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In this paper, the graphene oxide nanosheets are simultaneously reduced and deposited on nickel foam (denoted as Ni-foam@GNS) by one step electrodeposition method. The interconnected crumpled graphene nanosheets grown on Ni foam serve as a three-dimensional (3D) conductive skeleton for hydrothermal deposition of MnO 2 nanosheets by in-situ redox reaction. The MnO 2 nanosheets anchored on the graphene covered nickel foam (denoted as Ni-foam@GNS@MnO 2 ) show unique 3D porous interconnected networks. The samples are characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), N 2 adsorption–desorption measurements and fourier transform infrared spectroscopy (FT-IR). The capacitive performances are researched by cyclic voltammetry (CV), galvanostatic charge–discharge and electrochemical impedance spectroscopy (EIS). The results reveal that the Ni-foam@GNS@MnO 2 electrode exhibits a high specific capacitance of 462 F g −1 at 0.5 A g −1 and excellent capacitance retention of 93.1% after 5000 cycles at 10 A g −1 . Furthermore, the Ni-foam@GNS@MnO 2 electrode delivers a high energy density of 26.1 Wh kg −1 even at a high power density of 3981 W kg −1 . These results demonstrate that the Ni-foam@GNS@MnO 2 composite offers great promise in large-scale energy storage device applications. [ABSTRACT FROM AUTHOR]

Highlights: [•] β-Ni(OH)2 was modified via a template-free method by using different nickel salt. [•] The effects on the morphology and electrochemical behaviors were investigated. [•] The β-Ni(OH)2–SO4 2−/Ni-foam electrode displays 1025.3Fg−1 at 1.0Ag−1. [ABSTRACT FROM AUTHOR]

Summary: Doping Mn element into host material is an efficient approach to enhance the specific capacitance and cycling stability of supercapacitor. In this aspect, we fabricate Co‐Mn LDHs (CMLs) hollow polyhedron generated from ZIF‐67 via a template sacrifice method. Controllable doping of Mn element with gradient contents on the effect of electrochemical performance are investigated in detail. Moreover, in order to assemble a hybrid supercapacitor with superior energy and power output, a negative electrode based on MXene/rGO/V10O24 is synthesized considering the integration of EDLC and pseudocapacitance. As expected, the asymmetric supercapacitor of CMLs‐0.53//MXene/rGO/V10O24 delivers high energy density of 44.4 Wh kg−1, maximum power density of 12 750 W kg−1 and superior cycling life (91.6% capacitance retention after cycling 10 000 cycles). The special idea on the construction of CMLs with hollow structure can offer new insight to resolve the complicated steps during preparation procedure. The results also indicated that the device based on CMLs‐0.53 and MXene/rGO/V10O24 is a good candidate in the utilization of energy storage and conversion system in the future. [ABSTRACT FROM AUTHOR]

As a recently emerging group of 2D materials, MXene has attracted extensive attention in the energy storage field in recent years owing to their outstanding features. However, the notorious issues of inevitable oxidation stability and surface‐to‐surface self‐restacking for MXene significantly prevent its further wide‐ranging application. Herein, the 3D macroporous oxidation‐resistant Ti3C2Tx MXene/graphene/carbon nanotube (MRC) hybrid hydrogels are prepared by a simple gelation method assisted by l‐cysteine as crosslinker and l‐ascorbic acid (VC) as reductant. Benefitting from the effectively alleviated restacking, excellent electrical conductivity, and the 3D inter‐crosslinked macroporous architecture, as a supercapacitor electrode, the obtained MRC aerogel exhibits a superior specific capacitance of 349 F g−1, unparalleled rate capability (52.0% at 3000 mV s−1) and amazing cyclic stability (retention of 97.1% after 100 000 cycles). Moreover, the 3D MRC‐30 aerogel exhibits an impressive oxidation‐resistant performance with just a 9.3% increase in electrical resistance after storing in ambient condition for 60 days, effectively alleviating the oxidation problem of MXene. This work demonstrates a new method for construction of 3D oxidation‐resistant MXene hydrogel, shedding new light on the promising applications of MXene materials, especially in high humidity and oxygen environment. [ABSTRACT FROM AUTHOR]

Abstract: Ni(OH)2 nanosheets are directly grown on nickel foam by a simple template-free growth process. Their microstructure and surface morphology are studied by X-ray diffraction spectroscopy and scanning electron microscopy. The XRD and SEM results show that Ni(OH)2 has a β-phase structure and covers the nickel foam skeleton with nanosheets. This β-Ni(OH)2/Ni-foam electrode exhibits a high specific electric quantity of 790.3 C g−1 approaching the theoretical value (1040.6 C g−1) and high electrochemical activity. Asymmetric supercapacitor has been fabricated successfully using β-Ni(OH)2/Ni-foam nanosheets as positive electrode and activated carbon as negative electrode in a KOH aqueous electrolyte. The electrochemical capacitances of this supercapacitor are investigated by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. An asymmetric supercapacitor AC/6 mol L−1 KOH/β-Ni(OH)2/Ni-foam could be cycled reversibly in the high-voltage region of 0–1.6 V and displays intriguing performances with a specific capacitance of 105.8 F g−1 and high energy density of 36.2 W h kg−1. Importantly, this asymmetric supercapacitor device exhibits an excellent long cycle life along with 92% specific capacitance retained after 1000 cycles. [Copyright &y& Elsevier]

Abstract: The electrode of array of CuO nanosheet is prepared via a template-free growth method, and it is doped by Ag via the silver mirror reaction. The morphology of Ag-doped CuO nanosheet is examined by scanning electron microscopy. The phase structure of the Ag-doped CuO nanosheet is analyzed by X-ray diffraction spectroscopy. The supercapacitance behavior of Ag-doped CuO nanosheet is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy. The results show that the thickness of a single nanosheet is up to around 150nm. The specific capacitance of the Ag-doped CuO nanosheet electrode is 689Fg−1 at 1Ag−1 and 299Fg−1 at 10Ag−1, respectively, much higher than that of the unmodified CuO nanosheet arrays (418Fg−1 at 1Ag−1 and 127Fg−1 at 10Ag−1). The improved capacitance is explained in terms of the presence of dispersed Ag particle coated the CuO nanosheet arrays having good electrical conductivity. [Copyright &y& Elsevier]

2D MXene materials have attracted intensive attention in energy storage application. However, MXene usually undergoes serious face‐to‐face restacking and inferior stability, significantly preventing its further commercial application. Herein, to suppress the oxidation and self‐restacking of MXene, an efficient and fast self‐assembly route to prepare a 3D porous oxidation‐resistant MXene/graphene (PMG) composite with the assistance of an in situ sacrificial metallic zinc template is demonstrated. The self‐assembled 3D porous architecture can effectively prevent the oxidation of MXene layers with no evident variation in electrical conductivity in air at room temperature after two months, guaranteeing outstanding electrical conductivity and abundant electrochemical active sites accessible to electrolyte ions. Consequently, the PMG‐5 electrode possesses a striking specific capacitance of 393 F g−1, superb rate performance (32.7% at 10 V s−1), and outstanding cycling stability. Furthermore, the as‐assembled asymmetric supercapacitor possesses a pronounced energy density of 50.8 Wh kg−1 and remarkable cycling stability with a 4.3% deterioration of specific capacitance after 10 000 cycles. This work paves a new avenue to solve the two long‐standing significant challenges of MXene in the future. [ABSTRACT FROM AUTHOR]

Summary: Transition metal sulfides show excellent performance in an aqueous supercapacitor. However, all‐solid‐state supercapacitors are attracting more and more interest because of thinner, lighter, and more flexible. Binary sulfides Ni3Co6S8 nanowire arrays (NCS) are directly grown on a nitrogen‐doped carbon foam (NCF) through hydrothermal reaction, which is applied as a binder‐free electrode for all‐solid‐state supercapacitor. The unique needlelike structure assembled by nanosheet effectively increases the utilization efficiency of active materials and promotes electrochemical performance. The NCS‐NCF electrode shows promising application potential for wearable electronic devices due to the flexibility of NCF. A high‐specific capacitance of 243 mAh g−1is delivered by NCS‐NCF electrode, which also exhibits good rate behavior along with outstanding cycle stability. The NCS‐NCF electrode (positive electrode) and NCF electrode (negative electrode) are employed to assemble asymmetric all‐solid‐state supercapacitor. When the high power density is 675 W kg−1, the energy density of supercapacitor reaches the maximum of 28.31 Wh kg−1. The specific capacitance of supercapacitors could maintain 84%, after 10 000 cycles of galvanostatic charge and discharge under 4 A g−1, indicating the potential application of NCS‐NCF electrode as an excellent supercapacitor electrode material in flexible, wearable energy storage systems. [ABSTRACT FROM AUTHOR]

Potassium‐ion hybrid capacitors have attracted increasing attention due to good energy density, high power density, and low cost. Ti3C2Tx‐MXene is considered as a promising anode material for K ion storage. However, undesirable stacking issues decrease its exposed area and breeds sluggish K ion transport. Herein, a facile spray‐lyophilization strategy is proposed to construct stacking‐resistant Ti3C2Tx with 3D structures. As‐prepared Ti3C2Tx hollow spheres/tubes present stack resistance, a large specific surface area, and a short ion diffusion pathway. When serving as an anode material, it shows enhanced capacity and thickness‐independent rate performance compared to 2D Ti3C2Tx. After 10 000 cycles, a specific capacity of 122 mAh g−1 is obtained at 1 A g−1. Systematic kinetics analyses demonstrate the significance of concentration polarization on the electrode's rate ability. Furthermore, a 3D Ti3C2Tx‖hierarchical porous activated carbon (HPAC) K‐ion hybrid capacitor is assembled and displays remarkable energy and power densities with energy retention of 100% after 10 000 cycles at 1 A g−1. Following this strategy, other 3D structures from nanosheets can also be obtained, such as 3D Ti3C2Tx microtubes and graphene oxide nanoscrolls. This study provides a viable approach to solve the stacking issues of 2D nanosheets to promote the application of 2D materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Unique nanostructure, high electrical conductivity, satisfactory energy density, and extraordinary cycling stability are important evaluation criteria for high-efficient energy storage devices. Herein, Fe 3 O 4 nanospheres are successfully in situ decorated on graphene nanosheets through an environmentally benign and facile solvothermal procedure. When utilized as an electrode for supercapacitor, the graphene/Fe 3 O 4 nanocomposite exhibits a notably enhanced specific capacity (268 F·g−1 at 2 mV·s−1) and remarkable cycling performance with 98.9% capacity retention after 10,000 cycles. Furthermore, the fabricated graphene/MnO 2 //graphene/Fe 3 O 4 asymmetric supercapacitor device displays a desirable energy density (87.6 Wh·kg−1) and superior cycling stability (93.1% capacity retention after 10,000 cycles). [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Flexible supercapacitor plays a progressively more important part in power source for smart electronic devices and how to enhance its energy density is the urgent issue to be addressed. Hence, a hybrid electrode of Polypyrrole@reduced graphene oxide hydrogel (PPy@rGOH) is synthesized via a combine hydrothermal treatment of GO solution to assemble hydrogel and subsequently in-situ electropolymerization preparation of PPy on the surface of graphene. Through controlling the time of electropolymerization, the resultant PPy@rGOH-20 s with high specific surface area exhibits an excellent specific capacitance of 340 F g−1 at a current density of 1 A g−1 and superior cycling stability of 87.4% capacitance retention after 10,000 charging/discharging cycles at 3 A g−1 in 1 M KNO 3. The assembled flexible asymmetric supercapacitor (FASC) by employing the PPy@rGOH-20s as positive electrode and pure rGOH as negative electrode presents a maximum operational voltage window of 1.6 V and high energy density of 46.9 W h kg−1, which is higher than polymer/carbon-based supercapacitors previously reported. [ABSTRACT FROM AUTHOR]

Highlights • A gas foaming strategy is adopted to prepare the 3D hierarchical porous carbon. • NaHCO 3 is used as activator based on its multistep pyrolysis process. • The HPC shows high specific capacitance and outstanding stability. Abstract Inspired by people to make flour food, a one-pot, low-cost, green and environmental friendly gas foaming strategy is adopted here to prepare the three-dimensional hierarchical porous carbon (HPC) by introducing NaHCO 3 as foaming and activation agent. During the pyrolysis process, the CO 2 gas produced during the transforms from NaHCO 3 into Na 2 CO 3 will resulted in the producers of the macro-pores and meso-pores, meanwhile, the as-produced Na 2 CO 3 further reactor with the carbon intermediate at a high temperature, and finally result in forming a micro-pores porous structure. Such intimate structural interconnectivities provide three-dimensional continuous pathway for electron rapid transfer and the interconnected pores allow for the ion to penetrate and evenly contact the electrode material quickly. The electrochemical performance of HPC exhibits a high specific capacitance of 350 F g−1 at 1 A g−1 and outstanding electrochemical stability with capacitance retention up to 97% after 10,000 cycles. Moreover, the as-assembled symmetric supercapacitor exhibits an ultrahigh energy density of 27.4 Wh kg−1, much higher than most of carbon-based supercapacitors. These results demonstrate a straightforward environment friendly method to mass-produce economical, robust carbon materials as promising candidates for supercapacitor application. [ABSTRACT FROM AUTHOR]

In this work, for the first time, we design a high-energy-density double-chamber capacitor which consists of the cathode chamber (polyaniline@carbon fiber cloth electrode in HCl/FeCl 3 solution), anion-exchange membrane and the anode chamber (polyaniline@carbon fiber cloth electrode in HCl/FeCl 2 solution). Since the redox state of polyaniline can be continuously altered by the external potential during charging and discharging process, the addition of FeCl 3 (or FeCl 2 ) in the electrolyte works as chemical oxidant (or reductant) to oxidize (or reduce) the reduced (or oxidized) polyaniline to offer extended capacitance. Results show the double-chamber supercapacitor has a high area specific capacitance of 1.22 F cm −2 and an energy density of 108.44 μWh cm −2 , which are ∼3.5 times as large as those of the conventional single-chamber capacitor (0.35 F cm −2 / 31.11 μWh cm −2 ). This work demonstrates an innovative strategy by incorporating supercapacitor with fuel cell to improve the energy density. [ABSTRACT FROM AUTHOR]

The flexible solid-state supercapacitor (FSSC) has attracted many attentions due to its feature of high power density with stable cycling performance, as well as lightweight and flexible features and is expected as an ideal candidate power supply for portable and wearable electronics devices. In general, the electrode plays an important role in determining the overall performance of the FSSC. Therefore, to meet the requirement of practical applications, a simple, facile and environment friendly strategy to prepare deformable/flexible electrodes with high energy density is the target issue to be considered. Herein, we report a generalized “soaking-recrystallization-calcination” method to enhance the capacitance performance of commercialized carbon fiber cloth. Thanks to the in-situ etching process to increase the surface area and the synchronous heteroatom doping to induce pseudocapacitive behavior, the resultant activated carbon fiber cloth sample exhibits an ultra-high areal capacitance up to 362 mF cm −2 , is about 1448 fold enhancement than that of fresh carbon fiber cloth calcined at 750 °C. Meanwhile, the assembled FSSC based on the activated carbon fiber cloth exhibits a maximum volumetric energy density of 0.35 mWh cm −3 and gravimetric energy density of 0.84 Wh kg −1 . Such results represent a novel and promising direction to prepare high performance flexible electrode for FSSC application. [ABSTRACT FROM AUTHOR]

Flexible solid-state supercapacitor (FSSC) holds great promise as power source to supply the next generation of portable and wearable electronics. Assembling asymmetric supercapacitor constructed with broadening cell voltage ( V ) is the promising way to increase the energy density. However, the imparity reaction kinetics between EDLC and pseudocapacitive materials will further lead to inferior power density. Hence, to pursue higher working voltage and energy density, a hybrid configuration of cobalt hexacyanoferrate/reduced graphene oxide hydrogels (PB-Co/rGOH) is prepared through a one-pot hydrothermal method. With highly interconnected 3D network structure, excellent mechanical robustness and the synergistic effects between the graphene and PB-Co, the resultant PB-Co/rGOH exhibits a high specific capacitance of 220 F g −1 and well cycle stability (83% capacitance retention after 10,000 cycles at 5 A g −1 ). Moreover, the assembled PB-Co/rGOH//PB-Co/rGOH symmetric flexibly solid-state supercapacitor exhibits an amazing higher working voltage of 2.0 V and a remarkable energy density of 57.5 Wh kg −1 , which is comparable with that of Ni/MH batteries (60–120 Wh kg −1 ). These excellent electrochemical performances of the hybrid electrode provide a rational design strategy for developing supercapacitors with high energy density. [ABSTRACT FROM AUTHOR]

Prussian Blue (PB) coordination compound is a well-known ideal candidate for energy storage due to its tunable open framework structure. Especially transition metal hexacyanoferrate displays excellent performance in supercapacitor. In this paper, a facile one-step co-precipitation synthesis method is developed to prepare hybrid K 2.25 Ni 0.55 Co 0.37 Fe(CN) 6 /CNTs composite, aiming at increasing the electric conductivity of electrode material by introducing carbon nanotube conductive skeleton to the Cobale-Nickel hexacyanoferrate hybrid nanoparticles. The TEM image shows that K 2.25 Ni 0.55 Co 0.37 Fe(CN) 6 presents nanoparticles with a diameter about 20 nm, which are connected along the surface of carbon nanotube. Such special structure could facilitate the electric transportation between each nanoscale K 2.25 Ni 0.55 Co 0.37 Fe(CN) 6 particle, efficiently improving the utilization of active material. Considering the intrinsic abundant channels for ions insertion/extraction of nanoparticles and good conductivity of carbon nanotubes, our creative electrode is expected to display fantastic supercapacitor performance. The electrochemical data demonstrate that the K 2.25 Ni 0.55 Co 0.37 Fe(CN) 6 /CNTs electrode exhibits a high specific capacitance of 600 F g −1 at 0.2 A g −1 and excellent rate performance of 90.4% when the current density ranged from 0.2 A g −1 to 5 A g −1 . Furthermore, the K 2.25 Ni 0.55 Co 0.37 Fe(CN) 6 /CNTs composite achieves decent cycling stability with maintaining 94% of its initial specific capacitance after 2000 discharge/charge cycles. The excellent energy storage property offers a great promise as supercapacitor materials. [ABSTRACT FROM AUTHOR]

Carbon materials, especially graphene nanosheets (GNS) and/or multi-walled carbon nanotube (MWNT), have been widely used as electrode materials for supercapacitor due to their advantages of higher specific surface area and electronic conductivity, but the relatively low specific capacitance thus results in low energy density hindering their large applications. On the contrary, MnO 2 exhibits higher energy density but poor electrical conductivity. In order to obtain high performance supercapacitor electrode, here, combining the advantages of these materials, we have designed a facile two-step strategy to prepare 3D MnO 2 -GNS-MWNT-Ni foam (MnO 2 -GM-Ni) electrode. First, GNS and MWNT is wrapped on the surface of Ni foam (GM-Ni) via a “dip & dry” method by using an organic dye as a co-dispersant. Then, by using this 3D GM-Ni as substrate, MnO 2 nanoflakes are in-situ supporting on the surface of GNS and MWNT through a hydrothermal reaction. The specific capacitances of MnO 2 -GM-Ni electrode reach as high as 470.5 F g −1 at 1 A g −1 . Furthermore, we have successfully fabricated an asymmetric supercapacitor with MnO 2 -GM-Ni and GM-Ni as the positive and negative electrodes, respectively. The MnO 2 -GM-Ni//GM-Ni asymmetric supercapacitor exhibits a maximum energy density of 35.3 Wh kg −1 at a power density of 426 W kg −1 and also a favorable cycling performance that 83.8% capacitance retention after 5000 cycles. These results show manageable and high-performance which offer promising future for practical applications. [ABSTRACT FROM AUTHOR]

For the first time, hierarchically porous carbon materials with a sandwich-like structure are synthesized through a facile and efficient tri-template approach. The hierarchically porous microstructures consist of abundant macropores and numerous micropores embedded into the crosslinked mesoporous walls. As a result, the obtained carbon material with a unique sandwich-like structure has a relatively high specific surface (1235 m2 g−1), large pore volume (1.30 cm3 g−1), and appropriate pore size distribution. These merits lead to a comparably high specific capacitance of 274.8 F g−1 at 0.2 A g−1 and satisfying rate performance (87.7 % retention from 1 to 20 A g−1). More importantly, the symmetric supercapacitor with two identical as-prepared carbon samples shows a superior energy density of 18.47 Wh kg−1 at a power density of 179.9 W kg−1. The asymmetric supercapacitor based on as-obtained carbon sample and its composite with manganese dioxide (MnO2) can reach up to an energy density of 25.93 Wh kg−1 at a power density of 199.9 W kg−1. Therefore, these unique carbon material open a promising prospect for future development and utilization in the field of energy storage. [ABSTRACT FROM AUTHOR]

Facile in-situ etching current collector prepares corresponding oxide or sulfide, which is directly used as faradic electrode material, supplying faster electron transportation and better connection, and thus displaying good supercapacitor performance. Here, we prepare Cu x S via etching copper foam and investigate the influence of etching time on the morphology and electrochemical performance. The results show that compared with the nano-rod Cu x S-1h/CF, nano-rod/wire Cu x S-2h/CF and block/nanorod Cu x S-4h/CF, the nano-rod/ribbon Cu x S-3h/CF electrode exhibits the highest specific capacity (448.8C g −1 at current density of 5 mA cm −2 ). We fabricate asymmetric supercapacitor based on Cu x S-3h/CF as positive electrode and AC as negative electrode to further evaluate the supercapacitor property and the device achieves a high energy density of 35 Wh kg −1 at power density of 266 W kg −1 . Furthermore, the outstanding cycling stability of 88% capacitance retention after 5000 charge-discharge cycles more enable the Cu x S-3h/CF become promising faradic electrode material. [ABSTRACT FROM AUTHOR]

In this work, Co(OH) 2 buds direct growth on Ni foam (Co(OH) 2 buds/Ni foam) is prepared via a hydrothermal method. Their structure and morphologies are characterized by using X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy. Result shows that the Co(OH) 2 buds are assembled by several nanorods and uniformly covered on the surface of Ni foam. Due to its unique structure, the Co(OH) 2 buds/Ni foam electrode shows high capacitive performance and long cycle life. The specific capacitance of Co(OH) 2 buds/Ni foam is as high as 2041 F g −1 at a current density of 3 mA cm −2 in 6 M KOH electrolyte, and 811 F g −1 even at a high current density of 60 mA cm −2 . The capacitance of the Co(OH) 2 buds/Ni foam electrode remained 72.4% after 1000 cycles at 18 mA cm −2 . An asymmetric supercapacitor was successfully assembled, in which Co(OH) 2 buds/Ni foam and AC used as positive and negative electrode, respectively. The energy density of the AC//Co(OH) 2 buds/Ni foam supercapacitor reaches to 20.3 W h kg −1 at a power density of 90.6 W kg −1 . Our result shows that the Co(OH) 2 materials are promising candidate for electrochemical energy applications. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) multilayer porous MnO 2 /reduced graphene oxide composites are coated on a nickel foam substrate (denoted as MnO 2 /R-GO@Ni-foam) by a facile and scalable spray method following by low temperature annealing. The composite electrodes are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. The content of MnO 2 in the MnO 2 /R-GO@Ni-foam composites is determined by thermal gravimetric analysis. The supercapacitive performance of the composite electroides is investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The results show that the MnO 2 /R-GO@Ni-foam composite displays a high specific capacitance of 267 F g −1 at 0.25 A g −1 and excellent capacitance retention of 89.5% after 1000 cycles. This study provides a facile way for the preparation of composite electrodes for high-performance supercapacitor. [ABSTRACT FROM AUTHOR]

Highlights: [•] MnO2/C/TiO2 shell/shell/core arrays electrode has been prepared by simple thermal reaction and electrodeposition method. [•] The unique shell/shell/core structure has easy access of electrolyte ions, large surface to volume and high electrochemical activity. [•] The MnO2/C/TiO2 shell/shell/core arrays exhibits high specific capacitance of 639 F g−1 at a charge/discharge current density of 1 A g−1. [ABSTRACT FROM AUTHOR]

Highlights: [•] Fe2O3 sheets have been synthesized on nickel foam by a simple template-free growth process and heat treatment. [•] The Fe2O3 electrode exhibits a specific capacitance of 147Fg−1 at 0.36Ag−1 and 98Fg−1 at 3.6Ag−1. [•] The as-prepared Fe2O3 electrode presents a wider potential window of 1.0V. [Copyright &y& Elsevier]

Abstract: Nanostructured Co x Ni1−x (OH)2 (x = 0, 0.053, 0.068, 0.116, 0.192) composites are synthesized via a simple template-free growth process onto nickel foam by using a mixed aqueous solution of nickel nitrate, cobalt nitrate and ammonia. Their structure and surface morphology are characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and scanning electron microscopy. The SEM images show changes in the microstructure of β-Ni(OH)2 by the doping of cobalt. The effects of cobalt content on the electrochemical behaviors of β-Ni(OH)2 are investigated by cyclic voltammetries, galvanostatic charge/discharge and electrochemical impedance spectroscopy. The results show that the Co0.116Ni0.884(OH)2 composite electrode exhibits a drastic improvement in the capacitive characteristics of β-Ni(OH)2 with a specific capacitance increase from 386.4 to 1082.6 F g−1 at a high discharging current density of 6 A g−1. This work suggests that the as-prepared Co0.116Ni0.884(OH)2 composite electrode has a promising future as higher charging/discharging rate materials for pseudo-supercapacitors. [Copyright &y& Elsevier]

• α-MnSe Nanosheets are prepared via a facile hydrothermal method. • The effect of reaction time on electrochemical performance is investigated. • The α-MnSe electrode delivers a high capacity of 88.3 mAh g−1 at 1 A g−1. • The asymmetric supercapacitor exhibits a high energy density of 39.3 Wh kg−1. Transition metal selenides are regarded as emerging materials for energy storage devices because of their good electrical conductivity and electrochemical activity. Here, a binder-free ultrathin α-MnSe nanosheets electrode is prepared and the supercapacitor performance is comprehensively explored. Due to the increased active sites, enlarged contact area for electrolyte, as well as shorten ions diffusion pathway, the prepared electrode delivers high capacity of 88.3 mAh g−1 at 1 A g−1, good rate capability, and long-term durability (91% remain after 5000 cycles). Moreover, the asymmetric supercapacitor, fabricated by α-MnSe anode and active carbon cathode, displays a high energy density of 39.3 Wh kg−1 at a power density of 0.92 kW kg−1 and satisfying cycle performance. This study demonstrates that the binder-free α-MnSe electrode holds great promise for supercapacitor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Cd(OH)2 nanowires was directly grown on nickel foam via a simple template-free method. [•] Cd(OH)2 nanowires exhibits a high specific capacitance of is 1164.8Fg−1 at 1Ag−1 in 6moldm−3 KOH solution. [•] The as-prepared Cd(OH)2 nanowires has potential applications in electrochemical capacitors. [Copyright &y& Elsevier]

Abstract: Nanostructured CuO with diverse morphology was directly grown on copper foam. Their supercapacitance performance was investigated and correlated with the morphology. CuO nanowires, nanosheets, and flower-like nanostructures were formed on copper foam which acts as both the substrate of CuO formation and the current collector of the electrode. Their morphology was examined by scanning and transmission electron microscopy and their phase structure was analyzed by X-ray diffraction spectroscopy. The supercapacitance of the nanostructured CuO on copper foam was investigated by cyclic voltammetry, galvanostatic charge/discharge measurements and electrochemical impedance spectroscopy. Results showed that the specific capacitance of the nanostructured CuO strongly depends on its morphology and dimension. CuO nanosheets exhibited higher specific capacitance than nanowires and flower-like nanostructure. The specific capacitance of the CuO nanosheets reached 212Fg−1 at a current density of 0.41mAmg−1 in 6.0moldm−3 KOH electrolyte. The capacitance loss is around 15% after 850 charge/discharge cycles at 0.41mAmg−1 and the majority of capacitance loss occurred in the initial 50 cycles (8.1%). [Copyright &y& Elsevier]

Abstract: CuO nanosheet arrays freely standing on nickel foam are prepared via a template-free growth method. The morphology of CuO nanosheet arrays is examined by scanning and transmission electron microscopy and the phase structure of nanosheets is analyzed by X-ray diffraction spectroscopy. The supercapacitance of CuO nanosheet arrays is investigated by cyclic voltammetry, galvanostatic charge/discharge test and electrochemical impedance spectroscopy. The results show that the array of CuO nanosheets forms a uniform film of around 5μm in thickness on nickel foam skeleton. The film is composed of clusters of arrays of nanosheets with a thickness up to around 150nm. The CuO nanosheet arrays exhibit a specific capacitance of 569Fg−1 at a current density of 5mAcm−2 in 6.0moldm−3 KOH electrolyte. The capacitance loss is less than 17.5% after 500 charge/discharge cycles at 10mAcm−2 and with columbic efficiency higher than 93%. [Copyright &y& Elsevier]

Developing novel materials with rational structures and excellent electrical conductivity is vitally important for energy storage devices. Herein, hollow cobalt molybdenum selenide (Co–Mo–Se) nanosheet arrays are fabricated via a self-sacrificing template method and selenization process, where cobalt-organic framework serves as the template. Benefiting from unique hollow nanoarrays structure, the Co–Mo–Se electrode offers rich electroactive sites, large accessible regions for electrolyte, and short ions diffusion pathways. Additionally, it is observed that the Co–Mo–Se possesses a low charge transfer resistance owing to the intrinsic metallicity. As a result, the Co–Mo–Se electrode exhibits favorable energy storage properties, including high capacity (221.7 mAh g−1), good rate property, and outstanding stability (95% after 8000 cycles). More importantly, the assembled Co–Mo–Se//active carbon (AC) achieves high energy density (44.7 Wh kg−1) and remarkable durability. Notably, two hybrid devices connected in series successfully power an electronic watch for 70 min, demonstrating its practical applicability. These results indicate that the synthesized hollow Co–Mo–Se nanosheet arrays have promising applications as electrode materials for high-performance energy storage devices. • Co-MOF was employed as template to obtain hollow Co–Mo–Se nanosheet arrays. • The Co–Mo–Se delivers a specific capacity of 221.7 mAh g−1 at 1 A g−1. • The ion exchange/etching method was applied in this work. • The asymmetric supercapacitor delivers high energy and power densities. [ABSTRACT FROM AUTHOR]

Bimetallic metal selenides have gained increasing attention as potential electrode materials for energy storage systems owing to good electrical conductivity and superior electrochemical activity. Herein, the Ni x Co y Se 2 (x+y=1) electrodes are prepared by a facile and rapid electrodeposition process. The electrochemical performance is optimized via adjusting the ratio of Co and Ni. It is turned out that equivalent Co and Ni in the composite (Ni 1/2 Co 1/2 Se 2) shows the best supercapacitor performance, including high specific capacity (166.1 mAh g−1) and long-term stability. Moreover, Density Functional Theory (DFT) calculation confirms the covalent interaction between nickel and cobalt, implying the existence of synergistic effect. To assess the practical value of the rationally designed Ni 1/2 Co 1/2 Se 2 electrode material, an asymmetric supercapacitor device is fabricated (Ni 1/2 Co 1/2 Se 2 //AC), which delivers a high energy density of 46.0 Wh kg−1 at 1141 W kg−1, coupled with 9.8% capacity loss after 10000 cycles. Notably, the low-voltage setups (LED and electric fan) can be easily activated by two devices in series, further demonstrating the great potential for practical application of Ni 1/2 Co 1/2 Se 2 electrode. [ABSTRACT FROM AUTHOR]

• Bimetallic (Ni,Mo)S 2 was synthesized through a two-step solvothermal approach. • The (Ni,Mo)S 2 /G composite exhibits high specific capacity of 951 C g−1. • The ASC device shows a ultrahigh energy density of 84.5 Wh kg−1. Thanks to their high electrical conductivity, electrochemical stability and activity, transition metal sulfides have been widely designed and developed for supercapacitors with excellent electrochemical performances. Herein, we report the NiS 2 /MoS 2 mixed phases with abundant exposed active edge sites decorated on graphene nanosheets (named as (Ni,Mo)S 2 /G) through a facile two-step hydrothermal approach. Benefitting from its unique chemical property and structure, the as-prepared (Ni,Mo)S 2 /G composite possesses impressive electrochemical performances as electrodes of battery-type supercapacitors in 2 M KOH, such as high specific capacity of 951 C g−1 (2379 F g−1) at 1 A g−1 with superb rate capability (60.7% at 100 A g−1). Additionally, the asymmetric supercapacitor (ASC) device assembled based on the active edge site-enriched (Ni,Mo)S 2 /G as positive electrode and nitrogen-doped porous graphene as negative electrode displays an ultrahigh energy density of 84.5 Wh kg−1, superior to those of the Ni- and Mo-based ASCs in aqueous electrolytes reported so far. Such novel strategy may hold great promise for exploring other polymetallic sulfides with abundant exposed active edge sites for energy storage and conversion. [ABSTRACT FROM AUTHOR]

Flexible electrochemical energy storage devices have great potential in wearable and portable electronic devices. However, their practical applications have been deferred by mechanical damages such as repeated stretching, bending and squeezing. Self-healing hydrogel electrolytes can automatically repair such physical damages and maintain good electric contact at electrode/electrolyte interface. Herein, we report a hydrogel electrolyte with excellent tensile properties and good conductivity under large strain/stress. A solid state supercapacitor was further demonstrated, showing a high energy density of 21.3 Wh kg-1 at a power density of 350 W kg-1. The as-fabricated supercapacitor possesses good stretchability, with a 68% of retention of its initial capacitance after 40 breaking/healing cycles. The excellent self-healing capability of the hydrogel electrolyte can be attributed to the presence of hydrogen bonds and molecular chain fluidity within its structural motif. Our work provides promising routes towards developing new self-healing solid-state electrolytes for next-generation electrochemical energy storage and conversion applications with good performance and high safety. [ABSTRACT FROM AUTHOR]

• Ultrathin in-plane 1T-2H MoS 2 heterostructures are coaxially arrayed on 3D CFs. • The 1T-2H ultrathin heterostructures exhibit surprising structure stability. • Our ASC device exhibits an ultrahigh energy density of 81.4 Wh kg−1. Metallic 1T MoS 2 is a promising anode candidate for supercapacitors due to its intrinsically excellent electrical conductivity and high electrochemical activity. However, it is quite unstable and hard to be massively synthesized through common methods. Herein, structurally stable ultrathin (1–3 layers) in-plane 1T-2H MoS 2 heterostructures have been rationally modulated and coaxially aligned on three-dimensional carbon nanofibers (MoS 2 /CF) through a facile hydrothermal approach for supercapacitors and electrocatalysis. Benefiting from the unique heterostructure, the MoS 2 /CF composite shows amazing stability with no obvious change after being stored in air for over 36 months. In addition, it presents high specific capacitance of 310 F g−1 and remarkable rate capability of 78% at 100 mV s−1. The fabricated asymmetric supercapacitor delivers an impressive energy density of 81.4 Wh kg−‍‍‍‍‍1 in 1 M Na 2 SO 4 solution attributed to the high specific capacitance and large operating voltage range of 2 V. Moreover, the MoS 2 /CF composite also demonstrates enhanced electrocatalytic activity for hydrogen evolution reaction with a low overpotential of 194 mV at 10 mA cm−2. The work may promote the developments of high-performance bifunctional energy conversion and storage systems in future. [ABSTRACT FROM AUTHOR]

• A PPy-rGO Janus-faced film is prepared through a facile and scalable method. • The PPy-rGO electrode reveals a ultra-high specific capacitances of 1380 mF cm−2. • The assembled PPy-rGO//PPy-rGO device delivers a high energy density of 31.95 Wh L−1. The flexible supercapacitors have attracted tremendous attention, but challenges still remain in seeking suitable electrode materials to enhance the energy density and other aspects. To this end, a unique Polypyrrole (PPy)-reduced graphene oxide (rGO) Janus-faced film is prepared through a facile and scalable method consisting of the deposition of graphene film on the surface of copper foil via a Cu||GO electrochemical cell followed by the self-assembly of PPy at the heterogeneous interface. Such a distinctive structure, in which the PPy layer acts as the source of high pseudo-capacitance, while the graphene layer is employed as the "high way" for rapid electron transport and as well as the strong π-π coupling effect between graphene and polymer nanosheets, endows the resultant electrode ultra-high specific capacitances (1380 mF cm−2 at 1 mA cm−2) and excellent rate capability (65.1% capacitance retention with the current density increases to 20 mA cm−2). Furthermore, the assembled PPy-rGO//PPy-rGO symmetric supercapacitors deliver a maximum energy density of 31.95 Wh L−1, remarkable cyclic stability (89.7% capacitance retention after 10,000 cycles) and superior mechanical property (82% capacitance retention after 8000 cycles under different bending conditions). [ABSTRACT FROM AUTHOR]

• The human hair with high elasticity capable can serve as a promising flexible supporter for the electrode. • The reduced graphene oxide nanosheets can effectively improve the electrical conductivity of the electrode. • The Ni(OH) 2 nanoribbon-intercalated rGO nanosheets shows an interconnected porous structure. • The solid-state flexible supercapacitor delivers high energy density and good cycling stability. The demands for wearable energy storage devices keep growing and novel flexible electrode materials and facile prepared methods for these devices are crucial and attractive. In this work, human hair fiber is employed as the flexible fiber-based material due to the high utilization values of low cost, controllable length and high elasticity capable. Herein, an effective and hazard-free microwave-assisted method is reported to develop superelastic reduced graphene oxide coating human hair (rGO@Hh) to achieve conductive and high-strength fibrous electrode. With the braided rGO@Hh fibers, nickel hydroxide nanoribbon-intercalated rGO nanosheets (Ni(OH) 2 /rGO@Hh) are further prepared through microwave radiation treatment, which shows an interconnected porous structure with outstanding electrochemical performances of high specific capacitance (316 F g−1 at 1 A g−1) and good cycling performance. Moreover, a solid-state fiber-based asymmetric supercapacitor (FASC) is assembled with rGO@Hh fibers and Ni(OH) 2 /rGO@Hh fibers as negative and positive electrodes, which demonstrates a high energy of 27.6 Wh kg−1 and a power density of 699 W kg−1, respectively. The FASC also can be further used for numerous electronic products, presenting its prospect for portable wearable devices with high tensile strength and excellent performances. [ABSTRACT FROM AUTHOR]

Developing advanced supercapacitors with both high areal and volumetric energy densities remains challenging. In this work, self‐supported, compact carbon composite electrodes are designed with tunable thickness using 3D printing technology for high‐energy‐density supercapacitors. The 3D carbon composite electrodes are composed of the closely stacked and aligned active carbon/carbon nanotube/reduced graphene oxide (AC/CNT/rGO) composite filaments. The AC microparticles are uniformly embedded in the wrinkled CNT/rGO conductive networks without using polymer binders, which contributes to the formation of abundant open and hierarchical pores. The 3D‐printed ultrathick AC/CNT/rGO composite electrode (ten layers) features high areal and volumetric mass loadings of 56.9 mg cm−2 and 256.3 mg cm−3, respectively. The symmetric cell assembled with the 3D‐printed thin GO separator and ultrathick AC/CNT/rGO electrodes can possess both high areal and volumetric capacitances of 4.56 F cm−2 and 10.28 F cm−3, respectively. Correspondingly, the assembled ultrathick and compact symmetric cell achieves high areal and volumetric energy densities of 0.63 mWh cm−2 and 1.43 mWh cm−3, respectively. The all‐component extrusion‐based 3D printing offers a promising strategy for the fabrication of multiscale and multidimensional structures of various high‐energy‐density electrochemical energy storage devices. The all‐graphene‐oxide (GO)‐based symmetric supercapacitor is assembled with a thin GO separator and compact active carbon/carbon nanotube/reduced graphene oxide composite electrodes with tunable thickness, which are fabricated using the advanced extrusion‐based 3D printing technology. The 3D‐printed ultrathick and compact symmetric supercapacitor with a high mass loading can achieve both high areal and volumetric energy densities. [ABSTRACT FROM AUTHOR]

Composites of LiFePO4 and activated carbon (LFP-AC) were prepared by a ball milling method. Their morphologies were investigated by scanning electronic microscopy and energy dispersive spectroscopy. Hybrid supercapacitors were assembled using the LFP-AC composites as the positive electrode and Li4Ti5O12 as the negative electrode (LFP-AC/Li4Ti5O12). Effects of the positive electrode composition (ratio of LiFePO4 to AC) on the performance of LFP-AC/Li4Ti5O12 were investigated via constant current charge-discharge tests. The results demonstrated that the specific capacity and the specific power of the LFP-AC/Li4Ti5O12 hybrid supercapacitor significantly depend upon the content of LiFePO4 in the LFP-AC positive electrode. At 0.5 A g-1 charge-discharge current, the specific capacity of the LFP-AC/Li4Ti5O12 with 30 wt. % LiFePO4 and 70 wt. % AC in the positive electrode is 42% higher than that of AC/Li4Ti5O12, and the two supercapacitors have the same specific power. After 500 charge-discharge cycles at 1.0 A g-1, the specific capacity of the LFP-AC/Li4Ti5O12 with 80 wt. % LiFePO4 and 20 wt. % AC in the positive electrode is 53% higher than that of AC/Li4Ti5O12. The hybrid device stores electric energy via both the double-layer electrostatic adsorption and the intercalation/deintercalation of lithium ions. [ABSTRACT FROM AUTHOR]