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La-doped ceria (LDC)/lanthanum silicate (LS) and Ga-doped ceria (GDC)/LS composites were prepared, and the influence of cation interdiffusion during co-firing on the electrical properties of composites was investigated. The electrical conductivity of GDC/LS was lower than that of LDC/LS despite the higher conductivity of GDC compared to LDC. The crystal phases of LDC/LS and GDC/LS were detected as fluorite-type cubic ceria (Fm 3 ‾ m) and a hexagonal lanthanum silicate (P63/m), respectively, by X-ray diffraction (XRD). From energy dispersive X-ray spectroscopy (EDS) measurements, it was found that the compositions of the ceria and silicate phases in LDC/LS were nearly stoichiometric after co-firing. In contrast, interdiffusion between Gd3+ in the ceria phase and La3+ in the silicate phase was recognized for the GDC/LS. The compositions of the ceria and silicate phases in GDC/LS after co-firing were estimated as Gd0.035La0.065Ce0.9O1.95 and La7.910Gd0.423(SiO4)6O0.5, respectively. The Gd3+ substitution for La3+ in the silicate phase in GDC/LS decreased the amounts of 4f site cations. Then, the lattice parameter of the silicate phase decreased. As a result, the decrease in electrical conductivity of GDC/LS is attributed to the decrease in the oxide anion at the 2a site, which is a conduction carrier. It was found from Raman spectroscopy that cation interdiffusion decreased the symmetry mode of the SiO4 tetrahedra for the silicate phase in GDC/LS and brought about increases in the activation energy of electrical conductivity for GDC/LS.

Perovskite oxides ABO3 (A = Sr, Ba, B = Ti, Zr, Hf) were prepared at around room temperature using the reaction between alkaline earth hydroxides and metal oxide hydrous gels. The products of the reaction crystallized without any calcination. High-symmetry perovskite oxides, such as cubic perovskite, were obtained at lower temperatures. The Madelung energy of each perovskite oxide was calculated from the crystal structure and the lattice parameter obtained by XRD measurement. The calculated Madelung energy change in the synthesis reaction showed a linear relationship with the synthesis temperature. A rise in the synthesis temperature increased the change of the Madelung energy. The results thus confirmed that the synthesis temperature depended on the symmetry of the perovskite oxide in this study. Drawing from these results, we concluded that the synthesis temperature could be estimated by considering the crystal structure and Madelung energy change in the synthesis reaction.

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.

A multi-layered electrolyte structure is proposed for proton-conducting solid oxide fuel cells (SOFCs) to achieve higher power density and higher open-circuit voltage (OCV). Although recent proton-conducting SOFCs have demonstrated high power density, their OCVs have been lower than that of conventional SOFCs with stabilized zirconia because proton-conducting oxides intrinsically have electron-hole conduction. The proposed electrolyte structure has a porous BaZr0.1Ce0.7Y0.1Yb0.1O3–δ (BZCYYb) layer deposited on a dense BZCYYb layer. This structure effectively improves both cathode polarization and ionic transport property, resulting in higher power density with higher OCV. Also, discussion based on an equivalent circuit model of proton-conducting SOFCs clearly reveals a mechanism that determines OCV, namely, higher ohmic resistance and lower electrode polarization resistance lead to higher OCV. Our results suggest that higher electrode performance is essential for proton-conducting SOFCs to achieve higher OCV, particularly in the case of anode-supported configurations with thin electrolyte.

The dissociation behavior of protons incorporated in yttrium-doped barium zirconate (BZY20) was investigated via combination of in-situ diffuse reflectance Fourier transform infrared spectroscopy (FT-IR) and evolved gas analysis. The vicinities of dopant or host ions were considered as sites of proton dissolution. The temperature dependence of the dissociation of protons from each site was evaluated. Protons which were considered to have dissolved in the vicinity of dopant ions were easily removed and dissociated as water. On the other hand, those which dissolved in the vicinity of host ions were dissociated as hydrogen at high temperatures. Such dissociation behavior was also detected after using D2O saturated gas for pre-treatment. These results suggest that some protons which dissolved in the perovskite oxide could dissociate as hydrogen without forming oxygen vacancies. (131words)

A solid oxide fuel cell (SOFC) for high power density operation was developed with a microstructure-controlled cathode using a nano-composite powder of Sr-doped LaMnO 3 (LSM) and Y 2 O 3 -stabilized ZrO 2 (YSZ) synthesized by spray pyrolysis. The individual LSM-YSZ nano-composite particles, formed by crystalline and amorphous nano-size LSM and YSZ particles, showed spherical morphology with uniform particle size. The use of this powder for cathode material led to an extremely fine microstructure, in which all the LSM and YSZ grains (approximately 100–200 nm) were highly dispersed and formed their own network structures. This microstructure was due to the two phase electrode structure control using the powder, namely, nano-order level in each particle and micro-order level between particles. An anode-supported SOFC with the LSM-YSZ cathode using humidified H 2 as fuel and ambient air as oxidant exhibited high power densities, such as 1.29 W cm −2 under a voltage of 0.75 V and a maximum power density of 2.65 W cm −2 at 800 °C. Also, the SOFC could be stably operated for 250 h with no degradation, even at a high temperature of 800 °C.

Solid oxide electrolysis cells can theoretically achieve high energy-conversion efficiency, but current density must be further increased to improve the hydrogen production rate, which is essential to realize widespread application. Here, we report a structure technology for solid oxide electrolysis cells to achieve a current density higher than 3 A cm−2, which exceeds that of state-of-the-art electrolyzers. Bimodal-structured nanocomposite oxygen electrodes are developed where nanometer-scale Sm0.5Sr0.5CoO3−δ and Ce0.8Sm0.2O1.9 are highly dispersed and where submicrometer-scale particles form conductive networks with broad pore channels. Such structure is realized by fabricating the electrode structure from the raw powder material stage using spray pyrolysis. The solid oxide electrolysis cells with the nanocomposite electrodes exhibit high current density in steam electrolysis operation (e.g., at 1.3 V), reaching 3.13 A cm−2 at 750 °C and 4.08 A cm−2 at 800 °C, corresponding to a hydrogen production rate of 1.31 and 1.71 L h−1 cm−2 respectively., High-temperature solid oxide electrolysis cells are a promising technology for energy conversion, but higher current density is needed to increase efficiency. Here the authors design nanocomposite electrodes to improve electronic and ionic conductivity to achieve a high current density.

Nano-composite powders consisting of Sr-doped SmCoO 3 (SSC) and Sm-doped CeO 2 (SDC) were synthesized by spray pyrolysis using different cation concentration solutions, and the effect of this cation concentration on the electrochemical performance of electrodes fabricated using the powders was investigated. Regardless of the cation concentration, spherical particles consisting of nano-order fine SSC and SDC crystallites were successfully obtained. Although the crystal size of all the synthesized powders was almost the same, the particle size increased with increasing cation concentration. The microstructure of the cathodes fabricated using the nano-composite powders clearly depended on the particle size of the starting powders; the microstructure became coarser with increasing particle size and the original particle shapes partially remained in the cathode network. Also, electrochemical measurements for solid oxide fuel cells with these cathodes revealed that the electrode performance was related to the microstructure. The electrode polarization resistance decreased with decreasing particle size, and a relatively fine microstructure cathode exhibited lower electrode polarization resistance, resulting in a high performance of 1.52 W cm −2 at 700 °C. These results indicate that controlling the particle size, as well as controlling the nanostructure within the particles, is crucial to attain high performance electrodes.

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.

Barium zirconate have high chemical stability with CO2 comparison with barium cerate. Acceptor doped barium zirconate show high proton conductivity [1]. The proton conductivity of yttrium doped barium zirconate is 1×10-2 Scm-1 at 600 ℃ and it is attracted as the electrolyte of fuel cell and water vapor electrolysis cell. The fuel cell using proton conducting oxide was called to PCFC (proton ceramic fuel cell) and work at the intermediate temperature. PCFC is expected to be the energy conversion device in future because of high efficiency [2] and low production cost [3]. Generally, nickel is used as anode of PCFC. The anode overpotential of nickel is lower than that of the other metals. However, the nickels dissolve to the proton conducting oxide and possibly increase the ohmic resistance of electrolyte. Moreover, the nickel and the electrolyte possibly form the blocking layer such as the complex oxide. Although the proton conductivity of yttrium doped barium zirconate is highest in the zirconate-type proton conductor, BaY2NiO5 is formed between the nickel and the yttrium doped barium zirconate [4] and it might work as the blocking layer of proton. In this study, the reaction product between NiO and BaZr0.8 M 0.2O3-δ (M=Sc, In, Yb, Y, Gd) were confirmed by X-ray diffraction analysis. In order to clarify the NiO dissolution effect on the proton transport properties of BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y), the partial conductivity of the proton and the hole for BaZr0.8 M 0.2O3-δ (M=Sc, In, Lu, Yb, Y) with NiO were measured at temperature range of 200-600 ℃ by impedance analysis. The current efficiency on the polarization properties, then was examined for the fuel cell system using Acceptor-doped barium zirconate with NiO as electrolyte. Moreover, we investigated the effect of dopants on the ease of cell fabrication. The conventional ceramic tape-casting and firing process for fabricating laminated ceramic electronic devices was used, which is important for practical use. The power generation performance of planer cells fabricated by this process was also measured. The X-ray diffraction patterns of 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb, Y, Gd) were measured for the the samples as-sintered and annealed under 1%H2 at 873K. The peak of the NiO or Ni phase except the barium zircanate phase was observed for 0.4 mol% NiO doped BaZr0.8 M 0.2O3-δ (M= Sc, In, Yb). On the other hand, the BaM 2NiO5 phase was observed for M=Y, Gd. When the ionic radius of dopant is in excess of the size of Yb, the BaM 2NiO5 was formed as the reaction product between NiO and BaZr0.8 M 0.2O3-δ. The proton conductivity of the series of BaZr0.8 M 0.2O3-δ containing no NiO increased in the order of InM20 (M=Lu, Yb, Tm, Y) has an energy efficiency of more than 0.8 at 873 K. The proton conductivity decreased and the hole conductivity did not change for all series of BaZr0.8 M 0.2O3-δ due to NiO dissolution in BaZr0.8 M 0.2O3-δ. Therefore, proton transport number and the efficiency of the fuel cell decrease by addition to NiO. Considering the above, the ytterbium-doped barium zirconate did not form a complex oxide with NiO and might have high proton conductivity. The performance of PCFC using BZYb20 as electrolyte was measured. The maximum power density values at 600 and 700 °C were 0.50 and 0.70 Wcm−2 for the planar cells using BZYb20, respectively. Electrochemical impedance spectroscopy of the cell showed that the ohmic resistance was 0.28 Ωcm2 at 600 °C, which was approximately three times larger than the resistance value calculated using the bulk conductivity of BZYb20 and the electrolyte thickness and was in agreement with the resistance value of BZYb20 with NiO. [1] K.D. Kreuer et al., Solid State Ionics 145(2001)295-306. [2] Y. Matsuzaki et al., Scientific Reports, 5:12640(2015)1-10. [3] A. Doubois et al., ECS Transaction 78(1) (2017)1963-1972. [4] J. Tong et al., J. Mater. Chem. , 20(2010)6333.

High power density solid oxide electrochemical cells were developed using nanostructure-controlled composite powder consisting of Sr-doped SmCoO 3 (SSC) and Sm-doped CeO 2 (SDC) for electrode material. The SSC-SDC nano-composite powder, which was synthesized by spray pyrolysis, had a narrow particle size distribution ( D 10 , D 50 , and D 90 of 0.59, 0.71, and 0.94 μm, respectively), and individual particles were spherical, composing of nano-size SSC and SDC fragments (approximately 10–15 nm). The application of the powder to a cathode for an anode-supported solid oxide fuel cell (SOFC) realized extremely fine cathode microstructure and excellent cell performance. The anode-supported SOFC with the SSC-SDC cathode achieved maximum power density of 3.65, 2.44, 1.43, and 0.76 W cm −2 at 800, 750, 700, and 650 °C, respectively, using humidified H 2 as fuel and air as oxidant. This result could be explained by the extended electrochemically active region in the cathode induced by controlling the structure of the starting powder at the nano-order level.

In the scope of electrochemical phenomena, concentration polarization at electrodes is theoretically inevitable, and lowering the concentration overpotential to improve the performance of electrochemical cells has been a continuing challenge. Electrodes with highly controlled microstructure, i.e., high porosity and uniform large pores are therefore essential to achieve high performance electrochemical cells. In this study, state-of-the-art technology for controlling the microstructure of electrodes has been developed for realizing high performance support electrodes of solid oxide fuel cells (SOFCs). The key is controlling the porosity and pore size distribution to improve gas diffusion, while maintaining the integrity of the electrolyte and the structural strength of actual sized electrode supports needed for the target application. Planar anode-supported SOFCs developed in this study realize 5 μm thick dense electrolyte (yttria-stabilized zirconia: YSZ) and the anode substrate (Ni-YSZ) of 53.6 vol.% porosity with a large median pore diameter of 0.911 μm. Electrochemical measurements reveal that the performance of the anode-supported SOFCs improves with increasing anode porosity. This Ni-YSZ anode minimizes the concentration polarization, resulting in a maximum power density of 3.09 W cm −2 at 800 °C using humidified hydrogen fuel without any electrode functional layers.

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

Micro flat-tube solid-oxide fuel cell (SOFC) modules consisting of 1 mm thick, 1.2 cm wide micro flat-tube SOFCs, gas manifold, and insulator have been fabricated and evaluated using simple gas heating apparatus. The cell consists of NiO – yttria stabilized zirconia (YSZ) as an anode (flat-tube support), 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, which has been fabricated using cost effective extrusion technique and dip-coating technique. The cell has been investigated between 600 and 650 °C operating temperature and showed the power density at 0.75 V of 0.19 and 0.385 W cm−2, respectively. Using the cell, a five and ten-series modules were assembled and stored in insulator with small gas heaters powered by a 24 V power source for start-up. The module successfully operated using hydrogen and methane fuel.

Conductive Ag-precipitated glass powder was prepared by a heat reduction process of the glass/AgCl composite powder and its electrical conductivity was compared to conventional Ag-particle mixed glass powder. The Ag-precipitated glass powder with 30 wt.% dispersed Ag particles of diameter of 20 to 300 nm and the baked film made of the powder showed a good electrical conduction from 400 °C to 700 °C. On the other hand, the baked films made of the Ag-particle mixed glass powders of Ag particle size of 300 nm with 35 wt.% Ag content and that of size of 20 nm with 30 wt.% Ag content showed a poor electrical conduction. The electrical conduction of the film of Ag-precipitated glass powder resulted from a uniform dispersion of Ag particles. Since no continuous network of Ag particles was found in the microstructure observation of the glass powders, or films, the origin of the electrical conduction was considered to be due to a tunneling effect between the well-dispersed Ag particles.

The effects of anode microstructure on mechanical and electrochemical properties were investigated for anode-supported microtubular solid oxide fuel cells (SOFCs). The anode microstructures can be varied by the change in pore formers. For example, the acrylic resin pore former was burnt more rapidly at lower temperature than the graphite pore former during sintering. The acrylic resin pore former can introduce macropores with a diameter of several micrometers in nickel–yttria-stabilized zirconia (Ni–YSZ) anode. The walls of the macropores were packed with the nickel and YSZ particles. Although the Ni–YSZ anode microtube using the 10 wt% acrylic resin pore former was compatible with high porosity and mechanical strength, the maximum fuel utilization was limited to 72%. On the other hand, the graphite pore former can produce a relatively uniform distribution of micropores with a diameter of several hundred nanometers. The mechanical strength was reduced with a rise in porosity for the Ni–YSZ microtube using the graphite pore former in comparison with the acrylic resin. However, a high fuel utilization of 93% was realized for the microtubular SOFCs using the 10 wt% graphite pore former in spite of lower porosity than the acrylic resin. The selection of a pore former is important to obtain higher power generation efficiency for anode-supported microtubular SOFCs.

The performance of a conventional anode-supported microtubular SOFC using doped ceria as an electrolyte and Ni-based cermet as an anode is evaluated at low operating temperature between 294 and 542°C. An open-circuit voltage (OCV) of >0.9 V is obtained at all measured operating temperatures, and power generation is observed at temperatures as low as 294°C. The power density of the cell is 0.6 W/cm2 at 542°C operating temperature with 47% fuel utilization and is 5 mW/cm2 at 294°C operating temperature with an open-circuit voltage of 0.95 V. According to impedance spectroscopy, a greater influence of gas flow rate, on the cell performance, is observed at higher operating temperature.

The perovskite La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 –Ce 0.9 Gd 0.1 O 1.95 (LSCF–GDC) nanoparticulate cathode was applied for microtubular solid oxide fuel cells operated at intermediate temperatures. For the cell with the cathode sintered at 950 °C, maximum power densities of 0.26, 0.54 and 0.73 W cm −2 were obtained at 550, 600 and 650 °C, respectively. The ohmic resistance increased for the cathode sintered at 850 °C, and the polarization resistance increased for the cathode sintered at 1050 °C. The cathode polarization resistances of ionic conduction process in the LSCF bulk and adsorption/desorption process on the LSCF surface were estimated by the distribution of relaxation times analysis, which were only 0.066 and 0.065 Ω cm 2 at 600 °C for the cathode sintered at 950 °C. The grain size of the cathode was less than 100 nm, which resulted in high performance due to an overall decrease in cathode polarization resistance.

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.

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.

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

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.

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.

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.

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.

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.

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.

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

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

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

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.