Effect of expanded graphite lattice in exfoliated graphite nanoribers on hydrogen storage

被引:83
作者
Lueking, AD [1 ]
Pan, L
Narayanan, DL
Clifford, CEB
机构
[1] Penn State Univ, Energy Inst, Dept Energy & Geoenvironm Engn, University Pk, PA 16802 USA
[2] Penn State Univ, Mat Res Inst, University Pk, PA 16802 USA
关键词
D O I
10.1021/jp0512199
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
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 degrees C for 2 min had dislocations in the graphitic structure and a 4% increase in graphitic lattice spacing to 3.5 angstrom. The fibers treated at 1000 degrees 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 m(2)/g for the 700-degrees C treatment and to 555 m(2)/g for the 1000-degrees 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-degrees 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-degrees 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.
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收藏
页码:12710 / 12717
页数:8
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