The observed CN value of Co-Fe path after OER for 180 min suggests that one-third Co ions form a Co-Fe interaction. This ratio is higher than the Fe:Co ratio determined by post-catalytic ICP-AES. The discrepancy is attributed to the higher surface sensitivity of the fluorescence-yield XAS (< 100 nm) compared to ICP-AES (bulk). It is noted that the first coordinated shell of Co-Fe-N-C remains nearly identical during OER, indicating that the in-situ formed Co-Fe-N-C double-atomic structure is stable during extended OER. Notably, the possibilities of the formation of CoOOH and any type of cobalt oxides can be excluded even after reacting for 5 h, since the spectroscopic features of Co-N-C and Co-Fe-N-C are evidently different from those cases (Fig. ).