Showing papers on "Capacitance published in 2014"

Solid‐State Supercapacitor Based on Activated Carbon Cloths Exhibits Excellent Rate Capability

Abstract: Activated carbon cloth is used as an electrode, achieving an excellent areal capacitance of 88 mF/cm(2) (8.8 mF/g) without the use of any other capacitive materials. Significantly, when it is incorporated as part of a symmetric solid-state supercapacitor device, a remarkable charge/discharge rate capability is observed; 50% of the capacitance is retained when the charging rate increases from 10 to 10,000 mV/s.

Super Long-Life Supercapacitors Based on the Construction of Nanohoneycomb-Like Strongly Coupled CoMoO4–3D Graphene Hybrid Electrodes

Abstract: Nanohoneycomb-like strongly coupled CoMoO4 -3D graphene hybird electrodes are synthesized for supercapacitors which exhibit excellent specific capacitance and superior long-term cycle stability. The supercapacitor device can power a 5 mm-diameter LED efficiently for more than 3 min with a charging time of only 2 s, and shows high energy densities and good cycle stability.

Capacitance of carbon-based electrical double-layer capacitors

Abstract: Experimental electrical double-layer capacitances of porous carbon electrodes fall below ideal values, thus limiting the practical energy densities of carbon-based electrical double-layer capacitors. Here we investigate the origin of this behaviour by measuring the electrical double-layer capacitance in one to five-layer graphene. We find that the capacitances are suppressed near neutrality, and are anomalously enhanced for thicknesses below a few layers. We attribute the first effect to quantum capacitance effects near the point of zero charge, and the second to correlations between electrons in the graphene sheet and ions in the electrolyte. The large capacitance values imply gravimetric energy storage densities in the single-layer graphene limit that are comparable to those of batteries. We anticipate that these results shed light on developing new theoretical models in understanding the electrical double-layer capacitance of carbon electrodes, and on opening up new strategies for improving the energy density of carbon-based capacitors.

Amorphous Ni(OH)2 @ three-dimensional Ni core–shell nanostructures for high capacitance pseudocapacitors and asymmetric supercapacitors

Abstract: A complex hydroxide/metal Ni(OH)2@Ni core–shell electrode was developed for a high-performance and flexible pseudocapacitor. Compared to the conventional Ni(OH)2 electrode, the as-prepared amorphous Ni(OH)2@ three-dimensional (3D) Ni core–shell electrode shows a large specific capacitance of 2868 F g−1 at a scan rate of 1 mV s−1 and a good cycling stability (3% degradation after 1000 cycles) at a scan rate of 100 mV s−1. Furthermore, the high rate capability with a specific capacitance of 2454 F g−1 can be achieved at a charge–discharge current density of 5 A g−1. An amorphous Ni(OH)2@3D Ni-AC based asymmetric supercapacitor could be cycled reversibly in the high-voltage region of 0–1.3 V, and the specific capacitance of 92.8 F g−1 at 1 A g−1. This research demonstrates that introduction of a metal core to conventional hydroxide supercapacitor electrodes could open up new opportunities for designing and developing high-performance supercapacitors.

Colossal pseudocapacitance in a high functionality–high surface area carbon anode doubles the energy of an asymmetric supercapacitor

Abstract: Here we demonstrate a facile template-free synthesis route to create macroscopically monolithic carbons that are both highly nitrogen rich (4.1–7.6 wt%) and highly microporous (SA up to 1405 m2 g−1, 88 vol% micropores). While such materials, which are derived from common chicken egg whites, are expected to be useful in a variety of applications, they are extremely promising for electrochemical capacitors based on aqueous electrolytes. The Highly Functionalized Activated Carbons (HFACs) demonstrate a specific capacitance of >550 F g−1 at 0.25 A g−1 and >350 F g−1 at 10 A g−1 in their optimized state. These are among the highest values reported in the literature for carbon-based electrodes, including for systems such as templated carbons and doped graphene. We show that HFACs serve as ideal negative electrodes in asymmetric supercapacitors, where historically the specific capacitance of the oxide-based positive electrode was mismatched with the much lower specific capacitance of the opposing AC. An asymmetric cell employing HFACs demonstrates a 2× higher specific energy and a 4× higher volumetric energy density as compared to the one employing a high surface area commercial AC. With 3.5 mg cm−2 of HFAC opposing 5.0 mg cm−2 of NiCo2O4/graphene, specific energies (active mass normalized) of 48 W h kg−1 at 230 W kg−1 and 28 W h kg−1 at 1900 W kg−1 are achieved. The asymmetric cell performance is among the best in the literature for hybrid aqueous systems, and actually rivals cells operating with a much wider voltage window in organic electrolytes.

Multifunctional g-C3N4 Nanofibers: A Template-Free Fabrication and Enhanced Optical, Electrochemical, and Photocatalyst Properties

Abstract: We have developed a facile, scale up, and efficient method for the preparation of graphitic-C3N4 nanofibers (GCNNFs) as electrodes for supercapacitors and photocatalysts. The as-synthesized GCNNFs have 1D structure with higher concentration of nitrogen that is favorable for higher conductivity and electrochemical performance. Secondly, the high surface area of GCNNF provides a large electrode–electrolyte contact area, sufficient light harvesting and mass transfer, as well as increased redox potential. Thus, the GCNNF supercapacitor electrode shows high capacitance of 263.75 F g–1 and excellent cyclic stability in 0.1 M Na2SO4 aqueous electrolyte with the capacitance retention of 93.6% after 2000 cycles at 1 A g–1 current density. GCNNFs exhibit high capacitance of 208 F g–1 even at 10 A g–1, with the appreciable capacitance retention of 89.5%, which proves its better rate capability. Moreover, the GCNNF shows enhanced photocatalytic activity in the photodegradation of RhB in comparison to the bulk graphit...

Facile Synthesis of MnO2/CNTs Composite for Supercapacitor Electrodes with Long Cycle Stability

Abstract: The MnO2/carbon nanotubes (CNTs) composites were prepared through a modified one-pot reaction process, in which CNTs were coated by cross-linked MnO2 flakes uniformly. The composition, morphology, and microstructure of the products were characterized using TG, XRD, XPS, Raman, FESEM, TEM, and STEM. It reveals that the MnO2 layer stands on the sidewalls of the inner nanotubes uniformly about 50 nm thick, and the loading of MnO2 on the CNTs reaches 84%. Furthermore, the supercapacitive performances were investigated by cyclic voltammogram (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS). The experimental results indicate that the composite exhibits not only high specific capacitance of 201 F g–1 and rate capability (the specific capacitance at 20 A g–1 is 70% of that at 1 A g–1), but also excellent cycle stability (no obvious capacitance decay after 10 000 cycles at 1 A g–1). An asymmetric electrochemical capacitor was assembled by using the obtained MnO2/CNTs composite...

3D micro-porous conducting carbon beehive by single step polymer carbonization for high performance supercapacitors: the magic of in situ porogen formation

Abstract: We report non-templated synthesis of interconnected microporous carbon (IMPC) sheets having beehive morphology by direct pyrolysis of poly(acrylamide-co-acrylic acid) potassium salt in inert atmosphere without any activation. The presence of the alkali metal in the selected polymer precursor results in a high specific surface area of 1327 m2 g−1. Importantly, 80% of the pore volume is contributed by micropores with pore size ranging from 1–2 nm which is ideal for use as an electrode for supercapacitors. Whereas the rest of the surface area was contributed by a small fraction of mesopores and macropores due to the interconnected structure. The presence of three different types of pores make the material ideal for supercapacitor electrodes. IMPC was tested as an electrode in both aqueous and non-aqueous supercapacitors. All the aqueous measurements were done in 1 M H2SO4 solution with a potential window 1 V. A specific capacitance of 258 F g−1 was realized at a constant charge–discharge current of 0.5 A g−1 and it maintained at a value of 150 F g−1 at 30 A g−1. A long cycle stability of 90% capacitance retention was observed after 5000 charge–discharge cycles at a current density of 2 A g−1. At the highest power density 13 600 W kg−1 the energy density was found to be 3.1 W h kg−1. Non aqueous performance was tested in the presence of 1 M LiPF6 in ethylene carbonate–di-methyl carbonate with 5 mg active material loading. A specific capacitance of 138 F g−1 was obtained at a current density of 0.25 A g−1 and it retained at a value of 100 F g−1 at 10 A g−1. The material can deliver an energy density of 31 W h kg−1 at its highest power density of 11 000 W kg−1 in a two electrode system based on active material loading.

Core-Double-Shell, Carbon Nanotube@Polypyrrole@MnO2 Sponge as Freestanding, Compressible Supercapacitor Electrode

Abstract: Design and fabrication of structurally optimized electrode materials are important for many energy applications such as supercapacitors and batteries. Here, we report a three-component, hierarchical, bulk electrode with tailored microstructure and electrochemical properties. Our supercapacitor electrode consists of a three-dimensional carbon nanotube (CNT) network (also called sponge) as a flexible and conductive skeleton, an intermediate polymer layer (polypyrrole, PPy) with good interface, and a metal oxide layer outside providing more surface area. These three components form a well-defined core-double-shell configuration that is distinct from simple core-shell or hybrid structures, and the synergistic effect leads to enhanced supercapacitor performance including high specific capacitance (even under severe compression) and excellent cycling stability. The mechanism study reveals that the shell sequence is a key factor; in our system, the CNT–PPy–MnO2 structure shows higher capacitance than the CNT–MnO...

Flexible and Wire-Shaped Micro-Supercapacitor Based on Ni(OH)2-Nanowire and Ordered Mesoporous Carbon Electrodes

Abstract: Portable and multifunctional electronic devices are developing in the trend of being small, flexible, roll-up, and even wearable, which asks us to develop flexible and micro-sized energy conversion/storage devices. Here, the high performance of a flexible, wire-shaped, and solid-state micro-supercapacitor, which is prepared by twisting a Ni(OH)2-nanowire fiber-electrode and an ordered mesoporous carbon fiber-electrode together with a polymer electrolyte, is demonstrated. This micro-supercapacitor displays a high specific capacitance of 6.67 mF cm-1 (or 35.67 mF cm-2) and a high specific energy density of 0.01 mWh cm-2 (or 2.16 mWh cm-3), which are about 10-100 times higher than previous reports. Furthermore, its capacitance retention is 70% over 10 000 cycles, indicating perfect cyclic ability. Two wire-shaped micro-supercapacitors (0.6 mm in diameter, approximate to 3 cm in length) in series can successfully operate a red light-emitting-diode, indicating promising practical application. Furthermore, synchrotron radiation X-ray computed microtomography technology is employed to investigate inner structure of the micro-device, confirming its solid-state characteristic. This micro-supercapacitor may bring new design opportunities of device configuration for energy-storage devices in the future wearable electronic area.

Ultrahigh energy density realized by a single-layer β-Co(OH)2 all-solid-state asymmetric supercapacitor.

Abstract: A conceptually new all-solid-state asymmetric supercapacitor based on atomically thin sheets is presented which offers the opportunity to optimize supercapacitor properties on an atomic level. As a prototype, β-Co(OH)2 single layers with five-atoms layer thickness were synthesized through an oriented-attachment strategy. The increased density-of-states and 100 % exposed hydrogen atoms endow the β-Co(OH)2 single-layers-based electrode with a large capacitance of 2028 F g−1. The corresponding all-solid-state asymmetric supercapacitor achieves a high cell voltage of 1.8 V and an exceptional energy density of 98.9 Wh kg−1 at an ultrahigh power density of 17 981 W kg−1. Also, this integrated nanodevice exhibits excellent cyclability with 93.2 % capacitance retention after 10 000 cycles, holding great promise for constructing high-energy storage nanodevices.

Scalable self-growth of Ni@NiO core-shell electrode with ultrahigh capacitance and super-long cyclic stability for supercapacitors

Abstract: Three-dimensional (3D) electrodes have been demonstrated to be promising candidates for high-performance supercapacitors because of their unique architectures and outstanding electrochemical properties. However, the fabrication process for current 3D electrodes is not scalable. Herein, a novel and cost-effective activation process has been developed to macroscopically produce 3D porous Ni@NiO core-shell electrodes with enhanced electrochemical properties. The porous Ni@NiO core-shell electrode obtained by activated commercial Ni foam (NF) in a 3 M HCl solution yields an ultrahigh areal capacitance of 2.0 F cm−2 at a high current density of 8 mA cm−2, which is substantially higher than that of most reported 3D NF-based electrodes. Moreover, the activated NF (ANF) electrode exhibited super-long cycling stability. Owing to the increased accessible surface area and continual formation of electrochemically active NiO during cycling, the areal capacitance of the ANF electrode did not exhibit any decay and instead increased from 0.47 to 1.27 F cm−2 after 100 000 cycles at 100 mV s−1. This is the best cycling stability achieved by a 3D NF-based electrode. Additionally, a high-performance asymmetrical supercapacitor (ASC) device based on the as-prepared ANF cathode and a reduced graphene oxide (RGO) anode was also prepared. The ANF//RGO-ASC device was able to deliver a maximum energy density of 1.06 mWh cm−3 and a maximum power density of 0.42 W cm−3. Researchers from China have discovered a cost-effective way to produce supercapacitors on large scales using nickel foam. This three-dimensional porous metal is an ideal electrode for high-capacity energy storage because of its lightweight, corrosion-resistant structure. To achieve supercapacitance, however, researchers must insert active substances, such as graphene, deep into the nickel pores. Xihong Lu and colleagues from Sun Yat-Sen University solved this problem by immersing commercial-grade nickel foam into hot hydrochloric acid for several minutes. The one-step reaction pitted the formerly smooth nickel foam surface and created a thin outer ‘shell’ of nickel oxide that surrounded an inner nickel ‘core’. Electrochemical experiments revealed that the favorable core–shell structure, combined with a more accessible surface area achieved from the acid etching, yielded an energy-dense supercapacitor electrode that was effective for more than 100,000 charge–recharge cycles. A novel and cost-effective activation process has been developed to macroscopically produce three-dimensional (3D) porous Ni@NiO core-shell electrode by activated Ni foam (ANF) in HCl aqueous solution. The ANF electrode yielded a remarkable areal capacitance of 2.0 F cm−2 at a high current density of 8 mA cm−2 and exhibited ultrahigh long-term cycling stability without any decay of capacitance after 100 000 cycles.

Direct Growth of NiCo2S4 Nanotube Arrays on Nickel Foam as High-Performance Binder-Free Electrodes for Supercapacitors

Abstract: Arrays of NiCo2 S4 nanotubes on nickel foam were prepared by means of a two-step method, and were directly applied as a binder-free supercapacitor electrode. Such a binder-free method enables intimate contact between the current collector and the active materials, and can effectively improve ion and charge transportation. As a result, the electrochemical performances of supercapacitors can be improved. The as-prepared NiCo2 S4 nanotubes/Ni foam electrode shows a high specific capacitance (738 F g-1 at 4 A g-1 ), excellent rate capability (78 % capacitance retention at 32 A g-1 ), and good cycling stability (retention capacity of 93.4 % after 4000 cycles), which suggests its promising application for electrochemical capacitors.

Defect density and dielectric constant in perovskite solar cells

Abstract: We report on measurement of dielectric constant, mid-gap defect density, Urbach energy of tail states in CH3NH3PbIxCl1−x perovskite solar cells. Midgap defect densities were estimated by measuring capacitance vs. frequency at different temperatures and show two peaks, one at 0.66 eV below the conduction band and one at 0.24 eV below the conduction band. The attempt to escape frequency is in the range of 2 × 1011/s. Quantum efficiency data indicate a bandgap of 1.58 eV. Urbach energies of valence and conduction band are estimated to be ∼16 and ∼18 meV. Measurement of saturation capacitance indicates that the relative dielectric constant is ∼18.

Shape-controlled synthesis of NiCo2S4 and their charge storage characteristics in supercapacitors

Abstract: In this work, a facile hydrothermal approach for the shape-controlled synthesis of NiCo2S4 architectures is reported. Four different morphologies, urchin-, tube-, flower-, and cubic-like NiCo2S4 microstructures, have been successfully synthesized by employing various solvents. The obtained precursors and products have been characterized by X-ray diffraction, field-emission scanning electron microscopy and transmission electron microscopy. It is revealed that the supersaturation of nucleation and crystal growth is determined by the solvent polarity and solubility, which can precisely control the morphology of NiCo2S4 microstructures. The detailed electrochemical performances of the various NiCo2S4 microstructures are investigated by cyclic voltammetry and galvanostatic charge–discharge measurements. The results indicate that the tube-like NiCo2S4 exhibits promising capacitive properties with high capacitance and excellent retention. Its specific capacitance can reach 1048 F g−1 at the current density of 3.0 A g−1 and 75.9% of its initial capacitance is maintained at the current density of 10.0 A g−1 after 5000 charge–discharge cycles.

Highly Conductive Ordered Mesoporous Carbon Based Electrodes Decorated by 3D Graphene and 1D Silver Nanowire for Flexible Supercapacitor

Abstract: Ordered mesoporous carbon (OMC) is considered one of the most promising materials for electric double layer capacitors (EDLC) given its low-cost, high specific surface area, and easily accessed ordered pore channels. However, pristine OMC electrode suffers from poor electrical conductivity and mechanical flexibility, whose specific capacitance and cycling stability is unsatisfactory in flexible devices. In this work, OMC is coated on the surface of highly conductive three-dimensional graphene foam, serving as both charge collector and flexible substrate. Upon further decoration with silver nanowires (Ag NWs), the novel architecture of Ag NWs/3D-graphene foam/OMC (Ag-GF-OMC) exhibits exceptional electrical conductivity (up to 762 S cm−1) and mechanical robustness. The Ag-GF-OMC electrodes in flexible supercapacitors reach a specific capacitance as high as 213 F g−1, a value five-fold higher than that of the pristine OMC electrode. Moreover, these flexible electrodes also exhibit excellent long-term stability with >90% capacitance retention over 10 000 cycles, as well as high energy and power density (4.5 Wh kg−1 and 5040 W kg−1, respectively). This study provides a new procedure to enhance the device performance of OMC based supercapacitors, which is a promising candidate for the application of flexible energy storage devices.

Asymmetric supercapacitors based on nano-architectured nickel oxide/graphene foam and hierarchical porous nitrogen-doped carbon nanotubes with ultrahigh-rate performance

Abstract: A pulsed laser deposition process using ozone as an oxidant is developed to grow NiO nanoparticles on highly conductive three-dimensional (3D) graphene foam (GF). The excellent electrical conductivity and interconnected pore structure of the hybrid NiO/GF electrode facilitate fast electron and ion transportation. The NiO/GF electrode displays a high specific capacitance (1225 F g−1 at 2 A g−1) and a superb rate capability (68% capacity retention at 100 A g−1). A novel asymmetric supercapacitor with high power and energy densities is successfully fabricated using NiO/GF as the positive electrode and hierarchical porous nitrogen-doped carbon nanotubes (HPNCNTs) as the negative electrode in aqueous KOH solution. Because of the high individual capacitive performance of NiO/GF and HPNCNTs, as well as the synergistic effect between the two electrodes, the asymmetric capacitor exhibits an excellent energy storage performance. At a voltage range from 0.0 to 1.4 V, an energy density of 32 W h kg−1 is achieved at a power density of 700 W kg−1. Even at a 2.8 s charge–discharge rate (42 kW kg−1), an energy density as high as 17 W h kg−1 is retained. Additionally, the NiO/GF//HPNCNT asymmetric supercapacitor exhibits excellent cycling durability, with 94% specific capacitance retained after 2000 cycles.

Electrochemical Kinetics of Nanostructured Nb2O5 Electrodes

Abstract: Pseudocapacitive charge storage is based on faradaic charge-transfer reactions occurring at the surface or near-surface of redox-active materials. This property is of great interest for electrochemical capacitors because of the substantially higher capacitance obtainable as compared to traditional double-layer electrode processes. While high levels of pseudocapacitance have been obtained with nanoscale materials, the development of practical electrode structures that exhibit pseudocapacitive properties has been challenging. The present paper shows that electrodes of Nb2O5 successfully retain the pseudocapacitive properties of the corresponding nanoscale materials. For charging times as fast as one minute, there is no indication of semi-infinite diffusion limitations and specific capacitances of 380 F g−1 and 0.46 F cm−2 are obtained in 40-μm thick electrodes at a mean discharge potential of 1.5 V vs Li+/Li. In-situ X-ray diffraction shows that the high specific capacitance and power capabilities of Nb2O5 electrodes can be attributed to fast Li+ intercalation within specific planes in the orthorhombic structure. This intercalation pseudocapacitance charge-storage mechanism is characterized as being an intrinsic property of Nb2O5 that facilitates the design of electrodes for capacitive storage devices. We demonstrate the efficacy of these electrodes in a hybrid electrochemical cell whose energy density and power density surpass that of commercial carbon-based devices.

Vapor-phase polymerization of nanofibrillar poly(3,4-ethylenedioxythiophene) for supercapacitors.

Abstract: Nanostructures of the conducting polymer poly(3,4-ethylenedioxythiophene) with large surface areas enhance the performance of energy storage devices such as electrochemical supercapacitors. However, until now, high aspect ratio nanofibers of this polymer could only be deposited from the vapor-phase, utilizing extrinsic hard templates such as electrospun nanofibers and anodized aluminum oxide. These routes result in low conductivity and require postsynthetic template removal, conditions that stifle the development of conducting polymer electronics. Here we introduce a simple process that overcomes these drawbacks and results in vertically directed high aspect ratio poly(3,4-ethylenedioxythiophene) nanofibers possessing a high conductivity of 130 S/cm. Nanofibers deposit as a freestanding mechanically robust film that is easily processable into a supercapacitor without using organic binders or conductive additives and is characterized by excellent cycling stability, retaining more than 92% of its initial capacitance after 10,000 charge/discharge cycles. Deposition of nanofibers on a hard carbon fiber paper current collector affords a highly efficient and stable electrode for a supercapacitor exhibiting gravimetric capacitance of 175 F/g and 94% capacitance retention after 1000 cycles.

Hierarchical Composite Electrodes of Nickel Oxide Nanoflake 3D Graphene for High-Performance Pseudocapacitors

Abstract: NiO nanoflakes are created with a simple hydrothermal method on 3D (three-dimensional) graphene scaffolds grown on Ni foams by microwave plasma enhanced chemical vapor deposition (MPCVD). Such as-grown NiO-3D graphene hierarchical composites are then applied as monolithic electrodes for a pseudo-supercapacitor application without needing binders or metal-based current collectors. Electrochemical measurements impart that the hierarchical NiO-3D graphene composite delivers a high specific capacitance of ≈1829 F g−1 at a current density of 3 A g−1 (the theoretical capacitance of NiO is 2584 F g−1). Furthermore, a full-cell is realized with an energy density of 138 Wh kg−1 at a power density of 5.25 kW kg−1, which is much superior to commercial ones as well as reported devices in asymmetric capacitors of NiO. More attractively, this asymmetric supercapacitor exhibits capacitance retention of 85% after 5000 cycles relative to the initial value of the 1st cycle.

Energy Storing Electrical Cables: Integrating Energy Storage and Electrical Conduction

Abstract: DOI: 10.1002/adma.201400440 approach proposed by Simon and Gogotsi is depositing pseudocapacitive material (like MnO 2 ) onto a nanostructured current collector. [ 9 ] Despite some achievements that have been made by using similar methods, such as depositing MnO 2 onto nanowires, [ 10 ] nanotubes, [ 11 ] and nanopillars, [ 12 ] these arrays usually suffer from structural collapse, resulting in a decrease of useful surface area, reduction of deposited active materials and limited accessibility of electrolyte. Furthermore, these nanostructured current collectors are either derived from expensive and environment-unfriendly template methods or tedious fabrication processes. Therefore, it is still a challenge to readily and simply fabricate nanostructured electrodes with large area, template-free, and high aspect ratio arrays without nanostructures clumping together. Here we developed a large area, template-free, high aspect ratio, and freestanding CuO@AuPd@MnO 2 core-shell nanowhiskers (NWs) design. Our electrochemical measurements show that these CuO@AuPd@MnO 2 NWs exhibit remarkable properties including high specifi c capacitance, excellent reversible redox reactions, and fast charge-discharge ability. Moreover, a novel coaxial supercapacitor cable (CSC) design which combines electrical conduction and energy storage by modifying the copper core used for electrical conduction was demonstrated. For accomplishing large surface area necessary for high supercapacitor performance, we developed NWs on the outer surface of the electrical copper wire. The NWs structure is developed by just heating the inner core and therefore is practical to upscale the process to make extended lengths. An attractive advantage of using the coaxial design is that electricity can be conducted through the inner conductive metal wire and electrical energy can be stored in the nanostructured concentric layers added to this inner metal wire with an oxide layer in between. It is always a vital task for many applications including aviation to fi nd better methods to save weight and space, while maintaining the intended purpose. Therefore, integration of electrical cable and energy storage device into one unit offers a very promising opportunity to transmit electricity and store energy at the same time. In addition, CSC built from these NWs exhibits excellent fl exibility and bendability, superior long-term cycle stability, and high power and energy densities. The development of this innovative lightweight, fl exible, and space saving CSC will be very attractive for many applications including hybrid and allelectric vehicles, electric trains, heavy machineries, aircrafts and military. Fabrication of electrode involves three steps: (1) growth of CuO NWs from a pure copper wire by heat treatment; (2) deposition of a conducting metal layer by sputter-coating; (3) electrodeposition of active material onto the nanostructures ( Figure 1 a). Scanning electron microscope (SEM) image (Figure 1 b) clearly Currently, millions of miles of electrical cables have been used for providing electrical connections in machineries, equipment, buildings and other establishments. Energy storage devices are completely separated from these electrical cables if used. However, it will revolutionize energy storage applications if both electrical conduction and energy storage can be integrated into the same cable. Coaxial cable, also called coax, is one of the most common and basic cable designs that is used to carry electricity or signal. It has an inner conductor enclosed by a layer of electrical insulator, and covered by an outer tubular conducting shield (see Supporting Information, SI, Figure S1). The term “coaxial” is used because both the inner and outer conductors share the same geometric axis. In a coaxial design, it is possible to combine two different functional devices into one device that can still perform the original functions independently. Supercapacitors, also known as electrochemical capacitors, have become one of the most popular energy storage devices in recent years. Compared to other energy storage devices like batteries, supercapacitors have faster charge-discharge rates, higher power densities, and longer life times. [ 1 ] As a signature of their performance, safety, and reliability, they have recently been employed in the emergency doors of Airbus A380. Supercapacitors store energy by Faradaic or non-Faradaic reactions. Supercapacitors which utilize the Faradaic reactions are also called pseudocapacitors. Metal oxides/hydroxides like ruthenium oxide (RuO 2 ), [ 2 ] manganese dioxide (MnO 2 ), [ 3 ] cobalt oxide (Co 3 O 4 ), [ 4 ] nickel oxide (NiO), [ 5 ] and nickel hydroxide (Ni(OH) 2 ), [ 6 ] have been extensively studied as electrode materials in pseudocapacitors. Among them, MnO 2 has stood out due to its outstanding characteristics such as high theoretical specifi c capacitance (∼1,400 F g −1 ), natural abundance, and environmental friendliness. [ 7 ] However, the poor electrical conductivity of MnO 2 (∼10 −5 – 10 −6 S cm −1 ) is a limiting factor in achieving its theoretical specifi c capacitance. [ 7b , 8 ] One feasible

Facile synthesis of ZnCo2O4 nanowire cluster arrays on Ni foam for high-performance asymmetric supercapacitors

Abstract: ZnCo2O4 nanowire cluster arrays (NWCAs) were directly grown on Ni foam via a facile hydrothermal method. The resulting products were analyzed by using X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The ZnCo2O4 NWCAs on Ni foam were directly used as integrated electrodes for supercapacitors and exhibited a high specific capacitance of 4.05 F cm−2 at 20 mA cm−2 (1620 F g−1 at 8 A g−1) in 3 M KOH aqueous solution, and an excellent cycling ability at various current densities up to 100 mA cm−2 (40 A g−1); 90% of the initial capacitance remained after 6000 cycles. Moreover, the asymmetric supercapacitor had a high energy density of 41.00 W h kg−1 at a power density of 384 W kg−1 and 16.63 W h kg−1 at a high power density of 2561 W kg−1. Such excellent rate properties and superior cycling life suggest that ZnCo2O4 NWCAs can not only be applied in high energy density fields, but also used in high power density applications.

Highly flexible, all solid-state micro-supercapacitors from vertically aligned carbon nanotubes

Abstract: We report a highly flexible planar micro-supercapacitor with interdigitated finger electrodes of vertically aligned carbon nanotubes (VACNTs). The planar electrode structures are patterned on a thin polycarbonate substrate with a facile, maskless laser-assisted dry transfer method. Sputtered Ni is used to reduce the in-plane resistance of the VACNT electrodes. An ionogel, an ionic liquid in a semi-solid matrix, is used as an electrolyte to form a fully solid-state device. We measure a specific capacitance of 430 μF cm−2 for a scan rate of 0.1 V s−1 and achieve rectangular cyclic voltammograms at high scan rates of up to 100 V s−1. Minimal change in capacitance is observed under bending. Mechanical fatigue tests with more than 1000 cycles confirm the high flexibility and durability of the novel material combination chosen for this device. Our results indicate that this scalable and facile fabrication technique shows promise for application in integrated energy storage for all solid-state flexible microdevices.