Page 220 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

Chapter 8

Cell and Stack Designs

Kevin Kendall, Nguyen Q. Minh and Subhash C. Singhal

8.1 Introduction
Over the years, many ingenious designs of solid oxide fuel cells (SOFCs) have
been devised, starting from pressed thimbles and discs in the 1930s. Since the
1960s, most development has focused on planar and tubular design cells and
other geometries have become less popular. This chapter describes the two main
types of SOFCs, the planar and the tubular, emphasising their fabrication
methods and performance characteristics. Each of these two designs has a
number of interesting variants: for example, the planar SOFC may be in the form
of a circular disc fed with fuel from the central axis, or it may be in the form of a
square plate fed from the edges. The tubular SOFCs may be of large diameter
(> 15 mm), or of much smaller diameter ( < 5 mm). Also the tubes may be flat
and joined together to give easily printable surfaces for manufacturing the
electrode layers. Other designs which have fallen out of favour, for example the
corrugated monolithic design [l], are not described here.
Under typical operating conditions, a single cell produces less than 1 V. To
obtain high voltage and power from the SOFCs, it is necessary to stack many cells
together and this can be done in a number of ways using interconnect materials
which are often fabricated into complex shapes to provide for other functions
such as air and fuel channelling and sealing. This chapter describes the various
kinds of stack designs that have been tested by a number of manufacturers in
recent years, and analyses the advantages and disadvantages of the various
schemes. Planar SOFCs and stacks are described first, followed by tubular and
then the microtubular SOFCs.

8.2 Planar SOFC Design

In a planar SOFC, cell components are configured as flat plates which are
connected in electrical series [2, 31. Figure 8.1 shows an example of typical