Activation of Catalytically Active Edge-Sharing Domains in Ca₂FeCoO₅ for Oxygen Evolution Reaction in Highly Alkaline...

Rechargeable zinc-air batteries are considered as one of the possible candidates to replace conventional lithium-ion batteries. One of the requirements for effective battery operation is an oxygen evolution reaction (OER) that needs to be generated in a highly alkaline electrolyte. The A₂BB'O₅ brownmillerite-type Ca₂FeCoO₅ electrocatalyst having a 57 Pbcm symmetry exhibits very high electrocatalytic activity toward OER in 4 mol dm^-3 KOH. Our studies show that the electrocatalyst undergoes bulk amorphization upon OER and adequately activates catalytically active domains. The synchrotron radiation studies using the extended X-ray absorption fine structure (EXAFS) technique show that the central structural unit found in the polarized Ca₂FeCoO₅ is a cluster of edge-sharing CoO₆ octahedra. The electrochemical data indicate that OER preferentially takes place on the edge-sharing CoO₆ octahedra catalytic centers reconstructed in the brownmillerite-type electrocatalyst. The EXAFS second shell peaks at an interatomic distance of 2.8 Å are the fingerprints of the catalytically active domains.