Effect of Expanded Graphite Lattice in Exfoliated Graphite Nanofibers on Hydrogen Storage
A graphite exfoliation technique, using intercalation of a concentrated sulfuric/nitric acid mixture followed by a thermal shock, has successfully exfoliated a herringbone graphite nanofiber (GNF). The exfoliated GNF retains the overall nanosized dimensions of the original GNF, with the exfoliation temperature determining the degree of induced defects, lattice expansion, and resulting microstructure. High-resolution transmission electron microscopy indicated that the fibers treated at an intermediate temperature of 700 °C for 2 min had dislocations in the graphitic structure and a 4% increase in graphitic lattice spacing to 3.5 Å. The fibers treated at 1000 °C for 36 h were expanded along the fiber axis, with regular intervals of graphitic and amorphous regions ranging from 0.5 to > 50 nm in width. The surface area of the starting material was increased from 47 m 2/g to 67 m2/g for the 700-°C treatment and to 555 m 2/g for the 1000-°C treatment. Hydrogen uptake measurements at 20 bar indicate that the overall hydrogen uptake and operative adsorption temperature are sensitive to the structural variations and graphitic spacing. The increased surface area after the 1000-°C treatment led to a 1.2% hydrogen uptake at 77 K and 20 bar, a 3-fold increase in hydrogen physisorption of the starting material. The uptake of the 700-°C-treated material had a 0.29% uptake at 300 K and 20 bar; although low, this was a 14-fold uptake over the starting material and higher than other commonly used pretreatment methods that were tested in parallel. These results suggest that selective exfoliation of a nanofiber is a means by which to control the relative binding energy of the hydrogen interaction with the carbon structure and thus vary the operative adsorption temperature.
A. D. Lueking et al., "Effect of Expanded Graphite Lattice in Exfoliated Graphite Nanofibers on Hydrogen Storage," Journal of Physical Chemistry B, vol. 109, no. 26, pp. 12710-12717, American Chemical Society (ACS), Jun 2005.
The definitive version is available at https://doi.org/10.1021/jp0512199
Chemical and Biochemical Engineering
Pennsylvania State University. Institute for the Environment
Pennsylvania State University. Energy Institute
Pennsylvania State. College of Earth and Mineral Sciences
Pennsylvania State University. H2E Center
Keywords and Phrases
Energy carrier; Graphite exfoliation techniques; Graphite lattice; High temperature treatment; Adsorption; Carbon; Coal ash; Crystal lattices; Electrodes; Graphite; Heat treatment; High resolution electron microscopy; Hydrogen; Hydrogen bonds; Phase transitions; Synthesis (chemical); Transmission electron microscopy; Nanostructured materials
International Standard Serial Number (ISSN)
Article - Journal
© 2005 American Chemical Society (ACS), All rights reserved.
01 Jun 2005