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 °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 CNx 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 CNx. 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.

Active catalysts for the oxygen reduction reaction were prepared by growing nitrogen-containing carbon nanofibers during acetonitrile pyrolysis over Fe or Co metal particles. The particles were supported by silica or magnesia, which could subsequently be removed with KOH or HCl washing, respectively. Half-cell activity testing demonstrated comparable activity to state-of-the-art platinum catalysts. The figure is a TEM image of a fiber grown over a 2-wt% Co/MgO support.Figure optionsDownload as PowerPoint slide