TY - JOUR
T1 - Structure and stability of small H clusters on graphene
AU - Sljivancanin, Zeljko
AU - Andersen, Mie
AU - Hornekær, Liv
AU - Hammer, Bjørk
PY - 2011/5/15
Y1 - 2011/5/15
N2 - The structure and stability of small hydrogen clusters adsorbed on graphene is studied by means of density functional theory (DFT) calculations. Clusters containing up to six H atoms are investigated systematically, with the clusters having either all H atoms on one side of the graphene sheet (cis-clusters) or having the H atoms on both sides in an alternating manner (trans-clusters). The most stable cis-clusters found have H atoms in ortho- and para-positions with respect to each other (two H’s on neighboring or diagonally opposite carbon positions within one carbon hexagon), while the most stable trans-clusters found have H atoms in ortho-trans-positions with respect to each other (two H’s on neighboring carbon positions, but on opposite sides of the graphene). Very stable trans-clusters with 13–22 H atoms were identified by optimizing the number of H atoms in ortho-trans-positions and thereby the number of closed, H-covered carbon hexagons. For the cis-clusters, the associative H2 desorption was investigated. Generally, the desorption with the lowest activation energy proceeds via para-cis-dimer states, i.e., involving somewhere in the H clusters two H atoms that are positioned on opposite sites within one carbon hexagon. H2 desorption from clusters lacking such H pairs is calculated to occur via hydrogen diffusion causing the formation of para-cis-dimer states. Studying the diffusion events showed a strong dependence of the diffusion energy barriers on the reaction energies and a general odd-even dependence on the number of H atoms in the cis-clusters.
AB - The structure and stability of small hydrogen clusters adsorbed on graphene is studied by means of density functional theory (DFT) calculations. Clusters containing up to six H atoms are investigated systematically, with the clusters having either all H atoms on one side of the graphene sheet (cis-clusters) or having the H atoms on both sides in an alternating manner (trans-clusters). The most stable cis-clusters found have H atoms in ortho- and para-positions with respect to each other (two H’s on neighboring or diagonally opposite carbon positions within one carbon hexagon), while the most stable trans-clusters found have H atoms in ortho-trans-positions with respect to each other (two H’s on neighboring carbon positions, but on opposite sides of the graphene). Very stable trans-clusters with 13–22 H atoms were identified by optimizing the number of H atoms in ortho-trans-positions and thereby the number of closed, H-covered carbon hexagons. For the cis-clusters, the associative H2 desorption was investigated. Generally, the desorption with the lowest activation energy proceeds via para-cis-dimer states, i.e., involving somewhere in the H clusters two H atoms that are positioned on opposite sites within one carbon hexagon. H2 desorption from clusters lacking such H pairs is calculated to occur via hydrogen diffusion causing the formation of para-cis-dimer states. Studying the diffusion events showed a strong dependence of the diffusion energy barriers on the reaction energies and a general odd-even dependence on the number of H atoms in the cis-clusters.
M3 - Journal article
SN - 2469-9950
VL - 83
JO - Physical Review B
JF - Physical Review B
IS - 20
ER -