Defect chemistry and oxygen non-stoichiometry in SrFe0.2Co0.4Mo0.4O3-δ ceramic oxide for solid oxide fuel cells

Abstract

SrFe0.2Co0.4Mo0.4O3-δ (SFCM) is a ceramic oxide that has the potential to replace conventional Ni-based cermet anodes and is appropriate for use in solid oxide fuel cells operating at low temperatures (below 650 °C). SFCM was shown to be phase stable with n-type conductivity above 43 S/cm under reducing conditions and reversibly creates secondary phases under oxidizing conditions with p-type conductivity around 4 S/cm at 600 °C. SFCM begins desorbing oxygen and creating vacancies under nitrogen at 350 °C and continues to do so above 800°C. Under oxidizing conditions, SFCM remains near stoichiometric, with oxygen non-stoichiometry changes below δ = 0.003. Once exposed to reducing conditions, SFCM can obtain a non-stoichiometry up to δ = 0.176 due to the reduction of the three multivalent B-site cations resulting in a low enthalpy of formation for oxygen vacancies at 109 kJ mol − 1. This data is used to propose a low pO2 defect equilibrium model and diagram to explain the oxygen vacancy generation behavior under reducing conditions across temperatures.