Structural, electrical and electrochemical characterizations of SrNb_0.1Co_0.9O_3-δ as a cathode of solid oxide fuel cells operating below 600 °C

SrNb_0.1Co_0.9O_3-δ (SNC) perovskite oxide has been prepared by high-energy ball milling followed by calcination at 1100 °C. According to oxygen temperature-programmed desorption and thermogravimetry analysis results, highly charged Nb⁵⁺ successfully stabilizes the perovskite structure to avoid order-disorder phase transition. The electrical conductivity reaches 550 S cm^-1 at 300 °C in air and as high as 106 S cm^-1 under P(O₂) = 1 × 10^-5 atm at 900 °C. The high electrical conductivity is beneficial in improving the charge-transfer process for the oxygen reduction reaction on the cathode. Based on the defect chemical analysis, the Nb-doping in SrCoO_3-δ perovskite facilitates the formation of Co²⁺, which increases oxygen nonstoichiometry and, subsequently, the mixed valence of [Co²⁺]/[Co³⁺] under lower oxygen partial pressure. A relatively low thermal expansion coefficient of 19.1 × 10^-6 K^-1 in air was achieved. All above properties show SNC to be a promising cathode material in the practical application of low-temperature solid oxide fuel cells.