Modification of graphene has been undertaken in many research contexts in order to improve its properties. In this study, we examine Ni-nanoparticles decoration on graphene and its effect on sodiumion battery performance. A definite trend is observed on the relationship between Ni-nanoparticles concentration (and hence size) and battery performance. Comparable capacities on the order of 420 mAhg1 after 20 cycles at 100 mAg1 is observed for the 3 relatively high Ni-concentration samples NiC10, NiC40, and NiC80. As the Ni:C ratio decreases, a decreasing trend is observed in the measured capacity, with NiC200, NiC500, and NiC1000 producing capacities of 350 mAhg1, 380 mAhg1, and 300 mAhg1 respectively after 20 cycles at the same rate. Ex situ energy dispersive X-ray spectroscopy, scanning, and transmission electron microscopy shows the morphology of the Ni-nanoparticles decorated graphene and assists in quantifing their sodium content, emphasizing the increasing sodium content with increasing Ni-nanoparticles concentration. This systematic study details how Ninanoparticles concentration on graphene surfaces can be manipulated to enhance electrochemical performance, and that higher concentrations up to NiC10 favour better performance. For a compromise between performance and cost (Ni cost), the best composition is NiC500 which favors best performance with the least Ni decoration.
Reproduced with permission. Copyright 2018, Elsevier
Single-walled carbon nanotubes (SWCNTs) possessing a confined inner space protected by chemically resistant shells are promising for delivery, storage, and desorption of various compounds, as well as carrying out specific reactions. Here, we show that SWCNTs interact with molten mercury dichloride (HgCl2) and guide its transformation into dimercury dichloride (Hg2Cl2) in the cavity. The chemical state of host SWCNTs remains almost unchanged except for a small p-doping from the guest Hg2Cl2 nanocrystals. The density functional theory calculations reveal that the encapsulated HgCl2 molecules become negatively charged and start interacting via chlorine bridges when local concentration increases. This reduces the bonding strength in HgCl2, which facilitates removal of chlorine, finally leading to formation of Hg2Cl2 species. The present work demonstrates that SWCNTs not only serve as a template for growing nanocrystals but also behave as an electron-transfer catalyst in the spatially confined redox reaction by donation of electron density for temporary use by the guests.
We present a detailed NMR study of the insulator-to-metal transition induced by an applied pressure p in the A15 phase of Cs3C60. We evidence that the insulating antiferromagnetic (AFM) and superconducting (SC) phases coexist only in a narrow p range. At fixed p, in the metallic state above the SC transition Tc, the 133Cs and 13C NMR spin-lattice relaxation data are seemingly governed by a pseudogaplike feature. We prove that this feature, also seen in the 133Cs NMR shift data, is rather a signature of the Mott transition which broadens and smears out progressively for increasing (p, T). The analysis of the variation of the quadrupole splitting νQ of the 133Cs NMR spectrum precludes any cell symmetry change at the Mott transition and only monitors a weak variation of the lattice parameter. These results open an opportunity to consider theoretically the Mott transition in a multiorbital three-dimensional system well beyond its critical point.
We report on the C60, Na, and Li dynamics in NaxLi6−xC60 fullerides (x = 0, 1, 5, and 6) in the temperature range 80−550 K by using 13C, 23Na, and 7Li solid state NMR. The results show that the C60 reorientation dynamics is hindered at room temperature for the Li-enriched fullerides, but it is active for the Na rich ones with a rate of the order of few kilohertz. 23Na and 7Li NMR measurements show the presence of two dominant thermally activated dynamics that can be associated with Li/Na ionic motions within the octahedral sites (intrasite motion) and between the octahedral and tetrahedral sites (intersite motion). The substitution of one Na or one Li ion in the end members Li6C60 and Na6C60, respectively, yields to an increase of the hopping rate of the intersite motion, which is necessary for the ionic diffusion in possible fulleride-based ionic conductors.
