Property evaluation of Sm 1‐x Sr x Fe 0.7 Cr 0.3 O 3‐δ perovskites as cathodes for intermediate temperature solid oxide fuel cells

Abstract

Perovskite-type (ABO3) complex oxides of Sm1-xSrxFe0.7Cr0.3O3-δ (x = 0.5-0.7) series were prepared by a glycine-nitrate combustion process. The crystal structure, oxygen nonstoichiometry, electrical conducting, thermal expansion, and electrocatalytic properties of Sm1-xSrxFe0.7Cr0.3O3-δ perovskites were inspected in view of their use as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). Changing the content of Sm3+ at the A-site was demonstrated to be effective in tuning the structure and properties. The variation of the various properties with Sm3+ content was explained in relation to the corresponding evolution of the crystal structure and oxygen nonstoichiometry. Sm0.3Sr0.7Fe0.7Cr0.3O3-δ (x = 0.7) was determined to be the optimal composition in the Sm1-xSrxFe0.7Cr0.3O3-δ series based on a trade-off between the thermal expansion and electrocatalytic properties. Sm0.3Sr0.7Fe0.7Cr0.3O3-δ ceramic specimen exhibited an electrical conductivity of approximately 40 S·cm−1 at 800°C and a thermal expansion coefficient of 14.1 × 10−6 K−1 averaged in the temperature range from 40°C to 1000°C. At 800°C in air, Sm0.3Sr0.7Fe0.7Cr0.3O3-δ electrode showed a cathodic polarization resistance of 0.19 Ω·cm2, a cathodic overpotential of 30 mV at current density of 200 mA·cm−2, and an exchange current density of 257 mA·cm−2. It is suggested that Sm0.3Sr0.7Fe0.7Cr0.3O3-δ is a potential candidate material for cathode of IT-SOFCs in light of its overall properties.