Nitrogen-doped carbon nanotubes with high activity for oxygen reduction in alkaline media

Nitrogen-doped carbon nanotubes (NCNTs) were prepared using a floating catalyst chemical vapour deposition method. The multiwalled NCNT contains 8.4 at% nitrogen and has a dimension of 100 nm in the diameter and 10–20 nm in the wall thickness. The catalytic activity and durability of the NCNTs towards oxygen reduction reaction (ORR) were evaluated by cyclic voltammetry (CV) and rotating ring-disk electrode (RRDE) techniques in KOH solution. In addition, the effects of KOH concentration on several ORR performance indicators of the NCNT catalyst, such as the number of electrons transferred, the diffusion-limiting current density, the onset and half-wave potentials, were also examined in electrolytes of various KOH concentrations, ranging from 0.1 to 12 M. Experimental results show that NCNTs exhibited comparable activity for ORR in alkaline electrolyte as compared with commercially available Pt/C catalyst, and much higher activity than commercial Ag/C catalysts. In addition, the NCNTs showed good stability from the potential cycling test, and the concentration of KOH had significant impact on the ORR performance indicators of the NCNT catalysts.