Stability of hydrogenation states of graphene and conditions for hydrogen spillover

Sang Soo Han, Hyun Jung, Dong Hyun Jung, Seung-Hoon Choi, and Noejung Park

Phys. Rev. B 85, 155408 – Published 4 April 2012

Abstract

The hydrogen spillover mechanism has been discussed in the field of hydrogen storage and is believed to have particular advantage over the storage as metal or chemical hydrides. We investigate conditions for practicality realizing the hydrogen spillover mechanism onto carbon surfaces, using first-principles methods. Our results show that contrary to common belief, types of hydrogenation configurations of graphene (the aggregated all-paired configurations) can satisfy the thermodynamic requirement for room-temperature hydrogen storage. However, the peculiarity of the paired adsorption modes gives rise to a large kinetic barrier against hydrogen migration and desorption. It means that an extremely high pressure is required to induce the migration-derived hydrogenation. However, if mobile catalytic particles are present inside the graphitic interstitials, hydrogen migration channels can open and the spillover phenomena can be realized. We suggest a molecular model for such a mobile catalyst which can exchange hydrogen atoms with the wall of graphene.

Received 23 October 2010

DOI:https://doi.org/10.1103/PhysRevB.85.155408

Authors & Affiliations

Sang Soo Han¹, Hyun Jung², Dong Hyun Jung^3,*, Seung-Hoon Choi³, and Noejung Park^2,†

¹Korea Research Institute of Standards and Science, Daejon, 305-340, Korea
²Interdisciplinary School of Green Energy and Low Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Korea
³Insilicotech Co., Ltd., C602, Korea Bio Park, 694-1, Sampyeong-dong, Seongnam-si, Gyeonggi-do 463-400, Korea

^*Corresponding author: dhjung@insilicotech.co.kr
^†Corresponding author: noejung@unist.ac.kr

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Issue

Vol. 85, Iss. 15 — 15 April 2012

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Images

Figure 1
(a) Schematic description of the hydrogen spillover process. C and R indicate the catalytic metal island and the receptor surface, respectively. (b) Chemical potential (eV) of H $_{2}$ gas with respect to the zero-temperature static energy of the H $_{2}$ molecule. (c) Static chemisorption binding energy (eV) per H $_{2}$ onto graphene. The energy reference is with respect to pristine graphene and an isolated H $_{2}$ molecule. The inset shows the chemisorption geometry of 24 hydrogen atoms in the chairlike aggregated configuration. Small (pink) balls represent hydrogen atoms. The carbon atoms to which hydrogen atoms are attached are described with larger gray balls. Other parts of the graphene are denoted only with the wire frame.Reuse & Permissions
Figure 2
Models for the chemisorbed hydrogen dimers on the graphene plane. The (uu) in (a)–(d) indicate that two hydrogen adatoms are on the up side of the plane. The same dimer configurations with one hydrogen adatom on the up and the other one on the down side, as depicted with (ud), are shown in (e)–(h). The total energy differences (eV) are given with respect to the case of ortho(ud). Atomic symbols follow the same convention as in Fig. 1.Reuse & Permissions
Figure 3
Energy barriers along the desorption of H $_{2}$ from (a) the meta-dimer configuration, (b) the unpaired chairlike four hydrogen adatoms, and (c) the paired chairlike six hydrogen adatoms configuration. (d) The migration barrier for one unpaired hydrogen atom from the IS of (b). IS, FS, and TS represent the initial state, final state, and transition state, respectively. The geometries of each IS and FS are shown in the left and right panels of each energy curve. The dashed curves connecting IS, FS, and TS are only for guide. Atomic symbols follow the same convention used in Fig. 1.Reuse & Permissions
Figure 4
The optimized geometries of 24 hydrogen adatoms in (a) all-paired aggregated chairlike configuration, (b) one-hydrogen-migrated, and (c) two-hydrogen-migrated configurations, respectively. (d),(e), and (f) correspond to the same configurations of 54 hydrogen adatoms, respectively. The energies denoted in (b) and (c) are with respect to that of (a), and those shown in (e) and (f) are with respect to that of (d). Atomic symbols follow the same convention used in Fig. 1. In (b), (c), (e), and (f), the carbon atoms from which hydrogen atoms migrated are emphasized with a different gray scale (blue).Reuse & Permissions
Figure 5
The energy barrier along the migration of (a) one and (b) two hydrogen adatoms from the edge of a paired chairlike hydrogenated domain. The atomic symbols and abbreviations follow the same convention used in Fig. 4.Reuse & Permissions
Figure 6
Hydrogen exchange between BH $_{4}^{-}$ and graphene. (a) Optimized geometry of BH $_{4}^{-}$ anion on graphene. (b) The energy barrier along the hydrogen transfer from BH $_{4}^{-}$ to graphene. (c) The optimized geometry after one hydrogen atom transferred onto graphene. The abbreviation IS, TS, FS indicate initial states, transition state, and final state, respectively. Inset of (b) shows the TS.Reuse & Permissions

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