Fabrication of large-area and high-crystallinity photoreduced graphene oxide films via reconstructed two-dimensional multilayer structures

TL;DR: The state-of-the-art advancements in FSSCs are reviewed to provide new insights on mechanisms, emerging electrode materials, flexible gel electrolytes and novel cell designs.

TL;DR: Graphene has recently enabled the dramatic improvement of portable electronics and electric vehicles by providing better means for storing electricity as mentioned in this paper, with specific emphasis placed on the processing of graphene into electrodes, which is an essential step in the production of devices.

TL;DR: The demand for flexible/wearable electronic devices that have aesthetic appeal and multi-functionality has stimulated the rapid development of flexible supercapacitors with enhanced electrochemical performance and mechanical flexibility and current progress made with graphene-based electrodes is summarized.

TL;DR: 3D cellular graphene films with open porosity, high electrical conductivity, and good tensile strength, can be synthesized by a method combining freeze-casting and filtration, resulting in supercapacitors with extremely high specific power densities and high energy densities.

TL;DR: It is reported that chemically converted graphene sheets obtained from graphite can readily form stable aqueous colloids through electrostatic stabilization, making it possible to process graphene materials using low-cost solution processing techniques, opening up enormous opportunities to use this unique carbon nanostructure for many technological applications.

TL;DR: CMG materials are made from 1-atom thick sheets of carbon, functionalized as needed, and here their performance in an ultracapacitor cell is demonstrated, illustrating the exciting potential for high performance, electrical energy storage devices based on this new class of carbon material.

Abstract: Graphene is the name given to a two-dimensional sheet of sp2-hybridized carbon. Its extended honeycomb network is the basic building block of other important allotropes; it can be stacked to form 3D graphite, rolled to form 1D nanotubes, and wrapped to form 0D fullerenes. Long-range π-conjugation in graphene yields extraordinary thermal, mechanical, and electrical properties, which have long been the interest of many theoretical studies and more recently became an exciting area for experimentalists. While studies of graphite have included those utilizing fewer and fewer layers for some time,1 the field was delivered a jolt in 2004, when Geim and co-workers at Manchester University first isolated single-layer samples from graphite (see Figure 1).2 This led to an explosion of interest, in part because two-dimensional crystals were thought to be thermodynamically unstable at finite temperatures.3,4 Quasi-twodimensional films grown by molecular beam epitaxy (MBE) are stabilized by a supporting substrate, which often plays a significant role in growth and has an appreciable influence on electrical properties.5 In contrast, the mechanical exfoliation technique used by the Manchester group isolated the two-dimensional crystals from three-dimensional graphite. Resulting singleand few-layer flakes were pinned to the substrate by only van der Waals forces and could be made free-standing by etching away the substrate.6-9 This minimized any induced effects and allowed scientists to probe graphene’s intrinsic properties. The experimental isolation of single-layer graphene first and foremost yielded access to a large amount of interesting physics.10,11 Initial studies included observations of graphene’s ambipolar field effect,2 the quantum Hall effect at room temperature,12-17 measurements of extremely high carrier mobility,7,18-20 and even the first ever detection of single molecule adsorption events.21,22 These properties generated huge interest in the possible implementation of graphene in a myriad of devices. These include future generations of high-speed and radio frequency logic devices, thermally and electrically conductive reinforced composites, sensors, and transparent electrodes for displays and solar cells. Despite intense interest and continuing experimental success by device physicists, widespread implementation of graphene has yet to occur. This is primarily due to the difficulty of reliably producing high quality samples, especially in any scalable fashion.23 The challenge is really 2-fold because performance depends on both the number of layers present and the overall quality of the crystal lattice.19,24-26 So far, the original top-down approach of mechanical exfoliation has produced the highest quality samples, but the method is neither high throughput nor high-yield. In order to exfoliate a single sheet, van der Waals attraction between exactly the first and second layers must be overcome without disturbing any subsequent sheets. Therefore, a number of alternative approaches to obtaining single layers have been explored, a few of which have led to promising proof-ofconcept devices. Alternatives to mechanical exfoliation include primarily three general approaches: chemical efforts to exfoliate and stabilize individual sheets in solution,27-32 bottom-up methods to grow graphene directly from organic precursors,33-36 and attempts to catalyze growth in situ on a substrate.37-43 Each of these approaches has its drawbacks. For chemically derived graphene, complete exfoliation in solution so far requires extensive modification of the 2D crystal lattice, which degrades device performance.31,44 Alternatively, bottom-up techniques have yet to produce large and uniform † Department of Chemistry and Biochemistry and California NanoSystems Institute. ‡ Department of Materials Science and Engineering and California NanoSystems Institute. Chem. Rev. 2010, 110, 132–145 132

TL;DR: Graphene dispersions with concentrations up to approximately 0.01 mg ml(-1), produced by dispersion and exfoliation of graphite in organic solvents such as N-methyl-pyrrolidone are demonstrated.