Takaaki Shibayama

Intermediate Temperature Solid Oxide Fuel Cells Using a New LaGaO3 Based Oxide Ion Conductor I. Doped as a New Cathode Material

‐based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this study, the stability of ‐based oxide was investigated. The ‐based oxide was found to be very stable in reducing, oxidizing, and atmospheres. Solid oxide fuel cells (SOFCs) using ‐based perovskite‐type oxide as the electrolyte were studied for use in intermediate‐temperature SOFCs. The power‐generation characteristics of cells were strongly affected by the electrodes. Both Ni and (Ln:rare earth) were suitable for use as anode and cathode, respectively. Rare‐earth cations in the Ln site of the Co‐based perovskite cathode also had a significant effect on the power‐generation characteristics. In particular, a high power density could be attained in the temperature range 973–1273 K by using a doped for the cathode. Among the examined alkaline earth cations, Sr‐doped exhibits the smallest cathodic overpotential resulting in the highest power density. The electrical conductivity of increased with increasing Sr doped into the Sm site and attained a maximum at . The cathodic overpotential and internal resistance of the cell exhibited almost the opposite dependence on the amount of doped Sr. Consequently, the power density of the cell was a maximum when was used as the cathode. For this cell, the maximum power density was as high as 0.58 W/cm2 at 1073 K, even though a 0.5 mm thick electrolyte was used. This study revealed that a ‐based oxide for electrolyte and a ‐based oxide for the cathode are promising components for SOFCs operating at intermediate temperature.

Intermediate Temperature Solid Oxide Fuel Cells Using LaGaO3 Electrolyte II. Improvement of Oxide Ion Conductivity and Power Density by Doping Fe for Ga Site of LaGaO3

Effects of small amounts of Fe doping for Ga site in LaGaO 3 -based oxide on oxide ion conductivity is investigated in this study. It is found that doping a small amount of Fe is effective for improving the oxide ion conductivity in La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3 (LSGM). The highest oxide ion conductivity was exhibited at x = 0.03 in La 0.8 Sr 0.2 Ga 0.8 Mg 0.2-x Fe x O 3 among the Fe-doped samples. Electron spin resonance (ESR) measurements suggest that Fe is trivalent in LaGaO 3 lattice. The application of the Fe-doped LaGaO 3 -based oxide for the electrolyte of solid oxide fuel cell was further investigated. Power density of the solid oxide fuel cell was increased by using Fe-doped LSGM for electrolyte. This can be explained by the decrease in electrical resistance loss by improving the oxide ion conductivity. A maximum power density close to 700 mW/cm 2 was obtained at 1073 K on the cell using 0.5 mm thick La 0.8 Sr 0.2 Ga 0.8 Mg 0-17 Fe 0.03 O 3 (LSGMF) and O 2 as the electrolyte and the oxidant, respectively. Therefore, close to the theoretical open-circuit potential was exhibited by the LSGMF cell. On the other hand, the power density was slightly smaller than that of the cell using Co-doped LSGM as electrolyte, especially, at temperatures lower than 973 K. This may result from the large activation energy for ion conductivity. However, the power density of the LSGMF cell was higher than that of the LSGM cell. Therefore, LSGM doped with a small amount of Fe is a promising electrolyte similar to Co-doped LSGM for the intermediate solid oxide fuel cell.

Nickel-Gd-doped CeO2 cermet anode for intermediate temperature operating solid oxide fuel cells using LaGaO3-based perovskite electrolyte

Abstract Ni–CeO 2 doped with 20 mol.% Gd 3+ (GDC) cermet was investigated as the anode of an intermediate temperature operating solid oxide fuel cell using LaGaO 3 -based oxide electrolyte. It was found that the anodic overpotential decreased by mixing Ni with mixed electronic-ionic conductor, in particular, mixing with doped CeO 2 is the most effective for decreasing the overpotential of the anode. Anodic overpotential became a minimum at 10 vol.% GDC to NiO. Using Ni–GDC cermet is also effective for improving the stability of the power density at the constant current output. Impedance analysis suggests that the improvement of anodic activity by mixing Ni with GDC was brought about by decreasing the diffusion overpotential, which was a result of the enlarged effective electrode area.

Oxide ion conductivity in La0.8Sr0.2Ga0.8Mg0.2−XNiXO3 perovskite oxide and application for the electrolyte of solid oxide fuel cells

Although hole conduction was present, it was found that doping with Ni was effective in improving the oxide ion conductivity in La0.8Sr0.2Ga0.8Mg0.2O3 based perovskite oxides. Considering the ionic transport number and the electrical conductivity, the optimized composition for Ni doped samples was La0.8Sr0.2Ga0.8Mg0.13Ni0.07O3 (LSGMN). In this composition, electrical conductivity was found to be virtually independent of the oxygen partial pressure from 1 to 10−21 atm. Consequently, the oxide ion conductivity was still dominant in this optimized composition. In agreement with the improved oxide ionic conductivity, the power density of the solid oxide fuel cell using LaGaO3 as an electrolyte increased by doping with a small amount of Ni on the Ga site. In particular, the power density of 224 mW/cm2 at 873 K, which is the maximum power density in the cells using LaGaO3 based oxide as the electrolyte, was attained using LSGMN in spite of the use of electrolyte plates with a thickness of 0.5 mm. Therefore, LSGMN is highly attractive for the electrolyte material of low temperature operating SOFCs.

An intermediate temperature solid oxide fuel cell utilizing superior oxide ion conducting electrolyte, doubly doped LaGaO3 perovskite

LaGaO3-based perovskite oxide doped with Sr and Mg exhibits high ionic conduction over a wide oxygen partial pressure. In this study, the stability of the LaGaO3 based oxide was investigated. It became clear that LaGaO3 based oxide is very stable for reduction and oxidation. SOFCs utilizing LaGaO3-based perovskite type oxide for electrolyte were further studied for the decreased temperature solid oxide fuel cells. The power generation characteristics of cells were strongly affected by the electrode, both anode and cathode. It became clear that Ni and LnCoO3 (Ln: rare earth) are suitable for anode and cathode, respectively. Rare earth cations in the Ln-site of Co-based perovskite cathode also have a great effect on the power generation characteristics. In particular, high power density could be attained in the temperature range from 973 to 1273 K by using doped SmCoO3 for the cathode. The electrical conductivity of SmCoO3 increases with increasing Sr amount doped for the Sm site and attained the maximum at Sm0.5Sr0.5CoO3. The cathodic overpotential and the internal cell resistance exhibit almost opposite dependence on the amount of doped Sr. Consequently, the power density of the cell reaches a maximum when Sm0.5Sr0.5CoO3 is used for cathode. On this cell, the maximum power density is as high as 0.58 W/cm2 at 1073 K, although a 0.5 mm thick electrolyte is used. Therefore, this study reveals that the LaGaO3 based oxide for electrolyte and the SmCoO3 based oxide for cathode are promising for solid oxide fuel cells at intermediate temperature.

Novel fast oxide ion conductor and application for the electrolyte of solid oxide fuel cell

Abstract Effects of Co doping to Ga sites of a LaGaO 3 based oxide on the oxide ion conductivity was investigated. Oxide ion conductivity increased by doping with Co and it was found that usage of a LaGaO 3 -based perovskite type oxide, doped with Sr for the A site and Co and Mg for the B site (La 0.8 Sr 0.2 Ga 0.8 Mg 0.115 Co 0.085 O 3 denoted as LSGMC), for the electrolyte of the fuel cell gave a notably large power density at an intermediate temperature of 873 K on a cell using H 2 and O 2 as fuel and oxidant, respectively. The power density increased as the thickness of the electrolyte was decreased. The maximum power density was attained at values of 1.4 and 0.5 W/cm 2 at 1073 and 873 K, respectively, when 0.18 mm thick LSGMC was used for the electrolyte. Electrical conductivity in the LSGMC was also estimated using polarization methods. Electrical conductivity was also increased by doping with Co, resulting in an increased amount of chemically leaked oxygen. Consequently, the theoretical calculation demonstrated that the highest energy conversion efficiency would be achieved when the thickness of the LSGMC electrolyte was 100 μm.

Solid oxide fuel cell using Co doped La(Sr)Ga(Mg)O3 perovskite oxide with notably high power density at intermediate temperature

Power generation characteristics of fuel cells was greatly improved by using La0.8Sr0.2Ga0.8Mg0.115Co0.085O3 as electrolyte. In particular, the maximum power density attained a value of 1.53 and 0.50 W cm–2 at 1073 and 873 K, respectively, in an H2–O2 cell when the thickness of electrolyte was 0.18 mm.