A density functional theory study of oxygen reduction reaction on Me–N4 (Me = Fe, Co, or Ni) clusters between graphitic pores

Abstract

In this study, we performed first-principles density functional theory (DFT) calculations to investigate the reaction pathway of oxygen reduction reaction (ORR) on Me–N₄ (Me = Fe, Co, or Ni) catalytic clusters formed between pores in graphene supports. Our DFT results indicate that formation of Me–N₄ clusters at the edges of graphitic pores is energetically feasible. The catalytic mechanism of the Me–N₄ clusters for ORR was elucidated by calculating the binding energies of ORR intermediates O₂, O, OH, OOH, HOOH, and H₂O on these clusters. It was found that O₂ could be chemisorbed on the Co–N₄ and Fe–N₄ clusters but not on the Ni–N₄ clusters. Thus, the Co–N₄ and Fe–N₄ clusters are predicted to be active for catalyzing ORR. Moreover, we observed that the O–O bond in HOOH was broken in the lowest-energy adsorption configuration of HOOH on the Fe–N₄ and Co–N₄ clusters. This process of breaking the O–O bond suggests that the Fe–N₄ and Co–N₄ clusters between graphitic pores could promote 4e⁻ reduction of O₂ with a single active site. Here, our theoretical study provides an explanation to the experimental findings of 4e⁻ ORR on nitrogen-derived transition metal/carbon electrocatalysts. Furthermore, we illustrated that the ORR activity of the Me–N₄ clusters could be gauged by an electronic descriptor related to the d-electron orbitals of the transition metal atom.