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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) S-corner and (b) Mo-corner of MoS2/Graphene nanocontact.The optimized structures of initial, transition, and final structures along the paths are also plotted. The curves serve to guide the eye.
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f5: Calculated energy profile involved in the recombination of 2H on (a) S-corner and (b) Mo-corner of MoS2/Graphene nanocontact.The optimized structures of initial, transition, and final structures along the paths are also plotted. The curves serve to guide the eye.

Mentions: The activation energies for the recombination and release of hydrogen were determined to be 1.40 and 2.10 eV, respectively, for highly trapped S and Mo corners in the case of MoS2/graphene substrate. The hydrogen atoms at the S corner stay bound to different S atomic sites initially. As shown in Figure 5, when they start to react, one of the H atoms remains bonded to the S corner site while the other migrates to a nearby Mo neighbour. The subsequent reaction process involves both H atoms breaking from the bonded sites and the H2 molecule is assumed to form, but has slightly higher energy than the initial structure. From the Mo-corner site, the two H atoms are initially bound to the same corner Mo atom. The meta-stable product on the potential energy surface, that is 0.22 eV more stable than the physically bonded H2, consists of two H atoms located on bridge positions near the Mo corner site, with H-H optimized distances around 0.78 Å. Along the further reaction pathway, the H–H bond length starts to decrease to a final equilibrium value of 0.75 Å.


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) S-corner and (b) Mo-corner of MoS2/Graphene nanocontact.The optimized structures of initial, transition, and final structures along the paths are also plotted. 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

f5: Calculated energy profile involved in the recombination of 2H on (a) S-corner and (b) Mo-corner of MoS2/Graphene nanocontact.The optimized structures of initial, transition, and final structures along the paths are also plotted. The curves serve to guide the eye.
Mentions: The activation energies for the recombination and release of hydrogen were determined to be 1.40 and 2.10 eV, respectively, for highly trapped S and Mo corners in the case of MoS2/graphene substrate. The hydrogen atoms at the S corner stay bound to different S atomic sites initially. As shown in Figure 5, when they start to react, one of the H atoms remains bonded to the S corner site while the other migrates to a nearby Mo neighbour. The subsequent reaction process involves both H atoms breaking from the bonded sites and the H2 molecule is assumed to form, but has slightly higher energy than the initial structure. From the Mo-corner site, the two H atoms are initially bound to the same corner Mo atom. The meta-stable product on the potential energy surface, that is 0.22 eV more stable than the physically bonded H2, consists of two H atoms located on bridge positions near the Mo corner site, with H-H optimized distances around 0.78 Å. Along the further reaction pathway, the H–H bond length starts to decrease to a final equilibrium value of 0.75 Å.

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.