Effect of NiO addition on properties of bulk yttria-doped ceria sintered from their spray pyrolyzed powder

Since a nickel-containing anode (Ni content of generally >40 vol%) and electrolytes are commonly co-fired at high temperature (>1200 °C) in solid oxide fuel cell (SOFC) manufacturing, if Ni diffuses toward the electrolyte, the effects of the NiO on the properties of the electrolyte become relatively important. In the present study, nickel was added directly into the electrolyte ceramic, 10 mol% yttria-doped ceria (10YDC), during powder preparation to investigate the effects of the presence of NiO on the related properties of YDC electrolyte. 10YDC ceramics were sintered from spray pyrolyzed powders with various amounts of nickel addition (≤15 at%). The phase of the resulting powders was identified as a mixture of YDC and NiO after calcination in air. The grain size of as-pyrolyzed YDC particles decreased as NiO addition increased; however, the grain size of sintered YDC composite was increased by a small addition of NiO. NiO is believed to dissolve in YDC at high temperature, but it exhibits negligible solubility at room temperature. The excess NiO tended to segregate at the grain boundaries and thereby retard the grain growth in YDC matrices. The ac impedance data revealed that the precipitated NiO may reduce the conduction activation energy of the YDC electrolyte, increasing the conductivity of the YDC composite.