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WIREs Energy Environ.
Impact Factor: 3.297

Graphene nanostructures toward clean energy technology applications

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Abstract Graphene, a one‐atom‐layer‐thick carbon‐structured material, has attracted global research attention due to its unique two‐dimensional structure, high electrical conductivity, superior electron‐transfer properties and charge‐carrier charge‐carrier mobility, large specific surface area, high transparency, and good mechanical properties. After its successful isolation into the free standing form in 2004, various graphene nanostructures have been developed and incorporated as key components in supercapacitors, lithium‐ion batteries, solar cells, and fuel cells; the energy supporting devices which hold the key role to sustain our energy demand well into the future. Herein, we summarized the recent progress and performance of these graphene–nanostructure‐based devices. This article is categorized under: Energy Infrastructure > Science and Materials Energy and Development > Science and Materials Energy Research & Innovation > Science and Materials
(a) Schematic pictures of the microwave exfoliation/reduction of the graphite oxide (GO) and the following chemical activation of microwave exfoliated graphite oxide (MEGO) with KOH which create pores whilst retain high electrical conductivity. (b) Low‐magnification scanning electron microscopy (SEM) image of a three‐dimensional a‐MEGO piece. (c) High‐resolution SEM image of a different sample region that demonstrates the porous morphology. (d) Annular dark field (ADF)‐scanning transmission electron microscopy (STEM) image of the area in (c), acquired simultaneously. As observed, a‐MEGO contains micro and mesopores with a size distribution between 1 nm and 10 nm. (e) High‐resolution phase contrast electron micrograph on the thin edge of a‐MEGO chunk, taken at 80 kV. There is a variation in focus across the image due to the sloped nature of the sample and changes in sample thickness. The image shows the presence of a dense network of nanometer‐scale pores surrounded by highly curved, predominantly single‐layer carbon. (f) Exit wave reconstructed high‐resolution–transmission electron microscopy (HR‐TEM) image at the edge of a‐MEGO. The in‐plane carbon atoms are clearly resolved, and a variety of n‐membered carbon rings is displayed. Substantial curvature of the single‐carbon sheets is visible, with the in‐plane crystallinity being preserved. (Reprinted with permission from Ref 29. Copyright 2011, AAAS.)
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(a) Scheme shows a formation route to anchor Pt nanoparticles onto chemically converted graphene (CCG) nanosheets. (1) Oxidation of pure graphite powder to graphite oxide. (2) Formation of Pt/CCG hybrids. (b) Electrochemical catalytic performances of Pt/CCG and Pt/MWCNT hybrids. The electrochemically active surface areas measured from (a) for Pt/CCG and Pt/MWCNT are 36.27 and 33.43 m2 g−1, respectively. The If/Ib ratios measured from (b) for Pt/CCG and Pt/MWCNT are 0.83 and 0.72, respectively. (Reprinted with permission from Ref 101. Copyright 2010, Elsevier.)
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(a) Digital photo image of transparent nitrogen‐doped graphene film floating on water after removal of the nickel layer by dissolving in an aqueous acid solution. (b) The electrocatalytical mechanism of nitrogen‐doped graphene in acidic environment. (Reprinted with permission from Refs 99 and 100. Copyright 2010 and 2011, American Chemical Society.)
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(a) Scheme shows dispersion of Pt nanoparticles on a two‐dimensional carbon sheet (graphene) to facilitate an electrocatalytic reaction. (b) Galvanostatic fuel cell polarization (I‐V) curves (a–c) and power characteristics (a′–c′). The cathode was composed of (a, a′) Pt, (b, b′) GO‐Pt, and GO‐Pt (hydrazine, 300°C treated). The partially reduced GOPt‐based fuel cell delivered a maximum power of 161 mW cm−2 compared to 96 mW/cm−2 for an unsupported Pt‐based fuel cell. (Reprinted with permission from Ref 95. Copyright 2009, American Chemical Society.)
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The preparation of newly reduced graphene oxide (pr‐GO) was with a novel p‐TosNHNH2 reductant. The pr‐GO was used as an efficient anode interfacial layer for high‐performance and high‐stability OSCs. The efficiency of the cells with pr‐GO (3.63%) was highly comparable to those of the PEDOT:PSS‐based devices. Furthermore, the pr‐GO‐based organic solar cells showed a much longer cell lifetime in air stability tests in comparison with PEDOT:PSS‐based cells. (Reprinted with permission from Ref 76. Copyright 2011, John Wiley and Sons, Ltd.)
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A transparent graphene film with 85% transparency obtained by a bottom‐up chemical approach involving the thermal reaction of synthetic nanographene molecules of giant polycyclic aromatic hydrocarbons which are cross‐linked with each other and further fused into larger graphene sheets. Such graphene films were applied as window electrodes in organic solar cells. The four layers of the solar cell illustration, from bottom to top are Ag, a blend of P3HT and PCBM, TGF, and quartz, respectively. (Reprinted with permission from Ref 69. Copyright 2008, John Wiley and Sons, Ltd.)
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Graphene films, as an alternative to the metal oxides window electrodes for solid‐state dye‐sensitized solar cells. (a) Atomic force microscopy (AFM) height image of graphene films (∼10 μm2). (b) Transmittance of a ca. 10 nm thick graphene film (red), in comparison with that of indium tin oxide (black) and fluorine tin oxide (FTO) (blue). (c) Illustration of dye‐sensitized solar cell using graphene film as electrode, the four layers from bottom to top are Au, dye‐sensitized heterojunction, compact TiO2, and graphene film. (d) IV curve of graphene‐based cell (black) and the fluorine‐tin‐oxide‐based cell (red). (Reprinted with permission from Ref 68. Copyright 2008, American Chemical Society.)
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(a) Scanning electron microscopy (SEM) micrograph of coated Ni electrode. (b) SEM micrograph of a coated fiber, showing plan and shallow‐angle views. (Reprinted with permission from Ref 31. Copyright 2010, AAAS.)
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Electrochemical characterizations of a half‐cell composed of Mn3O4/RGO and Li. The specific capacities are based on the mass of Mn3O4 in the Mn3O4/RGO hybrid. (a) Charge (red) and discharge (blue) curves of Mn3O4/RGO for the first cycle at a current density of 40 mA g−1. (b) Representative charge (red) and discharge (blue) curves of Mn3O4/RGO at various current densities. (c) Capacity retention of Mn3O4/RGO at various current densities. (d) Capacity retention of free Mn3O4 nanoparticles without graphene at a current density of 40 mA g−1. (Reprinted with permission from Ref 59. Copyright 2010, American Chemical Society.)
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(a) Schematic illustration of the fabrication of nano‐graphene‐based hollow carbon spheres. (b, c) Transmission electron microscopy images of nano‐graphene‐based hollow carbon spheres. In the exterior walls of NGHCs, nanochannels arrange perpendicularly to the surface of curved spheres which is favorable for lithium‐ion diffusion from different orientations; the interior graphitic solid walls also facilitate the collection and transport of electrons during the cycling process. (Reprinted with permission from Ref 52. Copyright 2009, John Wiley and Sons, Ltd.)
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(a) Low‐magnification FEG–SEM image of loose graphene nanosheet (GNS) powders. (b) High‐magnification FEG–SEM view of GNS petals. (Reprinted with permission from Ref 47. Copyright 2010, Elsevier.)
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Supercapacitor performance of a‐MEGO (SSA ∼ 2400 m2 g−1) in the BMIM BF4/AN electrolyte. (a) CV curves at different scan rates. Rectangular shapes indicate the capacitive behavior. (b) Galvanostatic charge–discharge curves of a MEGO‐based supercapacitor under different constant currents. (Reprinted with permission from Ref 29. Copyright 2011, AAAS.)
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