Kind Of Supercapacitor Research Articles

Density functional theory study of supercapacitor for energy storage electrode materials

Double electric layer capacitor is a kind of supercapacitor with high power density, but has relatively low energy density. Improving the quantum capacitances of materials will be a new way to increase their total interface capacitances. We design a two-dimensional electrode material with a high specific capacity and stable crystal structure. Due to the quantum confinement effect and the density of states, the quantum capacitances of two-dimensional materials such as graphene and silicene approach to zero when they are near the Fermi level. On the basis of the first principles of density functional theory, doping and adsorption can effectively modulate the electronic structure of two-dimensional electrode material such as graphene. It promotes the formation of the local state of the electrode material near the Dirac point and/or the movement of the Fermi level, thereby improving the quantum capacitance. Compared with the quantum capacitance of Ti (Au, Ag, Cu, Al), and 3-B (N, P, S) doped single-vacancy graphene (silicene, germanene), the quantum capacitance of 3-N doped single-vacancy graphene and of Ti atom adsorbed single-vacancy silicene/germanene are both significantly improved, and their quantum capacitances are as high as 118.42 μF/cm<sup>2</sup>, 79.84 μF/cm<sup>2</sup>, and 76.54 μF/cm<sup>2</sup>. The concentration effects of 3N-doped three kinds of alkenes are studied, and the results show that the quantum capacitance is enhanced with the doping concentration increasing. It is also found by studying the thermodynamic stability of the doped systems that Ti is the most stable adsorbed atom because of the strong bond between Ti atom and C atom. The S is the most stable doping atom in B, N, P, S doped single-vacancy silicene and germanene. For graphene, N doping has the lowest formation energy and the best quantum capacitance. This study intends to clarify the controversy regarding the energy storage enhancement of two-dimensional double-layer supercapacitor materials, and to improve the quantum capacitance. The research results provide the guidance for understanding the quantum effects caused by optimizing the structure of two-dimensional electrode material. The above theoretical calculation of the mentioned two-dimensional electrode material provides some research ideas for improving the low energy density of electric double-layer supercapacitors.

Synthesis of Sub-nanometer Porous Carbon Film for Energy Storage.

Carbon-based supercapacitors are a kind of supercapacitors with very promising applications because of their low cost, good stability and adjustable properties. Simple and rapid syntheses of carbon materials with a high surface area and narrow pore size distribution are of great significance to practical applications of carbon-based supercapacitors. Here we report a new strategy to synthesize sub-nanometer porous carbon films (Snp-CF) via a condensation reaction under mild conditions. Carbon films exhibit a narrow pore size distribution (6.6 Å) and high surface area (508 m2 g-1 ) after annealing at 700 °C. Snp-CF-700 displays a good specific capacity and excellent cycle performance (130 F g-1 after 5000 cycles, 118 % of initial 110 F g-1 ).

Improved redox-active ionic liquid-based ionogel electrolyte by introducing carbon nanotubes for application in all-solid-state supercapacitors

More attention has been focused on the design of all-solid-state supercapacitors (ASSCs) due to that this kind of supercapacitors can avoid some problems such as electrolyte leakage occurring in liquid electrolyte-based supercapacitors. However, ASSCs present lower specific energy, which is generally in great relation with the very low ionic conductivity of utilized electrolyte. To achieve high-specific-energy ASSCs with superior performance, a redox-active ionic liquid-based ionogel electrolyte (IGE) consisting of 1-butyl-3-methylimidazolium iodide (BMIMI) IL, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and carbon nanotubes (CNTs) was prepared by a solution-casting method. By optimizing BMIMI/PVDF-HFP and CNTs/PVDF-HFP mass ratios, the obtained PVDF-HFP/BMIMI/CNTs IGE presents the maximum ionic conductivity as high as 17.6 mS cm−1. A sandwiched ASSC constructed by two identical activated carbon electrodes and an as-prepared PVDF-HFP/BMIMI/CNTs IGE possesses a high specific energy of 50.1 Wh kg−1 as a result of the extra pseudocapacitance contribution from the redox-reactions related to I-based ions happening at the interface between electrolyte and electrode and the increased ionic conductivity of IGE for the existence of CNTs network into the IGE providing fast ion transfer channel. The self-discharge behavior of this device is effectively weakened due to the addition of CNTs. Furthermore, the promising cyclic stability is achieved.

Nanoflake NiMoO4 based smart supercapacitor for intelligent power balance monitoring

A supercapacitor is well recognized as one of emerging energy sources for powering electronic devices in our daily life. Although various kind of supercapacitors have been designed and demonstrated, their market aspect could become advanced if the utilisation of other physicochemical properties (e.g. optical) is incorporated in the electrode. Herein, we present an electrochromic supercapacitor (smart supercapacitor) based on a nanoflake NiMoO4 thin film which is fabricated using a facile and well-controlled successive ionic layer adsorption and reaction (SILAR) technique. The polycrystalline nanoflake NiMoO4 electrode exhibits a large electrochemically active surface area of ~ 96.3 cm2. Its nanoporous architecture provides an easy pathway for the intercalation and de-intercalation of ions. The nanoflake NiMoO4 electrode is dark-brown in the charged state and becomes transparent in the discharged state with a high optical modulation of 57%. The electrode shows a high specific capacity of 1853 Fg–1 at a current rate of 1 Ag–1 with a good coloration efficiency of 31.44 cm2/C. Dynamic visual information is obtained when the electrode is charged at different potentials, reflecting the level of energy storage in the device. The device retains 65% capacity after 2500 charge-discharge cycles compared with its initial capacity. The excellent performance of the nanoflake NiMoO4 based smart supercapacitor is associated with the synergetic effect of nanoporous morphology with a large electrochemically active surface area and desired chemical composition for redox reaction.

Supramolecular Design of Carbons for Energy Storage with the Reactanse-Sensor Functional Hybridity

The purpose of this work is to expand the class of electrical energy storage devices with non-conjugate functional hybridity. Cyclodextrins of β- and γ-modifications has used as a starting material for research. These materials containing intramolecular voids, which are able to accommodate guest components by molecular recognition on the "lock-key" principle. Methods of precision porometry and impedance spectroscopy has used to study the obtained carbon structures, electrochemical and magnetic measurements has performed to study the obtained carbon structures. Data of the precision porometry has indicated a bimodal porous structure of the synthesized chars. The total specific surface area of active surface of the β-cyclodextrin carbonizate was about 72 m2/g. After KOH-modification, the specific capacity for β-cyclodextrin char was 158 F/g, and in the negative potential range – 203 F/g. The last value for γ-cyclodextrin carbon was 162 F/g. The ability of β-cyclodextrin to molecular recognition of ferrocene (FC) has used and this cavitat has subjected to activation carbonation according to the same modes as β-cyclodextrin. The specific capacity of the obtained char of the β-CD complex after the KOH-modification was 110 F/g, the specific capacity of the cavitate carbon synthesized on γ-CD has dropped twice. The study of complexes host-guest inclusions β-cyclodextrin with molecular iodine has indicated a slight increase of capacity. However, their interface with 30 % aqueous electrolyte solution has shown high photosensitivity. The specific capacitance of the cavitate carbon without KOH-modification has increased four times when it was illuminated with integral and monochromatic light from LEDs of the same intensity. Magnetic studies of the synthesized carbonates have shown that they all demonstrate ferromagnetic properties. Measurement under normal conditions and in a constant magnetic field of cells of symmetric configuration on carbon-based electrodes synthesized with γ-CD and γ-CD has showed that their capacitance practically does not change, but their reactance parameters change significantly. Supercapacitors based on these carbonates can serve as sensors of a weak magnetic field at room temperature. Magnetovarionistors is a new class of devices, which are forming on such kind of supercapacitors.

Insights into the energy storage mechanism of hybrid supercapacitors with redox electrolytes by Electrochemical Impedance Spectroscopy

Recently, new electrode materials and electrolytes for hybrid supercapacitors with enhanced performance have been extensively studied. However, the energy storage mechanism of these hybrid devices has not been assessed in detail. In this sense, Electrochemical Impedance Spectroscopy is one of the most powerful techniques to better understand the physicochemical phenomena involved in this new kind of supercapacitors. In this work, Impedance Spectroscopy was used for the first time to analyse the energy storage mechanism in supercapacitors with non-aqueous electrolytes with organic redox molecules dissolved, as a function of the frequency and bias voltage. In addition, a simple electrical model has been developed to describe the behavior of the supercapacitor with a very good correlation with the experimental results. This investigation provides useful information delving into the behavior of the devices which is fundamental for their future practical applications.

Dependence of Double Layer Capacitance on Pore Diameter of Carbon Coated Porous Si

Recent growth of using electric vehicles and electronic devices, the increasing demand for energy storage devices. Supercapacitors, also known as ultracapacitors, are the promising energy storage devices with high power density, fast charge discharge properties and long cycle life. 1 Electrical double layer capacitor (EDLC) is a kind of supercapacitors and stores electric energy at solid-electrolyte interfaces by applying a bias voltage, and its specific capacitance mainly depends on specific surface area, therefore there are often utilized graphene based materials, porous materials, pillar like materials, and so on. On the other hand, it is known the nm-sized pore affects the double layer capacity.2 Porous silicon (PSi) is a candidate for supercapacitor for naturally abundant resources of silicon and easy to control porous structure by changing the etching condition and the wafers.3 In this study, to investigate the pore size contribution on specific capacitance we used graphene coated PSi with various pore diameter as a model of porous electrode. PSi was prepared in a homemade etch cell by anodizing the highly antimony doped Si (100) wafers (~0.02 Ω cm-1) using a HF (~48%)-ethanol mixture as the electrolyte at a various current density (50-150 mA/cm) for 3 min, and then, PSi was rinsed with ethanol and dried under vacuum for 2-3 h. The carbonization of PSi was carried out in a tube furnace with a quartz tube under a 1 L/min of Ar and 200 mL H2 flow while the furnace was heated to 650 ˚C When the furnace reached 650 ˚C, 10 ml/min of C2H2 was added to the gas mixture, and the temperature was increased to 750 ˚C for 10 minutes, and increased to 850 ˚C for another 10 minutes. The C2H2 was then turned off, and the P-Si was cooled in the presence of Ar and H2 until the sample reached a room temperature. Analysis of PSi and carbonized PSi was performed with a FESEM and Raman spectroscopy. Electrochemical measurement was carried out utilizing PSi materials in a two-electrode homemade electrochemical test cell. Cyclic voltammetry and electrochemical impedance spectroscopy were conducted in a trimethylpropylammonium bis(trifluoromethanesulfonyl)amide (TMPATFSA) ionic liquid. The scan range was -3.0 to 3.0 V. Impedance measurements were performed around zero bias with a signal amplitude of 10 mV. SEM images of PSi and carbonized PSi indicated that PSi’s was obtained with the pore diameter of 10, 20 and, 80 nm. Also it is confirmed that there is little change during the carbonization of PSi. Raman spectroscopy was carried out to confirm graphene coating on PSi, and after the carbonization of PSi. We observed Si Raman peak near 520 cm-1 from the pre-coated PSi, and the D (1350 cm-1) and G (1580 cm-1) peaks corresponding to sp3 and sp2-hybridized carbons from the carbonized PSi, respectively. EIS shows drastic change between before or after graphene coating on PSi. This is because the contact resistance decreased by graphene coating and good wettability of graphene. For observation of dependence of double layer capacitance on pore diameter of carbon coated porous Si, we performed cyclic voltammetry of carbonized PSi as shown in Fig.1. The largest electrochemical capacitance was observed from the carbonized PSi with pore diameter of 20 nm. The contact resistance of graphene coated PSi decreased in inverse proportion to the size of the electric potential window. It is suggested that the decrease of the adsorption site of the ion by the decrease in surface area for 10 nm of pore size by hindrance of ionic mobility or decrease of electronic double layer.4 【Reference】[1] M. Winter et al., Chem. Rev. 104,4245 (2004). [2] C.-H. Hou et al., J. Colloid Interface Sci. 302,54(2006). [3] L. Oakes wt al., Sci. Reports, [4] Y. Kitazumi et al., Electrochim. Acta, 112, 171(2013). Figure 1

Vanadium based materials as electrode materials for high performance supercapacitors

Abstract As a kind of supercapacitors, pseudocapacitors have attracted wide attention in recent years. The capacitance of the electrochemical capacitors based on pseudocapacitance arises mainly from redox reactions between electrolytes and active materials. These materials usually have several oxidation states for oxidation and reduction. Many research teams have focused on the development of an alternative material for electrochemical capacitors. Many transition metal oxides have been shown to be suitable as electrode materials of electrochemical capacitors. Among them, vanadium based materials are being developed for this purpose. Vanadium based materials are known as one of the best active materials for high power/energy density electrochemical capacitors due to its outstanding specific capacitance and long cycle life, high conductivity and good electrochemical reversibility. There are different kinds of synthetic methods such as sol-gel hydrothermal/solvothermal method, template method, electrospinning method, atomic layer deposition, and electrodeposition method that have been successfully applied to prepare vanadium based electrode materials. In our review, we give an overall summary and evaluation of the recent progress in the research of vanadium based materials for electrochemical capacitors that include synthesis methods, the electrochemical performances of the electrode materials and the devices.

Hierarchically Layered MoS2/Mn3O4 Hybrid Architectures for Electrochemical Supercapacitors with Enhanced Performance

We for the first time report a novel kind of supercapacitor using hierarchical MoS2/Mn3O4 hybrid architectures as electrodes based on layered MoS2 and Mn3O4 nanoparticles via a simple and low-cost hydrothermal and chemical precipitation route. The Mn3O4 nanoparticles are homogeneously incorporated into thin layers of MoS2 hierarchical architectures. The cycle stability of MoS2/Mn3O4 nanostructure is greatly improved, still reserves a capacity of 119.3Fg−1 after 2000 cycles at a current density of 1.0Ag−1, about 69.3% reservation of the initial capacitance, more than two times higher than that of pure layered MoS2 electrode. The good performance is due to the synergistic effect between the layered MoS2 and Mn3O4 nanoparticles. The layered hybrid displays a larger specific surface to provide enough active sites for the redox reaction and shorten the distance of charge transfer for ions and electrons. While Mn3O4 acts as a holder to enhance the stability of the MoS2 framework and provides additional capacity. The Mn3O4 nanoparticles can serve as a holder and prevent MoS2 nanosheets from restacking. Moreover, the MoS2 sheets act as subtracts to improve to the conductivity of Mn3O4. The layered MoS2/Mn3O4 hybrid inspires a new way of designing high-performance electrochemical supercapacitors.

Supercapacitor based on graphene and ionic liquid electrolyte

A new kind of supercapacitor by using chemical reduced graphene (CRG) as electrode material and ionic liquid with addition of acetonitrile as electrolyte is assembled and investigated. CRG materials with high surface area are prepared by chemical reduction of graphene oxide. The capacitive properties of the supercapacitor composed of the CRG and ionic liquid electrolyte are studied by electrical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge. With the combined advantages of graphene and ionic liquid, the supercapacitor shows perfect performance. The supercapacitor possesses wide cell voltage and good stability. The specific capacitance, energy density, and specific power density of the present supercapacitor are 132 Fg−1, 143.7 Wh kg−1, and 2.8 kW kg−1, respectively. The results demonstrate the potential application of electrical energy storage devices with high performance based on this new kind of supercapacitor.