Endohedral metallofullerenes Mn@C60 (M = Mn, Co, Ni, Cu; n = 2–5) as electrocatalysts for oxygen reduction reaction: a first-principles study

Endohedral metallofullerenes (EMFs) have rarely been studied in relation to the oxygen reduction reaction (ORR); however, they have attracted a wide attention due to their unique structures and properties. On the basis of density functional theory, the ORR catalytic activities of Mn@C60 (M = Mn, Co, Ni, Cu; n = 2–5) have been investigated systematically in the present work. At first, the structures of all EMF models can be obtained by relaxing the C60 cage that contains a lowest energy structure of a metal cluster inside. Then, the active site is determined by a charge distribution analysis. The calculated results uncover that for the probed EMFs, there is an almost linear relationship between the adsorption energies of OOH, O, and that of OH intermediate. This slightly linear relationship indicates OH may be used as a descriptor in predicting their ORR activities to a certain degree. Further analysis of the reversible potentials of ORR uncovers that compared to other tested EMFs, Mn5@C60, Cu4@C60, Co2@C60, and Ni4@C60 have relatively better ORR activities, with the calculated reversible potentials of 0.71, 0.645, 0.64, and 0.62 V, respectively. In addition, these four screened EMFs, which have good activities toward ORR, also have good poisoning-tolerance abilities to some impurity gases, such as SO2 and CO. However, the influence of fuel molecules, such as methanol, formic acid, and ethanol, on these four EMFs cannot be neglected.