Abstract
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.
Highlights
Carbon has been widely studied as a cathode catalyst in polymer electrolyte membrane fuel cell and lithium battery through the development of non-noble metal catalysts for the high oxygen reduction reaction (ORR) activity
Nitrogen ion doping into carbon-based materials, such as highly ordered pyrolytic graphite (HOPG), graphene, and carbon nanotube, is used as one of most effective ways to substitute nitrogen atoms for carbon atoms
By means of new doped technique using low-energy atomic nitrogen ion, we experimentally examined the relationship between the ORR activity and the surface properties of HOPG film
Summary
Carbon has been widely studied as a cathode catalyst in polymer electrolyte membrane fuel cell and lithium battery through the development of non-noble metal catalysts for the high oxygen reduction reaction (ORR) activity. The irradiation energy of nitrogen ion treatment was mainly carried out between several hundreds of electron volts and several kilo electron volts.[7,8,9,10,11,12] Kondo et al irradiated a HOPG surface with an Nþ beam more than 200 eV, where the conventional ion beam gun was used.[8] They observed two types of nitrogen species, that is, pyridinic-N and graphitic-N Such high energy may cause a significant damage on the surface morphology of carbon material
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