Role of the carbon defects in the catalytic oxygen reduction by graphite nanoparticles: A spectromagnetic, electrochemical and computational integrated approach

The chemical groups present at the surface of graphite have been thought for a long time to be mainly
responsible for its catalytic activity in the oxygen reduction reaction. Recently, it was proposed that the
surface defects of graphite also significantly contribute to promote this reaction. Although the behaviour
of surface defects has been reported, only few comments have been dedicated to their involvement in
the mechanism and the possible intermediate species in the oxygen reduction reaction. Herein, we aim
to present a more detailed explanation of the catalytic activity of graphite particles based on the
structure of their defects and their size. Structural, spectroscopic and magnetic investigation (X-ray
diffraction, Raman and electron spin resonance) and electrochemical measurements were performed to
describe the nature of the defects and their aptitude to transfer electrons. Computational description
supplied precise details of the energy of the different defects and their ability to promote the reduction,
also suggesting the structure of the intermediate adduct in the oxygen reduction. The results indicated
that molecular oxygen preferentially interacts with graphite defects, which involve the p-electron system
and accumulation of the spin density on the edges of the grains, in particular, on the zig-zag edges
present on ball-milled graphite. This promotes the reactivity of this nanomaterial. Furthermore, the
activation increases by decreasing the particle size.