M₃C (M: Fe, Co, Ni) Nanocrystals Encased in Graphene Nanoribbons: An Active and Stable Bifunctional Electrocatalyst for Oxygen Reduction and Hydrogen Evolution Reactions

Transition metal carbide nanocrystalline M₃C (M: Fe, Co, Ni) encapsulated in graphitic shells supported with vertically aligned graphene nanoribbons (VA-GNRs) are synthesized through a hot filament chemical vapor deposition (HF-CVD) method. The process is based on the direct reaction between iron group metals (Fe, Co, Ni) and carbon source, which are facilely get high purity carbide nanocrystals (NCs) and avoid any other impurity at relatively low temperature. The M₃C-GNRs exhibit superior enhanced electrocatalystic activity for oxygen reduction reaction (ORR), including low Tafel slope (39, 41, and 45 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively), positive onset potential (∼0.8 V), high electron transfer number (∼4), and long-term stability (no obvious drop after 20 000 s test). The M₃C-GNRs catalyst also exhibits remarkable hydrogen evolution reaction (HER) activity with a large cathodic current density of 166.6, 79.6, and 116.4 mA cm^–2 at an overpotential of 200 mV, low onset overpotential of 32, 41, and 35 mV, small Tafel slope of 46, 57, and 54 mV dec^–1 for Fe₃C-GNRs, Co₃C-GNRs, and Ni₃C-GNRs, respectively, as well as an excellent stability in acidic media

Reductive roasting of nickel laterite ore with sodium sulfate for Fe-Ni production. Part I: Reduction/sulfidation characteristics

<p>The selective reduction of nickel and adequate growth of ferronickel grains are imperative for efficient preparation of ferronickel from nickeliferous laterite ore via the process of direct reduction followed by magnetic separation. In Part I, reduction/sulfidation behaviors of a saprolitic laterite ore in the presence of sodium sulfate were investigated, with an emphasis on thermodynamic analysis, selective reduction/sulfidation ratios and kinetics. To separate the interactions between Ni and Fe, chemical titration analysis was adopted to determine the contents of various Ni and Fe species in the roasted pellets, and a modified equation to assay metallic iron content was proposed.</p

Flexible and Stackable Laser-Induced Graphene Supercapacitors

In this paper, we demonstrate that by simple laser induction, commercial polyimide films can be readily transformed into porous graphene for the fabrication of flexible, solid-state supercapacitors. Two different solid-state electrolyte supercapacitors are described, namely vertically stacked graphene supercapacitors and in-plane graphene microsupercapacitors, each with enhanced electrochemical performance, cyclability, and flexibility. Devices with a solid-state polymeric electrolyte exhibit areal capacitance of >9 mF/cm² at a current density of 0.02 mA/cm², more than twice that of conventional aqueous electrolytes. Moreover, laser induction on both sides of polyimide sheets enables the fabrication of vertically stacked supercapacitors to multiply its electrochemical performance while preserving device flexibility

Superacid-Surfactant Exchange: Enabling Nondestructive Dispersion of Full-Length Carbon Nanotubes in Water

Attaining aqueous solutions of individual, long single-walled carbon nanotubes is a critical first step for harnessing the extraordinary properties of these materials. However, the widely used ultrasonication–ultracentrifugation approach and its variants inadvertently cut the nanotubes into short pieces. The process is also time-consuming and difficult to scale. Here we present an unexpectedly simple solution to this decade-old challenge by directly neutralizing a nanotube-chlorosulfonic acid solution in the presence of sodium deoxycholate. This straightforward superacid-surfactant exchange eliminates the need for both ultrasonication and ultracentrifugation altogether, allowing aqueous solutions of individual nanotubes to be prepared within minutes and preserving the full length of the nanotubes. We found that the average length of the processed nanotubes is more than 350% longer than sonicated controls, with a significant fraction approaching ∼9 μm, a length that is limited by only the raw material. The nondestructive nature is manifested by an extremely low density of defects, bright and homogeneous photoluminescence in the near-infrared, and ultrahigh electrical conductivity in transparent thin films (130 Ω/sq at 83% transmittance), which well exceeds that of indium tin oxide. Furthermore, we demonstrate that our method is fully compatible with established techniques for sorting nanotubes by their electronic structures and can also be readily applied to graphene. This surprisingly simple method thus enables nondestructive aqueous solution processing of high-quality carbon nanomaterials at large-scale and low-cost with the potential for a wide range of fundamental studies and applications, including, for example, transparent conductors, near-infrared imaging, and high-performance electronics

Graphene Nanoribbon/V₂O₅ Cathodes in Lithium-Ion Batteries

Nanocrystalline V₂O₅ particles were successfully entrapped by graphene nanoribbons (GNRs) derived from unzipped carbon nanotubes. The electrical conductivity of V₂O₅ nanoparticles was enhanced after introducing the GNRs. The 3-dimensional conductive framework in the composites plays a significant role in improving the rate performance and cyclability of the material when used as a cathode in lithium-ion batteries. By tailoring the mass ratio between the GNRs and the V₂O₅ nanoparticles, the fabricated composites can deliver a high capacity of 278 mAh g^–1 at 0.1 <i>C</i>, which is close to its theoretical value, whereas a capacity of 165 mAh g^–1 can be maintained at 2 <i>C</i>. The delivered capacity at 0.1 <i>C</i> can maintain 78% of its initial capacity after 100 cycles

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

Chemical Gating of a Synthetic Tube-in-a-Tube Semiconductor

A critical challenge to translating field effect transistors into biochemical sensor platforms is the requirement of a gate electrode, which imposes restrictions on sensor device architectures and results in added expense, poorer scalability, and electrical noise. Here we show that it is possible to eliminate the need of the physical gate electrode and dielectrics altogether using a synthetic tube-in-a-tube (Tube^∧2) semiconductor. Composed of a semiconducting single-walled carbon nanotube nested in a charged, impermeable covalent functional shell, Tube^∧2 allows the semiconducting conduction pathway to be modulated solely by surface functional groups in a chemically gated-all-around configuration. The removal of physical gates significantly simplifies the device architecture and enables photolithography-free, highly scalable fabrication of transistor sensors in nonconventional configurations that are otherwise impossible. We show that concomitant FET sensitivity and single-mismatch selectivity can be achieved with Tube^∧2 even in a two-terminal, thin film transistor device configuration that is as simple as a chemiresistor. Miniaturized two-terminal field effect point sensors can also be fabricated, using a straightforward dice-and-dip procedure, for the detection of tuberculosis biomarkers

Functionalized Graphene Nanoribbons <i>via</i> Anionic Polymerization Initiated by Alkali Metal-Intercalated Carbon Nanotubes

The preparation of polymer-functionalized graphene nanoribbons (PF-GNRs) in a one-pot synthesis is described. Multiwalled carbon nanotubes (MWCNTs) were intercalated by potassium under vapor- or liquid-phase conditions, followed by the addition of vinyl or epoxide monomers, resulting in PF-GNRs. Scanning electron microscopy, thermogravimetric mass spectrometry, and X-ray photoelectron spectroscopy were used to characterize the PF-GNRs. Also explored here is the correlation between the splitting of MWCNTs, the intrinsic properties of the intercalants and the degree of defects and graphitization of the starting MWCNTs. The PF-GNRs could have applications in conductive composites, transparent electrodes, heat circuits, and supercapacitors

Graphene Nanoribbon and Nanostructured SnO₂ Composite Anodes for Lithium Ion Batteries

A composite made from graphene nanoribbons (GNRs) and tin oxide (SnO₂) nanoparticles (NPs) is synthesized and used as the anode material for lithium ion batteries (LIBs). The conductive GNRs, prepared using sodium/potassium unzipping of multiwall carbon nanotubes, can boost the lithium storage performance of SnO₂ NPs. The composite, as an anode material for LIBs, exhibits reversible capacities of over 1520 and 1130 mAh/g for the first discharge and charge, respectively, which is more than the theoretical capacity of SnO₂. The reversible capacity retains ∼825 mAh/g at a current density of 100 mA/g with a Coulombic efficiency of 98% after 50 cycles. Further, the composite shows good power performance with a reversible capacity of ∼580 mAh/g at the current density of 2 A/g. The high capacity, good power performance and retention can be attributed to uniformly distributed SnO₂ NPs along the high-aspect-ratio GNRs. The GNRs act as conductive additives that buffer the volume changes of SnO₂ during cycling. This work provides a starting point for exploring the composites made from GNRs and other transition metal oxides for lithium storage applications

3‑Dimensional Graphene Carbon Nanotube Carpet-Based Microsupercapacitors with High Electrochemical Performance

In this research, 3-dimensional (3D) graphene/carbon nanotube carpets (G/CNTCs)-based microsupercapacitors (G/CNTCs-MCs) were fabricated in situ on nickel electrodes. The G/CNTCs-MCs show impedance phase angle of −81.5° at a frequency of 120 Hz, comparable to commercial aluminum electrolytic capacitors (AECs) for alternating current (ac) line filtering applications. In addition, G/CNTCs-MCs deliver a high volumetric energy density of 2.42 mWh/cm³ in the ionic liquid, more than 2 orders of magnitude higher than that of AECs. The ultrahigh rate capability of 400 V/s enables the microdevices to demonstrate a maximum power density of 115 W/cm³ in aqueous electrolyte. The high-performance electrochemical properties of G/CNTCs-MCs can provide more compact ac filtering units and discrete power sources in future electronic devices. These elevated electrical features are likely enabled by the seamless nanotube/graphene junctions at the interface of the differing carbon allotropic forms