First principles study of oxygen molecule interaction with the graphitic active sites of a boron-doped pyrolyzed Fe-N-C catalyst.

Abstract

We study the adsorption and the dissociation of O2 molecules on the active sites of a boron-doped pyrolyzed Fe-N-C catalyst using density functional theory. Initially, we determine the possible structure of the FeN4 active site of the pyrolyzed Fe-N-C catalyst doped with a boron atom by considering the presence of a nitrogen atom as a metal-free site. The most stable configuration of the structure occurs when the boron and nitrogen atoms coalesce with the FeN4 site forming a complex site. This structure has higher stability compared to the undoped FeN4 site. The doped FeN4 possesses the unique ability to adsorb an oxygen molecule in a side-on mode due to the presence of the boron-nitrogen pair acting as a supporting site. One O atom of the O2 molecule sticks strongly to the top of the iron atom, while the other binds with the boron atom. This O2 side-on adsorption stretches the O-O bond length by 15%. Furthermore, the examined catalyst surface can dissociate the oxygen molecule easily with only half the energy barrier of the undoped FeN4 structure.