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An oxygen reduction electrocatalyst based on carbon nanotube–graphene complexes

 

1Y. Li, W. Zhou, H. Wang, L. Xie, Y. Liang, F. Wei, J.C. Idrobo, S.J. Pennycook, and H. Dai, “An oxygen reduction electrocatalyst based on carbon nanotube–graphene complexes,” Nature Nanotechnology 7, 394–400 (2012).


Text Box:
(Top) Z-contrast image of a carbon nanotube partially covered with nanosized graphene pieces, showing many heavy atoms; red circles highlight Fe atoms.  The area marked by the red square shows a region that was further characterized by EELS. (Bottom) Spectrum images showing that the nanotube-graphene material incorporates nitrogen and iron impurities.  Iron atoms are frequently observed on the edges of graphene sheets in close proximity to nitrogen species.

We show that carbon nanotube-graphene systems represent an economical technological alternative to replace platinum and its alloys in oxygen reduction reaction catalysts,1 catalysts that are essential for the reliability and performance of the next generation of fuel cells.  Aberration-corrected scanning transmission electron microscopy was used to show that graphene sheets contain extremely small amounts of iron (originated from carbon nanotube growth seeds) and nitrogen impurities, which form catalytic sites of 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 of oxygen reduction reaction catalysts, but these alternatives usually suffer from low activity and/or gradual deactivation during use.  Our nanotube-graphene system using low cost transition metal offers an attractive alternative to the use of precious metals.

This work was supported in part by a Stinehart Grant for Energy Research at Stanford from the Stanford Precourt Institute for Energy, Intel and NCEM at Lawrence Berkeley Laboratory, which was supported by the US Department of Energy (DE-AC02-05CH11231), by the National Science Foundation (DMR-0938330) (WZ), by Oak Ridge National Laboratory’s Shared Research Equipment (ShaRE) User Facility Program (JCI), which is sponsored by the Office of Basic Energy Sciences, US Department of Energy and by the Basic Energy Sciences program of the Materials Sciences and Engineering Division of the US Department of Energy (SJP).


 Oak Ridge National Laboratory