Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy Analysis of Hydrogenated Nanostructured Graphite Prepared by Mechanical Milling

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Hydrogen trapping sites in hydrogenated nanostructured graphite (HNG) prepared by mechanical milling under hydrogen atmosphere were intensively studied with transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Measurements of $\sigma$- and $\pi$-plasmon dispersion and $1s\rightarrow 2p^{*}$ excitation spectra of the graphitic matrix suggested the existence of at least two types of hydrogen trapping states: one was the conventional C–H covalent bond, and the other was related to the $\pi$-orbitals of the carbon atoms extending normal to the graphene layers. We found that iron carbide particles incorporated as contamination during the mechanical milling also stored a significant amount of hydrogen, as revealed by the change in the Fe-$L_{2,3}$ spectrum when the sample was annealed. We re-assigned the assumed hydrogen trapping sites to the hydrogen desorption peaks in the thermal desorption spectrum (TDS) based on these experimental results.
2005-04-15