The physical state of the catalyst and its impact on the growth of single-walled carbon nanotubes (SWNTs) is the subject of a long-standing debate. We addressed it here using in situ Raman spectroscopy to measure Fe and Ni catalyst lifetimes during the growth of individual SWNTs across a wide range of temperatures (500-1400 °C). The temperature dependence of the Fe catalyst lifetimes underwent a sharp increase around 1100 °C due to a solid-to-liquid phase transition. By comparing experimental results with the metal-carbon phase diagrams, we prove that SWNTs can grow from solid and liquid phase-catalysts, depending on the temperature.

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Elucidating the origin of carbon nanotube chirality is key for realizing their untapped potential. Currently, prevalent theories suggest that catalyst structure originates chirality via an epitaxial relationship. Here we studied chirality abundances of carbon nanotubes grown on floating liquid Ga droplets, which excludes the influence of catalyst features, and compared them with abundances grown on solid Ru nanoparticles. Results of growth on liquid droplets bolsters the intrinsic preference of carbon nuclei toward certain chiralities. Specifically, the abundance of the (11,1)/χ = 4.31° tube can reach up to 95% relative to (9,4)/χ = 17.48°, although they have exactly the same diameter, (9.156 Å). However, the comparative abundances for the pair, (19,3)/χ = 7.2° and (17,6)/χ = 14.5°, with bigger diameter, (16.405 Å), fluctuate depending on synthesis temperature. The abundances of the same pairs of tubes grown on floating solid polyhedral Ru nanoparticles show completely different trends. Analysis of abundances in relation to nucleation probability, represented by a product of the Zeldovich factor and the deviation interval of a growing nuclei from equilibrium critical size, explain the findings. We suggest that the chirality in the nanotube in general is a result of interplay between intrinsic preference of carbon cluster and induction by catalyst structure. This finding can help to build the comprehensive theory of nanotube growth and offers a prospect for chirality-preferential synthesis of carbon nanotubes by the exploitation of liquid catalyst droplets.

Recent reports on high capacity lithium ion batteries based on carbon nanostructures aroused expectations of realizing high energy density devices. We have studied the performances of a wide variety of carbon nanostructures with surface areas from a few up to 1400 m 2 /g as anode materials in Li-ion batteries by using three different experimental setups aiming to clarify the origin of high capacities. The obtained charge values consumed in the initial intercalation/deintercalation cycles of Li ions for high surface area nanostructures indeed correspond to capacities that exceed the theoretical limit for pristine graphite (372 Ah/kg; as LiC 6 ) up to a factor of six. Yet, typically these large excess capacity values were irreversibly diminished during further charge/discharge cycling. Density functional theory (DFT) calculations reveal a decisive role of edge carbon atoms in high surface nanostructures as active sites that contribute not only to an initial high capacity, but to the formation of a solid-electrolyte interphase and thereby to the irreversible capacity loss (ICL). These results question the feasibility of stable large excess Li capacity values in studied carbon nanostructures, yet suggest the design of nanostructures for reducing the ICL.For more than three decades, graphite has been the subject of intense research for Li-ion battery anodes due to its suitable properties and layered structure that allows intercalation/deintercalation of Liions without significantly compromising the overall battery durability. However, the specific capacity of Li ions in graphite is 372 Ah/kg (corresponding to the LiC 6 structure) and is limited by the peculiarities of the intercalation in the layered structure, Li clustering and phase separation processes. There have been a number of attempts to increase the Li storage capacity by exploiting modified graphite (for example, by varying flake diameter, pore size distribution, doping, and surface treatment), graphitic particles and disordered carbons, also called "soft" and "hard" carbons. 1-4 Various models, sometimes controversial, have been suggested in order to explain the high capacity values. For instance, the excess storage capacities have been explained by the existence of Li 2 covalent molecules that correspond to the Li 2 C 6 composition, 5 adsorption of Li at the graphite edges, 6 formation of LiC 2 in the carbon with larger interlayer spaces, 7 formation of a thin film of Li on the carbon surface, 8 or adsorption of Li on both sides of the graphene layer, the so-called "house of cards" model. 9 Nevertheless, up to this day the essential drawbacks for practical exploitation of graphitic carbon in Li-ion battery anodes are reproducibility and loss of the initial capacity during charge/discharge cycling. Indeed, studies have revealed strong correlations between the ICL and particle size, surface area and crystallinity. 10-14 In general, these previous studies have emphasized the importance of the ratio between the surface of the basal plane and the edge thickness...