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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.

Although protonic ceramic fuel cells (PCFCs) have a great potential to realize higher energy-conversion efficiency compared with all other conventional devices, actual PCFCs have shown current leakage loss due to their intrinsic transport property with electron-hole conduction of proton-conducting electrolytes, resulting in a decrease in efficiency. The present study shows a new finding that open-circuit voltage (OCV), which is an indicator of current leakage loss, depends on the ratio of the electrode polarization resistance to the electrolyte ohmic resistance within a PCFC and experimentally demonstrates improvement in OCV by developing high-performance cathode and anode. Results show that our anode-supported PCFC with BaZr0.1Ce0.7Y0.1Yb0.1O3−δ electrolyte and high-performance electrodes achieves extremely high OCV, e.g., 1.112 V at 600 °C (≈ 98% of the theoretical OCV) and 1.132 V at 550 °C (≈ 99% of the theoretical OCV). Compared with recently reported OCVs for PCFCs, these measured OCVs are remarkabl...

Diffusion behavior of Ni during high temperature co-sintering was quantitatively investigated for anode-supported solid oxide fuel cells (SOFCs) that had BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3− δ (BZCYYb) proton-conducting electrolyte and NiO-BZCYYb anode. Although diffused Ni in such SOFCs effectively acts as a sintering aid to densify the BZCYYb electrolyte layer, it often negatively affects the electrolyte conductivity. In the present study, field emission electron probe microanalysis (with wavelength dispersive X-ray spectroscopy) clearly revealed that Ni diffused into the BZCYYb electrolyte layer, and that the amount of diffused Ni increased with increasing co-sintering temperature. In particular, relatively high Ni concentration within the electrolyte layer was observed near the electrolyte/anode interface, e.g., approximately 1.5 and 2.8 wt% at co-sintering temperature of 1300 and 1400 °C, respectively. Electrochemical measurements showed that, compared with the lower co-sintering temperatures (1300–1350 °C), the highest co-sintering temperature (1400 °C) led to the highest ohmic resistance because of lower electrolyte conductivity. These results suggest that high co-sintering temperature causes excessive Ni diffusion into the BZCYYb electrolyte layer, thus degrading the intrinsic electrolyte conductivity and consequently degrading the SOFC performance.

High power density operation is essential for cost reduction in solid oxide fuel cells (SOFCs), and thus the present work proposes a highly active Gd0.5Sr0.5CoO3−δ (GSC) and Ce0.8Gd0.2O1.9 (GDC) nanocomposite cathode for intermediate-temperature SOFCs. Its nanocomposite structure is formed by using GSC-GDC nanocomposite particles synthesized via spray pyrolysis, which produces uniform-sized secondary particles consisting of nano-sized GSC and GDC crystallites. The resulting cathode has an extensive electrochemically active triple-phase boundary and has electrically conductive networks formed with highly dispersed GSC and GDC crystallites. In addition, the GSC-GDC nanocomposite cathode exhibits a performance comparable to a high-performance Sm0.5Sr0.5CoO3−δ and Ce0.8Sm0.2O1.9 nanocomposite cathode. An anode-supported SOFC with the GSC-GDC nanocomposite cathode achieves remarkably high power densities at 0.75 V, i.e., 3.66, 2.60, 1.66, and 0.98 W cm−2 at 800, 750, 700, and 650 °C, respectively. These results suggest the proposed nanocomposite cathode yields a synergistic effect of a high catalytic activity of GSC-GDC and a fine nanocomposite structure, leading to high power density operation of an SOFC.

This study shows the fabrication process of an anode-supported proton-conductive cell, then the electrochemical performances were investigated under SOFC mode in a wide temperature range from 222 to 486 °C. Ba(Ce0.7Zr0.1Y0.1Yb0.1)O3–δ (BCZYYb) was selected as an electrolyte material, and Ni–BCZYYb cermet and (La,Sr)(Co,Fe)O3–BCZYYb composite were selected as a fuel and an air electrodes materials, respectively. The cell showed open circuit voltages over 1.1 V and worked as a SOFC within the whole temperature range.

The nickel–zirconia cermet is widely used as an anode of solid oxide fuel cells (SOFCs). On the other hand, the nickel–ceria based anode indicates high electrochemical activity for hydrogen oxidation and hydrocarbon reforming. In this study, electrochemical and microstructural properties of microtubular SOFCs with Ni-based composite anodes containing yttria-stabilized zirconia (YSZ) and gadolinia-doped ceria (GDC) are investigated electrochemically using impedance spectroscopy (EIS) and microstructurally using focused ion beam-scanning electron microscopy (FIB-SEM). The solid solution of YSZ and GDC was easily formed after mechanical mixing and sintering at 1400 °C. The electrical conductivity and mechanical strength for the Ni–YSZGDC composite anodes are low relative to Ni–YSZ due to poor sinterability. The GDC-containing anodes show improved electrochemical activity for hydrogen oxidation, despite having lower three-phase boundary densities. Distribution of relaxation times (DRT) analysis of the EIS data shows that the concentration polarization is lower for the Ni–GDC anode, due to a higher measured pore volume. The maximum power density for the cell with the Ni–YSZGDC composite anode was higher than those with the Ni–YSZ and Ni–GDC anodes.

Distribution of relaxation times (DRT) analysis is a powerful assistant tool for electrochemical impedance spectroscopy (EIS) deconvolution. In the present work, electrode degradation is evaluated by estimation of polarization resistances using DRT analysis. Five or six DRT peaks are detected for anode-supported microtubular solid oxide fuel cells (SOFCs) at 600–650 °C. In a reduction-oxidation (redox) cycling test, the polarization resistance of charge transfer and ionic conduction processes in the anode increases due to the decrease in triple phase boundary (TPB) length. On the other hand, initial electrode degradation is also successfully evaluated using DRT analysis during a galvanostatic test. The rapid growth of nickel grains in the anode and the relatively slow growth of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) grains in the cathode are observed after the test, which corresponds with the increase in the polarization resistance of charge transfer and ionic conduction processes in the anode and that of oxygen surface exchange and diffusion processes in the cathode, respectively.

Perovskite (Ba,Sr)(Co,Fe)O3 (BSCF) cathodes are highly electrochemically active in the oxygen reduction process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). However, the phase of perovskite zirconate is formed between the BSCF cathode and yttria-stabilized zirconia (YSZ) electrolyte, which increased the cathode polarization resistance. In the present work, the (Ba,Sr)ZrO3 formation was not prevented by the insertion of a porous gadolinia-doped ceria (GDC) interlayer between the cathode and the electrolyte, when the BSCF cathode was sintered at 1100 °C. Energy dispersive X-ray spectroscopy showed that the product of (Ba,Sr)ZrO3 formed between BSCF and YSZ was thicker than that of SrZrO3 formed between a conventional (La,Sr)(Co,Fe)O3 (LSCF) and YSZ. When a BSCF cathode was sintered at 900 °C, no (Ba,Sr)ZrO3 formation was observed between the cathode and the electrolyte. The maximum power density at 650 °C was improved from 7.5 to 740 mW/cm2 by decreasing the sintering temperature of BSCF cathode from 1100 °C to 900 °C. Distribution of relaxation times (DRT) analysis showed that the polarization resistance of the oxygen exchange process in the BSCF cathode sintered at 900 °C was lower than that in the LSCF cathode. The sintering temperature is important for obtaining high-performance BSCF cathodes for IT-SOFCs.

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.

When hydrocarbons are used as a fuel in solid oxide fuel cells (SOFCs), internal steam reforming increases the energy conversion efficiency and simplifies the system, including the balance-of-plant. However, conventional nickel–yttria stabilized zirconia (Ni–YSZ) anodes are prone to deterioration at high temperatures and high humidity. This paper focuses on effects in anode microstructure on performance and durability of microtubular SOFCs. The evaluations were conducted under high steam content and internal methane reforming conditions using Ni–YSZ anodes using acrylic resin and graphite pore formers. The initial cell performance was almost identical to that of SOFCs with anodes using acrylic resin and graphite pore formers in 40% H2–3% H2O at 700 °C. However, the anode using acrylic resin deteriorated rapidly in 40% H2–30% H2O over a period of 28 h. Furthermore, it generated almost no electric power by internal steam reforming of methane. The local oxidation of nickel particles was observed at the interface between the electrolyte and the deteriorated anodes. The anode using graphite pore former provided stable power generation in 40% H2–30% H2O, and was able to generate power in 10% CH4–30% H2O. The pore formers strongly affect fuel diffusivity in the SOFC anodes, which is an important factor in stable internal steam reforming of methane. Keywords: Solid oxide fuel cell (SOFC), Nickel–yttria stabilized zirconia (Ni–YSZ) anode, Internal steam reforming, Pore former, AC impedance

Microtubular solid oxide fuel cells (SOFCs) with a diameter on the millimeter scale are suitable for small-scale applications such as micro combined heat/power systems and portable power sources. However, the use in reducing purge gas is not practical during start-up and shutdown in the small-scale applications. In this study, the redox tolerance was evaluated for nickel gadolinia-doped ceria (Ni–GDC) anode-supported microtubular SOFCs with an open-end at fuel outlet, when the hydrogen fuel supply was stopped 8 times for 10 min/cycle at 615 °C. The open circuit voltage was unchanged, and the degradation of less than 3% was confirmed after 8 redox cycles. The Ni–GDC anode-supported microtubular SOFCs have redox tolerance at 615 °C. Each electrode polarization resistance can be separated by the distribution of relaxation times (DRT) analysis from the measurement of AC impedance between the anode and the cathode. While the anode activation polarization (10–100 Hz) was clarified to increase because of the decrease in the TPB length, the anode concentration polarization (

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 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.

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.

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

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

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.

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 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.

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.

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

Simultaneous decomposition of nitrogen oxides (NO x ) and solid state graphite particles were carried out using a 8 mol% Y 2 O 3 doped ZrO 2 (YSZ) based electrochemical reactor with a nano-structured NO x selective multilayer cathode and an oxidative porous anode. The ceramic electrochemical cell was prepared by screen-printing a Pt and a NiO–YSZ pastes as cathode layers and a 12 CaO7Al 2 O 3 –Pt paste as an anode layer on the YSZ electrolyte, respectively. Simultaneous decomposition of NO x and graphite particles was investigated using the cell with coated graphite particles on the surface of the 12 CaO7Al 2 O 3 –Pt composite anode in 1000 ppm NO x –He gas flow under applying DC voltage at 475 °C. The coated graphite particles at the anode were removed completely with 80% NO x decomposition by electrochemical reactions.

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.

Dramatic improvements in the selective separation and purification of NOx in exhaust gases by an electrochemical reactor have been achieved. The novel electrochemical cells for NOx decomposition were developed by nano-scale control of penetrating pores from the catalytic electrode surface to the bottom of the catalytic electrode layer, and by distribution at the interfaces of ionic and electronically conducting grains through the electro-catalytic electrode of the cells. Dramatic improvement in the current efficiency and suppression of the working voltage of the cells enabled their application as a novel reactor for NOx decomposition of gases from gasoline- and diesel-engine vehicles, gas engines, and other industrial equipment with the advantage of less energy consumption in comparison to “the fuel penalty” for presently used catalytic systems. The cells are able to work as a deNOx reactor even under excess oxygen contents up to 10% because of the selective separation to NOx molecules by the nano-space reaction. For the first time such nano-reaction has been shown to realize sufficiently applicable yielding rates. Enlarged cells revealed high performance similar to the small experimental cells.

Direct oxidation of solid state graphite particles was carried out using a 10 mol% Gd-doped CeO 2 (CGO) based electrochemical reactor with an oxidative porous anode consisting of 12CaO7Al 2 O 3 . A ceramic electrochemical cell was prepared by screen-printing Ag, NiO-CGO and 12CaO7Al 2 O 3 -Ag pastes on CGO plates. Simultaneous decomposition of NOx and oxidation of graphite particles was investigated in 1000 ppm NOx-He gas flowing at 475°C. Graphite particles on the surface of the 12CaO7Al 2 O 3 -Ag composite anode were oxidized by applying 1.5 V DC voltage at 475°C. The coated graphite particles on the anode were removed directly with 80% decomposed NOx by electrochemical reaction.

A new family of electrochemical cells for decomposition of NO gas in the presence of excess O2, in which the cathode was covered with mixed oxide layer of NiO and YSZ (electro-catalytic electrode) were designed and investigated. The deNO x properties were increased by microstructural and compositional control of the electro-catalytic electrode. Nano-size Ni grains were self-assembled at NiO/YSZ interfaces by oxidation-reduction reaction of the NiO during the cell operation. In order to use the reduced Ni for NO decomposition reaction effectively, the authors investigated multilayering of the electro-catalytic electrode. Through this process, the adsorption of coexisting O2 was prevented and the deNO x properties of the electrochemical cell were improved.

We report the effect of a catalytic layer on a solid-oxide fuel cell (SOFC) anode surface on the fuel cell performance. A Ru/CeO2 catalytic layer has been applied on the anode surface and tested in the operating temperature of 650 and 700 °C. It has shown that application of the catalytic layer on the anode surface improves the cell performance especially at high fuel utilization condition. The energy efficiency at 0.7 V operating voltage has reached over 40% (LHV) below 700 °C operating temperature in flowing 20% H2–Ar fuel at the power density of over 0.5 W cm−2. Keywords: Catalytic layer, Solid-oxide fuel cell, SOFC, Anode, Performance

Bi-layers consisting of porous La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) substrate and dense film of Ce0.9Gd0.1O1.95 (CGO) have been successfully fabricated using slurry-coating process. A CGO powder dispersed in acetone was deposited onto a pre-sintered LSCF (containing 50 mass% CGO) substrate, and then co-fired such that the thin electrolyte was fully densified and the substrate remains highly porous. Co-fired CGO film was well bonded to the substrate; crack- and pinhole-free, and exhibited very low ohmic resistance. The NO decomposition properties of electrode-supported type electrochemical cell, LSCF (substrate) |CGO (film)| LSCF (screen-printed) were investigated. A strong correlation between the structure of the working electrode and the NO decomposition characteristics were observed. By using electrode-supported thin electrolyte, the required electric power for NO decomposition could be remarkably reduced.

A high performance small-scale solid oxide fuel cell supported by a microtubular cathode was successfully developed via the extrusion of a (La0.8Sr0.2)0.97MnO3 cathode support and subsequent surface coating with a (La0.8Sr0.2)0.97MnO3–Ce0.9Gd0.1O1.95 activation layer followed by Sc2O3-doped ZrO2 electrolyte and NiO–Ce0.9Gd0.1O1.95 anode slurries. The cell was electrochemically evaluated in a humidified hydrogen (3% H2O) atmosphere, and exhibited a stable open circuit voltage above 1.05 V in the temperature range from 550 to 750 °C. Maximum power densities of 46.5, 163.2 and 452.8 mW cm−2 were generated at 550, 650 and 750 °C, respectively. The results indicate the realization of a stable and high performance cathode-supported micro SOFC. Keywords: Micro SOFC, Tubular LSM support, Wet coating, Activation layer, ScSZ electrolyte

The catalytic and electrical properties of an electrochemical NOx reduction system were investigated. A power above 3.5W/cm2 reduced more than 60% of NOx to N2 over the (La,Sr)CoO3-α/Ce0.9Gd0.1O1.95/Pt laminated system in a temperature range of 450°C to 650°C. O2- transportation removed the oxygen around the cathode layer through the Ce0.9Gd0.1O1.95 electrolyte layer, then NO was able to decompose to N2 at the cathode. This ceria-based system exhibited stable NOx reduction with respect to electrical power, regardless of operating temperature.

Dramatic improvement in the selective separation and purification of NOX in exhaust gases by an electrochemical reactor with a catalytic electrode has been achieved. The novel electrochemical cells for NOX decomposition were developed by nano-scale control of penetrating pores from the catalytic electrode surface to the bottom of the catalytic electrode layer. The penetration pores and nano-size Ni grains are self-assembled at NiO/YSZ interfaces in the catalytic electrode by oxidization-reduction reaction of the NiO during the cell operation. In order to use reduced Ni for NOX decomposition reaction efficiently, we successfully designed a functional multilayer catalytic electrode. By multilayering of the catalytic electrode, adsorption and decomposition of coexisting oxygen in exhaust gases was suppressed and the selectivity of NOX decomposition reaction is improved. Structural change of the catalytic electrode as a result of the electrochemical processes was investigated and correlated with the NO decomposition properties of the cell.

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.

The effect of anode microstructure on the electrochemical performance of cathode-supported micro solid oxide fuel cells (SOFCs) was evaluated using current-voltage and ac impedance measurements. Small-scale cells were fabricated by the extrusion of a microtubular (La 0.8 Sr 0.2 ) 0.97 MnO 3 support and subsequent surface coating with a Ce 0.9 Gd 0.1 O 1.95 /Sc 2 O 3 -doped ZrO 2 bilayer electrolyte and NiO-Ce 0.9 Gd 0.1 O 1.95 anode layers. Impedance analysis and scanning electron microscopy observations indicate that an anode layer with coarse NiO particles has a higher porosity and electrode activity than that with fine NiO particles. The SOFC with coarse NiO particles generated more than twice the power density of that with fine NiO particles.

The performance of a cathode-supported solid oxide fuel cell (SOFC) was improved by using a microtubular LaSrMnO 3 (LSM) support. The cell had a laminated structure, with a bilayer of dense gadolinium-doped ceria (GDC) layer and scandia-stabilized zirconia as the electrolyte and a NiO-GDC layer as the anode on the microtubular LSM support. It was fabricated by extrusion of the cathode support and subsequent surface coating by a wet process. Microstructural observations and electrochemical analyses showed that the cell has a stable and durable structure for rapid start-up operation at a heating rate of 60°C/min.

In this study, we fabricated an anode-supported microtubular solid oxide fuel cell (SOFC) with the cell configuration La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF)-Ce 0.8 Gd 0.2 O 1.9 (CGO) cathode/CGO buffer layer/(ZrO 2 ) 0.89 (Sc 2 O 3 ) 0.1 (CeO 2 ) 0 . 01 (ScSZ) electrolyte/ Ni-ScSZ anode. A power generation test of the SOFC was carried out at 0.1-0.7 MPa at 650°C. By using a wet H 2 -N 2 gas mixture and air, the maximum power density of the microtubular cell was found to be 0.68 W cm -2 (at 2.6 A cm -2 , U f = 78%) at atmospheric pressure (0.1 MPa). With increasing the operating pressure, the performance of the cell was improved, and the power density reached 1.48 W cm -2 (at 2.8 A cm -2 , U f = 86%). It was confirmed by the current interruption method that both polarization and ohmic resistances decrease under a pressurized condition.

A gadolinium-doped ceria (GDC)/scandia-stabilized zirconia (ScSZ) bilayer electrolyte on a microtubular (La, Sr) x MnO 3-δ (LSM) support was prepared via extrusion of a microtubular cathode support and subsequent surface coatings with electrolyte and anode slurries. The GDC/ScSZ bilayer electrolyte was obtained on the LSM support using a cosintering technique, and the LSM-supported microtubular solid oxide fuel cells (SOFCs) were evaluated using field-emission scanning electron microscopy, X-ray diffraction, and electrochemical measurements in wet hydrogen (3% H 2 O) atmosphere. An LSM-GDC activation layer was also introduced between the cathode tube and the electrolyte layers for improvement of cell performance. The micro-SOFC exhibited a stable open-circuit voltage above 1.03 V in the temperature range from 450 to 750°C, and the cell generated a maximum power density of 15, 73, 230, and 378 mW/cm 2 at 500, 600, 700, and 750°C, respectively. This result indicates that our developed cosintering fabrication technology can realize a stable and high-performance, LSM-supported micro-SOFC.

Here, we report a chip-type module [size: 0.3 X 1 X 3 cm (∼ 1 cm 3 ) + fuel manifold] using micro-solid oxide fuel cell (SOFC) bundles which consist of anode-supported microtubular SOFCs with 2 mm diameter, porous cathode matrices, sealing layers, and interconnects. The module is a three-bundle stack with fuel manifolds and is designed to apply to small-sized power sources. The performance of the module was shown to be 2.85-2.6 V open-circuit voltage, with maximum power outputs of 0.91, 1.54, and 1.79 W at 450, 500, and 550°C operating temperatures, respectively, where the air was applied only by natural convection. An increase of the fuel flow rate effectively improved the performance of the module due to an improvement of the gas transport process. The fuel utilization of the module was also estimated for the optimization of the module operating conditions, which was strongly influenced by the fuel flow rates and the operating temperatures.

Multilayered electrolytes for microtubular solid-oxide fuel cells (SOFCs) have been prepared and their electrochemical properties investigated. SC 2 O 3 -stabilized ZrO 2 (ScSZ) and Gd 2 O 3 -doped CeO 2 (GDC) were selected for the electrolyte materials; the multilayered electrolyte of GDC-ScSZ-GDC was successfully prepared on an anode tube (1.8 mm diameter) using multiple dip coating and a cofiring technique. The thickness of each electrolyte layer was about 3, 3, and 12 μm, respectively. The cell performance test showed an open-circuit voltage (OCV) of over 1 V at 600°C or higher temperature for the SOFC with a multilayered electrolyte, while a SOFC with a 12 μm thick GDC electrolyte showed an OCV of 0.84 V at 600°C. The cell performances of 0.35 W cm -2 at 0.7 V and 0.27 W cm -2 at 0.8 V were obtained for the SOFC with multilayered electrolyte at the operating temperature of 650°C.

We report the designing and evaluation of a cathode-honeycomb-supported solid oxide fuel cell (SOFC), capable of generating high volumetric power density. The numerical analyses showed that the cathode-honeycomb-supported SOFC can be the most efficient form with the lowest current collection loss, as compared with the electrode- or anode-honeycomb-supported ones. The cathode-honeycomb-supported SOFC, which was fabricated via the extrusion of a LaSrMnO 3 honeycomb monolith and the channel surface coating by our developed wet process using electrolyte/anode bilayers, exhibited the high volumetric power density above 1 and 2 W/cm 3 at 600 and 650°C, respectively, under a wet H 2 fuel flow.