M-Porphyrin (M = Mn, Co) Carbon Materials As Oxygen Reduction Catalysts From Density Functional Studies

The development of high efficient cathode catalyst is known to be very important for the large-scale application of fuel cells. In this work, by using the density functional theory, metal-porphyrin (M = Mn, Co) carbon materials (Mn/CoN4-C) have been investigated as possible oxygen reduction reaction (ORR) catalysts. The calculated formation energies indicate that Mn/CoN4-C is stable thermodynamically. For MnN4-C, ORR proceeds with a four-electron process. While for CoN4-C, both two-electron pathway and four-electron pathway are competitive, with the former being slightly favoured. For both compounds, the O-2 hydrogenation pathway is favoured compared with O-2 dissociation pathway. In CoN4-C, the energy barrier is 0.13 eV for the two-electron pathway, while it is 0.47 eV for the four-electron pathway, much lower than 0.80 eV for pure Pt. These energy barriers are also much lower than that in MnN4-C, showing that CoN4-C has a better ORR activity than MnN4-C. The calculated working potential is 0.30 eV for CoN4 in the four-electron pathway.