Properties of screen-printed nickel/scandia-stabilized-zirconia anodes fabricated using rheologically optimized inks during redox cycles

Cyclic reduction and oxidation (redox) of solid oxide fuel cell (SOFC) anodes generally leads to cell degradation and reduces the cell lifetime. The investigation of the sequential cyclic redox of nickel/scandia-stabilized-zirconia (Ni/ScSZ) SOFC anode films presented in this study is aimed at understanding the properties of screen-printed Ni/ScSZ anode films fabricated using a rheologically optimized ink under redox condition. An optimized NiO/ScSZ screen-printing ink containing 28 vol% of solids and 2 wt% binder was chosen for the fabrication of the anode films. The mechanical properties, DC conductivity and electrochemical performance of Ni/ScSZ films were measured between 0 and 15 cycles and related to the microstructural change of the anode. All these properties degraded with increasing redox cycles. The mechanical hardness of re-oxidized anode decreases from 8753 to 1314 MPa, while the DC conductivity of re-reduced anode decreases from 1400 to 410 S/cm at 800 °C. Also, the anode polarization resistance increases from 0.75 to 2.7 Ωcm2 at 800 °C. This degradation is related to the separation of Ni particles, which reduces the density and Ni–Ni particle connectivity. The decrease in electrochemical performance can be related to a decrease in the anode triple-phase boundary density in the fabricated films. However, all the printed films remain stable with acceptable electrical and electrochemical performance without any cracks or delamination even after 15 cycles. This indicates that ink optimization through rheological testing is an important way to prevent crack formation in printed anode films that results from redox processes in real SOFC operating conditions.