As illustrated in Fig. , the oxidation state of Co is significantly higher than +3 after 45 min of OER and it reaches an even higher value after 180 min of OER. This observation would be consistent with a Co(IV)=O species acting as the intermediate of OER. Because of the fundamental challenge to obtain in-situ the XAS spectrum of Fe ions in Co-Fe-N-C due to the extreme low Fe amount, XAS analysis of Fe K edge was conducted on the post-catalytic samples of Co-Fe-N-C. Both the XANES and EXAFS spectra are characteristic of a divergent feature from those of reference cases including the FeOOH, metal oxides and metallic foil (Fig. and), while the oxidation state of Fe is approximately +3. The major coordinated element in the first shell is oxygen. The presence of a rather weak peak at the second scattering shell is attributed to the single-scattering path of Fe-Co, in which the CN and the apparent distance is ~0.96 and 2.69 Å, respectively (Fig. ). The CN value (~0.9) indicates that most Fe ions are bonded with Co ions to form the double-atom moiety as proposed in Fig. . The distance of Fe-Co obtained from the Fe K edge data is consistent with that obtained from the Co K edge data.