Graphene has attracted tremendous research interest in recent years, owing to its exceptional properties. The scaled-up and reliable production of graphene derivatives, such as graphene oxide (GO) and reduced graphene oxide (rGO), offers a wide range of possibilities to synthesize graphene-based functional materials for various applications. This critical review presents and discusses the current development of graphene-based composites. After introduction of the synthesis methods for graphene and its derivatives as well as their properties, we focus on the description of various methods to synthesize graphene-based composites, especially those with functional polymers and inorganic nanostructures. Particular emphasis is placed on strategies for the optimization of composite properties. Lastly, the advantages of graphene-based composites in applications such as the Li-ion batteries, supercapacitors, fuel cells, photovoltaic devices, photocatalysis, as well as Raman enhancement are described (279 references).

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Graphene-based composites

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

We report a novel procedure to synthesize a new type of water separation membrane using graphene oxide (GO) nanosheets such that water can flow through the nanochannels between GO layers while unwanted solutes are rejected by size exclusion and charge effects. The GO membrane was made via layer-by-layer deposition of GO nanosheets, which were cross-linked by 1,3,5-benzenetricarbonyl trichloride, on a polydopamine-coated polysulfone support. The cross-linking not only provided the stacked GO nanosheets with the necessary stability to overcome their inherent dispensability in water environment but also fine-tuned the charges, functionality, and spacing of the GO nanosheets. We then tested the membranes synthesized with different numbers of GO layers to demonstrate their interesting water separation performance. It was found that the GO membrane flux ranged between 80 and 276 LMH/MPa, roughly 4–10 times higher than that of most commercial nanofiltration membranes. Although the GO membrane in the present deve...

Enabling graphene oxide nanosheets as water separation membranes.

Composite Photocatalysts Nan Zhang,†,‡ Min-Quan Yang,†,‡ Siqi Liu,†,‡ Yugang Sun,* and Yi-Jun Xu*,†,‡ †State Key Laboratory of Photocatalysis on Energy and Environment, College of Chemistry, Fuzhou University, Fuzhou 350002, P.R. China ‡College of Chemistry, New Campus, Fuzhou University, Fuzhou 350108, P.R. China Center for Nanoscale Materials, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States

Waltzing with the Versatile Platform of Graphene to Synthesize Composite Photocatalysts.

The high cost of low temperature fuel cells is to a large part dictated by the high loading of Pt required to catalyse the oxygen reduction reaction (ORR). Arguably the most viable route to decrease the Pt loading, and to hence commercialise these devices, is to improve the ORR activity of Pt by alloying it with other metals. In this perspective paper we provide an overview of the fundamentals underlying the reduction of oxygen on platinum and its alloys. We also report the ORR activity of Pt5La for the first time, which shows a 3.5- to 4.5-fold improvement in activity over Pt in the range 0.9 to 0.87 V, respectively. We employ angle resolved X-ray photoelectron spectroscopy and density functional theory calculations to understand the activity of Pt5La.

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Understanding the electrocatalysis of oxygen reduction on platinum and its alloys

Graphene oxide (GO) nanosheets have many semiconducting π-conjugated sp2 domains of various sizes within an oxygenated sp3 domain. The chemical and physical properties, therefore, can be widely tuned by adjusting the degree of oxidation through photoreaction, because the semiconducting domains act as a semiconducting photocatalyst when irradiated with light of energy exceeding the band gap of the domains. In this paper, we report new photoreactions similar to photocatalytic reactions in which H2 and CO2 are evolved from an aqueous suspension of GO nanosheets under UV irradiation; these reactions are based on the photoreactions of oxygen-containing functional groups and carbon. As a result, reduced GO (rGO) nanosheets with many holes and defects were produced. We conjecture that some carbons in the holes belong to zigzag edges, CH bonds, or both and that the rGO nanosheets therefore have ferromagnetic properties. In photoelectrochemical measurements of a GO nanosheet electrode, a large anodic photocurrent ...

Photoreaction of Graphene Oxide Nanosheets in Water

Graphene oxide (GO) nanosheets were reduced by UV irradiation in H2 or N2 under mild conditions (at room temperature) without a photocatalyst. Photoreduction proceeded even in an aqueous suspension of nanosheets. The GO nanosheets reduced by this method were analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy. It was found that epoxy groups attached to the interiors of aromatic domains of the GO nanosheet were destroyed during UV irradiation to form relatively large sp2 islands resulting in a high conductivity. I−V curves were measured by conductive atomic force microscopy (AFM; perpendicular to a single nanosheet) and a two-electrode system (parallel to the nanosheet). They revealed that photoreduced GO nanosheets have high conductivities, whereas nonreduced GO nanosheets are nearly insulating. Ag+ adsorbed on GO nanosheets promoted the photoreduction. This photoreduction method was very useful for photopatterning a conducting section of micrometer size on insulating GO. The developed pho...

Simple Photoreduction of Graphene Oxide Nanosheet under Mild Conditions

Proton conductivities of layered solid electrolytes can be improved by minimizing strain along the conduction path. It is shown that the conductivities (σ) of multilayer graphene oxide (GO) films (assembled by the drop-cast method) are larger than those of single-layer GO (prepared by either the drop-cast or the Langmuir-Blodgett (LB) method). At 60 % relative humidity (RH), the σ value increases from 1×10−6 S cm−1 in single-layer GO to 1×10−4 and 4×10−4 S cm−1 for 60 and 200 nm thick multilayer films, respectively. A sudden decrease in conductivity was observed for with ethylenediamine (EDA) modified GO (enGO), which is due to the blocking of epoxy groups. This experiment confirmed that the epoxide groups are the major contributor to the efficient proton transport. Because of a gradual improvement of the conduction path and an increase in the water content, σ values increase with the thickness of the multilayer films. The reported methods might be applicable to the optimization of the proton conductivity in other layered solid electrolytes.

Proton Conductivities of Graphene Oxide Nanosheets: Single, Multilayer, and Modified Nanosheets

Many unique properties of graphene oxide (GO) strongly depend on the oxygenated functional groups and morphologies. Here, the photoreaction process is demonstrated to be very useful to control these factors. We report the fast, simple production of nanopores in porous GO via photoreaction in O2 under UV irradiation at room temperature. Quantitative analysis using X-ray photoelectron spectroscopy showed that nanopores were produced in areas of oxygenated groups (sp3 carbon bonds), creating porous reduced graphene oxide (rGO). The photoreaction mechanism was proposed on the basis of changes in the number of oxygenated groups. Proton conduction occurred at the basal plane of epoxide groups in virgin GO, even at low humidity, and at carboxyl groups for porous rGO at high humidity. Thus, GO and rGO samples with various morphologies, oxygenated functional groups, and conduction types can be easily fabricated by controlling the photoreaction conditions.

Photochemical Engineering of Graphene Oxide Nanosheets

Reduced graphene oxide (rGO) and reduced graphite oxide (rGtO) were analyzed by X-ray photoelectron spectroscopy. rGO and rGtO were prepared by photochemical, electrochemical, hydrazine-assisted, a...

Hikaru Tateishi

Papers

Photoreaction of Graphene Oxide Nanosheets in Water

Simple Photoreduction of Graphene Oxide Nanosheet under Mild Conditions

Proton Conductivities of Graphene Oxide Nanosheets: Single, Multilayer, and Modified Nanosheets

Photochemical Engineering of Graphene Oxide Nanosheets

Analysis of reduced graphene oxides by X-ray photoelectron spectroscopy and electrochemical capacitance