O-Functionalization of N-Doped Reduced Graphene Oxide for Topological Defect-Driven Oxygen Reduction

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