Optimizing the electronic structures of CaxSr1-xCo0.7Fe0.3O3-δ anodes for high-temperature oxygen evolution reaction

CO2 electrolysis in solid oxide electrolysis cells (SOECs) is restricted by sluggish oxygen evolution reaction (OER) kinetics. Optimizing the electronic structure of anode material is an efficient strategy to improve OER activity and stability. Herein, the electronic structures of CaxSr1-xCo0.7Fe0.3O3-δ (x = 0, 0.5, 1) anodes are modified by A-site-induced structural transformation. Physiochemical characterizations and density functional theory calculations reveal that the crystalline structural transformation from orthorhombic brownmillerite CaCo0.7Fe0.3O3-δ to tetragonal perovskite SrCo0.7Fe0.3O3-δ lifts up the O 2p-band center to the Fermi level, which strengthens the M 3d-O 2p orbitals hybridization and increases the oxygen vacancy concentration, oxygen ion migration capacity, and electrical conductivity. At 800°C, SOEC with the SrCo0.7Fe0.3O3-δ anode achieves the highest current density of 2.03 A cm−2 at 1.6 V with a stable operation of 487 h at 1.2 V, superior to the benchmark La0.6Sr0.4Co0.2Fe0.8O3-δ, Ba0.5Sr0.5Co0.8Fe0.2O3-δ and PrBaCo2O6-δanodes.