Project description:We report a gel polymer electrolyte (GPE) supercapacitor concept with improved pathways for ion transport, thanks to a facile creation of a coherent continuous distribution of the electrolyte throughout the electrode. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer framework for organic electrolytes. A permeating distribution of the GPE into the electrodes, acting both as integrated electrolyte and binder, as well as thin separator, promotes ion diffusion and increases the active electrode-electrolyte interface, which leads to improvements both in capacitance and rate capability. An activation process induced during the first charge-discharge cycles was detected, after which, the charge transfer resistance and Warburg impedance decrease. We found that a GPE thickness of 12 μm led to optimal capacitance and rate capability. A novel hybrid nanocomposite material, formed by the tetraethylammonium salt of the 1 nm-sized phosphomolybdate cluster and activated carbon (AC/TEAPMo12), was shown to improve its capacitive performance with this gel electrolyte arrangement. Due to the homogeneous dispersion of PMo12 clusters, its energy storage process is non-diffusion-controlled. In the symmetric capacitors, the hybrid nanocomposite material can perform redox reactions in both the positive and the negative electrodes in an ambipolar mode. The volumetric capacitance of a symmetric supercapacitor made with the hybrid electrodes increased by 40% compared to a cell with parent AC electrodes. Due to the synergy between permeating GPE and the hybrid electrodes, the GPE hybrid symmetric capacitor delivers three times more energy density at higher power densities and equivalent cycle stability compared with conventional AC symmetric capacitors.
Project description:In this study, we report a facile fabrication of ultrathin two-dimensional (2D) nanosheet hybrid composite, ?-Fe2O3 nanosheet@Ni(OH)2 nanosheet, by a two-step hydrothermal method to achieve high specific capacitance and good stability performance at high charging/discharging rates when serving as electrode material of supercapacitors. The ?-Fe2O3@Ni(OH)2 hybrid electrode not only has a smooth decrease of the specific capacitance with increasing current density, compared with the sharp decline of single component of Ni(OH)2 electrode, but also presents excellent rate capability with a specific capacitance of 356?F/g at a current density of 16?A/g and excellent cycling stability (a capacity retention of 93.3% after 500?cycles), which are superior to the performances of Ni(OH)2 with a lower specific capacitance of 132?F/g and a lower capacity retention of 81.8% at 16?A/g. The results indicate such hybrid structure would be promising as excellent electrode material for good performances at high current densities in the future.
Project description:Modern society is hungry for electrical power. To improve the efficiency of energy harvesting from heat, extensive efforts seek high-performance thermoelectric materials that possess large differences between electronic and thermal conductance. Here we report a super high-performance material of consisting of MoS2/WS2 hybrid nanoribbons discovered from a theoretical investigation using nonequilibrium Green's function methods combined with first-principles calculations and molecular dynamics simulations. The hybrid nanoribbons show higher efficiency of energy conversion than the MoS2 and WS2 nanoribbons due to the fact that the MoS2/WS2 interface reduces lattice thermal conductivity more than the electron transport. By tuning the number of the MoS2/WS2 interfaces, a figure of merit ZT as high as 5.5 is achieved at a temperature of 600 K. Our results imply that the MoS2/WS2 hybrid nanoribbons have promising applications in thermal energy harvesting.
Project description:In this paper, we report a complete solution for enhanced sludge treatment involving the removal of toxic metal (Cu(II)) from waste waters, subsequent pyrolytic conversion of these sludge to Cu-doped porous carbon, and their application in energy storage systems. The morphology, composition, and pore structure of the resultant Cu-doped porous carbon could be readily modulated by varying the flocculation capacity of Cu(II). The results demonstrated that it exhibited outstanding performance for supercapacitor electrode applications. The Cu(II) removal efficiency has been evaluated and compared to the possible energy benefits. The flocculant dosage up to 200 mg·L-1 was an equilibrium point existing between environmental impact and energy, at which more than 99% Cu(II) removal efficiency was achieved, while the resulting annealed product showed a high specific capacity (389.9·F·g-1 at 1·A·g-1) and good cycling stability (4% loss after 2500 cycles) as an electrode material for supercapacitors.
Project description:Ordered mesoporous carbon materials show great potential for electric double-layer supercapacitors because of their high specific surface area, designable pore structure, and tunable morphology. However, low graphitic crystallinity nature and poor contact between particles lead to their high inherent resistance, which limits the supercapacitance performance. Herein, we report on a hierarchically rambutan-morphological design of carbon composites with ordered mesoporous carbon as the core and carbon nanotubes as the shell, which significantly improve the electric contact between mesoporous carbon particles and promote the electrochemical performance. By an ultrafast microwave process in a household microwave heater under ambient condition, carbon nanotubes grow out from the pores of ordered mesoporous carbon and are dispersed on its surface like the whiskers of rambutan. As-synthesized ordered mesoporous carbon CMK-3/carbon nanotubes nanocomposites show significantly enhanced specific capacitance (315.6 F·g-1 at 1 A·g-1, as compared with 172.1 F·g-1 of CMK-3), high rate capability (214.6 F·g-1 at 50 A·g-1), and cycling durability (10,000 cycles, 99.32%). The structural design and microwave synthesis enable a facile preparation of the hybrid ordered mesoporous carbon CMK-3/carbon nanotubes nanocomposites, and show potential for easy and low-cost production of high performance electric double-layer supercapacitors materials.
Project description:Nanocomposites of Ni(OH)? or NiO have successfully been used in electrodes in the last five years, but they have been falsely presented as pseudocapacitive electrodes for electrochemical capacitors and hybrid devices. Indeed, these nickel oxide or hydroxide electrodes are pure battery-type electrodes which store charges through faradaic processes as can be shown by cyclic voltammograms or constant current galvanostatic charge/discharge plots. Despite this misunderstanding, such electrodes can be of interest as positive electrodes in hybrid supercapacitors operating under KOH electrolyte, together with an activated carbon-negative electrode. This study indicates the requirements for the implementation of Ni(OH)?-based electrodes in hybrid designs and the improvements that are necessary in order to increase the energy and power densities of such devices. Mass loading is the key parameter which must be above 10 mg·cm−2 to correctly evaluate the performance of Ni(OH)? or NiO-based nanocomposite electrodes and provide gravimetric capacity values. With such loadings, rate capability, capacity, cycling ability, energy and power densities can be accurately evaluated. Among the 80 papers analyzed in this study, there are indications that such nanocomposite electrode can successfully improve the performance of standard Ni(OH)? (+)//6 M KOH//activated carbon (−) hybrid supercapacitor.
Project description:Nitrogen doped carbon materials as electrodes of supercapacitors have attracted abundant attention. Herein, we demonstrated a method to synthesize N-doped macroporous carbon materials (NMC) with continuous channels and large size pores carbonized from polyaniline using multiporous silica beads as sacrificial templates to act as electrode materials in supercapacitors. By the nice carbonized process, i.e., pre-carbonization at 400 °C and then pyrolysis at 700/800/900/1000 °C, NMC replicas with high BET specific surface areas exhibit excellent stability and recyclability as well as superb capacitance behavior (~413 F ⋅ g-1) in alkaline electrolyte. This research may provide a method to synthesize macroporous materials with continuous channels and hierarchical pores to enhance the infiltration and mass transfer not only used as electrode, but also as catalyst somewhere micro- or mesopores do not work well.
Project description:Recently, plant pollen has been used as a source of activated carbon to produce carbon-containing supercapacitor electrodes. However, in this study, pollen was used as a biotemplate with a completely different approach. As a biotemplate, pollen offers a wide range of varieties in terms of exterior, porosity, shape, and size. An electrode formed by the use of metal oxide grown on the pollen exine layer (sporopollenin microcapsules) as the active substance will inevitably exhibit good electrochemical capacitive properties. Juglans male flowers have been distinguished by dissection from anthers. Isolation of pollen grains from anthers was carried out using sieving from suitable sieves (45-200 μm). Juglans sporopollenin exine microcapsules (SECs) were separated from the intine and protoplasm by acetolysis in combination with reflux. The solution containing SECs, metal ions, and Ni foam was put into a Teflon-lined hydrothermal container, and then, it was reacted at 120 °C for 15 h. The resulting precipitate, as well as the Ni foam, was heat-treated at 300 and 360 °C for 3 h in air. The raw pollen, chemically treated pollen, and cobalt-coated SEC (CoSEC) and CoSEC/Ni foam were characterized using scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and X-ray diffraction techniques. Two different types of supercapacitor electrode designs, with the use of exine microcapsules of Juglans sporopollenin, were performed for the first time. The maximum specific capacitance was up to 1691 F g-1 at 5 A g-1.
Project description:In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm2 and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm2 for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm2 and a power density value of 3.82 μW/cm2 and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.
Project description:An economical and binder-free electrode was fabricated by impregnation of sub-5 nm MoS2 nanodots (MoS2 NDs) onto a three-dimensional (3D) nickel substrate using the facile dip-coating method. The MoS2 NDs were successfully synthesized by controlled bath sonication of highly crystalline MoS2 nanosheets. The as-fabricated high-surface area electrode demonstrated promising electrochemical properties. It was observed that the as-synthesized NDs outperformed the layered MoS2 peers as the electrode for supercapacitors. MoS2 NDs exhibited an excellent specific capacitance (C sp) of 395 F/g at a current load of 1.5 A/g in a three-electrode configuration. In addition, the fabricated symmetric supercapacitor demonstrated a C sp value of 122 F/g at 1 A/g and a cyclic performance of 86% over 1000 cycles with a gravimetric power and energy density of 10,000 W/kg and 22 W h/kg, respectively. Owing to its simple and efficient fabrication and high surface area, such 3D electrodes show high promise for various energy storage devices.