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Bilayered Y2O3-stabilized ZrO2 (YSZ)/Sm2O3-doped CeO2 (SDC) electrolyte films were successfully fabricated on porous NiO–YSZ composite substrates by electrophoretic deposition (EPD) based on electrophoretic filtration followed by co-firing with the substrates. In EPD, positively charged YSZ and SDC powders were deposited directly on the substrates, layer by layer from ethanol-based suspensions. Delamination between YSZ and SDC films was avoided by reducing the SDC films’ thickness to ca. 1 μm. A single cell was constructed on the bilayered electrolyte films composed of ca. 4 μm-thick YSZ and ca. 1 μm-thick SDC films. As a cathode in the cell, La0.6Sr0.4Co0.2Fe0.8O3−x (LSCF) was used. Maximum output power densities greater than 0.6 W cm−2 were obtained at 700 °C for the bilayered YSZ/SDC electrolyte cells thus constructed.

We report a cost-effective processing method for fabricating intermediate temperature solid oxide fuel cells (SOFCs) with Ni-samaria doped ceria (SDC) anode. First, SDC and NiO powders were mechanically treated to make their composite powder. Then, the composite powder was applied into a ceramic tape casting method to form a thick layer for the anode supporting. Finally, an anode supported single cell with a configuration of Ni-SDC/SDC/La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 − δ (LSCF) was prepared. Because of the usage of the composite powder, homogenous distribution and connection of each Ni and SDC were achieved. Peak power densities of 460, 750 and 910 mW cm −2 were obtained on the single cell at 550, 600 and 650 °C, respectively.

Ni–Y2O3-stabilized ZrO2 (Ni–YSZ) cermet anode was fabricated for solid oxide fuel cells (SOFCs) by conventional ceramic processing using NiO–YSZ composite particles. Microstructures of the anode were carefully characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Ni–YSZ cermet anode was consisting of fine YSZ connections, as the conducting pass of oxygen ions, on the surface of Ni network, as that of electrons, with continuous pore structure and as that of gaseous species. No amorphous phases were present at the interface between Ni and YSZ, and there was an orientation relationship between Ni and YSZ grains, (111)Ni//(111)YSZ. The cermet anode showed a high electrical performance at 800 °C. These results indicated that the electrochemical activity of the Ni–YSZ cermet anode was enhanced with the present microstructure.

A La0.6Sr0.4Co0.2Fe0.8O3−a (LSCF) powder was prepared through a citric synthesis route and subsequent media agitating milling. The milling for 1.5 and 3 h reached the average particle sizes of 0.66 and 0.53 μm, respectively. Then, the LSFC cathodes were formed using the two powders in a conventional manner. It was shown that the cathode performance was strongly influenced by the starting particle size as well as sintering temperature. The smallest cathode polarization for both 700 and 800 °C operations was obtained when using the finer powder (0.53 μm) and sintering at 850 °C, suggesting an excellent cathode morphology. An anode-supported single cell with this cathode structure was fabricated and demonstrated a good generation performance under intermediate temperature operation.

NiO/Y2O3-stabilized ZrO2 (YSZ) composite particles for solid oxide fuel cell (SOFC) anode was fabricated by an advanced mechanical method using an attrition type particle composing machine in dry ambient. In this study, two sets of composite particles with different mixing time were prepared. Structure of the composite particles was markedly influenced by the mixing time since the morphology of the resultant Ni/YSZ cermet anode changed with the mixing time. Then, the relationship between the structure of composite particles and the properties of the Ni/YSZ cermet anode were examined. When the composite particles processed with mixing time of 5min were used, the cermet anode showed lower electrical performance at both 800°C and 1000°C. On the other hand, the longer processed composite particles (30min) resulted in higher electrical performance. The difference of anode performances was explained by the change in cermet morphology associated with the mechanical processing time. These results suggested that the mechanical processing for NiO/YSZ composite particles significantly influenced SOFC anode performance.

The effect of annealing on the electrical conductivity of the Y 2 O 3 –ZrO 2 system (8.0–10.0 mol% Y 2 O 3 ) was investigated by the direct current four-probe technique at several temperatures for 1000 h. The difference of the crystal structure before and after annealing was investigated by X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The decrease of the conductivity for the specimens with composition of 8.0–9.0 mol% Y 2 O 3 was caused by the formation of a fine tetragonal phase. On the other hand, the sample of 9.5 mol% Y 2 O 3 after annealing for 1000 h supported a single phase with cubic structure. Therefore, the optimum composition as electrolyte for solid oxide fuel cell in the Y 2 O 3 –ZrO 2 system was considered to be 9.5 mol% Y 2 O 3 from the viewpoint of long-term stability with the relatively high conductivity.

The electrical conductivity change with annealing at 1000 °C in the Y2O3–ZrO2 (YSZ) system was examined. Among the sintered samples doped with 8.0 mol% Y2O3 (8.0YSZ), 8.5 mol% Y2O3 (8.5YSZ), 9.0 mol% Y2O3 (9.0YSZ), 9.5 mol% Y2O3 (9.5YSZ) and 10.0 mol% Y2O3 (10.0YSZ), 9.5- and 10.0YSZ showed no conductivity decrease even for the annealing period of 1000 h, while 8.0- and 8.5YSZ showed significant decrease with time although the initial conductivities were higher than those of 9.5- and 10.0YSZ. The 9.0YSZ showed only slight conductivity decrease. The measurement of Raman spectra demonstrated that the deterioration in conductivity related to the gradual formation of fine tetragonal phase in the cubic phase. Consequently, 9.5YSZ was seemed to be optimum as the electrolyte material of solid oxide fuel cells from the point of stability in high conductivity.

A NiO–Y2O3 stabilized ZrO2 (YSZ) composite particles for solid oxide fuel cell (SOFC) anode was fabricated by advanced mechanical method in dry process. The processed powder achieved better homogeneity of NiO and YSZ particles, where submicron NiO particles were covered with finer YSZ particles. A Ni–YSZ cermet anode fabricated from the NiO–YSZ composite particles showed the porous structure in which Ni and YSZ grains of less than several hundred nano-meter as well as micron-size pores were uniformly dispersed. The cermet anode achieved high electrical performance at low temperature operation (

Nickel Oxide-Yttria Stabilized Zirconia (YSZ) composite powders for the fabrication of the cermet anode of solid oxide fuel cell (SOFC) was produced by an advanced dry mechanical process. The morphology of the Ni-YSZ cermet anode fabricated from NiO-YSZ composite powder could be controlled by the operating conditions of the mechanical process. Highly homogeneous cermet anode with very fine Ni and YSZ grains was obtained by applying the mechanical process. As a result, the Ni-YSZ cermet anode showed exceptional performance at low operating temperatures (≤800°C) for the SOFC. It is evident that the homogeneous Ni and YSZ grain structure in the size of less than several hundred nano-meters has increased the Three Phase Boundary (TPB) length for the electrochemical reaction, which contributed to the performance improvement of the cermet anode.

NiO/YSZ composite particles with 20–35 mol% Y2O3 stabilized ZrO2 (YSZ) were synthesized by the spray pyrolysis (SP) method. The NiO/YSZ composite particles showed morphology of NiO grains partially or fully covered with fine YSZ grains. The composite particles also had good interface connection between nickel oxide and yttria stabilized zirconia (YSZ). The morphology of the Ni/YSZ cermet anode fabricated from composite particles is noticeably influenced by the YSZ content of the composite particles. Ni/YSZ cermet anodes with 25 mol% YSZ show the highest electrochemical activity and lowest internal resistance (IR). The electrochemical activity and IR of the anode in solid oxide fuel cells (SOFCs) highly depend on the three-phase boundary structure based on the metal (Ni) and ceramic (YSZ) interface as well as the network structure of each Ni grains. Moreover, the cell voltage of a single cell with the Ni/YSZ cermet anode kept almost constant value during 7200 h of operation. Consequently, it is concluded that the performance and stability of the Ni/YSZ cermet anode is improved by controlling the morphology of the NiO/YSZ composite particles.

Ni–YSZ cermet anodes for solid oxide fuel cells (SOFCs) were fabricated at various sintering temperatures from NiO–YSZ composite particles made by spray pyrolysis (SP) technique. NiO particles covered with fine YSZ (Y 2 O 3 stabilized ZrO 2 ) particles were used as the composite particles, and the initial ratio of Ni and YSZ was set at 75:25 (mol%). As a result, the cermet anode sintered at 1350 °C showed the morphology in which fine YSZ grains were uniformly dispersed on the surface of Ni grain network. Electrical performance such as electrochemical activity and internal resistance of a Ni–YSZ cermet anode changed with sintering temperature. The anode fabricated at 1350 °C showed the highest electrical performance. Especially, a single cell voltage with the Ni–YSZ cermet anode kept very stable for 8000 h at 1000 °C in the SOFC operation condition of H 2 —3% H 2 O and air. The cermet anode after a long-term test had its initial morphology. It indicates that the Ni–YSZ cermet anode fabricated from NiO–YSZ composite particles is a very promising material for its practical use as SOFCs.

A solid oxide fuel cell constructed from Ni–SDC anode and LSGM electrolyte was applied to the partial oxidation of methane to syngas (CO+H2) at 700–800 °C with the merits of co-generation of electricity and controllable O2 supply. It was found that the co-generated syngas at H2/CO ratio of 1.4–2.0 varied with applied current densities, CH4 flow rates and operating temperatures. The cell voltage at 100 mA cm−2 and 800 °C was 0.90 V, i.e. about 90 mW cm−2 power density could be obtained. The cell operating at 50 mA cm−2 for 24 h almost showed no degradation of the cell performance. The observed carbon deposition seemed mainly taking place by CH4 cracking reaction.

A La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 (LSGM) thin film was fabricated by the usual tape casting method using a doctor blade to reduce the operating temperature in solid oxide fuel cells (SOFCs). The resultant LSGM film was 130 ± 3 μm in thickness and its relative density was over 99%. Also, the thin LSGM film showed a single phase, and its conductivity was 0.113 S/cm at 800 °C and 0.054 S/cm at 700 C, respectively. Therefore, it seemed that the thin LSGM film was suitable as an electrolyte for intermediate temperature operating SOFCs. Ni-SDC and La(Sr)CoO 3 synthesized by spray pyrolysis were used as an anode and a cathode, respectively, and a single cell was fabricated with the thin LSGM film as an electrolyte. This single cell with the thin LSGM electrolyte exhibited excellent electrical performance, of which power density was over 0.7 W/cm 2 at 800 C and 0.4 W/cm 2 at 700 C. These results suggested that the LSGM-based SOFCs with the thin LSGM film in this study would exhibit adequate performance at a temperature lower than 700 °C.

The sintering behavior of Ln-doped ceria (Ln=Y, Gd, Sm, Nd, La) containing gallia (Ga 2 O 3 ) was investigated. Ln-doped ceria samples containing gallia were well sintered at 1500 °C by a common solid-state reaction method. On the other hand, Ln-doped ceria samples without gallia did not become well sintered until the sintering temperature was raised to 1600 °C. We investigated the crystal structures, microstructures, density, and electrical conductivity of Ln-doped ceria sintered with gallia. The grain sizes of Ln-doped ceria sintered with gallia were much larger than those of Ln-doped ceria sintered without gallia. All samples except Y-doped ceria showed improvement in conductivity by the addition of gallia. The variation in acceleration of grain growth with Ln 3+ radius was consistent with the tendency of the melting points of solid solutions of Ln 2 O 3 and gallia, indicating that the acceleration of sintering was due to the effect of the liquid phase partly formed from Ln 2 O 3 and gallia during sintering.

In this study, the interactions of a Sr- and Mg-doped lanthanum gallate (LSGM with composition La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3− δ ) electrolyte with Fe 2 O 3 , Co 2 O 3 and NiO as the anode starting materials were investigated. It was found that the order of reactivity of the LSGM with the three oxides was Co 2 O 3 >NiO>Fe 2 O 3 , and La-containing oxides were detected in these binary powder mixtures after firing. The anode performance was greatly influenced by the interaction. The Fe 2 O 3 –LSGM anode, mixed with 40 vol.% LSGM powder and sintered at 1150°C, exhibited the highest initial performance in comparison with NiO–LSGM and Co 2 O 3 –LSGM anodes. It seems that Fe 2 O 3 is a possible anode starting material for a LSGM-based solid oxide fuel cell.

We report a new sealant material for solid oxide fuel cells (SOFCs) using glass-ceramic. A glass-ceramic based on the CaO-Al2O3-SiO2 system was selected as a sealant because it can be easily molded to give a gastight seal and remains in a solid-like state under typical fuel cell operating conditions. Calcium alumina silicate glass powder is placed in the gas-sealing area before crystallization. During heating, the glass softens and bonds with the SOFC components. At higher temperatures, bulk crystallization occurs in the glass and the viscosity of the glass-ceramic sealant increases. We show that this sealing material which is able to seal at higher viscosities compared with the melt sealing method produces a good gas-tight seal and is chemically stable in contact with SOFC components, e.g., yttria-stabilized zirconia electrolytes and lanthanum chromite separators.

The reactivity of NiO–SDC (samaria-doped ceria) anode material with a Sr- and Mg-doped lanthanum gallate (LSGM) electrolyte was studied by X-ray diffraction (XRD) and electrical measurements. It was found that a LaNiO3-based compound in hexagonal structure formed in binary powder mixtures of NiO and LSGM after firing at 1150°C. Reaction between SDC and LSGM was also observed. Several SDC peaks merged with the adjacent LSGM peaks during firing, and a SrLaGa3O7 compound was identified as a reaction product. Reaction between LSGM and SDC could cause more than 50% loss in the ionic conductivity of LSGM–SDC electrolytes sintered at 1350°C. The measured conductivity of an LSGM electrolyte with a NiO–LSGM anode prepared at 1350°C was extremely low, indicating that the LaNiO3-based new phase is highly insulating. The reaction between NiO and SDC was not so obvious in comparison with NiO–LSGM and SDC–LSGM binary mixtures.

The reduced temperature solid oxide fuel cell (SOFC) with 0.5 mm thick La0.9Sr0.1Ga0.8Mg0.2O3−α (LSGM) electrolyte, La0.6Sr0.4CoO3−δ (LSCo) cathode, and Ni-(CeO2)0.8(SmO1.5)0.2 (SDC) cermet anode showed an excellent initial performance, and high maximum power density, 0.47 W/cm2, at 800°C. The results were comparable to those for the conventional SOFC with yttria-stabilized zirconia (YSZ) electrolyte, La(Sr)MnO3-YSZ cathode and Ni–YSZ cermet anode at 1000°C. Using an LSCo powder prepared by spray pyrolysis, and selecting appropriate sintering temperatures, the lowest cathodic polarization of about 25 mV at 300 mA/cm2 was measured for a cathode prepared by sintering at 1000°C. Life time cell test results, however, showed that the polarization of the LSCo cathode increased with operating time. From EPMA results, this behavior was considered to be related to the interdiffusion of the elements at the cathode/electrolyte interface. Calcination of LSCo powder could be a possible way to suppress this interdiffusion at the interface.

A variety of spray pyrolysis (SP) techniques have been developed to directly produce ceramic powders from solutions. Examples that are discussed include the following powders: (La0.8Sr0.2)0.9MnO3-YSZ (La(Sr)MnO3-YSZ), La0.6Sr0.4CoO3 (La(Sr)CoO3), (CeO2)0.8(SmO1.5)0.2-NiO (SDC-NiO) and La0.9Sr0.1Ga0.8Mg0.2O3-NiO (LSGM-NiO). For all these powders, spherical, non-agglomerated, submicrometer particles were obtained from aqueous solution of metal salts into a furnace using an ultrasonic atomizer at 1.7 MHz. After SP some of the particles exhibit a hollow-shell morphology. Subsequent calcination at 1000°C yielded crystalline particles. The electrical performance of Ni-SDC/LSGM/La(Sr)CoO3 fuel cells operating at 800°C, prepared from the powders obtained by SP, is reported.

The polarization properties and microstructure of Ni-SDC (samaria-doped ceria) cermet anodes prepared from spray pyrolysis (SP) composite powder, and element interface diffusion between the anode and a La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) electrolyte are investigated as a function of anode sintering temperature. The anode sintered at 1250°C displays minimum anode polarization (with anode ohmic loss), while the anode prepared at 1300°C has the best electrochemical overpotential, viz., 27 mV at 300 mA cm−2 operating at 800°C. The anode ohmic loss gradually increases with increase in the sintering temperature at levels below 1300°C, and sharply increases at 1350°C. Electron micrographs show a clear grain growth at sintering temperatures higher than 1300°C. The anode microstructure appears to be optimized at 1300°C, in which nickel particles form a network with well-connected SDC particles finely distributed over the surfaces of the nickel particles. The anode sintered at 1350°C has severe grain growth and an apparent interface diffusion of nickel from the anode to the electrolyte. The nickel interface diffusion is assumed to be the main reason for the increment in ohmic loss, and the resulting loss in anode performance. The findings suggest that sintering Ni-SDC composite powder near 1250°C is the best method to prepare the anode on a LSGM electrolyte.

The electrode performance of a single solid-oxide fuel cell (SOFC) was evaluated using a 500 {micro}m thick La{sub 0.9}Sr{sub 0.1}Ga{sub 0.8}O{sub 0.3} (LSGM) as the electrolyte membrane. A doped lanthanum cobaltite, La{sub 0.6}Sr{sub 0.4}CoO{sub 3{minus}{delta}} was selected as the cathode material, and a samaria-doped ceria-NiO composite powder was used as the anode material. The spray-pyrolysis method was applied for synthesis of the starting powders of the cathode and anode. In this study, different microstructures of the cathode were obtained by varying the sintering temperature from 950 to 1200 C. High power density (the maximum power density of the cell was about 425 mW/cm{sup 2}, which is 95% of the theoretical value) of the solid oxide fuel cell at 800 C was achieved. The cell performance showed that, with a proper choice of electrode materials with optimized microstructure and LSGM as the electrolyte, a SOFC operating at temperatures T{sub op} {le} 800 is a realistic goal.

To develop higher protonic conductivity, we have been studying a new perovskite-type oxide and found that BaPrO 3 based perovskite oxides showed high conductivity in a moist H 2 atmosphere. Their conductivity was about 0.1 S/cm at a temperature of 500°C and remained almost constant up to 700°C, which is much higher than that of Ba(Ce 0.8 Gd 0.2 )O 3− α . Ba(Pr 1− x Gd x )O 3− α prepared by solid state reaction exhibited an orthorhombic and/or cubic perovskite structure and with a high Gd content was stable in a reducing atmosphere. When Ba(Pr 0.7 Gd 0.3 )O 3− α was used as an electrolyte, the open circuit voltage of the cell was about 1 V and this cell was able to operate at 500°C. During the testing of the cell, the formation of water on an air electrode led us to conclude that mobility of protons in the electrolyte occurred. The dominant conduction species in Ba(Pr 1− x Gd x )O 3− α electrolyte were considered as oxygen ions and/or protons.

NiO/YSZ composite particles with 20 to 35 mol% Y2O3 stabilized ZrO2 (YSZ) are prepared by Spray Pyrolysis (SP) method. The NiO/YSZ composite particles are NiO particles coated with fine YSZ grains. The morphology of Ni/YSZ cermet anode fabricated from the composite particles is noticeably influenced by the YSZ content of the composite particles. Ni/YSZ cermet anode with 25 mol% YSZ shows the highest electrochemical activity and the lowest IR. The electrochemical activity and internal resistance (IR) of the anode in Solid Oxide Fuel Cells (SOFCs) highly depend on the boundary structure between Ni and YSZ grains as well as the network structure of each Ni grains. Consequently, it is concluded that the performance of the Ni/YSZ cermet anode is improved by controlling the morphology of the NiO/YSZ composite particles.

Nickel Oxide (NiO) - Yttria Stabilized Zirconia (YSZ) composite powders for the fabrication of the cermet anode of Solid Oxide Fuel Cell (SOFC) were processed by a novel processing unique in dry phase. The morphology of the Nickel (Ni)-YSZ cermet anode fabricated from the NiO-YSZ composite powder showed homogeneous porous structure consisted of sub-micron sized Ni and YSZ grains. Moreover, it was found from Auger Electron Spectroscopy observation that several hundred nano-meter shed YSZ grnins and fine Ni grains achieved good connections. As a result, the Ni-YSZ cermet anode showed excellent electric performance at lower operating temperatures less than 800°C. The homogeneous morphology consisted of fine Ni and YSZ grains would lead to increasing of the Three Phase Boundary (TPB) length for the electrochemical reaction, which contributed to the performance improvement of the cermet anode.

Publisher Summary The functions inherent in nanoparticles can be maintained while lowering their reactivity by fabricating nanoparticles into nanostructures. Stable nanostructured materials, fully utilizing the functions of nanoparticles, can be created by fabricating composite and bulk materials from nanoparticles, depending on their intended use. This chapter deals with such nanostructured materials and their various functions and the characteristic evaluation by function. It summarizes the nature of nanostructures, relevant examples of the relations between nanostructures and their characteristics, and the functionality and the evaluation of the characteristics of nanostructures. The chapter describes an electrode of a solid oxide fuel cell (SOFC), the structure of which is controlled using surface-coating type composite particles and the inner-dispersion type composite particles, as an example to explain the relation between nanostructures and their functional performance. In fabricating nanostructures in the application of nanoparticles, new functionalities are expected to produce many applications ranging over almost all fields in the coming years, with the advancement of technology. The chapter discusses the functional characteristics that are expected to be implemented in nanostructures in the coming future, including mechanical characteristics, thermal characteristics, electrical characteristics, electrochemical characteristics, electromagnetic characteristics, optical characteristics, catalytic characteristics, and gas permeability and separation characteristics.

The performance of a Sr- and Mg- doped lanthanum gallate (LSGM) electrolyte based solid oxide fuel cell is greatly affected by the interfacial reaction of electrode material with the LSGM electrolyte. The reactivity is closely related to the electrode composition and the sintering temperature. The ohmic loss is a good indicator of the reactivity (i.e., an overly-high and unequal ohmic loss between the anodic and the cathodic). The interfacial reaction also interferes with the measurement of the electrode overpotential. Care should be taken in the interpretation of measured electrode overpotentials if an interfacial reaction occurs in the cell.