Shoji Yamashita

Electrically conducting ceramic and fuel cell using the same

The present invention is an electrically conducting ceramic having improved electrical conductivity which comprises a perovskite-type composite oxide of a composition represented by the following formula (La1-x-y Ax By)z (Mn1-u Cu)v O.sub.δ wherein A represents at least one type of atom selected from the group consisting of Sc, Y, Nd, Yb, Er, Gd, Sm and Dy, B represents at least one type of atom selected from the group consisting of Ba, Sr and Ca, and C represents at least one type of atom selected from the group consisting of Co, Fe, Ni, Ce, Zr, Mg, Al, Sb and Cr, and x, y, z, u, v and δ are the numbers that satisfy the following formulas: 0.02≦x≦0.5, 0.1≦y≦0.6, 0.90≦z≦1.05, 0≦u≦0.5, v=1.0, and at a temperature of 1000° C. in the open air, 2.97≦δ≦3.04. A tubular-type fuel cell containing an electroconductive ceramic in accordance with this invention as an air electrode does not deform during operation for long period of time and yields a stabilized output and a planar type fuel cell which is free from peeling of air electrodes or does not decrease its output by the deformation of the cell.

Development of Segmented-in-series Cell-stacks with Flat-tubular Substrates

The SOFC cell-stacks called “flat-tube segmented-in-series cellstacks” have been developed jointly by Tokyo Gas and Kyocera. The cell-stacks were composed of multiple single-cells (8YSZ electrolyte, Ni/8YSZ anode, and LaSrCoFe cathode) and currentcollectors, placed on both sides of the flat-tubular substrate. The fuel to electric power-generation efficiency of the latest cell-stack converted as the methane fuel was estimated to be more than 53% HHV-DC at 1023 K at the current density, 0.2 A/cm 2 . The complex impedance spectra of the cell-stacks were measured under the operating conditions, for investigations of the relation between the performance and components design. By the measurements under several conditions, we identified the relationship between the impedance spectra and the fuel usage dependence and degradation of the segmented-in-series type cell-stack performance. Based on these results, we are continuing further studies of the component design (especially anode), for higher efficiency and long-term durability of the cell-stacks.

Solid Oxide Fuel Cells as Promising Candidates for Distributed Generators

SOFCs have a potential of showing extraordinarily high electric conversion efficiency. Thus they are considered as promising candidates for future distributed generators. However operations of SOFCs are not simple compared with the other generators such as gas engines or gas turbine since SOFCs have to be operated at a high temperature. It is difficult to start up SOFCs rapidly and thus they are not suitable for situations where there is a large fluctuation of demand. This limits the application of SOFCs and the introduction is restricted within a narrow market. In order to promote the introduction of SOFCs to a market, how to make use of SOFCs is a very significant factor. Techniques to operate and control SOFCs are key factors to draw the potential of SOFCs. Therefore information technologies are expected as a powerful tool to improve the total performance of SOFCs.

Development of Segmented-in-Series SOFC Stacks Using Numerical Models and Parametric Study

The voltage loss in a single cell of a segmented-in-series flat-tube-type solid oxide fuel cell (SOFC) stack was evaluated. The stack exhibits a particular configuration, and the current flows along an in-plane direction in the anode and cathode; this differs from conventional planar-type SOFCs. Distributions of the current in the cell were studied in detail for many parameters such as the length of electrodes and conductivities of the cell components. Gas diffusion in a porous substrate and anode and the fuel utilization affect the concentration polarization; thus, they were also considered. By using the simulation results, appropriate configurations for the cell and stack were designed, and the simulation was validated by performance tests for a practical fuel cell stack. The stack exhibited a high performance of 0.76 V at 0.2 A/cm2 at Uf = 81.6% with dry H2 fuel, yielding a DC energy conversion efficiency of 53.6% HHV. Moreover, a bundle comprising 34 stacks was also fabricated, and excellent values of output voltage (342.5 V), output power (338.3 W), and electrical efficiency (49.5% HHV) at a current density of 0.2 A/cm2 were obtained.Copyright