Masamichi Ippommatsu

Kinetic studies of the reaction at the nickel pattern electrode on YSZ in H2H2O atmospheres

In order to elucidate the reaction mechanism at the anode of solid oxide fuel cells (SOFC) in H2ue5f8H2O atmospheres, instead of conventional nickel-zirconia cermet anodes, we employed nickel stripe patten electrodes prepared on the surface of 8m/o Y2O3- doped ZrO2 (YSZ), which have well-defined length and morphology of the gas/nickel/YSZ triplet phase boundary (TPB). On the surface of single crystalline YSZ-plates, compact nickel layer was prepared by ICB (ionized cluster beam) method. By photolithography, the stripe patterns of alternative nickel and YSZ lines were prepared. Electrochemical measurements were made on the electrode impedence and steady-state polarization current using a terminal method in the H2ue5f8H2Oue5f8Ar gas mixtures with hydrogen partial pressure, PH2 = 102−104 Pa and water vapor pressure, pH20=3×10su2−2×103 Pa at 700°C. It was shown that the rate of electrode reaction at 700°C can be approximately expressed by I=kPH2aO−k′PH2O12aO−12 (k, k′: rate constant), where aO is the oxygen activity at the TPB which is related to the electrode potential E versus 1.013×105 Pa O2 (g) by RTO=2EF. The rate of anodic reaction was found to be essentially determined by the reaction of H2(g) and the adsorbed oxygen on the nickel surface, while the rate of cathodic reaction seems to be determined by the first order reaction or surface diffusion process of adsorbed hydrogen, Had, which may take place after the reaction of H2O(g)→H2Oad→Had+OHad.

Study on the sensing mechanism of tin oxide flammable gas sensors using the Hall effect

Measurements were made on the Hall effect of SnO2 thin‐film inflammable gas sensors prepared by using the reactive sputtering method. The results revealed that when the electrical conductivity of the sensors changed with a change in the flammable gas concentration in air, the apparent carrier density changed significantly while apparent mobility hardly changed at all. However, detailed analysis revealed that these experimental results could not be explained by using the double Schottky model or the neck model that had been proposed. In order to provide satisfactory explanation of the experimental results, the authors clarified that for SnO2 thin films there exists no distinction between bulk and surface of the grain while the carrier densities of bulk and surface of the grain simultaneously change with a change in oxygen absorption of the SnO2 surface in the presence of flammable gas. This model was in good agreement with the results of transmission electron microscopy observations.

Sensing mechanism of SnO2 gas sensors

Studies have been made of the gas sensing properties of both steady and unsteady state SnO2 thin film gas sensors in contact with CH4 and H2 in air from 400 to 500° C. The results suggest a new sensing mechanism model for SnO2 semiconductor flammable gas sensors. This model is based on the following points: (i) Sensor conductivity is determined by the concentration of carrier electrons. (ii) Carrier concentration is controlled by surface unsaturated oxygen adsorption site concentration which is decided by the balance between oxygen adsorption and the surface reaction between oxygen adsorbate and flammable gases. (iii) The activation energy of the reaction is changed by the Fermi energy change for any change in sensor conductivity. This model explains all experimental results.

Fabrication of high power density tabular type solid oxide fuel cells

Abstract Tubular-type solid oxide fuel cell (SOFC) with interconnector has been successfully fabricated, with a maximum single cell power density of 0.9 W/cm2, the highest value reported so far. A self supporting La(Sr)MnOx tube was used for the cathode. The La(Sr)CrOx interconnector was made using the laser oblation method. The yttria-stabilized zirconia (YSZ) electrolyte and Ru/YSZ cermet anode were fabricated by the electrochemical vapor deposition (EVD) process.

Dynamic Properties of SnO2 Semiconductor Gas Sensors Sensing of Hydrogen Contained in Air

The dynamic properties of SnO 2 semiconductor gas sensors were studied by measuring the transient response conductivity after rapid changes in the concentration of H 2 in air at 773 K using pulse reaction technique. The sensor used was a thin film SnO 2 semiconductor without other additives, which was produced by reactive sputtering process. Transient response conductivity after a rapid change from pure air to H 2 in air was measured

High-power-density-solid-oxide-electrolyte fuel cells

This paper reports that, the authors succeeded in fabricating a solid-oxide-electrolyte fuel cell, with the highest power-generation density, with a maximum single-cell-level density of 1550 mW/cm{sup 2}. This cell was made by depositing a 10{mu}m thick 10 mol% (m/o) yttria stabilized zirconia (YSZ) electrolyte layer on a porous La(Sr)MnO{sub x} cathode tube using the electrochemical vapor deposition method and then making a Ru/YSZ cermet anode on top of it.

Study of La1−xMnO3−δ non-stoichiometry and defect structure using ESR and iodometry

The oxidation states of manganese in the La1−xMnO3−δ (x = 0.09–0.11) were investigated by electron spin resonance (ESR) and iodometry. The ESR analysis carried out at room temperature for the samples prepared in air revealed the presence of broad peaks at g = 2.0, considered to be relevant to Mn2+. It was also found that the intensity of the peak increased as lanthanum vacancy content increased. The average valence state of manganese, determined by iodometry, was approximately 3.2, and decreased by 1 as the lanthanum vacancy increased by 1. Similar trends were observed with the samples prepared at Po2 = 1×10−7. The results indicated that Mn2+ is stably present in the La1−xMnO3−δ having an average valence number exceeding 3.0. A series of experimental results with respect to the non-stoichiometry of La1−xMnO3−δ can be explained by assuming that Mn2+ is stabilized after forming a complex with a lanthanum vacancy and two oxygen vacancies.