Page 231 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

208 High Temperature Solid Oxide Fuel Cells: Fundamentals. Design and Applications

planar SOFCs must have the stability in oxidising and reducing environments,
chemical compatibility with cell/stack components, and proper sealing and
insulating properties. Examples of glass and glass ceramic sealants being
developed for planar SOFCs are families of modified borosilicate and
aluminosilicate glasses [ 191.

8.22 Cell and Stack Performance
Planar SOFCs of various sizes have been fabricated and operated under various
conditions. Single cells have been shown to have extraordinarily high areal
power densities. For example, power densities of up to 1.8 W/cm2 at 800°C and
0.8 W/cm2 at 650°C have been obtained for anode-supported planar cells with
hydrogen fuel and air oxidant (Figure 8.9) [20].

Figure 8.9 Performance ofanode-supportedcell with hydrogen fuel and air oxidant 1201.

Figure 8.10 shows examples of planar SOFC stacks [6,21-231. Planar stacks
have been operated for thousands of hours, and operation of multi-cell stacks at
multi-ItW power levels has been demonstrated. An example of performance of a
planar SOFC stack is given in Figure 8.11 [24].
The planar cell design offers high power density but currently has a
number of significant issues such as requiring high-temperature gas seals at
the edges of the cell components to isolate oxidant from fuel. Difficulties in
successfully developing such high-temperature seals have slowed the
development and use of planar design cells for SOFC generators. However, SOFC
stacks in 1-2 5 kW size utilising planar cells are now beginning to be designed,
fabricated, and electrically tested. Also, power systems (up to several kilowatt
size) based on planar SOFCs have been assembled and tested, as described in
Chapter 13.