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Origin of nanopores in graphene-based carbon materials

Junjie Guo, James R. Morris, Yungok Ihm, Cristian I. Contescu, Nidia C. Gallego, Gerd Duscher, Stephen J. Pennycook, and Matthew F. Chisholm, Small 8, 3283-3288, (2012).

Research at ORNL was supported by the Materials Science and Engineering Division, Office of Basic Energy Science, U. S. Department of Energy.


The hexagonal lattice of coplanar carbon atoms interrupted by interconnected 5- and 7- atom defects (marked in red) is clearly resolved in ADF STEM image of nanoporous carbon. The corrugated structure generated by atomic level simulations contains random sequences of topological defects identified in the electron microscopy image.

 

Using aberration-corrected low voltage scanning transmission electron microscopy combined with simulations, we show that nanoporous carbons comprise wrinkled, defective sheets of graphene. The wrinkling arises from the presence of correlated 5- and 7- fold defects that buckles the sheets creating porosity.

Nanoporous carbons are of remarkable scientific interest for their high surface area and large internal porosity, which are attractive features for numerous applications ranging from hydrogen or natural gas storage for transportation applications, gas separation and purification through molecular sieving, and electrochemical energy storage in supercapacitors. In the paper published in Small, the researchers at Oak Ridge National Laboratory demonstrate that disordered, three-dimensional carbon atom networks in nanoporous carbons consist of wrinkled one atom-thick graphene sheets that frequently contain large domains of correlated topological defects in the form of 5- and 7-atom rings. Combined results from atomic resolution electron microscopy and molecular dynamics simulation show that non-hexagonal defects in graphene sheets give rise to sheet corrugation, which consequently affects the stacking of graphitic layers and determines macroscopically measurable properties such as surface area, pore volume distribution, gas adsorption capacity and molecular sieving selectivity. By understanding the origin of the porosity we expect to be able to tailor future properties through selective processing and doping.


 Oak Ridge National Laboratory