Flexible Supercapacitor Device Research Articles

Revealing 1T-MoS2 with 76 % purity induced by various saccharides for supercapacitor performance

The preparation of metallic phase molybdenum disulfide (1T-MoS2) through an implementable method has become a top priority in research due to its excellent electrochemical performance. In this study, 1T-MoS2 using a facile one-pot hydrothermal method is successfully synthesized by incorporating saccharides. Moreover, a comprehensive understanding of the synthesis mechanism is induced by various saccharides. Glucose, a monosaccharide, not only possesses reducibility but also plays a crucial role in preparation of sulfur vacancies. Maltose is a disaccharide that can hydrolyze into glucose and fructose, both of which exhibit reducibility. On the contrary, dextrin is difficult to break down into fructose or glucose, and faces certain challenges in promoting the formation of 1T-MoS2. Importantly, 1T-MoS2 with 76 % purity obtained in our study exhibits exceptional electrochemical performance, demonstrating a high specific capacitance of 228.4 F g−1 at 2 A g−1 and maintaining a cycling stability of 97 % after 10,000 cycles. Furthermore, an asymmetric flexible supercapacitor device is assembled by 1T-MoS2 and active carbon on carbon cloths, which shows superior flexibility, high power density, and energy density. Notably, this work not only unveils the mechanism by which saccharides influence the synthesis of 1T-MoS2 but also provides support for the preparation of other metallic members in the transition metal dichalcogenides (TMDs) family.

Fabrication of highly flexible, wearable, free-standing symmetric supercapacitors with high voltage operation enabled by hierarchical graphene/cerium oxide/polypyrrole hybrid films

Flexible, free-standing supercapacitors play a significant role in the development of future wearable energy storage devices. Herein, we successfully fabricated the highly flexible and free-standing graphene/cerium oxide/polypyrrole hybrid films by thermal reduction of graphene oxide (GO) followed by the sol–gel synthesis of CeO2 and then the addition of PPy. By regulating oxygen functional groups in GO, the electronic conductivity and electroactive sites of the hybrid films are significantly controlled, leading to enhanced energy storage capability. Finally, a symmetric flexible supercapacitor (FSC) device was developed using the prepared films as electrodes. Resulting, the integrated symmetric GO-400/CeO2/PPy FSC manifests excellent areal capacitance of 49.0 mF cm−2 at 1 mA cm−2, with a durability of 83.1 % over 10,000 cycles. Specifically, the FSC exhibited capacitance retention of 77.2 % after 10,000 cycles under bending state with exceptional rate ability. Meanwhile, an impressive energy density of 19.69 µW h cm−2 was attained at a power density of 0.85 mW cm−2. Evidently, the synergistic interactions between GO and PPy nanosheets, along with CeO2 favour the rapid electron movement of electrode material for next-generation wearable, portable electronics.

The construction of a flexible solid-state asymmetric supercapacitor device using nickel-copper oxide nanoplates and carbon nanosphere serving as positive and negative electrode, respectively with excellent electrochemical capabilities

Here, nickel-copper oxide nanoplates (NCN) and carbon nanosphere (CNS) as positive and negative electrodes are synthesised via a hydrothermal protocol without adding any surfactant and binders. The NCN and CNS electrodes in KOH electrolyte exhibit superior specific capacitance of ∼ 2362.5 F g−1 and ∼ 246.11 F g−1 at 1 A g−1 respectively. The NCN and CNS retained 98.54 % and 97.88 % of the initial capacitance after 3000 galvanostatic charge–discharge (GCD) cycles, respectively. Additionally, an asymmetric supercapacitor (ASC) device NCN//CNS is constructed using NCN and CNS as positive and negative electrodes, utilizing poly(vinyl alcohol) PVA − KOH gel electrolyte separator. The ASC device demonstrates a maximum energy density of 50.4 Wh kg−1 (181.44 KJ kg−1) with a power density ∼ 750 W kg−1 at 1 A g−1, maintaining 90.4 % cyclic stability after 10,000 GCD cycles. The electrochemical outputs of the device present significant potential for the advancement of high-performance ASC devices in electronic applications.

Self-healable PVA-Borax-K2SO4 hydrogel electrolyte for flexible symmetric supercapacitors

The self-healing hydrogel materials are formed from the reaction between polyvinyl alcohol (PVA) and sodium tetraborate (Borax). The O-B-C vibration peak from the FT-IR spectrum is used to confirm the formation of the self-healing hydrogel structure. With 0.5 M concentration K2SO4, the resistivity of PVA-Borax-K2SO4 material is evaluated by Bode cure and obtained at 4.13 Ω.cm. With the improvement in hybrid structure, the flexible supercapacitor (FSS) devices were fabricated from two carbon fiber fabrics as symmetric electrodes with a self-healing hydrogel material (PVA-Borax-K2SO4) as electrolyte and separator. The electrochemical performances of flexible symmetric supercapacitor (FSS) devices are measured by cyclic voltammetric, charge/discharge, and impedance tests. The specific capacitance of FSS obtained 1.725 mF/cm2 at 0.05 mA/cm2 discharge current. Moreover, the stability of the FSS device attained confirmation by the comparison of the specific capacitance at 2 and 50 cycles.

Preparation and electrochemical performances of core-shell microtubular PPy/CNT/MOF ternary composites with spherical Co-MOF as sacrificial template

Here we developed PPy/CNT/MOF ternary composites with microtubular structure, which was triggered by both the disassembly of Co-MOF and the reassembly of phosphomolybdate acid (PMA) and the released ligand. As a result, the CNTs and polypyrroles (PPys) are intertwined and deposited on the surface of the composites, forming a core-shell structure. Among the ternary composites, the PM/CNT/MOF-2 electrode (PMA concertation of 5 mM) provides a specific capacitance of 650 F g−1 at 1 A g−1. The assembled flexible supercapacitor device delivered a high energy density of 68.9 μWh cm−2 (45.9 Wh kg−1) at power density of 800 μW cm−2 (800 W kg−1), a good long-term cyclic stability, and superior mechanical flexibility.

Facile and Nondestructive Transformation of Intrinsic Hydrophobic Behavior of a Carbon Nanotubes Sheet to Hydrophilic.

It is imperative to induce hydrophilicity in intrinsically hydrophobic carbon nanotubes (CNTs) without losing their superior properties for applications that specifically deal with aqueous media. A method for transforming a CNTs sheet from hydrophobic to hydrophilic by treatment with N-methyl-2-pyrrolidone (NMP) is explored. The NMP-treated CNT sheets are assessed based on complementing characterization, and it is concluded that the binding of NMP to a CNTs surface is through noncovalent interaction without the incorporation of defects in CNTs. The induced hydrophilicity in the CNTs sheet is stable for water exposure over a longer duration while it displays a semireversible nature upon heat treatment. The mechanical and electrical properties of the NMP-treated CNTs sheet revealed enhancement in the tensile strength from 221 to 421 MPa while maintaining a good electrical conductivity of ∼1.22 × 104 S/m because of the improved interfacial properties. The hydrophilic CNTs exhibited excellent adsorption capacity for methylene blue dye. The NMP-treated CNTs sheets demonstrated their suitability in flexible hybrid supercapacitor (FHSC) devices with improved electrochemical performance with enhancement in the capacitance from 5.4 to 7.6 F/g and a decrease in the equivalent series resistance from 53 to 34 Ω compared to pristine CNTs-based devices. These solid-state FHSC devices displayed excellent cyclic charge-discharge performance along with robust behavior over thousands of bending cycles without significant performance degradation. The excellent dye removal capability and superior electrochemical performance of the NMP-treated CNTs sheet is a consequence of their improved interface with aqueous media, which is governed by the hydrophilic nature of the CNTs sheet.

Flexible electrodes composed of flower-like MoS2 and MXene for supercapacitor applications

Flexible supercapacitors with high charge storage ability are needed for emerging applications in wearable electronics. Here, we introduce a novel flexible supercapacitor electrode by incorporating flower-like MoS2 into MXene via a hydrothermal technique. We mostly focused on the structural design for electrode configuration to enhance the charge storage mechanism. Three different electrodes composed of MoS2, MXene, and MoS2@MXene were fabricated via a versatile drop-casting and drying method. There are unique advantages of incorporating MoS2 with MXene such as the fast electron transfer, hydrophilicity of the interface, and structural stability. The MoS2@MXene // MXene flexible asymmetric supercapacitor device offered a high energy density of 1.21 W h /kg and a power density of 54.45 W /kg. Moreover, the asymmetric device exhibits nearly identical electrochemical behavior following 100 bending cycles at different angles. The high electrochemical activity of MoS2 and MXene and good interaction are ascribed to the superior electrochemical performance of the composite material. Furthermore, this research could guide the development of flexible, high-performance, and low-cost electrodes which will be useful in wearable electronics.

Bio-based conductive polyurethane composites derived from renewable castor oil with enhanced self-healing ability for flexible supercapacitors

To alleviate the pressure on the petrochemical industry and address environmental concerns, the utilization of polyurethane (PU) derived from castor oil (CO) (as an ester polyol replacement of petrochemical-based materials) has garnered significant attention in recent decades. Extending the service life of materials requires imparting self-healing properties to vegetable oil-based polymers, an aspect that has received limited attention in current studies. However, low self-healing efficiency still poses a significant challenge, and non-conductivity also remains an obstacle in current research, crucial for their application in electronic devices. In this work, we present the first series of electrically self-healing biopolymer composites constructed by incorporating carbon nanotube (CNT) networks into crosslinked castor oil-based polyurethane (BPU) through a simple curing process. These materials address the challenges mentioned above and exhibit improved mechanical, electrical, and self-healing capabilities compared to other bio-based self-healing materials. The resulting BPU/CNT composite demonstrated exceptional repeated self-healing capacity, restoring both mechanical properties and electrical performance even after experiencing severe mechanical damage. Notably, this composite served as a conductive substrate in flexible solid-state supercapacitor (FSSC) devices. Consequently, the FSSC derived from the composite conductive substrate achieved an impressive 92.4 % self-healing efficiency even after undergoing 7 cutting/healing cycles. The device remained virtually unchanged even after being bent at a 180° angle with a bending radius of 1.6 mm, indicating excellent repeatability and durability. The exceptional self-healing ability, with ∼98 % electrical recovery at 100 °C for 70 s and 93 % at 80 °C after 6 min, of these composites was attributed to the synergistic interactions of the dynamic exchange reactions of disulfide bonds and dense hydrogen bonds within the BPU matrix, which provide a reversible dynamic polymer network. The healing efficiency of these dynamic bonds was evaluated by adjusting the composition ratio of the long linear chain of pTHF in hybrid polyols of the crosslinked polymer network. Overall, this work highlights a series of green, simple, and highly efficient self-healing polymer composites derived from renewable castor oil, and it establishes an essential framework for future sustainable polymer composite design.

In situ growth of a redox-active metal-organic framework on electrospun carbon nanofibers as a free-standing electrode for flexible energy storage devices.

The rational construction of free-standing and flexible electrodes for application in electrochemical energy storage devices and next-generation supercapacitors is an emerging research focus. Herein, we prepared a redox-active ferrocene dicarboxylic acid (Fc)-based nickel metal-organic framework (MOF) on electrospun carbon nanofibers (NiFc-MOF@CNFs) via an in situ approach. This in situ approach avoided the aggregation of the MOF. The NiFc-MOF@CNF flexible electrode showed a high redox-active behavior owing to the presence of ferrocene and flexible carbon nanofibers, which led to unique properties, including high flexibility and lightweight. Furthermore, the prepared electrode was utilized in a supercapacitors (SC) without the use of any binder, which achieved a specific capacity of 460 C g-1 at 1 A g-1 with an excellent cyclic retention of 82.2% after 25 000 cycles and a good rate capability. A flexible asymmetric supercapacitor device was assembled, which delivered a high energy density of 56.25 W h kg-1 and a long-lasting cycling performance. Also, the prepared electrode could be used as a freestanding electrode in flexible devices at different bending angles. The obtained cyclic voltammetry curves showed negligible changes, indicating the high stability and good flexibility of the electrode. Thus, the use of the in situ strategy can lead to the uniform growth of redox-active MOFs or other porous materials on CNFs.

Effect of in situ annealing on pulsed laser ablated mixed metal oxide (BixMyOz; M=Mn, Mo) thin film electrodes for flexible hybrid supercapacitor devices

Recently, solid-state thin film hybrid supercapacitor devices (TFHSCs) have had greater attention due to their miniaturized device assembly, portability, and superior cycling stability. Herein, for the first time, we assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 thin-film solid-state supercapacitor devices by pulsed laser deposition (PLD) technique. In the present work, Bi2MoO6 and BiMnxOy thin film electrodes are fabricated at in-situ annealed conditions and their structural, morphological, and electrochemical performances are examined distinctly. We assembled a thin-film based BiMnxOy ǁ PVA-KOH ǁ BiMnxOy symmetric supercapacitor device (SSD) and that device delivers a functioning voltage of 1.4 V. Also, the device exhibits an extremely specific areal capacitance of 41 mF cm−2 at 1 mA cm−2. Similarly, a thin film-based Bi2MoO6 ǁ PVA-KOH ǁ Bi2MoO6 SSD attained a maximum specific areal capacitance of 13.33 mF cm−2. Further, the assembled BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device delivers a voltage of 1.6 V and the TFHSC device exhibited a maximum specific areal capacitance of 52 mF cm−2 at a fixed current density of about 2 mA cm−2. The BiMnxOy ǁ PVA-KOH ǁ Bi2MoO6 TFHSC device shows outstanding stability performances such as 99 % of capacitance retention as well as 93 % of coulombic efficiency after 25,000 charge/discharge cycles. Additionally, the TFHSC device delivers a maximum areal energy density and power density of 18.5 μWh.cm−2, and 978.7 μW cm−2, respectively.

Protective hydrothermal treatment to improve ion pathway in Ti3C2Tx MXene for high-performance flexible supercapacitors

The strong re-stacking of Ti3C2Tx MXene nanosheets severely blocks ion transport pathway and sacrifices electrochemical performance. Here, a protective hydrothermal treatment is used to improve ion pathway in Ti3C2Tx MXene. The protective hydrothermal treatment is simply conducted in the hydrothermal kettle (filled with N2 atmosphere) placed in vacuum oven. The optimal Ti3C2Tx is achieved by the hydrothermal treatment of 150 °C for 12h, and recorded as h-Ti3C2Tx@150 °C/12h. The h-Ti3C2Tx@150 °C/12h film electrode achieves significantly improved ion transport pathways and enhanced ion accessibility with more pseudocapacitive active sites due to the increased interlayer spacing and pores as well as decreased flake size. According to DFT calculations, a small number of oxides (TiO2 nanoparticles) produced during the hydrothermal treatment also facilitate to increase the capacitive performance of h-Ti3C2Tx@150 °C/12h. Therefore, the h-Ti3C2Tx@150 °C/12h film electrode achieves significantly increased capacitance and rate performance. The h-Ti3C2Tx@150 °C/12h film electrode exhibits excellent capacitance (498.3 F g−1 and 1911 F cm−3 at 1 A g−1) and rate performance (63 % retention from 1 to 20 A g−1) with high cycling stability (98.2 % retention after 20 000 cycles), which are among the best electrochemical performances of undoped Ti3C2Tx based film electrodes reported so far. Thick h-Ti3C2Tx@150 °C/12h film electrode of 33.1 μm thickness exhibits an ultra-high areal capacitance of 3.23 F cm−2 at 1 A g−1. Moreover, the h-Ti3C2Tx@150 °C/12h-based flexible symmetric supercapacitor device exhibits excellent energy storage performance (117 F g−1 at 0.5 A g−1 and 23.4 Wh kg−1 at 299.8 W kg−1) with high cycling stability (84 % retention after 3000 cycles) and bending stability, outperforming most of previously reported Ti3C2Tx-based flexible supercapacitors. The impressive results indicate the great application potential of the h-Ti3C2Tx@150 °C/12h film in flexible energy storage devices.

Activated Carbon Nanofiber Sheets Derived from Electrospun Lignin: PVA Blend for Flexible Supercapacitors

The present investigation reports the performance of ultra-flexible activated carbon nanofiber sheets (ACNF) as a flexible electrode for supercapacitors application. ACNF was fabricated by pre-carbonization at 600 °C and then by activation using potassium hydroxide (KOH) at 800 °C.These ACNF sheets prepared via the facile electrospinning technique possess the morphology of the nanofiber network with the diameter range (600-1400 nm) of the carbon. The findings demonstrate that the activation method not only enhances the sheet's surface area (806.9 m2/g) and total pore volume (0.519 cc/g) but also eliminates the lignin polymer's inherent sodium (Na) impurity through washing. This interconnected nanofiber sheet possesses high electrical conductivity of 8.40 S/cm. These sheets exhibit cloth-like flexibility with high electrical conductivity and porosity, making them suitable candidates for flexible electrodes. Raman spectroscopy was also carried out to get information about sp2 carbon. Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD), and Electrochemical Impedance Spectroscopy (EIS) were performed to understand the electrochemical performance of the sheets as electrodes. This ACNF sheet demonstrate a higher specific capacitance of 203.29 F/g at a current density of 1 A/g in a three-electrode configuration. Furthermore, a flexible supercapacitor device was fabricated using an ACNF sheet due to its high flexibility, stand-alone character, and excellent performance as an electrode. The device exhibits a high energy density of 65.52 Wh/kg and a power density of 1036.27 W/kg with high coulombic efficiency (99.6%) after 10,000 cycles. Also, the prepared device illuminated the seven-segment display in various bending conditions showing its flexibility.

Gel Polymer Electrolytes for Flexible LiXPO4 (X=Mn,Fe,Co)-Fractal-like Fe2O3 Hybrid Supercapacitor Devices

In the recent years, the development of electrochemical energy storage device has been widely investigated. Supercapacitors are known for their excellent power density and superb cycling stability but restricted by low charge storage capacity, on the other hand batteries provide high energy density, limited by low power density. Here, olivine-structured LiXPO4 (X=Mn,Fe,Co) possessing high energy storage capability is used as a positive electrode. Our recent research demonstrated that Fe2O3-based Fractal-like structures supported on Ni Foam exhibit extremely high specific capacitance of ~2708 F g-1 at 1 A g-1 in 1 M KOH electrolyte, when used as negative electrode [1]. Hence, the Fractal-like Fe2O3 is used as the negative electrode for the envisaged hybrid supercapacitor device. The flexibility is imparted to these devices by employing carbon cloth as the current collector. The choice of suitable electrolyte is crucial for supercapacitor applications as it decides the working potential window, electrode-electrolyte interaction, and ionic conductivity. Here, PVA based gel polymer electrolyte (GPE) is used due to the ease in gel formation and non-toxicity to make flexible hybrid supercapacitor device. Different PVA based GPEs are synthesized using H3PO4, H2SO4 and KOH with Ionic liquids viz. EMIMBF4 and EMIMCl. The role of GPEs in the performance of LiXPO4 (X=Mn,Fe,Co)//GPE//Fe2O3 hybrid supercapacitors is understood through charge storage mechanisms deciphered from galvanostatic charge-discharge (GCD) experiments, Electrochemical Impedance Spectroscopy (EIS).

Cerium-assembled tungsten oxide composite fibers: Adhesive-free electrodes for high performance asymmetric supercapacitors

In this study, in-situ cerium-assembled tungsten oxide carbon nanofibers were successfully prepared via simple electrospinning and calcination technology and were used as flexible electrodes without conductive agent and adhesive. It was confirmed that the introduction of Ce has better maintained the continuous morphology of one-dimensional fibers to provide a continuous uninterrupted reaction position by the SEM TEM and XPS results. The addition of cerium improved the wettability of the material, which was propitious to the penetration of the electrolyte, made the electrolyte more fully contact with the active site, and enhanced the interface transmission effectiveness by the liquid contact angle test. Otherwise, the XRD and XPS results exhibited that the addition of cerium has caused the lattice expansion of the tungsten oxide, which generated the self-adjustable strain relaxation ability of electrode material in the process of continuous constant voltage charge and discharge. It proved that the introduction of cerium has promoted electron transfer, which improved the electrochemical performance of electrode material. In this paper, compared with WO3-CNFs without Ce, the Ce/WO3-CNFs have wide lattice spacing and hydrophilicity, fully contact with the electrolyte in the electrochemical reaction, and provide high electron transfer ability. The Ce/WO3-CNFs shows the maximum specific capacitance (407 F g−1) and excellent cycling stability (10,000 cycles at 5 A g−1 with a retention rate of 80 %). Otherwise, the flexible asymmetric supercapacitor device was prepared using the Ce/WO3-CNFs as cathode, and the CNFs as the anode, which exhibited the maximum energy density was 35.75 Wh kg−1 and a power density was 362.54 W kg−1 at 0.5A g−1. The results show that rare earth doping is an effective way and that the Ce/WO3-CNFs are promising electrode materials for supercapacitors.

Flower-like FeCoNi ternary composite formed by interweaving nano needles for positive electrode material of supercapacitor

Ternary layered double hydroxide (LDH) are potential electrode material choices for supercapacitors (SCs) due to their various oxidation states and high theoretical specific capacitance. In this paper, FeCoNi-LDH composite with cross-braided flowers of nanoneedles has been prepared by a single-step hydrothermal method. By highlighting the structural and morphological advantages, the obtained ternary LDH shows lower resistivity in comparison with the binary LDH. As electrode material, the ternary LDH exhibits excellent electrochemical properties, such as superb specific capacitance of 2163.3 F·g−1 at 0.5 A·g−1 and good cycle retention rate of 93.8% after 5000 cycles at 20 A·g−1. Meanwhile, the assembled asymmetric flexible solid-state supercapacitor device can provide 44.8 Wh·kg−1 energy density at 807.5 W·kg−1. Moreover, two devices in series can also light up miniature light bulbs of different hues and maintain them for a long period when they are connected in series.

A green approach for synthesis of an efficient nano pebbles-like BiVO4@C electrode for supercapacitor application

A simple, sustainable, cost-effective, and environmentally benign BiVO4@C electrode is developed via an in-situ bio-mediated green SILAR approach. The optimized synthesis and electrochemical characterization of a BiVO4@C and BiVO4 electrode are reported. The in-situ incorporation of carbon in the BiVO4 (BiVO4@C) was determined by Raman, XPS, and FTIR spectroscopy. The BiVO4@C electrode demonstrates a large specific surface area (106.7 m2 g−1), higher charge storage, superior capacitive performance, longer discharge time, and excellent cycling stability when compared to BiVO4. The flexible solid-state symmetric supercapacitor (SSC) device using BiVO4@C electrode material with PVA/KOH electrolyte gel delivered maximum specific capacitance (Csp) (154.6 F g−1) and energy density of 42.0 Wh kg−1 at a power density of 571.6 W kg−1. Moreover, the symmetric device exhibited cycle stability of 5000 cycles with 97.4 % capacitance retention paving the way for developing sustainable supercapacitors for commercial application.

Designing dynamic metal-coordinated hydrophobically associated mechanically robust and stretchable hydrogels for versatile, multifunctional applications in strain sensing, actuation and flexible supercapacitors

Combining the synergistic effect of dynamic metal–ligand cross-linking and hydrophobic association along with low density chemical cross-linking, we have developed a mechanically robust and stretchable hydrogel that was synthesized by micellar copolymerization of acrylamide (AM), maleic acid (MA) and butyl acrylate monomer. With optimized composition, this hydrogel showed ∼ 3 MPa tensile strength & ∼ 60 MPa compressive strength. The hydrogel is stretchable ∼ 7 times of its original length. These hydrogel materials are flexible and can be folded, bent, and twisted due to their high toughness (∼10 MJ m−3) and low elastic modulus (0.56 MPa). Because of the dynamic nature of metal–ligand interaction and hydrophobic association, the hydrogel showed high energy dissipation under tensile deformation and quick recovery of the dissipated energy after repeated loading and unloading. This hydrogel showed pH responsive mechanical properties. At lower pH, the mechanical strength and elastic modulus of the hydrogel deteriorated due to the dissociation of metal–ligand interaction. This concept was further used for demonstrating shape memory effect in these materials. Utilizing the colorimetric change in presence of Fe3+ and H+, the hydrogel can be used for data encryption-decryption technology. Combining with a thermoresponsive hydrogel (Poly (N-Isopropyl acrylamide)) layer, our hydrogel showed excellent thermoresponsive reversible actuation effect. Furthermore, because of its high ionic conductivity and strain dependent resistance change, the hydrogel can be used as a flexible strain sensor and as a compressible electrolyte in flexible supercapacitor devices.

A flexible wearable self-supporting hybrid supercapacitor device based on hierarchical nickel cobalt sulfide@C electrode

A flexible wearable electrode consisting of nickel–cobalt sulfide (NCS) nanowires was fabricated in this study. Self-supporting NCS was grown in situ on porous carbon nanofibers without a binder as a novel material for supercapacitor electrodes. The NCS nanowires were grown using cyclic voltammetry electrodeposition, which proved to be a fast and environmentally friendly method with good controllability of the material structure. One-dimensional carbon nanofibers (C) have high surface-area-to-volume ratios, short ion transmission distances, excellent mechanical strengths, and remarkable flexibilities. Moreover, the NCS@C flexible electrode exhibited a synergetic effect with the active compounds, and the dense active sites were uniformly distributed across the entire surface of the carbon fibers, enabling rapid electron transport and enhancing the electrochemical properties of the NCS@C nanowires. The NCS@C achieved specific capacitances of 334.7 and 242.0 mAh g−1 at a current density of 2 A g−1 and high current densities (up to 40 A g−1), respectively, corresponding to a 72.3% retention rate. An NCS@C-nanofilm-based cathode and an activated-carbon-based anode were used to fabricate a flexible asymmetric supercapacitor. The device exhibited high energy and power densities of 12.91 Wh kg−1 and 358 W kg−1, respectively.

Fabrication of flexible and aqueous hybrid supercapacitors with diffusion channels contained copper cobalt bi-Metal Organic Framework nanosheets and ionic conductivity optimized semi-solid electrolyte

Metal-Organic Frameworks (MOFs) have established as important energy storage materials owing to their tunable pore diameter, high specific surface area, low density, easily accessible metal active centers, tunable morphology, and high catalytic activity. Supercapacitor electrode materials should be specifically needed some properties like high specific surface area, electrochemically active, and high electrical as well as ionic conductivity. Copper has high electrical conductivity, and cobalt has high electrochemical activity. Using their advantages in this work, copper and cobalt are used as metal active centers for bi-Metal Organic Framework (bMOF). The morphology of bMOF is tuned by temperature-assisted solvothermal synthesis method, and a perfect nanosheet-like structure is obtained at 140 °C. It exhibited a high specific capacity of 1049.5 C g−1 at 1 A g−1. Aqueous and flexible hybrid supercapacitor devices are fabricated using bMOF and activated carbon. Aqueous hybrid supercapacitor device provides a maximum specific energy of 91.3 W h kg−1 and a maximum specific power of 14.14 kW kg−1. For a flexible hybrid supercapacitor device (FHSD), semi-solid electrolyte's ionic conductivity is optimized by injecting water with various weight ratios. FHSD exhibits a maximum specific energy of 82.3 W h kg−1 and a maximum specific power of 16.23 kW kg−1 in an optimized semi-solid electrolyte. It retains 82.9 % of its initial specific capacity after 12,000 charge-discharge cycles. The flexibility of FHSD is investigated by cyclic bending and stretching of it during charge-discharge.

Achieving enhanced pseudocapacitance in MoS2 nanowires rationally sputtered over NiMnIn shape memory alloy for flexible Na-ion supercapacitor

The present study reports a flexible supercapacitor device incorporating thin-film electrodes (TFEs) of MoS2 nanowires integrated with NiMnIn shape memory alloy nanoparticles fabricated in situ via magnetron sputtering technique. Electrochemical analyses reveal the MoS2-NiMnIn superior pseudocapacitive charge-storage potential through Na+ and Li+ kinetics, primarily attributed to the synergistically coupled heterojunctions between MoS2 nanowires and NiMnIn nanoparticles resulting in enhanced ionic conductivity, increased specific surface area, improved substrate adherence, and overall better electrical conductivity. Consequently, the flexible MoS2/NiMnIn/SS TFE attains a high specific capacitance of ~487.86 F.g−1 (87.82 mF.cm−2, 355.53 F.cm−3) in 1 M Na2SO4 at 0.7 A.g−1. Moreover, an extensive qualitative and quantitative analysis through voltammetry and AC impedance-derived techniques has been presented, revealing a dominant contribution from surface-controlled capacitive and pseudocapacitive kinetics in both Na+ and Li+ storage. An all-solid-state flexible symmetric supercapacitor (SSC) device fabricated using PVA-Na2SO4 gel electrolyte exhibits a maximum cell capacitance of ~208 F.g−1 (37.57 mF.cm−2, 192.07 F.cm−3) at 0.56 A.g−1. Interestingly, the Na+-charged SSC device presents an attractive balance of high energy (~28.99 Wh.kg−1) and power densities (~12.81 kW.kg−1) while simultaneously delivering an exceptional electrochemical cyclability, retaining ~97.5% over 6000 charge-discharge cycles. In addition, a highly desirable mechanical stability of ~93.68% for the TFE and ~88% for the SSC device at +90° bending over 1000 GCD cycles illustrates the robust structural integrity exhibited by the 3D nanostructured MoS2-NiMnIn material.