Design and Fabrication of a 600W Anode Supported Flat Tubular SOFC Stack

Keywords: SOFC stack, flat tube, metallic support, Ag-Cu air braze,

  Introduction

Recently, great interests are focused on Solid Oxide Fuel Cells for future energy economy. In order to reduce the cost and increase the lifetime of SOFCs, lowering the working temperature is necessary. To meet the demands, new stack structures and materials are developed. Among them, flat tubular stacks are shown to be promising for their performance and fabrication techniques, and also metallic materials are applied as interconnect and support for their characteristics [1].    

In this work, we design and fabricate a 600W anode supported flat tubular SOFC stack. The stack is composed of 36 flat tubular cassettes made by FeCrAl alloy. Cells composed of NiO-YSZ (anode)/ YSZ (electrolyte)/LSM-YSZ (cathode) are sealed on cassettes by Ag-Cu air braze. Experimental

The schematic diagram of stack structure is shown in Fig 1. A short stack is composed of several metallic cassettes made by FeCrAl (a commercial product: 1Cr21Al4). Five frames are located on the surface of the cassette, on which cells are sealed on the anode side by Ag-Cu air brazing. Ag-Cu brazes also serve as the electrical connect to the anode. FeCrAl interconnects with Ag mesh serve as the electrical connect to the cathode. Ag wires connect th e Ag-Cu braze with interconnects. Fuel inlet pipe is located at one end of the cassette and outlet is on the other end. Pipes are sealed by Ag rings with ceramic tubes. Fuel flows along the pipes and the ceramic tubes.      

Cells of 5x5cm² are produced as described in previous results [2]. Anode substrates of NiO-YSZ are produced by conventional tape casting and sintering methods. YSZ electrolytes of 15 um are produced by spray and cathodes of 4x4cm² LSM/YSZ are produced by screen printing.

Results and Discussion

   Stack of 36 cassettes are produced and tested. Humidified H₂(2-3% H2O) is applied as the fuel and air as the oxidant. A mean open circuit voltage of 1.03V per cassette is obtained under working temperature 750 centigrade. The stack has been tested for 1000 hours. Ag-Cu braze and FeCrAl show good stability and reliability.

  Fig.2 shows the performance of the 36-cassette stack under different fuel flow. When 15slm H2 is supplied to the stack, a maximum output of 614W and an average power density of 213mw/cm²are obtained. The fuel utilization efficiency is 51%.

Conclusions

  An anode supported flat tubular stack is designed and produced. Stack of 36 cassettes are produced and tested with humidified H₂ as fuel. An average power density of 213mw/cm²is obtained, higher than those reported results of the stacks [1].

References

[1] Ludger Blum etc, Int. J. Appl. Ceram. Technol., 2 [6] 482–492 (2005).

[2] Lei Zhang etc, Journal of Alloys and Compounds 586 (2014) 10–15