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

Abstract

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.