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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.


Calculated energy profile involved in the recombination of 2H on (a) Mo-edge and (b) S-edge of MoS2 nanolayer as supported on graphene sheet (red curve) and isolated (black curve) for comparison.The optimized structures of selective images along the energy path for MoS2/graphene nanocontact are also plotted in the inset. The curves serve to guide the eye.
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f4: Calculated energy profile involved in the recombination of 2H on (a) Mo-edge and (b) S-edge of MoS2 nanolayer as supported on graphene sheet (red curve) and isolated (black curve) for comparison.The optimized structures of selective images along the energy path for MoS2/graphene nanocontact are also plotted in the inset. The curves serve to guide the eye.

Mentions: In Figure 4, we show the minimum energy profile along the H recombination path at the a) Mo and b) S edge sites for the isolated and attached MoS2 nanolayer, relative to the energy of the initial structure in each case. The detailed atomic configurations of the initial state, a number of intermediate states, and the final state are also plotted. For two H atoms on the Mo-edge, the global process is exothermic with an activation barrier around 0.17 eV for the free-standing MoS2 nanolayer and 0.11 eV for the attached nanolayer. During the reaction path the first step is a rotation of one H atom on the S site followed by a later migration to a high coordination number inner Mo atom of the nanolayer. After overcoming an energy barrier in the subsequent step, we found both H atoms are situated above the nanolayer and come closer to each other. The distance between them decreases to 0.75 Å in the final state, indicating that an H-H bond is formed. The lower barrier of H recombination from the Mo edge on attached MoS2 could be due to the nanocontact-induced diminishment of metallic states on filling the antibonding 2π* orbital of formed H2. We note that the final energy of the H2 on the substrate is lower than the separated substrate and H2, which might suggest that it remains bound at low temperatures.


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)

Calculated energy profile involved in the recombination of 2H on (a) Mo-edge and (b) S-edge of MoS2 nanolayer as supported on graphene sheet (red curve) and isolated (black curve) for comparison.The optimized structures of selective images along the energy path for MoS2/graphene nanocontact are also plotted in the inset. The curves serve to guide the eye.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Calculated energy profile involved in the recombination of 2H on (a) Mo-edge and (b) S-edge of MoS2 nanolayer as supported on graphene sheet (red curve) and isolated (black curve) for comparison.The optimized structures of selective images along the energy path for MoS2/graphene nanocontact are also plotted in the inset. The curves serve to guide the eye.
Mentions: In Figure 4, we show the minimum energy profile along the H recombination path at the a) Mo and b) S edge sites for the isolated and attached MoS2 nanolayer, relative to the energy of the initial structure in each case. The detailed atomic configurations of the initial state, a number of intermediate states, and the final state are also plotted. For two H atoms on the Mo-edge, the global process is exothermic with an activation barrier around 0.17 eV for the free-standing MoS2 nanolayer and 0.11 eV for the attached nanolayer. During the reaction path the first step is a rotation of one H atom on the S site followed by a later migration to a high coordination number inner Mo atom of the nanolayer. After overcoming an energy barrier in the subsequent step, we found both H atoms are situated above the nanolayer and come closer to each other. The distance between them decreases to 0.75 Å in the final state, indicating that an H-H bond is formed. The lower barrier of H recombination from the Mo edge on attached MoS2 could be due to the nanocontact-induced diminishment of metallic states on filling the antibonding 2π* orbital of formed H2. We note that the final energy of the H2 on the substrate is lower than the separated substrate and H2, which might suggest that it remains bound at low temperatures.

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.