Enhancing the Stability of Infiltrated Ni/YSZ Anodes

Abstract

One possible solution to the redox cycling problem in Ni-based anodes is the fabrication of a pre-sintered porous electrolyte matrix, followed by infiltration of 10-20 vol% of a Ni-based catalyst into this scaffold. However, this can lead to instability as a result of sintering of the infiltrated phase at SOFC working temperatures. In this study, various Ni-containing solutions were infiltrated into a symmetrical tubular half-cell, with electrochemical impedance spectroscopy (EIS) and electron microscopy imaging used to determine the long term stability of the cells. It was found that the amount of infiltrated Ni has a significant impact on the long term stability of the Ni/YSZ anodes, explained by the better connectivity between Ni particles when there is more Ni present. It was also demonstrated that high temperature treatment of the infiltrated Ni/YSZ anodes just after the first few infiltrations, followed by several further Ni infiltration steps, has a significant effect not only on the stability of the anode at 800 oC, but also on the anode performance. As the YSZ backbone has the ability to dissolve NiO at higher temperatures, the dissolved NiO can be ex-soluted in the form of at least partially inter-connected nano-sized Ni particles at cell working temperatures under a reducing atmosphere.