High-Temperature Reactions, Cathode

Introduction

Solid oxide fuel cells (SOFCs), typically based on an oxide ion conducting electrolyte as previously discussed in earlier chapters, have a fundamental requirement for the high-temperature reduction of the oxidizing species. In general this reaction is viewed as the simple oxygen reduction reaction, as summarized in Eq. 1:

$$ {O_{2(g) }}+4{e^{-}}\to 2{O^{2- }} $$

(1)

Despite the apparent simplicity of this reaction, the process by which the oxygen reduction occurs followed by incorporation of the ionic species into the electrolyte is the subject of some debate and is dependent on the mode of operation of the cathode material. Two typical cathode types are currently utilized in SOFCs – electronic conductors and mixed ionic-electronic conductors (MIECs). The cathode reactions, while nominally the same in both types of materials, occur at different locations, and hence, the active region varies, leading to differences in the operating regime and ultimately performance. In the...