Page 21 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

2 High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Apjdications

This is almost magical in its elegance and simplicity, and it is astonishing that
this process has not yet been commercialised to supplant the inefficient and
polluting combustion heat engines which currently dominate our civilization.
Largely, this failure has stemmed from a lack of materials knowledge and the
absence of chemical engineering skills necessary to develop electrochemical
technology. Our belief is that this knowledge and expertise is now emerging
rapidly. The purpose of this book is to present this up-to-date knowledge in order
to facilitate the inventions, designs and developments necessary for commercial
applications of solid oxide fuel cells.
An essential aspect of SOFC design and application is the heat produced by the
electrochemical reaction, not shown in Fig. 1.1. As Chapter 3 shows, heat is
inevitably generated in the SOFC by ohmic losses, electrode overpotentials etc.
These losses are present in all designs and cannot be eliminated but must be
integrated into a heat management system. Indeed, the heat is necessary to
maintain the operating temperature of the cells. The benefit of the SOFC over
competing fuel cells is the higher temperature of the exhaust heat which makes
its control and utilization simple and economic.
Because both electricity and heat are desirable and useful products of SOFC
operation, the best applications are those which use both, for example residential
combined heat and power, auxiliary power supplies on vehicles, and stationary
power generation from coal which needs heat for gasification. A residential SOFC
system can use this heat to produce hot water, as currently achieved with simple
heat exchangers. In a vehicle the heat can be used to keep the driver warm. A
stationary power system can use the hot gas output from the SOFC to gasify coal,
or to drive a heat engine such as a Stirling engine or a gas turbine motor.
These ideas, from fundamentals of SOFCs through to applications, are
expanded in the sections below to outline this book’s contents.

1.2 Historical Summary
The development of the ideas mentioned above has taken place over more than a
century. In 1890, it was not yet clear what electrical conduction was. The
electron had not quite been defined. Metals were known to conduct electricity in
accord with Ohm’s law, and aqueous ionic solutions were known to conduct
larger entities called ions. Nernst then made the breakthrough of observing
various types of conduction in stabilised zirconia, that is zirconium oxide doped
with several mole per cent of calcia, magnesia, yttria, etc. Nernst found that
stabilised zirconia was an insulator at room temperature, conducted ions in red
hot conditions, from 600 to 1000°C and then became an electronic and ionic
conductor at white heat, around 1500°C. He patented an incandescent electric
light made from a zirconia filament and sold this invention which he had been
using to illuminate his home [l-31. He praised the simultaneous invention of the
telephone because it enabled him to call his wife to switch on the light device
while he travelled back from the university. The heat-up time was a problem
even then [4].