Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

Isolated graphene, a nanometer-thick two-dimensional analog of fullerenes and carbon nanotubes, has recently sparked great excitement in the scientific community given its excellent mechanical and electronic properties. Particularly attractive is the availability of bulk quantities of graphene as both colloidal dispersions and powders, which enables the facile fabrication of many carbon-based materials. The fact that such large amounts of graphene are most easily produced via the reduction of graphene oxide--oxygenated graphene sheets covered with epoxy, hydroxyl, and carboxyl groups--offers tremendous opportunities for access to functionalized graphene-based materials. Both graphene oxide and graphene can be processed into a wide variety of novel materials with distinctly different morphological features, where the carbonaceous nanosheets can serve as either the sole component, as in papers and thin films, or as fillers in polymer and/or inorganic nanocomposites. This Review summarizes techniques for preparing such advanced materials via stable graphene oxide, highly reduced graphene oxide, and graphene dispersions in aqueous and organic media. The excellent mechanical and electronic properties of the resulting materials are highlighted with a forward outlook on their applications.

Graphene oxide, highly reduced graphene oxide, and graphene: versatile building blocks for carbon-based materials.

Chemically modified graphene and polyaniline (PANI) nanofiber composites were prepared by in situ polymerization of aniline monomer in the presence of graphene oxide under acid conditions. The obtained graphene oxide/PANI composites with different mass ratios were reduced to graphene using hydrazine followed by reoxidation and reprotonation of the reduced PANI to give the graphene/PANI nanocomposites. The morphology, composition, and electronic structure of the composites together with pure polyaniline fibers (PANI-F), graphene oxide (GO), and graphene (GR) were characterized using X-ray diffraction (XRD), solid-state 13C NMR, FT-IR, scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). It was found that the chemically modified graphene and the PANI nanofibers formed a uniform nanocomposite with the PANI fibers absorbed on the graphene surface and/or filled between the graphene sheets. Such uniform structur...

Graphene/Polyaniline Nanofiber Composites as Supercapacitor Electrodes

Graphene is an intriguing material with properties that are distinct from those of other graphitic systems1,2,3,4,5. The first samples of pristine graphene were obtained by ‘peeling off’2,6 and epitaxial growth5,7. Recently, the chemical reduction of graphite oxide was used to produce covalently functionalized single-layer graphene oxide8,9,10,11,12,13,14,15. However, chemical approaches for the large-scale production of highly conducting graphene sheets remain elusive. Here, we report that the exfoliation–reintercalation–expansion of graphite can produce high-quality single-layer graphene sheets stably suspended in organic solvents. The graphene sheets exhibit high electrical conductance at room and cryogenic temperatures. Large amounts of graphene sheets in organic solvents are made into large transparent conducting films by Langmuir–Blodgett assembly in a layer-by-layer manner. The chemically derived, high-quality graphene sheets could lead to future scalable graphene devices. The first samples of pristine graphene were obtained by 'peeling off' and epitaxial growth, but chemical approaches are more suited to large-scale production. Exfoliation, reintercalation and expansion of graphite can produce high-quality single-layer graphene sheets suspended in organic solvents, and these sheets can be made into large transparent films by Langmuir–Blodgett assembly.

Highly conducting graphene sheets and Langmuir–Blodgett films

A composite of graphene oxide supported by needle-like MnO2 nanocrystals (GO−MnO2 nanocomposites) has been fabricated through a simple soft chemical route in a water−isopropyl alcohol system. The formation mechanism of these intriguing nanocomposites investigated by transmission electron microscopy and Raman and ultraviolet−visible absorption spectroscopy is proposed as intercalation and adsorption of manganese ions onto the GO sheets, followed by the nucleation and growth of the crystal species in a double solvent system via dissolution−crystallization and oriented attachment mechanisms, which in turn results in the exfoliation of GO sheets. Interestingly, it was found that the electrochemical performance of as-prepared nanocomposites could be enhanced by the chemical interaction between GO and MnO2. This method provides a facile and straightforward approach to deposit MnO2 nanoparticles onto the graphene oxide sheets (single layer of graphite oxide) and may be readily extended to the preparation of othe...

Graphene Oxide−MnO2 Nanocomposites for Supercapacitors

Graphene-based metal oxides generally show outstanding electrochemical performance due to the superior properties of graphene. However, the aggregation of active metal oxide nanoparticles on the graphene surface may result in a capacity fading and poor cycle performance. Here, a mesostructured graphene-based SnO2 composite is prepared through in situ growth of SnO2 particles on the graphene surface using cetyltrimethylammonium bromide as the structure-directing agent. This novel mesoporous composite inherits the advantages of graphene nanosheets and mesoporous materials and exhibits higher reversible capacity, better cycle performance, and better rate capability compared to pure mesoporous SnO2 and graphene-based nonporous SnO2. It is concluded that the synergetic effect between graphene and mesostructure benefits the improvement of the electrochemical properties of the hybrid composites. This facile method may offer an attractive alternative approach for preparation of the graphene-based mesoporous composites as high- performance electrodes for lithium-ion batteries.

Graphene-Based Mesoporous SnO2 with Enhanced Electrochemical Performance for Lithium-Ion Batteries

The intercalation of large organic ammonium ions (tetramethylammonium ions (TMA+), tetraethylammonium ions (TEA+), tetrapropylammonium ions (TPA+), and tetrabutylammonium ions (TBA+)) into layered graphite oxide (GO) was systematically investigated. The intercalation reactions were completed at 25 °C after 3 days, and stable colloidal suspensions were obtained at TAAl/Hs = 5 (molar ratio of tetraalkylammonium ions (TAA+) over exchangeable protons in GO). The sediments after centrifuging the colloidal suspensions showed amorphous phase X-ray diffraction patterns, indicating that exfoliation of the layered structure into nanosheets took place in the suspension. When the sediments were dried at 70 °C for 3 days, layered structures of TAA+-intercalated GO materials with basal spacings of 1.56, 1.67, 1.84, and 2.37 nm, respectively, appeared. The basal spacing of the layered compounds decreased with a decrease of relative humidity during drying. When the dried TAA+-intercalated GO compounds were exposed to a h...

Intercalation of Organic Ammonium Ions into Layered Graphite Oxide

This work reports a green and facile approach to the synthesis of graphene nanosheets through the zinc reduction of a graphene oxide precursor in alkaline media. Compared to the chemical reduction of GO by using hydrazine or its derivations, the present route is operationally easy and environmentally friendly. Moreover, the reduction degree of GO in the present condition is much higher than that in either Zn or alkaline solutions alone, indicating a cooperative mechanism, and the as-prepared graphene exhibits a good stability in solution. This simple method shows promising applications in the bulk-quantity production of graphene and graphene-based materials.

A facile green strategy for rapid reduction of graphene oxide by metallic zinc

We report in this paper the studies on protonation, exfoliation, and self-assembly of birnessite-type manganese oxide single crystals. The protonation was carried out by extracting K+ ions from the potassium manganese oxide single crystals in a (NH4)2S2O8 aqueous solution heated at 60 °C, exfoliation to nanosheets by the intercalation of TMA+ ions followed by water-washing, and the self-assembly of MnO2 nanosheets in a dilute NaCl solution. The structures of the samples at these stages were systematically investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared, thermogravimetric analysis-differential thermal analysis, and chemical compositional analysis. Electron density distribution in the protonated single crystal was visualized by whole-pattern fitting based on the maximum entropy method. The results indicated that the protonated single crystals can be exfoliated to MnO2 u...

Structural Characterization of Self-Assembled MnO2 Nanosheets from Birnessite Manganese Oxide Single Crystals

A layered manganese oxide nanocomposite (PDDAMO) with poly(diallyldimethylammonium chloride), PDDA, incorporated between manganese oxide sheets, was synthesized by a delamination/reassembling process. The product was characterized by powder X-ray diffraction, elemental analysis, thermal analysis, FT-IR spectroscopy, and FE-SEM observation. XRD analysis showed that the expansion of the interlayer depended on the amount of PDDA intercalated; the largest expansion was 1.09 nm, corresponding to a bilayer of PDDA chains in the interlayer. Chemical analysis results showed that the PDDA intercalation progressed by an ion-exchange mechanism, and the PDDA polymer existed in a polycation form, not as a chloride salt. PDDAMO was comprised of platelike nanocomposite particles that were 1−5 μm in width. The thickness of each plate was 30 nm on average, which corresponds to the stacking of about 20 sheets of manganese oxide. The formation of the PDDAMO nanocomposite was hardly affected by the pH of the solution. PDDAMO...

Xiaojing Yang

Papers

Graphene-Based Mesoporous SnO2 with Enhanced Electrochemical Performance for Lithium-Ion Batteries

Intercalation of Organic Ammonium Ions into Layered Graphite Oxide

A facile green strategy for rapid reduction of graphene oxide by metallic zinc

Structural Characterization of Self-Assembled MnO2 Nanosheets from Birnessite Manganese Oxide Single Crystals

Preparation of a Polycation-Intercalated Layered Manganese Oxide Nanocomposite by a Delamination/Reassembling Process