| 1. |
- Wang, Yang, et al.
(författare)
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Role of point defects on the reactivity of reconstructed anatase titanium dioxide (001) surface
- 2013
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4, s. 2214-
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Tidskriftsartikel (refereegranskat)abstract
- The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. The anatase TiO2(001) and its (1 x 4) reconstructed surfaces were theoretically considered to be the most reactive and have been heavily pursued by synthetic chemists. However, the lack of direct experimental verification or determination of the active sites on these surfaces has caused controversy and debate. Here we report a systematic study on an anatase TiO2(001)-(1 x 4) surface by means of microscopic and spectroscopic techniques in combination with first-principles calculations. Two types of intrinsic point defects are identified, among which only the Ti3+ defect site on the reduced surface demonstrates considerable chemical activity. The perfect surface itself can be fully oxidized, but shows no obvious activity. Our findings suggest that the reactivity of the anatase TiO2(001) surface should depend on its reduction status, similar to that of rutile TiO2 surfaces.
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| 2. |
- Cao, Lina, et al.
(författare)
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Atomically dispersed iron hydroxide anchored on Pt for preferential oxidation of CO in H-2
- 2019
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Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 565:7741, s. 631-635
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Tidskriftsartikel (refereegranskat)abstract
- Proton-exchange-membrane fuel cells (PEMFCs) are attractive next-generation power sources for use in vehicles and other applications(1), with development efforts focusing on improving the catalyst system of the fuel cell. One problem is catalyst poisoning by impurity gases such as carbon monoxide (CO), which typically comprises about one per cent of hydrogen fuel(2-4). A possible solution is on-board hydrogen purification, which involves preferential oxidation of CO in hydrogen (PROX)(3-7). However, this approach is challenging(8-15) because the catalyst needs to be active and selective towards CO oxidation over a broad range of low temperatures so that CO is efficiently removed (to below 50 parts per million) during continuous PEMFC operation (at about 353 kelvin) and, in the case of automotive fuel cells, during frequent cold-start periods. Here we show that atomically dispersed iron hydroxide, selectively deposited on silica-supported platinum (Pt) nanoparticles, enables complete and 100 per cent selective CO removal through the PROX reaction over the broad temperature range of 198 to 380 kelvin. We find that the mass-specific activity of this system is about 30 times higher than that of more conventional catalysts consisting of Pt on iron oxide supports. In situ X-ray absorption fine-structure measurements reveal that most of the iron hydroxide exists as Fe-1(OH)(x) clusters anchored on the Pt nanoparticles, with density functional theory calculations indicating that Fe-1(OH)(x)-Pt single interfacial sites can readily react with CO and facilitate oxygen activation. These findings suggest that in addition to strategies that target oxide-supported precious-metal nanoparticles or isolated metal atoms, the deposition of isolated transition-metal complexes offers new ways of designing highly active metal catalysts.
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| 3. |
- Chen, Lan, et al.
(författare)
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Mechanism for negative differential resistance in molecular electronic devices : Local orbital symmetry matching
- 2007
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 99:14
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Tidskriftsartikel (refereegranskat)abstract
- A new mechanism for negative differential resistance (NDR) originating from local orbital symmetry matching between an electrode and a molecule in a single molecular electronic device is proposed and demonstrated by a joint experimental and theoretical scanning tunneling microscope study of a cobalt phthalocyanines (CoPc) molecule on a gold substrate. For two different metal tips used, Ni and W, NDR occurs only with Ni tips and shows no dependence on the geometrical shape of the tip. Calculations reveal that such a behavior is a result of local orbital symmetry matching between the Ni tip and Co atom.
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| 4. |
- Feng, Feng, et al.
(författare)
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Room-temperature large magnetic-dielectric coupling in new phase anatase VTiO4
- 2013
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Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 49:89, s. 10462-10464
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Tidskriftsartikel (refereegranskat)abstract
- The synthetic new-phase VTiO4, as a new solid solution structure of anatase type, brings a large magnetodielectric ratio (Delta epsilon/epsilon(0)) of 7.2% at 300 K, representing a new simple-oxide structural catalogue exhibiting a room-temperature large magnetic-dielectric effect.
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| 5. |
- Feng, Jun, et al.
(författare)
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Giant Moisture Responsiveness of VS2 Ultrathin Nanosheets for Novel Touchless Positioning Interface
- 2012
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Ingår i: Advanced Materials. - : Wiley. - 0935-9648 .- 1521-4095. ; 24:15, s. 1969-1974
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Tidskriftsartikel (refereegranskat)abstract
- Utilizing a thin film of VS2 ultrathin nanosheets with giant and fast moisture responsiveness, a brand-new model of moisture-based positioning interface is put forward here, by which not only the 2D position information of finger tips can be acquired, but also the relative height can be detected as the third dimensionality, representing a promising platform for advanced man-machine interactive systems.
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| 6. |
- Fu, Qiang, et al.
(författare)
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First-principles calculations of adsorption and dehydrogenation of trans-2-butene molecule on Pd(110) surface
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:15
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption and dehydrogenation processes of trans-2-butene molecule on the Pd(110) surface have been studied by density functional theory calculations. Different adsorption configurations of the reactant, the dehydrogenated product, and the most favorable reaction pathway have been determined. The calculated energy barrier agrees well with the value deduced from experiments. It is found that the reactant molecule must undergo a rotation before the C-H bond cleavage, and surface Pd atoms are involved in the dehydrogenation reaction through the formation of the Pd-C-H three-membered metallacycle. Our calculations have not only provided reliable interpretation for various experimental observations but also shed more light on the dynamics of the reaction processes.
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| 7. |
- Fu, Qiang, et al.
(författare)
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Mechanism for tautomerization induced conductance switching of naphthalocyanin molecule
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 95:18
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Tidskriftsartikel (refereegranskat)abstract
- Reaction mechanism for tautomerization process of a single naphthalocyanin molecule has been studied using density functional theory. It is found that tautomerization of the naphthalocyanin molecule is not a concerted reaction, but a step-wise process in that one hydrogen atom transfers after another. A stable intermediate state and the possible transition state of the reaction processes have been located. The occurrence of the intermediate state suggests that the tautomerization induced conductance switching involves four conductance states with different conductances, and the earlier proposed two-state system model is not valid.
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| 8. |
- Fu, Qiang, et al.
(författare)
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Understanding the concept of randomness in inelastic electron tunneling excitations
- 2010
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 12:38, s. 12012-12023
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Tidskriftsartikel (refereegranskat)abstract
- Inelastic electron tunneling excitation has been realized in the last decade as an effective way to probe reliably detailed atomic structures and control precisely behaviors of surface adsorbates at a single molecule level. A good understanding of rich and complex processes on the surface under inelastic electron excitations is of great importance, not only from a fundamental scientific point of view but also for potential practical applications. In this perspective paper, we give an overview of recent developments on excitations and characterizations of inelastic electron tunneling processes in surface adsorbates and molecular junctions. Special attention has been paid to the understanding of the randomness of the processes. A recently proposed general statistical model is introduced which has resolved a long-standing puzzle concerning the experimentally observed non-integer power law relationship between the rate of molecular conformation changes and the tunneling current. The success of the new model is highlighted by its applications for molecular switches.
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| 9. |
- Hao, Ren, et al.
(författare)
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Simulation of inelastic electronic tunneling spectra of adsorbates from first principles
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 130:134707
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Tidskriftsartikel (refereegranskat)abstract
- We present first-principles simulations for inelastic electron tunneling spectra of molecules adsorbed on metal surface as measured in scanning tunneling microscopy experiments. Both elastic and inelastic tunneling processes are modeled in terms of Tersoff-Hamann approximation with a full vibration analysis at density functional theory levels. The calculated spectra of carbon oxide and acetylene molecules adsorbed on Cu(100) surface have well reproduced their experimental counterparts. The inelastic electron tunneling images of the observable vibration modes have been provided. The performance of gradient-corrected density functional is compared with that of local density functional.
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| 10. |
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