The inherent kinetic electrochemical reduction of oxygen into H2O on FeN4-carbon: A density functional theory study

Metal-coordinated nitrogen-doped carbons are highly active in promoting electrochemical oxygen reduction reaction (ORR). This study describes in detail the ORR kinetics on FeN4-graphene based on a density functional theory calculation. O-2 molecules chemisorbed on Fe site prefer hydrogenation into OOH species rather than direct breakage of the O-O bond. The subsequent reduction of OOH species into H2O2 has a slightly high barrier (1.13 eV). However, this barrier could be bypassed by hydrogenation dissociation into O and H2O, which displays a low barrier (0.47 eV). Further O -> OH and OH -> H2O reactions are kinetically simple. Throughout the entire ORR, the initial O-2 -> OOH reaction determines the total rate and displays a reaction barrier of 0.62 eV. This kinetic profile suggests that O-2 molecules are inherently favorable for reduction into H2O on FeN4-graphene following a four-electron process. (C) 2014 Elsevier B.V. All rights reserved.