Oxygen Binding to Active Sites of Fe–N–C ORR Electrocatalysts Observed by Ambient-Pressure XPS

We report the first in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) study of the binding of oxygenated species to the active sites of iron–nitrogen–carbon oxygen reduction reaction (ORR) electrocatalysts. To better interpret the results, DFT calculations were used to calculate absorption energies of reactants and intermediates on potential active sites and calculate the core level shifts for those. The observed oxygen binding to nitrogen coordinated to iron centers correlates with the enhanced measured ORR fuel cell activity of these materials with respect to metal-free analogs and sheds light on the ORR mechanism on PGM-free electrocatalysts.