Origin of the catalytic activity of graphite nitride for the electrochemical reduction of oxygen: geometric factors vs. electronic factors.

Graphite nitride (GN) was prepared from graphite oxide (GO) by reacting with ammonia at high temperature. Its electrochemical properties as catalyst for oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and steady state polarization (SP) measurements. In order to explore the origin of the activity of the catalysts, the lattice symmetry, the component and the band structure of the catalyst surface were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS), respectively. The results indicate that the geometric factors, e.g. the surface area and the disorder degree, play only a minor role in the enhancement of the electrocatalytic activity of GN for ORR. The correlation between the electrocatalytic activity and the density of state (DOS) at 6.5 eV below Fermi level of GN demonstrates that the activity of the catalysts arises from the electronic states near Fermi level developed as a result of the incorporation of hetero-atoms, N and (or) Fe, especially N, into the graphite lattice.