O‑Functionalization\nof N‑Doped Reduced\nGraphene Oxide for Topological Defect-Driven Oxygen Reduction

Abstract

Understanding the origin of the active sites in the heteroatom-doped\ncarbon material plays a vital role in designing novel electrocatalysts\nfor the oxygen reduction reaction (ORR) in fuel cell cathodes. Besides\nheteroatoms, the defects in the carbon materials are believed to be\nthe potential active sites for oxygen reduction. The simple peracetic\nacid oxidation of nitrogen-doped reduced graphene oxide improved the\nORR activity with the positive shift in onset (60 mV) and half-wave\npotential (120 mV). The spectroscopic (X-ray diffraction, infrared,\nRaman, X-ray photoelectron) and thermogravimetric analysis of oxidized\ncarbon materials demonstrate the formation of the carbonyl functional\ngroup. The theoretical models were developed with various structural\nmotifs to analyze the active sites. Based on the experimental and\ntheoretical results, the oxidation of nitrogen-doped carbon materials\nusing peracetic acid generates edge epoxides, followed by acid hydrolysis\nto form vicinal diols. Subsequently, the diols undergo pinacol-pinacolone\nrearrangement in the acidic medium, resulting in cyclopentadiene adjacent\nto the seven-membered heptagon ring containing the amide group, known\nas topological defects.