The reduction of nickel---zirconia cermet anodes and the effects on supported thin electrolytes

An important objective in the development of solid oxide fuel cells (SOFC) is to produce thin stabilized zirconia electrolytes that are supported upon the nickel---zirconia cermet anode. Although this will reduce some of the problems associated with SOFCs by permitting lower temperature operation, this design may encounter problems during the cell start-up. The first step in a start-up involves the reduction of nickel oxide in the anode to metallic nickel and the volume change associated with this may damage the supported electrolyte. In this work, the effects of this reduction both on the anode and the supported electrolyte have been investigated. The findings show that the initial reduction does not seem to damage the cell, although an increase in volume with respect to the initial volume upon reoxidation of the anode cracks the electrolyte and will fracture the cell when constrained in an operational environment. The reason for this increase appears to be linked to the sintoring of the nickel while in its reduced state.