Page 20 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

Chapter 1

Introduction to SOFCs

Subhash C. Singhal and Kevin Kendall

1.1 Background
Solid oxide fuel cells (SOFCs) are the most efficient devices yet invented for
conversion of chemical fuels directly into electrical power. Originally the basic
ideas and materials were proposed by Nernst and his colleagues [l-31 in
Gottingen at the end of the nineteenth century, as described in Chapter 2,
but considerable advances in theory and experiment are still being made over
100 years later.
Figure 1.1 shows an SOFC scheme. It contains a solid oxide electrolyte made
from a ceramic such as yttria-stabilised zirconia (YSZ) which acts as a conductor
of oxide ions at temperatures from 600 to 1000°C. This ceramic material allows
oxygen atoms to be reduced on its porous cathode surface by electrons, thus
being converted into oxide ions, which are then transported through the ceramic
body to a fuel-rich porous anode zone where the oxide ions can react, say with
hydrogen, giving up electrons to an external circuit as shown in Figure 1.1. Only
five components are needed to put such a cell together: electrolyte, anode,
cathode and two interconnect wires.

Fuel (e g hydrogen) Oxygen
Solid oxide
Porous anode \ /Porous cathode
electrolyte
fuel oxidation Oxysen reduction
HI + 0.- - 2 e+H10 0+2e + 0.-
A

Electrons to external circuit Electrons from external circuit
Figure 1.1 Schematicofsolidoxide fuel cell (SOFC).