An Intermetallic CaFe6Ge6 Approach to Unprecedented Ca−Fe−O Electrocatalyst for Efficient Alkaline Oxygen Evolution Reaction

Based on the low‐cost and relatively high catalytic activity, considerable efforts have been devoted towards developing redox‐active transition metal (TM)‐oxygen electrocatalysts for the alkaline oxygen evolution reaction (OER) while the role of redox‐inactive alkaline earth metals has often been neglected in OER. Herein, for the first time, we developed a novel ternary intermetallic CaFe6Ge6 precatalyst, whose surface rapidly transforms into a porous ultrathin Ca−Fe−O heteroshell structure during alkaline OER through the oxidative leaching of surficial Ge. Benefiting from synergistic effects, this highly efficient OER‐active material with distinct Ca−Fe−O layers has a large electrochemical surface area and more exposed active Fe sites than a Ca‐free FeOx phase. Also, the presence of Ca in Ca−Fe−O is responsible for the enhanced transport and activation of hydroxyls and related OER reaction intermediate as unequivocally illustrated by a combination of quasi in‐situ Raman spectroscopy and various ex‐situ methods.