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The judicious design of highly electrochemically active materials on 1D fiber substrate to form a hierarchical integrated hybrid structure is an efficient technique to improve the limited cylindrical space and volumetric energy density of fiber‐shaped supercapacitors (FSCs). Herein, a 3D negative electrode, consisting of vertically aligned interconnected mesoporous Co‐N/C leaf‐like structure on 1D MXene‐carbon fiber (Co‐N/C@MX/CF) is prepared by controlling the composition and morphology. At the same time, a 3D positive electrode is also prepared by introducing Mo in NiCo‐LDH anchored on Co‐N/C@MX/CF (Mo‐NiCo‐LDH@Co‐N/C@MX/CF) by electrodeposition method. Benefitting from the systematic hierarchical structures with highly accessible surface area, adequate pore size and easy permeation of electrolyte, both positive and negative electrodes demonstrate highly improved electrochemical performance with areal capacity/capacitance of 0.96 mAh cm−2/4.55 mF cm−2 at a current density of 3.86 mA cm−2, respectively. Furthermore, the fiber‐shaped solid‐state hybrid supercapacitor (FSHSC) based on Mo1.5NiCo‐LDH@Co‐N/C@MX/CF(+)//Co‐N/C0.5@MX/CF(−) is fabricated, exhibiting compelling energy density of 86.72 mWh cm−3 at a power density of 480.30 mW cm−3 with an outstanding capacitance retention of 80.2% after 20000 galvanostatic‐charge‐discharge cycles. This study puts forward a new perspective on the development of highly efficient FSCs for practical application. [ABSTRACT FROM AUTHOR]

Abstract: Highly flexible supercapacitors (SCs) have great potential in modern electronics such as wearable and portable devices. However, ultralow specific capacity and low operating potential window limit their practical applications. Herein, a new strategy for the fabrication of free‐standing NiMoS and NiFeS nanosheets (NSs) for high‐performance flexible asymmetric SC (ASC) through hydrothermal and subsequent sulfurization technique is reported. The effect of Ni2+ is optimized to attain hierarchical NiMoS and NiFeS NS architectures with high electrical conductivity, large surface area, and exclusive porous networks. Electrochemical properties of NiMoS and NiFeS NS electrodes exhibit that both have ultrahigh specific capacities (≈312 and 246 mAh g−1 at 1 mA cm−2), exceptional rate capabilities (78.85% and 78.46% capacity retention even at 50 mA cm−2, respectively), and superior cycling stabilities. Most importantly, a flexible NiMoS NS//NiFeS NS ASC delivers a high volumetric capacity of ≈1.9 mAh cm−3, excellent energy density of ≈82.13 Wh kg−1 at 0.561 kW kg−1, exceptional power density (≈13.103 kW kg−1 at 61.51 Wh kg−1) and an outstanding cycling stability, retaining ≈95.86% of initial capacity after 10 000 cycles. This study emphasizes the potential importance of compositional tunability of the NS architecture as a novel strategy for enhancing the charge storage properties of active electrodes. [ABSTRACT FROM AUTHOR]

Abstract: A facile two‐step strategy is developed to design the large‐scale synthesis of hierarchical, unique porous architecture of ternary metal hydroxide nanowires grown on porous 3D Ni foam and subsequent effective sulfurization. The hierarchical Zn–Co–S nanowires (NWs) arrays are directly employed as an electrode for supercapacitors application. The as‐synthesized Zn–Co–S NWs deliver an ultrahigh areal capacity of 0.9 mA h cm−2 (specific capacity of 366.7 mA h g−1) at a current density of 3 mA cm−2, with an exceptional rate capability (≈227.6 mA h g−1 at a very high current density of 40 mA cm−2) and outstanding cycling stability (≈93.2% of capacity retention after 10 000 cycles). Most significantly, the assembled Zn–Co–S NWs//Fe2O3@reduced graphene oxide asymmetric supercapacitors with a wide operating potential window of ≈1.6 V yield an ultrahigh volumetric capacity of ≈1.98 mA h cm−3 at a current density of 3 mA cm−2, excellent energy density of ≈81.6 W h kg−1 at a power density of ≈559.2 W kg−1, and exceptional cycling performance (≈92.1% of capacity retention after 10 000 cycles). This general strategy provides an alternative to design the other ternary metal sulfides, making it facile, free‐standing, binder‐free, and cost‐effective ternary metal sulfide‐based electrodes for large‐scale applications in modern electronics. [ABSTRACT FROM AUTHOR]

Hierarchical Zn-doped SnO2 nano-urchins decorated on RGO nanosheets were fabricated for supercapacitor applications. In this study, SnO2 nanospheres were doped with Zn2+ to tailor their electrical and morphological properties. Zn2+ doping of the SnO2 nanospheres prevented Sn clustering and thereby reduced the particle size leading to the formation of urchin-like nanostructures. These urchins with a high surface area and short transport paths can offer high capacitive performance by assembling with RGO nanosheets. The X-ray photoelectron spectroscopy and X-ray diffraction analyses confirmed the presence of SnO2 crystal planes and successful doping of the Zn2+. The incorporation of the RGO nanosheets augmented the coulombic efficiency, specific capacitance, and cycling performance. The enhancement of the capacitive behavior resulted from the synergistic effects owing to the combined properties of pseudocapacitance and double layer capacitance. The composite electrode material offered a specific capacitance of 635 F g−1 at a current density of 1 A g−1 and has a high cycling stability up to 5000 cycles with a capacitance retention of 78.4%. [ABSTRACT FROM AUTHOR]

The present work highlights the effective H-π interaction between metallocenes (ferrocene; Fc) and graphene and their stabilization in the presence of polyaniline (PANI) through π-π interactions. The PANI-stabilized Fc@graphene nanocomposite (FcGA) resembled an intertwined network-like morphology with high surface area and porosity, which could make it a potential candidate for energy-storage applications. The relative interactions between the components were assessed through theoretical (DFT) calculations. The specific capacitance calculated from galvanostatic charging/discharging indicated that the PANI-stabilized ternary nanocomposite exhibited a maximum specific capacitance of 960 F g− at an energy density of 85 Wh Kg−1 and a current density of 1 A g−. Furthermore, electrochemical impedance spectroscopy (EIS) analysis confirmed the low internal resistance of the as-prepared nanocomposites, which showed improved charge-transfer properties of graphene after incorporation of Fc and stabilization with PANI. Additionally, all electrodes were found to be stable up to 5000 cycles with a specific capacitance retention of 86 %, thus demonstrating the good reversibility and durability of the electrode material. [ABSTRACT FROM AUTHOR]

Vanadium pentoxide (V2O5) nanorod decorated graphene polypyrrole nanocomposites have been synthesized successfully by a facile hydrothermal process for supercapacitor (SC) applications. The morphological study revealed the successful decoration of V2O5 nanorods and polypyrrole (PPy) within the intergallery of graphitic materials due to their high degree of propensity for intercalation which leads to the formation of mesoporous 3D nanostructures. These mesoporous structures can efficiently allow fast diffusion and ion transport at the electrode–electrolyte interface towards high electrochemical utilization and superior performance. Here, decoration of V2O5 within a polymer matrix along with a graphitic material renders different electrical profiles by virtue of their electron hopping within nanocomposites. Galvanostatic charging discharging revealed that VGP was found to be superior with a maximum specific capacitance of 787 F g−1 at a current density of 1 A g−1 using KCl as an electrolyte. These observations were also confirmed by electrochemical measurements through CV and EIS studies. Furthermore, cyclic stability performed for 5000 consecutive cycles also substantiate their high durability and high power delivery uptake. Thus, considering all such key features, V2O5 based nanocomposites can be suitable for SC applications. [ABSTRACT FROM AUTHOR]

To meet a fast‐emerging demand, flexible energy storage applications have a great interest in the development of highly flexible hierarchical nanoarchitectures. Metal nitrides have recently been paid a significant interest as a promising electrode material for supercapacitors (SCs) owing to their high electrical conductivity, excellent redox properties, and outstanding mechanical strength. However, poor electrochemical stability seriously limits the commercialization possibilities. Herein, a novel strategy is presented for the synthesis of nitrogen‐doped graphene encapsulated with ultrasmall nickel–cobalt nitride (NiCo2N) and nickel–iron nitride (NiFeN) core–shell architectures that are explored as advanced electrodes for flexible solid‐state SC. The flexible NiCo2N@NG//NiFeN@NG asymmetric SC delivers an ultrahigh energy density of ≈94.93 Wh kg−1 at 0.79 kW kg−1, exceptional power density (≈74.67 Wh kg−1 at 39.53 kW kg−1), and ultralong cycle life (≈5.07% drop in initial capacity after 25 000 cycles). These results promote the core–shell hybrids that can be served as advanced supercapacitor materials for flexible energy storage applications. A novel strategy for the synthesis of nitrogen‐doped graphene encapsulated nickel–cobalt nitride (NiCo2N) and nickel–iron nitride (NiFeN) core–shell architectures is demonstrated herein. The composites are explored as advanced electrodes for flexible asymmetric supercapacitors (ASCs). The flexible ASC delivers an ultrahigh energy density of ≈94.93 Wh kg−1 at 0.79 kW kg−1 and ultralong cycle life. [ABSTRACT FROM AUTHOR]

[Display omitted] • Flexible ultrafast supercapacitor is derived from 2D Borophene-stacked MXene hybrid. • The MxB (50:50) electromaterial exhibits high capacitance of 626.7 F·g−1 at 1 A·g−1. • The MxB (50:50) electromaterial shows high capacitance retention and long-term life. • The developed supercapacitor displays an exceptional energy density of 75.6 Wh·kg−1. Two-dimensional (2D) materials provide slit-shaped ion diffusion channels that enable the rapid movement of ions. Building high-performance energy storage devices requires electrode materials with enhanced electronic conductivity, quantity of intercalation sites, and stability during prolonged cycling to maximize the energy density, power density, and cycle life of the devices. In this work, we develop the flexible ultrafast supercapacitor derived from conductive 2D MXene/Borophene (MxB) electrodes via an electrophoretic deposition method. The electrostatically self-assembled positively charged Borophene and negatively charged MXene nanosheets effectively avoid MXene nanosheet self-restacking, thus resulting in a significantly larger interlayer gap, as well as reaching more exposed electroactive sites owing to accelerated electrolyte ion diffusion. The freestanding MxB (50:50) electrode exhibits a remarkable rate capability with 85.14% capacitance retention at 20 A·g−1, long-term cycle life, and high gravimetric capacitance of 626.7F·g−1 at 1 A·g−1. The developed supercapacitor displays an exceptional energy density of 75.6 Wh·kg−1, the highest values recorded for carbon- or MXene-based materials in aqueous electrolytes. This work illuminates the design of next-generation flexible, portable, and highly integrated supercapacitor with high volumetric and rate capabilities, while offering basic insight into the impact of interlayer spacing on the electrochemical performance of 2D hybrid materials. [ABSTRACT FROM AUTHOR]

Abstract Supercapacitors suffer from lack of energy density and to achieve better energy density, a new class of hybrid architectures with controlled morphology is prerequisite. Here, a facile polyol method is successfully used for the synthesis of MnCo 2 O 4 /nitrogen doped graphene 2D/2D hybrid nanoarchitectures and this combination successfully avoids the restacking and agglomeration of nitrogen−doped graphene nanosheets. The formation of MnCo 2 O 4 /NG 2D/2D hybrid nanoarchitectures are confirmed by state−of−art techniques. This combination leads to a large conducting network that improves the exposure of active sites at the electrode−electrolyte interface for the transportation of electrons and ions. The synergistic effect of 2D MnCo 2 O 4 nanoflakes over the 2D nitrogen−doped graphene serves the capacitance of ca. 1170 F g−1 at 1 A g−1 with an excellent rate capability of 818 F g−1 at 20 A g−1. An asymmetric supercapacitor is successfully fabricated using these MnCo 2 O 4 /NG 2D/2D hybrid nanoarchitectures as the cathode and 2D nitrogen−doped graphene as the anode electrodes, which exhibits better performance than previously reported spinel metal oxide materials. The asymmetric supercapacitor exhibits excellent energy density (∼48.5 Wh kg−1 at ∼808 W kg−1) and power density (∼16000 W kg−1 at ∼32.1 Wh kg−1), with an outstanding cyclic durability of 85.9% retention after 10,000 cycles. Graphical abstract Image 1 Highlights • MnCo 2 O 4 /NG 2D/2D heteronanostructures are synthesized via a facile polyol method. • The 2D MnCo 2 O 4 NFs helps to reduce the restacking of NG via π−π interactions. • It exhibits specific capacitance of 1170 F g−1 at 1 Ag−1 with excellent stability. • Asymmetric device exhibits enhanced energy density of 48.5 Wh kg−1 at 809.5 w kg−1. • It exhibits excellent specific capacitance retention of 85.9% after 10,000 cycles. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Ni 3 V 2 O 8 and Fe 2 VO 4 NPs anchored NG synthesized by simple and cost-effective hydrothermal technique. • Ni 3 V 2 O 8 /NG and Fe 2 VO 4 /NG hybrids are employed as supercapacitor electrodes. • Both electrodes show ultra-high specific capacitance with excellent rate capability and superior cycling stability. • The ASC achieves a high energy density of ∼77.2 W h kg−1 at 863 W kg−1 and an ultra-long cycle life. Abstract Solid-state supercapacitors (SCs) are well-known as one of the most competitive power sources for modern electronics. However, most of the reported solid-state SCs suffer from low specific capacitance and energy density. Herein, a novel strategy for the synthesis of nickel vanadium oxide (Ni 3 V 2 O 8) and iron vanadium oxide (Fe 2 VO 4) nanoparticles (NPs) anchored nitrogen doped graphene (NG) for high energy solid-state asymmetric SC (ACS) through a simple and cost-effective hydrothermal technique was demonstrated. SEM and TEM analysis reveals that active Ni 3 V 2 O 8 and Fe 2 VO 4 NPs with uniform size are anchored on NG sheets. Electrochemical performance of Ni 3 V 2 O 8 /NG and Fe 2 VO 4 /NG electrodes showed that both have ultra-high specific capacitances (∼1898 F g−1 and 590 F g−1 at current density of 1 A g−1, respectively), tremendous rate capabilities, and superior cycling stabilities. Most significantly, solid-state ASC consisting of Ni 3 V 2 O 8 /NG as a cathode and Fe 2 VO 4 /NG as an anode which achieves a high energy density of ∼77.2 W h kg−1 at a power density of 863 W kg−1 and an ultra-long cycle life (capacitance retention of ∼83.3% after 20,000 cycles). This study emphasizes the development of a wide variety of energy storage systems for modern electronics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Unique 3D graphene-CNTs framework was fabricated by CVD method. • MoO 3 nanoplates were grown on the GF-CNTs framework using hydrothermal method. • GF-CNTs/MoO 3 exhibits excellent specific capacitance and high cyclic stability. • The GF-CNTs/MoO 3 //GF-CNTs device exhibits a high energy density of 75.27 W h kg−1. Abstract Recently, three-dimensional (3D) architectures of graphene-carbon nanotubes (CNTs) have attracted a lot of attention due to their multifunctional properties. In this study, we have reported a novel 3D graphene-CNTs/MoO 3 hybrid film as a binder free electrode material with unique morphology and outstanding electrochemical performance. The optimized 3D graphene-carbon nanotubes (GF-CNTs) framework was fabricated by a chemical vapor deposition (CVD) process on Ni foam skeleton. Further, controlled loading of MoO 3 nanoplates were grown on the GF-CNTs framework as a hybrid film, using an easy and low cost hydrothermal method. The as-fabricated hybrid electrode exhibits remarkable specific capacitance of 1503 F g−1 at 1 A g−1 and 798.93 F g−1 at a current density of 10 A g−1, as well as exceptional capacitance retention of 96.5% after 10,000 cycles. The excellent electrochemical performance of the electrode material can be attributed to the combination of pseudocapacitance and electric double layer capacitance contributed by the MoO 3 nanoplates and graphene foam/CNTs in the hybrid system, respectively. The asymmetric supercapacitor (ASCs), assembled from GF-CNTs/MoO 3 and GF-CNTs as positive and negative electrode, respectively, delivers excellent specific capacitance of 211.71 F g−1 at current density of 1 A g−1. The ASCs device also exhibits a maximum energy density of 75.27 W h kg−1 at a power density of 816.67 W kg−1 with excellent cycling ability of 94.2% of the initial capacitance after 10,000 cycles. These results suggest that the as-fabricated GF-CNTs/MoO 3 hybrid architecture can be used as a promising electrode material for the next generation supercacitor devices. [ABSTRACT FROM AUTHOR]

The development of new advanced nanostructures based on the hybridization of different carbon nanomaterials to obtain enhanced performance of energy storage devices has attracted considerable attention. Herein, a hierarchical nanostructure of carbon nanotubes supported electrospun carbon nanofiber networks (CNTs@CNFs) was successfully fabricated by using two facile techniques: – electrospinning and chemical vapor deposition (CVD). Such CNTs@CNFs hybrid showed the uniform and high density of CNTs directly grown on the surface of carbon nanofiber networks, leading to the formation of a hierarchical nanostructure with a large surface area and highly porous characteristics. The enhanced interactions between the CNTs and the CNFs networks were found to improve the electrical conductivity and electrochemical stability of the material. Owing to its unique nanoarchitectures and physicochemical properties, the CNTs@CNFs hybrid was demonstrated to be a potential electrode material for an electrochemical capacitor, in which a high specific capacitance of 464.2 F g −1 at 0.5 A g −1 and long-term stability with 97% retention after 10,000 repeated charge–discharge cycles were achieved. The obtained results suggest that the present CNTs@CNFs hybrid is a promising candidate for an electrochemical capacitor in energy storage technologies. [ABSTRACT FROM AUTHOR]

To accomplish high-performance flexible energy storage devices, a new class of flexible electrodes with prosperous constructions bearing exceptional electrical conductivity, exclusive porosity, and outstanding mechanical stability is extremely needed. Here, we have successfully fabricated a highly flexible electrode with nanocomposite of polyaniline/manganese hexacyanoferrate PANI/MnHCF nanocomposite (PANI/MnHCF) on highly conductive carbon fiber (FCF). The nanocomposite exhibits an ultra-high specific capacitance of 730 F g −1  at a current density of 1 A g −1 with exceptional rate capability (350 F g −1 capacitance retention at a current density of 20 A g −1 ), and outstanding cycling performance (capacitance retention of ∼85% after 1000 cycles). The PANI/MnHCF/FCF electrode shows better electrochemical performance due to their exclusive properties such as excellent electrical conductivity, unique porous network and outstanding mechanical flexibility. Furthermore, the higher surface area of PANI/MnHCF nanocomposite facilitates the transport of electrons and electrolyte ions during rapid charge/discharge process. This present work offers a simple, scalable and cost-effective method for fabrication of other PANI/MnHCF nanocomposite based electrode, which is applicable for providing energy in practical flexible portable devices. [ABSTRACT FROM AUTHOR]

Heteroatom co-doped carbon-based materials have been demonstrated to be an effective way to realize their new functions in electrode materials for energy storage devices. Herein, a novel strategy for synthesis of highly porous nitrogen-sulfur co-doped graphene nanoribbons (NS-GNRs) with enhanced active sites was developed. The highly porous NS-GNR channels provide efficient ion transport path for electrolyte ions, which enhances the overall conductivity and stability of the electrode materials by energising storage sites. The TEM and STEM-EDS analysis revealed that the NS-GNR materials exhibit uniform distribution of N and S heteroatoms into GNRs matrices. The NS-GNR electrode materials exhibited a high specific capacitance of 442 F g −1 at 0.5 A g −1 , excellent rate capability and cycling performance with ∼98.6 % retention of the initial capacitance after 10,000 cycles. Most importantly, the fabricated symmetric supercapacitor device with a wide operating voltage window of ∼1.8 V yield an excellent energy density of ∼23.85 Wh kg −1 , high power density of ∼8753 W kg −1 and superior cycle life (97.9% capacitance retention after 10,000 cycles). Thus, these results exhibit a novel metal-free and low-cost design of electrode materials for high-performance energy storage devices. [ABSTRACT FROM AUTHOR]

Sulfonated polyaniline (SPANI) functionalized reduced graphene oxide (SPANI/G-1) was prepared by aniline initiated polymerization of m -aminobenzene sulfonic acid in presence of graphene oxide (GO), followed by reduction with hydrazine hydrate. Fourier transform infrared, Raman, and X-ray photoelectron spectroscopy analyses confirmed successful surface modification of graphene using SPANI. The presence of sulfonic acid groups in SPANI accelerated the redox reaction and provided pseudocapacitance. SPANI/G-1 based electrode showed high specific capacitance of 1107 F g −1 at a current density of 1 A g −1 in a three electrode set up. An asymmetric supercapacitor (ASC) device was fabricated using SPANI/G-1 as positive electrode and chemically reduced GO (RGO) as a negative electrode. ASC showed specific capacitance of 157 F g −1 at a current density of 1.5 A g −1 and 94% retention in specific capacitance after 5000 charge-discharge cycles at a current density of 3.8 A g −1 . The ASC exhibited maximum energy density of 31.4 W h kg −1 and a large power density of 14,764 W kg −1 . Nyquist data of the device was fitted with Z-view and different components (solution resistance, charge-transfer resistance and Warburg elements) were calculated from the fitted curve. [ABSTRACT FROM AUTHOR]

Novel vanadium nitride/nitrogen-doped graphene (VN/NG) composite was fabricated and used as stable high performance anode materials for supercapacitors. The VN/NG composite anode material exhibited excellent rate capability, outstanding cycling stability, and superior performance. FE-SEM and TEM studies of VN/NG composite revealed that ultra-thin VN nanostructures were homogeneously distributed on flexible NG nanosheets. The NG provided a highly conductive network to boost the charge transport involved during the capacitance generation and also aided the dispersion of nanostructured VN within the NG network. The synergetic VN/NG composite exhibited an ultra-high specific capacitance of 445 F g −1 at 1 Ag −1 with a wide operation window (−1.2 to 0 V) and showed outstanding rate capability (98.66% capacity retention after 10,000 cycles at 10 Ag −1 ). The VN/NG electrode offered a maximum energy density (∼81.73 Wh kg −1 ) and an ultra-high power density (∼28.82 kW kg −1 at 51.24 Wh kg −1 ). The cycling performance of the VN/NG composite was superior to that of pure VN nanostructure. These finding open a new path way to the designated fabrication of VN/NG composite as anode materials in the development of high performance energy storage devices. [ABSTRACT FROM AUTHOR]

• Co-MOF structures were anchored on the flexible MX-CNF. • Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF electrodes were derived from Co-MOF@MX-CNF. • A flexible and wearable hybrid supercapacitor was assembled using these electrodes. • The device shows an energy density of 72.5 Wh kg−1 at 832.4 W kg−1. Freestanding and flexible electrodes are crucial for advancing flexible and wearable energy storage devices (FW-ESD). However, the significant trade-off between mechanical flexibility and electrochemical performance of electrodes limits the development of high-performance FW-ESD. Therefore, flexible and freestanding multi-component hybrid electrodes with improved electrochemical properties are in high demand. This work reports a rational design of cobalt-metal organic framework (Co-MOF) structures on a highly flexible and electroconductive MXene-carbon nanofiber mat (MX-CNF). Further, the Co-MOF@MX-CNF was used as a starting material to derive capacitive-type Co-PC@MX-CNF and battery-type MnO 2 @Co 3 O 4 -PC@MX-CNF functional multi-component electrodes for a high-performance flexible wearable hybrid supercapacitor (FW-HSC). Owing to their high specific surface area (SSA), wettability, conductivity, and abundant active sites, Co-PC@MX-CNF and MnO 2 @Co 3 O 4 -PC@MX-CNF exhibited a specific capacitance of 426.7 F g−1 and a specific capacity of 475.4 mAh g−1 at 1 A g−1, respectively, with excellent mechanical flexibility. Moreover, the two electrodes were used to fabricate an FW-HSC with an operating voltage window of 1.5 V, delivering an energy density of 72.5 Wh kg−1 at a power density of 832.4 W kg−1 with long-term stability (90.36 % capacitance retention). Furthermore, a series connection of two identical FW-HSC devices could power a digital clock and light up a green LED, demonstrating its potential as a power source for various wearable devices. [ABSTRACT FROM AUTHOR]

In this work, cobalt vanadate/reduced graphene oxide (Co 3 V 2 O 8 /RGO) composite nanostructure has been synthesized via in-situ reduction of graphene oxide (GO) in the presence of cobalt chloride and sodium metavanadate through hydrothermal following post calcinations treatment. Characterizations through various techniques have been performed to probe the physicochemical properties of Co 3 V 2 O 8 /RGO, RGO and Co 3 V 2 O 8 nanostructures. Our Results show that because of the synergistic effect, Co 3 V 2 O 8 /RGO composite nanostructure exhibits superior electrochemical properties as compared to bare RGO and Co 3 V 2 O 8. At a current density of 0.5 A/g the specific capacity has been recorded to be 118.82, ∼179, and ∼241.67 Cg-1 in case of Co 3 V 2 O 8 , RGO and Co 3 V 2 O 8 /RGO nanostructures, respectively. Moreover, Co 3 V 2 O 8 /RGO composite nanostructure (positive electrode) and RGO (negative electrode) have been employed to prepare the asymmetric supercapacitor, exhibited high specific capacity (127.62Cg-1), energy density (28.36 Whkg−1), and power density (400 Wkg-1) at a current density 0.5 A/g. This asymmetric supercapacitor shows excellent capacity retention (∼91.64%) and columbic efficiency (∼98.61%) measured at a current density of 5 A/g after 10,000 charge/discharge cycles. More importantly, a dramatic increase ∼170% (344 Cg-1) and ∼67% (185 Cg-1) in the specific capacity have been recorded at a current density of 0.5 A/g and 1.0 A/g, respectively when asymmetric supercapacitor device is subjected to an external magnetic field of strength of 0.5 T. Additionally, under the applied magnetic field, capacity retention ∼97.75% and columbic efficiency ∼98.84% has been recorded at a current density of 5 A/g after 10,000 cycles. [Display omitted] • Synthesis of Co 3 V 2 O 8 /RGO composite nanostructure via a facile in-situ reduction. • Co 3 V 2 O 8 /RGO nanostructure exhibited specific capacity of ~242 Cg-1 at 0.5 Ag-1. • Co 3 V 2 O 8 /RGO exhibits ~103% higher specific capacity compare to bare Co 3 V 2 O 8 NPs. • ASc exhibits energy density ~28.36 Whkg-1 and power density ~ 400 Wkg-1 at 0.5 Ag-1. • Capacity retention ~91.64 % and columbic efficiency ~98.61 % at 5 Ag-1 after 10,000 cycles. • Magnetic field induced ~170% enhanced capacity at 0.5 Ag-1. [ABSTRACT FROM AUTHOR]

This study investigates the synthesis and application of boron nitride quantum dot (BNQD) covalently bonded reduced graphene oxide (rGO) hybrid materials as a novel electrode material for supercapacitors. Because of the p-doping as well as the enhanced hydrophilicity and interfacial bonding force enabled by the hybridization of amine-functionalized boron nitride quantum dot (A-BNQD) with rGO via the chemical coupling reaction, the A-BNQD/rGO shows improved charge carrier density, wettability of electrolyte, and durability. As a result of the synergistic effects, the A-BNQD/rGO as a supercapacitor electrode shows much higher specific capacitance compared to those of rGO and raw BNQD/rGO at a current density of 1 A g−1. Further, the A-BNQD/rGO shows high cycling stability, maintaining almost 94.38%, even after 10,000 cycles due to the enhanced interfacial bonding force between the A-BNQD and rGO. Besides, the fabricated symmetric supercapacitor exhibits high specific capacitance (90 F g−1@1 A g−1), an energy density (12.5 Wh kg−1@0.5 kW kg−1), and good cycling stability. This result suggested that the fabricated A-BNQD/rGO has great potential as electrode materials for high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

[Display omitted] • A high-performance, porous, faradaic CeO 2 /NiV–LDH nanocomposite is prepared. • Various components clearly reveal the strong synergistic effect for energy storage. • The CeO 2 /NiV-LDH (2:2) composite can act as electrocatalyst for methanol oxidation. • 3D flowerlike Bi 2 O 3 is synthesized and investigated as negative electrode material. • A quasi-solid-state ASC device is fabricated to examine its practicality. High-performance electrochemical supercapacitors should demonstrate notably high energy density along with ultralong cycling life for wide commercial applications. Hence, significant efforts are being made to improve the specific capacitance as well as expand the operating voltage of the fabricated supercapacitor device. Herein, a novel quasi-solid-state asymmetric supercapacitor (ASC) device employing porous nanostructured CeO 2 /NiV–LDH (2:2) composite positive electrode and 3D flowerlike Bi 2 O 3 negative electrode is reported. The positive electrode material shows an efficiently improved electrochemical feature from synergistic integration between high surface area CeO 2 nanorods, and 2D NiV–LDH nanosheets with short diffusion distance for the charge carriers. In addition, the CeO 2 /NiV–LDH (2:2) composite acts as highly active and stable electrocatalyst when investigated for the methanol electrooxidation. The as-fabricated gel electrolyte based quasi-solid-state CeO 2 /NiV–LDH (2:2)//Bi 2 O 3 ASC device exhibits an excellent and stable electrochemical performance (highest energy density of 62.5 Wh kg−1 at a power density of 1595.2 W kg−1) with long cycle life displaying 86.4% capacitance retention still after 10,000 GCD cycles. This work confirms the high suitability of the rare earth metal oxide and LDH-based composite electrode materials, as well as Bi chalcogenides, for the quasi-solid-state ASCs as proficient portable energy systems. [ABSTRACT FROM AUTHOR]

• Development of MXene nanocomposites is an effective way to improve the properties of MXene for various applications. • Research on MXene nanocomposite has been emerging. • Recent advances in synthesis methods and properties of MXene nanocomposites have been updated. • Electrochemical applications and forthcoming opportunities of MXene nanocomposites have been discussed. Since the first exfoliation of a few atomic layers of transition metal carbides (Ti 3 C 2) from the three-dimensional (3D) MAX phase (Ti 3 AlC 2) in 2011, a family of two-dimensional (2D) layered metal carbides and nitrides also known as MXene has drawn great attention as a promising 2D material in various applications. The hydrophilic nature, excellent conductivity and electrochemical properties make MXene a fascinating 2D candidate for electrochemical energy storage applications. However, the aggregation, restacking, and oxidation of MXene nanosheets (NSs) significantly hinder their performance. To address these issues, an effective and straightforward strategy is to combine MXene with other materials including polymers, metal oxides, and carbon to form MXene nanocomposites. Making MXene nanocomposites with other materials is an effective way to tune the properties of MXene for many applications. In the current research trend, the most important application of MXene-based nanocomposite is electrochemical energy storage due to the improved electrochemical and physicochemical properties. Therefore, this review presents the current advances in MXene nanocomposites, especially for electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]

• The novel M x Co 3-x S 4 @NiMoS 4 [M = Ni, Mn, Zn] nanostructure core@shell was designed. • The best core cation in core@shell with binder-free electrode was studied for the first time. • Optimal charge storage properties of NiCo 2 S 4 @NiMoS 4 electrode was discussed in detail. • Merits of core@shell and assemble of ASC solid-state device system was demonstrated. • The materials device exhibits high energy density of 72.3 Wh kg−1 with the power density of 460 W kg−1. A supercapacitor would be one of the most reliable energy storage device, but due to inadequate energy density, it is restricted to commercialization. The bimetallic core nanoparticles possess multiple oxidation states in their core@shell design, and understanding the effect of tuning of core cations are noble artifacts for effective research. Here, an effective strategy of varying the cations (M = Ni, Zn and Mn) in the M x Co 3-x S 4 @NiMoS 4 core@shell is demonstrated. Among the M x Co 3-x S 4 @NiMoS 4 electrodes, the NiCo 2 S 4 @NiMoS 4 core@shell showed better electrochemical storage properties with areal capacity/gravimetric capacity of 0.92 mAh cm−2/287.5 mAh g−1 at 3 mA cm−2 (3410.0 F g−1 capacitance), and superior cycle life with ca. 92.3% capacity retention at high current density of 50.0 mA cm−2 after 10,000 cycles. Moreover, real–time application was monitored by assembling an asymmetric solid–state device, taking NiCo 2 S 4 @NiMoS 4 as the cathode and Fe 2 O 3 /NG hydrogel as the anode. The device delivers an excellent cell capacity of 90.4 mA hg−1 with a remarkable cycle life of 90.5% after 10,000 cycles. The device stored a very high energy density of 72.3 Wh kg–1at 460.0 W kg−1 and retained an energy density of 32.6 Wh kg−1 at a high power density of 11,844.0 W kg−1, demonstrating high applicability towards practical energy storage devices. [ABSTRACT FROM AUTHOR]

• Carbon composited with pseudocapacitive material emerged with great interest. • The electrochemical performance of hybrid composites is discussed systematically. • This review provides a comprehensive study. • Future perspectives and challenges in practical application also discussed. Supercapacitors are considered reliable devices for energy storage. However, supercapacitor has some limitations, such as relatively low capacitance and low energy density, which affect it as a promising energy storage device. In this context, carbon based nanocomposites have been widely studied in the past few years due to their excellent physical, mechanical and electrical properties. A lot of studies have been reported on carbon based materials with different 0D, 1D, 2D and 3D carbon nanostructures. The unique combination of pseudo-material with carbon material greatly improves the electrochemical performance of the composite as compared to individual candidate. However, developing high energy density supercapacitor devices with high cycling stability in a simple and cost effective way is still a challenge. This review provides the current progress on the carbon based pseudo-material composites for supercapacitor application in a well-systematic and easy manner which can guide the early researchers and emerging scientists dealing with or interested in supercapacitor. [ABSTRACT FROM AUTHOR]

• Cu@Ni@NiCoS core-shell nanofiber network electrode structured was fabricated. • Cu@Ni NFs network electrode exhibit excellent chemical stability. • Cu@Ni@NiCoS NFs network electrode shows excellent electro-optical performance. • The electrode exhibits a high areal capacity of 6.94 μA h/cm2 at ~76% transmittance. • The device demonstrates a high energy density of ~0.48 μWh/cm2 at ~11.15 μW/cm2 power density. Transparent flexible supercapacitors are crucial for the progress of high-tech modern transparent wearable electronic gadgets. Thus, fabricating high opto-electrochemical performance electrodes is crucial for the development of high energy density transparent flexible supercapacitors. Herein, direct growth of battery-type ternary nickel-cobalt sulfide (NiCoS) nanosheets on Cu@Ni NFs network transparent electrode forming a seamless Cu@Ni@NiCoS NFs core-shell electrode structured is reported to boost the energy density of transparent supercapacitors. The core Cu@Ni nanofibers network electrode exhibited both excellent electro-optical performance (sheet resistance ~12.19 Ω/sq at ~89% transmittance) and high mechanical flexibility. NiCoS thin nanosheets shell offer high porosity, abundant active sites, and large electrode-electrolyte contact area, thus facilitating the fast diffusion of electrolytes into active materials. The Cu@Ni@NiCoS NFs core-shell electrode demonstrated remarkable high opto-electrochemical performance (transparency of ~76.83%, an areal capacity of 6.94 μA h/cm2, and high rate capability) and excellent mechanical properties. Finally, a transparent flexible symmetric supercapacitor device (SSC device) assembled by employing Cu@Ni@NiCoS NFs as both electrodes demonstrates an outstanding energy density of 0.48 μW h/cm2 at a power density of 11.15 μW/cm2 with device transparency of ~65%. [ABSTRACT FROM AUTHOR]

• The rational design strategy of hierarchical Fe x Co 3-x Se 4 nanostructures was developed. • The charge storage mechanism of the Fe x Co 3-x Se 4 electrodes have been revealed. • The solid-state ASC exhibited ultrahigh energy density and ultralong cycle life. Hierarchical nanoarchitectures with large void space, unique porous networks, and numerous active sites for advanced supercapacitor (SC) electrodes has attracted great attention in modern electronics. Herein, a novel strategy is established to rational design of hierarchical iron cobalt selenide (Fe x Co 3-x Se 4) with tunable nanostructure and morphology by adjusting the stoichiometric ration of Fe: Co in order to enhance the energy density of SCs. The optimal FeCo 2 Se 4 nanosheet arrays (NAs) enhances the electrical conductivity, electroactive sites, and intrinsic reactivity, achieving an ultra-high specific capacity of ~398.5 mA h g−1 at a current density of 1 mA cm−2 with an exceptional rate capability (~304.2 mA h g−1 at a current density of 50 mA cm−2), and ultra-long cycle life (~98.2% retention after 10,000 cycles). Taking advantage of FeCo 2 Se 4 NAs positive electrode, we have successfully assembled solid-state asymmetric SC (ASC) with Fe 2 O 3 @NG hydrogel as the negative electrode. Impressively, the solid-state ASC achieves high operating voltage window upto 1.6 V, and thus delivers ultrahigh energy density of ~84.1 Wh kg−1 at a power density of 0.69 kW kg−1, and exceptional cycling stability (5.5% of capacity decay after 10,000 cycles), which outperform the recently reported metal selenide-based ASCs. These consequences clearly designate FeCo 2 Se 4 NAs as an advanced electrode for next-generation energy storage technologies. [ABSTRACT FROM AUTHOR]

The freestanding hierarchical core-shell nanoarchitectures exemplify the substantial interest in the development of next-generation electrode materials for energy storage systems. Herein, the hierarchical 3D CoS@MoS 2 nanowire arrays (NWAs) are synthesized through a cost-effective hydrothermal process and followed by an effective sulfurization. The structural and morphological investigations of hierarchical 3D CoS@MoS 2 NWAs are carried out for each stage. The 3D CoS@MoS 2 NWAs yields a high specific capacity of 374.75 mA h g−1 and an areal capacity of 1.39 mA h cm−2 at a current density of 4 mA cm−2, exceptional rate capability (∼70.1% retention of the capacity at 20 mA cm−2), and remarkable cycling performance (∼96.2% retention of the capacity after 10,000 consecutive charge-discharge cycles), which are superior to the corresponding CoS nanowires and MoS 2 nanosheets counterparts. The assembled CoS@MoS 2 //Fe 2 O 3 @rGO asymmetric supercapacitor (ASC) exhibits a broader working potential window of 1.7 V, ultrahigh energy density of 95.7 W h Kg−1 at the power density of 711.2 W kg−1, and super-long cycling stability (∼95.5% retention of capacity after 10,000 cycles), demonstrating that the hierarchical 3D CoS@MoS 2 NWAs are promising as potential candidates for hig-performance SCs. Image 1 • Hierarchical CoS@MoS 2 NWAs have fabricated by simple and cost-effective method. • CoS@MoS 2 delivers an ultrahigh specific capacity of 374.75 mA h g−1 at 4 mA cm−2. • ASC assembled with CoS@MoS 2 as positive and Fe 2 O 3 @rGO as negative electrodes. • ASC device exhibits an ultrahigh energy density of 95.7 W h Kg−1 at 711.2 W kg−1. [ABSTRACT FROM AUTHOR]

• Novel strategy for the design of Cu x Co 1−x Se 2 nanostructures has been established. • The optimal (Cu 0.5 Co 0.5)Se 2 is proposed as SC electrode for the first time. • The charge storage mechanism of Cu x Co 1−x Se 2 electrodes are discussed in detail. • Merits of binder-free/freestanding electrodes for SC applications is demonstrated. • The assembled ASC exhibits an excellent energy density and ultralong cycle life. Transition-metal chalcogenides (TMCs) have attracted numerous interests in the field of energy storage owing to their exceptional electrical conductivity, ultrahigh specific capacity, etc. Herein, with inspiration from the attractive nanostructures of hierarchical frameworks with interconnected networks, we endeavored to design ternary copper cobalt selenide (Cu x Co 1–x Se 2) nanostructures through a facile and cost-effective hydrothermal and followed by selenization process. The effects of Cu2+ is investigated and shows significant enhancement in the electrochemical performances. The optimal Cu 0.5 Co 0.5 Se 2 nanosheets (NSs) possess hierarchical architectures, large specific surface area, unique porous networks, and excellent intrinsic conductivity that result in superior electrochemical properties by their excellent synergistic effects. Taking advantage of the merits of the rational nanostructures, the Cu 0.5 Co 0.5 Se 2 NSs significantly boost the capacitive performances as ultrahigh specific capacitance of ~1695 F g−1 at a current density of 1 A g−1, and long-term cycling stability (~94.9%). An asymmetric supercapacitor (ASC) device is fabricated using the Cu 0.5 Co 0.5 Se 2 NSs as a positive electrode, and multilayered MXene (Ti 3 C 2) as a negative electrode. Remarkably, the ASC operates at a working potential of 1.6 V and delivers a high energy density (~84.17 Wh kg−1 at 0.604 kW kg−1), high power density (~14.95 kW kg−1 at 57.73 Wh kg−1), and exceptional cycling stability (~91.1% after 10,000 charge–discharge cycles). The energy-storage properties are superior to recently reported TMCs-based ASC, proposing that the Cu 0.5 Co 0.5 Se 2 //MXene ASC has massive potential for next-generation energy-storage systems. [ABSTRACT FROM AUTHOR]

Hererin, we report Co–Ni–Zn ternary oxide@NiWo 4 core-shell nanowire arrays on Ni foam (Co–Ni–Zn–O@NiWO 4) and Fe 2 O 3 nanosheets interconnected with carbon nanotubes on 3D graphene Ni foam (Fe 2 O 3 -CNTs@GF) as the binder-free electrodes for supercapacitor applications. In the optimized conditions, the unique Co–Ni–Zn–O@NiWO 4 electrode exhibits an excellent areal capacitance of 9.31 (2909.9 F g−1) F cm−2 at a current density of 2.5 mA cm−2 and an outstanding rate capability of 65.7% up to the current density of 60 mA cm−2. In addition, Fe 2 O 3 -CNTs@GF is prepared using chemical vapor deposition (CVD) followed by the hydrothermal method. Under the optimized conditions, Fe 2 O 3 -CNTs@GF shows a high areal capacitance of 812 (386.7 F g−1) mF cm−2 at 2 mA cm−2 and excellent rate performance of 59.1%. Moreover, an asymmetric supercapacitor (ASC) device fabricated with Co–Ni–Zn–O@NiWO 4 as positive electrode and Fe 2 O 3 -CNTs@GF as negative electrode delivers an excellent specific capacitance of 229.7 F g−1 at 0.5 A g−1 and rate capability of 52.2% up to 16 Ag-1. The as-fabricated device also exhibits an ultra-high energy density of 81.6 W h kg−1 and outstanding capacitance retention of 93.1% up to 10,000 cycles. Due to these excellent supercapacitive properties, as-fabricated ASC device may be used in energy storage application. The asymmetric supercapacitor fabricated by Co–Ni–Zn ternary Oxide@NiWO 4 core-shell nanowire arrays and Fe 2 O 3 -CNTs@GF electrodes exhibits excellent supercapacitive performance. Image 1 • Unique Co–Ni–Zn–O@NiWO 4 electrode is prepared using hydrothermal method. • The optimized electrode exhibits an excellent areal capacitance of 9.31 F cm−2. • The Fe 2 O 3 -CNTs@GF electrode shows high areal capacitance of 812 mF cm−2. • The asymmetric supercapacitor delivers excellent energy density of 81.6 W h kg−1. • The capacitance retention of device is 93.1% after 10,000 cycles. [ABSTRACT FROM AUTHOR]