Fluorinated Reduced Graphene Oxide as an Interlayer in Li-S Batteries

International audienceWe report on the synthesis of fluorinated reduced graphene oxide (F-rGO) by a direct fluorination of reduced graphene oxide (rGO) with F2 or XeF2/BF3 in anhydrous HF. Characterization performed by high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM) and NMR confirmed the formation of C-F bonds, which is also supported by the color change from graphite gray to light yellow. F-rGO has been used as an interlayer additive supported by a glass fiber separator in lithium-sulfur (Li-S) batteries in order to block the diffusion/migration of polysulfides from the porous positive electrode to the metallic lithium electrode and to prevent the redox shuttle effect. Electrochemical cycling of Li-S batteries has confirmed the beneficial role of F-rGO separators, with a more pronounced effect observed for high degrees of fluorination. X-ray photoelectron spectroscopy (XPS) studies have shown a direct effect on the amount of Li2S and polysulfides found on the lithium electrode and evidenced a better reversibility of reduction/oxidation mechanisms of sulfur at the positive electrode upon discharge/charge. © 2015 American Chemical Society

Composites of Graphene Nanoribbon Stacks and Epoxy for Joule Heating and Deicing of Surfaces.

A conductive composite of graphene nanoribbon (GNR) stacks and epoxy is fabricated. The epoxy is filled with the GNR stacks, which serve as a conductive additive. The GNR stacks are on average 30 nm thick, 250 nm wide, and 30 μm long. The GNR-filled epoxy composite exhibits a conductivity >100 S/m at 5 wt % GNR content. This permits application of the GNR-epoxy composite for deicing of surfaces through Joule (voltage-induced) heating generated by the voltage across the composite. A power density of 0.5 W/cm(2) was delivered to remove ∼1 cm-thick (14 g) monolith of ice from a static helicopter rotor blade surface in a -20 °C environment

Synthesis of Dispersible Ferromagnetic Graphene Nanoribbon Stacks with Enhanced Electrical Percolation Properties in a Magnetic Field

Iron-intercalated and tetradecyl-edge-functionalized graphene nanoribbon stacks (Fe@TD-GNRs) can be made from commercially available carbon nanotubes by a facile synthesis. The physical properties of the Fe@TD-GNRs were analyzed by transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, evolved gas analysis, Raman spectroscopy, and scanning electron microscopy. By the intercalation of iron, the alignment of the Fe@TD-GNRs in a magnetic field was enabled. The aligned structures enhanced electrical percolation at given concentrations in previously nonconductive solvents

<i>In Situ</i> Intercalation Replacement and Selective Functionalization of Graphene Nanoribbon Stacks

A cost-effective and potentially industrially scalable, <i>in situ</i> functionalization procedure for preparation of soluble graphene nanoribbon (GNRs) from commercially available carbon nanotubes is presented. The physical characteristics of the functionalized product were determined using SEM, evolved gas analysis, X-ray diffraction, solid-state ¹³C NMR, Raman spectroscopy, and GC–MS analytical techniques. A relatively high preservation of electrical properties in the bulk material was observed. Moreover, replacement of intercalated potassium with haloalkanes was obtained. While carbon nanotubes can be covalently functionalized, the conversion of the sp²-hybridized carbon atoms to sp³-hybridized atoms dramatically lowers their conductivity, but edge functionalized GNRs permit their heavy functionalization while leaving the basal planes intact

Thermal decomposition synthesis of functionalized PdPt alloy nanodendrites with high selectivity for oxygen reduction reaction

Pt-based bimetallic nanostructures have found intriguing applications in electrocatalysis. However, the pristine Pt-based nanostructures generally lack the selectivity for the target reaction because of their high activity for both oxygen reduction reactions (ORRs) and fuel molecule oxidation reactions. By employing a recently developed chemical functionalization strategy, the functionalized Pt-based nanostructures have achieved their selectivity for the target reaction in fuel cells. In this work, we report a facile thermal decomposition route to synthesize the polyallylamine (PAH)-functionalized Pd–Pt bimetallic core–shell nanodendrites with a Pd-rich PdPt alloy core and a Pt-rich PtPd alloy shell (PdPt@PtPd CSNDs) by using PAH that serves as a complexant, reductant and chemical functionalization molecule. The composition, morphology and structure of PdPt@PtPd CSNDs are characterized in detail. Compared with commercial Pt black electrocatalyst, the PAH-functionalized PdPt@PtPd CSNDs show improved electrocatalytic activity and durability for the ORR, and achieve good selectivity for the ORR in the presence of ethanol molecules. The study shows a promising cathode electrocatalyst for direct alcohol fuel cells (DAFCs).MOE (Min. of Education, S’pore)Published versio