Oxygen reduction reaction activity and surface properties of nanostructured nitrogen-containing carbon

Nitrogen-containing carbon nanostructures were prepared from the decomposition of acetonitrile at 900 degrees C over silica and magnesia supports impregnated with Fe, Co, or Ni. For the carbon grown from supported Fe and Co particles, compartmentalized fibers with a stacked cup structure predominantly formed, while mostly broken multi-walled nanotubes formed from Ni particles. The fibers were purified from the support by removing silica with 1 M KOH, or removing metal particles and magnesia with 1 M HCl. Surface analysis was performed with XPS and hydrophobicity comparisons. Surface properties were related to nanostructure and edge plane exposure. Activity for the ORR was highest over CN, fibers grown from supported Fe and Co particles, which may also be related to edge plane exposure, and not necessarily to the presence of metal contamination. The most active materials were generally the most selective catalysts as well. Moreover, from Tafel plot slopes a trend was observed depending on the precursor metal used to prepare the CTI,. The magnitude of the Tafel slope was smallest for the samples prepared from Fe or Co precursors. Compared to a state-of-the-art platinum catalyst, the most active alternative non-noble metal catalysts had less than 100 mV potential drop difference, high selectivity for complete oxygen reduction, a similar Tafel slope, and good electrical conductivity. (c) 2006 Elsevier B.V. All rights reserved.