The development of a dense chemical reaction blocking layer (CRBL) for micro-tubular solid oxide fuel cells (SOFC) was the aim of this study. The electrochemical performance and stability of SOFCs were also investigated since they strongly depend on fabrication conditions for the electrolyte and CRBL layers. Slurries of two commercial Ce_0.8Gd_0.2O_1.90 powders were prepared and deposited by dip coating onto micro-tubular SOFCs. The results indicate that the layer density and homogeneity are essentially determined by the width of particle size distribution (PSD) apart from the colloidal stability. Two methods were applied for achieving a narrow PSD additional to dispersion: grinding and centrifugation. Particles with a very narrow PSD obtained through centrifugation process could be sintered together even at 1300°C and a layer with a density close to 99% could be reached. In contrast, simple ultrasonic dispersion of powders diminished the distribution width insufficiently and gave porous layer. Impedance measurements showed clear relationship between GDC layer density and ohmic resistance of the cells which directly correlates to their performance with a power density 0.75 W/cm² at 0.7 volt and OCV~1.06 V obtained at 850°C for the cells with the densest GDC layer.

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Segmented-in-series solid oxide fuel cells (SIS-SOFC) have been stacked on all sides of a porous ceramic support using decalcomania method. When cells are stacked using decalcomania method, the cell components do not penetrate into the porous support or neighboring layers, resulting in excellent interfacial bonding. The cell components formed uniform thickness as well. Since the current flows laterally in SIS-SOFC, the cells are prepared having dimensions of 8 and 5 mm in length to minimize their lateral resistance. Subsequent power output characteristics have been studied. As cell length decrease from 8 to 5 mm, the open circuit voltage and maximum power density increase. This is attributed to the lower lateral resistance due to shorter current path. Impedance analysis also shows that ohmic resistances decrease substantially with decreasing cell length.

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Preparation of Microtubular cell using doped lanthanum gallate (LSGM) electrolyte with a dip coating and co-sintering process was studied. In order to suppress Ni diffusion from Ni-based anode substrate to LSGM electrolyte layer, Ti added La-doped ceria (Ti-LDC) was inserted as buffer layer. The amount of Ni diffused in LSGM electrolyte was investigated by EDX analysis as a function of sintering temperatures. It was found that sintering at 1350°C is suitable from the sintering density and the Ni diffusion. The cell sintered at 1350°C exhibited the higher power density than that of the conventional LSGM micro-tubular cell, even though a small amount of Ni diffusion was still observed at the Ti-LDC buffer layer/LSGM electrolyte interface. The micro-tubular cell with around 50 µm thickness showed the open circuit potential higher than 1.0 V and the maximum power density of 0.69, 0.31 and 0.12 W/cm² at 700, 600 and 500°C, respectively, were achieved.

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In this study, Sr(Ce_0.6Zr_0.4)_0.8Y_0.2O_3−δ proton-conducting ceramics are synthesized both using the solid-state reaction (SSR) and ethylenediaminetetraacetic acid (EDTA)-citrate complexing methods. The crystal structure, electrical conductivity, electrochemical performance and hydrogen permeation of the Sr(Ce_0.6Zr_0.4)_0.8Y_0.2O_3−δ ceramics are investigated. The conductivity of the Sr(Ce_0.6Zr_0.4)_0.8Y_0.2O_3−δ prepared by EDTA-citrate complexing method is 0.0081 S/cm at 800°C, which is about twice that of sample prepared by SSR method (0.0039 S/cm). The hydrogen permeation flux of the Sr(Ce_0.6Zr_0.4)_0.8Y_0.2O_3−δ prepared by EDTA-citrate complexing method increases from 1.102 to 1.745 ml min⁻¹ cm⁻² as the temperature increases from 500 to 800°C, which is higher than that of sample prepared by SSR method (0.574 to 1.466 ml min⁻¹ cm⁻²). The structure stability of the all Sr(Ce_0.6Zr_0.4)_0.8Y_0.2O_3−δ samples is good in water, no structure decomposition phenomenon is oberved.

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Ba_0.8Sr_0.2Ce_0.8−x−yZr_yIn_xY_0.2O_3−δ (x = 0.05, 0.1 y = 0, 0.1) proton-conducting oxides are prepared using a solid state reaction process. The effect of indium contents on the microstructures, chemical stability, electrical conductivity, and sintering ability of these Ba_0.8Sr_0.2Ce_0.6Zr_0.2In_xY_0.2−xO_3−δ oxides were systemically investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and two probe conductivity analysis. The results reveal that the Ba_0.8Sr_0.2Ce_0.6Zr_0.2In_xY_0.2−xO_3−δ oxides are cubic perovskite crystal structure without second phase. Surface morphology of 1450°C, 4 h sintered oxides shows a dense microstructure. The optimum conductivity of Ba_0.8Sr_0.2Ce_0.75In_0.05Y_0.2O_3−δ oxide is 0.011 S/cm measured at 800°C. Chemical stability of the oxides to resist CO₂ at 600°C is effectively improved by doping 0.1 at % indium or more. In addition, the laminated electrolyte and anode layers which fabricated by tape casting were co-sintered at 1450°C for 4 h. The sintered half-cell coated with Pt paste as cathode was used for I–V curve performance testing. The performance of the single cell of anode supported proton-solid oxide fuel cell (P⁺-SOFC) have powder density of 139.8 mW/cm at 800°C. Therefore, the Ba_0.8Sr_0.2Ce_0.75In_0.05Y_0.2O_3−δ ceramic is suggested to be a potential electrolyte material for P⁺-SOFC applications.

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The regenerability and stability of lanthanum strontium manganite (LSM)/yttria doped zirconia (YSZ)/LSM symmetrical cells have been examined after the cells were exposed to real-world air environment containing H₂O and CO₂. An alternate exposure experiment in 20% H₂O-air and dry air has been conducted to test the reversibility of the cell degradation in H₂O/air. Long-term experiment in 3% H₂O-0.5% CO₂-air, dry air, 0.5% CO₂-air, and 10% CO₂-air has shown the stability and regenerability of the cell performance. Additional experiments show that periodic water content fluctuation causes the cell performance fluctuation. Electrochemical performance measurements and post-test microstructure analysis indicate that the segregation of SrO on the LSM surface and formation of La₂Zr₂O₇ at the LSM/YSZ interface degraded the electrochemical performance by increasing the polarization resistance. The cell performance degradation can be partially recovered by exposure to dry air. Thermogravimetric analysis (TGA) has been conducted for the LSM as well as its constituent oxides to elucidate degradation mechanisms. Mechanisms related to the performance degradation and regenerability have been proposed.

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A long term durability test is conducted on a large area 10 × 10 cm² metal-supported cell. The cell that consists of a porous nickel-iron substrate as a support, an La_0.75Sr_0.25Cr_0.5–Mn_0.5O_3−δ (LSCM) interlayer, a nano-structured Ce_0.55La_0.45O_2−δ (LDC)-Ni anode, an LDC isolation layer, an La_0.8Sr_0.2Ga_0.8Mg_0.2O_3−δ (LSGM) electrolyte, a Sm_0.15Ce_0.85O_3−δ (SDC) barrier layer and a SDC-Sm_0.5Sr_0.5CoO_3−δ (SSC) cathode is prepared by using an atmospheric plasma spraying technology. The measured maximum output powers are 40.4, 31.2 and 22.7 W at 750, 700 and 650°C respectively. In the long term durability test, the cell voltages are measured in a constant current mode (400 mA cm⁻²) for 3000 h at 700°C. The measured I–V curves and AC impedance data are used to trace the variations of ohmic and non-ohmic resistances at different times. It is found that the dominant factors in the degradation of the tested cell are the increases of activation polarization and ohmic resistances. The tested cell is heat treated at the condition of 820°C and OCV for 4 h after 500 h durability test, the measured I–V curves and cell voltages show that the tested cell is recovered and demonstrate that the heat treated process at the condition of 820°C and OCV for 4 h is effective to recover the performance of the prepared cell. Based on the measured experimental data and the post microstructure analysis, the degradation of the tested cell is mainly due to the microstructural change in the anode and micro-cracks formed at layer interfaces that have significant thermal expansion mismatches, they cause the increases of activation polarization and ohmic resistances. After the recovery process, it is found the ohmic resistance decreases.

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Solid oxide fuel cells (SOFCs) can, in principle, directly use hydrocarbon fuels. However, nickel-stabilized zirconia anode deteriorated rapidly under direct butane utilization due to carbon deposition. The cracking rate is faster, when carbon number is larger and straight chain is longer in methane, propane, i-butane and n-butane. However, microtubular SOFCs with nickel-gadolinia doped ceria (Ni-GDC) anode can generate power continuously at 650°C over a period of 100 h in propane and butane, because the Ni-GDC has high catalytic activities of hydrocarbon reforming and carbon oxidation. The Ni-GDC is one of the desirable anodes for direct propane and butane utilization in SOFCs.

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The anode-supported solid oxide fuel cell (SOFC) is constructed by a screen-printed double-layer cathode, an air-tight yttria-stabilized zirconia (YSZ) as electrolyte, and a porous Ni-YSZ as anode substrate. A thin Ni film is fabricated as an anode current collector layer to improve the performance of the SOFC. The operation parameters are systematically investigated, such as feed rates of the reactants, operation temperature, contact pressure between current collectors and unit cell on the cell performance. The SEM results show that the YSZ thin film is fully dense with a thickness of 8 µm and exhibits the good compatibility between cathode and electrolyte layers. The maximum power density of the cell with Ni current collector layer is 366 mW cm⁻² at 800°C. This value is approximately 1.3 times higher than that of the cell without Ni layer. According to the electrochemical results, the Ni current collector layer decreases the ohmic and polarization resistances. The contact pressure results between cell and test housing show that cell performance efficiency is enhanced at the high current density region.

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In this study, the effects of various amounts of Ga³⁺ dopants on the densification, phase structure, microstructure and electrical conductivity of La_9.5Ge_6.0O_26.25 ceramics are examined. The incorporation of Ga³⁺ ions into the La_9.5Ge_6.0O_26.25 lattices leads to the retardation of the densification and an increase in the triclinic structure, caused by the evaporation of GeO₂ and the largeness of the size difference between the Ga³⁺ ions and Ge⁴⁺ ions. Of the compositions studied, the La_9.5Ge_5.7Ga_0.3O_26.1 ceramic sintered at 1450°C shows an electrical conductivity of 4.02 × 10⁻² Scm⁻¹ at 800°C, which is higher than that of an 8YSZ ceramic. The calculated thermal expansion coefficient (CTE) of this ceramic of 10.4 × 10⁻⁶ K⁻¹ appears to be compatible with those of the common adjacent materials used in solid oxide fuel cells (SOFCs). A single cell with a La_9.5Ge_5.7Ga_0.3O_26.1 electrolyte 0.51 mm in thickness is built and evaluated. The cell has R₀ and R_P values of 0.80 and 0.28 Ω·cm², respectively, at 850°C. The open circuit voltage (OCV) and maximum power density (MPD) of the single cell are recorded as 1.002 V and 0.24 Wcm⁻² at the measurement temperature of 850°C. Through the incorporating of a thick La_9.5Ge_5.7Ga_0.3O_26.1 layer, the cell performance of the single cell with the La_9.5Ge_5.7Ga_0.3O_26.1 electrolyte is superior to that of SOFC cells with a similar electrolyte thickness reported in the literature, thus qualifying the La_9.5Ge_5.7Ga_0.3O_26.1 ceramic as a potential electrolyte material for SOFCs.

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Nanocrystalline Yb-doped scandia-stabilized zirconia (6Yb4ScSZ) powders are prepared using co-precipitation process. The effects of calcination treatments on factors such as phase evolution, crystallite size, and specific surface area are investigated. The synthesized electrolyte powders have a high specific area of 25 m² g⁻¹, nanocrystalline size of 17 nm and ionic conductivity of 0.7 S cm⁻¹ at 800°C with a cubic structure. Solid oxide fuel cell (SOFC) with anode-supported electrolyte, in which the electrolyte layer consists of nanocrystalline 6Yb4ScSZ powders calcined at 850°C, is fabricated by tape casting and co-sintering. The open-circuit voltage of the SOFC single cell is approximately 1.07 V at 800°C, indicating negligible leakage of fuel through the electrolyte layer. As a result, power density of 1.30 W cm⁻² is obtained at 2.0 A cm⁻² and 800°C due to the drastic reduction of ohmic resistance in the SOFC cell.

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Bilayer Ni-YSZ anode films for SOFCs were prepared by electrophoretic deposition (EPD). The thickness of each layer of the bilayer anode films, which consist of 50 wt %Ni-YSZ as the active layer and 70 wt %Ni-YSZ as the current collecting layer (50Ni-YSZ/70Ni-YSZ), were controlled by the deposition time of the EPD process. For the monolayer anodes, 70Ni-YSZ showed a better performance than 50Ni-YSZ. The bilayer film, 50Ni-YSZ/70Ni-YSZ, showed an even better performance than the 70Ni-YSZ monolayer film. Probably, 50Ni-YSZ anode has more reaction sites compared to 70Ni-YSZ; on the other hand, 70Ni-YSZ has higher porosity to be a gas diffusion (or current collecting) layer. The anodic performance of the bilayer film significantly depended on the film thickness of the 50Ni-YSZ layer, and 3 µm was found to be the optimized thickness as the active layer, which suggests that the charge transfer reaction site extended up to a 3-µm thickness from the anode/electrolyte interface.

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A series of barium-aluminum-borosilicate system glasses, designated as GC9, with the formula of 34BaO–4.5Al₂O₃–9.5B₂O₃–34SiO₂–1ZrO₂–xLa₂O₃–(17–x)CaO, where x = 0, 1, 3, 5, 7 in mol %, have been developed as the high-temperature sealants using for solid oxide fuel cells (SOFCs). The effects of lanthanum-to-calcium (La/Ca) ratios on the thermal and crystalline properties of the GC9 glass were investigated in the present study. The density, glass transition temperature (T_g), and softening temperature (T_s) of the GC9 glass increase with increasing the La/Ca ratio. The average coefficient of thermal expansion (CTE) in the temperature range from 25 to 650°C for the glass system varies from 8.25 × 10⁻⁶ to 9.49 × 10⁻⁶ K⁻¹. The T_g, T_s and CTE for the optimized GC9 glass are 652, 745°C, and 9.48 × 10⁻⁶ K⁻¹, respectively, at the La/Ca ratio of 0.833. After annealing at 750°C for 4 h in air, the crystallinity of the GC9 glass increases with increasing the La/Ca ratio and the crystalline phase is mainly Ba₃La₆(SiO₄)₆. In addition, the GC9 glass with a La/Ca ratio of 0.833 possesses well wetting and adhesion joining with metallic interconnect, and ceramic positive electrode-electrolyte-negative electrode (PEN) plate after sealed at 850°C for 4 h.

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We studied Σ3 BaZrO₃ (210)[001] tilt grain boundaries using density functional theory and a space charge layer model. Formation enthalpies of BaZrO₃ and competing oxides were calculated using fitted elemental-phase reference energy (FERE) correction, and a stable region of BaZrO₃, as functions of Ba and O chemical potentials, was determined. Grain boundary energies were evaluated as functions of Ba and O chemical potentials within the determined stable region of BaZrO₃ from the FERE correction. Among the six tested grain boundaries, an energetically favorable nonstoichiometric grain boundary was determined. Based on the nonstoichiometric grain boundary, we calculated the electrostatic potential and concentrations of proton and oxygen vacancy using a space charge layer model.

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Yttria stabilized zirconia (YSZ) thin films are deposited on thin Si₃N₄ layer coated Si substrates by RF-sputtering with different substrate temperatures, room temperature (YSZ-RT) and 550°C (YSZ-550). Fine polycrystalline structure is observed for YSZ-RT (thickness = 620 nm), while columnar crystal structure (111) oriented for YSZ-550 (thickness = 660 nm), respectively. The conductivity measurement shows that the activation energies of YSZ-RT and YSZ-550 are 1.34 and 1.58 eV, respectively, indicating that grain boundary conduction is dominant. Shear strengths of the YSZ films are determined by using a micro-blade cutting system to be 150 MPa for YSZ-RT and 200 MPa for TSZ-550, respectively. YSZ-550 is found to be better for solid oxide fuel cell application from mechanical and electrically properties point of view.

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Electrical conduction properties of the aragonite-type LaBO₃-based materials, in which La was substituted partially by Ca, Sr and Ba, were investigated at 500–925°C with conductivity and transport-number measurements. From X-ray diffraction measurements, it was confirmed that a solubility limit of Sr to the La site is between 1 and 2 mol %. When the substitution content exceeded the solubility limit, the conductivities decreased with increasing the concentration. Such a deterioration in the conductivity was considered to be resulted from an impurity-phase formation. Regardless of substitution species, the LaBO₃ exhibited predominant protonic conduction by the partial substitution of the alkaline earth elements for La, and the Sr-substituted sample showed the highest conductivities. The proton transport numbers were estimated as 0.7–0.9 from electromotive forces of water-vapor and oxygen concentration cells.

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Yttria doped barium cerate (BCY) electrolyte, Ni+BCY anode supported cells were fabricated, and their stability and the mechanism of their degradation were investigated through constant current tests under various operating conditions, especially negative cell voltage operation (with respect to degradation phenomenon due to cell imbalance in a series connected stack). The results of electrochemical tests (I–V characteristics and impedance spectra) indicate that the degradation rate was significant when the cell was operated under higher current densities (regardless of the sign of cell voltage) and only the ambient air was used for the cathode. Post-material analyses revealed that microstructural and compositional changes were obvious in the BCY electrolyte and the BCY of the cathode functional layer because of BCY decomposition in the wet atmosphere at the cathode. Thus, the present work concludes that the degradation rate of BCY electrolyte-based cell depends on operating conditions, i.e., the amount of current density (the water vapor production rate at the cathode) and the air flow rate (flushing water vapor at the cathode).

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To investigate the possibility of reducing the thickness of the yttria-stabilized zirconia (YSZ) blocking layer of the gadolinia-doped ceria (GDC) electrolyte of the thin-film solid oxide fuel cell (TF-SOFC), a sandwich electrolyte configuration consisting of GDC/YSZ/GDC tri-layers is constructed. With only a 100 nm-thick YSZ layer, the TF-SOFC yielded high open circuit voltage (OCV) values (1.05 V at 650°C), which indicates that the ultra-thin YSZ layer is deposited without massive defects and functions properly as a reduction blocking layer of the GDC electrolyte. The peak power density reaches approximately 2.1 W cm⁻² at 650°C, which is at the ultimate performance level of the TF-SOFC. In electrochemical impedance spectra (EIS) analyses, an exaggerated low-frequency (LF) impedance at OCV is observed, which is considered to be originated from the chemical capacitance of the bottom GDC layer acting as an anode. In some cases, certain defects at the bottom GDC layer are identified, which are postulated to be caused by the chemical expansion and mechanical frailty of GDC exposed to the reducing atmosphere. Therefore, both the advantage and the disadvantage should be considered for reliably employing the sandwich electrolyte configuration.

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Measurements of a system consisting of cathode/doped ceria diffusion barrier/doped zirconia electrolyte were made using two- and three-electrode configuration. Results obtained on a three-electrode measurement configuration were compared with and reflect the results obtained in two-electrode configuration. Three-electrode measurements allowed separating the impact of the symmetrical interface in the investigated system. They also enabled to obtain additional information about the investigated interface, such as the behavior of the system under an external polarization voltage. It has been shown that the 200 to 1200 nm thick CGO diffusion barrier layer fabricated by spray pyrolysis significantly reduces the polarization resistance of the interface. It also minimizes the impact of the polarization resistance in the presence of external polarization voltage.

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Sinterable lanthanum silicate oxyapatite (LSO) powders were prepared by the combination of solid-state reaction synthesis and particle size control via planetary ball-milling. We successfully fabricated the LSO ceramics with relative densities exceeding 94% at 1773 K even though it was suggested that the densified LSO ceramics could not be obtained below 1923 K using a powder synthesized by a solid-state reaction. Impurity phases resulting from contamination due to the ball and pod during the planetary ball milling were, in some cases, detected by the X-ray diffraction analysis of the sintered ceramics. The planetary ball-milling conditions were deemed important for the successful fabrication of the sinterable LSO powder.

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Li₄Mn_5−xTi_xO₁₂ (x = 0–0.5) powders were successfully prepared by ultrasonic spray pyrolysis. As-prepared Li₄Mn_5−xTi_xO₁₂ powders were calcined from 500 to 700°C. The chemical and physical properties of as-prepared Li₄Mn_5−xTi_xO₁₂ powders and the calcined powders were characterized by XRD, TG-DTA, and SEM. The crystal phases of as-prepared Li₄Mn_5−xTi_xO₁₂ powders crystallized to the spinel structure (Fd-3m) by the calcination at 500°C. As-prepared Li₄Mn_5−xTi_xO₁₂ powders and the calcined powders obtained by spray pyrolysis exhibited spherical morphology with approximately 2 µm. The electrochemical measurement showed that the discharge capacity of the Li₄Mn_5−xTi_xO₁₂ (x = 0) cathodes was 111 mAh/g at the rate of 0.2 C. The discharge capacity of the Li₄Mn_5−xTi_xO₁₂ cathodes increased with the concentration of Ti ion increased. The discharge capacity of the Li₄Mn_5−xTi_xO₁₂ (x = 5) cathodes increased to 171 mAh/g (0.2 C) with increasing up to x = 5. The retention rates of the Li₄Mn_5−xTi_xO₁₂ (x = 0, 2, 3, 5) cathodes discharge capacities were approximately 84, 66, 61, and 98% after 100 cycles at the rate of 1 C, respectively.

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Controlling the substitution sites of Ho³⁺ in BaTiO₃ was demonstrated with a water-soluble precursor method in a relatively high concentration region. Ho³⁺ was added in three different manners to replace either Ba²⁺ or Ti⁴⁺, or both Ba²⁺ and Ti⁴⁺ as Ba_1−xHo_x TiO₃ (A-site substitution), Ba Ti_1−xHo_xO_3−x/2 (B-site substitution) and Ba_1−x/2Ho_x/2 Ti_1−x/2Ho_x/2 O₃ (A/B-sites substitution). The substitution sites were carefully investigated with X-ray diffraction, elemental mapping analysis, X-ray absorption fine structure analysis and the electric properties measurements. The results revealed the difference in the properties such as solubility, local environments around the lanthanides and electric properties depending on the substitution site, which indicated the successful control of the substitution sites simply with the starting composition of the solution. The compositional uniformity of the water-soluble precursor was advantageous in controlling the substitution sites of a rare-earth in BaTiO₃.

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Perhydropolysilazane (PHPS) was chemical modified with alcohol derivative (ROH, R = CH₃, i-C₃H₇, n-C₅H₁₁, n-C₁₀H₂₁) at the silicon (Si) of PHPS/ROH molar ratio of 4/1. The alkoxy group-functionalized PHPS was converted into amorphous silica powders by curing at 270°C to promote oxidative crosslinking, followed by pyrolysis at 600°C in air to complete the polymer/amorphous silica conversion. Thermogravimetric analysis in air of the 270°C-crosslinked PHPS showed an approximately 18% weight gain at 200 to 500°C. This weight gain was suppressed consistently with the number of carbon atoms of the alkoxy groups introduced to PHPS. Upon heating to 600°C, the PHPS modified with n-C₅H₁₁OH showed a total weight loss of 12%, and further weight loss of 31% was observed for the PHPS modified with n-C₁₀H₂₁OH. The nitrogen sorption analysis revealed that micropore volume of the polymer-derived amorphous silica increased consistently with the weight loss during the pyrolysis up to 600°C, and the amorphous silica derived from the PHPS modified with n-C₁₀H₂₁OH exhibited the highest micropore volume. Further increase in the micropore volume was achieved by increasing the Si/n-C₁₀H₂₁OH molar ratio from 4/1 to 2/1. The micropore volume and specific surface area of the resulting amorphous silica powders were 0.193 cm³/g and 370 m²/g, respectively.

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Mg₂Si thin films were successfully fabricated on 125-µm-thick flexible polyimide substrates by radio-frequency (RF) magnetron sputtering deposition using a sintered polycrystalline Mg₂Si target. The crystalline orientation of the films was influenced by the substrate temperature (Ts). The produced films exhibit n-type carriers. The electron concentration and mobility of nondoped Mg₂Si films at Ts = RT were 1.9 × 10¹⁶ cm⁻³ and 1.2 cm²/(V s), respectively. The Seebeck coefficient was −748 µV/K at 336 K, and its absolute value decreased with increasing temperature. The power factor was 3.3 × 10⁻⁷ W/(cm K²) at 710 K, which is approximately one order of magnitude lower than that of the bulk sintered Mg₂Si sample.

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