Good Capacitance Research Articles

Low Cost Commercially Available Block Copolymer Derived Highly Porous Carbon for Advanced Supercapacitors

Increasing global warming and CO2 emission have created an urgent requirement of clean and green energy solutions which can resolve these issues. These energy solutions include fuel cells, batteries, and supercapacitors (SCs). Among them SCs are the devices of prime importance owing to their long cycle life (>106 charge discharge cycles) and wide applicability in variety of fields. Carbon based SC are commercialized and are being utilized worldwide, however their energy density (ED) is still limited to ~ 5 Wh.kg-1. Researchers have tried and reported various ways to improve its ED and overall performance. The surface area and porosity play a crucial role in deciding the overall performance of SCs. The higher specific surface area (SSA) and hierarchical pore structure with the good conductivity values are the desirable properties for the most suitable carbon electrode material. Block copolymers taking the advantage of structure directing property makes them suitable for tunning the surface area and porosity of product carbon material.Here, we have used the commercially available low-cost block copolymers including F127, and Brij-58 for the preparation of highly porous carbon materials. We have used low-cost glucose as the carbon precursor with KOH activation for improving the surface area values. The brief synthesis route includes the first step as the self-assembly of block copolymer template in the solvents like D.I. water and THF. Then the impregnation of carbon material is followed with the refluxing procedure followed by the hydrothermal treatment at 180 ºC for 5 h. Then the KOH activation and the further carbonization at various temperatures 700, 800 and 900 is performed. All the samples then washed with 5% HCl solution followed by repetitive D.I., methanol and ethanol washing. The final black colored powder is then utilized for various material and SC characterizations.The as synthesized material shows broad peaks around 25º in powder x-ray diffraction pattern. Moreover, the BET surface area measurement predicted the SSA in the range of 500-600 m2.g-1 for most of the samples. These SSA values are pretty much desirable for good capacitance storage. In addition to this the FESEM images shown in Figure 1 confirms the formation of spherical particles due to the structure direction of block copolymers. Along with this, the structural characterization including EDS and XPS further confirms the good carbon content in the developed material.The various developed materials were then tested for SC electrode in three electrode and two electrode measurements. The F127 directed carbon material has exhibited the maximum performance of ~ 250 F.g-1 at the scan rate of 5 mV.s-1, which is very good keeping in mind the low cost strategy for the synthesis of material. In two electrode packed device, the materials shows excellent specific energy of ~15 Wh.kg-1 with high specific power of 270 W.kg-1.Figure 1. a) low magnification FESEM image showing the formation of spherical shape particles directed by F127, b) high magnification image showing the single spherical particle directed by Brij 58, c) three electrode CV results at various scan rates for F127 derived spheres. Figure 1

Redox-Active Organic Molecules and Modified Graphene-Based Materials As Active Material Composites for Supercapacitor Applications

Green and sustainable energy demand has directed the modern world toward producing clean energy storage devices to cut down fossil fuel consumption. Supercapacitors are energy storage devices that have attracted much attention due to owning outstanding properties. Supercapacitors use two main mechanisms to storge charge: I) electrical double layer II) pseudocapacitance. Graphene-based materials have shown promising performance in supercapacitors due to their high surface area and proper electrical conductivity. One of the challenges of working with graphene is the restacking of the graphene sheets, leading to poor performance and lower capacitance. Studies have used doping graphene with different heteroatoms as one of the techniques to overcome the restacking and enhancement of its electrochemical performance. Moreover, redox-active organic molecules, including anthraquinones, phenols, and phenathrequinones, also can be employed to modify graphene.In this work we develop composite active material structures consisting of modified graphene-based materials and organic molecules containing redox active functional groups to provide pseudo-capacitance capabilities. By combining these materials, specific capacitance values above 600 F/g were obtained (at cyclic voltammetry scan rates of 50 mV/s) along with good capacitance retention following repeated electrochemical cycling. In this presentation we will discuss the influence of synthesis route and processing parameters and the resulting structures and performance of the active supercapacitor materials. By correlating these results, we provide insight into the energy storage mechanisms and durability considerations pertaining to these hybrid materials.

High performance multi-color prussian blue/poly(indole-5-carboxylic acid) nanocomposites with multiple layer nanosphere structure for electrochromic supercapacitor application

A novel Prussian blue/poly(indole-5-carboxylic acid) (PB/P5ICA) nanocomposites with multiple layer nanosphere structure are successfully prepared. The structure and morphology of the prepared PB/P5ICA nanocomposites are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), Raman and X-ray photoelectron spectroscopy (XPS) techniques. Due to the synergistic effect of the electrochromic properties of PB and P5ICA, the PB/P5ICA nanocomposites have good electrochromic performance and rich color changes, which can be reversibly changed among light yellow, light green, blue, and yellow-green. In addition, PB/P5ICA also shows good capacitance performance and cycle stability. The specific capacitance value reaches up to 98.12 mF cm−2 (723.48 F g−1) at the current density of 0.2 mA cm−2, which is much higher than PB and P5ICA at the same current density. A symmetric electrochromic supercapacitor device (ESD) is fabricated based on the PB/P5ICA nanocomposite. The supercapacitive properties, color changes and cycle stability of the device are also studied. The results indicate that the device has good energy storage capacity. When the current density is 0.2 mA cm−2, the specific capacitance of the device is 36.2 mF cm−2 (321.09 F g−1). Moreover, the color of the electrode material changes obviously during the charging and discharging process of the device, which can realize the visual monitoring of the device’s energy storage state. Through long-term cyclic voltammetry (CV) and galvanostatic charge and discharge (GCD) test, the device shows good cycle stability. The research is of great significance to the preparation of multifunctional energy storage materials and the application of electronic devices.

A novel hybridized needle-like Co3O4/N-CNO composite for superior energy storage asymmetric supercapacitors

The controlled growth of needle-like Co3O4 and composite formation with highly graphitic carbons such as N-CNOs is critically essential for obtaining high-performance energy storage supercapacitors. In this study, the needle-like Co3O4 and graphitic N-CNOs are synthesized by the simple solvothermal and pyrolysis methods, respectively. The Co3O4/N-CNO composite enhances the fast charge transfer by reducing ion diffusion. The Co3O4/N-CNO composite demonstrated an improved specific capacitance (3066 F g−1) than the needle-like structure of Co3O4 (2068 F g−1). The Co3O4/N-CNO composite exhibited very good rate capability and high capacitance retention of 82% at a high current density of 8 A g−1 meanwhile the Co3O4/N-CNO//AC ASC device shows high power and energy densities with capacitance retention of 78% and Coulombic efficiency of 100% over 2000 cycles. This attractive electrochemical performance of Co3O4/N-CNO composite makes it a favorable device for practical applications of supercapacitors.

Nanosized V2CTx with Boosting Super Capacitance via Engineering Alkalization Assisted K+ Interlayer Coordination

Although V2CTx MXenes is extremely attractive as electrodes for supercapacitors, a bottleneck that restricted its application was set due to the lengthened ion pathway and the resulting F-based surface terminations, which creates a barrier for the V2CTx to achieve increased capacity. In this work, the nano-sized V2CTx with enlarged interlayer space and decreased F-based surface terminations was synthesized by alkalization assisted K+ interlayer coordination, exhibiting an ultra-high capacitance of 665 F g−1 at 2 mV s−1 in 1 M H2SO4 with capacitance retention rates of 81.9% after 10000 charge/discharge cycles. Moreover, it also produces a good specific capacitance in Li2SO4 and KOH with excellent stability. This excellent performance can be attributed to the porous structure with atomic increase of interlayer spacing (0.969 nm), reduced flake size, as well as small holes generated, which will greatly shorten ion transport and provide an ion “highway.”

Enhanced electrochemical performance of porous carbon from wheat straw as remolded by hydrothermal processing

To improve the electrochemical properties of lignocellulose-derived carbon, wheat straw was hydrothermally processed at different temperatures followed by KOH activation for the preparation of porous carbons. Their physical, chemical, and electrochemical properties were analyzed to clarify the effects of hydrothermal processing. The results indicated that high-temperature hydrothermal processing fragmented the wheat straw and increased the heteroatoms content to make the hydrochars more conducive to activation, thereby improving the specific surface area, N-heteroatoms and phenolic hydroxyl groups of activated carbons. A maximum specific surface area of 2034.4 m2 g−1 was achieved by HAC-300 (the activated carbon derived from hydrothermally processed wheat straw at 300 °C) with more N-heteroatoms and phenolic hydroxyl groups. Correspondingly, the excellent electrochemical performance of the three-electrode supercapacitor device assembled by HAC-300 showed a specific capacitance of 286.95 F g−1 at 0.5 A g−1, representing an improvement of 89.5 % over than that of the original wheat straw without hydrothermally processing. Its symmetric supercapacitor also realized a good capacitance retention of 95.8 % after 10,000 cycles at 5 A g−1, suggesting the excellent cycling stability of the porous carbon from the hydrothermally processed wheat straw.

Dielectric, AC Conductivity, and DC Conductivity Behaviours of Sr2CaTeO6 Double Perovskite.

Relatively new double perovskite material, Sr2CaTeO6, has been prepared through conventional solid-state procedures. Structural, dielectric, and optical characteristics of this exquisite solid-state material were analysed in this study. The single-phase monoclinic P21/n structure of this prepared compound was well correlated with the literature review. Good distribution of grain sizes and shapes was observed in the morphological study of this compound. The discussions on its optical and dielectric properties are included in this manuscript. High dielectric real permittivity, low dielectric loss, and good capacitance over a range of temperatures possessed by this compound, as shown in dielectric and electrical modulus studies, indicated good potential values for capacitor applications. The Ro(RgQg)(RgbQgb) circuit fitted well with the impedance and electrical modulus plot of the compound. Its relatively high electrical DC conductivity in grain at high frequencies and its increasing value with the temperature are typical of a semiconductor behaviour. This behaviour might be attributed to the presence of minor oxygen vacancies within its lattice structure and provides a long-range conduction mechanism. A small difference between activation energy and Ea of DC conductivity indicates that the same charge carriers were involved in both grains and the grain boundaries’ long-range conduction. The electrical AC conductivity of this compound was found to contribute to the dielectric loss in grain structure and can be related to Jonscher’s power law. The presence of polarons in this compound was exhibited by non-overlapping small polaron tunnelling (NSPT) and overlapping large polaron tunnelling (OLPT) conduction mechanisms over a range of temperatures. Wide optical band gap and Eopt in the range of 2.6 eV to 3.6 eV were determined by using an indirect and direct allowed mechanism of electrons transitions. These values supported the efficient semiconducting behaviour of the grain in this material and are suitable for applications in the semiconductor industry.

Lx‐β‐NiMoO4 (L = None, Al, V, Fe, Co) Nanocomposites: Facile Solid‐State Synthesis, Magnetic, Optical, and Electrochemical Properties

AbstractSynthesis of a class of Lx‐β‐NiMoO4 (L = None, Al, V, Fe, Co) nanocomposites by a facile one‐step solid‐state route at 700, 800, and 900 °C for 8 h is introduced in the present study. The physical and electrochemical properties of the fabricated compounds are studied by X‐ray powder diffraction (XRPD), field‐emission scanning electron microscope, energy‐dispersive X‐ray spectroscopy, Fourier‐transform infrared spectroscopy, UV‐vis, vibrating sampling magnetometer (VSM), and cyclic voltammetry (CV) analyses. XRPD patterns associated with Rietveld analysis data performed by the FullProf program confirm that the as‐prepared samples are crystallized in the β polymorph monoclinic NiMoO4 crystal system. The magnetic property investigated by VSM analysis data shows that the fabricated samples have ferromagnetic behavior. It is found that the highest Ms value is obtained when Fe3+ is doped into the NiMoO4 crystal system. The smallest direct band gap energy (Eg) is obtained for V‐doped NiMoO4 nanocomposite. The electrochemical property of the prepared NiMoO4 nanocomposites is studied by CV analysis. The data confirm that NiMoO4 can be used in energy storage applications. An impedance spectroscopy plot of NiMoO4 reveals that the Z value is about 30 Ω cm−2. The slope of the curve is near to 90° representing a good capacitance behavior of NiMoO4.

Preparation of N/Ni co-doped cellulose-based porous carbon and its supercapacitor performance

A green and effective nitrogen and nickel in-situ doping strategy was designed to prepare cellulose-based N/Ni co-doped porous carbon (PC). The co-hydrothermal pretreatment induced by hydrazine hydrate and nickel acetate effectively modifies the physico-chemical structure of PC and further improves its electrochemical performance. The efficient N-supply and unique heteroatom regulation performance of hydrazine hydrate is related to its strong reducibility. The specific surface area and total pore volume of the synthesized N4NiPC220-3 are 1383.66 m2 g−1 and 0.59 cm3 g−1, while the N and O contents are 1.35 and 10.41%, respectively. At current densities of 0.5 and 20 A g−1, N4NiPC220-3 exhibits a high specific capacitance of 415 F g−1 and a good capacitance retention of 72.22%, respectively. After 10,000 charge/discharge cycles, the retention rate is as high as 96.06%, confirming its excellent cycling stability. The two-electrode system test results further show that the energy density of N4NiPC220-3 is as high as 35.6 W h kg−1 at a power density of 500.1 W kg−1, while a high retention rate of 87.87% is still obtained after 10,000 cycles. This green and efficient synthesis method based on in-situ co-doping of hydrazine hydrate and nickel acetate is a promising alternative strategy for producing carbon-based supercapacitors.

Design and Preparation of NiCoMn Ternary Layered Double Hydroxides with a Hollow Dodecahedral Structure for High-Performance Asymmetric Supercapacitors

Layered double hydroxides (LDHs) are prospective cathode materials for supercapacitors because of their outstanding theoretical specific capacitance and unique layered structure. However, the finite electroactive sites and cation species confine their practical application in supercapacitors. In this work, a hollow polyhedral ternary metallic Ni2CoMn1-LDH is prepared using zeolitic imidazolate framework-67 (ZIF-67) as the template. It has been found that the hollow dodecahedral structure constructed by thin nanosheets endows the Ni2CoMn1-LDH sample with abundant specific area and more ion-/electron-transport channels, which facilitate ion/electron transfer. Meanwhile, Ni2CoMn1-LDH can achieve the maximum synergistic effect of the different transition metals due to its optimal composition and content, which is conducive to improving the electrochemical behavior of supercapacitors. Benefiting from the advantages of their structure and composition, the as-prepared Ni2CoMn1-LDH electrode presents an excellent capacitance performance of 1634.4 F g–1 at 0.5 A g–1. Moreover, an asymmetric supercapacitor fabricated with a Ni2CoMn1-LDH cathode and an activated carbon (AC) anode reveals a good specific capacitance of 123.4 F g–1 at 1 A g–1 and a maximum energy density of 43.9 Wh kg–1 at a power density of 800 W kg–1. Therefore, constructing ternary LDHs with a unique hollow structure and optimal element composition has a promising prospect in the industrial application of supercapacitors and large-scale energy-storage devices.

Solid-state 3D micro-supercapacitors based on ionogel electrolyte: Influence of adding lithium and sodium salts to the ionic liquid

The ever-increasing interest in miniaturized Internet of Things devices and embedded electronics has given rise to a host of inquiries surrounding the need for safe, high performance energy storage devices. Solid-state 3D micro-supercapacitors based on ionogels provide a promising response to many of these pressing questions. Herein, leakage-free solid-state-like 3D micro-supercapacitors incorporating lithium and sodium salts added to 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide-based ionogels were investigated. The resulting micro-supercapacitors containing these lithium and sodium ions displayed energy densities of 10.2 and 9.5 µWh.cm−2 at power densities of 1.1 and 1.0 mW.cm−2, respectively. In those devoid of these alkaline ions, however, the energy density reached a mere 3 µWh.cm−2 at the same power density, thereby validating the proposed strategy. The 3D interdigitated MnO2 // MnO2 micro-supercapacitors were cycled 50 000 times at 1.75 mA.cm−2 with good capacitance retention (∼ 85 %). While performing under high temperatures (100°C), there was no evidence of electrolyte degradation, capacitance fading or electrolyte leakage.

Preparation of flexible conductive composite electrode film of PEDOT:PSS/Aramid nanofibers via vacuum-assisted filtration and acid post-treatment for efficient solid-state supercapacitor

A highly conductive and flexible composite film of Poly (3,4-ethylenedioxythiophene):polystyrene sulfonate and aramid nanofiber (PEDOT:PSS/ANFs) is prepared by vacuum-assisted filtration and post-treated by acid. The composite displays excellent mechanical integrity under bending together with flexibility, properties being attributed to the strong attachment of PEDOT:PSS onto the surface of the ANFs via hydrogen bonding and the ANF structure, respectively. The conductivity of the prepared composite is progressively enhanced by the post-treatment using sulfuric acids (1 M H2SO4 and 1.5 M H2SO4), reaching 20–25 times higher than that of untreated film. This enhancement is traced to the removal of the insulating PSS group together with an analyzable change in crystallization of the PEDOT:PSS component. However, excessive use of acid treatment is seen to reduce the mechanical strength, and, thus, ultimate loss of conductivity after frequent bending (up to 1000 times), only having 59% conductivity retention with high concentration acid treatment (1.5 M H2SO4) compared to a high conductivity retention of 95% with 1.0 M H2SO4. Adopting the relatively weaker acid enables a balance to be reached between these crucial factors of electrical conductivity versus mechanical integrity. The prepared film of PEDOT: PSS/ANFs treated by acid as an electrode of supercapacitor shows good electrochemical performances, including good volumetric specific capacitance (83.5 F/cm3 with 1.0 M H2SO4 and 75 F/cm3 with 1.5 M H2SO4 at 0.5 A/cm−3), cycle stability and capacitance retention of 83.3% and 87.5% after 2000 cycles, respectively. Furthermore, a solid flexible supercapacitor is finally assembled by the post-treatment of relatively low concentration acid with 1.0 M H2SO4. The configured supercapacitor displays excellent volumetric energy density of 23.44 mW h/cm2 (power density of 399.95 mW/cm2) at a very wide operating potential window of 0–1.6 V and cycle stability. Therefore, it is quite feasible method to fabricate a highly conductive and flexible composite film using PEDOT:PSS and ANFs by vacuum filtration and acid post-treatment, which expects to be a promising flexible composite electrode material applied in the preparation of energy storage devices.

Integrating MXene waste materials into value-added products for smart wearable self-powered healthcare monitoring

MXenes have gained significant attention for development of flexible or wearable electronics. However, intrinsic sediment waste from the MXene production process is usually discarded, greatly decreasing efficiency. Rational use of MXene waste (trash) in wearables may improve economic benefits. Here, a strategy that integrates MXene nanosheets (treasure) with sediment trash is employed to construct a smart wearable self-powered health monitoring system. A flexible solid-state supercapacitor (FSSC) consisting of a robust MXene/polyamide (MX-PA) film delivers good specific capacitance and mechanical properties. An MXene trash-based pressure sensor realizes effective monitoring of physiological signals. By integrating the FSSC and pressure sensor, the self-powered smart system can remotely receive physiological feedback for evaluating human health status. This work explores a feasible strategy to take full advantage of MXene starting materials and may expand scalable fabrication of MXene-based smart wearables in healthcare fields.

Use of a superbase/DMSO/CO2 solvent in order to incorporate cellulose into organic ionogel electrolyte for flexible supercapacitors

The facile preparation of sustainable polymer gel electrolyte by using renewable natural polymers has attracted much attention, and the development of new polymer gel electrolyte materials largely depends on the facile design and preparation of a polymer network capable of effectively loading external high-performance electrolyte. In this study, taking the advantages of a newly developed solvent system superbase/DMSO/CO2 for cellulose, a new and facile “all-in-one” strategy to engineer cellulose into flexible cellulosic poly (protic ionic liquids)/PVA-based composite organic ionogel electrolyte (CPOIE) has been developed through in situ derivatization, chemical cross-linking and compositing strategy using succinic anhydrides, epichlorohydrin, and polyvinyl alcohol, respectively. The findings show that CPOIEs exhibit both excellent mechanical properties and superior electrochemical properties (high ionic conductivity up to 4.2 mS/cm at room temperature with a wide electrochemical window of 2.0 V for C1P1OIE sample). A supercapacitor assembled by using the as-prepared C1P1OIE sample delivers a good specific capacitance of 122 F/g at 0.5 A/g, a high energy density up to 17.38 Wh/Kg at room temperature and an excellent cyclic stability up to 8000 cycles.

Electrochemical method integrating exfoliation and in-situ growth to synthesize MoS2 nanosheets/MnO2 heterojunction for performance-enhanced supercapacitor

Two-dimensional (2D) molybdenum disulfide (MoS2) nanomaterials have become one of the promising options for constructing excellent supercapacitors. However, the application of MoS2 materials is limited by low energy density, and the difficulty of large-scale and low-cost preparation seriously hinders its practical application in the field of energy storage. Here, the exfoliation of the MoS2 nanosheets and the loading of MnO2 nanoparticles on the MoS2 nanosheets are realized in one step by electrochemical method. A series of characterization methods have fully confirmed that the electrochemical method has successfully prepared the MoS2 nanosheet/MnO2 (MoS2 NS/MnO2) heterojunction. The experimental results show that the MoS2 NS/MnO2 heterojunction has better electrochemical performance than a single MoS2 nanosheet. It has a good capacitance even in a neutral solution, and its specific capacitance is 275 F g−1 at a current density of 2 A g−1. In addition, a supercapacitor device based on MoS2 NS/MnO2 heterojunction was constructed, which not only exhibited excellent capacitive performance, but also exhibited 10,000 charge-discharge cycle stability under 10 A g−1 conditions. This work provides an experimental basis for the preparation of 2D nanosheets and the large-scale preparation of functionalized 2D material heterojunctions by electrochemical methods.

CuMoO4 nanostructures: A novel bifunctional material for supercapacitor and sensor applications

Transition metal molybdates are considered a promising candidate for electrochemical applications due to their attractive chemical and physical assets. In this work, we demonstrated the preparation of the CuMoO4 nanostructures via a sonochemical approach and explored its bifunctional property of energy storage and nitrite sensor. Physicochemical and morphological characterization confirmed the formation of CuMoO4 nanostructures. Cyclic voltammograms and galvanostatic charge-discharge (CD) analyses reveal the charge storage in CuMoO4 is faradaic dominated capacitive behavior. The CuMoO4 delivered a high specific electrode capacitance of 281 F g−1 from the CD profile obtained at a current density of 0.5 mA cm−2 and exhibited good capacitance retention of 98% over continuous 3000 cycles. Furthermore, the CuMoO4//AC ASC device delivered a high specific capacitance of 100.23 F g−1 with an extraordinary energy density (31.25 Wh kg−1), power density (661.76 W kg−1) and cycle-life. Furthermore, the CuMoO4 electrode can be used for electrochemical detection of nitrite as confirmed using CV and LSV analysis. In addition, the scanning electrochemical microscopic study confirms the better oxidation current at the electrode/electrolyte surface of the CuMoO4 electrode in the presence of the nitrite solution. Overall, the obtained experimental results highlighted the importance of CuMoO4 nanostructures as an electrode material towards the next-generation electrochemical energy storage and sensing applications.

Improving the surface area of metal organic framework-derived porous carbon through constructing inner support by compatible graphene quantum dots

Metal-organic frameworks (MOFs) have emerged as promising precursors to prepare porous carbons due to their unique coordination structure with abundant pores and various chemical compositions. However, the structural collapse and pore shrinkage during pyrolysis severely decrease the surface area of the prepared porous carbons. Herein, we propose an inner support strategy to prepare MOF-derived carbons with improved surface area using graphene quantum dots (GQDs) as the compatible frameworks. GQDs with abundant carboxyl groups (–COOH) and rigid structure can uniformly distribute in MOF-5 precursor by coordinating with [Zn4O]6+ clusters and effectively reinforce the carbon skeleton during pyrolysis. Therefore, the rational GQDs embedded MOF-5 derived porous carbon (GMPC-0.35) shows greatly improved specific surface area (1841 m2 g−1) and mesopore volume (1.62 cm3 g−1) than pure MOF-5 derived carbon (1358 m2 g−1, 0.59 cm3 g−1). As an application exemplification, GMPC-0.35 performs high specific capacitance of 200 F g−1 at 1 A g−1 and good capacitance retention of 53% at 100 A g−1 as the electrode material for supercapacitors, which are higher than most of the reported MOF-5 derived carbons. Therefore, the compatible GQDs support is promising for preparing functional MOF-derived carbon materials.

Synergistic effect of hydrothermal and physical activation approaches to fabricate activated carbon for energy storage applications

Carbon is the main constituent of all waste biomass. The extraction of activated carbonaceous materials from the waste biomass and their utilization in energy-storage applications is a green, cost-effective strategy. Herein, honeycomb-like activated carbon (AC) with a large surface area (2344 m2g-1) and improved conductivity was derived from palm seeds via hydrothermal followed by CO2 activation approaches. The AC sample was decorated over a carbon cloth (CC) current collector to form a flexible working electrode for next-generation electrochemical capacitors. As-prepared palm seed-derived activated carbon electrode delivered a good specific capacitance (Cs) of 294.9 Fg−1 @ 01 Ag−1, with exceptionally high cycling stability, showing 97.36% retention of its initial capacitance, even after 10,000 charge-discharge cycles in an alkaline electrolyte. The porous structure with microsized cavities enables the activated carbon-based electrode to show excellent rate capability (93.1% capacitance retention) even at nine-fold higher current density. As-prepared flexible electrode exhibits excellent electrochemical performance due to their unique three-dimensional network structure combined with porous architecture and good conductivity. This work provides a facile way to enhance activated carbon's capacitive performance and opens up new avenues for developing high-performance capacitive materials using waste biomass to reduce environmental concerns.

High-Energy-Density Asymmetric Supercapacitor Based on Free-Standing Ti3C2TX@NiO-Reduced Graphene Oxide Heterostructured Anode and Defective Reduced Graphene Oxide Hydrogel Cathode.

The rational design of an asymmetric supercapacitor (ASC) with an expanded operating voltage window has been recognized as a promising strategy to maximize the energy density of the device. Nevertheless, it remains challenging to have electrode materials that feature good electrical conductivity and high specific capacitance. Herein, a 3D layered Ti3C2TX@NiO-reduced graphene oxide (RGO) heterostructured hydrogel was successfully synthesized by uniform deposition of NiO nanoflowers onto Ti3C2TX nanosheets, and the heterostructure was assembled into a 3D porous hydrogel through a hydrothermal GO-gelation process at low temperatures. The resultant Ti3C2TX@NiO-RGO heterostructured hydrogel exhibited an ultrahigh specific capacitance of 979 F g-1 at 0.5 A g-1, in comparison to that of Ti3C2TX@NiO (623 F g-1) and Ti3C2TX (112 F g-1). Separately, a defective RGO (DRGO) hydrogel was found to exhibit a drastic increase in specific capacitance, compared to untreated RGO (261 vs 178 F g-1 at 0.5 A g-1), owing to abundant mesopores. These two materials were then used as free-standing anode and cathode to construct an ASC, which displayed a large operating voltage (1.8 V), a high energy density (79.02 Wh kg-1 at 450 W kg-1 and 45.68 Wh kg-1 at 9000 W kg-1), and remarkable cycling stability (retention of 95.6% of the capacitance after 10,000 cycles at 10 A g-1). This work highlights the unique potential of Ti3C2TX-based heterostructured hydrogels as viable electrode materials for ASCs.

Polyethylene‐Derived Activated Carbon Materials for Commercially Available Supercapacitor in an Organic Electrolyte System

High-performance supercapacitors based on activated carbons (AC) derived from polyethylene (PE), which is one of the most abundant plastic materials worldwide, are fabricated. First, PE carbons (PEC) are prepared via sulfonation, which is a reported solution for successful carbonization of innately non-carbonizable PE. Then, the physico-electrical changes of PECs upon a chemical activation process are explored. Interestingly, upon the chemical activation, PECs are converted ACs with a large surface area and high crystallinity at the same time. Subsequently, PE-derived ACs (PEAC) are exploited as electrode materials for supercapacitors. Resultant supercapacitors based on PEACs exhibit impressive performance. When compared to supercapacitors based on YP50f, representative commercial ACs, devices using PEACs presented considerably good capacitance, low resistance, and great rate capability. Specifically, the retention rate of devices using PEACs is significantly higher than that of YP50f-based devices. At the high rate of charge-discharge situation reaching 7Ag-1 , the capacitance of supercapacitors using PEACs is ≈70% higher than that of YP50f-based devices. It is assumed that the carbon structure accompanying both large surface area and high conductivity endows a great electrochemical performance at the high current operating conditions. Therefore, it is envisioned that PE may be a viable candidate electrode material for commercially available supercapacitors.