In summary, electrochemical activation of Co species atomically dispersed on nitrogen-doped carbon (Co-N-C) in Fe-containing alkaline electrolyte led to incidental Fe-incorporation and the formation of a Co-Fe double-atom catalyst (Co-Fe-N-C). Fe is essential for the enhanced activity of Co-Fe-N-C compared to Co-N-C, and the activity of the former scales with the amount of Fe. Operando XAS data indicate that Co-N-C undergo major structural changes upon immersion into an alkaline electrolyte, followed by Fe incorporation during electrochemical activation to yield a dimeric Co-Fe structural motif that is the active site for OER. This double-atom active site appears to be stable during OER. Its TOF is among the highest for non-precious OER catalysts. This work introduces an easily accessed, molecularly defined, and earth-abundant bimetallic electrocatalysts for OER. Such double-atom catalyst bridges the transitionally separated molecular and solid-sate catalysts, thereby offering an attractive platform for the fundamental studies of metal oxides in OER.