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: 33.27). 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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    • "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 · 6.16 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; DOI:10.1007/s10570-015-0702-3 · 3.03 Impact Factor
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    • "However, the performance of two-dimensional (2D) graphene sheets is severely limited by the poor accessibilities with electrolytes and the sheet aggregations during the processes of material syntheses and/or the electrode fabrications due to the strong van der Waals interactions between the neighboring sheets [12] [21], which lead to that the amount of effective surface electrostatic charge accumulation is low and the interlayer channels of the graphene for ionic/electronic transports are partially blocked. Thus, the capacitance values of the reported 2D graphene-based electrodes are usually in the range of 100– 200 F g À1 [22] [23] [24], which are far below the theoretical value of 550 F g À1 calculated for the graphenes with an ideal single layer distribution [5] [18]. "
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    ABSTRACT: Abstract Three-dimensional functionalized multilayer graphenes (3D FMG) with systematically controllable interconnected pores and surface functional groups are prepared by using combined hydrochloric acid-assisted ultrasonic exfoliation and thermal reduction approach. Electrochemical analyses show that the optimized 3D FMG owns an amazing high specific capacitance of 508 F g−1 at 5 mV s−1 in aqueous electrolyte system. The energy density of 15, 32, and 66 Wh kg−1 has been obtained at the power density of 14, 43, and 52 kW kg−1 for the 3D FMG-based supercapacitor in the aqueous, organic and ionic liquid electrolyte system, respectively. 94% of the initial capacitance of the 3D FMG-based supercapacitor is retained after 10,000 cycles at 1 A g−1 in the aqueous system. The outstanding electrochemical performances of the 3D FMG are attributed to the strong synergistic effect of the interconnected pores and surface functional groups. The hierarchical interconnected pore channels can efficiently facilitate the ionic/electronic transports between the electrodes and electrolyte ions and appropriately prevent the restacking of graphene sheets. The rational surface functional groups may improve a facile accessibility of the electrodes with the electrolytes and provide an additional pseudocapacitance.
    Carbon 04/2015; 85:351 - 362. DOI:10.1016/j.carbon.2015.01.001 · 6.16 Impact Factor
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