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Hybrid electric storage systems that combine capacitive and faradaic materials need to be well designed to benefit from the advantages of batteries and supercapacitors. The ultimate capacitive material is graphite (GR), yet high capacitance is usually not achieved due to restacking of its sheets. Therefore, an appealing approach to achieve high power and energy systems is to embed a faradaic 2D material in between the graphite sheets. Here, a simple one‐step approach was developed, whereby a faradaic material [layered double hydroxide (LDH)] was electrochemically formed inside electrochemically exfoliated graphite. Specifically, GR was exfoliated under negative potentials by CoII and, in the presence of MnII, formed GR‐CoMn‐LDH, which exhibited a high areal capacitance and energy density. The high areal capacitance was attributed to the exfoliation of the graphite at very negative potentials to form a 3D foam‐like structure driven by hydrogen evolution as well as the deposition of CoMn‐LDH due to hydroxide ion generation inside the GR sheets. The ratio between the CoII and MnII in the CoMn‐LDH was optimized and analyzed, and the electrochemical performance was studied. Analysis of a cross‐section of the GR‐CoMn‐LDH confirmed the deposition of LDH inside the GR layers. The areal capacitance of the electrode was 186 mF cm−2 at a scan rate of 2 mV s−1. Finally, an asymmetric supercapacitor was assembled with GR‐CoMn‐LDH and exfoliated graphite as the positive and negative electrodes, respectively, yielding an energy density of 96.1 μWh cm−3 and a power density of 5 mW cm−3. [ABSTRACT FROM AUTHOR]

Long-cycle stability and high-energy density are big challenges for developing high-performance hybrid supercapacitor (HSC) electrode materials. In this work, molybdenum-doped Co3O4 nanosheets arrays on nickel foam (noted as MoxCo1.5−xO/NF) are successfully prepared via facile one-step electrodeposition followed by annealing for hybrid supercapacitors. The experimental and calculated results indicate that the band gap modification and conductivity enhancement of MoxCo1.5−xO lead to excellent capacitive performance due to the doping of Mo into Co3O4. The as-prepared Mo0.25Co1.25/NF electrode demonstrates a high specific capacity of 128.2 mAh g−1 (923 F g−1) at 1 A g−1 (60% higher than the undoped Co3O4) and superior cycle stability with 95.2% capacity retention after 10,000 cycles at 10 A g−1. The assembled HSC delivers high-energy density of 64.3 Wh kg−1 at the power density of 794.1 W kg−1 and with 87.7% capacity retention after 10,000 cycles. This work can present a new strategy to fabricate the three-dimensional high-performance integrated electrode materials by a facile electrodeposition for heteroatom-doped transition metal oxide for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Tailoring of battery-type NiCo 2 O 4 with carbon-based materials for supercapacitors usually involves several steps, which require prolonged syntheses at high temperatures. Here, a facile one-step strategy is presented for the fabrication of a binder-free composite, made of NiO x decorated multi-walled carbon nanotubes (CNTs) and NiCo 2 O 4 nanoparticles on nickel foam to form a stable supercapacitor with high specific capacity. The process is based on the electrophoretic co-deposition of carboxylated-CNTs and NiCo 2 O 4 NPs, which were positively charged using Ni2+. The latter played a double role by stabilizing the nanomaterials and improving the electrochemical performance by decorating the nanomaterials with NiO x species. The well-dispersed NiCo 2 O 4 NPs in the highly conductive porous matrix of CNTs provide efficient electron transfer, high surface area and superior electrochemical performance, such as high charge storage, high rate delivery and good cycling stability. The nanocomposite film exhibited high specific capacitance of 1363 F gr−1 at 2 A gr−1, while retaining 82% of the capacitance at higher current density (20 A gr−1). The straightforward fabrication process and the excellent electrochemical activity are of generic nature and can be applied for assembling other well-structured carbon-based composites. [ABSTRACT FROM AUTHOR]

Supercapacitors are developing in terms of high power and energy densities. Carbon materials can meet this challenge to a certain extent. A sustainable high‐performance carbon material for supercapacitors was prepared through the simple and green thermal pyrolysis of orange peels as raw materials by using KOH as an activator. The biomass‐derived carbon materials activated at different temperatures were evaluated as electrode materials. The adsorption properties, structure, and surface elemental chemical states of the prepared materials were studied. Carbonation temperature plays a key role in the preparation of materials, and it has different effects on the physical and electrochemical properties of materials. The opc700 and opc800 samples have large pore volumes, which provide the necessary space for the storage of electrolyte ions. The temperature has a pronounced effect on the specific surface area and the electrochemical performance. The specific surface area of opc800 is as high as 2004 m2 g−1 and the pore volume is 1.24 cm3 g−1. The maximum specific capacity of opc800 is 306.6 F g−1 at 0.5 A g−1 and the specific capacitance is 251.2 F g−1 at 20 A g−1. [ABSTRACT FROM AUTHOR]

Abstract Despite many efforts devoted to explore novel electrode materials for lithium ion hybrid supercapacitors, the obtainable long-life cycling of existing anode materials are still inadequate for promising applications. This report demonstrates a new nanocomposite with TiNb 2 O 7 network nanostructure in situ anchored onto the holey graphene, which is designed as anode material for lithium ion hybrid supercapacitors. Impressively, electrochemical analyses show that the good rate performance (capacity retention of 73.5% from 0.05 to 5 A g−1) and long cycle life up to 1000 cycles at 1 A g−1 (a capacity retention of 91.5%) are attained. Furthermore, the lithium ion hybrid supercapacitor device consisting of this nanocomposite and activated carbon exhibits excellent cycling stability (90.2% of initial capacity after 3000 cycles), high energy density of 86.3 W h kg−1 (at 237.7 W kg−1) and high power density of 3.88 kW kg−1 (at 28.7 W h kg−1). This study ascribes the unprecedented performance to the high conductive holey graphene with abundant mesopores, the uniformly distributed TiNb 2 O 7 network nanostructure and the synergetic effect between them. Based on these findings, the presented nanocomposite has great potential in high performance lithium ion hybrid supercapacitors. Graphical abstract Image 1 Highlights • A novel composite of TiNb 2 O 7 network nanostructure and holey graphene was fabricated. • The long-term life with 91.5% capacity retention after 1000 cycles was obtained. • The Li-HSC device exhibits high energy density and excellent cycling stability. [ABSTRACT FROM AUTHOR]

The physicochemical property of chemically prepared graphene can be significantly changed due to the incorporating of heteroatoms into graphene. In this article, boron-doped graphene sheets are used as carbon substrates instead of graphene for loading polyaniline by in situ polymerization. Compared with the individual component and polyaniline/non-doped graphene, the sandwich-like polyaniline/boron-doped graphene exhibits remarkably enhanced electrochemical specific capacitance in both acid and alkaline electrolytes. In a three-electrode configuration, the hybrid has a specific capacitance about 406 F g −1 in 1 M H 2 SO 4 and 318 F g −1 in 6 M KOH at 1 mV s −1 . In the two-electrode system of a symmetric supercapacitor, this hybrid achieves a specific capacitance about 241 and 189 F g −1 at 0.5 A g −1 with a specific energy density around 19.9 and 30.1 Wh kg −1 , in the acid and alkaline electrolytes, respectively. The as-obtained polyaniline/boron-doped graphene hybrid shows good rate performance. Notably, the obtained electrode materials exhibit long cycle stability in both acid and alkaline electrolytes (∼100% and 83% after 5000 cycles, respectively). The improved electrochemical performance of the hybrid is mainly attributed to the introduction of additional p -type carriers in carbon systems by boron-doping and the well combination of pseudocapacitive conducting polyaniline. [ABSTRACT FROM AUTHOR]

Abstract: A novel high-performance electrode material based on fibrillar polyaniline (PANI) doped with graphene oxide sheets was synthesized via in situ polymerization of monomer in the presence of graphene oxide, with a high conductivity of 10Scm−1 at 22°C for the obtained nanocomposite with a mass ratio of aniline/graphite oxide, 100:1. Its high specific capacitance of 531F/g was obtained in the potential range from 0 to 0.45V at 200mA/g by charge–discharge analysis compared to 216F/g of individual PANI. The doping and the ratio of graphene oxide have a pronounced effect on the electrochemical capacitance performance of the nanocomposites. [Copyright &y& Elsevier]

Highlights: [•] CoMoO4/Graphene composites were prepared via one-step hydrothermal method. [•] The composites have high surface/body ratios and large electroactive regions. [•] The composites present better electrochemical properties than pure-CoMoO4. [•] The composite achieves a capacitance of 394.5Fg−1 at 1mVs−1. [ABSTRACT FROM AUTHOR]

Graphical abstract The novel electrode materials, NiO ultrathin nanosheets anchored to two types of needle-like NiCo 2 O 4 and slice-like NiCo 2 O 4 on carbon cloth (CC), are synthesized by a simple two-step method. Both as-prepared hierarchical electrodes deliver high specific capacitance and excellent cycling performance, which show the potential of its practical application. Highlights • A new strategy for designing freestanding hierarchical structure of CC/NiCo 2 O 4 @NiO. • The electrodes show high specific capacitance and excellent cycle stability. • The capacitive contributions are leading roles in both kinds of electrodes. • All-solid-state asymmetric supercapacitors deliver high energy and power density. Abstract To fabricate free-standing electrodes with hierarchical structured redox-type metal oxides has become a wise strategy for the development of high-performance energy storage systems. Two types of NiCo 2 O 4 with needle-like and slice-like morphologies act as the conducting cores and hydrothermally grow on carbon cloth (CC/NiCo 2 O 4 -N and CC/NiCo 2 O 4 -S). The mesoporous NiO ultrathin nanosheets further are anchored on the surface of the two types of CC/NiCo 2 O 4 to form the novel high-performance electrodes (CC/NiCo 2 O 4 -N@NiO and CC/NiCo 2 O 4 -S@NiO). Particularly, the formation mechanism of NiO ultrathin nanosheets is proposed. The two integrated electrodes of CC/NiCo 2 O 4 -N@NiO and CC/NiCo 2 O 4 -S@NiO exhibit high specific capacitance of 921.9 and 852.9 mF/cm2 (or 709.1 and 775.1F/g) at 2 mA/cm2, respectively and excellent long cycling lifespan (both 100% retention after 10,000 cycles). The assembled asymmetric supercapacitors, CC/NiCo 2 O 4 -N@NiO//graphene and CC/NiCo 2 O 4 -S@NiO//graphene, can still deliver the high energy density and power density, and possess excellent cycling stability (95.2% and 92.3% retention after 10,000 cycles, respectively). Our work not only provides an attractive strategy and a two-step facile method for construction of hierarchical electrodes based on ultrathin NiO sheets and nanostructured NiCo 2 O 4 , but also offers a strategy for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Highlights • A novel NC-Ti 3 C 2 T x hybrid has been synthesized. • NC-Ti 3 C 2 T x hybrid exhibits quick charge/discharge rate up to 3.0 V s−1. • NC-Ti 3 C 2 T x hybrid exhibits higher specific capacitance of 82.8 F g−1 at 1.0 A g−1. • The hybrid exhibits excellent cycling stability (100% retention after 5000 cycles). Abstract The MXenes with excellent chemical and physical properties are novel and promising electrode materials for supercapacitors. However, aggregation and restacking of MXene sheets limit material's electrochemical performance. Here, we report a method to prevent MXene sheets from restacking and significantly improved electrochemical capability of Ti 3 C 2 T x MXene by intercalating with N-doped carbon (NC) introduced from ZIF-8. Ti 3 C 2 T x MXene sheets were prepared by etching Ti 3 AlC 2 powder in HF, then ZIF-8/Ti 3 C 2 T x composite was prepared, followed by annealing in H 2 /Ar atmosphere. Benefited from higher specific surface area and electron conductivity, the obtained NC-Ti 3 C 2 T x hybrid shows the quick charge/discharge rate up to 3.0 V s−1, little IR drop at 50.0 A g−1, higher specific capacitance of 82.8 F g−1 at 1.0 A g−1 (about 210% of the origin), and 100% retention in capacitance after 5000 cycles. This new and effective approach efficiently enhanced the electrochemical performance of Ti 3 C 2 T x MXenes and improved them as one of auspicious electrode materials in future energy storage devices. [ABSTRACT FROM AUTHOR]

Abstract Sandwich-like ZIF-8 nanocrystal derived N-doped carbon decorated graphene sheets are developed through in-situ growth and followed by a thermal annealing treatment. The sandwich-like N-doped carbon decorated graphene sheets (NCGs) contain graphene substrate and the carbon nanoparticles with 30–50 nm in size. The sandwich-like NCGs generate a large specific surface area of 816.4 m2 g−1. With the high surface area and nitrogen doping, the as-fabricated NCGs as electrode materials for supercapacitor exhibit high specific capacitance of 225.0 F g−1 at 0.5 A g−1, an enhanced rate capability and excellent electrochemical stability with 96.8% retention after 10000 cycles even at 10 A g−1. The symmetry supercapacitor based on NCGs delivers an energy density of 12.7 Wh kg−1 at a specific power of 447 W kg−1. When the power density increases to 15126 W kg−1, the energy density can still keep 6.5 W h kg−1. Furthermore, the symmetry supercapacitor shows an excellent cycle stability with 96.6% capacitance retention at 2 A g−1 after 10000 cycles. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

To enhance the energy density of supercapacitors, an asymmetric supercapacitor was prepared by well-matched graphene@MnO 2 nanosheets (G@MnO 2 ) as cathode material and porous graphene as anode material. The hierarchical MnO 2 ultrathin nanosheets uniformly decorating on graphene sheets were prepared by polyaniline-assisted growth method. The obtained G@MnO 2 composite can provide fast electron transfer rate and efficient space to decrease the length of ion diffusion during energy storage. Therefore, the G@MnO 2 electrode exhibits a high specific capacitance reaching 245.0 F g −1 at 0.5 A g −1 , 74.5% of retention ratio at 20 A g −1 . Meanwhile the assembled asymmetric supercapacitor delivers a high energy density of 30.6 W h kg −1 , and a remarkable energy density of 7.9 W h kg −1 at ultrahigh power density of 11,804 W kg −1 due to the well-assembly of G@MnO 2 and porous graphene with the similar capacitance and rate performance. Moreover, the asymmetric supercapacitor also shows an excellent cycle life with 8.5% loss of the initial specific capacitance after 10,000 cycles. The excellent electrochemical performance of the asymmetric supercapacitor of G@MnO 2 //porous graphene makes it an attractive candidate for high power and energy storage systems. [ABSTRACT FROM AUTHOR]

A self-template method is developed for hierarchically yolk-shelled NiCo 2 O 4 spheres (YS-NiCo 2 O 4 ) through a controlled hydrolysis process and followed by a thermal annealing treatment. The yolk-shelled NiCo 2 O 4 spheres possess out-shell consisting of hundreds of ultrathin sheets with 3–5 nm in thickness and solid yolk composing of a large number of nanoparticles. The YS-NiCo 2 O 4 generates a large specific surface area of 169.6 m 2 g −1 . Benefit from the large specific surface area and rich oxygen vacancy, the as-fabricated YS-NiCo 2 O 4 as electrode materials for supercapacitor exhibits high specific capacitance of 835.7 F g −1 at 0.5 A g −1 , an enhanced rate capability and excellent electrochemical stability with 93% retention after 10,000 cycles even at 10 A g −1 . Moreover, a hybrid supercapacitor combined with YS-NiCo 2 O 4 and graphene shows a high energy density of 34.7 Wh kg −1 at the power density of 395.0 W kg −1 at 0.5 A g −1 , even at 20 A g −1 , the hybrid supercapacitor still delivers the energy density of about 12.1 Wh kg −1 and the power density of 11697 W kg −1 . The desirable performance of yolk-shelled NiCo 2 O 4 suggests it to be a promising material as supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Three-dimensionally ordered mesoporous NiCo 2 O x @CeO y was developed by a hard template method. • Ce-doping can effectively adjust the electronic structure and bonding configuration of NiCo 2 O x electrode material. • The hollow cubic structure has high permeability and excellent bearing capacity. • The designed architecture has high specific surface area and abundant paths for electron/ion transport. • The NiCo 2 O x @CeO y //AC exhibits superior activity and stability for asymmetric supercapacitors. From the perspective of nano science and nanotechnology, it is very interesting and important to develop a reasonable and practical synthesis route of nanomaterials for production and life. Here, we develop a strategy of hollow cubic metal oxide nanocages. The method was inspired by Pearson's Hard-Soft-Acid-Base (HSAB) theory, and nanocages with excellent performance were prepared by coordination etching and optimization of reaction conditions. Firstly, Cu 2 O nanocubes were prepared by redox reaction at room temperature. Then, the hollow cubic NiCo 2 O x /CeO y nanocages were obtained by HSAB theory and cerium doping. The nanomaterial has a specific capacitance of up to 1976 F/g at the current density of 1 A/g. In addition, the asymmetric supercapacitor (ASC) prepared with hollow cubic NiCo 2 O x /CeO y nanocage as cathode and active carbon as anode exhibits an energy density as high as 37.1 Wh kg−1 at the power density of 375 W kg−1. The capacitance retention rate of the device is 91.5 % after 10,000 cycles. The device can be charged to light up LED lights. These excellent electrochemical properties, due to their unique structure and synergistic effect between materials, indicate the potential application value of hollow cubic NiCo 2 O x /CeO y nanocages in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

• Ni(Co)MoO 4 hybrid electrode with a mixed structure was synthesized on nickel foam. • The hybrid electrode exhibits a remarkable cycling performance due to the mixed morphology. • The asymmetric supercapacitor shows a high energy density of 55.71 Wh kg−1 at the power density of 375 W kg−1. [Display omitted] In this work, the Ni(Co)MoO 4 (NMO-Co) hybrid materials with nanoneedle and nanosheet structure were prepared on nickel foam (NF) by the hydrothermal method for high-stability supercapacitors. The effect of Co presence on the structure and electrochemical properties of NMO-Co was investigated. As the molar of Cobalt increased, more nanoneedles grew on the surface of NiMoO 4 /NF. The combination of the Ni-doped CoMoO 4 nanoneedles and Co-doped NiMoO 4 nanosheets was irregularly arranged on the surface of NF, which emerged an improvement of the cycling performance. When the molar ratio of Co: Ni: Mo was 0.5: 1: 1, the capacitance retention of the hybrid electrode was 80.1% after 10,000 cycles at 10 A g−1, while the pure NiMoO 4 electrode was 53.1%. Moreover, an asymmetric supercapacitor device displayed high energy density and power density. The maximum energy density and power density could reach 55.71 Wh kg−1 and 14,999 W kg−1, respectively. The hybrid electrode's good electrochemical performance is due to the combination of mutual doping of Ni and Co with a mixed morphology. [ABSTRACT FROM AUTHOR]

Abstract: Novel three dimensional (3D) Co3O4/C flower-like nanostructures are synthesized via a facile solvothermal strategy. The samples are characterized by XRD, XPS, FT-IR, Raman, TG, SEM and HRTEM. The results show that the 3D flower-like nanostructures are consisted of numerous 2D nanosheets with the thickness of about 20 nm. The pseudocapacitive behaviors of Co3O4/C and bare Co3O4 flower-like nanostructures are investigated by cyclic voltammograms, galvanostatic charge–discharge and electrochemical impedance spectroscopy test. The results reveal that the Co3O4/C delivers a large specific capacitance of as high as 865 F g−1 and 330 F g−1 at 1 mV s−1 and 0.5 A g−1, according to CV and galvanostatic test, respectively; while the bare Co3O4 has a poor electrochemical performance, which exhibits specific capacitance of 131.7 F g−1 and 46.1 F g−1 at the same condition. The excellent electrochemical performance is attributed to the carbon present on the Co3O4 and the morphology, which possesses large surface area, unique flower-like nanostructures and low equivalent series resistance. [Copyright &y& Elsevier]

Highlights: [•] Graphene/SnO2/PEDOT composites were obtained via one-pot synthesis method. [•] No obvious capacitance loss was found for the composite at 1Ag−1 after 5000 cycles in 1M H2SO4. [•] The composites present the enhanced capacitance and energy density in both acidic and neutral electrolytes. [ABSTRACT FROM AUTHOR]

• NF/ZnCo 2 O 4 @NiCo 2 O 4 heterostructures electrodes are fabricated via facile two-step methods. • The impact of all components in integrated electrode was investigated and discussed. • The integrated electrode exhibits excellent specific capacitance and cycling stability. • The hybrid supercapacitor delivers high energy and power densities. [Display omitted] The hierarchical core-shell heterostructures ZnCo 2 O 4 @NiCo 2 O 4 on Ni foam (NF) for supercapacitors were prepared via two-step hydrothermal and electrodeposition reactions followed by two post-annealing treatments. The effect of deposition time on its morphology and electrochemical performance was investigated in detail. Combining high electric conductivity of ZnCo 2 O 4 with high stability of NiCo 2 O 4 as well as synergistic effect, the NF/ZnCo 2 O 4 @NiCo 2 O 4 -100 (NF/ZCO@NCO-100) integrated electrode exhibited high specific capacitance of 1728.1 F g−1 (240.0 mAh g−1) at 1 A g−1, and excellent long-term stability with 97.8% capacitance retention after 10,000 cycles. The assembled hybrid supercapacitor (HSC) delivered the specific capacitance of 133.6 F g−1 (55.7 mAh g−1) at 1 A g−1 and high energy density of 40.58 Wh kg−1 at 745.62 W kg−1 as well as the outstanding long-term stability of 91.3% capacitance retention after 10,000 cycles. These results provide insights into the rational design of transition metal compound composite materials to construct integrated electrodes for high performance supercapacitors. [ABSTRACT FROM AUTHOR]

Porous NiCo 2 S 4 nanosheets derived from bimetallic MOFs directly grow on a conductive substrate as a binder-free electrode. The unique open-structure NiCo 2 S 4 with porosity facilitates the diffusion of electrolyte and possess abundant electroactive sites, which presents a high specific capacity and long-term cycling stability. An assembled hybrid capacitor exhibits the practical performance of high energy density and excellent cycling property. • The porous NiCo 2 S 4 nanosheet arrays derived from bimetallic Metal-organic frameworks derivatives are prepared. • The effect of NiCo 2 S 4 morphology on electrochemical performance and reaction mechanism are discussed. • A hybrid supercapacitor device exhibits high energy density and superior cycling stability. Recently, metal-organic frameworks (MOFs) derived materials in the form of bulk powders with attractive chemical and structural properties show broad application in electrochemical energy storage. Bimetallic materials-based MOFs usually show better electrochemical properties than that of monometallic derivatives, while achieving the bimetallic MOFs-derived materials on current collector as a binder-free electrode is still a challenge. Here we report a new approach to directly obtain a binder-free electrode of bimetallic MOFs-derived NiCo 2 S 4 nanosheet arrays on nickel foam (NF) substrate. The porous NiCo 2 S 4 nanosheet arrays providing fast electrolyte permeation and rich electrochemical active sites, show an excellent specific capacity of 1354.4 C g−1, high rate performance, and outstanding cycling stability of 82.6% retention after 10,000 cycles. A hybrid supercapacitor assembled with the as-obtained binder-free electrode as a cathode and active carbon as an anode, exhibits high energy density of 49.1 Wh kg−1 at a power density of 375 W kg−1 and superior cycling stability of 94.5% retention after 10,000 cycles. These results offer a novel and general approach to construct binder-free electrode materials with advanced performance for the portable and practical energy storage device. [ABSTRACT FROM AUTHOR]