Sensitivity of Density Functional Theory Methodology for Oxygen Reduction Reaction Predictions on Fe–N4-Containing Graphitic Clusters

Abstract

Density functional theory (DFT) was used to examine the O2 reduction reaction on Fe–N4-containing graphitic carbon clusters (Fe–N4–G) modeled after recent experimentally identified active sites, Mossbauer spin-state predictions and electrochemical reaction behavior in alkaline media. A detailed analysis of the O2, O, H2O, OOH, and OH adsorbate interactions on the Fe–N4–G cluster with solvation and/or dispersion corrections are considered. The total and partial density of states for the α- and β-spin orbitals are compared for the adsorbate of interest, Fe atom and surrounding graphitic cluster. Relative free-energy diagrams are constructed, which allow us to compare DFT predictions to experimental results for O2 reduction on systems containing embedded Fe–N4 clusters. For all reaction steps, different DFT functionals are explored and the respective geometries, energetics, and spin-states for each adsorbate interaction are reported for six commonly used functionals including B3LYP, M06-2X, M06-L, PBE, TPSSh...