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    Active carbon/graphene hydrogel nanocomposites as a symmetric device for supercapacitors
    (Taylor & Francis Inc, 2016) Ates, Murat; Cinar, Damla; Caliskan, Sinan; Gecgel, Unal; Uner, Osman; Bayrak, Yuksel; Candan, Idris
    Activated carbons (ACs) are successfully synthesized from Elaeagnus grain by a simple chemical synthesis methodology and demonstrated as novel, suitable supercapacitor electrode materials for graphene hydrogel (GH)/AC nanocomposites. GH/AC nanocomposites are synthesized via hydrothermal process at temperature of 180 degrees C. The low-temperature thermal exfoliation approach is convenient for mass production of graphene hydrogel (GH) at low cost and it can be used as electrode material for energy storage applications. The GH/AC nanocomposites exhibit better electrochemical performances than the pure GH. Electrochemical performance of the electrodes is studied by cyclic voltammetry, and galvanostatic charge-discharge measurements in 1.0 M H2SO4 solution. A remarkable specific capacitance of 602.36 Fg(1) (based on GH/AC nanocomposites for 0.4 g AC) is obtained at a scan rate of 1 mVs(1) in 1 M H2SO4 solution and 155.78 Fg(1) for GH. The specific capacitance was increased 3.87 times for GH/AC compared to GH electrodes. Moreover, the GH/AC nanocomposites for 0.2 g AC present excellent long cycle life with 99.8% specific capacitance retained after 1000 charge/discharge processes. Herein, ACs prepared from Elaeagnus grain are synthesized GH and AC supercapacitor device for high-performance electrical energy storage devices as a promising substitute to conventional electrode materials for EDLCs.
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    The electropolymerization of N,N-(propane-1,3-diyl)bis(2-aminobenzamide), characterization, and capacitor study
    (Sage Publications Ltd, 2018) Ates, Murat; Kolancilar, Hakan; Caliskan, Sinan; Cinar, Damla
    In this study, aniline-based monomer, N,N-(propane-1,3-diyl)bis(2-aminobenzamide), (PAB), was synthesized and characterized by proton nuclear magnetic resonance (1H-NMR), carbon-13 nuclear magnetic resonance (13C-NMR), and Fourier transform infrared spectroscopy. The electropolymerization of the monomer was performed on glassy carbon electrode by cyclic voltammetry (CV). The effects of solvent, dopant, scan number, and scan rate on the electropolymerization and properties of the poly(PAB) films were investigated. The modified electrode was also characterized by Fourier transform infrared-attenuated total reflection spectroscopy and scanning electron microscopy-energy-dispersive X-ray analysis. The capacitive properties of the poly(PAB) films were firstly tested by electrochemical impedance spectroscopy. The highest specific capacitances (C-sp) of poly(PAB) films were obtained as C-sp = 6.22 mF cm(-2) in 0.1 M lithium perchlorate/acetonitrile (ACN) for [PAB]0 = 20 mmol dm(-3) and C-sp = 16.9 mF cm(-2) in 1 mol dm(-3) sulfuric acid for [PAB]0 = 5 mmol dm(-3) at the scan rate of 5 mV s(-1) from CV measurements. This study is novel because it was the first study on capacitance performances of poly(PAB) films in the literature.
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    Reduced graphene oxide/Titanium oxide nanocomposite synthesis via microwave-assisted method and supercapacitor behaviors
    (Elsevier Science Sa, 2017) Ates, Murat; Bayrak, Yuksel; Yoruk, Ozan; Caliskan, Sinan
    In this paper, graphene oxide (GO) was firstly synthesized by modification of Hummers method from the literature. Secondly, reduced graphene oxide (rGO)/Titanium oxide (TiO2) nanocomposites were synthesized with different wt/wt % of GO/TiO2 (1:1; 1:2; 1:5 and 1:10) by microwave-assisted method. By treating GO and GO/TiO2 nanocomposites in a microwave oven, reduced graphene oxide (rGO) and rGO/TiO2 materials could be obtained within power of 180 Win 10 min. The weight ratio of rGO and TiO2 was used to obtain the optimum conditions for nanocomposite materials. The rGO/TiO2 nanocomposite active materials were characterized by cyclic voltammetry (CV), Fourier-transform infrared - Attenuated total reflectance (FTIR-ATR), scanning electron microscopy-energy dispersion X-ray (SEM-EDX), thermogravimetry (TGA), differential thermal analyzer (DTA) and electrochemical impedance spectroscopy (EIS) analysis. Thirdly, supercapacitors were fabricated as a symmetric device with two electrode configuration. The device performances were tested by CV, galvanostatic constant current (CC), and EIS measurements. TGA analysis indicated that the thermal stability of the nanocomposites improved from rGO (40% at 892.8 degrees C) to nanocomposite as the initial feed ratio of [GO](o)/[TiO2](o) = 1/10 as (94% at 949.3 degrees C) increased. The result show that the as-prepared symmetrical rGO/TiO2 nanocomposite on the two-electrode system displays very high specific capacitance of 524.02 F/g at 2 mV/s for [GO](o)/[TiO2](o) = 1/5 with a high energy density of E = 50.07 Wh/kg at 2 mV/s for [GO](o)/[TiO2](o) = 1/1 and high power density of P = 58.6 kW/kg at a the scan rate 1000 mV/s for [GO](o)/[TiO2](o) = 1/1. Additionally, the symmetric electrode shows good cycling stability with a retention value of 6.6% for [GO](o)/[TiO2](o) = 1/1 after 1000 cycles. These good results suggest us that rGO/TiO2 nanocomposite which is obtained by microwave-assisted method has a great potential as an electrode material for supercapacitor applications. The equivalent circuit model of R-s(C-dl(RctW)) was used to explain parameters of solution resistance, double layer capacitance (Cdl), charge transfer resistance (R-ct), Warburg impedance (W). Theoretical and experimental values support with each other. (C) 2017 Elsevier B.V. All rights reserved.