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

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 σ- and π-plasmon dispersion and 1s→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 π-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.