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Electronic coupling and catalytic effect on H2 evolution of MoS2/graphene nanocatalyst.

Liao T, Sun Z, Sun C, Dou SX, Searles DJ - Sci Rep (2014)

Bottom Line: Inorganic nano-graphene hybrid materials that are strongly coupled via chemical bonding usually present superior electrochemical performance.An obvious reduction of the metallic state of the MoS2 nanolayer is noticed as electrons are transferred to form a strong contact with the reduced graphene support.The easiest evolution path is from the Mo edge sites, with the presence of the graphene resulting in a decrease in the energy barrier from 0.17 to 0.11 eV.

View Article: PubMed Central - PubMed

Affiliation: 1] AIBN Centre for Theoretical and Computational Molecular Science, University of Queensland, Brisbane, QLD 4072, Australia [2] Institute for Superconducting &Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia.

ABSTRACT
Inorganic nano-graphene hybrid materials that are strongly coupled via chemical bonding usually present superior electrochemical performance. However, how the chemical bond forms and the synergistic catalytic mechanism remain fundamental questions. In this study, the chemical bonding of the MoS2 nanolayer supported on vacancy mediated graphene and the hydrogen evolution reaction of this nanocatalyst system were investigated. An obvious reduction of the metallic state of the MoS2 nanolayer is noticed as electrons are transferred to form a strong contact with the reduced graphene support. The missing metallic state associated with the unsaturated atoms at the peripheral sites in turn modifies the hydrogen evolution activity. The easiest evolution path is from the Mo edge sites, with the presence of the graphene resulting in a decrease in the energy barrier from 0.17 to 0.11 eV. Evolution of H2 from the S edge becomes more difficult due to an increase in the energy barrier from 0.43 to 0.84 eV. The clarification of the chemical bonding and catalytic mechanisms for hydrogen evolution using this strongly coupled MoS2/graphene nanocatalyst provide a valuable source of reference and motivation for further investigation for improved hydrogen evolution using chemically active nanocoupled systems.

No MeSH data available.


(a) Orbital-decomposed partial density of states for each atom in nanocontacting model. The isosurface of the electron charge density difference with the isovalue of 5.0 × 10−3 /e/Å−3 is plotted in the inset with the red region denoting the electron gain and the blue region the electron loss. (b) Total and projected density of states (TDOS/PDOS) of MoS2 nanolayer attached on graphene sheet and as the free-standing one as well. The distinctive changes are pointed out by the arrows in the top part.
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f2: (a) Orbital-decomposed partial density of states for each atom in nanocontacting model. The isosurface of the electron charge density difference with the isovalue of 5.0 × 10−3 /e/Å−3 is plotted in the inset with the red region denoting the electron gain and the blue region the electron loss. (b) Total and projected density of states (TDOS/PDOS) of MoS2 nanolayer attached on graphene sheet and as the free-standing one as well. The distinctive changes are pointed out by the arrows in the top part.

Mentions: Characterization of the electronic bonding between the MoS2 nanolayer and graphene support was carried out. As shown in Figure 2a, there are several energy levels from −8.0 eV until the Fermi level aligned at the same positions in the projected density of states (PDOS) of MoS2/graphene, and significant overlap (i.e., orbital hybridization) was found between 3p orbitals of S and 2p orbitals of C in the wave functions, also indicating a strong covalent bond is formed between the nanolayer and the support. The character of the charge redistribution between the MoS2 nanolayer and graphene sheet can be also evaluated as the difference between the electron charges of the MoS2 nanolayer and graphene sheet alone and the one formed when they are in contact, and is shown in the inset of Figure 2a. The red colour denotes gain of electrons and the blue colour denotes electron loss. The contact-induced major charge redistribution is not equally distributed among all atoms but mainly occurs in the contact region between the MoS2 nanolayer and graphene support, originating from the vacancy-mediated hybridization between the C 2p and S 3p orbitals.


Electronic coupling and catalytic effect on H2 evolution of MoS2/graphene nanocatalyst.

Liao T, Sun Z, Sun C, Dou SX, Searles DJ - Sci Rep (2014)

(a) Orbital-decomposed partial density of states for each atom in nanocontacting model. The isosurface of the electron charge density difference with the isovalue of 5.0 × 10−3 /e/Å−3 is plotted in the inset with the red region denoting the electron gain and the blue region the electron loss. (b) Total and projected density of states (TDOS/PDOS) of MoS2 nanolayer attached on graphene sheet and as the free-standing one as well. The distinctive changes are pointed out by the arrows in the top part.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4150123&req=5

f2: (a) Orbital-decomposed partial density of states for each atom in nanocontacting model. The isosurface of the electron charge density difference with the isovalue of 5.0 × 10−3 /e/Å−3 is plotted in the inset with the red region denoting the electron gain and the blue region the electron loss. (b) Total and projected density of states (TDOS/PDOS) of MoS2 nanolayer attached on graphene sheet and as the free-standing one as well. The distinctive changes are pointed out by the arrows in the top part.
Mentions: Characterization of the electronic bonding between the MoS2 nanolayer and graphene support was carried out. As shown in Figure 2a, there are several energy levels from −8.0 eV until the Fermi level aligned at the same positions in the projected density of states (PDOS) of MoS2/graphene, and significant overlap (i.e., orbital hybridization) was found between 3p orbitals of S and 2p orbitals of C in the wave functions, also indicating a strong covalent bond is formed between the nanolayer and the support. The character of the charge redistribution between the MoS2 nanolayer and graphene sheet can be also evaluated as the difference between the electron charges of the MoS2 nanolayer and graphene sheet alone and the one formed when they are in contact, and is shown in the inset of Figure 2a. The red colour denotes gain of electrons and the blue colour denotes electron loss. The contact-induced major charge redistribution is not equally distributed among all atoms but mainly occurs in the contact region between the MoS2 nanolayer and graphene support, originating from the vacancy-mediated hybridization between the C 2p and S 3p orbitals.

Bottom Line: Inorganic nano-graphene hybrid materials that are strongly coupled via chemical bonding usually present superior electrochemical performance.An obvious reduction of the metallic state of the MoS2 nanolayer is noticed as electrons are transferred to form a strong contact with the reduced graphene support.The easiest evolution path is from the Mo edge sites, with the presence of the graphene resulting in a decrease in the energy barrier from 0.17 to 0.11 eV.

View Article: PubMed Central - PubMed

Affiliation: 1] AIBN Centre for Theoretical and Computational Molecular Science, University of Queensland, Brisbane, QLD 4072, Australia [2] Institute for Superconducting &Electronic Materials, University of Wollongong, Wollongong, NSW 2500, Australia.

ABSTRACT
Inorganic nano-graphene hybrid materials that are strongly coupled via chemical bonding usually present superior electrochemical performance. However, how the chemical bond forms and the synergistic catalytic mechanism remain fundamental questions. In this study, the chemical bonding of the MoS2 nanolayer supported on vacancy mediated graphene and the hydrogen evolution reaction of this nanocatalyst system were investigated. An obvious reduction of the metallic state of the MoS2 nanolayer is noticed as electrons are transferred to form a strong contact with the reduced graphene support. The missing metallic state associated with the unsaturated atoms at the peripheral sites in turn modifies the hydrogen evolution activity. The easiest evolution path is from the Mo edge sites, with the presence of the graphene resulting in a decrease in the energy barrier from 0.17 to 0.11 eV. Evolution of H2 from the S edge becomes more difficult due to an increase in the energy barrier from 0.43 to 0.84 eV. The clarification of the chemical bonding and catalytic mechanisms for hydrogen evolution using this strongly coupled MoS2/graphene nanocatalyst provide a valuable source of reference and motivation for further investigation for improved hydrogen evolution using chemically active nanocoupled systems.

No MeSH data available.