In situ analyses of carbon dissolution into Ni-YSZ anode materials

A combination of in situ analyses, including measurement of both electrical resistance and volumetric expansion, and thermogravimetric analysis (TGA) was employed to elucidate the deactivation process of a nickel-yttria-stabilized zirconia (Ni-YSZ) cermet (60 wt % NiO-YSZ) upon exposure to methane at 750 °C. In conjunction with the aforementioned in situ techniques, a number of ex situ analyses, including scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and Raman spectroscopy, revealed that carbon deposition initially occurred at the Ni centers, followed by carbon dissolution into the Ni-YSZ cermet after an induction period of 200 min, which then led to threedimensional expansion. The structural change of the Ni-based cermet induced increases in electrical resistance of the material. The increased electrical resistance likely originated from the breakage of the Ni-Ni conducting network as well as from the formation of microscopic cracks within the Ni-YSZ material, resulting from the observed process of carbon dissolution. Moreover, a combination of TGA involving measurements of electrical resistance was demonstrated to be useful for determining amounts of carbon deposits critical for carbon dissolution. These results strongly suggest that changes in electrical resistance can be utilized to monitor the extent of carbon dissolution into the Ni-YSZ catalysts in situ, which would be helpful for the development of an efficient curing system for solid oxide fuel cells (SOFCs).