Curvature and Strength of Ni-YSZ Solid Oxide Half-Cells After Redox Treatments

Abstract

One of the main drawbacks of anode-supported solid oxide fuel cell technology is the limited capability to withstand reduction and oxidation (“RedOx”) of the Ni phase. This study compares the effect of RedOx cycles on curvature and strength of half-cells, composed of a nickel-yttria-stabilized-zirconia (Ni-YSZ) support, a Ni-YSZ anode, and an 8YSZ electrolyte. Five different treatments are studied: (i) reduction at 600°C, (ii) reduction at 1000°C, (iii) 1RedOx cycle at 750°C, (iv) 5RedOx cycles at 750°C, and (v) 5RedOx cycles at 600°C. The strength is measured by the ball-on-ring method, where it is calculated analytically from the force. In this calculation the thermal stresses are estimated from the curvature of the half-cell. For each treatment, more than 30 samples are tested. About 20 ball-on-ring samples are laser cut from one original 12×12 cm2 half-cell. Curvature and porosity are measured for each sample before and after RedOx treatments. The first observations show that increasing the reduction temperature enhance strength but does not influence the curvature, whereas 1RedOx cycle at 750°C increases the curvature without changing the strength. Consecutive RedOx cycles seem to decrease anode-supported cell strength but this is coupled to lower porosity of the tested samples.