In situ formation of nitrogen-doped onion-like carbon as catalyst support for enhanced oxygen reduction activity and durability

•The OLC with various nitrogen doping degrees was successfully synthesized via an arc discharge in NH3 solution.•The N-OLC exhibited structural defects in the outermost shells, revealed via TEM, XRD, XPS and Raman spectroscopy.•The enhanced ORR activities could be ascribed to the defective outermost layers and the electronic modification.

Nitrogen-doped onion-like carbon was synthesized using an arc discharge in a liquid phase in the presence of different ammonia concentrations. The nitrogen-doped onion-like carbon was investigated as a catalyst support material for a catalytic oxygen reduction reaction. With increasing ammonia concentrations up to 5 M, the nitrogen doping degree increased to 1.7 at%, which created a highly defective onion-like structure. The edge and defective sites induced from nitrogen atoms effectively facilitated the nucleation of Pt clusters, which led to the stable dispersion and small size of Pt nanoparticles, as revealed via X-ray photoelectron spectroscopy, X-ray diffraction, Raman spectroscopy and electron microscopy. From the results of the electrochemical characterization, the Pt nanoparticles supported on the nitrogen-doped onion-like carbon with a nitrogen content of 1.7 at% exhibited the highest electrochemically active surface area, specific current density and half-wave potential. The enhanced oxygen reduction could be ascribed to the defective outermost layers and the electronic modification. Moreover, even after an accelerated durability test with 5000 cycles, the nitrogen-doped onion-like carbon with a nitrogen of 1.7 at% exhibited less degradation, indicating the excellent durability.