Search

Abstract: Porous calcium carbide-derived carbon (CCDC) has been prepared by one-step route from CaC2 in a freshly prepared chlorine environment at lower temperature, and following activated by ZnCl2 to get activated CCDC. The performances of the supercapacitors based on activated CCDC as electrode active material in aqueous KOH, K2SO4, KCl and KNO3 electrolytes are studied by cyclic voltammetry, constant current charged/discharged, cyclic life and electrochemical impedance spectroscopy. It has been found that the supercapacitor using 6 M KOH as electrolyte shows an energy density of 8.3 Wh kg−1 and a power density of 1992 W kg−1 based on the total weight of the electrode active materials with a voltage range 0 V–1 V. Meanwhile, the specific capacitance of the supercapacitor in 6 M KOH electrolyte is 68 F g−1 at the scan rate of 1 mV s−1 in the voltage range of 0 V–1 V, the charge-transfer resistance is extremely low and the relaxation time is the least of all. The supercapacitor also exhibits a good cycling performance and keeps 95% of initial capacity over 5000 cycles. [Copyright &y& Elsevier]

Abstract: Hierarchically porous carbons (HPCs) have been prepared by sol–gel self-assembly technology with nickel oxide and surfactant as the dual template. The porous carbons are further activated by nitric acid. The electrochemical behaviors of supercapacitors using HPCs as electrode material in different aqueous electrolytes, e.g., (NH4)2SO4, Na2SO4, H2SO4 and KOH are studied by cyclic voltametry, galvanostatic charge/discharge, cyclic life, leakage current, self-discharge and electrochemical impedance spectroscopy. The results demonstrate that the supercapacitors in various electrolytes perform definitely capacitive behaviors; especially in 6 M KOH electrolyte the supercapacitor represents the best electrochemical performance, the shortest relaxation time, and nearly ideal polarisability. The energy density of 8.42 Wh kg−1 and power density of 17.22 kW kg−1 are obtained at the operated voltage window of 1.0 V. Especially, the energy density of 11.54 Wh kg−1 and power density of 10.58 kW kg−1 can be achieved when the voltage is up to 1.2 V. [Copyright &y& Elsevier]

3D porous nitrogen-doped graphene nanosheets (PNGs) are facilely prepared via a simple one-step segmented thermal annealing method, using graphene oxide (GO) as carbon source, urea as nitrogen source and pore generator. During the pyrolysis process at 300 °C, urea and oxygenous groups on GO sheets can release large amounts of gas such as NH 3 , HCNO and H 2 O, which act as pore generators to tear and strike GO nanosheets to form 3D porous nanostructured material. When the temperature is increased up to 800 °C, a large amount of nitrogen-containing gas can react with the functional groups on GO. Consequently, the pore forming and nitrogen doping processes of GO are successfully realized and 3D PNGs are prepared. The research results show that the PNGs with an optimal N-doping content of 6.9% display a high surface area of 490.2 m 2  g −1 and excellent electrochemical capacitive performance. The outstanding electrical double-layer capacitance and the increasing pseudocapacitance are attributed to the large specific surface area and the high nitrogen content, respectively. In 1 M H 2 SO 4 electrolyte, the PNGs exhibit a specific capacitance of 337.0 F g −1 and a low capacitance loss of 2.4% after 5000 cycles. Moreover, a symmetric supercapacitor with a cell voltage of 1.3 V is assembled, which displays both high energy density and high power density of 19.9 W h kg −1 and 650 W kg −1 , respectively. The all-in-one material with excellent electrical double-layer capacitance and pseudocapacitance is promising in supercapacitor. [ABSTRACT FROM AUTHOR]

Hierarchical porous carbon spheres/graphene (CSG) composite was prepared by a simple self-assembled method for supercapacitor electrode materials. Carbon spheres (CS) was chosen as the spacer for graphene due to its submicron size. The morphology and structure of as-prepared samples were characterized by SEM, XRD and N 2 adsorption/desorption techniques. As a result, the aggregation of graphene was reduced by CS effectively, which leads to an enhanced specific surface area and more ion-accessible pores. This unique structure is conducive to the penetration/mobility of ions, especially for ionic liquid with large ionic sizes. The electrochemical performance of synthesized CSG was investigated and the composite offered an outstanding capacitive behavior. In the two-electrode system, CSG electrode displayed a specific capacitance of 303.8 F g −1 in KOH and 280.0 F g −1 in [BMIM]BF 4 . Remarkably, the CSG//CSG supercapacitor exhibited a high energy density of 87.5 Wh kg −1 in [BMIM]BF 4 electrolyte. After 5000 cycles, the specific capacitance of CSG could still remain 95.3% in KOH and 90.1% in [BMIM]BF 4 of the initial value, implying good long-term cycle stability of the composite. The outstanding electrochemical performance can be attributed to the novel hierarchical porous structure. [ABSTRACT FROM AUTHOR]

Abstract: With the direct carbonization using polyaniline/activated mesocarbon microbead (PANI/ACMB) composites as the precursor and subsequent activation treatment with 16 M HNO3, the activated nitrogen-enriched novel carbons (a-NENCs) can be prepared. Scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption/desorption isotherm at 77 K are utilized to characterize the structure, morphology and physicochemical properties of the a-NENCs. The result shows that the a-NENCs keep the original leechee-like morphology of the PANI/ACMB composites. The supercapacitive performances of the a-NENCs are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge tests, impedance spectroscopy (EIS) and cycle life measurements in 6 M KOH. The results based on galvanostatic charge/discharge tests demonstrate that the maximum specific capacitance of the a-NENCs electrode is 385 F g−1. Meanwhile, the specific capacitance of the button supercapacitor using a-NENCs as electrode active material is as high as 89.5 F g−1 at the charge/discharge current density of 500 mA g−1. These remarkable results demonstrate the exciting commercial potential for high performance, environmentally friendly and low-cost electrical energy-storage devices based on this new material. [Copyright &y& Elsevier]

Abstract: The polyaniline/activated mesocarbon microbeads (PANI/ACMB) composites are prepared by in situ chemical oxidation polymerization. Fourier infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM) have been utilized to characterize the structure and morphology of PANI/ACMB composites. It has been found that PANI is uniformly deposited on the surface of the ACMB to form the leechee-like morphology. The supercapacitive behaviors of the PANI/ACMB composites are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge and cycle life measurements. The results obtained from cyclic voltammograms show that the composites have a maximum specific capacitance of 433.75 F g−1. Moreover, the electrochemical performance of the coin supercapacitor used PANI/ACMB composites as electrode active material represents both high specific capacitance and excellent cycle stability, indicating that the PANI/ACMB composites will be a kind of potential electrode active materials with excellent specific capacitance and enhanced cycle life for application in high performance supercapacitors. [Copyright &y& Elsevier]

Abstract: The hierarchically porous carbons (HPCs) are prepared by sol–gel self-assembly technology at various surfactant concentrations (from 0 to 0.55molL−1). The influences of the surfactant (CTAB) concentration on the physical and electrochemical properties of the activated HPCs are investigated by nitrogen adsorption–desorption isotherm, cyclic voltammetry, galvanostatic charge–discharge, cycle life, electrochemical impedance spectroscopy (EIS) and self-discharging in 6M KOH electrolyte. The results demonstrate that the concentration of surfactant template is a crucial factor impacting the characteristics of HPCs. With the change of surfactant concentration, the activated HPCs at C CTAB =0.27molL−1 (HPCs-3) shows the largest specific surface area of 689m2 g−1. In addition, the activated HPCs show excellent supercapacitive behaviors and three sections self-discharge mechanism. Especially, the activated HPCs-3 appears superior electrochemical stability, low IR drop of 0.01V, and the maximum specific capacitance of 272Fg−1 obtained from cyclic voltammetry at the scan rate of 1mVs−1. Moreover, the supercapacitor used the activated HPCs-3 as electrode active material exhibits a specific capacitance of 61Fg−1 at the current density of 1Ag−1, and keeps a specific capacitance of 60Fg−1 after 5000 consecutive charge/discharge cycles. [Copyright &y& Elsevier]