Faradaic Energy Storage Research Articles

Hybrid and Asymmetric Supercapacitors: Achieving Balanced Stored Charge across Electrode Materials.

An electrochemical capacitor configuration extends its operational potential window by leveraging diverse charge storage mechanisms on the positive and negative electrodes. Beyond harnessing capacitive, pseudocapacitive, or Faradaic energy storage mechanisms and enhancing electrochemical performance at high rates, achieving a balance of stored charge across electrodes poses a significant challenge over a wide range of charge-discharge currents or sweep rates. Consequently, fabricating hybrid and asymmetric supercapacitors demands precise electrochemical evaluations of electrode materials and the development of a reliable methodology. This work provides an overview of fundamental aspects related to charge-storage mechanisms and electrochemical methods, aiming to discern the contribution of each process. Subsequently, the electrochemical properties, including the working potential windows, rate capability profiles, and stabilities, of various families of electrode materials are explored. It is then demonstrated, how charge balancing between electrodes falters across a broad range of charge-discharge currents or sweep rates. Finally, a methodology for achieving charge balance in hybrid and asymmetric supercapacitors is proposed, outlining multiple conditions dependent on loaded mass and charge-discharge current. Two step-by-step tutorials and model examples for applying this methodology are also provided. The proposed methodology is anticipated to stimulate continued dialogue among researchers, fostering advancements in achieving stable and high-performance supercapacitor devices.

A new streamlined electrochemical assembly procedure to improve conductive polymer-based metal chalcogenide electrodes for innovative energy systems

Reliable, effective, and environmentally friendly supercapacitors still need development despite the progress made in many nanoscale electrode materials. In this area, composite materials made of organic polymers with high electrical conductivity and metal sulfides with various oxidation states were more attractive. This article describes the design and synthesis of zinc sulfide and polyaniline nanocomposites employing a fast and straightforward electrochemical deposition method and their use as electrode materials for supercapacitors. The structural investigation showed clumped spherical for pAni, hexagonal for pure ZnS, and coexisting hexagonal and spherical phases for ZnS@pAni nanocomposites. The ZnS@pAni nanocomposite demonstrated remarkable electrochemical efficiency and faradaic energy storage capabilities with practical reversibility. Also, an impedance inquiry found that the ZnS@pAni composite has better conductivity and a lower charge transfer resistance than its bulk components. ZnS@pAni//AC was used to create a hybrid asymmetric supercapacitor and displayed a large voltage window up to 2.06 V, 235.24 F g−1 specific capacity, and an ultimate energy density of 144.08 Wh kg−1. Also, when energy density drops to 22 Wh kg−1, substantial power delivery is achieved at 6.3 kW kg−1. Moreover, 88.05% of the capacitance was retained after the device completed 5000 cycles, suggesting good ZnS@pAni//AC asymmetric supercapacitor stability.

Redox-Active Benzodithiophene-4,8-dione-Based conjugated microporous polymers for High-Performance faradaic supercapacitor energy storage

Conjugated microporous polymers (CMPs) are attractive materials due to their microporous architecture, modifiable physical–chemical characteristics, and extended π-conjugated structures. However, their low electronic conductivity limits the development of CMPs with high specific capacitance and excellent charge–discharge stability for supercapacitor energy storage. Furthermore, the redox-active moieties in CMPs for innovative electrode materials are still restricted. Herein, for the first time, two novel redox-active benzo[1,2-b:4,5-b']dithiophene-4,8-dione-based conjugated microporous polymers (DBTh-CMPs), namely, DBTh-TPA and DBTh-TPT CMPs, were prepared through the one-pot Suzuki coupling polymerization of 2,6-dibromobenzo[1,2-b:4,5-b']dithiophene-4,8-dione with triboronic-pinacolates. The DBTh-CMPs exhibited outstanding thermal stabilities (Td10: approximately 608.4 °C; char yield: approximately 71.76%) and surface areas (around 551 m2/g). Interestingly, incorporating redox-active DBTh structures into the backbone of the CMPs resulted in promising conductivity, exceptional faradaic energy storage, and efficient charge transfer. The DBTh-CMPs displayed an exceptional three-electrode capacitance of 1823F g−1 at a current density of 0.5 A g−1 with superior stability of 81.75% over 10,000 cycles; such a value is the largest specific capacity documented via the CMP to date. The two-electrode symmetric supercapacitor device by DBTh-TPT CMP showed a specific capacitance of 609F g−1 and a maximum energy density of 84.5 W h kg−1 operating at a power density equal to 500 W kg−1 and a potential of 1.0 V. The present research supplies a viable strategy for developing electrochemical gadgets and future-oriented supercapacitors.

High power aqueous hybrid asymmetric supercapacitor based on zero-dimensional ZnS nanoparticles with two-dimensional nanoflakes CuSe2 nanostructures

Energy storage materials, particularly chalcogenides, are fascinating electrode materials for supercapacitors (SCs) because of their high capacitance, remarkable electrical conductivity, and multiple oxidation states contributed by numerous metal cations. Herein, a novel nanocomposite based on zinc sulfide and copper diselenide, denoted as (ZnS–CuSe2), was prepared via a sonochemical-assisted method. The structural analysis revealed the cubic structure for pure ZnS, orthorhombic for CuSe2, and co-existing cubic and orthorhombic phases for ZnS–CuSe2 nanocomposites with high purity and crystallinity. The ZnS–CuSe2 nanocomposite offered exceptional electrochemical performance with redox peaks from the CV analysis, and coupled with plateaus in the charge/discharge profile, confirming the faradaic energy storage properties with functional reversibility. Similarly, a high conductive feature of the ZnS–CuSe2 composite was revealed by impedance study, with a minor charge transfer resistance than their bulk materials. A hybrid asymmetric supercapacitor (HASCs) composed of ZnS–CuSe2//AC was constructed, which manifested an enlarged voltage window up to 1.7 V with capacitance of 95 F g−1 and a maximum specific energy of 38 Wh kg−1. Also, high power delivery was attained at 3927 Wkg-1 when specific energy goes down to 12 Wh kg− at 5 A g−1. Interestingly, only 81.8% retention was left beneath when cycled to 8000 cycles, specifying decent stability of the ZnS–CuSe2//AC HASCs.

Structural, electronic, and electrochemical studies of WS2 phases using density functional theory and machine learning

Transition metal dichalcogenides have attracted significant attention in green energy production and storage due to their two-dimensional structure and tunable electronic properties. In this study, four phases of WS2, including 2H, 1H, 1 T’, and 1 T, were studied using Density Functional Theory (DFT) and Machine Learning (ML). Accordingly, diffraction pattern, stability, binding energy, phonon dispersion, band structure, work function, surface energy, and electrochemical activity were simulated. It was shown that 2H monolayers are the easiest to produce and 1 T monolayers are most vulnerable to restacking. It was also observed that intercalation is more likely to produce 1H phase rather than 1 T; while diffraction and Raman methods cannot distinguish these two phases. Additionally, it was found that increasing interlayer distance increases the band gap and vice versa. Finally, it was shown that trigonal phases are suitable for faradaic energy storage, while 1H phase shows promising capabilities for photoelectrochemical and double layer applications.

A Flexible, Redox‐Active, Aqueous Electrolyte‐Based Asymmetric Supercapacitor with High Energy Density Based on Keratin‐Derived Renewable Carbon

AbstractThis work exploits the advantage of asymmetric configuration over symmetric supercapacitor in designing high energy density flexible devices from two active electrode materials–keratin‐based renewable‐resource hierarchically porous carbon and hydrous ruthenium oxide (RuO2). The asymmetric device exhibits significantly high capacitance. Conventional estimation of energy storage parameters, however, cannot be applied for devices with a Faradaic energy storage contribution via redox charge transfer mechanism. Therefore, this work applies a precise measurement of pseudocapacitance contribution at various scan rates to correct the device data that reveals effective capacitance of 120 F g−1 with the energy density of 37 W h kg−1 at 776 W kg−1. It also retains excellent rate capability, >74% at high current density 25 A g−1. The charge storage activity and device stability can be further enhanced by introducing redox‐active electrolytes that improve specific capacitance, but the rate capabilities deteriorate at high current densities. Further, the principle of asymmetric electrode design is applied to fabricate a bending‐tolerant, flexible device by depositing active electrode material on wire‐shaped current collector followed by coupling those separated with polyvinyl alcohol gel containing redox electrolyte; it yields 36.8 mF cm−1 specific capacitance at a 0.2 mA cm−1 current density.

Increasing Charge Transfer at the Liquid−Solid Interface Using Electrodes Modified with Redox Mediators

The power density of redox flow batteries (RFBs) utilized on iron‐containing electrolytes is improved by incorporating iron particle redox mediators into the electrodes. Nonpurified carbon nanotube (CNT) electrodes containing iron nanoparticles, formed during the synthesis of CNTs using the ferrocene−xylene process, are activated to create “hotspots” for faradaic energy storage that reduces losses associated with kinetical, ohmic, and mass transfer resistances. CNT electrodes are activated through cyclic voltammetry to initiate charge transfer interactions between redox electrolytes and iron nanoparticles in the electrode. RFBs with modified electrodes experience a 140% increase in power density and a 57% increase in energy density in coin‐cell configurations. Economic value and ready availability of iron paired with enhanced performance make iron RFBs a viable option for future RFB research. Herein, the highest peak power density yet reported for an iron‐based RFB at 180 mW cm−2 with iron‐modified electrodes under no electrolyte flow is demonstrated.

Mixed mathematical and experimental modeling of electrospun metal oxide supercapacitor electrodes

Supercapacitors are an important energy storage technology that combine the high energy density of batteries with the high power density of capacitors. Freestanding Mn2O3 electrodes fabricated via electrospinning and calcination have the potential to provide high power and energy densities with low fabrication costs. In this work, a theoretical model is produced to describe the effects of the electrospun structure on electrode performance. The model uses theoretical predictions of capacitive and faradaic energy storage, based on system parameters measured from real electrodes to produce a realistic model that can be used for engineering design and optimization of the electrodes. Porosity-controlled discharge time and extremely stable energy densities are predicted by the model. Results are compared to discharge curves of a real electrode to examine model fidelity.

Physical, Chemical, and Electrochemical Properties of Redox-Responsive Polybenzopyrrole as Electrode Material for Faradaic Energy Storage.

Polybenzopyrrole (Pbp) is an emerging candidate for electrochemical energy conversion and storage. There is a need to develop synthesis strategies for this class of polymers that can help improve its overall properties and make it as suitable for energy storage applications as other well-studied polymers in this substance class, such as polyaniline and polypyrrole. In this study, by synthesizing Pbp in surfactant-supported acidic medium, we were able to show that the physicochemical and electrochemical properties of Pbp-based electrodes are strongly influenced by the respective polymerization conditions. Through appropriate optimization of various reaction parameters, a significant enhancement of the thermal stability (up to 549.9 °C) and the electrochemical properties could be achieved. A maximum specific capacitance of 166.0 ± 2.0 F g−1 with an excellent cycle stability of 87% after 5000 cycles at a current density of 1 A g−1 was achieved. In addition, a particularly high-power density of 2.75 kW kg−1 was obtained for this polybenzopyrrole, having a gravimetric energy density of 17 Wh kg−1. The results show that polybenzopyrroles are suitable candidates to compete with other conducting polymers as electrode materials for next-generation Faradaic supercapacitors. In addition, the results of the current study can also be easily applied to other systems and used for adaptations or new syntheses of advanced hybrid/composite Pbp-based electrode materials.

High-energy all-in-one micro-supercapacitors based on ZnO mesoporous nanosheet-decorated laser-induced porous graphene foams

Micro-supercapacitors with high power density and stability promise emerging energy storage devices. However, their relatively low energy density and poor mechanical stability largely restricts their application. Here, we report an all-in-one planar micro-supercapacitor (MSC) using ZnO nanosheets anchored on the porous and 3D laser-induced porous graphene foams (ZnO@LIG) as the electrode materials. Due to the 3D networks, the hybrid electrode exhibits fast charge transfer and diffusion channels. More importantly, the hybrid approach can simultaneously take advantage of double-layer capacitance and faradaic energy storage mechanisms. The ZnO@LIG electrode displays a high specific capacitance of 14.7 F cm−2, remarkable rate capability and cycling stability. Furthermore, the MSC showcases high energy density (10.0 Wh kg−1), high power density (0.5 Wh kg−1), long-term stability, and excellent mechanical stability upon bending. The excellent performance parameters of the MSC make it one of the promising micropower sources for flexible microelectronics.Graphic abstract

Co3O4@Ni3S4 heterostructure composite constructed by low dimensional components as efficient battery electrode for hybrid supercapacitor

Redox activity and electrons/ions mobilities of electrode material are significant prerequisites for faradaic charge storage, the compositing of battery materials with different dimensionalities can satisfy the above two requirements simultaneously. Herein, a unique heterostructured Co3O4@Ni3S4 composite battery electrode with the coating of Ni3S4 nanosheets around/onto Co3O4 nanowires array was prepared via tandem hydrothermal reaction of Co salt, pyrolysis and followed sulfidation etching of Ni foam substrate. The different dimensionalities of Co3O4 core and Ni3S4 shell created porous network composite with high faradaic activity, sufficient exposure of surface sites, efficient electrons/ions migration and robust structural tenacity, therefore could offer high areal capacity (CA, 2.46C cm−2 at 1 mA cm−2), slow self-discharge rate and good cycleability (91% CA maintaining ratio undergoes 5000 charge-discharge cycles). Furthermore, the hybrid supercapacitor (HSC) based on the Co3O4@Ni3S4 composite battery electrode exported high energy density (Ecell, 0.13 mW h cm−2 at 1.6 mW cm−2), slow self-discharge rate and good cycleability, showing the potential of heterostructured Co3O4@Ni3S4 composite electrode in faradaic energy storage.

Al doped Co hydroxyl fluoride nanosheets arrays as efficient faradaic electrode for hybrid supercapacitor

Al doped Co hydroxyl fluoride (Al–Co(OH)F) with vertically aligned nanosheets arrays architecture onto Ni foam substrate was prepared by hydrothermal hydrolysis of Co precursor mediated by F− and Al3+ ions. By virtue of the vertical electron and ions transfer channels along the nanosheets arrays, as well as the coexistence of different oxidation values of Co element, the faradaic Al–Co(OH)F electrode could offer a maximum specific capacitance (Cs) of 1576 F g−1 at 1.0 A g−1, and 624 F g−1 was still maintained at high current density of 20 A g−1. Additionally, 84 % of its initial Cs was maintained underwent 5000 repeated charge-discharge cycles at 5 A g−1. When used as faradaic electrode of hybrid supercapacitor (HSC), high energy density (Ecell) of 42.7 Wh kg−1 at power density (Pcell) of 382.6 W kg−1 was harvested, and Ecell declined to 18.2 Wh kg−1 with Pcell increased to 3123.5 W kg−1, showing the potential of Al–Co(OH)F in faradaic energy storage.

The influence of electrode matching on capacity decaying of hybrid lithium ion capacitor

Hybrid lithium-ion capacitors (HyLICs), combining a battery-type negative electrode and a composite positive electrode, can display a more comprehensive performance than conventional lithium-ion capacitors (LICs), e.g. high energy density. However, owing to the coexisting of non-Faradaic and Faradaic energy storage mechanism in the composite positive electrode, the insufficient cycle stability of device becomes an urgent problem. In this paper, we discussed the influence of electrode matching on the cycling stability of HyLICs with a L30/HC@SLMP structure. The three L30/HC mass ratios were 0.8, 1.0 and 1.2, respectively. Three full cells with above ratios exhibit great difference in cycle stability when charging/discharging at a current density of 1 A g−1. Various methods, including galvanostatic charging/discharging, three-electrodes test and scanning electron microscopy, were used to analyze the performance of difference cells. It turns out that the poor rate performance of HC electrode is the main limited factor in HyLICs' cycling stability. Compared with the composite positive electrode, HC electrode is more sensitive to the current densities. Under high current density, solid electrolyte interface layers on the HC electrode surface accumulated fast, which leads to the increase in the impedance of HC electrode. From the Ragone plot, the best matching strategy of L30/HC electrode was achieved when the mass ratio of L30/HC was 1.0. Finally, the optimal HyLICs with L30/HC mass ratio of 1.0 were assembled and performed an excellent cycle stability of more than 80% retention after 62,000cycles in 40C, as well as better power and energy density compared with LICs.

Electron Highways into Nanochannels of Covalent Organic Frameworks for High Electrical Conductivity and Energy Storage

To enhance the electron transfer within the covalent organic frameworks (COFs), we obtained a nanocomposite of conductive poly(3,4-ethylenedioxythiophene) (PEDOT) and redox-active AQ-COF by performing a facile in situ solid-state polymerization inside the nanochannels of COFs. The PEDOT chains functioned like electron highways within the nanochannels, resulting in a PEDOT@AQ-COF nanocomposite with an excellent electrical conductivity of 1.1 S cm-1 and a remarkably improved performance in faradaic energy storage. The all-organic PEDOT@AQ-COF electrode showed specific capacitance as high as 1663 F g-1 (at 1 A g-1), ultrafast charge/discharge rate performance (998 F g-1 at 500 A g-1), and excellent stability for 10 000 cycles. This research demonstrates a promising strategy for increasing the conductivity of COF-based materials and broadening their applications.

Ni3S2 nanorods and three-dimensional reduced graphene oxide electrodes-based high-performance all-solid-state flexible asymmetric supercapacitors

Exploring efficient all-solid-state flexible supercapacitors is particularly attractive to face the rapid growing demand of powers for flexible and wearable energy storage devices. Herein, we report a novel strategy to prepare high-performance all-solid-state flexible asymmetric supercapacitors based on nanostructured Ni3S2 nanorods as positive electrode and three-dimensional reduced graphene oxide (3DrGO) as negative electrode. Due to the tunable morphological structures and novel electronic properties of heazlewoodite phase Ni3S2 and interconnected porous 3DrGO, the synthesized electrode materials exhibit high specific capacitances, excellent rate performance and cycling stability. Furthermore, combining capacitive and faradaic energy storage mechanisms, the constructed asymmetric supercapacitor can work complementarily in separate operating voltage, thus leading to substantially enhanced energy and power densities. Remarkably, the optimized device is able to be cycled reversibly in the voltage range of 0–2.2 V, but still delivers high energy density (70.58 W h kg−1), high power density (33.0 kW kg−1 at 52.44 W h kg−1), and excellent cycling stability (with 90.4% specific capacitance retained even after 5000 cycles). Moreover, the device exhibits good flexibility without performance degradation. Significantly, the conception of the combining capacitive and faradaic energy storage mechanisms in this work undoubtedly enables new perspective in exploring high-performance energy storage systems.

Hybrid Graphene-Polyoxometalates Nanofluids as Liquid Electrodes for Dual Energy Storage in Novel Flow Cells.

Solid Hybrid materials abound. But flowing versions of them are new actors in the materials science landscape and in particular for energy applications. This paper presents a new way to deliver nanostructured hybrid materials for energy storage, namely, in the form of nanofluids. We present here the first example of a hybrid electroactive nanofluid (HENFs) combining capacitive and faradaic energy storage mechanisms in a single fluid material. This liquid electrode is composed of reduced graphene oxide and polyoxometalates (rGO-POMs) forming a stable nanocomposite for electrochemical energy storage in novel Nanofluid Flow Cells. Two graphene based hybrid materials (rGO-phosphomolybdate, rGO-PMo12 and rGO-phosphotungstate, rGO-PW12 ) were synthesized and dispersed with the aid of a surfactant in 1 M H2 SO4 aqueous electrolyte to yield highly stable hybrid electroactive nanofluids (HENFs) of low viscosity which were tested in a home-made flow cell under static and continuous flowing conditions. Remarkably, even low concentration rGO-POMs HENFs (0.025 wt%) exhibited high specific capacitances of 273 F/g(rGO-PW12 ) and 305 F/g(rGO-PMo12 ) with high specific energy and specific power. Moreover, rGO-POM HENFs show excellent cycling stability (∼95 %) as well as Coulombic efficiency (∼77-79 %) after 2000 cycles. Thus, rGO-POM HENFs effectively behave as real liquid electrodes with excellent properties, demonstrating the possible future application of HENFs for dual energy storage in a new generation of Nanofluid Flow Cells.

Controllable fabrication of redox-active conjugated microporous polymers on reduced graphene oxide for high performance faradaic energy storage

Two-dimensional (2D) composites composed of redox active conjugated microporous polymer (CMP) and reduced graphene oxide (rGO) enable efficient faradaic energy storage.

Novel ternary nanocomposites of MWCNTs/PANI/MoS2: preparation, characterization and enhanced electrochemical capacitance.

In this work, nanoflower-like MoS2 grown on the surface of multi-walled carbon nanotubes (MWCNTs)/polyaniline (PANI) nano-stem is synthesized via a facile in situ polymerization and hydrothermal method. Such a novel hierarchical structure commendably promotes the contact of PANI and electrolyte for faradaic energy storage. In the meanwhile, the double-layer capacitance of MoS2 is effectively used. The morphology and chemical composition of the as-prepared samples are characterized by scanning and transmission electron microscopies, X-ray diffraction and Fourier transform infrared spectra. The electrochemical performance of the samples is evaluated by cyclic voltammogram and galvanostatic charge–discharge measurements. It is found that the specific capacitance of the obtained MWCNTs/PANI/MoS2 hybrid is 542.56 F g−1 at a current density of 0.5 A g−1. Furthermore, the MWCNTs/PANI/MoS2 hybrid also exhibits good rate capability (62.5% capacity retention at 10 A g−1) and excellent cycling stability (73.71% capacitance retention) over 3000 cycles.

Hierarchical architecture of ultrashort carbon nanotubes/polyaniline nanocables coated on graphene sheets for advanced supercapacitors

Multilayer super-short carbon nanotubes (SSCNTs) could be prepared by tailoring raw multiwalled carbon nanotubes (MWCNTs) with mechanical-stirring and ultrasonic oxidation-cut method. The SSCNTs/polyaniline/reduced graphene oxide (SSCNTs/PANI/RGO) ternary hybrid composite was fabricated by reducing SSCNTs/PANI/GO precursor prepared by self-assembly from the complex dispersion of graphene oxide (GO) and the as-prepared SSCNTs/PANI nanocables, followed by redoping and reoxidation of the reduced PANI to restore the conducting structure of PANI in the ternary composite. The microscope images indicated that SSCNTs/PANI nanocables could uniformly distribute in the conductive network of graphene sheets and prevent the agglomeration of graphene. Such the hierarchical structure perfectly facilitates the contact between PANI for faradaic energy storage and electrolyte ions, and efficiently utilizes the double-layer capacitance of SSCNTs and graphene sheets at the electrode–electrolyte interfaces. The maximum specific capacitance of the SSCNTs/PANI/RGO composite achieved 845 F g−1, which was much higher than that of pure PANI and SSCNTs/PANI nanocables. Moreover, the ternary composite also showed the good cycling stability, retaining about 96% of its initial capacitance after 1000 cycles because of the synergistic effect and conductive network of SSCNTs/PANI nanocables and graphene sheets. Therefore, the combined effects between SSCNTs/PANI nanocables and graphene sheets taking advantage of both charging and faradaic processes could readily explain the excellent electrochemical performance for supercapacitors.

Well-Ordered Oxygen-Deficient CoMoO4 and Fe2O3 Nanoplate Arrays on 3D Graphene Foam: Toward Flexible Asymmetric Supercapacitors with Enhanced Capacitive Properties.

In this work, we report the development of well-ordered hydrogenated CoMoO4 (H-CoMoO4) and hydrogenated Fe2O3 (H-Fe2O3) nanoplate arrays on 3D graphene foam (GF) and explore their practice application as binder-free electrodes in assembling flexible all-solid-state asymmetric supercapacitor (ASC) devices. Our results show that the monolithic 3D porous GF prepared by solution casting method using Ni foam template possesses large surface area, superior electrical conductivity, and sufficient surface functional groups, which not only facilitate in situ growth of CoMoO4 and Fe2O3 nanoplates but also contribute the double-layer capacitance of the resultant supercapacitor. The well-ordered pseudocapacitive metal oxide nanoplate arrays standing up on 3D GF scaffold can provide efficient space and shorten the length for electrolyte diffusion from the outer to the inner region of the electrode material for Faradaic energy storage. Furthermore, one of our major findings is that the introduction of oxygen vacancies in CoMoO4 and Fe2O3 nanoplates by hydrogenation treatment can increase their electronic conductivity as well as improve their donor density and surface properties, which gives rise to a substantially improved electrochemical performance. Benefiting from the synergistic contributions of different components in the nanohybrid electrode, the resultant flexible ASC device with GF/H-CoMoO4 as the positive electrode and GF/H-Fe2O3 as the negative electrode achieves a wide operation voltage of 1.5 V and a maximum volumetric specific capacitance of 3.6 F cm-3, which is two times larger than that of the Ni/GF/CoMoO4//Ni/GF/Fe2O3 device (1.8 F cm-3), and the rate capability is up to 70% as the current density increases from 2 to 200 mA cm-3. Moreover, the Ni/GF/H-CoMoO4//Ni/GF/H-Fe2O3 device also exhibits a high energy density of 1.13 mWh cm-3 and a high power density of 150 mW cm-3, good mechanical flexibility with the decrease in capacitance of less than 4% after being bent inward to different angles and inward to 90° 200 times, and good cycling stability of 93.1% capacitance retention after 5000 cycles.