Forming indium-carbon (In–C) bonds at the edges of graphitic nanoplatelets

Indium (In), one of the soft and malleable post-transition metals, was introduced along the broken edges of graphitic nanoplatelets (GnPs) by mechanochemically ball-milling graphite in the presence of solid state In beads. After completely leaching off unreacted In using royal water (aqua regia), the formation of In–C bonds in the resulting In-doped graphitic nanoplatelets (InGnPs) was confirmed using various analytical techniques, including atomic-resolution transmission electron microscopy (AR-TEM). Scanning TEM (STEM) image shows that In elements instead of In clusters were uniformly distributed in the InGnPs, suggesting the formation of In–C bonds. The content of In in the InGnPs was 0.34 at% (3.01 wt%), as determined by X-ray photoelectron spectroscopy (XPS). The mechanochemically induced chemical reaction was powerful enough to form In–C bonds. Further, the InGnPs demonstrated catalytic activity toward the oxygen reduction reaction (ORR) comparable to commercial Pt/C catalysts, as well as excellent durability and tolerance against impurities (methanol and CO) in alkaline medium.