Journal
NATURE NANOTECHNOLOGY
Volume 7, Issue 6, Pages 394-400Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/NNANO.2012.72
Keywords
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Funding
- Stanford Precourt Institute for Energy
- Intel
- NCEM at Lawrence Berkeley Laboratory
- US DOE [DE-AC02-05CH11231]
- NSF [DMR-0938330]
- Oak Ridge National Laboratory's Shared Research Equipment (ShaRE) User Facility
- Office of Basic Energy Sciences, US Department of Energy
- Materials Sciences and Engineering Division of the US DOE
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0938330] Funding Source: National Science Foundation
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Oxygen reduction reaction catalysts based on precious metals such as platinum or its alloys are routinely used in fuel cells because of their high activity. Carbon-supported materials containing metals such as iron or cobalt as well as nitrogen impurities have been proposed to increase scalability and reduce costs, but these alternatives usually suffer from low activity and/or gradual deactivation during use. Here, we show that few-walled carbon nanotubes, following outer wall exfoliation via oxidation and high-temperature reaction with ammonia, can act as an oxygen reduction reaction electrocatalyst in both acidic and alkaline solutions. Under a unique oxidation condition, the outer walls of the few-walled carbon nanotubes are partially unzipped, creating nanoscale sheets of graphene attached to the inner tubes. The graphene sheets contain extremely small amounts of irons originated from nanotube growth seeds, and nitrogen impurities, which facilitate the formation of catalytic sites and boost the activity of the catalyst, as revealed by atomic-scale microscopy and electron energy loss spectroscopy. Whereas the graphene sheets formed from the unzipped part of the outer wall of the nanotubes are responsible for the catalytic activity, the inner walls remain intact and retain their electrical conductivity, which facilitates charge transport during electrocatalysis.
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