B‐Site Engineering in Ba‐Based Perovskites via Solid‐State Synthesis Unlocks High Power Density in SOFCs

This study introduces three novel perovskite‐based cathode materials; Ba 3 CoNb 2 O 9 , Ba 3 FeNb 2 O 9 , and Ba 6 CoFeNb 9 O 30 , synthesized via a solid‐state reaction using camphor as a pore‐former. The suitability of the cathode materials for solid oxide fuel cells (SOFCs) is evaluated at temperatures ≤700 °C. The influence of surface and lattice oxygen content, along with B‐site doping effects, is systematically analyzed in relation to their electrochemical behaviors. At temperatures below 550 °C, Ba 3 CoNb 2 O 9 and Ba 3 FeNb 2 O 9 exhibit ≈1.5 times higher power densities than Ba 6 CoFeNb 9 O 30 , attributed to superior surface area. At higher temperatures (≥600 °C), Ba 6 CoFeNb 9 O 30 demonstrates superior performance due to more efficient surface oxygen utilization. All three materials benefit from high thermal stability and electrochemically active compositions, achieving power outputs surpassing many existing SOFC cathodes. This study highlights the importance of carefully engineered cathode composition and microstructure in developing advanced materials for efficient and stable SOFC operation at reduced temperatures.