Title

Effect of Expanded Graphite Lattice in Exfoliated Graphite Nanofibers on Hydrogen Storage

Abstract

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.

Department(s)

Chemical and Biochemical Engineering

Sponsor(s)

Pennsylvania State University.Institute for the EnvironmentPennsylvania State University.Energy InstitutePennsylvania State.College of Earth and Mineral SciencesPennsylvania State University.H2E Center

Comments

This work was funded through start-up funds proved by the Institute for the Environment, the Energy Institute, and the College of Earth and Mineral Sciences, Penn State University. Funding for exfoliation of carbon for hydrogen storage was provided, in part, by the H2E Center at Penn State University.

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)

1520-6106

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2005 American Chemical Society (ACS), All rights reserved.

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