Nitrogen doping of carbon nanoballoons by radiofrequency magnetron plasma and evaluation of their oxygen reduction reaction activity

Abstract

Nitrogen-doped carbon materials exhibit a catalytic activity, such as an oxygen reduction reaction (ORR). In this study, we performed nitrogen doping on a carbon nanoballoon (CNB), which is a nanometer-sized carbon particle in the form of a hollow sphere made of graphite by radiofrequency (RF) magnetron plasma in a gas mixture of nitrogen and helium. Nitrogen-doped CNBs (N-doped CNBs) were prepared by different plasma irradiation conditions: the sample installation positions, input powers, and irradiation times. The samples were examined for chemical state by X-ray photoelectron spectroscopy (XPS). Hydrodynamic voltammetry was used for the evaluation of the catalytic activity of a N-doped CNB with a pyridinic N concentration of 0.4-1.0 at.%. As a result, the onset potential was measured to be 0.13 V versus RHE (reversible hydrogen electrode), which was close to the previously reported data of highly oriented pyrolytic graphite (HOPG) with a pyridinic N concentration of 0.57 at.%, which was prepared by annealing under NH3.