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 μm3) 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.

Accelerated ageing of Ni-Yttria Stabilized Zirconia (YSZ) anode functional layers (AFLs) in solid oxide fuel cells (SOFCs) is carried out at 1000-1200°C, the resulting morphological changes are investigated using transmission X-ray microscopy (TXM), and properties are characterized using electrochemical impedance spectroscopy (EIS). Prior to ageing, the as prepared NiO-YSZ AFLs are reduced to Ni-YSZ and then aged at 1100°C for 100 h in order to eliminate early-stage morphological changes. Measured particle size and three phase boundary (TPB) density changes with ageing time and temperature are fit reasonably well using a power-law coarsening model. This model is also used in conjunction with an electrochemical model to predict changes in the anode charge-transfer polarization resistance.

Anode-supported solid oxide cells (SOCs) with thin bi-layer Y 0.16 Zr 0.92 O 2Àd (YSZ)/Gd 0.1 Ce 0.9 O 1.95 (GDC) electrolytes were prepared by a reduced-temperature (1250 C) co-firing process enabled by the addition of a Fe 2 O 3 sintering aid. The Fe 2 O 3 amounts in the layers affected the formation of voids at the GDC/YSZ interface; the case with 1 mol% Fe 2 O 3 in the YSZ layer and 2 mol% Fe 2 O 3 in the GDC layer yielded minimal interfacial voids, presumably because of optimized shrinkage matching between the electrolyte layers during co-firing. The best cells yield fuel cell power density at 0.7 V in air and humidified hydrogen of 1.74 W cm À2 (800 C) and 1.0 W cm À2 (700 C). Under electrolysis conditions, i.e., air and 50 vol% H 2 O-50 vol% H 2 , the best cell area specific resistance is 0.12 U cm 2 at 800 C and 0.27 U cm 2 at 700 C. This excellent cell performance was explained by a number of factors related to the reduced firing temperature: (1) low electrolyte resistance due to minimization of YSZ/GDC interdiffusion; (2) minimal zirconate phase formation between the YSZ and the La 0.6 Sr 0.4 Fe 0.8 Co 0.2 O 3 (LSFC) cathode because of the dense GDC barrier layer; (3) high three phase boundary density in the Ni-YSZ anode functional layer; and (4) good pore connectivity in the Ni-YSZ support. Preliminary life testing under fuel cell and electrolysis operation shows promising cell stability.