Fig. 6. Elucidation of the mechanism of efficient ORR catalysis by the FeN_5−xO_x sites for H₂O₂ production.

a Volcano plots of the computed activity of electrochemical H₂O₂ production via the 2e⁻ ORR. The horizontal dash line indicates the equilibrium potential of O₂/H₂O₂. Except for the FeN₃O₂, FeN₄O, FeN₄, and O/C sites, the sites labelled in black were adapted from the references. b Calculated *OOH adsorption energies and charges of the valence electron number of the C atom in the FeN₃O₂, FeN₄O, and FeN₄ sites. c Free energy diagram for the 2e⁻ ORR of the FeN₃O₂, FeN₄O, and FeN₄ sites. The annotation values represent the computed kinetic barriers for *OOH to H₂O₂. d Calculated *OOH adsorption energies and changes in the C atom charge state at the FeN₃O₂, FeN₄O, and FeN₄ sites.