Iranian Journal of Materials Science and Engineering

HIGHLIGHTS:
 Gd-doping enhances IT-SOFC cathode performance via TPB density.
 Mixed BaSrCoO3−δ phases reduce area-specific resistance.
 Sol–gel thermolysis enables controlled synthesis of Ba0.5Sr0.5−xGdxCoO3−δ.
 Oxygen-vacancy engineering improves ORR kinetics in BaSr1−xGdxCo2O5+δ.
 Ba0.5Sr0.3Gd0.2CoO3−δ shows optimized electrochemical performance.