RESUMO
A theoretical study based on density functional theory for H2O dissociation on the metal surface of Pt(111) alloyed simultaneously with Ru and Mo was performed. The determination of the minimum energy path using the climbing image nudged elastic band (CI-NEB) method shows that the dissociation reaction of H2O with this catalyst requires almost no energy cost. This dissociation reaction is not only kinetically favored but also almost thermodynamically neutral and somewhat exothermic. The electronic structure analysis showed that much more charge was released in Mo and was used to bind the adsorbed hydroxyl (OHad). Further analyses of the density of states (DOS) showed that the large number of orbitals that overlap when OH binds to Mo are responsible for the stabilization of the OH-surface bond. The stability of the OHad fragment on the surface is believed to be a descriptor for the dissociation of H2O with an almost spontaneous process.
RESUMO
The transport properties of single-walled carbon nanotubes (SWNTs) above room temperature are studied in this work. The infrared optical properties of SWNTs were investigated to clarify their conduction mechanism at high temperature. We present reflectivity spectra of SWNT mats in the infrared region between 0.08 eV and 0.8 eV under Ar gas flow at temperatures between 330 K and 840 K. These spectra have the typical appearance of the metallic reflectivity. Examination within the framework of the Drude-Lorentz model was performed to work out the electric resistivity for each reflectivity spectrum. It was found that the resistivity of SWNTs increases superlinearly with increasing the temperature from 330 K to 690 K, which can be explained by the quasi-1D metallic term model very well. However, the resistivity at higher temperatures than 690 K exhibited the tendency of saturation and deviated from the quasi-1D metallic term model. This behavior could be attributed to the thermal excitation of free carriers in the semiconducting SWNTs included in the mats.