the operating temperature of 600 C, the maximum power density increased nearly 100% using Fe-Ni (after reducing) bimetal anode. From the impedance spectra, it is deduced that the improvement in power density is due to the decrease of overpotential resistance (low frequency part) related to gas transportation.

Fabrication process of 0.2 cm thick, 1.3 cm wide micro flat tube solid oxide fuel cells has been developed using cost effective extrusion and dip-coating method. The cell consists of NiO–yttria stabilized zirconia (YSZ) as an anode (support flat tube), scandia stabilized zirconia (ScSZ) as an electrolyte gadolinia doped ceria (GDC) for an interlayer, and (La, Sr)(Fe, Co)O3 (LSCF)–GDC as a cathode. The cell has been investigated between 500 and 700 °C operating temperature and showed the power density of 0.1 and 0.55 W cm−2, respectively, with diluted hydrogen fuel. The effect of fuel flow rate has also been studied at each operating temperature, showing strong influence at higher operating temperatures. Keywords: Micro, SOFC, Flat-tube, Solid oxide, Fuel cells, Energy

Energy efficiency of a single solid-oxide fuel cell (SOFC) has been studied in various experimental conditions and directly correlated to the character of the cell. A microtubular cell, which has the exact geometry for stack/module application, is used for this study. The energy efficiency simply improves by increasing the operating temperature, and reaches over 40% (lower heating value: LHV) at the operating temperature of over 700 °C in flowing 20% H2–Ar fuel inside the tube. Impedance analysis has shown that the gas transport is the limiting factor for improving the energy efficiency at lower operating temperatures.

NiO-GDC, NiO-YSZ, NiO-Fe2O3-GDC, NiO-Fe2O3-YSZ anode tube supported tubular fuel cells was fabricated at the co-sintering temperature from 1250 oC to 1400 oC to investigate how the co-sintering temperature affect the open-circuit voltage. To focus on the changing of anode tube, all the tubular fuel cells support a ScSZ electrolyte layer and a LSCF cathode layer. The microstructure of the electrolyte layer sintered under 1300 oC included pores inside it, and the densification of the electrolyte completed at the sintering temperatures above 1300 oC. Furthermore, the shrinkage both in length and in diameter of a tubular fuel cell reaches as much as 20% at co-sintering temperature of 1400 oC. The densification of ScSZ electrolyte layer and shrinkage of anode tube will result in the changing of open-circuit voltage of fuel cell from 1.0 V to 1.1 V.

Performance and energy efficiency of a single microtubular solid-oxide fuel cell (SOFC) has been studied in various experimental conditions and directly correlated to the character of the cell. The performance of the cell with Ni-YSZ anode supported, ScSZ electrolyte increases from 0.25 to 0.42 Wcm-2 by increasing the fuel flow rate at 620 oC cell temperature. On the other hand, the energy efficiency of the cell simply improves by decreasing the fuel flow rate, and reaches 26% (LHV) in flowing 20% H2 - Ar fuel inside the tube. Impedance analysis has suggested that the improvement of polarization resistances will effectively increase the energy efficiency of the cell at lower operation temperatures.

Realization of highly efficient SOFC(solid oxide fuel cell) modules, which are compact and capable of quick startup and shut-down operation, is strongly expected because it would be useful to solve environmental problems. In order to yield new outcomes in new energy production industry market, we have carried out continuous R&D directly linked with the original idea, trial production, and evaluation by using the ceramics integration manufacturing platform. In consequence, original, compact and high-power SOFC modules operable at low temperature have been realized by upgrading of function-structure integration technology. These are drawing attention as products of ingenious technology. This paper presents, in addition to industrial needs, approaches and methods in industry-academia-government collaborative research to overcome tasks toward productization.

Solid-oxide fuel cells (SOFCs), which consist of ceramic components, directly convert the chemical energy of a fuel into electrical energy with the highest efficiency among various kinds of fuel cells. Because SOFCs are operated at high temperatures, typically in excess of 700 °C, direct use of hydrocarbon fuel becomes possible, which minimizes the system size as well as reducing the cost. It is, however, difficult to utilize direct reforming of hydrocarbon fuel when the operating temperature is below 600 °C, which is the target for intermediate temperature SOFCs. Here, we report a new concept of an SOFC utilizing a functional layer on the surface of an anode, for the direct reformation of a hydrocarbon fuel using a micro-tubular design. Preparation of the functional layer is cost-effective and the cell with a pure-ceria (CeO2) functional layer was successfully fabricated. The cell displays practical cell performance below 500 °C using methane–water mixture as the fuel gas, and shows enhanced performance compared to systems without a functional layer.

This study discusses the fabrication and electrochemical performance of micro-tubular solid oxide fuel cells (SOFCs) with an electrolyte consisting a single-grain-thick yttria stabilized zirconia (YSZ) layer. It is found that a uniform coating of an electrolyte slurry and controlled shrinkage of the supported tube leads to a dense, crack-free, single-grain-thick (less than 1 μm) electrolyte on a porous anode tube. The SOFC has a power density of 0.39 W cm −2 at an operating temperature as low as 600 °C, with YSZ and nickel/YSZ for the electrolyte and anode, respectively. An examination is made of the effect of hydrogen fuel flow rate and shown that a higher flow rate leads to better cell performance. Hence a YSZ cell can be used for low-temperature SOFC systems below 600 °C, simply by optimizing the cell structure and operating conditions.

We attempted to fabricate and evaluate various nanofibrous multi layer structures and composite structures by using a multiple-nozzle electrospinning under various AC high voltage. To electrospun fibers, we prepared two kinds of precursor solutions. One is an aqueous solution containing poly (vinyl pyrrolidonel) (PVP) and metal nitrates. Another is slurry containing alcohol, poly (vinyl butyral) (PVB, Woko, Mw=340000 g/mol) and oxide powder. This method enables to make a composite fibrous structure that consists of an intertwined nano fibers with different composition. Adjusting an alcoholic vapor pressure of the synthesized atmosphere can variously change the structure. Therefore, it might be effective in the production of electrodes with a high specific surface area necessary for the improvement of reaction efficiency of the electrochemical reactor.

A novel solid oxide fuel cell (SOFC) stack based on a cathode-supported honeycomb SOFC single unit, capable of generating high volumetric power density, was fabricated. Facile connection of the honeycomb single units is achieved using a metal interconnect with a gastight conductive paste. The honeycomb single unit is designed to use the outer honeycomb face and the anode layer on the honeycomb edge face as the current collection paths for the cathode and anode sides, respectively. Current is conducted between the cathode of a single unit and the anode of an adjacent single unit through the metallic interconnect. A two-unit stack exhibited an open circuit voltage of approximately 2 V and twice the power of a single unit at 600 °C under wet H 2 fuel flow. The volumetric power density of the honeycomb SOFC stack at 600 °C was calculated to be approximately 0.6 W/cm 3 .

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.

Solid oxide fuel cells (SOFCs) are environmentally friendly and have good energy efficiency. Currently, many researchers have studied reduction of the operating temperatures, saving space and increasing speed of the start-up/shut-down of SOFCs for applications, such as a compact portable power supply. Reduction of SOFC operating temperatures would lead to a decrease in material degradation, and decrease cost by allowing use of metallic materials. We have been developing a novel high performance SOFC supported by a cathode-honeycomb monolith. In this study, the fabrication technique of porous cathode supported honeycomb SOFCs was investigated and the effects of cathode porosity on the SOFC performance were investigated using a practical electrochemical evaluation. Open circuit voltages and performances were affected by cathode porosity, especially those measured in air as cathode atmosphere has large differences.

The effect of anode composition on the electrochemical performance of cathode-supported micro solid oxide fuel cells (SOFCs) was evaluated using current-voltage and AC impedance measurements. The micro SOFCs were fabricated by the extrusion of a microtubular (La0.8Sr0.2)0.97MnO3 support and subsequent surface coating with a Ce0.9Gd0.1O1.95 (GDC)/Sc2O3-doped ZrO2 bilayer electrolyte and NiO-GDC anode layers. Impedance analysis indicated that 50wt%NiO-50wt%GDC anode has higher electrode activity than 70wt%NiO-30wt%GDC anode. The SOFC with 50wt%NiO generated approximately eight times higher power density than that with 70wt%NiO.

Cathode supported honeycomb SOFCs have developed recently for intermediate temperature operation, space saving, and quick start and stop. In this study, the effect of anode length, thickness, and conductivity on the performance of cathode supported honeycomb SOFCs by electrical simulation. In the case of 10mm anode length, to suppress the deviation from the ideal current (current loss) under 10%, the anode thickness needs to be 20 µm. And, honeycomb SOFCs with different anode thickness could be prepared by lowering the heat treatment temperature before forming anode layer. Electrochemical evaluations for honeycomb SOFCs with the anode thickness of 4.6 or 10.2 µm were conducted. The performance of honeycomb with 10.2 µm thick anode was twice as good as that with 4.6 µm thick anode. The activation and gas diffusion polarization were decreased.

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.

Mixed oxides and pyrochlore-type materials based on the Sr, Ce, Sn, and Mn elements have been prepared by hydrothermal method using a mixture of nitrate salts at 200 °C for 40 h under N2 atmosphere. Two groups of solids were synthesized: (i) (SrxCe1−x)2Sn2O7±δ (0.345 ≤ x ≤ 0.365) and (ii) (SrxCe1−x)2(SnyMn1−y)2O7±δ (0.345 ≤ x ≤ 0.365, 0.385 ≤ y ≤ 0.395). The structure of the solids were studied by X-ray diffraction and the main crystal phases determined were SnO2, (SrCe)2Sn2O7 and a trace amount of CeO2 in group (i) and only SnO2 and CeO2 were detected in group (ii). The mixed oxides/stannate pyrochlore have been tested as catalyst for NO reduction with hydrocarbons (CH4, C2H4, and C3H6) in the presence of O2. The CeO2 containing stannate Sr2xCe2−2xSn2O7±δ pyrochlore coexist with SnO2 (group (i)) was found to be the best for NO + C3H6 reaction giving very high N2 production at 350 °C in the presence of O2 and water vapor. SnO2 as well as CeO2 alone were also synthesized by the hydrothermal method and their NO reduction properties have been compared with those of the groups (i) and (ii).

The perovskites La0.8A0.2MnO3 (A = Cs) and La0.8A0.2Mn0.8B0.2O3 (A = Cs and B = Ga) have been synthesized by a solution-combustion method using metal nitrates, urea and glucose as the fuel materials. The structures of the synthesized products were studied by XRD, FT-IR, SEM, and BET analyses. The morphology of La0.8Cs0.2MnO3 (LCM) was cotton-like whereas the product of La0.8Cs0.2Mn0.8Ga0.2O3 (LCMG) was comprised of rather voluminous cotton-like morphology coexisting with nanorods. The nanorods are quite long, straight, and round and have a much smoother surface structure. The perovskite products have been tested as catalysts for NO + NO2 (NOx) adsorption. The formation of various species during the adsorption of NOx, issuing from a synthetic, lean-burn exhaust gas upon LCM and LCMG was studied using FT-IR. Rapid adsorption of NOx by the perovskites with cotton-like morphology consisting of nanoparticles and nanorods was highly effective for NOx removal from the gas phase.

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 fabrication technology has been developed for a novel high-performance solid oxide fuel cells with honeycomb structure via the extrusion of a cathode-honeycomb monolith and subsequent channel surface coating with electrolyte/anode bilayers. A novel coating technique for the preparation of dense electrolyte films on the channel surfaces in cathode honeycomb supports is reported. When the dipping method is used, the high viscous resistance of the electrolyte slurry inhibited slurry penetration into the microchannels, which resulted in insufficient channel surface coating. By contrast, the newly developed channel coating technique, i.e. the slurry injection method, allowed the slurry to be injected into the honeycomb channels without the formation of any coating defects.

A highly crystallized hexagonal structure with large aspect-ratios, almost uniform diameter and length of several tens of microns of Y(OH)3 nanowires, have been successfully synthesized by controlling the hydrothermal reaction time as well as an addition of 5 mol% Sm3+ at 180 °C for 24 h under N2 atmosphere. The hydrothermal products of yttrium nitrate precursor alone have showed merely nanosheets like structure under the same reaction conditions. The microstructures of the Y(OH)3 nanowires were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution (HR)TEM and selected area electron diffraction (SAED). After heat treatment, the as-prepared Y(OH)3 could be completely transformed into Y2O3 while maintaining the nanowires structure up to the temperature at 400 °C in air. The Y2O3:Sm3+ have been tested for the reduction of NO under an oxidizing atmosphere with hydrocarbons. Moreover, the NO reduction activity under atmosphere containing water vapor was also investigated.

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.

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.

The electrochemical properties of a novel honeycomb solid oxide fuel cell (SOFC), supported by an extruded cathode monolith and capable of generating high-volumetric power density under intermediate temperature operation, are reported. The SOFC was fabricated via the extrusion of a cathode honeycomb support and channel surface coating with electrolyte/anode bilayers using a wet chemical process. Under humidified H 2 fuel flow, high-volumetric power density above 2 and 3 W cm −3 at 0.7 V was exhibited at 700 and 750 °C, respectively. In addition, microstructure observation and electrochemical analyses confirmed that the honeycomb SOFC has structural durability for the rapid start-up operation with a heating rate of 100 °C min −1 .

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.

The relationship between microstructure and electrical conductivity of porous (La 0.8 Sr 0.2 ) 0.99 MnO 3 (LSM) ceramics were investigated. The porous LSM ceramics were prepared by sintering the cylindrically-extruded compacts at 1573 K for 6 h. The bulk density and porosity of LSM ceramics were measured by Archimedes technique. The electrical conductivities were measured using 4-probe DC technique as functions of temperature and bulk density. The open porosity was approximately proportional to the amount of binder in the LSM/water/binder mixture. The electrical conductivity decreased with decreasing bulk density, and the amount of decrease was more than predicted by the open porosity. This was related to the tortuosity of the carrier path.

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 attempted to fabricate and evaluate a new electrochemical reactor with an additional NOx adsorption layer on a multilayer catalytic cathode and investigated a cell operating method to achieve a low temperature operation. To clarify the capability of a NOx adsorption layer, we carried out the NOx decomposition measurements of the cell. As a result, NOx adsorption layers have improved the NOx decomposition properties though the current values of each cell were almost the same. The NO decomposition by a GDC (10mol% Gd doped CeO2) -based cell with a Pt/K/Al2O3 adsorbent took onset around 225°. It was clarified that the starting temperature and the efficiency of the NOx decomposition are heavily dependent on the adsorptivity of NOx adsorbent and the cell operating voltage mode.

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

We have developed a planar type NOX sensor with a dense sensing layer that consists of nano-size grains and a reference electrode buried in an electrolyte by a pulsed laser deposition method, and examined for the mixed-potential-type NOX sensor. This sensor shows a high NO sensitivity at low temperature (300–450 °C). Electromotive force (EMF) values were almost linear to the logarithm of NO concentration, and the response was reproducible. The magnitude of EMF response was about − 90 mV upon exposure to 1000 ppm of NO at 350 °C. And, the 90% response and recovery times were found to be about 5 and 25 s at 450 °C, respectively. This cell opens up the possibilities for development of an integrated electrochemical device for NOX gas treatment in combustion exhausts.

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.

The electrochemical reduction of nitric oxide in the presence of the excess oxygen was reviewed. It was shown that the selectivity and activity of the cathodes is strongly dependent on the composition and on the microstructure of the cathode material. A concept of electrochemical reactor with multilayer electro-catalytic electrode was proposed and successfully designed in Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Nagoya, Japan. The typical values of current efficiency in such electrochemical reactors are of the order of 10–20% at gas composition: 1,000 ppm NO and 2% O2 balanced in He and at gas flow rate 50 ml/min. The value of current efficiency depends on the functional multi-layer electrode composition, structure, and operating temperature. Such electrochemical reactors show the value of NO/O2 selectivity (νsel) higher than 5 (νsel > 5) at intermediate temperature and up to νsel = 25 at low temperature operation. It was shown that multilayer electro-catalytic electrode should consist at list from three main functional layers: cathode, electro-catalytic electrode, covering layer, in order to operate as an electrode with high selectivity.

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.

Recently, the fabrication and development of novel solid oxide fuel cell (SOFC) structures were conducted with the aim of enhancing power generation. Newly cathode-supported honeycomb-type SOFC with a promising power/volume ratio is under development. However, the conventional processing techniques used for the fabrication of different SOFC cell components (electrolyte and electrode) are not compatible with the newly constructed honeycomb structure. The ink-jet printing technique may offer the ability to design and fabricate SOFC components on honeycomb substrates and complex 3D structures. In this study, the formation of a dense Gadolinium-doped ceria thin film on a cathode-supported LaSrMnO 3 substrate by the ink-jet printing technique was investigated.

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.