Synthesis of Few-Layer Graphene by Ball-Milling for Oxygen Reduction: Kinetics and Mechanistic Insights

Abstract

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.

Active site exploration of core–corona structured bifunctional cobalt ferrite-containing nitrogen-doped carbon nanotubes for rechargeable zinc–air battery application

“…A self-made aqueous zinc–air battery was assembled using CF10-N/C4 catalyst coated (loading density is 1 mg cm −2 ) air electrode, as described in previous work. 39,40 The carbon paper (Toray) was used as an air electrode, and the zinc plate (0.5 mm thickness) was used as the anode. The electrolyte is a mixture of KOH (6 M) and Zn(CH 3 COO) 2 (0.2 M) solution.…”