Grooves of bundled single-walled carbon nanotubes dramatically enhance the activity of the oxygen reduction reaction

Nitrogen-doped graphitic structures (N-GSs) are promising and cheap catalyst candidates for the oxygen reduction reaction (ORR). In this paper, we describe, first, the synthesis of singlewalled carbon nanotubes (SWNTs) coated by a N-GS (SWNT/NGS) and, second, the dramatic enhancement in the activity of the ORR by using this catalyst relative to that observed for the analogue composite composed of multiwalled carbon nanotubes (MWNTs) coated by a N-GS (i.e., MWNT/N-GS). Scanning electron microscopy and gas-adsorption experiments revealed that the SWNT/N-GS formed a bundled structure and that superior gas adsorption behavior originated from this groove structure. It is assumed that the grooves of the bundled SWNT/N-GS dramatically enhance the activity of the ORR owing to superior O₂ adsorption on the grooves.