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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]

Rechargeable lithium–sulfur batteries (LSBs) are recognized as a promising candidate for next‐generation energy storage devices because of their high theoretical specific capacity and energy density. However, the insulating of sulfur, Li2S2/Li2S, and the shuttling effect of high order lithium polysulfides (LiPSs) hinder its practical applications. Herein, a heterostructure is explored to enhance the conversion reaction kinetics and adsorption ability of LiPSs. By rationally designing a conductive carbon framework and polar metal sites, both experimental and theoretical results show strong adsorption abilities for dissolved LiPSs and promote the conversion reaction rate. A CoSe2/Co3O4@NC‐CNT/S cathode shows an excellent rate performance (≈1457 mAh g−1 at 0.1 C and still retains ≈688 mAh g−1 at a high rate of 5 C). When performing charge–discharge in long‐term stability at 2 C, the CoSe2/Co3O4@NC‐CNT/S cathode delivers a high initial specific capacity of ≈780 mAh g−1 and retains ≈602 mAh g−1 after 500 cycles with an excellent Coulombic efficiency of ≈95.4%. Remarkably, the battery can entirely operate even at a very high sulfur loading of ≈10.1 mg cm−2 and lean electrolyte condition. This work emphasizes a new strategy to rationally design heterostructures that can encourage the industrial application of LSBs. [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]

The design of three-dimensional (3D) nanoarchitectures on a flexible substrate has emerged as a novel strategy for fabricating cutting-edge wearable and portable power sources. Herein, we propose a simple and versatile approach towards the fabrication of hierarchical nanoporous manganese nickel selenide (Mn x Ni 1-x Se 2) and manganese iron selenide (Mn x Fe 1-x Se 2) nanosheets as positive and negative electrodes for flexible charge storage devices to achieve ultra-high energy density. The Mn substitution into Ni/Fe-selenide results in hierarchical architecture with highly altered electronic structure, offering enhanced electrical conductivity, increased catalytic activity, and improved stability of Ni/Fe phases upon cycling. Under optimized conditions, the Mn 0.33 Ni 0.67 Se 2 and Mn 0.33 Fe 0.67 Se 2 electrodes showed high specific capacities of ∼333 and 251 mAh g−1 at a current density of 1 mA cm−2, superior rate capabilities of 81.4 and 80.9% capacity retention at 50 mA cm−2, respectively, and outstanding cycling stability. Most importantly, in flexible solid-state assembly, the Mn 0.33 Ni 0.67 Se 2 //Mn 0.33 Fe 0.67 Se 2 based SC delivers the excellent energy density of 87.2 Wh kg−1 at a power density of 0.672 kW kg−1, along with ultra-long durability of 96.2% capacity retention after 10,000 cycles at 30 mA cm−2. Thus, it would be believed this new fabrication strategy certainly promising for flexible electronics devices in the near future. Image 1 • Nanostructured Mn x Ni 1-x Se 2 and Mn x Fe 1-x Se 2 were directly grown on CFC via hydrothermal and subsequent selenization process. • Mn 0.33 Ni 0.67 Se 2 and Mn 0.33 Fe 0.67 Se 2 electrodes are used as positrode and negatrode for flexible ASC. • Structural investigation and charge storage mechanism of the Mn 0.33 Ni 0.67 Se 2 and Mn 0.33 Fe 0.67 Se 2 electrodes are discussed. • Merits of freestanding and binder-free for flexible solid-state ASC is demonstrated. • The use of both binder-free electrode in flexible ASC result in superhigh energy and power densities. [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]

A series of proton-functionalized graphitic carbon nitride ( f gC 3 N 4 ) modified reduced graphene oxide (rGO)/nickel-aluminium layered double hydroxide (LDH) composites ( f gC 3 N 4 -rGO/LDH-1 and f gC 3 N 4 -rGO/LDH-2) were prepared by a novel scalable strategy using different amounts of f gC 3 N 4 -rGO as a conductive matrix. The morphological analyses reveal that the LDH sheets are gradually assembled on the f gC 3 N 4 -rGO matrix. The f gC 3 N 4 -rGO and LDH mutually minimize their self-aggregation in f gC 3 N 4 -rGO/LDH composite. The porous skeleton of f gC 3 N 4 -rGO/LDH-1 (highest loading of f gC 3 N 4 -rGO matrix) produces a high surface area (240 m 2 /g) and mesopores (diameter; 2.2 nm). The f gC 3 N 4 -rGO/LDH-1 electrode generates a specific capacitance value of 1190 F g −1 at 1 A g −1 , excellent rate performance (71% at 10 A g −1 ), and good cycling stability (90% after 3000 cycles), in a three-electrode setup. Hierarchical f gC 3 N 4 functionalized rGO composite (3D- f gC 3 N 4 @rGO) was used as a negative material. The 3D- f gC 3 N 4 @rGO produces an excellent capacitance of 345 F g −1 at 1 A g −1 , high rate capability (74% at 10 A g −1 ) and good cyclic stability (90% after 3000 cycles). The f gC 3 N 4 -rGO/LDH-1 and 3D- f gC 3 N 4 @rGO were assembled to fabricate a solid-state asymmetric supercapacitor device using KOH/PVA gel electrolyte. The device operates within the potential window of 1.6 V and produces the highest energy density and power density of 54.76 W h kg −1 and 12031.92 W kg −1 , respectively. The solid-state device shows an excellent cycle life of 91% after 7000 cycles, and it can power a red LED, suggesting very efficient for practical application. [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]

In this study, a novel 4,4′-diaminostilbene-2,2′-disulfonic acid (DASDSA)-functionalized reduced graphene oxide (DASDSA-rGO) was prepared via simple refluxing method involving GO and DASDSA in the presence of ammonia solution followed by reduction with hydrazine hydrate. FTIR spectroscopy, Raman scattering, X-ray photoelectron spectroscopy (XPS), and XRD analyses confirmed the successful functionalization and reduction of GO in DASDSA-rGO. The FTIR and XPS analyses also confirmed covalent bond formation between DASDSA and graphene. The DASDSA spacer successfully minimized the restacking of rGO sheets as observed from FESEM analysis. Several redox transition states and SO 3 H groups of grafted DASDSA moieties provided excellent pseudocapacitance performance of the DASDSA-rGO electrode. The DASDSA-rGO electrode showed high specific capacitance ( C ) value of 1042 F g −1 at a current density of 1 A g −1 , good cycling stability (95% capacitance retention after 3000 cycles), and excellent rate capability in a three-electrode setup. The DASDSA-rGO (positive electrode) and rGO (negative electrode) were assembled to prepare an asymmetric supercapacitor (ASC) device. The power density values of the ASC device were calculated to be 650 and 7800 W kg −1 at energy density values of 37.37 and 23.78 W h kg −1 , respectively. The ASC device exhibited C value of 159 F g −1 at 1 A g −1 and displayed 86% retention in C after 8500 cycles. The EIS data of the three-electrode system and ASC device were fitted with Z-views to determine the different resistance components after a different number of charge–discharge cycles in a cycling stability test. [ABSTRACT FROM AUTHOR]

A three-dimensional (3-D) porous structure was designed based on carbon dot (CD)-supported copper sulphide (CuS)-decorated graphene oxide (GO) hydrogel for using in a high-performance asymmetric supercapacitor device to improve the specific capacitance, cyclic stability and energy density of CuS as well as GO based supercapacitors. CD coated CuS (CuS@CD) decorated GO hydrogels (CuS@CD-GOH) were prepared by a simple hydrothermal reaction at 180 °C and optimized through different spectroscopic, diffraction, microscopic and electrochemical analyses. CD acted as a stabilizer for the CuS nanoparticles and help to bind strongly CuS nanoparticles with GO inside the 3-D hydrogel structure. The CuS@CD-GOH exhibited high specific capacitance of 920 F g −1 at a current density of 1 A g −1 . The optimal CuS@CD-GOH was used as a positive electrode for the fabrication of asymmetric supercapacitor along with reduced GO as the negative electrode, which delivered the highest energy density up to 28 W h kg −1 along with long cycling life and retains up to 90% specific capacitance after 5000 cycles. The results are excellent in comparison to the reported CuS and composite GO hydrogel based supercapacitors. Thus, this work will provide a new insight of CuS and GO based composite 3-D structures for supercapacitor applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • An integrated hybrid fiber-shaped cathode electrode (P x –V 2 O 5–x @CoNC@MX/CF) was prepared through sequential steps involving wet-spinning, co-precipitation, electrodeposition and post-synthesis treatment. • At the same time, dendrite free anode (ZnNS@MX/CF) was also prepared. • Using P x –V 2 O 5–x @CoNC@MX/CF and ZnNS@MX/CF as electrodes, a fiber-shaped solid-state ZIB (FSSZIB) was fabricated. • The FSSZIB delivered an energy density of 133 mWh/cm3 at a power density of 425.2 mW/cm3. Aqueous zinc-ion batteries (ZIBs) are instrumental in advancing sustainable energy storage technologies, primarily due to their affordability and eco-friendliness. However, their further development into fiber-shaped ZIBs (FSZIBs) has been impeded by challenges related to appropriate 1D cathode materials coupled with low conductivity, sluggish kinetics, structural instability, low mass loading, inefficient ion pathways, and lack of flexibility. Herein, an integrated hybrid fiber-shaped cathode electrode (P x –V 2 O 5–x @CoNC@MX/CF) for the FSZIB is developed. The reported electrode design incorporates bimetallic metal–organic framework (MOF)-derived leaf-like CoNC structures, providing active sites and conductive connections for vanadium oxide-based nanofibril structure and the porous MXene-carbon fiber (MX/CF) substrate. Tuning the electronic structure, through phosphorus doping and creating oxygen vacancies, provides the resulting P x –V 2 O 5–x @CoNC@MX/CF electrode with good Zn2+ diffusion ability and stabilizes the vanadium oxide structure, to exhibit exceptional electrochemical performance as cathode for FSZIB. This strategy simultaneously enhances active material growth, prevents structural degradation, and facilitates a highly reversible de/intercalation process of Zn2+ ions. The assembled fiber-shaped solid-state ZIB (FSSZIB) based on P x –V 2 O 5–x @CoNC@MX/CF as the cathode and ZnNS@MX/CF as the anode demonstrates high energy density of 133 mWh/cm3 and power density of 425.2 mW/cm3. Moreover, the FSSZIB exhibits excellent cycling stability, with capacity retention of 79.8 % after 20,000 charge–discharge cycles, demonstrating its long-term durability. [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]

• Rationally designed MWCNTs enriched hollow spheres of NiCo 2 O 4 as positrode. • Novel porous structures of Cu 2 WS 4 intermingled with MWCNTs as negatrode. • Positrode and negatrode displayed high specific capacitance of 2240 and 1420 F g−1. • The fabricated asymmetric device showed ultrahigh energy density of ~87 Wh kg−1. • The solid-state supercapacitor exhibited durable performance for >10,000 cycles. To develop a high-performance supercapacitor, synergy between the positive and negative electrodes is essential. On the positive side, saturation is achieved in exploring novel materials, whereas on the negative side, there are extremely limited options. In this study, we propose a novel combination of hollow metal oxide positive and porous metal sulfide negative electrodes incorporated with MWCNTs to achieve advanced supercapacitors. We have rationally designed hierarchical hollow spheres of NiCo 2 O 4 , as positive electrodes, by carefully tuning the reaction and annealing parameters. We propose a novel material, i.e., porous Cu 2 WS 4 , which has never, to the best of our knowledge, been explored as negative electrodes for supercapacitors. Even though both the materials showed reasonably good electrochemical performance, to further improve their output, they were clubbed with MWCNTs to form composites. The strategy of incorporating MWCNTs worked well and the electrochemical properties were significantly improved. Both the composite electrodes exhibited an ultrahigh specific capacitance of 2240 and 1420 F g−1, respectively. The fabricated solid-state asymmetric supercapacitor exhibited remarkably high specific capacity and energy density 116 mAh g−1 and 87 Wh kg−1, respectively, at 1 A g−1. The device was also perfect in terms of power, coulombic efficiency and cycling stability for >10,000 cycles with ~88% capacity retention. The observed results pave a modern way of optimizing electrode materials and combining them to achieve high-performance hybrid supercapacitors for large scale integrated energy-storage systems. [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]

• 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]

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]

• The 3D Zn-Ni-Co oxide@NiMoO 4 nanostructure supported Ni foam electrode was made. • The electrode delivers excellent specific capacity of 0.98 mA h cm−2 at 3 mA cm−2. • The solid-state asymmetric supercapacitor shows an energy density of 70 W h kg−1. • The asymmetric supercapacitor shows high rate capability of 50.5% at 50 mA cm−2. • The capacitance retention of asymmetric supercapacitor is 91% after 10,000 cycles. In the search for advanced positive pseudocapacitive electrode material for potential application to practical energy storage and conversion devices, innovative design and alteration of the assemblage of the complex transition metal oxide based core-shell heterostructures are technically highly essential undertakings. Herein, uniquely assembled three-dimensional porous Zn-Ni-Co oxide (ZNCO)@NiMoO 4 core-shell nanowire/nanosheet arrays (NWNSAs) supported on Ni foam as integrated pseudocapacitive electrode are fabricated for the first time by a facile and scalable two-step hydrothermal process combined with post-annealing methods. Taking advantage of the synergistic interaction in core-shell architecture, the hierarchical porous ZNCO@NiMoO 4 NWNSAs offers excellent conductivity, durability, effective nanoporous network, and proper channels for the rapid transfer of ions/electron for reversible Faradaic reaction. In a three-electrode assembly, the hierarchical as-synthesized ZNCO@NiMoO 4 electrode exhibits higher specific capacity (C S ; 338.5 mA h g−1 at 3 mA cm−2), rate performance (71% up to 25 mA cm−2), and good cyclic stability (86% capacity retention after 10,000 cycles) than the ZNCO electrode (C S ; 266.1 mA h g−1 and 57% up to 25 mA cm−2). The all-solid-state asymmetric supercapacitor (ASC) device consisting of ZNCO@NiMoO 4 NWNSAs as cathode and Fe 2 O 3 /graphene hydrogel as anode electrodes shows superior specific capacity (87.5 mA h g−1 at 4 mA cm−2), high rate capability (50.5% up to 50 mA cm−2), excellent life-span (91% after 10,000 GCD cycles), and very high energy and power densities (~70 W h kg−1 and 5115.1 W kg−1), suggesting its potential applicability to advanced hybrid supercapacitors. [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]

[Display omitted] • Novel core–shell PANI@WMoO 3 NRs is designed as an intercalated electrode material. • PANI@WMoO 3 exhibits high capacity, good reversibility, and structural stability. • PANI@WMoO 3 //ZnMnO 4 -based aqueous flexible ZIB exhibits the excellent performance. • ZIBs deliver high energy density of 394.8 W·h/kg at power density of 141.6 W/kg. With the rising technology of flexible and wearable portable smart devices, aqueous rechargeable zinc–ion batteries (ZIBs) are one of the potential candidates as energy storage devices, however, the uncontrollable growth of Zn dendrites owing to the uneven deposition of zinc during charging, and the scarcity of high-performance electrodes limit the development of high-performance flexible ZIBs. Herein, a novel PANI@WMoO 3 nanorods (NRs) core–shell nanostructure is designed as an intercalation electrode for the development of aqueous flexible ZIBs. Advancing from a PANI buffer layer and accelerating Zn2+ ion insertion/extraction owing to the hexagonal crystalline structure of WMoO 3 , the PANI@WMoO 3 //Zn/CC battery exhibits outstanding electrochemical performance, with a high specific capacity of 329.0 mA·h/g at 0.2 A/g, exceptional rate capability, and superior cyclic stability (∼90.09 % after 1,000 cycles). In addition, the fabricated flexible ZIBs demonstrate excellent mechanical characteristics. Moreover, the ZIBs deliver a high energy density of 394.8 W·h/kg at a power density of 141.6 W/kg. Additionally, a Zn metal-free aqueous Zn-ion battery is successfully assembled with PANI@WMoO 3 NRs/CC as anode and a ZnMnO 4 as cathode, which exhibits an excellent specific capacity of 247.3 mA·h/g at 0.2 A/g, good rate capability and cyclic stability (∼94.7 % after 1,000 cycles), signifying the practicability of PANI@WMoO 3 NRs/CC as an intercalated anode for Zn2+ ion full batteries. [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]

A facile, cost effective and additive-free successive ionic layer adsorption and reaction (SILAR) technique is demonstrated to develop layer-by-layer (LbL) assembly of reduced graphene oxide (RGO) and MnO 2 (MnO 2 -RGO SILAR ) on a stainless steel current collector, for designing light-weight and small size supercapacitor electrode. The transmission electron microscopy and field emission scanning electron microscopy images shows uniform distribution of RGO and MnO 2 in the MnO 2 -RGO SILAR . The LbL (MnO 2 -RGO SILAR ) demonstrates improved physical and electrochemical properties over the hydrothermally prepared MnO 2 -RGO (MnO 2 -RGO Hydro ). The electrochemical environment of MnO 2 -RGO SILAR is explained by constant phase element in the high frequency region, and a Warburg element in the low frequency region in the Z-View fitted Nyquist plot. The equivalent circuit of the MnO 2 -RGO Hydro , displays the co-existence of EDL and constant phase element, indicating inhomogeneous distribution of MnO 2 and RGO by the hydrothermal technique. An asymmetric supercapacitor device is designed with MnO 2 -RGO SILAR as positive electrode, and thermally reduced GO (TRGO) as negative electrode. The designed cell exhibits high energy density of ∼88 Wh kg −1 , elevated power density of ∼23,200 W kg −1 , and ∼79% retention in capacitance after 10,000 charge-discharge cycles. [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]

• MXene-carbon fiber (W-MX/CF) was prepared by the wet-spinning method. • W-MX/CF-4 (negatrode) and NiCo 2 S 4 -13@W-MX-4 (positrode) were derived from W-MX/CF. • A solid-state asymmetric fiber-shaped supercapacitor (SS-AFSSC) was assembled. • The SS-AFSSC delivered an energy density of 40.70 mWh/cm3. Fiber-shaped supercapacitors (FSSCs) are emerging potential power sources for next-generation flexible and wearable miniaturized electronic devices. However, the practical application of FSSCs is hindered by their low energy density due to limited design and constraints in fiber-shaped electrodes production. Herein, a rational design of wet spun MXene (Ti 3 C 2 T x)/PAN fibers derived multichannel porous MXene/Carbon Fiber (W-MX/CF) is reported as a negative electrode (negatrode), and ultrathin NiCo 2 S 4 electrodeposited W-MX/CF (NiCo 2 S 4 @W-MX/CF) as a positive electrode (positrode) for the fabrication of an asymmetric FSSC. It demonstrates high areal capacitance from both the negatrode (C A = 2160 mF cm−2) and positrode (C A = 1421 mF cm−2) fabricated from 80 wt% MXene loaded CF (W-MX/CF-4) with optimized multichannel porous features and faradaic NiCo 2 S 4 nanosheets arrays grown on W-MX/CF-4. Solid-state fiber-shaped asymmetric supercapacitor was assembled using NiCo 2 S 4 -13@W-MX-4 and W-MX/CF-4 as positrode and negatrode, respectively, with PVA/KOH as solid electrolyte. The device exhibits a remarkable energy density of 40.70 mWh cm−3 at a power density of 301.51 mW cm−3, demonstrating an efficient FSSC. The present work shows a novel way to enhance the performance of FSSCs by exploiting synergistic effects between MXene and carbon fiber derived from PAN, prepared by a facile wet-spinning method employing a solvent/non-solvent exchange process. [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]

Abstract: Porous nanostructured composites are emerging electrode materials for energy storage devices. This work reports the fabrication of metal-organic framework (MOF)-derived cobalt telluride-carbon porous structured composite on nickel foam (CoTe@C–NiF) as electrodes for supercapacitor. The CoTe@C–NiF electrode can store charge in different potential regions of 0 to 0.5 V as positive and −0.8 to 0 V as negative electrodes. Benefitting from its bifunctional charge storage property, the CoTe@C–NiF, when employed as electrodes in a symmetric supercapacitor, produces an optimum output voltage of 1.45 V in aqueous alkaline electrolyte, resulting in an energy density of 43.84 Wh Kg−1 at a power density of 738.88 W kg−1, and retains 21.95 Wh Kg−1 even at the high power density of 6173.44 W kg−1. Moreover, the CoTe@C–NiF is reproducible via a large-scalable and straightforward synthesis protocol, comprising two-steps, followed by an annealing process at 400 °C in argon. The results suggest that the CoTe@C–NiF is a promising electrode material for high-performance symmetric supercapacitor. [ABSTRACT FROM AUTHOR]

Transition-metal-based nanomaterials are preferred for electrochemcial supercapacitor applications owing to their low purchasing cost, facile synthesis process and high theoretical electrochemcial performance. However, these materials can not translate their excellent theoretical performance into commendable experimental values. In these circumstances, supercapacitors based on new class of highly conductive and electroactive hybrid nanomaterial are recommended. Herein, for the first time, 2D CuMnO 2 -Mn x O y @graphene foam (GF) hybrid nanomaterial is constructed as a novel electrode material for asymmetric supercapacitor application. The CuMnO 2 -Mn x O y @GF hybrid nanomaterial displays an excellent areal capacitance of 7.82 F cm−2 at a current density value of 3 mA cm−2 , while it also maintains maximum areal capacitance of 67.51% at 60 mA cm−2. The CuMnO 2 -Mn x O y @GF hybrid nanomaterial retains a high capacitance of 92.15% after maximum 10,000 cycles. A high-performance asymmetric supercapacitor device is assembled based on CuMnO 2 -Mn x O y @GF and sulfur-nitrogen-codoped graphene nanosheets (SN-GNs) as positive and negative electrode materials, respectively. The CuMnO 2 -Mn x O y @GF//SN-GNs ASC device shows an ultra-high energy density value of 81.4 W h kg−1 at a minimum power density of 809.5 W kg−1. The CuMnO 2 -Mn x O y @GF//SN-GNs ASC device retains a specific capacitance of 88.88% after 10,000 cycles. The CuMnO 2 -Mn x O y @GF hybrid nanomaterial is beneficial to promote asymmetric supercapacitor device with an excellent electrochemcial performance. ga1 • Unique hierarchical nanosheet arrays of CuMnO2-MnxOy@graphene foam were synthesized. • Multi-valence CuMnO2-MnxOy nanosheet arrays impart rich electroactive sites. • Graphene provides highly conductive track for electrons flow during redox reaction. • Synergistic interaction is displayed with improved electrochemical outcome. • The asymmetric supercapacitor device displays high-energy density. [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]

• 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]

• A hierarchical three-dimensional ternary carbon hybrid nanostructure has been fabricated. • A device with negative CNTs@Gr-CNF and positive NiCo 2 S 4 /Ni electrode is prepared. • The device shows a capacitance of 218 F g−1 at 1 A g−1 and 94.98% retention after 10,000 cycles. • The device shows an energy density of 62.13 Wh kg−1 at 789.66 W kg−1 power. Carbon materials with hierarchical nanostructures are well accepted propitious materials for electrode application in supercapacitor devices. Herein, a hierarchical ternary carbon aerogel structure is designed by integrating graphene (Gr), carbon nanofibers (CNFs), and carbon nanotubes (CNTs). The as-synthesized CNTs@Gr-CNF materials are characterized by different analytical techniques for the electrode application in a supercapacitor. In the three-electrode system, CNTs@Gr-CNF electrode material exhibits an enhanced electrochemical performance in which a high specific capacitance of 521.5 F g−1 was obtained at 0.25 A g−1 along with the excellent capacitance retention of 98% after consecutive 10,000 charge-discharge cycles at 5 A g−1 in 6 M KOH. In addition, a hybrid supercapacitor device based on CNTs@Gr-CNF as the negative electrode and NiCo 2 S 4 nanoneedle grown on nickel foam as the positive electrode was fabricated. The hybrid device shows 218 F g−1 of specific capacitance at 1 A g−1 and an energy density of 62.13 Wh Kg−1 at a power density of 789.66 W kg−1. Moreover, the device exhibits an excellent cyclic stability with the retention of 91.7% of its specific capacitance after 10,000 charge-discharge cycles. The obtained results signify that the CNTs@Gr-CNF material possesses highly desirable properties for negative electrode application in advanced hybrid supercapacitor. [ABSTRACT FROM AUTHOR]