Papers by Keyword: Specific Capacitance

Abstract: Energy storage devices have become essential in modern life, and supercapacitors are among the prominent choices. Reduced graphene oxide (rGO) is a promising material for electrochemical double layer capacitors (EDLC). However, its drawback lies in its relatively lower electrical conductivity compared to pristine graphene. Doping mechanism utilizing nitrogen could enhance the electrical conductivity of rGO. In parallel, CuCr₂O₄ has been identified as a suitable material for pseudocapacitor. In this study, hybrid supercapacitors of EDLC and pseudocapacitor were fabricated through the utilization of N-doped rGO/CuCr₂O₄ composites. The fabrication process involved varying the duration of microwave-assisted solvothermal radiation at 180 W to synthesize N-doped rGO, with variations of 30, 45, and 60 minutes. The impact of varying radiation duration on the structures and morphologies of the materials was investigated using X-Ray Diffractometer (XRD), Fourier-Transformed InfraRed (FTIR), Scanning Electron Microscope (SEM), and Energy Dispersive Spectroscope (EDS) instruments. The capacitive properties of the fabricated supercapacitors were evaluated through Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). From the CV measurements, the specific capacitances of the supercapacitors synthesized with radiation durations of 30, 45 and 60 minutes were found to be 397.72 Fg^-1, 245.79 Fg^-1, and 237.74 Fg^-1, respectively. The specific capacitance values were strongly influenced by the electrical conductivities of the materials, which were measured as 0.2, 0.18, and 0.13 Scm^-1 for radiation durations of 30, 45, and 60 minutes, respectively. It was observed that longer radiation durations appeared to induce structural damage to the material, leading to decreased conductivity in the resulting material.

Abstract: A hybrid supercapacitor is an energy storage device that combines the properties of EDLCs and pseudocapacitors. In this research, the goal was to analyze the effect of hydrothermal temperature on the structure, morphology, and capacitive properties of the N-Doped reduced graphene oxide/Copper Chromite (N-Doped rGO/CuCr₂O₄) composite, which was being investigated as a potential material for hybrid supercapacitor electrodes. The method used was hydrothermal, with temperature variations of 120°C, 140°C, and 160°C. The structure and morphology of the composites were analyzed using Scanning Electron Microscope (SEM) and Energy Dispersive X-Ray Analysis (EDX), X-Ray Diffractometer (XRD), and Fourier Transform Infrared Spectrometer (FTIR). Meanwhile, the capacitance and conductivity values of N-doped rGO/CuCr₂O₄ were measured using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) tests. The results of the XRD tests showed that an increase in temperature led to a greater d_spacing value, indicating the presence of more substituted nitrogen atoms. This was supported by the results from EDX, which showed that the sample with a hydrothermal temperature of 160°C had the largest percentage of nitrogen. Nitrogen is important in increasing the conductivity of the material. The FTIR results revealed a covalent bond between Carbon (C) and Nitrogen (N). Meanwhile, the results of the CV test, performed at a scan rate of 5 mV/s and a potential window of 0-0.8 V, showed that the specific capacitance values were 99.5, 196.16, and 221.59 Fg^-1 for the samples with hydrothermal temperatures of 120°C, 140°C, and 160°C, respectively. The EIS test measured the conductivity values of the samples, which were 0.123, 0.518, and 0.549 S/m for the samples with hydrothermal temperatures of 120°C, 140°C, and 160°C, respectively. Thus, the specific capacitance values were influenced by the electrical conductivity of the materials and the nitrogen doping content in the electrode composite material.

Abstract: To improve the specific capacitance, power and energy of electrical energy storage devices, in particular hybrid capacitors, various methods of cathode material modification are used. One of the methods of modifying nanostructured materials without applying high temperatures, pressures and long reaction times is ultrasonic treatment. Although the interaction of ultrasound with the structure and surface of electrode materials is well enough studied, there are few works that investigate the optimal duration of ultrasonic treatment and its relationship with the capacitive characteristics of these materials. Therefore, we investigated the efficiency of ultrasonic dispersion of nanocrystalline nickel molybdate hydrate for 15, 60 and 90 minutes. The appearance of two cathodic peaks on cyclic voltammetry patterns was analyzed and the charge / discharge mechanism of the electrode based on nanocrystalline NiMoO₄ hydrate was presented. Based on the results of potentiodynamic and galvanostatic studies the specific capacitances of the initial NiMoO₄ and the material modified by ultrasound for 15, 60 and 90 minutes were calculated. The proton diffusion coefficients of nickel molybdate hydrate were determined on the basis of the Randles–Sevcik equation. NiMoO₄ subjected to ultrasonic dispersion for 60 min as a cathode material in a hybrid electrochemical system was tested.

Abstract: In recent years, nickel tungstate has attracted considerable research interest as an electrode material for supercapacitors. In this work, NiWO₄ was synthesized by co-precipitation and exposed to laser irradiation. The structure of nickel tungstate was investigated by X-ray diffraction and its electrochemical properties by potentiodynamics, galvanostatic and impedance spectroscopy methods. The results show that NiWO₄ subjected to laser irradiation for 180 s showed higher specific characteristics than the initial material. Namely, at a discharge current of 1 mA, NiWO₄ achieves a specific capacitance of 153 F/g, and this value is 48% higher than that of the initial material. The higher specific characteristics of laser-modified NiWO₄ result from the ability of the material to interact better with electrolyte ions due to the passage of fast redox reactions and the capacitance of the electrical double layer, which is confirmed by impedance studies.

Abstract: The equivalent series resistances (ESR) and specific capacitances (C_s) of supercapacitors carbon electrodes have been investigated using cyclic voltammetry and electrochemical impedance spectroscopy. Commercial activated carbon electrodes employing organic electrolyte have been tested using a potential window in the range of 2.7–3.8 V. Specific capacitances were calculated from cyclic voltammetry curves at room temperature employing various scan rates (30 and 100mVs^-1). Internal series resistances of the supercapacitors were measured using the galvanostatic curves at room temperature and above (25 and 50°C). The ESR increase to 9.8 Ω at 25° and 2.7V to 78.8 Ω at with operating temperature raise and also with overpotential. A compositional and morphological evaluation of these electrodes showed a very homogeneous structure. It has been shown that the specific capacitance decreased considerably with scan rate, current density, electrochemical potential window and working temperature.

Abstract: The microstructure, chemical composition, equivalent series resistance (ESR) and specific capacitance (C_s) of supercapacitors electrodes have been investigated. Commercial activated carbon electrodes employing organic electrolyte have been tested at a potential window of 1.1 and 2.7 V. Specific capacitances were calculated from cyclic voltammetry curves at room temperature employing various scan rates (2-70 mVs^-1). Internal resistances of the supercapacitors were calculated using the galvanostatic cycling curves at several current densities (10-175 mAg^-1). A maximum specific capacity of 58 Fg^-1 has been achieved with the organic electrolyte at a current density of 30 mAg^-1 and a potential window of 2.7V. After this initial study, the organic electrolyte was removed from the electrodes by back pumping vacuum. Two new aqueous electrolytes have been substituted in the commercial electrodes for a comparison: Na₂SO₄ and KOH (1.0 mol.L^-1). At a discharge density of 75 mAg^-1, the electrodes with KOH showed a maximum specific capacitance of 53 Fg^-1 whereas the Na₂SO₄ showed only 6 Fg^-1. ESR of the electrodes with organic electrolyte and KOH were in the range of 20 Ωcm² whereas with Na₂SO₄ of 14 Ωcm². The microstructures of the electrode material have been investigated using scanning electron microscopy (SEM) and chemical microanalyses employing energy dispersive X-ray analysis (EDX). A compositional and morphological evaluation of these electrodes showed a very homogeneous structure.

Abstract: Electric double-layer capacitors prepared using activated carbons have been subjected to vacuum heat treatments at low and high temperatures (200, 400, 600, 800 and 1000°C). The electrodes have been tested at a potential of 1.1 V employing a KOH electrolyte (1.0and 6.0 mol.L^-1). The effect of or HDDR upon the electrical properties has been investigated by cyclic voltammetry. It has been shown that the specific capacitance at 5 msV^-1 increases from 50 Fg^-1 to 130 Fg^-1 after a heat treatment at 400°C for 1 hour under back pump vacuum. At 400°C the diminution in the specific capacitance with higher scanning rate (10 msV^-1) was much less pronounced (from 130 Fg^-1 to 100 Fg^-1). Equivalent series resistance (ESR) and equivalent parallel resistance of supercapacitors electrodes have also been investigated. Internal resistances of the supercapacitors were calculated using the galvanostatic curves at current densities (100 mAg^-1).A compositional and morphological evaluation of these electrodes showed no significant change on the activated carbon structure.

Abstract: The effects of the separator thickness (δ) upon the equivalent series resistances (ESR) and specific capacitances (C_s) of supercapacitors electrodes have been investigated using commercially available porous filter paper (δ=150 μm, pores size=7.5 μm, 80 gm^-2). Commercial activated carbon electrodes immersed in 1molL^-1 KOH electrolyte (25°C) have been employed in this study. The specific capacitances were calculated from cyclic voltammetry curves at room temperature employing various scan rates (5, 10, 15 and 30 mVs^-1). Internal series resistances of the supercapacitors were measured using the galvanostatic charge discharge curves also at room temperature. A maximum of 28 separators (δ=4200 μm) have been employed in this investigation. It has been shown that the ESR increases substantially with separator thickness (from 3.1 to 7.9 Ωcm²). The specific capacitance decreased somewhat with increasing separator thickness and scan rates (from 64 to 52 Fg^-1; at 5 mVs^-1). The microstructures of the electrode material have been investigated using scanning electron microscopy (SEM) and chemical microanalyses employing energy dispersive X-ray analysis (EDX). A compositional and morphological evaluation of these electrodes showed a very homogeneous microstructure.

Abstract: In the present work, attempts of reducing a graphene oxide powder using a low temperature hydrogenation disproportionation desorption and the recombination process (L-HDDR) has been carried out. A lower processing temperature in large scale production is significant when costs are concerned. Graphite oxide was prepared using a modified Hummers’ method dispersed in ethanol and exfoliated using ultrasonication to produce Graphene Oxide (GO). Investigations have been carried out by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results of L-HDDR processing graphene oxide powder, using unmixed hydrogen at 400°C and relatively low pressures (<2 bars) have been reported. X-ray diffraction patterns showed a reduction of graphene oxide with the L-HDDR process. The results showed that both processes, the L-HDDR as well as the standard HDDR, may be applied to the reduction of graphene oxide in order to produce supercapacitor materials. The advantage of employing the L-HDDR process is a relatively low temperature reducing the cost of treatment, what is a very important factor for producing a large amount of material. Thus, the L-HDDR process has been considered a promising alternative method of reducing graphene oxide with efficiency, with the possibility of large scale production.

Abstract: Nickel cobaltite has become a popular energy storage material in recent years for high performance energy storage devices because of its low lost, high electronic conductivity, high electrochemical activity and environmental benignity. Nickel cobaltite (NCO)/porous graphene nanosheets network (PG) composites were synthesized via the two-steps hydrothermal method to enhance electrochemical properties in this study. The NCO/PG composite electrode demonstrated high specific capacitance of 3965 F g^-1 at the current density of 1 A g^-1 compared with the value of NCO that capacitance is 644 F g^-1, and it maintained the 72% of the original capacitance after 3,000 charge-discharge cycles. It showed the maximum energy density of 46.3 Wh kg^-1 and maximum power density of 1450 W kg^-1. The NCO/GO composite has high potential as a psudocapacitance material for energy storage devices.