Probing the activity of transition metal M and heteroatom N4 co-doped in vacancy fullerene (M–N4–C64, M = Fe, Co, and Ni) towards the oxygen reduction reaction by density functional theory

Abstract

In this study, a novel type oxygen reduction reaction (ORR) electrocatalyst is explored using density functional theory (DFT); the catalyst consists of transition metal M and heteroatom N₄ co-doped in vacancy fullerene (M–N₄–C₆₄, M = Fe, Co, and Ni). Mulliken charge analysis shows that the metal center is the reaction site of ORR. PDOS analysis indicates that in M–N₄–C₆₄, the interaction between Fe–N₄–C₆₄ and the adsorbate is the strongest, followed by Co–N₄–C₆₄ and Ni–N₄–C₆₄. This is consistent with the calculated adsorption energies. By analyzing and comparing the adsorption energies of ORR intermediates and activation energies and reaction energies of all elemental reactions in M–N₄–C₆₄ (M = Fe, Co, and Ni), two favorable ORR electrocatalysts, Fe–N₄–C₆₄ and Co–N₄–C₆₄, are selected. Both exhibited conduction through the more efficient 4e⁻ reduction pathway. Moreover, PES diagrams indicate that the whole reaction energy variation in the favorable ORR pathways of Fe–N₄–C₆₄ and Co–N₄–C₆₄ is degressive, which is conducive to positive-going reactions. This study offers worthwhile information for the improvement of cathode materials for fuel cells.