Electroactive polymers are a new generation of "green" cathode materials for rechargeable lithium batteries. We have developed nanocomposites combining graphene with two promising polymer cathode materials, poly(anthraquinonyl sulfide) and polyimide, to improve their high-rate performance. The polymer-graphene nanocomposites were synthesized through a simple in situ polymerization in the presence of graphene sheets. The highly dispersed graphene sheets in the nanocomposite drastically enhanced the electronic conductivity and allowed the electrochemical activity of the polymer cathode to be efficiently utilized. This allows for ultrafast charging and discharging; the composite can deliver more than 100 mAh/g within just a few seconds.
Electrochemically active LiMnPO(4) nanoplates have been synthesized via a novel, single-step, solid-state reaction in molten hydrocarbon. The olivine-structured LiMnPO(4) nanoplates with a thickness of approximately 50 nm appear porous and were formed as nanocrystals were assembled and grew into nanorods along the [010] direction in the (100) plane. After carbon coating, the prepared LiMnPO(4) cathode demonstrated a flat potential at 4.1 V versus Li with a specific capacity reaching as high as 168 mAh/g under a galvanostatic charging/discharging mode, along with an excellent cyclability.
Uniform Au-Ag alloy nanoparticles have been synthesized on cellulose nanocrystal (CNXL) by the coreduction method of corresponding metal ions. CNXL that plays a dual role of a matrix and of a stabilizer has been used to obtain stable dispersions of alloy nanoparticles. The composition of alloy nanoparticles indicates a quantitative deposit of metal ions on CNXL surface followed by reduction. The sizes of alloy nanoparticles were controlled in the range of 3-7 nm by capping agent, sodium citrate, and their average diameter was increased with an increase of Ag content. Aqueous suspensions of Au-Ag alloy nanoparticles and their dried films are characterized by UV-vis spectroscopy, field emission-scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and X-ray diffraction (XRD).
Electronic aspects of an iron porphyrin, 5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine iron(III) chloride (FeTMPPCl) molecularly dispersed on a high area carbon black (Black Pearls 2000, BP) and then heat-treated (or thermally activated) at 800°C in a flowing inert atmosphere, were investigated in situ in 1.0 M H 3 PO 4 by Fe K-edge X-ray near-edge structure (XANES). Profound differences were observed between the ex situ (dry) XANES of electrodes incorporating FeTMPPCl/BP before and after heat treatment and, likewise, in the case of the thermally treated FeTMPPCl/BP before and after immersion of the electrodes in the electrolyte. Monotonic shifts in the absorption edge toward higher energies were observed for heattreated FeTMPPCl/BP as the potential was increased over a range of over 1 V. The overall magnitude of the shift, ca. 2.5 eV, was virtually the same as that obtained with non-heat-treated (or intact) FeTMPPCl/BP, which occurred in a much narrower potential range, ca. 0.2 V. In contrast to the behavior observed for the intact adsorbed macrocycle, its heat-treated counterpart displayed no affinity for CO, indicating that, to the level of sensitivity of this technique, iron sites in the thermally activated material are quite different from those in the N 4 environment of the intact macrocycle.
This report shows that the size, shape, and composition of presynthesized copper nanoparticles can be nanoengineered through exploiting concurrent interparticle aggregative growth and interfacial carbon−sulfur cleavage in a thermally activated evolution route. This is demonstrated by thermally activated processing of ultrafine copper nanoclusters encapsulated with thiolate monolayer (Cu
n
(SR)
m
) toward semiconducting copper sulfide (Cu2S) nanodiscs with controllable sizes and shapes. Under controlled temperatures (120−150 °C), the ultrafine Cu
n
(SR)
m
nanoclusters, with a size of ∼0.5 nm evidenced by TEM, SAXS-WAXS, DCP-AES, and MALDI-TOF measurements, were shown to evolve into thiolate-capped Cu2S nanodiscs via thermally activated coalescence and copper-catalyzed interfacial C−S cleavage reactivities. The Cu2S nanodiscs, as confirmed by XPS and HRTEM analyses, exhibited controllable and monodispersed sizes depending on the thermal processing parameters, ranging from 5 to 35 nm in the disk dimension and 3−6 nm in the thickness dimension. These nanodiscs are stable and display remarkable 1D/2D ordering upon self-assembly. This process is not a simple digestive ripening of smaller particles because it involves an aggregative nucleation and growth process distinctively different from traditional ripening and a reactive carbon−sulfur bond cleavage controlled by the catalytic effect of copper under the specified temperatures. The coupling of the thermally activated coalescence and C−S bond cleavage to convert the ultrafine Cu nanoclusters toward the formation of Cu2S nanodiscs is highly effective for tuning nanoscale size, shape, and composition, and could find applications in nanoengineering a variety of semiconducting nanocrystals for applications in nanostructured electronic, sensing, and photochemical devices.
We have examined amorphous structures of silicon carbide (SiC) using both transmission electron microscopy and a molecular-dynamics approach. Radial distribution functions revealed that amorphous SiC contains not only heteronuclear (Si-C) bonds but also homonuclear (Si-Si and C-C) bonds. The ratio of heteronuclear to homonuclear bonds was found to change upon annealing, suggesting that structural relaxation of the amorphous SiC occurred. Good agreement was obtained between the simulated and experimentally measured radial distribution functions.
Colloidal carbon spheres have been prepared from aqueous R-, β-, and γ-cyclodextrin (CD) solutions in closed systems under hydrothermal conditions at 160 °C. Both liquid and solid-state 13 C NMR spectra taken for samples at different reaction times have been used to monitor the dehydration and carbonization pathways. CD slowly hydrolyzes to glucose and forms 5-hydroxymethyl furfural (HMF) followed by carbonization into colloidal carbon spheres. The isolated carbon spheres are 70-150 nm in diameter, exhibit a core-shell structure, and are comprised of a condensed core (CdC) peppered with resident chemical functionalities including carboxylate and hydroxyl groups. Evidence from 13 C solid-state NMR and FT-IR spectra reveal that the evolving carbon spheres show a gradual increase in the amount of aromatic carbon as a function of reaction time and that the carbon spheres generated from γ-CD contain significantly higher aromatic carbon than those derived from Rand β-CD.
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