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To study the reaction kinetics at the anode of solid-oxide fuel cells, a nickel stripe pattern was prepared on the surface of yttria-stabilized zirconia (YSZ) [8 mole percent (m/o) Y 2 O 3 -doped ZrO 2 ] by an ionized cluster beam (ICB) method and photolithography. Due to grain growth of nickel film at high temperatures, the minimum possible width of the stripes was found to be ca. 5 μm. By impedance measurements in H 2 -H 2 O atmospheres at 100 to 850 o C, it was shown that the reaction proceeds through the triple-phase boundary (TPB) of H 2 -H 1 O/Ni/YSZ and the mechanism of the rate-determining reaction is different from that at the TPB of H 2 -H 2 O/Pt/YSZ

In this paper we try to tailor the chemical stability of cobalt-rich perovskite Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3 − δ (BSCF) by B-site doping Sb. The chemical stability of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.1 Sb 0.1 O 3 − δ (BSCFS) was investigated by studying the oxygen nonstoichiometry, crystal structure and oxidation state by means of coulometric titration, high-temperature X-ray diffraction (HT-XRD) and soft-X-ray absorption spectroscopy (s-XAS) in various oxygen pressure ( p (O 2 )) and temperatures. The results prove that chemical stability of BSCFS is successfully improved in intermediate temperature solid oxide fuel cell working condition owing to Co valence change which is controlled by high valence cation doping.

Temperature and oxygen partial pressure, P (O 2 ), dependence of oxygen nonstoichiometry of LaNi 0.6 Fe 0.4 O 3 − δ , which is a new candidate cathode material for solid oxide fuel cells, has been determined by the equilibrium thermogravimetry. The P (O 2 ) and temperature dependence of the electrical conductivity of LaNi 0.6 Fe 0.4 O 3 − δ has also been measured. It has been clarified that the oxygen content, 3 − δ of LaNi 0.6 Fe 0.4 O 3 − δ at temperatures between 300 °C and 700 °C under 10 − 4 bar ≤ P (O 2 ) ≤ 1 bar is around 2.90, which can be explained by Ni and Fe valence of + 2 and + 4, respectively. Temperature and P (O 2 ) dependence of the oxygen nonstoichiometry and the electrical conductivity is small for LaNi 0.6 Fe 0.4 O 3 − δ , which can be ascribed to small variation of the average valence of B-site ion by temperature and P (O 2 ) due to occurrence of charge compensation between Ni ion and Fe ion. The easy occurrence of the charge compensation corresponds to hopping conduction with small, temperature and P (O 2 ) independent activation energy. By combination of oxygen nonstoichiometry and electrical conductivity, it has been clarified that LaNi 0.6 Fe 0.4 O 3 − δ is p-type conductor with mobility of 0.257 cm 2 V − 1 s − 1 , which is independent on temperature and P (O 2 ). Hole concentration at temperatures between 300 °C and 800 °C under − 4 ≤ log( P (O 2 )/bar) ≤ 0 is 3–4 × 10 21 cm − 3 .

The effects of Nb doping on the chemical stability of Ba0.5Sr0.5Co0.8Fe0.2O3 − δ based solid solutions under high oxygen partial pressure (p(O2)) and CO2-containing atmospheres were studied. BSCF and Ba0.5Sr0.5Co0.9Nb0.1O3 − δ (BSCN) and Ba0.5Sr0.5Co0.8Fe0.1Nb0.1O3 − δ (BSCFN) were prepared and investigated by using TG–DTA analysis under p(O2) = 1 and 10− 3 bar with or without CO2. The results showed that the Nb substitution effectively improved the chemical stability under high oxidation condition and also improved the CO2-tolerance of BSCF-based materials.

In this study, the crystal structures and the thermal expansibilities of La 1 − x Sr x MnO 3 + δ (LSM) with oxygen stoichiometric composition, δ = 0, were studied by an atmosphere and temperature controlled X-Ray diffractometer (XRD). Pre-heat-treatment conditions for the samples and oxygen partial pressures for XRD measurements at high temperature were carefully selected to keep oxygen stoichiometric composition. The crystal structures of La 1 − x Sr x MnO 3 at room temperature were rhombohedral, tetragonal, and cubic symmetry for 0.2 ≤ x ≤ 0.45, 0.5 ≤ x ≤ 0.6, x = 0.7, respectively. The second order phase transition from rhombohedral to cubic symmetry was confirmed for x = 0.4 compound at 923–973 K. Meanwhile, the second order phase transition from tetragonal to cubic symmetry was confirmed for x = 0.5 compound at 623–673 K, x = 0.6 compound at 423–473 K, respectively. Furthermore, the pure thermal expansibilities of LSM without chemical expansion were discussed based on XRD analysis.

Structural phase transition behavior of Pr 2 NiO 4+ δ , which attracts interest as new cathode material for solid oxide fuel cells, was investigated by DSC and TG–DTA under controlled oxygen partial pressure, P (O 2 ). It was revealed that the structural phase transition from orthorhombic phase to tetragonal phase involved discrete decrease of oxygen content in Pr 2 NiO 4+ δ and that the phase transition temperature, T p , decreased with decreasing P (O 2 ). Variation of enthalpy, Δ H , and entropy, ΔS, at the phase transition per one molar Pr 2 NiO 4+ δ were calculated from the peak area of DSC and they were independent on P (O 2 ) between 1.0 × 10 −1 bar and 2.25 × 10 −3 bar. From the linear relationships between T p and RT p ln P (O 2 ) and between 1/ T p and R ln P (O 2 ), variation of standard enthalpy, Δ H °, and standard entropy, Δ S °, of the phase transition per one molar O 2 were calculated, showing fair agreement with Δ H and Δ S . The variation of oxygen content at the phase transition, Δ δ , increased with decreasing P (O 2 ), which can be attributed to valence variation of Pr in tetragonal Pr 2 NiO 4+ δ by P (O 2 ).

The effect of cation composition in LaNi1-x Fe x O3-δ on oxygen nonstoichiometry has been investigated with iodometric titration. For LaNi0.6Fe0.4O3-δ , temperature and oxygen partial pressure dependence of oxygen nonstoichiometry has been determined by equilibrium thermogravimetry. The P(O2) and temperature dependence of the electrical conductivity of LaNi0.6Fe0.4O3-δ has also been measured. It has been clarified that δ generates with Ni substitution and maximum δ was observed for LaNi0.6Fe0.4O3-δ . Temperature and P(O2) dependence of oxygen nonstoichiometry and electrical conductivity is small for LaNi0.6Fe0.4O3-δ , probably because variation of average valence of B-site ion by temperature and P(O2) is small since charge compensation between Ni and Fe is easy to occur. The easy occurrence of the charge compensation corresponds to hopping conduction with small, temperature and P(O2) independent activation energy. By combination of oxygen nonstoichiometry and electrical conductivity, it has been clarified that LaNi0.6Fe0.4O3-δ is p-type conductor with mobility of 0.257 cm2V-1s-1, which is independent on temperature and P(O2). Hole concentration at temperatures between 300 °C and 800 °C under -4 ≤ log{P(O2)/bar}≤0 is 3~4 x1021 cm-3.

Cubic perovskite Ba0.5Sr0.5Co0. 8Fe0.1R0.1O3–δ (R=Fe, Nb, Mo, Sb) was synthesized, and the chemical stability under high oxygen partial pressure (p(O2)) was studied by using HT-XRD in the temperature range of 773-1373 K. It was found that Ba0.5Sr0.5Co0. 8Fe0.1Sb0.1O3–δ was remarkably stable than Ba0.5Sr0.5Co0. 8Fe0.2O3–δ and Ba0.5Sr0.5Co0. 8Fe0.1Mo0.1O3–δ in high p(O2) condition. The effect of B-site substitution on the CO2-tolerance of Ba0.5Sr0.5Co0. 8Fe0.1R0.1O3–δ was also investigated by TG-DTA analysis at 300-1373 K. It was demonstrated that the chemical stability of Ba0.5Sr0.5Co0. 8Fe0.2O3–δ against CO2 could be significantly improved when Fe were partially substituted by Nb or Sb ions.

We previously developed a technique by which to measure the mechanical damage of SOFC using the acoustic emission (AE) method. In the present paper, we applied an adapted Self-Organizing Map (SOM), which is an artificial neural network model, to produce a cluster map reflecting the similarity of AE events. The obtained map visualized the change in occurrence patterns of similar AE events, revealing six phases of damage progress. Moreover, we inferred mechanical interactions among components of SOFC from a series of AE events by our proposed data mining method called co-occurring cluster mining. Our methods provide a common foundation for a comprehensive damage evaluation system and a damage monitoring system.

The effect of Mn-doping on the stability of ScSZ electrolyte under dual atmosphere of solid oxide fuel cells (SOFCs) was investigated in this study. Scandia stabilized zirconia electrolytes with and without 5 mol % MnO2 (ScSZ and Mn–ScSZ) were annealed under dual atmosphere of air and 1.2%H2O–H2 at T = 1273 K. The surfaces of the ScSZ electrolytes in the air side were not changed after annealing. On the other hand, the surface of the Mn–ScSZ electrolyte in the fuel side was damaged; fine particles were formed on the surface and increased with time. After annealing for 4 weeks, dusting of the electrolyte surface was observed. Mn-doping to ScSZ and annealing under dual atmosphere simulating SOFCs induced the degradation of ScSZ electrolyte.

La0.6Sr0.4Co1 − yFeyO3 − δ (LSCF) mixed-conducting perovskite oxides, a SOFC cathode candidate material, exhibit oxygen nonstoichiometry under reducing atmosphere and elevated temperatures. Reduction of the B-site transition metals and formation of oxygen vacancies result in chemical expansion of the LSCF lattice. Knowledge of both thermal and chemical lattice expansion as a function of composition is an essential tool to tailor mismatches between different materials exposed to reducing and high temperature environments and avoid mechanical failure of the device. In this paper, thermal and chemical expansion coefficients were determined by measurement of the lattice parameters by HT-XRD as a function of pO2 (in the range of 10− 4 to 1 bar), temperature (773–1173 K) and B-site composition. The lattice parameters were correlated with the previously investigated oxygen nonstoichiometry of the LSCF series. While the thermal expansion coefficient increases almost linearly with increasing Co content, the chemical expansion coefficient appears to be independent of B-site composition.

Oxygen isotope diffusion coefficient, D *, of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) was measured as a function of p(O2) and temperature. Vacancy diffusion coefficient, D V, was calculated from D * and reported values of oxygen nonstoichiometry, δ. There was little dependence of D V on δ or p(O2) while D V by conductivity relaxation method was reported to drastically decrease with decreasing p(O2) below 10-2 bar. The absolute values of D V in this study were about an order of magnitude larger than those by conductivity relaxation method.

Comprehensive modeling of the spectra of the state-of-the-art Ni–YSZ/YSZ/LSM solid oxide cells including the instrumental stray impedance allowed the systematic deconvolution of the four major polarization losses ranging over one order of impedance magnitude. The stray impedance can be successfully modeled as an inductor connected in parallel with a parasitic resistor whose resistance was shown proportional to the inductance. From the high frequency the ohmic losses, the ‘charge-transfer’ impedance of the Ni–YSZ electrode, the surface diffusion and reaction co-limited impedance of LSM electrode, and the gas phase transport impedance of Ni–YSZ electrode were successfully distinguished. The latter two were satisfactorily described by the ideal Gerischer impedance with two independent parameters, respectively. The gas-concentration impedance increases with electrolysis due to the gas density decrease with hydrogen production, while the LSM polarization decreases due to the increased oxygen activity. Compensation of the opposite polarization behavior of Ni–YSZ and LSM electrodes explains the apparently ohmic polarization over a wide electrolysis range until the upturn where exponentially increasing gas-concentration impedance of Ni–YSZ electrode prevails. Apparently being quite distinct from the fuel cell polarization behavior, the polarization of the high temperature electrolysis can be consistently explained by the chemical potential variations of the reactants and products, which is suggested to be general characteristic of the gas electrodes of solid oxide cells, co-limited by surface diffusion and reaction process. The finite-length Gerischer model constituted of series resistors, shunt resistors, and shunt capacitors, allows the evaluation of the surface diffusivity (ca. 2 ⋅ 10 − 4 cm 2 s − 1 ), reaction constant (ca. 10 3 s − 1 ), and the utilization length (ca. 5 μm) among the LSM–YSZ composite functional layer of thickness of ca. 10 μm. The strong decrease in LSM polarization with electrolysis at the humidity of 30% can be contributed by the increase in surface diffusivity, chemical capacitance, and the surface reaction constant in the decreasing order, while the adsorption capacitance increases is mainly responsible for the polarization decreases at higher humidity condition of 50%.

The oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ has been the topic of various reports in the literature, but has been exclusively measured at high oxygen partial pressures, pO2, and/or elevated temperatures. For applications of La0.6Sr0.4CoO3−δ, such as solid oxide fuel cell cathodes or oxygen permeation membranes, knowledge of the oxygen nonstoichiometry and thermo-chemical stability over a wide range of pO2 is crucial, as localized low pO2 could trigger failure of the material and device. By employing coulometric titration combined with thermogravimetry, the oxygen nonstoichiometry of La0.6Sr0.4CoO3−δ was measured at high and intermediate pO2 until the material decomposed (at log(pO2/bar)≈−4.5 at 1073 K). For a gradually reduced sample, an offset in oxygen content suggests that La0.6Sr0.4CoO3−δ forms a “super-reduced” solid solution before decomposing. When the sample underwent alternate reduction–oxidation, a hysteresis-like pO2 dependence of the oxygen content in the decomposition pO2 range was attributed to the reversible formation of ABO3 and A2BO4 phases. Reduction enthalpy and entropy were determined for the single-phase region and confirmed interpolated values from the literature.

Phase transformation of 1 mol% NiO doped yttria stabilized zirconia (YSZ) under SOFC operation atmospheres was analyzed by in situ Raman spectroscopy with simultaneous measurement of conductivity using a test cell consisting of air, Pt/NiO doped YSZ/Pt, wet Ar balanced 50 vol% H 2 . In situ measurement was carried out under open circuit voltage (OCV) condition at 1173 K for more than 20 h. Phase transformation from the cubic to the tetragonal phase progressively proceeded from the matting surface of the electrolyte on the anode side with increasing holding time. Simultaneously, the electrical conductivity of the electrolyte also exhibited monotonically decrease from about 0.103 S cm −1 to 0.084 S cm −1 . The phase transformation started from the anode/electrolyte interface. The tetragonal to cubic phase volume ratio evaluated from the Raman spectra, rapidly decreased with increasing depth from the anode/electrolyte interface towards the center of the electrolyte. We have experimentally demonstrated by the in situ measurement that the conductivity degradation of NiO doped YSZ is closely associated to the phase transformation under a reducing condition at a high temperature.

Ni-YSZ composites are widely used as SOFC anode materials for electrochemical devices. The mechanical properties of Ni-YSZ composites were investigated by using a Small Punch(SP) testing method under SOFC operating condition. The compositions of the Ni-YSZ composites tested in this study were 0:100 vol.%, 15:85 vol.%, 30:70 vol.%, and 50:50 vol.%. Electrical resistivity measurements suggested that the Ni particles formed a network-like structure at the Ni content greater than 30 vol.%. Experimental results obtained from the SP tests demonstrated that ductile-like deformation was induced under a reducing environment for the Ni contents of 30 and 50 vol. %. The ductile-like behavior could be attributed to the formation of Ni network. The first complete re-oxidation of NiO-YSZ composites then caused critical damage and resulted in a drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ composites under reducing environment.

In this study, NiO–Ce 0.9 Gd 0.1 O 1.95 (NiO–GDC) nanocomposite powders, which were applied as anode materials of low temperature solid oxide fuel cells (SOFCs), were synthesized by hydroxide and oxalate reverse co-precipitation methods, respectively. The crystal phases, crystallite size, particle size, particle size distribution, and sintering characteristics of the synthesized NiO–GDC nanocomposite powders were investigated and compared. Results showed that the different co-precipitation methods affected strongly the synthesis and characteristics of the NiO–GDC nanocomposite powders. The NiO–GDC nanocomposite powders could be synthesized at lower temperature by the hydroxide reverse co-precipitation method, and the synthesized NiO–GDC nanocomposite powders had better sinterability. The NiO–GDC nanocomposite powders synthesized by the oxalate reverse co-precipitation method had smaller particle size and uniform particle size distribution and, however, were easy to result in crack formation in the sintered disks.

The dependence of the structural phase transition behavior of Nd2NiO4 + δ between the tetragonal and orthorhombic phases on the oxygen partial pressure, P(O2), has been investigated by differential scanning calorimetry, DSC, and thermogravimetry and differential thermal analysis, TG-DTA. The structural phase transition temperature, TP, decreased with decreasing P(O2), while the variations of enthalpy, ΔH, entropy, ΔS, estimated from the peak area of DSC signals and oxygen content at the phase transition, Δδ, determined from TG curves, exhibited little dependence on P(O2). From the relationship between Tp and P(O2), the variations of standard enthalpy, ΔH°, and entropy, ΔS°, at the phase transition have been evaluated. By considering Δδ, ΔH° and ΔS° exhibited fair agreement with ΔH and ΔS evaluated by DSC.

The oxygen nonstoichiometry of La0.6Sr0.4FeO3 − δ was measured at intermediate temperatures (773 to 1173 K) between 1 bar and the decomposition oxygen partial pressure by thermogravimetry and coulometric titration. The decomposition of the ABO3 perovskite phase was found to occur at low oxygen partial pressures (below 10− 20 bar). Using an atmosphere-controlled high-temperature XRD setup, the rhombohedral lattice parameters were obtained between 10− 4 and 1 bar at 773 to 1173 K. A phase transition from rhombohedral to cubic might be expected to occur at high temperatures and for δ near the plateau at δ = [Sr] / 2. The lattice expansion was separated into “pure” thermal and chemically induced expansion by combining the lattice parameters with the oxygen nonstoichiometry data. The linear thermal expansion was formulated with a “pure” thermal expansion coefficient of αth = 11.052 · 10− 6 K− 1 and a chemical expansion coefficient of αchem = 1.994 · 10− 2. The results were compared with previous data obtained for La0.6Sr0.4Co1 − yFeyO3 − δ with y = 0.2–0.8. La0.6Sr0.4FeO3 − δ was confirmed to show the highest thermo-chemical stability. While the chemical expansion of La0.6Sr0.4Co1 − yFeyO3 − δ seems little affected by the iron content, the thermal expansion coefficient was the lowest for La0.6Sr0.4FeO3 − δ.

Effects of redox cycling on the mechanical properties of Ni-YSZ cermets were investigated by using an in-situ small punch (SP) testing method. The Ni contents in the Ni-YSZ cermets tested in this study were 0, 15, 30 and 50 vol. %. Electrical conductivity measurements suggested that the Ni particles formed a network-like structure at the Ni contents greater than 20 vol. %. Experimental results obtained from the in-situ SP tests at 800åC demonstrated that ductile-like deformation was induced under reducing environment (at an oxygen partial pressure of 10-18atm) for the Ni contents of 30 and 50vol. %. The ductile-like behavior was attributable to the formation of Ni network. The first complete re-oxidation of Ni-YSZ cermets then caused critical damage and resulted in drastic strength reduction, probably due to Ni agglomeration. This study revealed the first evidence for the presence of potential plastic deformation capacity in Ni-YSZ cermets under reducing environments.

Deformation and mechanical damage measurement techniques were developed in order to investigate the degradation process of SOFC cell/stack and module under SOFC operation. In this study, the deformation and mechanical damage test was applied to simulated cell and stack. The deformation, micro crack and delamination in the cell and stack were detected by displacement gauge and acoustic emission (AE) method. The observation method determined location of signal and mechanism of the deformation and microcrack in the SOFC cell/stack. By using this method, it was possible to show the possibility that the detailed deterioration process can be evaluated, visually, and in real-time, even when applied to cell and stack at the actual equipment level.

The oxygen nonstoichiometry of La0.6Sr0.4Co1-yFeyO3-δ (LSCF) mixed-conducting perovskite-oxides can be classified into two groups: the cobalt-rich compounds (y=0, 0.2, 0.4) were previously reported to show a sharp decrease in oxygen content with reducing atmosphere, while the oxygen vacancy concentration increased more smoothly for the iron-rich compounds (y=0.6, 0.8, 1). Here we measured the oxygen content of LSCF with y=0.5 by thermogravimetry and coulometric titration as a function of oxygen partial pressure and temperature. No transitional behavior could be observed for La0.6Sr0.4Co0.5Fe0.5O3-δ, the oxygen nonstoichiometry showed the same behavior as for the cobalt-rich compounds. Except for y=1, the thermo-chemical stability of LSCF was little affected by the iron dopant content, all compounds (y=0-0.8) decomposed at similar oxygen partial pressures.

Numerical simulations are performed to characterize the micro- and macro-scale aspects of the electro-chemo-mechanical coupling behavior of a positive-electrolyte-negative (PEN) structure under SOFC operation. The mathematical homogenization method is applied to evaluate the macroscopic material properties of porous electrodes by performing the corresponding microscopic analyses. In particular, the potential transfer conditions at pore surfaces and triple-phase boundaries are homogenized to be source terms in the macroscopic electron-ion coupled transport problem. A case study is conducted to identify the major source of generation and evolution of cracks running through a disc-shaped cell. In this context, we are concerned especially with the effects of the radius of the cell, the thickness of an electrolyte and the profile of temperature's in-plane distribution on the macroscopic tensile circumferential stress distributions.

Change in the lattice parameters of La0.6Sr0.4Co1 − yFeyO3 − δ (y = 0.2, 0.4, 0.6 and 0.8) was observed by in-situ XRD under the various temperature and oxygen partial pressure conditions for thermo-chemical expansivity study. By combination of the lattice parameters and oxygen non-stoichiometry, the linear thermal expansion rates were formulated in each compound. The obtained formulas are expressed as a linear function of temperature and oxygen deficiency with the standard deviations from measured data less than 1.2%. Based on the formulas, apparent thermal expansions were separated into thermally induced part and chemically induced part. Thermal expansion coefficient αth, which is proportional constant for temperature, is increased with increasing Co content in La0.6Sr0.4Co1 − yFeyO3 − δ while chemical expansion coefficient αchem, which is proportional constant for oxygen deficiency, shows very small dependence on the composition. Increase in apparent thermal expansion with increasing Co content in La0.6Sr0.4Co1 − yFeyO3 − δ was caused by the combination of αth and αchem.

The fuel cell is regarded as a highly efficient, low-pollution power generation system. In particular, Solid Oxide Fuel Cell (SOFC) has a high generation efficiency. However, a crucial issue in putting SOFC to practical use is the establishment of a technique for evaluating the deterioration. We previously developed a technique by which to measure the mechanical damage of SOFC using the Acoustic Emission (AE) method. In the present paper, we applied the kernel Self-Organizing Map (SOM), which is an extended neural network model, to produce a cluster map reflecting the similarity of AE events. The obtained map visualized the change in occurrence patterns of similar AE events, revealing four phases of damage progress. The methodology of the present study provides a common foundation for a comprehensive damage evaluation system and a damage monitoring system.

The defect chemical relationship in Nd doped BaCeO3 was discussed based on the defect concentration determined by thermogravimetry and electrical conductivity measured by D.C. 4-terminal method as a function of oxygen partial pressure, P(O2), water vapor partial pressure, P(H2O), and temperature. In BaCe0.9Nd0.1O3 − δ, the defect concentration strongly depended on P(O2), P(H2O) and temperature. This is different from the results of other acceptor-doped BaCeO3 such as BaCe0.9 M0.1O3 − δ (M = Y and Yb), which the concentration of protonic defects is independent of P(O2). The electrical conductivity of BaCe0.9Nd0.1O3 − δ, showed unique P(O2) dependence at high P(O2) atmospheres compared to other acceptor-doped BaCeO3. At temperature above 973 K, σ increased with increasing P(O2). However, at temperature below 873 K, σ decreased with increasing P(O2). This is also different from the general conductivity scheme in other acceptor-doped BaCeO3 that the σ values increase with increasing P(O2) in high P(O2) atmospheres. A different behavior of Nd doped BaCeO3 was explained by considering the changes of oxygen vacancy concentration accompanied by the valence changes of Nd ions between trivalent and tetravalent states.

In the present paper, we investigated the electrical performance of anode-supported solid oxide fuel cells (SOFCs) composed of Gd0.1Ce0.9O1.95 (GDC) electrolyte films of 1–75 μm in thickness prepared by simple and cost-effective methods (dry co-pressing process and spray dry co-pressing process), and discussed the effect of thickness of the GDC electrolyte films on the electrical performance of the anode-supported SOFCs. It was shown that reducing the thickness of the GDC electrolyte films could increase the maximum power densities of the anode-supported SOFCs. The increase of the maximum power densities was attributed to the decrease of the electrolyte resistance with reducing the electrolyte thickness. However, when the thickness of the GDC electrolyte films was less than a certain value (approximately 5 μm in this study), the maximum power densities decreased with the decrease in the thickness of the GDC electrolyte films. The calculated electron fluxes through the GDC electrolyte films increased obviously with reducing the thickness of the GDC electrolyte films, which was the reason why the maximum power densities decreased. Therefore, for anode-supported SOFCs based on electrolytes with mixed electronic–ionic conductivity, there was an optimum electrolyte thickness for obtaining higher electrical performance.

The influence of chemically induced expansion on the fracture damage of a nonstoichiometric oxide (ceria) based solid oxide fuel cell (SOFC) single cell laminate was investigated by using numerical stress analyses under oxidizing/reducing gradient condition. The single cell examined in this study was composed of electrolyte (Ce0.8Sm0.2O2−δ), anode (Cermets of Ni–Ce0.8Sm0.2O2−δ), and cathode (La0.6Sr0.4Co0.2Fe0.8O3−δ), respectively. The finite element method (FEM) was employed to calculate the residual stress, thermal stresses, and chemically induced expansion stresses for the single cell. The residual and thermal stresses were calculated much smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for primary part of the induced stress. It was shown from the FEM that the maximum circumferential stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission (AE) method.

In this study, NiO–Ce0.9Gd0.1O1.95 (NiO–GDC) nanocomposite powders were synthesized by hydroxide co-precipitation method, and applied to improve the microstructure of solid oxide fuel cell (SOFC) anodes. The NiO–GDC anodes prepared from the NiO–GDC nanocomposite powders showed uniform microstructure with uniform distribution of NiO and GDC phases. Due to the uniform phase distribution, the Ni–GDC anodes prepared from the NiO–GDC nanocomposite powders had longer triple phase boundary (TPB), which resulted in enhanced electrochemical reactions. The anode-supported SOFC fabricated from the co-precipitated NiO–GDC nanocomposite powders exhibited higher electrochemical performance than the anode-supported SOFC fabricated from the mechanically mixed NiO–GDC nanopowders. The experimental results show that the use of the Ni–GDC anodes with uniform microstructure can effectively improve the electrochemical performance of anode-supported SOFC.

The electrical conductivity of SrZr 0.99 Fe 0.01 O 3 − δ was evaluated by a four-probe ac technique. The measurements were conducted in hydrogen and in oxygen containing atmospheres at 823 ≤ T / K ≤ 1273. It was found from the X-ray absorption spectroscopic measurements that Fe in the oxide is trivalent both in hydrogen and in oxygen. In order to determine the major carrier in the oxide, gas partial pressure dependences and isotope effect of hydrogen and deuteron on the electrical conductivity was investigated. In humidified hydrogen, it was found that proton conduction is predominant in the lower temperature region while oxide ion conduction starts to contribute to the total by increasing temperature of above 1173 K. In oxygen containing gas, the protonic conduction is found to be predominant at lower temperatures while the contribution of the electron hole conduction is significant at higher temperatures. Hydrogen evolution property was evaluated using the SrZr 0.99 Fe 0.01 O 3 − δ disc as a solid electrolyte. Hydrogen evolution rate obeyed the Faraday's law in humidified hydrogen at 1173 K, suggesting that the transport number of ionic species is unity.

To elucidate the electronic state and the conduction mechanism of Nd2NiO4+δ series oxides at high temperatures, the electrical conductivity, Seebeck coefficient, and nonstoichiometric oxygen content of Nd2−xSrxNiO4+δ (x = 0, 0.2, 0.4) were measured as a function of the Sr content, temperature, and oxygen partial pressure. The hole mobility is estimated from the electrical conductivity and the hole concentration which is defect chemically determined. The mobility slightly decreases as temperature increases as in metals at high temperatures. The relationships between the Seebeck coefficient, electrical conductivity, and hole concentration can be explained by Mott's equation, which expresses the Seebeck coefficient for metals. Semi-quantitative analyses strongly indicate that the electron or hole is itinerant in Nd2−xSrxNiO4+δ, and the conduction mechanism is metal-like band conduction at high temperatures. Based on the experimental results, schematics for energy level and band structure are proposed. At high temperatures, free holes in the σx2−y2 band composed of dx2−y2 orbitals contribute to metallic conduction.

High temperature X-ray diffraction measurements were made on oxygen nonstoichiometric La2 − xSrxNiO4 + δ in N2–O2 atmosphere at 873–1173 K. Crystal structure of La2−xSrxNiO4 + δ at high temperatures was analyzed using the tetragonal symmetry, I4/mmm. As the amount of excess oxygen increases, the lattice parameter perpendicular to the perovskite and the rock salt layers increases and that parallel to the layers decreases. As a consequence, the cell volume is almost constant regardless of the oxygen content variation. The lattice parameters essentially depend on temperature and δ. The relationship among the lattice parameters, temperature, and δ is expressed by the total differential form of the lattice parameters. The model with linear approximation can well explain the variation of the lattice parameters with δ and temperature. Apparent and true thermal expansion coefficients were calculated from the variation of the lattice parameters with temperature. Crystal structure of La2 − xSrxNiO4 + δ was estimated by the Rietveld analysis. It is elucidated that the space in the rock salt layer decreases as the acceptor concentration (x + 2δ) increases. The variation of the space in the rock salt layer is consistent with the oxygen nonstoichiometric behavior that the interstitial oxygen formation is suppressed as x and δ increase.

High temperature X-ray diffraction measurements were carried out on K 2 NiF 4 -type Nd 2 − x Sr x NiO 4 + δ ( x = 0, 0.2, 0.4) in N 2 –O 2 atmosphere at 873–1173 K. Diffraction patterns of Nd 2 − x Sr x NiO 4 + δ were indexed by a tetragonal symmetry except for that of Nd 2 NiO 4 + δ measured at 873 K in 1 bar O 2 . Tetragonal-orthorhombic phase transition was observed in Nd 2 NiO 4 + δ . The phase transition temperature decreases as P (O 2 ) decreases, e.g., about 883 K in P (O 2 ) = 1 bar and about 758 K in P (O 2 ) = 10 − 4 bar. Temperature vs. oxygen content phase diagram for Nd 2 NiO 4 + δ is illustrated from the relationship between phase transition temperature and oxygen content. Lattice parameters and atomic arrangement were estimated by the Rietveld analysis. As the amount of excess oxygen increases, the lattice parameter perpendicular to the perovskite and the rock salt layers increases and that parallel to the layers slightly decreases. As a consequence, the cell volume is almost independent of δ . The lattice parameters essentially depend on temperature and the amount of excess oxygen. Apparent thermal expansion coefficient was calculated from temperature dependence of lattice parameters in a constant atmosphere, while true thermal expansion coefficient was calculated from the temperature dependence of lattice parameters at the same oxygen content. Isothermal chemical expansion coefficient was calculated from the variation of the lattice constants with oxygen content. Thermal and chemical expansion coefficients are compared with expansion coefficients of other nonstoichiometric oxides. To make clear the correlation between oxygen nonstoichiometry and structural parameters' variation, space in the rock salt layer where interstitial oxygen is located is calculated from the structural information. Space in the rock salt layer decreases as the calculated acceptor concentration, x + 2 δ , increases. This means that the interstitial oxygen formation is suppressed as the acceptor concentration increases. Similar tendency has been confirmed in oxygen nonstoichiometric behavior of Ni-based K 2 NiF 4 -type oxides.

For the evaluation of electrode reaction at H2–H2O(g), Pt/BaCe0.95Y0.05O3 − δ, the electrode impedance and steady-state polarization measurements were examined as the functions of hydrogen partial pressure, PH2, steam partial pressure, PH20 and hydrogen activity on the electrolyte surface at triple phase boundary (TPB), aH, using three-terminal method at 773 and 873 K. The electrode interfacial conductivity strongly depended on PH2. From the results of the polarization measurements, the aH dependence of the reaction rate can be related to the contribution of adsorbed hydrogen atoms on the BCY surface at TPB. Additionally, the PH2 dependence of the reaction rate is attributed to the contribution of the adsorbed hydrogen atoms on the Pt surface. In order to explain the PH2 dependence of reaction rate, we propose the two electrode reaction models by the magnitude of the concentration of adsorbed hydrogen atoms on the Pt surface. The following reaction processes were considered as the rate determining reaction step in H2–H2O(g), Pt/BaCe0.95Y0.05O3 − δ: (i) the surface diffusion of Had (Pt) near TPB, and (ii) the dissociative adsorption of H2 on the Pt surface at TPB. The reactions (i) and (ii) take place in parallel.

Acoustic Emission (AE) technique is employed to detect degradation events inside of lithium-ion batteries. A commercial 18650 type battery and a model half cell (Li/organic electrolyte /LiCoO2) are monitored with AE technique during charge and discharge cycles. In the commercial battery, AE events are detected during every discharge process at SOC of around 35% and 15%. These AE can be attributed to the fracture of cathode material by phase transition. In the model half cell, AE events are found early cycles in charge process owing to the SEI formation, however in discharge process detected only under high C rate.

In order to elucidate how oxygen content changes in Nd 2 − x Sr x NiO 4 + δ ( x = 0, 0.2, 0.4), defect chemical and statistical thermodynamic analyses were carried out. The relationship among δ , P (O 2 ), and T were analyzed by a defect equilibrium model. Since Nd 2 − x Sr x NiO 4 + δ shows metal like band conduction at high temperatures, chemical potential of hole is expressed by the integration of the Fermi-Dirac distribution function and the density of state. The nonstoichiometric variation of oxygen content in Nd 2 − x Sr x NiO 4 + δ can be explained by the defect equilibrium model with a regular solution approximation. Partial molar entropy and partial molar enthalpy of oxygen are calculated from the nonstoichiometric data and Gibbs–Helmholtz equation. The relationship among defect structure, defect equilibrium, and thermodynamic quantities is elucidated by the statistical thermodynamic model. Thermodynamic quantities are calculated by the statistical thermodynamic model with the results of defect chemical analysis and compared with those obtained from experimental results. Thermodynamic quantities calculated by the statistical thermodynamic model can explain rough tendency of those obtained from the δ – T – P (O 2 ) relationship.

Oxygen nonstoichiometry of La0.6Sr0.4Co1-yFeyO3-δ (y=0.2, 0.8) were measured by high temperature gravimetry and coulometric titration as a function of temperature and oxygen partial pressure. The lattice constant is also observed by HT-XRD as a function of temperature and oxygen partial pressure. The relationship between lattice constant and oxygen deficiency is determined from these results. Almost linear behavior was obtained between them.

A series of doped LaGaO3 perovskite type oxides is considered as the electrolyte of solid oxide fuel cells (SOFCs), due to their high oxide ionic conductivity. However, detailed defect chemistry, particularly the relationship between oxygen nonstoichiometry and lattice parameter under operating condition of SOFCs has not been understood well so far. To clarify the relationship, measurement was made on the oxygen nonstoichiometry of La0.8Sr0.2Ga0.8Mg0.15Co0.05O3-d by high temperature gravimetry, and on the crystal structure by in-situ high temperature XRD. Oxygen vacancy concentration increases with decrease in log (P(O2)) and increase in temperature, finally converging on 3-d=2.80. The large variation in the oxygen nonstoichiometry results from valence change of Co. The valence of Co at 3-d=2.80 is nearly +2.0, whereas, the valence of Co at 3-d=2.85 is considered close to +4.0. In-situ high temperature XRD confirmed that the oxygen vacancy formation led to increase in the lattice parameter, namely chemical expansion induced by oxygen nonstoichiometry.

Electrical conductivity, Seebeck coefficient, and nonstoichiometric oxygen content of La2-xSrxNiO4+δ (x = 0, 0.2, 0.4) were measured as a function of Sr content, temperature, and oxygen partial pressure. At above around 873 K, mobility of hole decrease as temperature increase. The temperature dependence of hole mobility indicate large polaron conduction. The relationship between Seebeck coefficient and electrical conductivity is explained by metal like band conduction model. The behavior of electrical conductivity and Seebeck coefficient strongly suggests that electron (hole) is itinerant in La2-xSrxNiO4+δ at high temperatures.