Effect of low-energy nitrogen ion treatment of highly ordered pyrolytic graphite on oxygen reduction reaction activity

We systematically investigated highly ordered pyrolytic graphite film doped by low-energy atomic nitrogen ion of 20 eV, addressing major issues that include the effect of treatment time on the oxygen reduction reaction activity of highly ordered pyrolytic graphite film, and the influence of treatment time on the chemical and physical structures of highly ordered pyrolytic graphite surface. From the experimental results, it was clarified that the treatment for 60 s or less in nitrogen plasma was effective to modify the highly ordered pyrolytic graphite surface with improved oxygen reduction reaction performance, where the oxygen reduction reaction current increases by about 2 times as compared to that of untreated specimen. Moreover, we discussed the content of various C-N bonds, the strain which derived from the substitution of carbon and nitrogen, and a modification of the highly ordered pyrolytic graphite surface due to treatment, on the basis of the results of Raman spectroscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.