Structural and Mechanical Stability of Reduced Nickel Oxide/Yttria-stabilized Zirconia Anode/Electrolyte Structures for Solid Oxide Fuel Cell Applications

Abstract

AbstractHighly porous Ni-8YSZ anodes supported by a thin and dense electrolyte layer of 8YSZ have been developed for solid oxide fuel cell applications by reducing a NiO-8YSZ anode/electrolye precursor structure in a gas mixture of 5% H2-95% Ar at 800°C for selected time periods up to 8 h. It appears that 2 h of exposure to the reducing conditions is enough to reduce∼80% of NiO. XRD and SEM analyses in the reduced samples disclose the formation of the Ni-8YSZ cermet structure with desired porosity and microstructure. The porosity in the anode samples, which increases with the increase in the fraction of reduced NiO, severely affects the hardness and elastic moduli of the anode samples. Vickers indentation tests show that a hardness value of 5.5 GPa in the unreduced anode samples (12% porosity) reduces to less than 1 GPa in the 8 h reduced samples (36.68 % porosity). Similarly, a decrease of ˜44% in the Young's modulus and ˜40% in shear modulus is observed in the 8 h reduced samples through impulse excitation techniques, in comparison to the unreduced anode precursor. Since the elastic properties of fully dense Ni, NiO and YSZ are comparable to each other, the decrease in the magnitude in elastic moduli and hardness is attributed to the colossal increase in porosity as a result of the reduction of NiO in H2 atmosphere.