No abstract

Active non-metal catalysts for the Oxygen Reduction Reaction (ORR) were prepared by decomposition of acetonitrile vapor at 900°C over a pure alumina support, and supports containing 2 wt% Fe or 2 wt% Ni on alumina. The exposed alumina and metal in the samples were subsequently washed away with HF acid to purify the solid carbon material. The sample prepared with iron was the most active sample for the ORR, with only 100 mV greater overpotential than a commercial 20 wt% Pt / Vulcan Carbon catalyst. However, nitrogen-containing carbon deposited on pure alumina (which contained less than 1 ppm metal contamination) was also quite active, demonstrating that platinum or iron is not required for ORR activity. Characterization by XPS and TEM revealed that the more active samples had nanostructured carbon with more edge plane exposure than the less active tube structures formed from the nickel sample.

Noble-metal-free active catalysts for the oxygen reduction reaction (ORR) in an acidic environment were prepared from the pyrolysis of acetonitrile at 900 degrees C over alumina and metal-doped alumina. This work includes analyses of the nitrogen-doped carbon preparation process, characterization of the carbon materials formed, and activity testing for the ORR. The nitrogen-containing carbon nanostructures that formed during the pyrolysis of acetonitrile could be purified by washing the product with hydrofluoric acid. A wide range of techniques were used to characterize the solid carbon products of the acetonitrile decomposition. While the samples have many similar physical properties, X-ray photoelectron spectroscopy and transmission electron microscopy showed evidence that differences in the nanostructure and surface functional groups of the samples are likely to account for observed differences in oxygen reduction activity. The most active catalysts were prepared over alumina impregnated with up to 2 wt % Fe, although the catalysts that were prepared by acetonitrile pyrolysis over alumina with no metal doping still had significant activity. In comparison to a 20 wt % platinum on Vulcan carbon catalyst, the most active samples only have an additional 100 mV overpotential. The selectivity of the catalysts for complete oxygen reduction to water followed a trend similar to activity. The best selectivity to water versus peroxide obtained was 99%, or equivalently, an n of 3.98 (i.e., 3.98 electrons transferred out of a maximum of 4 electrons per mole of oxygen that is reduced), as determined by rotating ring-disk electrode testing.

No abstract

Catalysts for the oxygen reduction reaction were prepared from the pyrolysis of acetonitrile at 900 °C over iron particles on various supports. The iron phases present in the active materials were characterized by XRD, TEM, and Mössbauer spectroscopy. Typically, the iron particles were encased in carbon after pyrolysis, explaining how they could survive subsequent acid washes. The Fe phases present included metallic gamma iron, cementite, and two oxidized phases. Although the relative abundance of the phases varied with different supports, with treatment time, and after washing, there was no apparent correlation between the presence or abundance of a phase and activity. The phases present are consistent with Fe particles used to catalyze the formation of carbon fibers by catalytic chemical vapor deposition. After being washed with acid, there was no evidence for the presence of nitrogen-stabilized Fe sites on the carbon surface. These results support the hypothesis that Fe catalyzes the formation of ORR-active carbon nanostructures during pyrolysis at 900 °C in a carbon and nitrogen atmosphere and is not part of an active site itself.

No abstract

No abstract

No abstract