Unraveling the promotional role of BaCO3 in the electrode reaction kinetics of an SmBaFe2O5+δ air electrode of reversible solid oxide cells

Abstract

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 SmBaFe₂O_5+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.