Performance Optimization of Cermet SOFC Anodes: An Evaluation of Nanostructured NiO

The electrochemical performance of the Ni-containing cermet anodes, widely used for all types of SOFCs, is essentially governed by the triple phase boundary (TPB) formed by metal, solid electrolyte and gaseous phase. Although the TPB length and electrode surface area may be drastically increased using nanostructured components, information on the resultant effects in terms of the cermet properties and SOFC production technology is still scarce. The present work is centered on the appraisal of NiO morphologies and optimization of pre-treatment conditions for the powders used for anode screen-printing, with commercial nanocrystalline nickel (II) oxide as a model starting material. A series of NiO powders were prepared via annealing at various temperatures (300 – 1100 o C) followed by chemical, structural and morphological characterization. The results of X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM/ TEM), thermogravimentry and Raman spectroscopy reveal core-shell structure of nanosized NiO grains, formed due to surface hydration and oxidation under ambient conditions. Thermally induced desorption, and likely oxidation of organic components of the screen-printing pastes by the hyperstoichiometric oxygen, lead to poor quality of the electrode layers, thus making it necessary to introduce an additional powder pre-annealing step. The optimum pre-treatment temperature enabling to remove the absorbates, simultaneously preserving submicron grain size in the electrodes, corresponds to approximately 700 o C.