Fig. 1: Theoretical calculations for two-electron ORR.

a Atomic structures of CoPc, CoPc/OCNT, CoPc-OCNT and CoN4 models. b Calculated activity-volcano curve for two-electron ORR. c Free-energy diagrams for two-electron ORR pathway at 0.7 V vs RHE, where * and *OOH denote an unoccupied active site and adsorbed *OOH, respectively. d–e Projected crystal orbital Hamilton populations (pCOHP) between Co and p-orbital of O of *OOH on CoPc/OCNT and CoPc-OCNT.