Unraveling the promotional role of BaCO3 in the electrode reaction kinetics of an SmBaFe2O5+δ air electrode of reversible solid oxide cells
Iron-based double perovskites, as mixed electronic and oxygen ionic conductors, are potential air electrodes for reversible solid fuel cells. However, their catalytic activity towards the oxygen reduction reaction/oxygen evolution reaction is inferior to that of cobalt-based perovskites. Herein, a BaCO3-infiltrated SmBaFe2O5+δ (SBF) electrode is proposed with significantly enhanced catalytic activity. The theoretical computation and experimental study demonstrate that BaCO3 can significantly accelerate the oxygen adsorption/dissociation kinetics, which is identified to be the rate-limiting step of the SBF electrode. The BaCO3 decoration decreases significantly the polarization resistance from 0.154 to 0.068 Ω cm2 at 700 °C in air, and enables superior electrochemical performance in both fuel cell (FC) and electrolysis cell (EC) modes. The single cell with BaCO3 infiltrated SBF as an air electrode exhibits good operational stability in a reversible FC/EC mode for 34 cycles at ±300 mA cm−2, manifesting the good structural stability of the BaCO3-infiltrated SBF composite electrode under redox conditions. This work highlights the importance of clarifying the rate-limiting step and finding an effective strategy to facilitate this specific process for the design of high performance electrode materials.
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