Mechanisms of fullerene and single-walled carbon nanotube composite as the metal-free multifunctional electrocatalyst for the oxygen reduction, oxygen evolution, and hydrogen evolution

The fullerene and single-walled carbon nanotube composite (C60-SWCNT) is experimentally investigated to have multifunctional catalytic activities for the oxygen reduction, oxygen evolution, and hydrogen evolution, however the mechanisms and the origin of activities are not clear at the molecular level. In this paper, by applying the density functional theory method, a highly active site of C60-SWCNT is identified (named as site-2). The oxygen reduction and oxygen evolution on the site-2 both can be completed through the four-electron reaction pathway and the corresponding overpotentials are 0.58 V and 0.62 V for them, respectively. Furthermore, the hydrogen adsorption free energy is calculated to be a small value of 0.39 eV, also indicating the high hydrogen evolution activity of the site-2. These calculation results are consistent with the experimental determinations. The source of the excellent activities of the C60-SWCNT composite should be attributed to the intermolecular charge transfer from the SWCNT to the C60, which leads to the increased positive charges of the site-2 in the C60-SWCNT. Therefore, the activity of the C60-SWCNT is enhanced and the binding of the reaction species is further improved.