“…[38][39][40] The high-resolution N 1s spectrum ( Figure S5B) could be deconvoluted into five peaks centered at 398.1, 399.1, 399.8, 401.2, and 403.1 eV, respectively, corresponding to pyridinic-N, Co-N x , pyrrolic N, graphitic-N, and oxidized graphitic-N. 41,42 Compared with C-C@NC (without Fe substitution) and C@NC (without Fe and Cu substitution), FC-C@NC exhibited energy shifts in binding energies in Co 2p and N 1s spectra (a positive shift of about 0.6 eV for Co 2p and a negative shift of about 0.6 eV for N 1s, as shown in Figure 3E,F), indicating Fe and Cu substitution into Co sites had a little influence on the chemical states of Co and N. In addition, FC-C@NC contained higher N content (10.8%), and the content of pyridinic N and graphitic-N was 60% of the total N content, which was supposed to be beneficial for ORR process. 43 The electrocatalytic activities of all samples for ORR were first evaluated using a three-electrode configuration cell in alkaline solution (0.1 M KOH) at room temperature. As shown in Figure S6, no redox peak was observed for FC-C@NC in Ar-saturated KOH solution, while a welldefined cathodic peak (0.85 V vs RHE and all the potentials in this study were compared with RHE) was observed in O 2 -saturated KOH solution, predicting its effective ORR catalytic activity.…”