FY 2000

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Flat-type solid oxide fuel cell (SOFC) attains world-best output of 15 kW

September 11, 2000

In a joint effort with Mitsubishi Heavy Industries (5-1, Marunouchi 2-chome, Chiyoda-ku, Tokyo; President Takashi Nishioka), we recently attained a world-best output of 15 kW for a flat-type solid oxide fuel cell (SOFC*1). Cell output has been continuous for over 1,000 hours.
In 1996, we achieved a then-world record of 5.1 kW using our own mono-block layer-built (MOLB*2) SOFC.

Improvements to cell structure in subsequent years enhanced power density and durability, and in 1998 we produced a world-best power density of 0.35 W/cm². Based on this technology, we made further improvements to cell power through this July, when we commenced a power generation test which ultimately led to the 15 kW output for a flat-type*3 cell. The cell has been operating to date for more than 1,000 hours with no decline in performance.

We now plan to continue cell operations and conduct further performance assessments over time.
These test results mark a great leap toward our planned commercialization of the SOFC as a battery for the electricity industry.
We are committed to continuing efforts to develop a larger version of the cell, and also plan to conduct feasibility studies on smaller distributed systems.

Features of the MOLB-type SOFC

1. (1) Power density of 0.35 W/cm², or about twice that of other SOFC types (0.15 to 0.2 W/cm²), permitting plant downsizing at a later date.
2. (2) Produced using continuous baking, which enables mass production at lower cost.
   
   • *1 SOFC: Solid Oxide Fuel Cell
   • *2 MOLB: Mono-block Layer Built
   • *3 Flat type: SOFC systems are available in two shapes: flat and cylindrical.

[Outline of research]

1. 1. Research background
   New energies such as solar power, wind power and fuel cells are drawing keen attention for their eco-friendly characteristics. Expectations for fuel cells are particularly high, with these cells now seen as a potential fourth major source of power, alongside hydro, thermal and nuclear, due to their superior generating efficiency.
   Among fuel cells, SOFCs can employ natural gas, LPG, methanol or coal gas as a power source.
   When run at 1,000°C, the SOFC can attain a generation efficiency of 65%, surpassing the 50% achieved by LNG compound-power generation, due to its ability to be used in combination with gas turbines using high-temperature gas exhaust.
   There are two types of SOFCs: flat types and cylinder types. In terms of our future electricity business, we are particularly interested in flat-type SOFCs, which will be less costly and allow downsizing. We have been studying this type of SOFC since fiscal 1990.


2. 2. Outline of development
   To create a practical, MOLB-type SOFC, we endeavored to improve gas-sealing capacity and strengthen structural components of a cell. We succeeded in enhancing cell durability and reliability substantially, by making the following improvements:

   [Improvements in MOLB-type SOFCs]

   1. (1) Instead of employing glass (the conventional choice) as a sealing material, we used high-density ceramics, thus improving durability and reliability.
   2. (2) A corrugated-shaped electrolyte was used between electrodes to enhance mechanical strength and power density, while at the same time downsizing the cell.
   3. (3) Thickness of the connection plate between cells was reduced from 2mm to 1mm, thus reducing electrical resistance.
   4. (4) Cells were composed of unit blocks to improve reliability and allow future mass production.
   The figure below shows the cell used in our test. The black section in the center is the cell. White sections on both side of the cell are manifolds (gas distribution chambers), through which gas circulates.


3. 3. Results of development
   On July 25, we began a power-generation test using an MOLB-type cell incorporated into a generator using an improved city gas.
   During the test, maximum power of 15 kW was attained. After more than 1,000 hours of generation, the cell has showed no signs of degeneration. This test marks a major leap toward near-term creation of an SOFC for the electricity business. Test operations to assess the SOFC's performance will continue.


4. 4. Others
   The details of our study will be presented at the 2000 Fuel Cell Seminar, scheduled to run from October 30 to November 2.

(For reference)
Types of fuel cells