Understanding the origin of the active sites in the heteroatomdoped 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.
Rechargeable metal-air batteries are an emerging electrochemical energy storage technology wherein the invention of bifunctional electrocatalysts for oxygen reduction (ORR) and evolution reactions (OER) play a critical role in the...
The carbon defects play a crucial
role in the electrocatalytic
activity of small molecule reduction. The carbon-based electrocatalysts
in electrochemical energy conversion and storage systems are more
promising alternatives to expensive platinum-group catalysts. The
various defects in the graphite materials were reported for their
improved oxygen reduction reaction activity. The edge defective few-layer
graphite material was synthesized using a ball-milling process with
different ball diameters and synthesis methods (dry or wet). Spectroscopic
and microscopic techniques characterize the ball-milled graphite materials.
The increase in the defect density is confirmed by Raman and supported
by the D parameter, estimated from X-ray Auger electron
spectra of carbon. The simple ball milling of graphite leads to a
20 times increase in the surface area compared with commercial graphite,
and its oxygen reduction activity is improved significantly. Mechanistic
analysis indicates that the edge defects improved the 2 + 2-electron
pathway by catalyzing the H2O2 reduction reaction.
Theoretical analysis demonstrates that edge pentagons facilitate the
dissociative H2O2 reduction activity with more
positive onset potentials followed by the zig-zag edges. This study
introduces the importance of ball-milling methods to synthesize the
defect-rich few-layer graphite for electrocatalytic applications without
harsh and corrosive chemicals.
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