Facile growth of N-doped CNTs on Vulcan carbon and the effects of iron content on electrochemical activity for oxygen reduction reaction

In order to develop cheap electrochemical oxygen reduction reaction (ORR) catalysts, N-doped CNTs grafted on Vulcan carbon were synthesized via pyrolysis of dicyandiamide on Fe2O3/C. Various contents of iron in Fe2O3/C (0, 20, 40 and 60 wt. %) were used as supports to investigate the effects and roles of iron content on ORR. It was shown that the iron acted as a promoter for doping nitrogen into carbon; as the iron content increased, the amount of nitrogen doping also increased. TEM and element analysis results indicated that iron induced growth of CNTs and facilitated N-doping in carbon. However, further increase in iron content higher than 20 wt. % showed negative effects on the ORR activity due to a decrease of the surface area of the prepared catalysts. Hence, the catalyst with the highest performance was observed when dicyandiamide was pyrolyzed with Fe2O3/C 20 wt. % (Fe-N-C-20) and the order of activity towards ORR was Fe-N-C-20 > Fe-N-C-40 > Fe-N-C-60 > Fe-N-C-0 > Vulcan XC-72R.

► N-doped CNTs are grown onto Vulcan carbon via pyrolysis of Dicyandiamide. ► The effects of Fe (or Fe2O3) on the ORR activity are investigated. ► Iron facilitates the doping of nitrogen into carbon structure. ► The ORR activity according to Fe content shows volcano-like plot due to decreased BET area of the catalysts.