Kenji Yasumoto

Pt-perovskite cermet cathode for reduced-temperature SOFCs

In order to develop a cathode for reduced-temperature solid oxide fuel cells, cermetting effect of LSCF with Pt was investigated. The effect of cermetting was observed. However, the obtained cathode activity was only an order of 0.5 S/cm2 at 973 K. The activation energy at low and high LSCF/Pt ratios was smaller than that at medium LSCF/Pt ratio region. The cathode interfacial conductivity, σE, of the very low Pt containing LSCF cermet cathode increased with increasing cathode thickness, whereas with high Pt content, σE showed optimum. These results suggested that Pt has both enhancing and obstructing functions. Based on SEM observation, the main reason of these complicated results was considered to be due to poor porosity and narrow surface area due to high electrode sintering temperature. Pt may enhance sintering of LSCF. So reduced-temperature cathode sintering should be investigated for LSCF/Pt cathode preparation.

The oxygen transport in Gd-doped ceria

Abstract The chemical diffusion coefficient in Ce0.8Gd0.2O1.9−δ was estimated by analyzing the weight relaxation behavior after an abrupt change of the oxygen partial pressure. The weight relaxation data were analyzed by fitting the data to solutions of Ficks second law for appropriate boundary conditions. The diffusion equation, which ignores the effect of surface reaction, failed to describe the transient behavior especially for the first stage. Taking the surface effect into account, the fitting gave a satisfactory interpretation of the overall relaxation process and allowed a precise determination of the chemical diffusion coefficient and surface reaction rate constant. The chemical diffusion coefficient was found to decrease with the decrease of the oxygen partial pressure, while the surface reaction rate constant increased with the decrease of the oxygen partial pressure. The increase of the surface reaction rate constant may be related to the increase of the oxygen nonstoichiometry, implying that the oxygen vacancies play an important role in the surface reaction kinetics. The ionic mobility was estimated from the obtained chemical diffusion coefficients, with the help of oxygen nonstoichiometry and electrical conductivity data obtained before.

An (La,Sr)(Co,Cu)O3−δ cathode for reduced temperature SOFCs

Abstract The oxygen nonstoichiometry of (La,Sr)(Co,Cu)O 3− δ (LSCC) was measured thermogravimetrically. It was found that LSCC has no oxygen excess region. Its behavior is similar to (La,Sr)FeO 3− δ (LSF) but not to (La,Sr)MnO 3± δ (LSM). The electrical conductivity decreases as compared to (La,Sr)CoO 3− δ (LSC). However, it was expected that the ionic conductivity in LSCC would increase, as is suggested from electrical conductivity measurement and oxygen nonstoichiometry measurements. High temperature XRD analysis showed the elimination of phase transformations by addition of Cu yet with no reduction in the thermal expansion coefficient. The cathode activity of LSCC, the electrode interfacial conductivity, σ E , was 15.32 S cm −2 in air at 1073 K. The electrode activity of LSCC is better than that of LSC, although the electrical conductivity of LSCC is lower.

Effect of Oxygen Nonstoichiometry on a La1 − x A x MnO3 + δ Cathode under a Polarized State

Lanthanum manganite, the air electrode material of solid oxide fuel cells, is well known for its complicated nonstoichiometry, which depends upon oxygen partial pressure and temperature. This nonstoichiometry has a relationship with electrode reactivity or the exchange current density because it affects the oxygen activation step. The electrode reactivity is usually studied in terms of its exchange current density, in other words, under a nonpolarized (equilibrium) state. This paper aims to elucidate the effect of oxygen nonstoichiometry on cathode reactivity under polarized states. The complex impedance was measured on an Ar-O 2 /porous La 0.9 Sr 0.1 MnO 3+δ /yttria-stabilized zirconia electrode under steady-state polarization in the oxygen partial pressure range of 10 2 -10 5 Pa and a temperature range of 873-1273 K. The results suggest that oxygen nonstoichiometry affects the cathode reactivity both under polarized and nonpolarized states through the exchange current density.