Engineering, Mechanical Engineering, Catalysis and Reaction Engineering
We demonstrate a new strategy for tuning the size of large-diameter and few-walled nitrogen-doped carbon nanotubes (N-CNTs) from 50 to 150 nm by varying the transition metal (TM = Fe, Co, Ni or Mn) used to catalyze graphitization of dicyandiamide. Fe yielded the largest tubes, followed by Co and Ni, while Mn produced a clot-like carbon morphology. We show that morphology is correlated with electrocatalytic activity for the oxygen reduction reaction (ORR). A clear trend of Fe > Co > Ni > Mn for the ORR catalytic activity was observed, in both alkaline media and more demanding acidic media. The Fe-derived N-CNTs exhibited the highest BET (∼870 m2 g−1) and electrochemically accessible (∼450 m2 g−1) surface areas and, more importantly, the highest concentration of nitrogen incorporated into the carbon planes. Thus, in addition to the intrinsic high activity of Fe-derived catalysts, the high surface area and nitrogen doping contribute to high ORR activity. This work, for the first time, demonstrates size-controlled synthesis of large-diameter N-doped carbon tube electrocatalysts by varying the metal used in N-CNT generation. Electrocatalytic activity of the Fe-derived catalyst is already the best among studied metals, due to the high intrinsic activity of possible Fe–N coordination. This work further provides a promising route to advanced Fe–N–C nonprecious metal catalysts by generating favorable morphology with more active sites and improved mass transfer.
Published in Nanoscale, Volume 7, Issue 47, 2015, pages 20290-20298.
© Nanoscale, 2015, Royal Society of Chemistry
Wang, X., Li, Q., Pan, H., Lin, Y., Ke, Y., Sheng, H., Swihart, M. T., Wu, G. (2015). Size-Controlled Large-Diameter and Few-Walled Carbon Nanotube Catalysts for Oxygen Reduction. Nanoscale, 7(47), 20290-20298.