Abdul-Rahman O. Raji

A seamless three-dimensional carbon nanotube graphene hybrid material.

Graphene and single-walled carbon nanotubes are carbon materials that exhibit excellent electrical conductivities and large specific surface areas. Theoretical work suggested that a covalently bonded graphene/single-walled carbon nanotube hybrid material would extend those properties to three dimensions, and be useful in energy storage and nanoelectronic technologies. Here we disclose a method to bond graphene and single-walled carbon nanotubes seamlessly during the growth stage. The hybrid material exhibits a surface area >2,000 m(2) g(-1) with ohmic contact from the vertically aligned single-walled carbon nanotubes to the graphene. Using aberration-corrected scanning transmission electron microscopy, we observed the covalent transformation of sp(2) carbon between the planar graphene and the single-walled carbon nanotubes at the atomic resolution level. These findings provide a new benchmark for understanding the three-dimensional graphene/single-walled carbon nanotube-conjoined materials.

Coal as an abundant source of graphene quantum dots

Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

Graphene‐Wrapped MnO2–Graphene Nanoribbons as Anode Materials for High‐Performance Lithium Ion Batteries

A facile and cost-effective approach for the fabrication of a hierarchical nanocomposite material of graphene-wrapped MnO2 -graphene nanoribbons (GMG) is developed. The resulting composite has a high specific capacity and an excellent cycling stability owing to the synergistic combination of the electrically conductive graphene, graphene nanoribbons, and MnO2 .

Large-Area Bernal-Stacked Bi-, Tri-, and Tetralayer Graphene

Few-layer graphene, with Bernal stacking order, is of particular interest to the graphene community because of its unique tunable electronic structure. A synthetic method to produce such large area graphene films with precise thickness from 2 to 4 layers would be ideal for chemists and physicists to explore the promising electronic applications of these materials. Here, large-area uniform Bernal-stacked bi-, tri-, and tetralayer graphene films were successfully synthesized on a Cu surface in selective growth windows, with a finely tuned total pressure and CH(4)/H(2) gas ratio. On the basis of the analyses obtained, the growth mechanism is not an independent homoexpitaxial layer-by-layer growth, but most likely a simultaneous-seeding and self-limiting process.

Nanocomposite of Polyaniline Nanorods Grown on Graphene Nanoribbons for Highly Capacitive Pseudocapacitors

A facile and cost-effective approach to the fabrication of a nanocomposite material of polyaniline (PANI) and graphene nanoribbons (GNRs) has been developed. The morphology of the composite was characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and X-ray diffraction analysis. The resulting composite has a high specific capacitance of 340 F/g and stable cycling performance with 90% capacitance retention over 4200 cycles. The high performance of the composite results from the synergistic combination of electrically conductive GNRs and highly capacitive PANI. The method developed here is practical for large-scale development of pseudocapacitor electrodes for energy storage.

In situ intercalation replacement and selective functionalization of graphene nanoribbon stacks.

A cost-effective and potentially industrially scalable, in situ 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 (13)C 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 sp(2)-hybridized carbon atoms to sp(3)-hybridized atoms dramatically lowers their conductivity, but edge functionalized GNRs permit their heavy functionalization while leaving the basal planes intact.

Lithium Batteries with Nearly Maximum Metal Storage

The drive for significant advancement in battery capacity and energy density inspired a revisit to the use of Li metal anodes. We report the use of a seamless graphene-carbon nanotube (GCNT) electrode to reversibly store Li metal with complete dendrite formation suppression. The GCNT-Li capacity of 3351 mAh g-1GCNT-Li approaches that of bare Li metal (3861 mAh g-1Li), indicating the low contributing mass of GCNT, while yielding a practical areal capacity up to 4 mAh cm-2 and cycle stability. A full battery based on GCNT-Li/sulfurized carbon (SC) is demonstrated with high energy density (752 Wh kg-1 total electrodes, where total electrodes = GCNT-Li + SC + binder), high areal capacity (2 mAh cm-2), and cyclability (80% retention at >500 cycles) and is free of Li polysulfides and dendrites that would cause severe capacity fade.

Enhanced Cycling Stability of Lithium Sulfur Batteries Using Sulfur–Polyaniline–Graphene Nanoribbon Composite Cathodes

A hierarchical nanocomposite material of graphene nanoribbons combined with polyaniline and sulfur using an inexpensive, simple method has been developed. The resulting composite, characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and X-ray diffraction analysis, has a good rate performance and excellent cycling stability. The synergistic combination of electrically conductive graphene nanoribbons, polyaniline, and sulfur produces a composite with high performance. The method developed here is practical for the large-scale development of cathode materials for lithium sulfur batteries.

Tin Disulfide Nanoplates on Graphene Nanoribbons for Full Lithium Ion Batteries.

A nanocomposite material made of layered tin disulfide (SnS2) nanoplates vertically grown on reduced graphene oxide nanoribbons (rGONRs) has been successfully developed as an anode in lithium ion batteries by a facile method. At a rate of 0.4 A/g, the material exhibits a high discharge capacity of 823 mAh/g even after 800 cycles. It shows excellent rate stability when the current density varies from 0.1 to 3.0 A/g with a Coulombic efficiency larger than 99%. In order to demonstrate the anode material for practical applications, SnS2-rGONR/LiCoO2 full cells were constructed. To the best of our knowledge, this is the first time that a full cell has been successfully developed using metal chalcogenides as an anode. The full cell delivers a high capacity of 642 mAh/g at 0.2 A/g, superior rate, and cycling stability after long-term cycling. Moreover, the full cell has a high output working voltage of 3.4 V. These excellent lithium storage performances in half and full cells can be mainly attributed to the synergistic effect between the highly conductive network of rGONRs and the high lithium-ion storage capability of layered SnS2 nanoplates.

Graphene Carbon Nanotube Carpets Grown Using Binary Catalysts for High-Performance Lithium-Ion Capacitors

Here we show that a versatile binary catalyst solution of Fe3O4/AlOx nanoparticles enables homogeneous growth of single to few-walled carbon nanotube (CNT) carpets from three-dimensional carbon-based substrates, moving past existing two-dimensional limited growth methods. The binary catalyst is composed of amorphous AlOx nanoclusters over Fe3O4 crystalline nanoparticles, facilitating the creation of seamless junctions between the CNTs and the underlying carbon platform. The resulting graphene-CNT (GCNT) structure is a high-density CNT carpet ohmically connected to the carbon substrate, an important feature for advanced carbon electronics. As a demonstration of the utility of this approach, we use GCNTs as anodes and cathodes in binder-free lithium-ion capacitors, producing stable devices with high-energy densities (∼120 Wh kg-1), high-power density capabilities (∼20,500 W kg-1 at 29 Wh kg-1), and a large operating voltage window (4.3 to 0.01 V).