Page 221 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

198 High Tenrprr~turr Solid Oxide Fwl Cells: Fundamentals, Design and Applications

FUEL
I NTE RC ON N E CT
ANODE
ELECTROLYTE
CATHODE

OXIDANT

Figure 8. I Planar SOFC design.

components of a planar SOFC. Advances in ceramic technology, especially in
synthesising fine powders, engineering material compositions, tailoring
composition/property/microstructure relationships, and fabricating/processing
intricate structures, have contributed to the increased interest in planar SOFCs
since early 1980s. Significant progress has now been made on the
demonstration of fabricability, performance, and operation of planar SOFCs.
A planar SOFC, like any other cell configuration, must be designed to have
the desired electrical and electrochemical performance, along with required
thermal management and mechanical/structural integrity to meet operating
requirements of specified power generation applications [3]. The key
requirements are discussed below: this discussion is qualitative because the
specific requirements depend on selected designs and intended applications.

6) Electrical performance. This requirement means that the design must
minimise ohmic losses in the stack. Thus, the current path in the
components (especially those having low electrical conductivity) must be
designed to be as short as possible. There must be good electrical contact
and sufficient contact area between the components. The current
collector must also be designed to facilitate current distribution and flow
in the stack.
(ii) Electrochemical performance. This requirement means that the design
must provide for full open circuit voltages and minimal polarisation
losses. Thus, any significant gas leakage or cross-leakage and electrical
short must be avoided. Fuel and oxidant must be distributed uniformly
not only across the area of each cell but also to each cell of the stack. The
gases must be able to quickly reach the reaction sites to reduce mass
transport limitation.
(iii) Thermal management. This requirement means that the design must
provide means for stack cooling and more uniform temperature
distribution during operation. The design must permit the highest
possible temperature gradient across the stack.