Flat-tube SOFC

Figure 8.5 Anode-supported flat-tube SOFCs. (From Kim et al., 2003, with permission from Elsevier.)...

A more recent development in high power density large-scale tubular SOFCs is that of flat tubes, which consist of a tube with two flat, parallel sides, and two rounded sides, with cross-connected current paths connecting the two flat faces of the tubes through the interior to minimize the length of the current path, as shown schematically in Figure 6.6 [48],... 

Integrated planar SOFC and flat-tube high-power density designs... 

Fig. 3c. Schematic view of SOFC cell design flat tube type.

The flat tube design (fig. 3c) was proposed to improve the sealing problems in the anode supported planar SOFCs without losing its high performance. The 1 kW SOFC stack of flat-type design was recently demonstrated by Kyocera Co. Japan in 2004. 

Tubular SOFC cathode supports with diameters or distance between flat faces on the order of 1 to 2 cm are commonly prepared by extrusion. Extrusion is a wet-ceramic process used to prepare tubes, and one which facilitates the formation... 

FIGURE 6.6 High power density (HPD) SOFC, consisting of a flattened tube with two flat faces. The vertical struts between the two flat faces provide shorter paths for the electronic current collection, eliminating the need for all of the electronic current to travel around the circumference of the cathode, as in the standard tubular cell design shown in Figure 6.5 [48], Reprinted from [48] with permission from Elsevier. 

The integrated planar (IP) SOFC stack concept, for instance, applied by Rolls-Royce Fuel Cell Systems, uses an array of series-connected cells deposited by screen printing onto a flat support tube, a schematic cross section of which is shown Fig. 21.23. The support tube, an inert, porous ceramic, is fabricated from a magnesia magnesium aluminate spinel (MMA), whereby the desired coefficient of thermal expansion is adjusted by the ratio of the base materials [76]. 

There are two basic designs of SOFC units. In the planar design, components are assembled in flat stacks where the air and hydrogen traditionally flow though the unit via channels built into the anode and cathode. In the tubular design, air is supplied to the inside of an extended solid oxide tube (which is sealed at one end), whilst fuel flows round the outside of the tube. The tube itself forms the cathode, and the cell components are constructed in layers around the tube. 

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