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Potassium‐ion hybrid capacitors (PIHCs) overcome the limitations of potassium‐ion batteries (PIBs) and supercapacitors (SCs) and integrate the advantages of both, including high energy density, high power density, low cost, long cycle life, and stable electrochemical performance. However, the development of PIHCs is hindered by thermodynamic instability and kinetic hysteresis. Additionally, the dynamic mismatch between anode and cathode materials poses an urgent challenge. To this end, many research works related to material development have been dedicated to overcoming the drawbacks. In this review, the energy storage mechanism of PIHCs is briefly introduced. Moreover, the research progress and achievements of anode and cathode materials in recent years are reviewed, including carbon‐based materials, MXenes, transition metal materials, Prussian blue and its analogues. Finally, the challenges and prospects of PIHCs are proposed, together with guiding significant research directions in the future. [ABSTRACT FROM AUTHOR]

Siloxane‐based molecular material, by virtue of its unique chemical structure, thermal and electrochemical properties, has triggered tremendous research interest and sparked a revolution for energy storage in the past years. Siloxanes and their analogues are generally demonstrated to be more environmentally friendly, durable, and safer when employed to reconstruct the nano‐micro surface structure of electrodes, separators, and their interfaces with electrolytes. To better understand the recent and comprehensive achievement of siloxane‐based materials in energy storage, a systematic summary is necessary to provide important clues, aiming at achieving better electrochemical properties. In this Minireview, siloxane materials are presented comprehensively and systematically in terms of molecule design, functionality, and unique superiority for lithium‐ion batteries and supercapacitors. The challenges, perspectives, and future directions of siloxane‐based organosilicon materials are put forward for higher performance and wider application in electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

Electrochemical proton storage provides high energy, fast kinetics, safety, and environmental friendliness for grid‐scale energy storage. However, the development of pseudocapacitive proton supercapacitors with fast chargeability and high stability is still challenging because of the unclear electrochemical reaction mechanism and unsuitable construction strategy. Here it is shown that a multi‐metallic Prussian blue analog—Cu0.82Co0.18HCF, which possesses enhanced electronic structure and ion transport path—can intercalate/de‐intercalate large amounts of proton at high rates. Ion‐induced transformation of magnetism, fast solid‐state proton transport, and reversible insertion/de‐insertion of protons lead to extremely excellent rate capacities and cycling stability for proton storage. An asymmetric pseudocapacitive proton supercapacitor (Cu0.82Co0.18HCF//WO3·nH2O) is fabricated with a voltage window of 1.7 V, delivering a maximum energy density of 35 Wh kg−1 and an energy density of 22 Wh kg−1 at a high power density of 26 kW kg−1. Combining systematical material design and mechanism study, this work not only broadens the preparation of electrode materials but also brings light to the construction of high‐performance devices for efficient proton storage. [ABSTRACT FROM AUTHOR]

Carbon materials are widely used as anodes of supercapacitors due to the long cycling stability, but the low capacitance results in low energy density of the supercapacitor device in aqueous solution, greatly limiting the application field of the supercapacitor. Here, the spiral low-crystalline Ni(OH)2 supported on self-standing layered film structure of N-doped graphene/carbon nanotubes film (NCF) is reported. The prepared flexible film electrode of low-crystalline Ni(OH)2/NCF is functioned as cathode directly, presenting high gravimetric capacitance (GC) and areal capacitance of 2130 F g − 1 (2 A g − 1 ) and 2.88 F cm − 2 (1 A g − 1 ). Also, this self-standing electrode film shows ultra-long cycle life, retaining 111.4% of initial capacitance after 30 000 circles at large current densities (20 A g − 1 ) and almost 0% fade before 10 000 circles. Moreover, Ni(OH)2/NCF and activated polyaniline derived carbon (APDC) have been assembled into an asymmetric supercapacitor, exhibiting a high gravimetric energy density of 60 Wh kg − 1 at 800 W kg − 1 , suggesting that the obtained electrode has a good prospect application in long cycling stability with high energy density of supercapacitor devices. Low-crystalline flower-like Ni(OH)2 nanosheets have been prepared on N-doped graphene/carbon nanotubes film (NCF) by hydrothermal process. The CF with oxygen-containing functional groups can absorb positively-charged Ni2+ through mutual electrostatic interactions. In addition, the introduction of nitrogen can enhance the coupling and electrostatic interaction between Ni(OH)2 and NCF. Therefore, Ni2+ could be easily adsorbed onto the surface of the NCF. The as-synthesized Ni(OH)2/NCF samples exhibited ultra-long cycle life and high specific capacitance. [ABSTRACT FROM AUTHOR]

Sodium‐ion capacitors (SICs), designed to attain high energy density, rapid energy delivery, and long lifespan, have attracted much attention because of their comparable performance to lithium‐ion capacitors (LICs), alongside abundant sodium resources. Conventional SIC design is based on battery‐like anodes and capacitive cathodes, in which the battery‐like anode materials involve various reactions, such as insertion, alloying, and conversion reactions, and the capacitive cathode materials usually depend on activated carbon (AC). However, researchers have attempted to construct SICs based on battery‐like cathodes and capacitive anodes or a combination of both in recent years. In this Minireview, charge storage mechanisms and material design strategies for SICs are summarized, with a focus on the battery‐like anode materials from both inorganic and organic sources. Additionally, the challenges in the fabrication of SICs and future research directions are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Mesoporous carbon can be synthesized with good control of surface area, pore‐size distribution, and porous architecture. Although the relationship between porosity and supercapacitor performance is well known, there are no thorough reports that compare the performance of numerous types of carbon samples side by side. In this manuscript, we describe the performance of 13 porous carbon samples in supercapacitor devices. We suggest that there is a “critical pore size” at which guest molecules can pass through the pores effectively. In this context, the specific surface area (SSA) and pore‐size distribution (PSD) are used to show the point at which the pore size crosses the threshold of critical size. These measurements provide a guide for the development of new kinds of carbon materials for supercapacitor devices. [ABSTRACT FROM AUTHOR]

Abstract: Highly conductive metal selenides are gaining prominence as promising electrode materials in electrochemical energy‐storage fields. However, phase‐pure bimetallic selenides are scarcely retrieved, and their underlying charge‐storage mechanisms are still far from clear. Here, first a solvothermal strategy is devised to purposefully fabricate monodisperse hollow NiCoSe2 (H‐NiCoSe2) sub‐microspheres. Inherent formation of metallic H‐NiCoSe2 is tentatively put forward with comparative structure‐evolution investigations. Interestingly, the fresh H‐NiCoSe2 does not demonstrate striking supercapacitive behaviors when evaluated for electrochemical supercapacitors (ESs). But it exhibits competitive pseudocapacitance of ≈750 F g−1 at a rate of 3 A g−1 with a high loading of 7 mg cm−2 after ≈100 cyclic voltammetry (CV) cycles. With systematic physicochemical/electrochemical analyses, intrinsic energy‐storage mechanism of the H‐NiCoSe2 is convincingly revealed that the electrooxidation‐generated biactive CoOOH/NiOOH phases in aqueous KOH over CV scanning, rather than the H‐NiCoSe2 itself, account for the remarkable pesudocapacitance observed after cycling. An assembled H‐NiCoSe2‐based asymmetric device has delivered an energy density of ≈25.5 Wh kg−1 with a power rate of ≈3.75 kW kg−1, and long‐span cycle life. More significantly, the electrode design and new perspectives here hold profound promise in enriching material synthesis methodologies and in‐depth understanding of the complex charge‐storage process of newly emerging pseudocapacitive materials for next‐generation ESs. [ABSTRACT FROM AUTHOR]

Abstract: Although two‐dimensional (2D) carbon materials are widely investigated, a well‐defined 2D carbon nanosheet with an ordered mesostructure has rarely been realized. Monolayer‐ordered mesoporous carbon nanosheets (OMCNS) were prepared through confinement assembly of resol and F127 in the interlayer of montmorillonite (MONT). The nanoscale distance of the interlayer space of MONT only allow the assembly of resol and F127 in the same plane, leading to ordered mesopores perpendicular to carbon nanosheets, and favor the formation of sp2 carbon, resulting in a high degree of graphitization. The mesopores on the carbon nanosheets provide efficient ion diffusion, and the high degree of graphitization provides a fast electron‐transport route, enabling OMCNS as excellent electrode materials for electric double layer capacitors. [ABSTRACT FROM AUTHOR]

Heteroatom-doped nanostructured porous carbons have attracted intensive attention for electrical-double layer capacitors (EDLCs) because of their large surface area and surface functionalization. Here we use biowaste sepia ink as a sustainable source to synthesize nitrogen-doped highly porous carbon nanospheres by a simple molten salt-based activation strategy. The introduction of molten salt is not only beneficial for repairing the carbon conjugate network, but can also further improve the activation effect of porogen. The as-obtained carbon nanospheres (MA-NCS) displayed a large surface area of 1760 m2 g−1, optimized pore architecture, and high nitrogen content (8.6 wt %). With this design, the MA-NCS as EDLCs electrode exhibited a remarkable specific capacitance of 320 F g−1 at the current density of 0.5 A g−1 and high rate capability in 6 m KOH electrolyte. Furthermore, the assembled EDLCs demonstrated a high specific capacitance of 130 F g−1 at 0.5 A g−1 in an organic electrolyte (1 m TEABF4/AN), obtaining a maximum energy density of 28.2 Wh kg−1 at a power density of 625 W kg−1. This novel biowaste precursor-synthesis route presents great potential for facile large-scale production of high-performance porous carbons for green and long-term energy storage. [ABSTRACT FROM AUTHOR]

In this contribution, a facile two‐step hydrothermal protocol to prepare hierarchical uniform hollow mesoporous NiCo2S4 microdumbbells (NCS‐MDs) for advanced supercapacitors is developed. Physicochemical investigations reveal that the as‐obtained NCS‐MDs with mesoporous channels in nanoshells possess high‐content Co(III) and Ni(III) species, large surface area (≈80 m2 g−1)/pore volume (≈0.12 m3 g−1), and high tap density (≈0.8 g cm−3). When evaluated as an attractive pseudocapacitive electrode, the unique NCS‐MDs with mass loading of 7 mg cm−2 exhibit remarkable gravimetric/volumetric specific capacitances of ≈912 F g−1 (≈729 F cm−3) at 3 A g−1, and even ≈767 F g−1 (≈613 F cm−3) at high current density of 10 A g−1. Additionally, capacitive degradations of ≈13% and ≈18% are observed over 5000 continous cycles at current rates of 6 and 10 A g−1, respectively. Furthermore, a high‐energy‐density hybrid device is fabricated by using hollow NCS‐MDs and biomass‐derived activated carbon as positive and negative electrodes, respectively, and delivers striking energy density of ≈35.4 Wh kg−1 at power density of ≈381.2 W kg−1, and excellent electrochemical stability at various rates over 11 000 consecutive cycles. These fascinating features strongly highlight that the as‐resulted hollow mesoporous NCS‐MDs could be highly anticipated as a promising electrode platform for next‐generation hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

High-performance electrical double-layer capacitors (EDLCs) require carbon electrode materials with high specific surface area, short ion-diffusion pathways, and outstanding electrical conductivity. Herein, a general approach combing the molten-salt method and chemical activation to prepare N-doped carbon nanosheets with high surface area (654 m2 g−1) and adjustable porous structure is presented. Owing to their structural features, the N-doped carbon nanosheets exhibited superior capacitive performance, demonstrated by a maximum capacitance of 243 F g−1 (area-normalized capacitance up to 37 μF cm−2) at a current density of 0.5 A g−1 in aqueous electrolyte, high rate capability (179 F g−1 at 20 A g−1), and excellent cycle stability. This method provides a new route to prepare porous and heteroatom-doped carbon nanosheets for high-performance EDLCs, which could also be extended to other polymer precursors and even waste biomass. [ABSTRACT FROM AUTHOR]

An efficient anion-exchange protocol was investigated for the controllable fabrication of hollow NiCo2S4 nanoboxes (NBs) from mesocrystalline nickel cobalt carbonate nanocubes as promising pseudocapacitive materials for electrochemical capacitors. The underlying processes of the formation of the hollow architecture were systematically investigated. Originating from the unique structural and compositional advantages, the resultant hollow NiCo2S4 NB electrode with a loading of 5 mg cm2 delivered a large specific capacitance of 777 F g−1 at a high rate of 4 A g−1 in a three-electrode configuration with 6 m KOH as electrolyte. Furthermore, an asymmetric device constructed with the hollow NBs and activated carbon (AC) as positive and negative electrodes, respectively, showed extraordinary supercapacitance within an electrochemically operating voltage window from 0.0 to 1.5 V. The unique AC//NiCo2S4 NB hybrid capacitor exhibited a large specific energy density (active mass normalized) of approximately 17.1 W h kg−1 at a high power density of 2250 W kg−1, and desirable cycling durability with approximately 75 % specific capacitance retention after 5000 consecutive cycles at a current rate of 2 A g−1. These electrochemical investigations strongly indicated that the as-fabricated hollow NiCo2S4 NBs can be elegantly utilized as powerful candidates for advanced electrode platforms. [ABSTRACT FROM AUTHOR]

Porous carbon with high specific surface area (SSA), a reasonable pore size distribution, and modified surface chemistry is highly desirable for application in energy storage devices. Herein, we report the synthesis of nitrogen-containing mesoporous carbon with high SSA (1390 m2 g−1), a suitable pore size distribution (1.5-8.1 nm), and a nitrogen content of 4.7 wt % through a facile one-step self-assembly process. Owing to its unique physical characteristics and nitrogen doping, this material demonstrates great promise for application in both supercapacitors and encapsulating sulfur as a superior cathode material for lithium-sulfur batteries. When deployed as a supercapacitor electrode, it exhibited a high specific capacitance of 238.4 F g−1 at 1 A g−1 and an excellent rate capability (180 F g−1, 10 A g−1). Furthermore, when an NMC/S electrode was evaluated as the cathode material for lithium-sulfur batteries, it showed a high initial discharge capacity of 1143.6 mA h g−1 at 837.5 mA g−1 and an extraordinary cycling stability with 70.3 % capacity retention after 100 cycles. [ABSTRACT FROM AUTHOR]

In this work, ternary metal nitrides are proposed as novel electrode materials for supercapacitors. We selectively fabricate ternary vanadium titanium nitride/carbon (VTiN/C) nanofibers through a facile electrospinning strategy and investigate their electrochemical performance for the first time. The obtained well-interconnected VTiN/C nanofibers with VTiN nanoparticles embedded into carbon ensure rapid electron/ion transfer and offer a highly ion-accessible surface. Appealingly, the VTiN-4/C nanofibers exhibit a greatly improved performance, with a high specific capacitance (430.7 F g−1, 0.5 A g−1) and a good rate capability. Furthermore, the performance of the VTiN/C nanofibers is found to be controllable by adjusting the V/Ti atomic ratio. The encouraging electrochemical performance suggests that ternary VTiN could be a promising electrode material for supercapacitors. [ABSTRACT FROM AUTHOR]

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities. [ABSTRACT FROM AUTHOR]

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities. [ABSTRACT FROM AUTHOR]

To push the energy density limit of supercapacitors, a new class of electrode materials with favorable architectures is strongly needed. Binary metal sulfides hold great promise as an electrode material for high-performance energy storage devices because they offer higher electrochemical activity and higher capacity than mono-metal sulfides. Here, the rational design and fabrication of NiCo2S4 nanosheets supported on nitrogen-doped carbon foams (NCF) is presented as a novel flexible electrode for supercapacitors. A facile two-step method is developed for growth of NiCo2S4 nanosheets on NCF with robust adhesion, involving the growth of Ni-Co precursor and subsequent conversion into NiCo2S4 nanosheets through sulfidation process. Benefiting from the compositional features and 3D electrode architectures, the NiCo2S4/NCF electrode exhibits greatly improved electrochemical performance with ultrahigh capacitance (877 F g−1 at 20 A g−1) and excellent cycling stability. Moreover, a binder-free asymmetric supercapacitor device is also fabricated by using NiCo2S4/NCF as the positive electrode and ordered mesoporous carbon (OMC)/NCF as the negative electrode; this demonstrates high energy density (≈45.5 Wh kg−1 at 512 W kg−1). [ABSTRACT FROM AUTHOR]

Binary metal oxides has been regarded as a promising class of electrode materials for high-performance energy storage devices since it offers higher electrochemical activity and higher capacity than mono-metal oxide. Besides, rational design of electrode architectures is an effective solution to further enhance electrochemical performance of energy storage devices. Here, the advanced electrode architectures consisting of carbon textiles uniformally covered by mesoporous NiCo2O4 nanowire arrays (NWAs) are successfully fabricated by a simple surfactant-assisted hydrothermal method combined with a short post annealing treatment, which can be directly applied as self-supported electrodes for energy storage devices, such as Li-ion batteries, supercapacitors. The as-prepared mesoporous NiCo2O4 nanowires consist of numerous highly crystalline nanoparticles, leaving a large number of mesopores to alleviate the volume change during the charge/discharge process. Electrode architectures presented here promise fast electron transport by direct connection to the growth substrate and facile ion diffusion path provided by both the abundant mesoporous structure in nanowires and large open spaces between neighboring nanowires, which ensures every nanowire participates in the ultrafast electrochemical reaction. Benefiting from the intrinsic materials and architectures features, the unique binder-free NiCo2O4/carbon textiles exhibit high specific capacity/capacitance, excellent rate capability, and cycling stability. [ABSTRACT FROM AUTHOR]

Flexible porous films are prepared from electrospun carbon nanofibers (CNFs) embedded with Co3O4 hollow nanoparticles (NPs) and are directly applied as self-supported electrodes for high-performance electrochemical capacitors. Uniform Co3O4 hollow NPs are well dispersed and/or embedded into each CNF with desirable electrical conductivity. These Co3O4-CNFs intercross each other and form 3D hierarchical porous hybrid films. Benefiting from intriguing structural features, the unique binder-free Co3O4 hollow NPs/CNF hybrid film electrodes exhibit high specific capacitance (SC), excellent rate capability and cycling stability. As an example, the flexible hybrid film with loading of 35.9 wt% Co3O4 delivers a SC of 556 F g−1 at a current density of 1 A g−1, and 403 F g−1 even at a very high current density of 12 A g−1. Remarkably, almost no decay in SC is found after continuous charge/discharge cycling for 2000 cycles at 4 A g−1. This exceptional electrochemical performance makes such novel self-supported Co3O4-CNFs hybrid films attractive for high-performance electrochemical capacitors. [ABSTRACT FROM AUTHOR]

A convenient method for the production of graphene is developed using the electrochemical reduction of graphite oxide (GO) in solution without assembling it onto the electrode. The samples were examined by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results show that the number of oxygen functional groups can be significantly decreased. The electrochemical capacitance of the prepared graphene after 8 h of reduction is 158.5 F g at 0.5 A g, much higher than that of GO and carbon nanotubes. The mechanism for this reaction is also proposed in this paper. [ABSTRACT FROM AUTHOR]

Porous nitrogen-doped carbon nanotubes (PNCNTs) with a high specific surface area (1765 m2 g−1) and a large pore volume (1.28 cm3 g−1) have been synthesized from a tubular polypyrrole (T-PPY). The inner diameter and wall thickness of the PNCNTs are about 55 nm and 22 nm, respectively. This material shows extremely promising properties for both supercapacitors and for encapsulating sulfur as a superior cathode material for high-performance lithium-sulfur (Li-S) batteries. At a current density of 0.5 A g−1, PNCNT presents a high specific capacitance of 210 F g−1, as well as excellent cycling stability at a current density of 2 A g−1. When the S/PNCNT composite was tested as the cathode material for Li-S batteries, the initial discharge capacity was 1341 mAh g−1 at a current rate of 1 C and, even after 50 cycles at the same rate, the high reversible capacity was retained at 933 mAh g−1. The promising electrochemical energy-storage performance of the PNCNTs can be attributed to their excellent conductivity, large surface area, nitrogen doping, and unique pore-size distribution. [ABSTRACT FROM AUTHOR]

MnO2 nanosheets have been synthesized by using a redox reaction of manganese nitrate tetrahydrate and potassium permanganate without any surfactants. The morphology and microstructure of the as-prepared material were characterized by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction (XRD). Electrochemical performances as electrode materials for supercapacitor were evaluated using cyclic voltammetry and galvanostatic charge-discharge in 1 M Na2SO4 aqueous electrolyte. It was found that MnO2 nanosheets showed an excellent capacitive behaviour with good cycling stability. The specific capacitance of the MnO2 nanosheet electrode can reach up to 332.8 Fg−1 at a current density of 500 mA/g and a stable cycling performance. [ABSTRACT FROM AUTHOR]

Nanostructured CoNi-Al layered triple hydroxides (CoNi-Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of CoNi-Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge-discharge techniques. Electrochemical data demonstrated that the CoNi-Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g at a current density of 0.5 A g and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge-discharge cycles at a current density of 2 A g. [ABSTRACT FROM AUTHOR]

A facile hydrothermal strategy was first proposed to synthesize flower-like Co(OH) hierarchical microspheres. Further physical characterizations revealed that the flower-like Co(OH) microspherical superstructures were self-assembled by one-dimension nanobelts with rich mesopores. Electrochemical performance of the flower-like Co(OH) hierarchical superstructures were investigated by cyclic voltammgoram, galvanostatic charge-discharge and electrochemical impedance spectroscopy in 3 M KOH aqueous electrolyte. Electrochemical data indicated that the flower-like Co(OH) superstructures delivered a specific capacitance of 434 F g at 10 mA cm (about 1.33 A g), and even kept it as high as 365 F g at about 5.33 A g. Furthermore, the SC degradation of about 8% after 1,500 continuous charge-discharge cycles at 5.33 A g demonstrates their good electrochemical stability at large current densities. [ABSTRACT FROM AUTHOR]

Abstract: Graphene nanosheets (GNS)/CoAl-layered double hydroxide (CoAl-LDH) composite with a laminated structure is fabricated by a simple refluxing method. It is found that CoAl-LDH lamellar crystallites gradually self-assemble on the graphene oxide (GO) which is reduced to GNS during the refluxing procedure in the presence of urea. The GNS/CoAl-LDH composite has a higher specific surface area (23.4m2 g−1) and superior electrochemical performance. As electrode material for supercapacitors, the composite shows a maximum specific capacitance of 711.5Fg−1 at low current density of 1Ag−1, and it remains 516.8Fg−1 when the current density increase to 10Ag−1. Furthermore, the capacitance keeps at least about 81% (compare with 64% for that of pure LDH) after 2000 cycles at 10Ag−1, indicating the composite has excellent high-current capacitive behavior. [Copyright &y& Elsevier]

In this work, various novel NiO hierarchical nanostructures, including mesoporous nanotubes by nanoparticles self-assembly, nanowire bundles, dandelions, hollow spheres by rods self–assembly, have been fabricated by a simple hydrothermal process and subsequent thermal decomposition at atmosphere. A detailed study of the effect of experimental parameters on the morphology is also presented. Results and analyses demonstrated that oxalic-acid/NaOH molar ratio has an immense function in the subtle morphology control of NiO products. Electrochemical characterization demonstrated that the mesoporous NiO nanotubes were capable of delivering a specific capacitance (SC) of 405 F g−1at the current density of 0.5 A g−1and offered good capacitance retention of ca.91% after 1500 continuous charge-discharge cycles. This soundly indicates that as electrode material, the as-prepared NiO mesoporous nanostructures could meet key requirements in terms of large power density, outstanding rate capability and excellent electrochemical stability. [ABSTRACT FROM AUTHOR]

Abstract: Doped polyaniline (PANI) nanofibers for use in supercapacitors were fabricated by the template method with the aid of ferric chloride (FeCl3) and ammonium persulfate (APS) as the oxidant, in which the organic composite fibers of methyl orange/FeCl3 (MO/FeCl3) functioned as the seed template. Transmission electron microscopy (TEM) revealed that PANI was a fiber in shape with a diameter of 20–40nm and length of about 200–400nm, and the template and oxidant played important roles in the formation of PANI nanofibers. The electrochemical performance of PANI electrode was evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). A high specific capacitance of 428Fg−1 was obtained within the potential range of −0.2 to 0.8V in 1M H2SO4 solution. Moreover, PANI electrode exhibited high discharge/charge efficiency of 93% and the capacitance retention of 83% at a current density of 5mAcm−2, indicating good electrochemical reversibility and rate capability. [Copyright &y& Elsevier]

Highlights: A green water-in-salt electrolyte was developed using lithium acetate as solute with a wide electrochemical stability window of 2.8 V. Molecular dynamics simulation confirmed the nature of water-in-salt electrolyte, where hydrogen bonds of water–water were disrupted and ionic interactions became stronger than dilute solution. Nb18W16O93-based lithium-ion capacitors delivered unexceptionable stability over 50,000 cycles. Aqueous hybrid supercapacitors are attracting increasing attention due to their potential low cost, high safety and eco-friendliness. However, the narrow operating potential window of aqueous electrolyte and the lack of suitable negative electrode materials seriously hinder its future applications. Here, we explore high concentrated lithium acetate with high ionic conductivity of 65.5 mS cm−1 as a green "water-in-salt" electrolyte, providing wide voltage window up to 2.8 V. It facilitates the reversible function of niobium tungsten oxide, Nb18W16O93, that otherwise only operations in organic electrolytes previously. The Nb18W16O93 with lithium-ion intercalation pseudocapacitive behavior exhibits excellent rate performance, high areal capacity, and ultra-long cycling stability. An aqueous lithium-ion hybrid capacitor is developed by using Nb18W16O93 as negative electrode combined with graphene as positive electrode in lithium acetate-based "water-in-salt" electrolyte, delivering a high energy density of 41.9 W kg−1, high power density of 20,000 W kg−1 and unexceptionable stability of 50,000 cycles. [ABSTRACT FROM AUTHOR]

The low capacitance utilization and capacitance fading of manganese dioxide (MnO 2) is mainly due to poor electro-conductivity and irreversible phase transform. This work proposes a new method of designing hierarchical and binder-free electrode based on MnO 2 material for stable supercapacitor with high specific capacitance. Herein, we fabricated the self-standing electrode of MnO 2 on nitrogen-doped graphene and single wall carbon nanotubes (SWCNTs) self-standing film (NGCF) by electrochemical deposition. As a result, as-prepared MnO 2 /NGCF cathode showed excellent electrochemical performance of 489.7 F g-1 at 1 A g-1. Assembled symmetric aqueous supercapacitor (SC) manifests high voltage of 2.4 V and presents excellent high energy density of 106.7 Wh kg-1 at 1200 W kg-1 and outstanding long-life stability without no decay after 10 000 charge-discharge circuits. This work proposes a new view of designing hierarchical and binder-free electrode with high energy density and long cycling stability based on MnO 2 material for stable symmetric supercapacitor. [ABSTRACT FROM AUTHOR]

Conductive polymer and porous carbon hold critical promise as capacitive materials. However, individual use of these materials seriously limits their applications due to poor rate capability and short lifetime or low capacitance. Herein, we successfully fabricate hierarchical polyaniline@N-doped porous carbon (PANI@NPC) double-shell frameworks by in-situ coating of PANI on the NPC surface, and achieve high charge-storage performance. The whole design involves multiple strategies of nanostructurization, constructing hierarchical structure, and hybridization, which will address the above electrochemical concerns. The best specific capacitance for PANI@NPC-2 with 32% NPC reaches 660.0 F g−1 at 0.5 A g−1 and remains 479.8 F g−1 at 5 A g−1, significantly higher that the results of PANI and other hybrids. Moreover, the symmetric supercapacitor using PANI@NPC-2 electrodes demonstrates good performance with an energy density of 8.0 Wh kg−1 at 0.5 A g−1 and a power density of 1750.0 W kg−1 at 10 A g−1. The promoted performance relies largely on the synergy of desirable properties of building blocks in hybrids. This research manifests a general yet efficient method for high-performance hybrid materials for promoting the development of sustainable energy. Display Omitted • Multiple strategies are proposed to design hybrid double-shell 3D frameworks. • Optimal hybrid delivers high capacitance and good rate performance. • The symmetric supercapacitor assembled exhibits high energy and power densities. [ABSTRACT FROM AUTHOR]

Abstract To obtain high performance supercapacitors suitable for tiny, compact and portable electronic devices, a new type of electrode with high energy density, high speed performance and long cycling-stability is essential. In practical applications, both volumetric capacitance and gravimetric capacitance should be regarded as equally important parameters. Due to their high open surface structures, high compressibility and high conductivity, low-density three-dimensional (3D) carbon scaffolds hold great promise for excellent electrochemical performance, high diffusion rates and low ion transport resistance. Here, a new 3D elastic sponge composed of single-walled carbon nanotubes/graphene (SWNT-rGO-S) was successfully prepared by a superfast and facile flame burning method in an open environment within 20 s. Moreover, the hierarchical NiCo 2 O 4 nanosheets were deposited on the SWNT-rGO-S scaffold through the hydrothermal method and the annealing treatment. Due to the 3D open pore and compositional features, the compressed NiCo 2 O 4 /SWNT-rGO-S electrode exhibits a high gravimetric capacitance of 2050 F g−1 and a volumetric capacitance of 1200 F cm−3, together with a high cycling stability with 115.3% capacitance retention after 6800 cycles at the current density of 20 A g−1 and a high rate performance of 73.2% capacitance retention with the current density being increased from 2 to 80 A g−1. Additionally, a high performance asymmetric supercapacitor was fabricated by using NiCo 2 O 4 /SWNT-rGO-S as the positive electrode and activated polyaniline derived carbon (APDC) as the negative electrode, presenting high gravimetric and volumetric energy densities of 53.5 Wh kg−1 and 26.9 Wh L−1, respectively, and exhibiting a very high 83.5% capacitance retention after 10,000 cycles. Highlights • Carbon nanotube/graphene sponge was prepared by a fast flame burning method. • 3D SWNT-rGO-S could provide fast electron conduction and ion transportation. • Compressible NiCo2O4/SWNT-rGO-S exhibits advanced electrochemical behaviour. • Asymmetric device shows high gravimetric, volumetric energy density with long life. [ABSTRACT FROM AUTHOR]

Abstract Supercapacitors (SCs) with high gravimetric and volumetric performances are highly demanded for diverse applications, but still remain challenge to achieve for traditional porous carbon materials due to the unbalance between porous properties and high density. Herein, we report a novel oxygen-enriched crumpled graphene (OCGN) with high density prepared through a simple and facile strategy. The as-prepared OCGN possesses several advantageous features of abundant stable active oxygen-containing functional groups (17.26%), high packing density (1.28 g cm−3) and facile ion channel, resulting in high gravimetric and volumetric specific capacitance (300.5 F g−1, 384.6 F cm−3), outstanding rate performance and cyclic stability. In addition, the assembled symmetric SC exhibits a large gravimetric and volumetric energy density of 20.4 Wh kg−1 and 26.1 Wh L−1 in aqueous electrolyte, which is higher than majority of previously reported carbon-based aqueous SCs. The encouraging results demonstrate that designing oxygen-enriched carbon materials with high density may be a novel strategy to realize both high gravimetric and volumetric performance. Graphical abstract Unlabelled Image Highlights • Oxygen-enriched crumpled graphene with high density was prepared through a simple and facile strategy. • Oxygen-enriched crumpled graphene possesses high specific gravimetric and volumetric capacitance. • Symmetric supercapacitor was fabricated based on oxygen-enriched crumpled graphene with a high volumetric performance. [ABSTRACT FROM AUTHOR]

• The synergistic effect exists in V s -NiCo 2 S 4 @NiCoS 2 core-shell electrode materials with interfacial sulfur vacancy modification. • The V s -NiCo 2 S 4 @NiCoS 2 provides a capacitance of 3200 f g −1 with the 1 + 1>2 effect compared to V s -NiCo 2 S 4 and NiCoS 2. • The V s -NiCo 2 S 4 @NiCoS 2 @AC devices deliver up to 46.3 Wh kg−1 energy density at 799.8 W kg−1 power density. Nickel-cobalt based bimetallic sulfide has attracted much attention as positive electrode materials for supercapacitors due to its microstructure designability. However, charge storage occurs mostly on the surface of the material, which limits the full utilization of the active material inside. Here, rich sulfur vacancies modified NiCo 2 S 4 @NiCoS 2 (V s -NiCo 2 S 4 @NiCoS 2) core-shell structures are grown tightly on a nickel foam substrate and prepared as positive material for supercapacitors. The rich sulfur vacancies in the V s -NiCo 2 S 4 "core" increase the electrochemical active sites and electron transport rates, while the amorphous NiCoS 2 "shell" facilitates the rapid diffusion of ions. The results show that V s -NiCo 2 S 4 @NiCoS 2 core-shell structure has a specific capacitance of 3200 F g −1, achieving the effect of "1 + 1>2". The excellent electrochemical performance is attributed to the surface/interface modification of rich sulfur vacancies and the synergistic effect induced by heterogeneous core-shell boundaries. Moreover, the asymmetric supercapacitor V s -NiCo 2 S 4 @NiCoS 2 //AC exhibits an energy density of 46.3 Wh kg−1 and a power density of 799.8 W kg−1, as well as excellent cyclic stability (nearly 80% capacity retention after 10,000 cycles). This work provides a new idea and strategy for core-shell structure design of nickel-cobalt sulfide electrode materials combined with surface/interface modification. Sulfur vacancy modified V s -NiCo 2 S 4 @NiCoS 2 core-shell structure electrode material has been synthesized by hydrothermal, chemical reduction and electrochemical deposition. [Display omitted] [ABSTRACT FROM AUTHOR]

Bacterial cellulose (BC), a typical biomass prepared from the microbial fermentation process, has been proved that it can be an ideal platform for design of three-dimensional (3D) multifunctional nanomaterials in energy storage and conversion field. Here we developed a simple and general silica-assisted strategy for fabrication of interconnected 3D meso-microporous carbon nanofiber networks by confine nanospace pyrolysis of sustainable BC, which can be used as binder-free electrodes for high-performance supercapacitors. The synthesized carbon nanofibers exhibited the features of interconnected 3D networks architecture, large surface area (624 m 2 g −1 ), mesopores-dominated hierarchical porosity, and high graphitization degree. The as-prepared electrode (CN-BC) displayed a maximum specific capacitance of 302 F g −1 at a current density of 0.5 A g −1 , high-rate capability and good cyclicity in 6 M KOH electrolyte. This work, together with cost-effective preparation strategy to make high-value utilization of cheap biomass, should have significant implications in the green and mass-producible energy storage. [ABSTRACT FROM AUTHOR]

High energy density batteries and high power density supercapacitors have attracted much attention because they are crucial to the power supply of future portable electronic devices, electric automobiles, unmanned aerial vehicles, etc. The electrode materials are key components for batteries and supercapacitors, which influence the practical energy and power density. Metal-organic frameworks possessing unique morphology, high specific surface area, functional linkers, and metal sites are excellent electrode materials for electrochemical energy storage devices. Herein, we review and comment on recent progress in metal-organic framework-based lithium-ion batteries, sodium-ion batteries, lithium-air batteries, lithium-sulfur/selenium batteries, and supercapacitors. Future perspectives and directions of metal-organic framework-based electrochemical energy storage devices are put forward on the basis of theoretical knowledge from the reported literature and our experimental experience. [ABSTRACT FROM AUTHOR]

High value-added utilization of ubiquitous low-grade heat shows great importance to energy regulation. liquid thermocell is considered as promising candidate for converting heat into electricity due to its high Seebeck coefficient and facile operation. However, the challenging integration of dozens of tiny devices is still required to generate a useful voltage, which greatly blocks the development of thermocells. Here, a well-defined nitrogen-doped hierarchical porous carbon (NHPC) obtained by self-template carbonization and alkaline activation is employed to construct high-performance zinc ion thermal charging supercapacitors (ZTSC) for the integration of energy conversion and storage. Significantly, continuous architecture of NHPC can enlarge the electrochemical active surface and shorten the diffusion pathways of electrolyte ions. Consequently, a high energy/power density of 71.8 Wh kg−1/10.3 kW kg−1 can be achieved. Moreover, NHPC based ZTSC can output an attractive voltage of 1.16 V, a high thermopower of 31.4 mV K−1, and a superior normalized power density of 15.3 mW m−2 K−2 with a temperature difference of 27 K. This work not only provides a facile strategy to prepare promising carbon materials, but also demonstrates the possibility of hybrid supercapacitors for heat-to-current conversion and storage. [Display omitted] • A facile strategy is proposed to form N-doped hierarchical porous carbon (NHPC). • The NHPC shows high capacitance and good rate capability in energy storage. • A high-performance zinc thermal charging supercapacitor is constructed. [ABSTRACT FROM AUTHOR]

In recent years, transition metal sulfides, especially nickel-cobalt sulfide materials play a crucial role for supercapacitor applications. In this work, the Ni 5 P 2 @Ni 9 S 8 /CoS 1.097 (Ni-P@NCS) core-shell material has been synthesized by simply phosphating the nickel mesh and subsequent electrodeposition of NCS to obtain a nanosheet heterostructure on nickel foam. The Ni-P@NCS composite material has a higher gravimetric capacitance of 2445.7 F g−1 than pure Ni-P of 1116.6 F g−1 and NCS materials of 1104.3 F g−1 at 1 A g−1. At the same time, Ni-P@NCS electrode yields excellent cycling stability (91.4% capacitance retention after 5000 charge–discharge cycles). An asymmetric supercapacitor (ASC) device assembled from Ni-P@NCS and activated carbon electrodes can deliver a highest energy/power density of 42.8 Wh kg−1/799.8 W kg−1, with 94.3% capacitance retention after 10,000 cycles at 5 A g−1. The improvement of electrochemical performance makes it possible to use it as an electrode material. • The Ni 5 P 2 @Ni 9 S 8 /CoS 1.097 electrode has high specific capacitance, working potential window. • The Ni 5 P 2 @Ni 9 S 8 /CoS 1.097 composite material has a higher gravimetric capacitance of 2445.7 F g-1. • The potential window of Ni 5 P 2 @Ni 9 S 8 /CoS 1.097 //AC is 0–1.6 V and the energy density is 42.8 Wh Kg-1. [ABSTRACT FROM AUTHOR]

Vanadium nitride has been the hot material for supercapacitors due to its excellent electrical conductivity and high specific capacitance. However, vanadium nitride nanoparticle usually suffers a poor performance due to its aggregation and lack of effective contact. In this work, one-dimensional (1D) vanadium nitride nanofibers are prepared by a combination of electrostatic spinning and high-temperature calcination in ammonia. The cross-linked nanofibers composed of nanoparticles construct a facile transport path for charge and electrolyte ion. Moreover, vanadium nitride nanoparticles encapsulated into carbon prevent grain growth and aggregation, which provide more active sites for electrolyte ion. Owing to this unique structure, vanadium nitride nanofibers exhibit high specific capacitance of 291.5 F g −1 at 0.5 A g −1 and rate capability with a capacitance of 105.1 F g −1 at 6 A g −1 . In addition, we find that annealing temperature has significant influence on the performance of vanadium nitride, which associates with fibrous structure and crystallinity, and a limited potential window can greatly improve the cycling stability (retains 50% of initial capacitance after 1000 cycles). [ABSTRACT FROM AUTHOR]

Because carbon based supercapacitor electrode has low energy density, so birnessite electrode material has attracted more and more attention due to its low cost, environmental friendliness, high oxygen evolution potential and high theoretical specific capacitance. In this work, novel nanoneedle-like rGO/V-Na x MnO 2 /CC cathode material with oxygen vacancies has been prepared, where rGO and CC represent reduced graphene oxide and carbon cloth, respectively. By using surface-protection strategy and introduction of abundant oxygen vacancies, high capacitance of rGO/V-Na x MnO 2 /CC is obtained with 362.5 F g−1 at 1 A g−1. After the current density increases to 24 A g−1, the capacitance retention is 56.56%, presenting excellent rate performance. In addition, after 10,000 charge/discharge cycles at 5 A g−1, the capacitance retention rate is 90.17%, showing excellent cycle stability. The aqueous asymmetric supercapacitor (ASC) of ACMK-3 // rGO/V-Na x MnO 2 /CC has a wide potential window of 0 ~ 2.5 V. And the energy density is as high as 72.2 Wh kg−1 at 1254 W kg−1. After 10,000 charge-discharge cycles at 4 A g−1, the ASC still remains a capacitance retention rate of 88.5%. This work provides a facial method to improve electrochemical properties and shed a light on fabricating a novel cathode for aqueous supercapacitors. ● The rGO/V-Na x MnO 2 /CC electrode with high specific capacitanceand high rate capability has been prepared. ● The cover of rGO and introduction of oxygen vacancies make Na x MnO 2 /CC high specific capacitance and high rate capability. ● ACMK-3//rGO/V-Na x MnO 2 /CC delivers a high energy density of 72.2 Wh kg−1 under the wide potential window of 0–2.5 V. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) mesoporous ternary Co-Ni-Mn oxide nanowires (CNMO NWs) have been controllably fabricated via a facile yet scalable template-free strategy involving a green hydrothermal route coupled with the following calcination. The composition of the reaction solvent system, i.e., the volume ratio of the ethylene glycol and deionized water, plays a significant role in tuning the specific morphologies and microstructures of the final CNMO products. The as-derived lD CNMO NWs are constructed with numerous nanoparticle subunits with the size of ≈5-10 nm, and possess lots of interparticle mesopores ranged from 2 to 6 nm. The well-defined mesoporous CNMO NWs apparently have appealing structural advantages, such as fast and convenient electron and ion transport, sufficient redox electrochemical centers with multiple valences, and large electroactive surface area. As a result, the as-fabricated mesoporous CNMO NWs manifest exceptional pesudocapacitance and excellent cycling stability at high rates when evaluated as a striking low-cost electrode for next-generation electrochemical capacitors. [ABSTRACT FROM AUTHOR]

Abstract: Graphene/MnO2 hybrid nanosheets were prepared by incorporating graphene and MnO2 nanosheets in ethylene glycol. Scanning electron microscopy and transmission electron microscopy analyses confirmed nanosheet morphology of the hybrid materials. Graphene/MnO2 hybrid nanosheets with different ratios were investigated as electrode materials for supercapacitors by cyclic voltammetry (CV) and galvanostatic charge–discharge in 1 M Na2SO4 electrolyte. We found that the graphene/MnO2 hybrid nanosheets with a weight ratio of 1:4 (graphene:MnO2) delivered the highest specific capacitance of 320 F g−1. Graphene/MnO2 hybrid nanosheets also exhibited good capacitance retention on 2000 cycles. [Copyright &y& Elsevier]

Abstract: We developed a direct carbonization strategy to efficiently fabricate mesoporous N-containing carbon nanosheets (N-CNSs) by using polyaniline nanosheets as a carbon precursor. Physicochemical characterizations revealed that the as-synthesized N-CNSs with 5.9wt.% N species possessed a well-developed mesoporous architecture with large specific surface area of 352m2 g−1, high mesoporous volume of 0.32cm3 g−1, and average pore size of ∼5.2nm. When further utilized as an electrode for electrochemical capacitors, the mesoporous N-CNSs delivered a large specific capacitance of 239Fg−1 at 0.5Ag−1, and even 197Fg−1 at a high current load of 8Ag−1, indicating its good rate behavior. Furthermore, the capacitance degradation of ∼4% over continuous 5000 charge–discharge cycles at 6Ag−1 further verified its good electrochemical stability at high rates for long-term electrochemical capacitors application. [Copyright &y& Elsevier]

The exploration of thermally chargeable supercapacitors has gained intensive interest. However, their practical application is still restricted by complex integration, poor Seebeck coefficient, and unsatisfactory conversion efficiency. Herein, we report a high-performance device with a simplified symmetric configuration based on activated carbon derived from elm bark mucus. Due to high specific surface area, hierarchical porosity, and moderate surface chemistry, such system displays excellent electrochemical properties such as high capacitance, rate capability and thermoelectrical behavior. When coupling with a concentrated electrolyte (26 m KOAc), a 2.0 V symmetric supercapacitor can be fabricated and a maximum energy density of 33.6 Wh kg−1 at power density of 500 W kg−1. A high-power density of 20 kW kg−1 also can be achieved at 21.7 Wh kg−1. Moreover, thermally rechargeable devices with quasi solid-state electrolyte exhibit a high open circuit voltage of ∼24.02 mV and a considerable Seebeck coefficient of about 1.97 mV K−1, indicating satisfying thermoelectrical performances. This work not only demonstrates the applicability of elm bark mucus-derived carbon as advanced materials for energy application, but also provides a new perspective for the development of multifunctional devices. [Display omitted] • A facile approach is proposed to prepare biomass-derived porous carbon. • The AMPC-3 material exhibits satisfactory electrochemical performance. • A high-performance thermally rechargeable supercapacitor is constructed. [ABSTRACT FROM AUTHOR]

Nickel cobalt sulfur is attracting more attention due to its great electrical conductivity and high specific capacitance for faraday pseudo-capacitors. Here, by evaporation-induced drying, heterostructure NiS 2 /NiCo 2 S 4 nanosheets on self-supporting substrate of nitrogen-doped single-walled carbon nanotubes sponge (NSCS) are obtained with the sponge volume significantly being reduced. With the electrode film thickness being 80 μm, the as-prepared heterostructure NiS 2 /NiCo 2 S 4 /NSCS electrode shows outstanding areal/gravimetric/volumetric capacitance of 10.5 F cm−2/2905 F g−1/1307.2 F cm−3 at 1 A g−1. With the increase of current density from 1 to 60 A g−1, the current retention rate maintains at 61%. When the active material loading is increased to 14 mg cm−2, the gravimetric capacitance can still maintain at 1725 F g−1, indicating the high ratio performance. After 10,000 cycles, the capacity retention still remains 83% at current density of 10 A g−1. In addition, an asymmetric supercapacitor (ASC) delivers have high gravimetric/volumetric energy density of 58.1 W h kg−1/52.3 W h L−1 with excellent cycle stability after 20,000 cycles. Therefore, the electrode material with high loading and high rate performance can be realized by this method. • By evaporation-induced drying, the volume of NiS 2 /NiCo 2 S 4 /NSCS shrinks obviously. • The electrode has high areal and volumetric capacitance with high loading. • Heterostructure material of NiS 2 /NiCo 2 S 4 greatly improves the electrochemical performance. • The asymmetric supercapacitor delivers high gravimetric/volumetric energy density. [ABSTRACT FROM AUTHOR]

Abstract: In the work, we developed an aqueous symmetric Ru–Cr binary oxide (Ru0.83Cr0.17O2·nH2O)-based electrochemical capacitor (EC) with unwonted high operating voltage in 1M KOH aqueous solution. Electrochemical performance of the symmetric EC was investigated by current-potential response and galvanostatic charge–discharge techniques. Electrochemical data demonstrated that the symmetric EC with a specific capacitance (SC) of ca. 148Fg−1 surprisingly can operate in a large electrochemical window of 1.4V in 1M KOH electrolyte, ensuring that the symmetric EC delivered an energy density of ca. 40Whkg−1. Moreover, the extended cycle life and good power property were obtained meanwhile, indicating that the Ru0.83Cr0.17O2·nH2O-based EC is a promising candidate for aqueous symmetric devices with high energy density and desirable power property. [Copyright &y& Elsevier]

Abstract: A novel two-step synthetic strategy was proposed to synthesize urchin-like nickel cobaltite (NiCo2O4) microspherical hierarchical superstructures constructed by one-dimension nanowires: hydrothermal precipitating (Ni, Co) carbonate hydroxide followed by calcinating process. Electrochemical data reveals that the as-synthesized urchin-like NiCo2O4 superstructures can deliver a specific capacitance (SC) of 296F/g at 1A/g, and keep it as high as 215F/g at 5A/g in 6M KOH aqueous solution. Such unique urchin-like hierarchical superstructures make each electroactive NiCo2O4 nanowire building block contacted easily by electrolyte ions and electrons at high rates, ensuring that sufficient Faradaic reactions take place at large current densities for energy storage. Moreover, no obvious SC degradation after 1000 continuous charge–discharge cycles at 2A/g demonstrates good electrochemical stability of the urchin-like microspherical superstructures, promising their great potential application in electrochemical capacitors. [Copyright &y& Elsevier]

Abstract: In the work, we develop a novel two-step strategy to synthesize self-supported hexagonal nickel oxide nanoplatelet arrays on Ni foam: precipitating hydroxides followed by calcinating process. These nanoplatelets are composed of a multilayer of ultrathin mesoporous NiO nanosheets. The unique Ni foam-supported mesoporous NiO nanoplatelet arrays electrode promises fast ion and electron transport, large electroactive surface area, and excellent structural stability. As a result, superior pseudocapacitive performance is achieved with large specific capacitance in the range of 1124–864Fg−1 and excellent cycling stability up to 5000 cycles, suggesting their promising application for electrochemical capacitors. [Copyright &y& Elsevier]

Abstract: A novel one-step electrochemical composite polymerization strategy was first proposed to prepare unique polypyrrole/reduced graphene oxide/carbon nanotubes (PPy/F-RGO/CNTs) ternary composites, where F-RGO, CNTs, and PPy were electrodeposited simultaneously to construct a three-dimensional (3-D) highly porous film electrode. Such ternary composite film electrode exhibits a high specific capacitance of 300Fg−1 at 1Ag−1 as well as a remarkable cycling stability at high rates, which is related to its unique nanostructure and high electrical conductivity. F-RGO and CNTs act as an electron-transporting backbone of a 3-D porous nanostructure, leaving adequate working space for facile electrolyte penetration and better faradaic utilization of the electro-active PPy. Furthermore, the straightforward approach proposed here can be readily extended to prepare other composite film electrodes with good electrochemical performance for energy storage. [Copyright &y& Elsevier]