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year-2014

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Publications during 2014

Article Reference Control of Carbon Nanotube Electronic Properties by Lithium Cation Intercalation
We show that the electronic properties of single walled carbon nanotubes (SWCNTs) can be tuned continuously from semiconducting to metallic by varying the location of ions inside the tubes. Focusing on the Li+ cation inside the (26,0) zigzag semiconducting and (15,15) armchair metallic SWCNTs, we found that the Li+-SWCNT interaction is attractive. The interaction is stronger for the metallic SWCNT, indicating in particular that metallic tubes can enhance performance of lithium-ion batteries. The electronic properties of the metallic SWCNT are virtually independent of the presence of ions: Li+ creates an energy level in the valence band slightly below the Fermi energy. On the contrary, the semiconducting SWCNT can be made metallic by placing ions close to the tube axis: Li+ generates a new bottom of the conduction band. Letting the ions approach SWCNT walls recovers the semiconducting behavior.
Article Reference Cu/ZnO nanocatalysts in response to environmental conditions: surface morphology, electronic structure, redox state and CO2 activation
Methanol synthesis is one of the landmarks of heterogeneous catalysis due to the great industrial significance of methanol as a clean liquid fuel and as a raw material for industry. Understanding in atomistic detail the properties of the underlying metal/oxide catalyst materials as a function of temperature and composition of the reactive gas phase is of utmost importance in order to eventually improve the production process. By performing extensive density functional theory based slab calculations in combination with a thermodynamic formalism we establish an atomistic understanding of gas phase-induced changes of surface morphology, redox properties and reactivity of ZnO supported Cu nanocatalysts. Extending our recent insights [Phys. Rev. Lett., 2013, 110, 086108], we explore surface stabilization mechanisms and site-dependent redox states of both catalyst components as well as the pronounced electronic charge transfer processes across the metal-support interface. Moreover, ab initio molecular dynamics simulations unveil the vital role played by dynamical shape fluctuations of the deposited Cu8 cluster. The pronounced structural flexibility of the metal nanoparticle is found to enhance CO2 activation over Cu8 at the elevated temperature conditions of the industrial methanol synthesis process, in addition to activation of CO2via electronic charge transfer from the ZnO support.
Article Reference Methanol synthesis on ZnO(0001¯). IV. Reaction mechanisms and electronic structure
 
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