Synthesis of nanocomposite nickel oxide/yttrium-stabilized zirconia (NiO/YSZ) powders for anodes of solid oxide fuel cells (SOFCs) via microwave-assisted complex-gel auto-combustion

Nanocomposite NiO/YSZ powders for high performance anodes of SOFCs have been synthesized via a microwave-assisted complex-gel auto-combustion approach using nitrates of Ni 2+, Zr 4+ and Y 3+, citric acid (CA) and ethyl glycol as starting materials. The complexing conditions including pH and molar ratio of CA to the metal ions in the aqueous solutions have been quantitatively analyzed and optimized to realize their complete chelating into the CA-based gel network. The processing features and the microstructural characteristics of NiO/YSZ phases formed during auto-combustion of gels have been investigated by FT-IR, TG-DSC, XRD, SEM, SAED and HRTEM. It has been found that the nanoscale composite powders of NiO/YSZ, directly obtained through the in situ auto-combustion reactions within the gels, are composed of loosely agglomerated particles with sizes of ∼200 nm, while these particles themselves are the aggregates of finer NiO and YSZ crystallites of ∼15 nm in size. Moreover, the anodes prepared with such nanoscale composite powders have been manifested to possess much better electrochemical properties than the ones obtained by normal NiO/YSZ powder (∼2.5 μm) according to their measurements of AC impedance and temperature programmed reduction behavior due to the highly enhanced three-dimensional transport network of oxide ions and triple-phase boundaries for surface reactions.