Correlation Between Microstructural and Electrochemical Characteristics during Redox Cycles for Ni–YSZ Anode of SOFCs

Abstract

Reoxidation of a nickel catalyst in anode generally leads to deterioration of cell performance for solid oxide fuel cells (SOFCs). The aim of this study is to clarify the correlation between microstructural and electrochemical characteristics during reduction–oxidation (redox) cycles of a Ni–yttria-stabilized zirconia (YSZ) anode. Cell performance was deteriorated after the first redox cycle because of the increase in the polarization resistance of the anode. Ohmic loss of the anode also increased after the thermal cycle in pure oxygen. For the Ni–YSZ anode after the redox cycles, the increase in surface area of the nickel phase was observed by focused ion beam–scanning electron microscopy, which indicated that the nickel particles became finer and more complicated in shape. The lengths of triple phase boundary (TPB) derived from three-dimensional-reconstructed images of the Ni–YSZ anodes were 2.39 and after the first and fourth redox cycles, respectively, which were smaller than that before the redox treatment with a TPB length of . Large cracks were produced on the Ni–YSZ anode after the thermal cycle, which led to the increase in the ohmic loss of the anode. The increase in the polarization resistance was caused by the decrease in the length of TPB during the early stage of the redox cycles for the Ni–YSZ anode.