Electrochemical Performance For Supercapacitors Research Articles

Fabrication of SrWO4/PPy composite as electrode material for high-performance supercapacitors

The societal major concern of the moment is energy storage, energy production and global warming. Researchers are striving to create novel, highly efficient energy storage materials for developing faster, safer as well as more effective energy storage systems. One effective method to improve the electrochemical performance of supercapacitors (SCs) is the construction of highly efficient electro active materials, employing multivalent binary transition metal oxides (BTMOs) with electrical conducting polymers (CPs). For the first time, we report SrWO4/PPy composite synthesized by In-situ chemical polymerization route. The physio-chemical characteristics of the synthesized material was extensively examined with spectral and analytical techniques. SrWO4/PPy composite on Ni foil was fabricated as an alternate electrode material and was investigated for its capacitive behaviour. SrWO4/PPy electrode achieved a high specific capacitance of 747 Fg-1 at 5 mVs−1 and a remarkable cyclic stability of 93.8% even after 5000 cycles at 1 Ag-1. The notable electrochemical property of the electrode was attributed to its distinctive composite morphology, which is crucial in facilitating high conductivity, quick electron transfer, short ion diffusion distance and excellent active sites for enhanced electrochemical performance. The substantial capacitive behaviour can be attributed to the synergetic effect of SrWO4 and PPy. This work introduces platform to design efficient electrodes for the energy storage devices as well as for wearable electronics.

Preparation and Characterization of Physically Activated Carbon and Its Energetic Application for All-Solid-State Supercapacitors: A Case Study.

Biomass-derived activated carbons have gained significant attention as electrode materials for supercapacitors (SCs) due to their renewability, low-cost, and ready availability. In this work, we have derived physically activated carbon from date seed biomass as symmetric electrodes and PVA/KOH has been used as a gel polymer electrolyte for all-solid-state SCs. Initially, the date seed biomass was carbonized at 600 °C (C-600) and then it was used to obtain physically activated carbon through CO2 activation at 850 °C (C-850). The SEM and TEM images of C-850 displayed its porous, flaky, and multilayer type morphologies. The fabricated electrodes from C-850 with PVA/KOH electrolytes showed the best electrochemical performances in SCs (Lu et al. Energy Environ. Sci., 2014, 7, 2160) application. Cyclic voltammetry was performed from 5 to 100 mV s-1, illustrating an electric double layer behavior. The C-850 electrode delivered a specific capacitance of 138.12 F g-1 at 5 mV s-1, whereas it retained 16 F g-1 capacitance at 100 mV s-1. Our assembled all-solid-state SCs exhibit an energy density of 9.6 Wh kg-1 with a power density of 87.86 W kg-1. The internal and charge transfer resistances of the assembled SCs were 0.54 and 17.86 Ω, respectively. These innovative findings provide a universal and KOH-free activation process for the synthesis of physically activated carbon for all solid-state SCs applications.

Composition engineering strategy of carbon–coated bimetallic phosphide for high energy density hybrid supercapacitors

Bimetallic phosphides hold great promise for using in hybrid supercapacitors (HSCs) as electrode material due to their synergistic effect of hetero-metal ions in ameliorating specific capacity and electrical conductivity. The production of bimetallic Ni1-xCoxP nanocrystals based on carbon-coated (Ni1-xCoxP@C) is described, and their potential application as positive electrodes in HSCs is also discussed. We give an insight into the significance of composition engineering for nickel-cobalt bimetallic phosphides in obtaining excellent electrochemical performance for supercapacitors. Ni0.9Co0.1P@C electrode reaches a maxima specific capacity as high as 4250 ± 48 mC cm−2 at 1 mA cm−2 (1327 ± 15 C g−1 at 1 A g−1), outperforming most transition metal phosphides (TMP)-based electrodes reported recently. Utilizing Ni0.9Co0.1P@C as electrode, the obtained HSC device provides a desired energy density of 46.9 ± 2.2 Wh kg−1 at 1600 W kg−1 and continues to sustain 26.2 ± 1.3 Wh kg−1 at a significant power density of 8000 W kg−1, capacitance retention remaining at 89.4 % after 10,000 cycles. It is believed that the Ni0.9Co0.1P@C has significant promise for application in extremely effective and affordable HSCs, as well as probably in other energy storage devices.

Effects of plasma on electrochemical performance of carbon cloth-based supercapacitor

In this work, the surface of carbon cloth is treated by plasma jet to improve its hydrophilicity. The symmetrical carbon cloth-based supercapacitor is assembled with the carbon cloth treated by plasma as the active electrodes and sodium chloride solution as the electrolyte. With the discharge time (1 min, 2 min, 3 min) and working gas types (argon, air, helium) of plasma as variables, the effects of different plasma on the hydrophilicity of carbon cloth are observed, and the changes of the electrochemical properties of the supercapacitors with single or double carbon cloth electrodes treated by different plasma are studied. The contact angle test results show that the plasma of different working gases can weaken the hydrophobicity of carbon cloth, and the helium plasma can make the carbon cloth change from hydrophobicity to hydrophilicity. The electric capacity calculated by cyclic voltammetry shows that plasma can increase the electric capacity of carbon cloth-based supercapacitors. The electric capacity of carbon cloth-based supercapacitors with two carbon cloth electrodes treated by plasma is larger than that of single carbon cloth electrode treated by plasma. The argon and helium plasma with longer discharge time can significantly improve the electric capacity of carbon cloth-based supercapacitors. The galvanostatic charge-discharge curve shows that different working gases of plasma can make carbon cloth-based supercapacitors obtain pseudocapacitance, increase the charge-discharge time and electric capacity. From the AC impedance spectrum, it can be concluded that the plasma of any kind of working gas can reduce the impedance and charge transfer resistance of the carbon cloth-based supercapacitor. The longer plasma discharge time lead to the smaller impedance, and the impedance of the supercapacitor with both carbon cloth electrodes treated by plasma is smaller.

Synthesis of nitrogen-doped hierarchically porous carbons with ordered mesopores from liquefied wood: Pore architecture manipulation by NH4Cl for improved electrochemical performance

Functional porous carbon materials have attracted significant attentions due to their unique characteristics. Herein, the synthesis of N-doped hierarchically porous carbon (N-HPC) with ordered mesopores from liquefied wood is reported through a soft-templating and chemical blowing method with the assistance of NH4Cl to regulate their pore architectures. The NH4Cl strengthens the interactions between the carbon sources and soft templates in the hydrothermal process to produce carbon materials with highly ordered mesostructure after carbonization. Then, the obtained carbon is ground with NH4Cl, where NH4Cl releases NH3 and HCl upon heating to introduce N atoms and micropores into the carbon structures. Highly ordered p6mm mesostructure, high specific surface area (1160 m2 g−1) and nitrogen content of 3.75 wt% are obtained with the assistance of NH4Cl, which together affords them enhanced electrochemical performance for supercapacitors. The obtained N-HPC electrode displays a specific capacitance of 282 F g−1 at 1 A g−1 and good rate capability.

Microwave-assisted dry synthesis of hybrid electrode materials for supercapacitors: Nitrogen-doped rGO with homogeneously dispersed CoO nanocrystals

In this research work, we have applied a dry microwave (MW) strategy to synthesize uniformly sized CoO nanocrystals homogeneously dispersed on the basal plane of nitrogen-doped reduced graphene oxide nanosheets (N-rGO NSs). The MW treatment is an ultra-fast process for exfoliation and in-situ reduction of graphite oxide and simultaneous decomposition of the cobalt precursor. The results show that during the MW-assisted synthesis process, the graphite oxide is exfoliated, reduced and combined with the available nitrogen from the precursor to form N-rGO NSs. Simultaneously; the Co ions react with oxygen functionalities on surface of N-rGO NSs to form CoO (N-rGO@CoO) nanocrystals. These processes, when combined, effectively prevented the aggregation of the CoO nanocrystals and the re-stacking of the N-rGO layers. The resulting N-rGO@CoO nanocomposites exhibited unique surface morphology and electrochemical performance for supercapacitor (SC) applications. As the SC electrode, the nanocomposite delivered high specific capacitance (744.1 F/g at 5 mV/s) and excellent cyclic stability (91.3 % over 5000 cycles). Thus, the MW-processing method proved to be a rapid, effective, and simple approach for single step synthesis of doped rGO-metal oxide electrodes for SC applications.

Design and regulation of FeCo2S4 nanoneedles deposited on carbon felt as binder-free electrodes for high-performance hybrid supercapacitor

Hybrid supercapacitors have drawn much attention since they possess both high energy density and power density. Carbon felt (CF) is chosen as the substrate in this work due to its 3D porous structure, good conductivity, and excellent flexibility. FeCo2S4 nanoneedles are uniformly deposited on CF via hydrothermal, annealing and sulfidation processes, forming the binder-free FeCo2S4 @CF electrode. The morphology of FeCo2S4 deposited on the CF can be designed and regulated by controlling the hydrothermal reaction time. The electrode with unique features is beneficial to the exposure of electroactive sites and the rapid transport of electrons/ions, showing a high specific capacitance of 847.8 mF cm−2 and outstanding rate performance. The hybrid supercapacitor assembled by FeCo2S4 @CF electrode and activated carbon felt exhibits the maximum specific capacitance of 309.7 mF cm−2, energy density of 110.1 μWh cm−2 and power density of 562.4 μW cm−2. Besides, the capacitance retention of the device reaches 98.5% after 10,000 charge-discharge cycles and 87.2% after 3000 bending cycles respectively, revealing its great cycling stability and flexibility. Therefore, this work provides an effective and feasible strategy for the morphology regulation of binary transition metal sulfides with superior electrochemical performance for supercapacitors.

Phase transformation of α-MnO2 to β- MnO2 induced by Cu doping: Improved electrochemical performance for next generation supercapacitor

With the advent of wearable/portable electronics and hybrid electric vehicles, supercapacitors have gained much interest owing to their high-power density. This work deals with ultralong MnO2 nanowires reinforced with different Cu contents as a new electrode material for supercapacitors fabrication. X-ray diffraction (XRD) results showed the MnO2 phase transformation from α-MnO2 to β- MnO2 induced by Cu doping. β-MnO2 due to its highest structural stability is expected to show the excellent cyclic stability of the electrode material. Field emission scanning electron microscopy (FESEM) confirmed the ultralong nanowires morphology. Ultralong nanowires with extremely interconnected network enable efficient electron transport between them, further enhancing the electrical conductivity of the material. Redox peaks present in the CV profile revealed that the preferred charge storage follows faradic mechanism, which was further confirmed by rate law. Nanosized morphology and spongy structure of the current collector exposed the maximal electrode area in conjunction with shielding from electrode pulverization.

Copper Oxide Nitrogen-Rich Porous Carbon Network Boosts High-Performance Supercapacitors

Transition metal oxides with various valence states have high specific capacitance and have attracted much attention. However, the poor cycle stability caused by material agglomeration seriously limits the play of its high activity. Herein, we create a stress dispersion structure (CuxO composite porous carbon net) by in situ lyophilization and one-step carbonization, effectively anchoring highly reactive copper oxides and highly conductive carbon networks combined with high nitrogen doping of 10.7%, to investigate their electrochemical performance in supercapacitors. Specifically, the specific capacitance of CuxO@NPC can be as high as 392 F/g (0.5 A/g) in the three-electrode system with 6 mol/L KOH as electrolyte. When applied to the two-electrode system, the cycle stability of the whole device can reach 97% after 10,000 cycles.

Optimization of electrochemical performance for double network electrically conductive aerogel-based supercapacitor electrode

In order to improve the energy density and optimize the electrochemical performance of supercapacitors, a new double network calcium alginate/polyaniline (CA/PANI) aerogels were designed in this study, in which sodium alginate (SA) cross-linked by Ca2+ was the first network and the phytic acid cross-linked PANI was the second network. Due to the strong hydrogen bonds between PANI and CA, and the ionic cross-linking between CA molecular chains, CA/PANI aerogels can form a stable porous network structure with excellent performance, such as high BET specific surface area (330 m2/g) and high conductivity (2.66 S/cm). The aerogel further used as a supercapacitor electrode showed enhanced capacitive performance (463 F/g at 0.5 A/g). After repeated 10,000 galvanostatic charge/discharge tests, more than 84% of the initial capacitance could be maintained, while the capacitance retention of PANI was only 45%. Therefore, this aerogel showed great potential as an electrode material for supercapacitors.

Modification and Supercapacitive Performance Enhancement of Calcium Carbide-Derived Carbon Prepared by a Green Solvent-Free Mechanochemical Route

A solvent-free mechanochemical method is a green and environmentally friendly preparation technology for the preparation of calcium carbide-derived porous carbon (CCDPC). Although CCDPC can be widely used in the fields of energy storage, gas separation, catalysis, and so on, the performance of CCDPC as an electrode material of supercapacitors still needs to be further improved. Based on the in situ chemical oxidation polymerization method, in this paper, polyaniline (PANI) is successfully introduced into CCDPC and covered on the surface and skeleton of CCDPC. It has been found that the as-prepared CCDPC/PANI composite electrode displays a high specific capacitance of 362 F g–1 at 0.5 A g–1, which is approximately 4 times higher than that of the pure CCDPC electrode. When assembling a symmetric supercapacitor by a CCDPC/PANI composite with a wide voltage window of 0–1.1 V, the supercapacitor delivers a higher energy density than CCDPC and reveals excellent capacitance retention of 77% after 10,000 cycles. Therefore, the preparation technology of the CCDPC/PANI composite provides significative exploration for the enhancement of electrochemical performance of high-performance supercapacitors and predicts a promising application prospect in the field of energy storage.

Construction of 3D carbon dots/Prussian blue analogue-derived phosphide nanocomposites on Ni foam for high-performance supercapacitors

A desirable electrode material with rational architecture and superior composition is the key to optimize the electrochemical performance of supercapacitor. Prussian blue analogues are a kind of promising precursors for electrode preparation with the features of adjustable compositions and rigid frame structure. In this work, carbon dots/nickel iron phosphide nanoparticles grown on Ni foam have been delicately designed and synthesized from PBAs for the application of cathode of hybrid supercapacitors (HSC). Introduction of CDs is found that not only favors the nanocubes growth of PBAs precursor but also alleviates aggregation of the nanocubes during calcination and phosphorization. The uniform coverage of carbon dots on the phosphides offers hydrophilic interfaces beneficial to the interaction between electrodes and electrolyte and improves the chemical stability of the electrodes. With these assets, the optimum electrode exhibits remarkable areal capacitance (2589 mF cm−2 at a current density of 2 mA cm−2), noteworthy rate performance and excellent cycling stability. Moreover, the as-fabricated hybrid supercapacitor shows a high energy density and power density, as well as high stability. These results indicate that the CDs/NiFeP-NF electrode has the desirable potential to be a candidate for energy storage devices. The structure modulation in this work may provide a new avenue for development of PBAs-based phosphides materials in the field of energy conversion and storage.

Pseudocapacitive charge storage behavior of cation-doped WS2 nanosheets electrode

Nanostructured two-dimensional layered semiconductors MX2 (M = Mo, W, and X = S, Se, Te) are potential candidates for electrochemical energy conversion and storage applications. Recently, different research strategies, including phase and heterostructure engineering, surface modification, and chemical doping have been employed with the aim to obtain high energy density MX2 supercapacitor electrodes. Here, we report the electrochemical supercapacitor performance of cation, Co, Ir, and Ru, doped WS2 nanosheets electrode in 1 M Na2SO4 and 2 M H2SO4 aqueous electrolyte. The structure of WS2 nanosheets is stabilized in the 2H hexagonal phase and the interlayer separation expanded after cation doping. The cation-doped WS2 nanosheet electrodes exhibit pseudocapacitive behavior with improved performance in both electrolytes. Among all, the best electrode, Ru doped WS2 nanosheets shows excellent energy storage capacity and attains a specific capacity of 438 Fg−1 in 2 M H2SO4 electrolyte. The analysis reveals that cation doping is one possible research strategy to improve the supercapacitor performance of WS2 nanosheets.

Investigation of the effect of degree of prelithiation on high-performing hybrid supercapacitors made with porous CaFe2O4 anodes

Prelithiation typically has a substantial impact on the electrochemical performance of lithium-ion batteries and hybrid supercapacitors (HSC), though the optimum prelithiation point of most materials, let alone conversion-type anodes, remains unexplored. In this study, the first HSCs made with porous CaFe2O4 (pCFO) anodes prelithiated to different degrees are investigated. While prelithiation affects the morphologies and compositions of pCFO anodes in predictable ways, prelithiation has a more stochastic influence on HSC electrochemical performance. Deeper probing into the electrode-specific characteristics via three-electrode cycling indicates that the anodes in all devices quickly drop near 0 V vs. Li/Li+. This low-voltage plateauing is a marker of lithium plating, which is usually parasitic for electrochemical energy storage devices and could interfere with the beneficial effects of prelithiation. However, many of the pCFO-based HSCs perform competitively with other HSCs, both with respect to energy and power density (20–140 Wh kg−1 at 1000–10,000 W kg−1) and long-term cycling stability (> 70 % capacity retention after 5000 cycles at 2 A g−1), indicating that pCFO may be uniquely resistant to the influence of lithium plating and so is a promising candidate for next-generation HSCs.

Dual Molecules Cooperatively Confined In-Between Edge-oxygen-rich Graphene Sheets as Ultrahigh Rate and Stable Electrodes for Supercapacitors.

Noncovalent modification of carbon materials with redox-active organic molecules has been considered as an effective strategy to improve the electrochemical performance of supercapacitors. However, their low loading mass, slow electron transfer rate, and easy dissolution into the electrolyte greatly limit further practical applications. Herein, this work reports dual molecules (1,5-dihydroxyanthraquinone (DHAQ) and 2,6-diamino anthraquinone (DAQ)) cooperatively confined in-between edge-oxygen-rich graphene sheets as high-performance electrodes for supercapacitors. Cooperative electrostatic-interaction on the edge-oxygen sites and π-π interaction in-between graphene sheets lead to the increased loading mass and structural stability of dual molecules. Moreover, the electron tunneling paths constructed between edge-oxygen groups and dual molecules can effectively boost the electron transfer rate and redox reaction kinetics, especially at ultrahigh current densities. As a result, the as-obtained electrode exhibits a high capacitance of 507 F g-1 at 0.5 A g-1 , and an unprecedented rate capability (203 F g-1 at 200 A g-1 ). Moreover, the assembled symmetrical supercapacitor achieves a high energy density of 17.1Wh kg-1 and an ultrahigh power density of 140kW kg-1 , as well as remarkable stability with a retention of 86% after 50 000 cycles. This work may open a new avenue for the efficient utilization of organic materials in energy storage and conversion.

Precise engineering of Fe3O4/MWCNTs heterostructures for high-performance supercapacitors

The development of electrode materials with well-defined interfaces plays a vital role on improving the electrochemical performance of supercapacitors. The hybridization of conductive carbon materials with metal oxides is recommended to fabricate improved supercapacitor electrodes. In this work, catalytic chemical vapor deposition (CCVD) and solvothermal methods were utilized to synthesize a Fe3O4/MWCNTs heterostructure with tuned size and morphology. The heterostructure-based electrode showed supreme specific capacitance, energy density, and cycling stability. The size of Fe3O4 as well as the diameter and the number of walls of the functionalized MWCNTs were optimized. Various characterization techniques such as Scanning Electron Microscopy (SEM) combined with Energy Dispersive X-ray (EDX) spectroscopy, Transmission Electron Microscopy (TEM), X-ray diffraction spectroscopy (XRD), and Raman Spectroscopy were utilized to explore the structural and surface properties of the engineered heterostructures. The electrochemical measurements were carried out in 6 M KOH for all synthesized electrodes. The Fe3O4/MWCNTs heterostructure showed a specific capacitance of 492.3 F/g, energy density of 115.55 Wh/Kg at 1 A/g, and capacitance retention of 165.7 % after 1000 cycles. The specific capacitance of the electrodes was further calculated using CV measurement achieving 921.3 F/g at 10 mV/s for the Fe3O4/MWCNTs heterostructure. The excellent electrochemical performances of MWCNTs/Fe3O4 heterostructures were mainly due to the homogenous distribution of Fe3O4 nanoparticles with multivalent oxidation states on the surface of MWCNTs. This led to faster surface oxidation-reduction reactions and consequently, higher reversible capacity and ultrahigh energy density in addition to improved cyclability. This work sheds light on the possibility of precisely controlling Fe3O4/MWCNTs heterostructure electrodes for high-performance energy storage applications.

Facile in-situ grown spinel MnCo2O4/MWCNT and MnCo2O4/Ti3C2 MXene composites for high-performance asymmetric supercapacitor with theoretical insight

The logical construction of electrode materials along with greater electrochemical features and solid architectural design is a strategic approach for boosting the electrochemical performance of supercapacitors. However, it is tough and complicated to develop diverse composite materials with better electronic conductivity and greater specific capacitance via rapid and cost-effective synthesis procedures. Herein, we propose a straightforward and simple approach by employing the hydrothermal technique for the synthesis of spinel MnCo2O4 composite nanostructures using 1D MWCNT and 2D MXene (Ti3C2Tx) materials with detailed analysis of the supercapacitor performance as compared to existing literature on similar studies. The MCO/TCX (MnCo2O4/Ti3C2Tx) composite shows an impressive capacitance of 860.22 F/g at a current density of 2 A/g after electrochemical optimization. Furthermore, an asymmetric supercapacitor device (ASCs) was constructed using MCO and its composites MCO/MWCNT and MCO/TCX as a positive, and AC was employed as a negative electrode to test its device capability. Comparatively, the MCO/TCX//AC SC device demonstrated exceptional energy storage properties with a better specific capacitance value of 126.58 F/g at 0.8 A/g of current density, an elevated energy density of 40 Wh/kg, with a power density of 4828 W/kg along a capacitance retention rate of 87 % over 5000 cycles, suggesting better cycle life. Whereas, the MCO/MWCNT//AC device shows a better cycling performance of 91 % after 5000 cycles with a superior energy and power density of 27.04 Wh/kg and 1448 W/kg respectively. Also the theoretical insight for further understanding of the charge-storage mechanism through DFT calculations provides an estimate of electronic properties and quantum capacitance calculated for the pristine MCO and its hybrids with CNT and Ti3C2Tx MXene and information on the interactions between orbitals, the bonding process, and the charge transfer capabilities of each electrode material. The theoretical studies also confirm that the electronic properties and therein charge storage performance have an increasing trend in the order of MCO < MCO/CNT < MCO/TCX consistent with the experimental findings. Additionally, these simulations conclude that the hybrid MCO/TCX has the largest quantum capacitance which is in accordance with the findings of the experiments. The improved performance of MCO/TCX is due to the enlarged surface area that allows higher charge transfer from TCX to MCO. The charge transferred from the C 2p orbital of TCX to the Mn 3d orbital of MCO is the leading cause for the capacitance improvement mechanism of hybrid MCO/TCX. This work offers a simple procedure for developing energy storage devices using spinel MnCo2O4-based composite electrode materials supported by 1D carbon nanotube and 2D MXene that offer superior electrochemical performance and the fabricated electrodes that could be employed further for energy storage-based applications.

Experimental study of a carbon-based planar supercapacitor in an aqueous electrolyte

One of the remarkable characteristics of supercapacitors is their ability to rapidly charge/discharge compared to a battery. The increase in the charging rate adversely affects the capacitance reduction. To address this issue, a planar interdigitated electrode that provides a good rate capability is implemented. In this paper, leveraging cyclic voltammetry, we investigate the specific capacitance of three difference patterns of carbon-based planar electrodes and conventional sandwich supercapacitors using two electrodes system of cyclic voltammetry technique. The capacitance of all planar samples reach the maximum peak, which is higher than its initial value even after increasing the scan rate by 50-fold. The narrow planar electrode fringe has a strong electric field and enhances the capacitance. The optimum applied scan rate can be manipulated by varying the electrolyte concentration. Thus, a simplified model of charge storage behavior is proposed. Furthermore, the influence of electrolyte concentration and applied scan rate on the total capacitance is discussed. The excellent rate capability observed herein demonstrates the superior electrochemical performance of supercapacitor with planar electrode configuration beyond the conventional sandwich structure.

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation.

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g-1 to 450 F∙g-1 at the current density of 1 A∙g-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg-1 at the specific power of 1520 W∙kg-1.

N-doped/oxygen-deficient Fe2O3−x @PEDOT cruciform nanosheet arrays: Boosting the performance of all-solid-state flexible supercapacitors

As an ideal Faradaic anode material, Fe2O3 is expected to achieve high electrochemical performance in supercapacitors. However, the application of Fe2O3 in supercapacitors is limited by poor conductivity. In this study, first, we synthesized Fe2O3@Poly(3,4-ethylenedioxythiophene) (Fe2O3@PEDOT) composite cruciform nanosheet arrays via a one-step Fe3+-induced growth strategy. Fe2O3 nanoparticles were uniformly confined in ultrathin PEDOT sheets to enhance the dispersibility and conductivity of Fe2O3. Then, oxygen vacancies and nitrogen doping were introduced in Fe2O3 nanoparticles by plasma treatment (N-Fe2O3−x@PEDOT), which further enhanced the conductivity of Fe2O3 and increased the number of active sites. The engineered N-Fe2O3−x@PEDOT composites exhibited a high area capacitance of approximately 751 mF cm−2 at a current density of 1 mA cm−2 and approximately 103 mF cm−2 at 5 mV s−1 for a corresponding symmetric solid-state flexible supercapacitor with a capacitance retention of ∼60% after 5000 cycles.