First-principles calculations based on density functional theory was performed to analyse the structural stability of transition metal carbides TMc (TM=Ru, Rh, Pd, Os, Ir, Pt). It is observed that zinc-blende phase is...
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First-principles calculations based on density functional theory was performed to analyse the structural stability of transition metal carbides TMc (TM=Ru, Rh, Pd, Os, Ir, Pt). It is observed that zinc-blende phase is the most stable one for these carbides. Pressure-induced structural phase transition from zinc blende to NiAs phase is predicted at the pressures of 248.5 GPa, 127 GPa and 142 GPa for Osc, Irc and Ptc, respectively. The electronic structure reveals that Ruc exhibits a semiconducting behaviour with an energy gap of 0.7056eV. The high bulk modulus values of these carbides indicate that these metal carbides are super hard materials. The high B/G value predicts that the carbides are ductile in their most stable phase.
catalysts play essential roles in the chemical vapor deposition of single-wall carbon nanotubes (SWcNTs). In this article, we summarize studies on catalysts for the structure-controlled growth and mass production of S...
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catalysts play essential roles in the chemical vapor deposition of single-wall carbon nanotubes (SWcNTs). In this article, we summarize studies on catalysts for the structure-controlled growth and mass production of SWcNTs, discussing the main progress and the remaining challenges.
In the present work, the effect of grain size distribution on the diffraction profile shape is inspected via analysis of the mutual ratio of Lorentz and Gauss components in pseudo-Voigt function which is used for simu...
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In the present work, the effect of grain size distribution on the diffraction profile shape is inspected via analysis of the mutual ratio of Lorentz and Gauss components in pseudo-Voigt function which is used for simulating X-ray profiles of nanoparticles. As established from the plotted dependences, the error in the average Pt nanoparticles size determination reaches 56% and the discrepancy between calculated Pt nanoparticle surface areas attains 60%. Furthermore, the determination error becomes greater with increasing the Lorentz contribution to pseudo-Voigt function, or, in fact, with enlarging particle size distribution. The empirically found electrochemical surface area of Pt/c electrocatalyst is compared with that evaluated from XRD data using the Scherrer formula and particle size distribution data analysis.
When the size and spacing of catalyst nanoparticles are well controlled on a substrate, carbon nanotubes (cNTs) can grow and assemble into a unique, vertically aligned structure frequently called a forest. Long, align...
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When the size and spacing of catalyst nanoparticles are well controlled on a substrate, carbon nanotubes (cNTs) can grow and assemble into a unique, vertically aligned structure frequently called a forest. Long, aligned, and pure cNTs can easily be synthesized in simple or highly complex configurations. First reported in 1996, cNT forests have been shown to be unique and useful forms of cNTs, as they have spurred the development of novel processes and applications and in addition, served as test beds for investigations into cNT growth mechanisms. This article provides an overview of two decades of research in this area.
converting unstable earth-abundant group VIIIB transition metals into stable catalysts with high oxygen reduction reaction (ORR) performances remains a critical challenge for electrochemical technologies. Iron (Fe)-ni...
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converting unstable earth-abundant group VIIIB transition metals into stable catalysts with high oxygen reduction reaction (ORR) performances remains a critical challenge for electrochemical technologies. Iron (Fe)-nitrogen (N)-carbon (c)-based electrocatalysts have recently demonstrated ORR performances comparable to platinum (Pt)-based catalysts. However, as their poor stability remains a critical issue, which needs to be resolved to satisfy commercial requirements. Here, we describe a methodology for preparing a high-performance and stable Fe-based ORR catalyst. The catalyst was obtained by the in-situ sandwiching of a Fe 3+ precursor in a nitrogenated holey two-dimensional network (denoted as c 2 N). Reduction of the sandwiched Fe 3+ results in the formation of Fe oxide (Fe x O y ) nanoparticles, which are simultaneously transformed into highly crystalline Fe 0 nanoparticle cores, while the c 2 N is catalysed into well-defined, encapsulating, nitrogenated graphitic shells ( [email protected] 2 N nanoparticles) during heat-treatment. The resultant Fe 0 @c 2 N nanoparticles are uniformly distributed on the c 2 N substrate, becoming the [email protected] 2 N catalyst, which displayed ORR activities superior to commercial Pt/c in both acidic and alkaline media. Furthermore, the [email protected] 2 N catalyst remained rust-free during harsh electrochemical testing even after 650 h, suggesting that its unusual durability originates from indirect-contact electrocatalysis.
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