Engineering Synergistic Edge-N Dipole in Metal-Free Carbon Nanoflakes toward Intensified Oxygen Reduction Electrocatalysis.

Nitrogen doping represents an effective way to induce charge/spin polarization in nanocarbons for promoting oxygen reduction reaction (ORR) activity. However, it remains elusive to define the dominant active sites with respect to two critical N-configurations of pyridinic-N and graphitic-N. Herein, a tandem catalytic graphitization and nitrogen modification strategy for the synthesis of metal-free nitrogen-doped carbon nanoflakes (NCF) featuring the edge-suffused and graphite-analogous structure is presented. NCF exhibits superb Pt-like ORR activity (0.85 V for half-wave potential and 5.9 mA cm-2 for diffusion-limited current density) but much stronger robustness in the alkaline medium. The experimental and theoretical studies suggest the key role of graphitic-N in ORR. Furthermore, it unveils that the high activity of NCF should be traced to a synergistic polarization of the edge-type pyridinic-N/graphitic-N dipole spaced by one edge peak carbon atom on the armchair edges. This study sheds light on the understanding of ORR active sites in the nitrogen-doped nanocarbons for ORR. [ABSTRACT FROM AUTHOR]