DFT-based study of single transition metal atom doped g-C3N4 as alternative oxygen reduction reaction catalysts

In this paper, the stability and the oxygen reduction reaction (ORR) catalytic activity of single transition metal atom doped g-C3N4 catalysts, M-C3N4 (M = Mn, Fe, Co, Ni, Cu, Rh, Pd, Ag, Pt, Au), were investigated in detail by performing density functional theory (DFT) calculations. The results of binding energy reveal all M-C3N4 are thermodynamically stable. Further dynamic calculations demonstrate they are also dynamically stable except Au-C3N4. Then, through comparing the value of overpotentials, we found that most of M-C3N4 exhibit no ORR catalytic activity except for Ag-C3N4 and Pd-C3N4, both of which have somewhat catalytic properties but still inferior to Pt(111). It may be caused by the strong adsorption between ORR intermediates (OOH, O, OH) and M-C3N4. We further preformed DFT calculation for the high-valent metal complexes of g-C3N4 (M-OH-C3N4) and the significant enhancement of activity is obtained. Due to the additional OH group, the overall adsorption energies of ORR intermediates on M-OH-C3N4 have been decreased and become more close to those on Pt(111), and ORR mechanisms have also been changed. In addition, the overpotentials of ORR on Ni-OH-C3N4 and Cu-OH-C3N4 are much close to that on the Pt(111), indicating that they possess the catalytic activity comparable to precious Pt catalyst.