Revealing Oxygen Reduction Reaction Activity Origin of Single Atom Supported on g-C3N4 Monolayer: A First-Principles Study

The potential of single transition metal atom (TM, from Ti to Au) supported on g-C3N4 (TM/g-C3N4) for oxygen reduction reaction (ORR) is investigated by first-principles calculation. It is demonstrated that the TM atom can stay stably in the cavity of g-C3N4 and interact with substrates via charge transferring from TM atoms to g-C3N4. Among all TM/g-C3N4, Pd/g-C3N4 stands out with a low overpotential of 0.46 V, showing the good performance of ORR. So it has great potential as a candidate to replace noble Pt catalyst. ORR activity of TM/g-C3N4 can behave as a function of ΔE*OH (energy descriptor). Furthermore, d-band center and ICOHP (electronic structure descriptors) can quantitatively describe the variation trend of ΔE*OH. So can Bader charge analysis (charge transfer descriptor). Considering the number of d orbital electron and the electronegativity of TM, φ (intrinsic descriptor) can be applied to predict and reveal the origin of the ORR activity. A bridge from intrinsic characteristics to electronic structures, to charge transfer, to electronic structures and then to adsorption energy has been established, which is conducive to better reveal the ORR activity origin and provides guidance for designing effective ORR electrocatalysts.