Enhanced electrochemical redox kinetics of La0.6Sr0.4Co0.2Fe0.8O3 in reversible solid oxide cells

Abstract

Due to its high conversion efficiency in fuel-to-power and power-to-fuel modes, reversible solid oxide cell (RSOC) is widely regarded as a promising device. In this study, La0.6Sr0.4Co0.2Fe0.7M0.1O3 (M=Fe, Mo, Nb) oxides are prepared and composited with Sm0.2Ce0.8O2-(Li0.67Na0.33)2CO3 to form reversible single component cell (RSCC). Among them, La0.6Sr0.4Co0.2Fe0.7Mo0.1O3 (LSCFM) shows the highest oxygen vacancy concentration, further promoting catalytic activity towards oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR). Besides, Mo or Nb doping enhances the surface reaction rate constant (kchem) and oxygen chemical bulk diffusion coefficient (Dchem) at the temperature range of 550–700 °C. LSCFM shows the highest kchem of 39.3 × 10−5 cm s−1, approximate 3.5 times as 11.1 × 10−5 cm s−1 for La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), and Dchem for LSCFM is 31.1 × 10−6 cm2 s−1, approximate 2.5 times as 12.4 × 10−6 cm2 s−1 for LSCF at 700 °C. Furthermore, the rate determining steps (RDS) of ORR and HOR for LSCFM-based cell are the reduction of oxygen atoms to O− and the charge transfer reaction, respectively. Under SOFC/SOEC reversible operation, the RSCC composed of LSCFM exhibits the best cell performance. In the solid oxide fuel cell mode, the maximum power density reaches 236.2 mW cm−2 and in the solid oxide electrolysis cell mode the current density at 1.3 V is -312.4 mA cm−2.