Flexible Polyester Cellulose Paper Supercapacitor with a Gel Electrolyte

A low-cost polyester cellulose paper has been used as a substrate for a flexible supercapacitor device that contains aqueous carbon nanotube ink as the electrodes and a polyvinyl alcohol (PVA)-based gel as the electrolyte. Gel electrolytes have attracted much interest due to their solvent-holding capacity and good film-forming capability. The electrodes are characterized for their conductivity and morphology. Because of its high conductivity, the conductive paper is studied in supercapacitor applications as active electrodes and as separators after coating with polyvinylidene fluoride. Carbon nanotubes deposited on porous paper are more accessible to ions in the electrolyte than those on flat substrates, which results in higher power density. A simple fabrication process is achieved and paper supercapacitors are tested for their performance in both aqueous and PVA gel electrolytes by using galvanostatic and cyclic voltammetry methods. A high specific capacitance of 270 F g⁻¹ and an energy density value of 37 W h kg⁻¹ are achieved for devices with PVA gel electrolytes. Furthermore, this device can maintain excellent specific capacitance even under high currents. This is also confirmed by another counter experiment with aqueous sulfuric acid as the electrolyte. The cycle life, one of the most critical parameters in supercapacitor operations, is found to be excellent (6000 cycles) and less than 0.5 % capacitance loss is observed. Moreover, the supercapacitor device is flexible and even after twisting does not show any cracks or evidence of breakage, and shows almost the same specific capacitance of 267 F g⁻¹and energy density of 37 W h kg⁻¹. This work suggests that a paper substrate can be a highly scalable and low-cost solution for high-performance supercapacitors.     

Rational Design of Porous Structured Nickel Manganese Sulfides Hexagonal Sheets-in-Cage Structures as an Advanced Electrode Material for High-Performance Electrochemical Capacitors

The design of hierarchical electrodes comprising multiple components with a high electrical conductivity and a large specific surface area has been recognized as a feasible strategy to remarkably boost pseudocapacitors. Herein, we delineate hexagonal sheets-in-cage shaped nickel–manganese sulfides (Ni-Mn-S) with nanosized open spaces for supercapacitor applications to realize faster redox reactions and a lower charge-transfer resistance with a markedly enhanced specific capacitance. The hybrid was facilely prepared through a two-step hydrothermal method. Benefiting from the synergistic effect between Ni and Mn active sites with the improvement of both ionic and electric conductivity, the resulting Ni-Mn-S hybrid displays a high specific capacitance of 1664 F g⁻¹ at a current density of 1 A g⁻¹ and a capacitance of 785 F g⁻¹ is maintained at a current density of 50 A g⁻¹, revealing an outstanding capacity and rate performance. The asymmetric supercapacitor device assembled with the Ni-Mn-S hexagonal sheets-in-cage as the positive electrode delivers a maximum energy density of 40.4 Wh kg⁻¹ at a power density of 750 W kg⁻¹. Impressively, the cycling retention of the as-fabricated device after 10 000 cycles at a current density of 10 A g⁻¹ reaches 85.5 %. Thus, this hybrid with superior capacitive performance holds great potential as an effective charge-storage material.     

Supercapacitor based on graphene and ionic liquid electrolyte

A new kind of supercapacitor by using chemical reduced graphene (CRG) as electrode material and ionic liquid with addition of acetonitrile as electrolyte is assembled and investigated. CRG materials with high surface area are prepared by chemical reduction of graphene oxide. The capacitive properties of the supercapacitor composed of the CRG and ionic liquid electrolyte are studied by electrical impedance spectroscopy, cyclic voltammetry and galvanostatic charge–discharge. With the combined advantages of graphene and ionic liquid, the supercapacitor shows perfect performance. The supercapacitor possesses wide cell voltage and good stability. The specific capacitance, energy density, and specific power density of the present supercapacitor are 132 Fg⁻¹, 143.7 Wh kg⁻¹, and 2.8 kW kg⁻¹, respectively. The results demonstrate the potential application of electrical energy storage devices with high performance based on this new kind of supercapacitor.

     

A hexaazatriphenylene-based porous organic polymer for high performance supercapacitor

Porous organic polymers (POPs) with high physiochemical stability and pseudocapacitive activity are crucial for supercapacitors with high specific capacitance and long cycle life. We report herein a hexaazatrinaphthylene-based POP (HPOP-1) for high-performance supercapacitor by introducing redox-active hexaazatrinaphthylene (HATN) moiety through Sonogashira–Hagihara coupling reaction. HATN moiety can undergo a proton-induced electron transfer redox reaction, which endows HPOP-1 with high pseudocapacitive activity. As electrode materials for supercapacitor application, HPOP-1 exhibits high specific capacitance (667 F g⁻¹ at 0.5 A g⁻¹) and long-term cyclic stability (90% capacitance retention after 10,000 cycles at 5 A g⁻¹) in a three-electrode system with 1 M H₂SO₄ as the electrolyte. In addition, HPOP-1 also exhibits a specific capacitance of 376 F g⁻¹ at 0.5 A g⁻¹ in 1 M KOH electrolyte. An asymmetric supercapacitor was further fabricated with HPOP-1 as negative electrode and rGO as positive electrode, respectively. The device delivers a specific capacitance of 63 F g⁻¹ at 0.5 A g⁻¹ and a rate performance of 37 F g⁻¹ at 5 A g⁻¹. Our work provides a facile approach for the design and preparation of pseudocapacitive POPs with high specific capacitance and long cycle life.     

A High-Performance Asymmetric Supercapacitor Based on Tungsten Oxide Nanoplates and Highly Reduced Graphene Oxide Electrodes

Tungsten oxide/graphene hybrid materials are attractive semiconductors for energy-related applications. Herein, we report an asymmetric supercapacitor (ASC, HRG//m-WO₃ ASC), fabricated from monoclinic tungsten oxide (m-WO₃) nanoplates as a negative electrode and highly reduced graphene oxide (HRG) as a positive electrode material. The supercapacitor performance of the prepared electrodes was evaluated in an aqueous electrolyte (1 m H₂SO₄) using three- and two-electrode systems. The HRG//m-WO₃ ASC exhibits a maximum specific capacitance of 389 F g⁻¹ at a current density of 0.5 A g⁻¹, with an associated high energy density of 93 Wh kg⁻¹ at a power density of 500 W kg⁻¹ in a wide 1.6 V operating potential window. In addition, the HRG//m-WO₃ ASC displays long-term cycling stability, maintaining 92 % of the original specific capacitance after 5000 galvanostatic charge–discharge cycles. The m-WO₃ nanoplates were prepared hydrothermally while HRG was synthesized by a modified Hummers method.     

Perovskite SrCo0.9Nb0.1O3−δ as an Anion‐Intercalated Electrode Material for Supercapacitors with Ultrahigh Volumetric Energy Density

We have synthesized and characterized perovskite‐type SrCo_0.9Nb_0.1O_3−δ (SCN) as a novel anion‐intercalated electrode material for supercapacitors in an aqueous KOH electrolyte, demonstrating a very high volumetric capacitance of about 2034.6 F cm⁻³ (and gravimetric capacitance of ca. 773.6 F g⁻¹) at a current density of 0.5 A g⁻¹ while maintaining excellent cycling stability with a capacity retention of 95.7 % after 3000 cycles. When coupled with an activated carbon (AC) electrode, the SCN/AC asymmetric supercapacitor delivered a specific energy density as high as 37.6 Wh kg⁻¹ with robust long‐term stability.     

High Energy Density Heteroatom (O,N and S) Enriched Activated Carbon for Rational Design of Symmetric Supercapacitors

Carbon-based symmetric supercapacitors (SCs) are known for their high power density and long cyclability, making them an ideal candidate for power sources in new-generation electronic devices. To boost their electrochemical performances, deriving activated carbon doped with heteroatoms such as N, O, and S are highly desirable for increasing the specific capacitance. In this regard, activated carbon (AC) self-doped with heteroatoms is directly derived from bio-waste (lima-bean shell) using different KOH activation processes. The heteroatom-enriched AC synthesized using a pretreated carbon-to-KOH ratio of 1:2 (ONS@AC-2) shows excellent surface morphology with a large surface area of 1508 m² g⁻¹. As an SC electrode material, the presence of heteroatoms (N and S) reduces the interfacial charge-transfer resistance and increases the ion-accessible surface area, which inherently provides additional pseudocapacitance. The ONS@AC-2 electrode attains a maximum specific capacitance (C_sp) of 342 F g⁻¹ at a specific current of 1 Ag⁻¹ in 1 m NaClO₄ electrolyte at the wide potential window of 1.8 V. Moreover, as symmetric SCs the ONS@AC-2 electrode delivers a maximum specific capacitance (C_sc) of 191 F g⁻¹ with a maximum specific energy of 21.48 Wh kg⁻¹ and high specific power of 14 000 W kg⁻¹ and excellent retention of its initial capacitance (98 %) even after 10000 charge/discharge cycles. In addition, a flexible supercapacitor fabricated utilizing ONS@AC-2 electrodes and a LiCl/polyvinyl alcohol (PVA)-based polymer electrolyte shows a maximum C_sc of 119 F g⁻¹ with considerable specific energy and power.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

High performance pliable supercapacitor fabricated using activated carbon nanospheres intercalated into boron nitride nanoplates by pulsed laser ablation technique

Pliable supercapacitor, yielding specific capacitance (C_s) and energy density as high as 348 F g⁻¹ and 48.3 Wh Kg⁻¹ respectively was fabricated using modified activated carbon electrodes. The nanospheres of activated carbon (AC) were anchored on the nanoplates of boron nitride (BN) by employing the facile technique of pulsed laser ablation in liquid (PLAL) using 532 nm focused laser beam. Four different variants of electrode materials were synthesized by varying the weight percentage (1%, 3%, 5% and 10%) of BN in AC in the PLAL precursor solution. The morphological characteristics, the elemental composition and the structural analysis of the synthesized electrode materials were studied respectively by FESEM, XPS and XRD. The morphological studies indicated that the PLAL synthesis of the electrode materials resulted in proper intercalation of carbon nanospheres into BN nanoplates, which resulted in the observed enhanced performance of the fabricated supercapacitor. Four supercapacitors in this work were fabricated using the four variants of synthesized electrode materials in conjunction with gel polymer electrolyte (GPE). GPE are well known for their non-corrosive nature and best sealing ability to avoid any leakage that results in increasing the cycle life of the device. The performance of the fabricated supercapacitors was evaluated using cyclic voltammetry (CV), galvanostatic charge discharge (GCD) measurement and electrochemical impedance spectroscopy (EIS). The results indicate that the supercapacitor fabricated using 3% BN in AC as electrode material manifested the best specific capacitance and energy density. Also it was found that the supercapacitor maintained 85% of its initial capacitance even after 5000 charge/discharge cycles.     

Strong and Robust Polyaniline‐Based Supramolecular Hydrogels for Flexible Supercapacitors

We report a supramolecular strategy to prepare conductive hydrogels with outstanding mechanical and electrochemical properties, which are utilized for flexible solid‐state supercapacitors (SCs) with high performance. The supramolecular assembly of polyaniline and polyvinyl alcohol through dynamic boronate bond yields the polyaniline–polyvinyl alcohol hydrogel (PPH), which shows remarkable tensile strength (5.3 MPa) and electrochemical capacitance (928 F g^?1). The flexible solid‐state supercapacitor based on PPH provides a large capacitance (306 mF cm^?2 and 153 F g^?1) and a high energy density of 13.6 Wh kg^?1, superior to other flexible supercapacitors. The robustness of the PPH‐based supercapacitor is demonstrated by the 100 % capacitance retention after 1000 mechanical folding cycles, and the 90 % capacitance retention after 1000 galvanostatic charge–discharge cycles. The high activity and robustness enable the PPH‐based supercapacitor as a promising power device for flexible electronics.     

Post-synthetic Modification of Covalent Organic Frameworks through in situ Polymerization of Aniline for Enhanced Capacitive Energy Storage

Covalent organic frameworks (COFs) having layered architecture with open nanochannels and high specific surface area are promising candidates for energy storage. However, the low electrical conductivity of two-dimensional COFs often limits their scope in energy storage applications. The conductivity of COFs can be enhanced through post-synthetic modification with conducting polymers. Herein, we developed polyaniline (PANI) modified triazine-based COFs via in situ polymerization of aniline within the porous frameworks. The composite materials showed high conductivity of 1.4–1.9×10⁻² S cm⁻¹ at room temperature with a 20-fold enhancement of the specific capacitance than the pristine frameworks. The fabricated supercapacitor exhibited a high energy density of 24.4 W h kg⁻¹ and a power density of 200 W kg⁻¹ at 0.5 A g⁻¹ current density. Moreover, the device fabricated using the conducting polymer-triazine COF composite could light up a green light-emitting diode for 1 min after being charged for 10 s.     

Ultrathin Mn Doped Ni-MOF Nanosheet Array for Highly Capacitive and Stable Asymmetric Supercapacitor

In this study, we demonstrate that an Mn-doped ultrathin Ni-MOF nanosheet array on nickel foam (Mn_0.1-Ni-MOF/NF) serves as a highly capacitive and stable supercapacitor positive electrode. The Mn_0.1-Ni-MOF/NF shows an areal capacity of 6.48 C cm⁻² (specific capacity C: 1178 C g⁻¹) at 2 mA cm⁻² in 6.0 m KOH, outperforming most reported MOF-based materials. More importantly, it possesses excellent cycle stability to maintain 80.6 % capacity after 5000 cycles. An asymmetric supercapacitor device utilizing Mn_0.1-Ni-MOF/NF as the positive electrode and activated carbon as the negative electrode attains a high energy density of 39.6 Wh kg⁻¹ at 143.8 Wkg⁻¹ power density with a capacitance retention of 83.6 % after 5000 cycles.     

High-performance Flexible Symmetric Supercapacitor Based on Heterostructured PANI@MoS2 Nanocomposite Electrode

Three-dimensional (3D) heterostructured molybdenum disulfide (MoS₂) is used as base materials for aniline monomer in situ polymerization on its surface. It is found that the aniline addition has a remarkable effect on the energy storage of the final compounds due to the improvement of the conductivity and structure stability combined with the synergistic effect between the two types of species. The optimal compound of PANI@MoS₂-150 not only shows a high capacitance value of 801.4 F ⋅ g⁻¹ at a current density of 0.5 A ⋅ g⁻¹ but also provides a high retention rate of 77.4 % after 10,000 cycles. The capacitance fading may be due to the increase of the internal resistance analyzed by EIS. Furthermore, a flexible symmetric supercapacitor based on PANI@MoS₂-150 has also been fabricated and the specific capacitance reaches 105 F ⋅ g⁻¹ at a current density of 1 A ⋅ g⁻¹. Impressively, the capacitance retention is larger than 100 % undergoing 10,000 cycles. Besides, the highest energy density of 21 Wh ⋅ kg⁻¹ was obtained. Additionally, the fabricated symmetric supercapacitor demonstrates excellent flexibility.     

ZIFs骨架型双壳层纳米笼状CoS/NiCo2S4的制备及其电化学性能

采用离子刻蚀和化学气相沉积法制备出具有沸石咪唑酯骨架(ZIFs)型双壳层纳米笼状的CoS/NiCo_2S_4并组装成超级电容器。该结构有较大的比表面积(98 m2·g-1),合适的孔道(孔径4 nm),且保留了ZIFs骨架构型。作为电极活性材料时,具有良好的结构稳定性和电化学活性,有利于增强所组装的超级电容器的循环稳定性和比容量。在三电极体系中,在1 A·g-1的电流密度下,容量为1 230 F·g-1;在3 A·g-1电流密度下循环9 000圈后,初始电容保持率为76.6%。在以该电极、活性炭电极与KOH/聚乙烯醇(PVA)凝胶态电解质组装的器件中,当功率密度为702 W·kg-1时,能量密度达31.6 Wh·kg-1;在7 056 W·kg-1的高功率密度下,仍保持16.5 Wh·kg-1的能量密度。     

Cold-Resistant Nitrogen/Sulfur Dual-Doped Graphene Fiber Supercapacitors with Solar–Thermal Energy Conversion Effect

Although graphene fiber-based supercapacitors are promising for wearable electronic devices, the low energy density of electrodes and poor cold resistance of aqueous electrolytes limit their wide application in cold environments. Herein, porous nitrogen/sulfur dual-doped graphene fibers (NS-GFs) are synthesized by hydrothermal self-assembly followed by thermal annealing, exhibiting an excellent capacitive performance of 401 F cm⁻³ at 400 mA cm⁻³ because of the synergistic effect of heteroatom dual-doping. The assembled symmetric all-solid-state supercapacitor with polyvinyl alcohol/H₂SO₄/graphene oxide gel electrolyte exhibits a high capacitance of 221 F cm⁻³ and a high energy density of 7.7 mWh cm⁻³ at 80 mA cm⁻³. Interestingly, solar–thermal energy conversion of the electrolyte with 0.1 wt % graphene oxide extends the operating temperature range of the supercapacitor to 0 °C. Furthermore, the photocatalysis effect of the dual-doped heteroatoms increases the capacitance of NS-GFs. At an ambient temperature of 0 °C, the capacitance increases from 0 to 182 F cm⁻³ under 1 sun irradiation because of the excellent solar light absorption and efficient solar–thermal energy conversion of graphene oxide, preventing the aqueous electrolyte from freezing. The flexible supercapacitor exhibits a long cycle life, good bending resistance, reliable scalability, and ability to power visual electronics, showing great potential for outdoor electronics in cold environments.     

Two-Dimensional Layered Metallic VSe2/SWCNTs/rGO Based Ternary Hybrid Materials for High Performance Energy Storage Applications

In this work, the ternary hybrid structure VSe₂/SWCNTs/rGO is reported for supercapacitor applications. The ternary composite exhibits a high specific capacitance of 450 F g⁻¹ in a symmetric cell configuration, with maximum energy density of 131.4 Wh kg⁻¹ and power density of 27.49 kW kg⁻¹. The ternary hybrid also shows a cyclic stability of 91 % after 5000 cycles. Extensive density functional theory (DFT) simulations on the structure as well as on the electronic properties of the binary hybrid structure VSe₂/SWCNTs and the ternary hybrid structure VSe₂/SWCNTs/rGO have been carried out. Due to a synergic effect, there are enhanced density of states near the Fermi level and higher quantum capacitance for the hybrid ternary structure compared to VSe₂/SWCNTs, leading to higher energy and power density for VSe₂/SWCNTs/rGO, supporting our experimental observation. Computed diffusion energy barrier of electrolyte ions (K⁺) predicts that ions move faster in the ternary structure, providing higher charge storage performance.     

Mn3−xFexO4 Hollow Nanostructures for High-Performance Asymmetric Supercapacitor Applications

Design of hollow nanostructure and controllable phase of mixed metal oxides for improving performance in supercapacitor applications is highly desirable. Here we demonstrate the rational design and synthesis of Mn_3−xFe_xO₄ hollow nanostructures for supercapacitor applications. Owing to high porosity and the specific surface area that provides more active sites for electrochemical reactions, the electrochemical performance of Mn_3−xFe_xO₄ hollow nanostructure substantially enhanced comparing with pristine Mn₃O₄. Particularly, in 1.0 M KOH electrolyte, Mn_0.16Fe_2.84O₄ with a typical diameter of 20 nm exhibits excellent specific capacitance of 2675, 2320, 1662, 987 F g⁻¹ at current densities of 1, 2, 5, 10 A g⁻¹, respectively, which is significantly superior to those of other transition metal oxides. Besides, an asymmetric supercapacitor is assembled by using Mn_0.16Fe_2.84O₄ and activated carbon as a positive and a negative electrode, respectively. Electrochemical results indicate a high energy density of 42 Wh kg⁻¹ at a power density of 0.75 kW kg⁻¹, which makes this hollow nanostructure a highly promising electrode for achieving high-performance next-generation supercapacitors.     

Enhanced Supercapacitor Performance Using a Co3O4@Co3S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃O₄ and Co₃S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃O₄@Co₃S₄ nanocomposite, the nanostructure of Co₃S₄ was fabricated from Co₃O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm⁻² (5651.24 F g⁻¹) at a current density of 6 mA cm⁻² compared to the Co₃O₄/rGO/NF electrode with a capacitance of 3.06 F cm⁻² (1230.77 F g⁻¹) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg⁻¹, specific power density of 6048.03 W kg⁻¹ and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s⁻¹). Finally, by using Co₃O₄ @Co₃S₄/rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm⁻² at the applied current density of 1 mA cm⁻², and delivered an energy density of 0.143 Wh kg⁻¹ at the power density of 5.42 W kg⁻¹.     

Hierarchical FeCo2S4@FeNi2S4 Core/Shell Nanostructures on Ni Foam for High-Performance Supercapacitors

The design of electrode materials with rational core/shell structures is promising for improving the electrochemical properties of supercapacitors. Hence, hierarchical FeCo₂S₄@FeNi₂S₄ core/shell nanostructures on Ni foam were fabricated by a simple hydrothermal method. Owing to their structure and synergistic effect, they deliver an excellent specific capacitance of 2393 F g⁻¹ at 1 A g⁻¹ and long cycle lifespan as positive electrode materials. An asymmetric supercapacitor device with FeCo₂S₄@FeNi₂S₄ as positive electrode and graphene as negative electrode exhibited a specific capacitance of 133.2 F g⁻¹ at 1 A g⁻¹ and a high energy density of 47.37 W h kg⁻¹ at a power density of 800 W kg⁻¹. Moreover, the device showed remarkable cycling stability with 87.0 % specific-capacitance retention after 5000 cycles at 2 A g⁻¹. These results demonstrate that the hierarchical FeCo₂S₄@FeNi₂S₄ core/shell structures have great potential in the field of electrochemical energy storage.     

Flaky Structured V2O5: Morphology,Formation Scheme and Supercapactive Performance

Vanadium pentoxide (V₂O₅) based electrodes for energy storage devices have captured sizeable attention in the past decade owing to their attractive physiochemical features. In the present work, flaky structured V₂O₅ was prepared using a single step hydrothermal route. The results from analytical investigations hold up well with the formation scheme proposed. The flaky morphology of V₂O₅ facilitates additional pathways for electron transport and effective ion access. When employed as a supercapacitor electrode in a neutral electrolyte, this flaky V₂O₅ electrode demonstrates a specific capacitance of 472 F g^?1. Besides, it retains maximum capacitance at higher current density confirming its good rate performance. An asymmetric type supercapacitor using flaky V₂O₅ as positive electrode and activated carbon as negative electrode exhibits specific capacitance of 69 F g^?1. This device shows energy density of 10 W h kg^?1 within the operational window of 1 V.