Page 284 - High Temperature Solid Oxide Fuel Cells Fundamentals, Design and Applications

Chapter IO

Testing of Electrodes, Cells and

Short Stacks

Mogens Mogensen and Peter Vang Hendri ksen

10.1 Introduction
This chapter describes electrochemical testing of individual electrodes and cells
and gives a brief discussion of stack testing. It is extremely important in testing
solid oxide fuel cells (SOFCs) to have a good understanding of the fundamental
principles of electrochemistry; to this end, classical textbooks [ 1-31, which are
based on liquid electrochemistry, are certainly helpful, but it is also extremely
important to be familiar with different aspects of solid-state electrochemistry,
especially those involving solid oxide electrolytes 14-12].
Testing of cells and stacks is conducted for two reasons; to assess their
commercial viability and for continued cell development. The information
required for these two purposes is usually different, and an interpretation of the
data, taking into account the effects of the test conditions, has to be done for
comparison of SOFCs from different sources. Despite the fact that many cell test
data have been reported [13-191, no general agreement on test procedures exists
and the actual test equipment is often not described in detail. Also the concept of
area-specific resistance (ASR) is not standardised when reporting the test results.
Although parameters such as temperature, inlet gas composition, fuel utilisation
and current density are normally given, substantial additional information is
required for complete evaluation of test data and detailed analysis of cell
behaviour. Four particular issues that are considered in this chapter are:
definition of area specific resistance (ASR), accuracy of temperature
measurement at the cell, the effects of gas leakage through the seals, and the use
of reference electrodes.
If a stack is to be tested as a commercial product, the test is usually performed
in a complete system with balance-of-the-plant components added and the stack
integrated into the system to the maximum possible extent. Such tests of
complete SOFC systems are both expensive and complex, and it is difficult to