AnOxygenReductionElectrocatalystBasedonCarbonNanotube–NanographeneComplexes英文书.pdf

ARTICLES PUBLISHED ONLINE: 27 MAY 2012 | DOI: 10.1038/NNANO.2012.72 An oxygen reduction electrocatalyst based on carbon nanotube–graphene complexes Yanguang Li1, Wu Zhou2,3, Hailiang Wang1, Liming Xie1, Yongye Liang1, Fei Wei4, Juan-Carlos Idrobo3,2, Stephen J. Pennycook3,2 and Hongjie Dai1* 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. There has been an intense search for ef?cient, durable and inexpensive alternatives to precious-metal electrocatalysts such as platinum (and its alloys) for the oxygen reduction reaction (ORR) in acidic media for proton-exchange membrane fuel cells1–5. For example, much has been done to produce metal(for example, iron