Suppression of Sr Segregation in La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O _3−δ Oxygen Electrode via Ca Doping for Enhanced Performance Stability of Reversible Solid Oxide Cell

A reversible solid oxide cell (RSOC) can generate electricity and hydrogen, respectively, when operating in solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes. However, at high current densities, serious Sr segregation in the traditional La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ -Gd 0.1 Ce 0.9 O 2−δ (LSCF-GDC) oxygen electrode leads to a decrease in the catalytic activity of the cathode and consequently poor performance stability of RSOC. In this work, Ca doping was proposed to suppress Sr segregation in the LSCF-based composite electrodes. The smaller radius of the Ca atom could reduce the elastic driving force of Sr segregation, while the reasonable Ca-doping concentration could alleviate the steep oxygen vacancy gradient formed under high current density and thereby reduce the electrostatic driving force of Sr segregation. Consequently, after appropriate Ca substitution at the A-site, the prepared La 0.6 Sr 0.2 Ca 0.2 Co 0.2 Fe 0.8 O 3−δ -Gd 0.1 Ce 0.9 O 2−δ (LSCCF-GDC) oxygen electrode reported significantly enhanced stability during long-term operation at high current density. At 750 °C and a current density of 1.2 A·cm –2, the degradation rates of the cell with LSCCF-based composite oxygen electrode were 10 mV/100 h in SOFC mode and 17 mV/100 h in SOEC mode, which was much lower compared with the corresponding values of the cell with the traditional LSCF-based composite oxygen electrode (18 mV/100 h in SOFC mode and 82 mV/100 h in SOEC mode).