Characterization of hydrogen absorption/desorption states on lithium-carbon-hydrogen system by neutron diffraction
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The nanostructural hydrogenated graphite (CnanoHx) was synthesized from graphite by ball milling under hydrogen (H2) atmosphere. In this product, characteristic hydrogenated states in the form of polarized hydrocarbon groups (―CH, ―CH2, and ―CH3) are realized in the nanoscale. By synthesizing the composite of CnanoHx and lithium hydride (LiH), known as the Li―C―H system, hydrogen was desorbed at 350 °C, which is a lower temperature compared to the decomposition temperature of each component. It is considered that this hydrogen desorption would be induced by destabilization of each hydrogen absorbed state due to an interaction between the polarized C―H groups in CnanoHx and LiH. Therefore, in order to understand the hydrogen absorption/desorption mechanism of the Li―C―H system, it is an important issue to investigate the change in the C―H groups during hydrogen absorption/desorption reactions in the composite. The correlations among atoms contained in this composite are examined by neutron diffraction measurements, where the protium/deuterium (H/D) isotopic substitution was used to clarify the location of hydrogen atoms in this composite. Some C―D and Li―D correlations are found from the radial distribution function [RDF(r)] obtained by the neutron diffraction for the CnanoDx and LiD composite. After dehydrogenation, C―C triple bond and Li―C bond, ascribed to lithium carbide (Li2C2), are observed. Furthermore, the RDF(r) corresponding to rehydrogenated composite indicates the presence of not only the Li―D correlation but also the C―D one.
Journal of Applied Physics
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American Institute of Physics
Copyright 2008 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Appl. Phys. 104, 053511 and may be found at http://dx.doi.org/10.1063/1.2956504.
Graduate School of Advanced Sciences of Matter
Institute for Advanced Materials Research