Page 64 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

42 High Temperature Solid Oxide Fuel CeIls: Fundamentals, Design and Applications

A significant step forward was made by Isenberg in 1970 with the
development of the electrochemical vapour deposition (EVD) method [12 71.
Then in 19 78, Westinghouse started a new programme, in which EVD method
was used for the perfect closing of the pores in the electrolyte and the
interconnecting layers. A new cell design was instrumental in the breakthrough;
long tubular cells (inside air, outside fuel), electrically interconnected by oxide
materials and ductile metallic conductors, were combined together in tube
bundles (Figure 2.13 [132]). This design led to the first 5 IrW SOFC generator
containing 324 cells (in 1986) [133] and to the 1152-cell 100 kW SOFC
power system which began operation near Arnhem in the Netherlands in
January 1998 [134].
Tubular cells are more stable against mechanical and thermal stresses than
planar cells. But modern technologies (tape casting, screen printing, vapour
deposition. plasma spraying, wet spraying and others) promise lower cost for the
fabrication of planar cells. Therefore in the 1980s and 199Os, an increasing
number of SOFC developments focused on planar designs [13 51. In 1983 co-fired
monolithic stacks of flat cells were fabricated and investigated at the Argonne
National Laboratory [ 13 61. Soon many possibilities were seen for the fabrication
and arrangement of planar cells (Figure 2.14). In 2000, a 25 kW system with
3840 planar electrolyte-supported cells (11 x 9 cm2) and with internal
reforming anodes was fabricated for operation on natural gas by Ceramic Fuel
Cells Ltd in Australia [137]. Many current developments are concentrated on
anode-supported planar SOFCs.

Positive Current
Collector \ ,\, \ -. .,\.
ickel Felt is the

Fuel Electrode
Figure 2.13 Cross-sections of Westinghouse multi-cell module concept, showing the components of the cells
as wellas series and parallelconnection (1 982).