Effective Ca-doping in Y1−xCaxBaCo2O5+δ cathode materials for intermediate temperature solid oxide fuel cells†
Ca-doping at the Y-site of Y1−xCaxBaCo2O5+δ (YCBC) double perovskites is shown as an effective strategy to develop a highly efficient, stable, lanthanide-free cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). The proposed Ca-doping has a beneficial influence on the structural stability, thermal expansion coefficient, electronic and ionic transport, and electrochemical properties of YCBC oxides. The phase stability and durability at evaluated temperature are greatly enhanced by Ca-doping. The thermal expansion coefficients of Y1−xCaxBaCo2O5+δ are calculated to be 18.1–18.7 × 10−6 K−1. At 800 °C, the conductivity is as high as 220 S cm−1 for the Y0.8Ca0.2BaCo2O5+δ sample. Area specific resistances as low as 0.010, 0.018, 0.032, 0.068 and 0.142 Ω cm2 at 850, 800, 750, 700 and 650 °C, respectively, are delivered by the Y0.8Ca0.2BaCo2O5+δ cathode in a La0.8Sr0.2Ga0.8Mg0.2O3−δ electrolyte supported symmetric cell. The maximum power densities of a full cell with the Y0.8Ca0.2BaCo2O5+δ/Ce0.9Gd0.1O2−δ composite cathode are registered to be 1066, 841, 634 and 430 mW cm−2 at 850, 800, 750 and 700 °C, respectively. All the results clearly demonstrate that Ca-doped Y1−xCaxBaCo2O5+δ double perovskites are highly stable and effectively working candidate cathodes for IT-SOFCs.