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A theoretical method for finding active alloy electrocatalysts is proposed, and the method is applied to the electrochemical half-cell reaction of reducing oxygen to water, which is vital for improving the efficiency of, for example, hydrogen fuel cells. Our method predicts adsorption energies between reaction intermediates and the alloy surface to discover which sites on the surface are the most active. Starting from the multicomponent alloy IrPdPtRhRu, the alloy composition with best predicted catalytic activity is found.

Multifunctional material brings many interesting issues because of various potential device applications. Using first principles calculations, we predict that the graphitic carbon nitride (g-C4N3) nanotubes can display multifunctional properties for both spintronics and optical device applications. Very interestingly, armchair tubes (n, n) with n = 2, 3, 4, 5, 6 and (5, 0) zigzag tubes are found to be half metallic, while zigzag tubes (n, 0) with n = 4, 6 show an antiferromagnetic ground state with band gaps. However, larger zigzag tubes of (7, 0), (8, 0), and (10, 0) are turned out to be half metallic. Along with the half metallic behavior of the tubes, those tubes seem to be optically transparent in the visible range. Due to these magnetic and optical properties, we suggest that the g-C4N3 nanotubes (CNNTs) can be used for both ideal spintronics and transparent electrode materials. We also explored the stability of magnetic state and nanotube structure using ab initio molecular dynamics. The CNNTs were found to be thermally stable and the magnetic moment was robust against the structural deformation at 300 K. Overall, our theoretical prediction in one dimensional CNNTs may provide a new physics in spintronics and also in other device applications because of potential multifunctional properties.

Scientific Reports 4 doi: 10.1038/srep06059

Publication date: November 2014
Source:Carbon, Volume 78
Author(s): Kaoru Sugano , Masashi Kurata , Hiroyuki Kawada
Carbon nanotubes (CNTs) with superior mechanical properties have been of interest as reinforcement for polymer composites. However, the length of individual CNTs is limited. As a solution, yarns spun by twisting together multi-walled carbon nanotubes (MWCNTs) have been reported. In this study, untwisted CNT yarns were prepared by a non-conventional method drawing CNTs through a die. The MWCNTs in these yarns are held together by strong van der Waals forces that arise due to the interactions on the long and smooth surfaces of the MWCNTs. Here, mechanical properties of untwisted CNT yarn were studied by tensile tests. The strength of the CNT yarn was increased by increasing the apparent density of the yarn. The CNT yarns showed high tensile strength of 1GPa and elastic modulus of 79GPa at a yarn diameter of 35μm. The interfacial shear strength between the CNT yarn and epoxy resin was studied by the microdroplet method, and it was very low. The wettability of the CNT yarn was affected by a type of curing agent. A unidirectional composite of epoxy resin and CNT yarn was prepared by the pultrusion molding method. Mechanical properties of the unidirectional composite were affected by the type of curing agent.

Publication date: November 2014
Source:Carbon, Volume 78
Author(s): Hoël Guerin , Hélène Le Poche , Roland Pohle , Laurent Syavoch Bernard , Elizabeth Buitrago , Raphaël Ramos , Jean Dijon , Adrian M. Ionescu
This paper reports the successful experimental demonstration of the localized growth of horizontal, dense carbon nanotube (CNT) arrays in situ and at the wafer scale. The selectivity and directionality of the CNT catalytic growth process along with the adequate design and fabrication of the catalyst support enables the direct integration of nanotubes arrays into heterogeneous devices. This novel CNT integration method is developed to manufacture conductance based gas sensors for ammonia detection and is demonstrated to produce a yield above 90% at the wafer scale. Owing to its flexibility, the integration process can be useful for a wide range of applications and complies with industrial requirements in terms of manufacturability and yield, requirements for the acceptance of CNTs as alternate materials. A state-of-the-art CNT array resistivity of 1.75×10⁻⁵ Ωm has been found from the CNT characterization. When exposed to low NH3 concentrations, the CNT sensors show good repeatability, long-term stability, and high design robustness and tackle the reproducibility challenge for CNT devices. Individual device calibration is not needed. The ammonia adsorption isotherm on the sensor is well fitted by Freundlich equation. The extrapolated detection limit is about 1ppm. The dependence of the sensitivity with temperature indicates that ammonia sensing is likely to involve an endothermic process. Finally, relative humidity cross sensitivity has been found to have no adverse effect on the ammonia response enabling NH3 monitoring in ambient conditions.

Article

There is strong interest in carbon nanotube assemblies for a variety of applications, many of which require combined high mechanical and electrical properties. Here, the authors demonstrate a rolling technique for performance improvement, reporting tensile strength of 4.34 GPa, ductility of 10% and electrical conductivity of 2.0 × 10 4  S cm −1 .

Nature Communications doi: 10.1038/ncomms4848

Authors: J. N. Wang, X. G. Luo, T. Wu, Y. Chen