To probe the structures of the active site in Co-Fe-N-C during OER, operando XAS is conducted (Fig. ). Even after OER for 180 min, no significant structural change was found in all interaction paths except for a minor change in the Co-Fe path, indicating the present double-atom electrocatalyst is robust. As compared to that of activation sample, the apparent distance of Co-Fe path during OER increases by approximately 0.12 Å, while the CN value of Co-Fe path also increases slightly, probably due to more Fe incorporation from the electrolyte. The increase in the bond length of the Co-Fe path might be due to the enhanced interaction of OH-/H2O with Co ions during OER, which weakens the Co-Fe interaction.