Principal Research Results

R&D on All Ceramics SOFC with High Power Density under 1,000℃
Operation
Background
Electric power generation using the solid oxide Fuel cells (SOFC) is believed to be a good candidate for a highly efficientelectric power generation system with effectively utilizing high temperature waste heat, and to be its excellent environmental characteristics additionally. In particular the 1,000℃ operating type SOFC are expected to achieve a simplified system based on the direct
reforming of gaseous fuel.
However, in the view of the hard operating conditions, it is necessary for high temperature SOFC to make up the system entirely with ceramics along with the optimization of the cell and stack structures, materials and manufacturing technologies while ensuring a low cost and achieving high power density and improved durability. The CRIEPI has proposed an anode supported typestructure to allow the 1,000 ℃ operation, that is all ceramics SOFC, and then has confirmed the excellent performance of the prototype
unit cell ＊ 1 using the basic material and membrane forming technique (Table 1). To validate the practical use of such unit cells, it isstill necessary to advance the electricity generation property and availability of the stack using multiple unit cells.

Objectives
To clarify the property and availability for the anode supported SOFC, two prototype all ceramic 3cell stack were prepared,
and then were overhauled and analyzed after the generation tests, in which the unit cells were developed by CRIEPI. The target of theperformance was over 0.5 W/cm2 in power density of the several unit cells, which is one indicator for cost reduction.

Principal Results
1. Stack structure (Table 1)
The all ceramic stack is configured as described below, incorporating the unit cells and connection parts.
① Concerning on the unit cells, a dense electrolyte layer and an interconnector membrane, specially developed by the CRIEPI, areformed on a porous anode substrate (5.0 cm × 5.0 cm) with gas channels which is made of along-life anode material, followed by
the introduction of a cathode (area of approximately 12.0 cm2) layer above the electrolyte layer to prepare the unit cell.
② The connection parts have roles in electrical connections between the unit cells and air channels for the cathode of the several cells.
This parts were prepared by using cathode material and were placed between the unit cells. The end part, where was settled on theend of the stack, was an anode substrate coverd over the entire surface by the interconnector membrane (Fig.1).
2. Electric Generation Properties at 1,000℃ (Tab1e 2, Fig.2 )The stacks were heated up to 1,000 ℃ and were fed with hydrogen gas and air to evaluate the electric generation properties .
① The fact that the open circuit voltage of the unit cell is practically identical to the theoretical value means that there is hardly any
cross leakage ＊ 2 of the gas fed to the unit cell, indicating a satisfactory gas sealing performance.
② At a unit cell voltage of 0.7 V, a power density exceeding the development target of 0.5 W/cm2 is obtained. The level of property
is maintained even after continuous generating operation for 150 hours.
3. Overhaul-Analysis of the Stack after Test
Any removement of the electrolyte layer and interconnector membranes formed on the anode substrate and/or any damage tothe unit cell are not observed hardly. The absence of decomposition of any part or reaction product between the any parts shows theavailability of the tested stack.
Results of the stack tests, the anode supported type SOFC using the unique technology developed by the CRIEPI shows ahigh electric power generation properties at 1,000 ℃ and availability vindicated by the absence of any damage or material degradation
which is a fatal problem for the unit cell to gain practicality, suggesting a positive prospect for its potential use in the future.

Future Developments
Further research will be conducted to remove the connection part from stack, to enlarge the surface area of the unit cell andto improve the gas manifold and output collector structure, all of which are essential for cost reduction, while establishment for the stacking technology is advanced to apply the SOFC for the practical use.
Main Researcher: Hibiki Itoh, Ph. D.,
Research Scientist, Materials Function and Mechanism Creation Sector, Materials Science Research Laboratory
Reference
Hibiki Itoh, Kenji Yasumoto, Tohru Yamamoto and Yasuo Takada, 2004, “Research and Development on Anode-Supported TypeSOFC Stack - Preparation and Investigation of the Electricity Generation Characteristics for 3 Cell Stacks with High Power Density inAll Ceramics Under 1,000 ℃ Operation”, CRIEPI Report W03039 (in Japanese)＊1：Single cell which is the unit of a stack: a stack is completed when multiple unit cells are connected.
＊2：Gas leakage at dense membrane (electrolyte and interconnector) formed on the unit cell.
When cross leakage occurs, the open circuit voltage fails to show the theoretical value.

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6. Fossil Fuel Power Generation - Improving the efficiency of thermal power generation

Table 1 Parts of Prototype Anode Supported Type SOFC StackUnit CellPartAnode (Porous Substrate)

Com poison/Material
Ni-YSZ cermet (developed by the 5 cm square sintered anode substrate with gas channels
CRIEPI)Electrolyte (Dense layer) YSZ powder (market product)
Formed on the anode substrate using the slurry coating method
Cathode (Porous Membrane) (La, Sr) MnO3 (developed by the Formed on the electrolyte membrane using the slurring coating method
CRIEPI)＊
lnterconnector(Dense Membrane)

Lanthanumchromite + Intermediate Intermediate membrane and lanthanumchromite formed on the anodeLayer (developed by the CRIEPI) substrate in that order using the slurry coating method

Connection Part (Porous Substrate) (La, Sr) MnO3 (developed by theCRIEPI)

5 cm square sintered anode with gas channels

End Part (Porous Substrate)

Ni-YSZ cermet (developed by theCRIEPI) + Interconnector membrane(developed by the CRIEPI)Interconnector membrane formed on the 5 cm square YSZ supported
type sintered material with gas channels

Sealing and Manifold Part

Glass ceramics

Gas channels added to the market productNote: Although a cathode material with a better performance in terms of the voltage loss and stability under a high current density has been developed, the previous cathodewithout such improvements is used for the present research.

Power Generating Part

Electrolyte

Fuel Gas

Unit Cell

Interconnector
Porous Anode Substrate

空気Air
Unit Cell

CathodeConnection PartConnection Part/(Porous Cathode Substrate)

Electrolyte

End Part

Interconnector
Porous Anode Substrate

End Part

Sealing/Manifold Part(a) Conceptual Structure of Prototype Stack(b) External Appearance of Prototype Stack

Fig.1 Structure and External Appearance of Prototype Stack
The gaseous fuel and air are supplied as parallel flows from the lower end of the stack to the upper end, and the generated
electricity is collected by pressing metal felt on the interconnector and end part of the unit cell placed at the end.

Table 2 Results of Electric Generation Tests
H2 (35℃ humidified) H2 (20℃ humidified)+ N2 (0.5 L/min)= 0.75 L/min)=2.0 L/min

Oxidizing Gas

Air= 4.0 L/min

Air = 1.5 L/min

Open Circuit Voltage

3.05 V3.33 V

Maximum Output(Power Density)

23.5 W(1.3 Vx 17.5 A)(0.64 W/cm2)

18.0 W(1.9 Vx 9.5 A)(0.52 W/cm2)

Output at 0.7 V(Power Density)

18.4 W(2.2 V x 8.7 A)(0.52 W/cm2)

17.5 W(2.1 V x 8.3 A)(0.50 W/cm2)

1.0

0.8
NEDOTarget
NEDO目標値（0.7V×0.2A/cmA/cm22））（0.7 V×0.2
0.6

0.8
0.6

0.4

0.4
No.1
StackStack
１号ｽﾀｯｸ No.2
２号ｽﾀｯｸ

0Note: The power densities in this table are the converted value to the unit cell
(output/3 cells/surface area of cathode).

0.2

j -– Vj -– P

0.2

0.3

0.6
0.9
1.2
Current Density: j（A/cm2）

Power Density: P（W/cm2）

Fuel Gas1.2No.2 Stack
Cell Voltage: V（V）

No.1 Stack

01.5Fig.2 Results of Electric Generation Tests

The power generation test using two prototype stacks was conducted for the present research to evaluate the availabilityof the unit cell and the stacks. The differences in the electric generation properties between the No.1 stack and No.2 one
are caused by the different flow rates of the supplied gases.

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