Measurement of the quantum capacitance of graphene

Center for Bioelectronics and Biosensors, Biodesign Institute, Department of Electrical Engineering, Arizona State University, Tempe, AZ 85287, USA.
Nature Nanotechnology (Impact Factor: 34.05). 09/2009; 4(8):505-9. DOI: 10.1038/nnano.2009.177
Source: PubMed

ABSTRACT Graphene has received widespread attention due to its unique electronic properties. Much of the research conducted so far has focused on electron mobility, which is determined by scattering from charged impurities and other inhomogeneities. However, another important quantity, the quantum capacitance, has been largely overlooked. Here, we report a direct measurement of the quantum capacitance of graphene as a function of gate potential using a three-electrode electrochemical configuration. The quantum capacitance has a non-zero minimum at the Dirac point and a linear increase on both sides of the minimum with relatively small slopes. Our findings -- which are not predicted by theory for ideal graphene -- suggest that charged impurities also influences the quantum capacitance. We also measured the capacitance in aqueous solutions at different ionic concentrations, and our results strongly indicate that the long-standing puzzle about the interfacial capacitance in carbon-based electrodes has a quantum origin.

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Available from: Nongjian Tao, Dec 31, 2014
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    • "Graphene has excellent electrical conductivity and large theoretical specific surface area (SSA) of 2630 m 2 g À1 [16], both of which are highly desirable for developing high-performance electrochemical capacitor [5] [17] [18]. It has been demonstrated that the graphene is capable of delivering a specific capacitance as large as 550 F g À1 providing that its surface is fully utilized for charge storage [19]. However, this value has yet been achieved as graphene sheets tend to restack into irreversible agglomerates through strong p-stacking and hydrophobic interactions, leading to a significant loss of surface area and remarkable decrease of ion diffusion rate in the interior of electrode. "
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    ABSTRACT: We present a facile and efficient route to introduce in-plane nanopores on the graphene sheets by activation of graphene aerogel (GA) with phosphoric acid (H3PO4). Results from N2 adsorption and TEM images showed that H3PO4 activation created mesopores with pore size of 2–8 nm on the graphene sheets. With such nanopores on graphene sheets, the activated GA exhibits a specific capacitance of 204 F g−1, enhanced rate capability (69% capacitance retention from 0.2 to 30 A g−1), reduced equivalent series resistance (3.8 mΩ) and shortened time constant (0.73 s) when comparing with the hydrothermally-derived pristine GA and thermally annealed GA in the absent of H3PO4. The excellent capacitive properties demonstrate that introduction of nanopores on GA by H3PO4 activation not only provides large ion-accessible surface area for efficient charge storage, but also promotes the kinetics of electrolyte across the graphene two-dimensional planes.
    Carbon 10/2015; 92. DOI:10.1016/j.carbon.2015.02.052 · 6.20 Impact Factor
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    • "For this purpose graphene, an atomically thin two-dimensional sheet of sp 2 -hybridized carbon atoms arranged in a honeycomb crystal lattice, is a very promising candidate as the carbon component in the hybrid due to its high carrier mobility, large electrical conductivity and high specific surface area [10e13]. It has been demonstrated that graphene's high specific surface area leads to a large theoretic double layer capacitance of up to 21 mFcm À2 [14]. However, agglomeration of graphene due to strong attractive forces among sheets is a challenging obstacle in the way of large scale production of high quality graphene hybrids for SC applications. "
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    ABSTRACT: In this work, we present a new synthesis method for surfactant stabilized graphene (SSG) combined with polyaniline nanofiber (PANI-Nf) and apply the composite material as supercapacitor (SC) electrodes by screen-printing technique. Surfactant stabilized graphene polyaniline nanofiber composite (PANI-SSG) was synthesized by electrolytic exfoliation of graphite and subsequent interfacial polymerization. Firstly, graphite was electrolytically exfoliated in an electrolyte containing anionic surfactant. Next, ammonium peroxydisulfate initiator and hydrochloric acid were added to the graphene dispersion to form the aqueous phase for interfacial polymerization of polyaniline nanofiber. This dispersion was then added to the water-insoluble solvent phase containing aniline monomer. The polymerization only occurred at the interface of the two immiscible phases leading to polyaniline nanofiber decorated graphene structures. Characterizations by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy suggested nanocomposite formation with intermolecular π-π bonding of graphene with polyaniline nanofibers. Pastes of the materials were screen printed on stainless steel current collectors and tested for SC performance by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements with 2 M H2SO4 electrolyte using a home-built two-electrode test-cell. CV results showed redox peaks of polyaniline with wide cyclic loop, indicating large pseudocapacitance of the nanocomposite. From GCD measurement, a high specific capacitance of 690 Fg−1 at 1 Ag−1 was achieved. Therefore, PANI-SSG nano-composite prepared by electrolytic exfoliation and interfacial polymerization is a promising candidate for SC applications.
    Composites Part B Engineering 08/2015; 77. DOI:10.1016/j.compositesb.2015.03.004 · 2.98 Impact Factor
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    • "In our previous study, we investigated the effect of polyethylene glycol (PEG) on the electromechanical properties of a CMC-based actuator created with BMIMBr ionic liquid (Ozdemir et al. 2015). Graphene, which is a stable 2D one-atom-layer material, shows excellent properties, i.e., good electrical conductivity and mechanical strength, a large surface area and superior performance (Huang et al. 2012; Lee et al. 2008; Novoselov et al. 2004; Xia et al. 2009). Feng et al. (2012) emphasized that graphene loading enhanced the electrical and mechanical properties . "
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    ABSTRACT: In this article, the effects of graphene loading (0.1, 0.2, 0.3 wt%) on both the electromechanical and mechanical properties of carboxymethylcellulose (CMC)-based actuators were investigated. CMC-based graphene-loaded actuators were prepared by using 1-butyl-3-methylimidazolium bromide. The synthesized graphene-loaded actuators were characterized by Fourier transform infrared, X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy, and tensile tests. Electromechanical properties of the actuators were obtained under DC excitation voltages of 1, 3, 5, and 7 V with a laser displacement sensor. According to the obtained results, the ultimate tensile strength of CMC-based actuators containing 0.3 wt% graphene was higher than that of unloaded actuators by approximately 72.8 %. In addition, the Young’s modulus value of the graphene-loaded actuators increased continuously with increasing graphene content. Under a DC excitation voltage of 5 V, the maximum tip displacement of 0.2 wt% graphene-loaded actuators increased by about 15 % compared to unloaded actuators.
    Cellulose 07/2015; 22(5). DOI:10.1007/s10570-015-0702-3 · 3.57 Impact Factor
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