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Surface modification on MoO_2+x/Mo(110) induced by a local electric potential.

ABSTRACT: Oxygen adatoms on the MoO_2+x/Mo(110) surface are observed to be removed when a sufficiently large bias is applied between the scanning tunneling microscope tip and the surface. Experimental observations, such as the bias polarity dependence of adatom removal and the observation of an intermediate state, indicate that the adatom penetrates the surface oxide layer. Through the comparison of finite element method simulations with various experimental relationships, the electric field is concluded to be the sole contributor to adatom penetration into the surface oxide layer. The energetic barrier to this process is estimated to be approximately 0.45 eV in magnitude. Furthermore, the resolution of this phenomenon is on the atomic scale: individual adatoms can undergo surface penetration whilst their nearest neighbour adatoms, separated by 5?Å, are unaffected. The mechanism reported here has the advantages of not strongly influencing the substrate and is exceptionally localised, which can be beneficial for the synthesis of single atom devices.

SUBMITTER: Bozhko SI

PROVIDER: S-EPMC6470205 | biostudies-literature | 2019 Apr

REPOSITORIES: biostudies-literature

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Surface modification on MoO<sub>2+x</sub>/Mo(110) induced by a local electric potential.

Bozhko Sergey I SI Walshe Killian K Tulina Natalia N Walls Brian B Lübben Olaf O Murphy Barry E BE Bozhko Vladimir V Shvets Igor V IV

Scientific reports 20190417 1

Oxygen adatoms on the MoO<sub>2+x</sub>/Mo(110) surface are observed to be removed when a sufficiently large bias is applied between the scanning tunneling microscope tip and the surface. Experimental observations, such as the bias polarity dependence of adatom removal and the observation of an intermediate state, indicate that the adatom penetrates the surface oxide layer. Through the comparison of finite element method simulations with various experimental relationships, the electric field is ...[more]

PMID: 30996282

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Project description:Photo- and electrocatalytic technologies hold great promise for activating inert chemical bonds under mild conditions, but rationally selecting a more suitable method in between to maximize the performance remains an open issue, which requires a fundamental understanding of their different catalytic mechanisms. Herein, by first-principles calculations, we systematically compare the activation mechanisms for the C-H bond of the CH4 molecule on TiO2(110) under the photo- and electrocatalytic modes without or with water involved. It quantitatively reveals that the activation barrier of the C-H bond decreases dramatically with a surprising 74% scale by photoexcitation relative to that in thermocatalysis (1.12 eV), while the barrier varies with a maximum promotion of only 5% even under -1 V/Å external electric field (EEF). By detailed geometric/electronic analysis, the superior photocatalytic activity is traced to the highly oxidative lattice Obr •- radical excited by a photohole (h +), which motivates the homolytic C-H bond scission. However, under EEF from -1 V/Å to 1 V/Å, it gives a relatively mild charge polarization on the TiO2(110) surface region and thus a limited promotion for breaking the weakly polar C-H bond. By contrast, in the presence of water, we find that EEF can facilitate CH4 activation indirectly assisted by the surface radical-like OH* species from the oxidative water cleavage at high oxidative potential (>1.85 V vs SHE), which explains the high energy cost to drive electrocatalytic CH4 conversion in experiment. Alternatively, we demonstrate that more efficient CH4 activation could be also achieved at much lower oxidative potential when integrating the light irradiation. In such a circumstance, EEF can not only promote the h + accumulation at the catalyst surface but also help H2O deprotonation to form hydroxide, which can serve as an efficient hole-trapper to generate OH• radical (OH- + h + → OH•), unveiling an interesting synergistic photoelectrocatalytic effect. This work could provide a fundamental insight into the different characteristics of photo- and electrocatalysis in modulating chemical bond cleavage.

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Surface modification on MoO_2+x/Mo(110) induced by a local electric potential.

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Surface modification on MoO<sub>2+x</sub>/Mo(110) induced by a local electric potential.

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Surface modification on MoO2+x/Mo(110) induced by a local electric potential.

Publications

Surface modification on MoO<sub>2+x</sub>/Mo(110) induced by a local electric potential.

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OmicsDI is part of the ELIXIR infrastructure

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Surface modification on MoO_2+x/Mo(110) induced by a local electric potential.