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The present study investigates protonic ceramic fuel cells (PCFCs) with composite cathodes consisting of an electronic conductive material and a protonic conductive material. PCFCs have been expected as a future high-efficiency and high-performance power generation device. Electronic conductive perovskite-type oxides such as (La,Sr)(Co,Fe)O3, (La,Sr)CoO3, and (La,Ba)CoO3 (LBC), which are commonly used for the cathode material of conventional solid oxide fuel cells with oxide ion-conducting electrolytes, are also used for that of PCFCs. However, these perovskite-type oxides have almost no protonic conductivity, resulting in poor catalytic activity for cathode electrochemical reaction in PCFCs. Thus, to enhance cathode performance, composite cathodes with a proton-conducting oxide BaZr0.1Ce0.7Y0.1Yb0.1O3–δ (BZCYYb) are applied to anode-supported PCFCs. Results show that the composite cathodes effectively enhance the cell performance, and the 50 wt% BZCYYb composite LBC-based cathode exhibits the highest performance among the evaluated composite cathodes.

Solid oxide fuel cells (SOFCs) can, in principle, directly use hydrocarbon fuels such as methane and liquefied petroleum gas (LPG). It was previously found that nickel-gadolinia doped ceria (Ni-GDC) anode has high durability under LPG utilization in SOFCs. However, the performance under direct LPG utilization was low compared to hydrogen fuel, because anode polarization resistance increased by internal reforming. Carbon was slightly deposited on the Ni-GDC anode after direct LPG utilization for 100 h at 650 oC. In this work, a catalytic partial oxidation reformer was developed for LPG utilization, and high performance was obtained using reformate gas as well as hydrogen without carbon deposition on the Ni-GDC anode for 100 h at 650 oC. Furthermore, microtubular SOFC stacks were developed using mass production technologies, and a proto-type 200 W micro power generator was demonstrated via NEDO project entitled "Technology Development for Promoting SOFC Commercialization".

We have been developing a tubular electrochemical cell composed of Ni-cermet support/YSZ/GDC/LSCF-GDC or Ni-cermet support/GDC/LSCF-GDC in order to synthesize energy-carrier chemicals (methane etc.) via co-electrolysis of H2O-CO2 mixed gas. In this report, we will show effects of (1) the cell fabrication processes, (2) the cell microstructure and (3) methanation ability of two types of SOECs at 400 ºC.

The effect of operating temperature on durability was investigated for direct butane utilization in anode-supported microtubular solid oxide fuel cells (SOFCs). At 710 oC, the performance of the Ni-Gd-doped ceria (Ni-GDC) anode deteriorated rapidly for less than 2 h at a relatively low steam/carbon (S/C) ratio of 0.044 in butane, because a large amount of carbon was deposited on the anode by butane cracking. On the other hand, the electric power could be generated continuously for more than 24 h at 610 oC and S/C = 0.044 in butane for the cell using the Ni-GDC anode. Lowering the operating temperature realized high durability against carbon deposition on the Ni-GDC anode under the direct butane utilization. We manufactured and demonstrated a prototype portable SOFC system using a microtubular cell-stack. It can be heated up to 400 oC within 2 minutes by burning an LPG burner, and drive a USB device for 24 h continuously using a LPG cartridge (250 g; 3.2 kWh). This development has shown the potential of the microtubular SOFC system as portable power sources in disaster and emergency situations, for outdoor use, and for small-scale electric vehicles.

Carbon growth site on the surface of a solid oxide fuel cell (SOFC) comprising yttria stabilized zirconia (YSZ) and Ni was observed using transmission electron microscopy (TEM). TEM observations of the YSZ and Ni powder mixture, which was heated in a methane atmosphere, confirmed that graphite was grown on the Ni surface only, and not deposited on the YSZ surface or the interface between YSZ and Ni. Additionally, the grown graphite was confirmed to have a curled structure and to terminate growth at the Ni-YSZ interface. These phenomena were likely caused by differences in the carbon wettability against Ni or YSZ, as well as oxygen diffusion from YSZ to Ni.

Solid oxide cells with reversible mode would generate power during high peak demand, and produce chemical fuel with renewable energy such as wind power and solar power. In this study the reversible performance of an anode-supported proton-conductive cell was investigated under SOFC and SOEC modes. The cell can show the reversible behaviors in lower temperature range below 600°C.

Microtubular SOFCs with a diameter on the millimeter scale are suitable for portable power sources due to rapid start-up characteristics. The performance of conventional Ni-stabilized zirconia anodes deteriorated rapidly over a period of 3-4 h at 610 oC 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 electric power could be generated continuously for more than 24 h at 610 oC and S/C = 0.044 in butane. We manufactured and demonstrated a prototype portable SOFC system using a microtubular cell-stack. It can heat up to 400 oC within 2 min by burning an external LPG burner, and drive a USB device for 24 h continuously using a LPG cartridge (250 g; 3.2 kWh). This development has shown the potential of the microtubular SOFC system as portable power sources in disaster and emergency situations, for outdoor use, and for small-scale electric vehicles.

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.

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.

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.

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.

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.

SOFC based on honeycomb support is known as one of the most compact SOFCs due to its large electrode area per a unit volume, which is attractive with regard to space saving, cost reduction and thermal control. In this study, the effects of material configuration and honeycomb channel number on the performance of SOFC were investigated using the simulation of equivalent electrical circuit. It was revealed that cathode- supported honeycomb type could be better for maximizing net electrode area per a unit volume and minimizing current collecting loss than any other types such as electrolyte- or anode-supported types due to its small current collecting loss.

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.

An electrode-supported honeycomb-type SOFC with multi sub- millimeter sized channels can hold large electrode area per a unit volume, which leads to space saving and cost reduction. In this study, a cathode-supported honeycomb-type SOFC has been prepared from integrating multi micro-cells via the fabrication processes; extrusion method for a cathode honeycomb monolith (LaSrMnO3 (LSM)) and new novel slurry injection method for subsequent inner wall coating (electrolyte/anode layers) of multi channels. The complete honeycomb-type SOFC has the cell density of about 1000 cpsi (channels per square inch) with wall thickness of 160 mm, dense electrolyte layer about 20 mm and anode layer about 10mm.

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.

SOFCs technology is important for developing high efficient energy conversion system. The application fields of SOFC system are possible to improve by among the module design, electrochemical properties and manufacturing speed and cost. In addition, compact modules with small SOFCs are interest for mobile power modules in future. For the purpose of developing ceramic manufacturing process of SOFCs, we are carrying out development of rapid-prototyping-like fabrication techniques using computer manipulation of micro-nozzle and ceramic pastes. Gd-doped CeO2 (GDC) based micro cells (

We attempted to fabricate new electrochemical cells for NOX decomposition using high oxygen ion conducting materials with a multilayer cathode operable in the intermediate temperature. Thermal measurements of the cells were carried out to clarify the correlation between the oxygen ion conductivity of the solid electrolyte and the NOX decomposition properties. The NO decomposition by the electrochemical cell with a NiO-ScCeSZ catalytic layer started at around 325{degree sign}C and it was shown that the starting temperature and the efficiency of the NOx decomposition are attributed to the oxygen ion conductivity of the electrolyte.