Three-Dimensional Microstructural Evolution of Ni- Yttria-Stabilized Zirconia Solid Oxide Fuel Cell Anodes At Elevated Temperatures

The microstructural evolution of Ni - Yttria-Stabilized Zirconia (YSZ) anode functional layers in anode-supported solid oxide fuel cells was studied after aging in humidified hydrogen at temperatures from 900–1100°C and times up to 500 h. The relatively large (∼6000 μm 3 ) three-dimensional transmission X-ray microscopy images provided good statistics in measured microstructural data. Feature sizes in the YSZ and Ni phases changed little until the highest temperature and time, whereas the pore phase feature size increased for all temperatures and times. Ni-YSZ interfacial area increased at the expense of pore-YSZ interfaces after moderate annealing, with a general decrease in interfacial areas observed at longer times and higher temperatures. Three-phase boundary (TPB) density decreased rapidly initially, but then more slowly, with increasing annealing temperature and time. Electrochemical impedance spectroscopy measurements showed a corresponding increase in the anode response associated with electrochemical hydrogen oxidation at TPBs. A higher fraction of isolated pores and larger pore tortuosity was observed at intermediate annealing temperatures and times, with a corresponding increase in the gas diffusion impedance response.