Density functional theory-based analysis on O2 molecular interaction with the tri-s-triazine-based graphitic carbon nitride

The structural and electronic properties of O2 molecular adsorption on the Tri-s-triazine-based graphitic carbon nitride (g-C3N4) surface was investigated through first principles calculation based on density functional theory (DFT). Here, we show that the O2 molecule is merely physisorbed on the surface of g-C3N4 through the interaction of its lowest unoccupied molecular orbital (LUMO) with the orbitals of the 2-coordinated nitrogen atoms of the surface. Though physisorbed, a stronger molecular adsorption was found as compared with its adsorption on pure graphene sheets. We also found that the O2 molecule gains very small amount of electron charges from the surface, which, together with a stronger adsorption energy, may attribute to a more effective oxygen reduction reaction (ORR) site as compared with pure graphene. These results would then be important for reactions with intermediate surface oxidation step in a carbon and nitrogen-based catalyst, and could lead to realization of an effective materials design for surface application, e.g. towards a more efficient catalyst for the ORR on the cathode side of the proton exchange membrane fuel cell (PEMFC).