Three-Dimensional MoS2 @CNT/RGO Network Composites for High-Performance Flexible Supercapacitors.

Binder-free hydrogen storage composite Co9S8/rGO: A prospective anode for flexible energy storage device with high energy density

Systematic design of MXene/thermoplastic polyurethane/carbon nanotube@polypyrrole fiber electrodes for efficient flexible fiber supercapacitors.

The weak stiffness, huge thickness, and low specific capacitance of commonly utilized flexible supercapacitors hinder their great electrochemical performance. Learning from a biomimetic interface strategy, we design flexible film electrodes based on functional intercalated structures with excellent electrochemical properties and mechanical flexibility. A composite film with high strength and flexibility is created using graphene (reduced graphene oxide (rGO)) as the plane layer, layered double metal hydroxide (LDH) as the support layer, and cellulose nanofiber (CNF) as the connection agent and flexible agent. The interlayer height can be adjusted by the ion concentration. The highly interconnected network enables excellent electron and ion transport channels, facilitating rapid ion diffusion and redox reactions. Moreover, the high flexibility and mechanical properties of the film achieve multiple folding and bending. The CNF-rGO-NiCoLDH film electrode exhibits high capacitance performance (3620.5 mF cm-2 at 2 mA cm-2), excellent mechanical properties, and high flexibility. Notably, flexible all-solid assembled CNF-rGO-NiCoLDH//rGO has an extremely high area energy density of 53.5 mWh cm-2 at a power density of 1071.2 mW cm-2, along with cycling stability of 89.8% retention after 10 000 charge-discharge cycles. This work provides a perspective for designing high-performance energy storage materials for flexible electronics and wearable devices.

Design and synthesis of novel electroactive 2,2′:5′,2″-terthiophene monomers including oxyethylene chains for solid-state flexible energy storage applications

Two-dimensional atomically thick materials such as graphene and layered molybdenum disulfide (MoS2) have been studied as potential energy storage materials because of their high specific surface area, potential redox activity, and mechanical flexibility. However, because of the layered structure restacking and poor electrical conductivity, these materials are unable to attain their full potential. Composite electrodes made of a mixture of graphene and MoS2 have been shown to partially resolve these issues in the past, although their performance is still limited by inadequate mixing at the nanoscale. Herein, we report three composites via a simple ball-milling method and analyze supercapacitor electrodes. Compared with pristine graphene and MoS2, the composites showed high capacitance. The as-obtained MoS2@Graphene composite (1:9) possesses a high surface area and uniform dispersion of MoS2 on the graphene sheet. The MoS2@Graphene (1:9) composite electrode has a high specific capacitance of 248 F g-1 at 5 A g-1 in an electrochemical supercapacitor compared with the other two composites. Simultaneously, the flexible symmetric supercapacitor device prepared demonstrated superior flexibility and a long lifespan (93% capacitance retention after 8000 cycles) with no obvious changes in performance under different angles. In portable and wearable energy storage devices, the current experimental results will result in scalable, freestanding hybrid electrodes with improved, flexible, supercapacitive performance.

Poly(vinyl alcohol) (PVA) hydrogel electrolytes are widely used in flexible energy storage devices because of their high safety, excellent flexibility and biocompatibility. However, PVA hydrogels suffer from low mechanical strength and poor electrochemical properties. To address this issue, in this study, a green composite hydrogel was prepared by introducing Illite, a silicate clay with a lamellar structure, into PVA hydrogel using a cyclic freeze-thaw method. Illite interacts with PVA molecular chains to form hydrogen bonds, leading to a robust cross-linked network structure, which significantly enhances the mechanical properties of the compliant hydrogels. The composite hydrogel prepared by adding 2% Illite to PVA (denoted as P-I2%) has a tensile strength of 1.52 MPa, elongation at break of 524%, and compressive strength of 0.97 MPa. Moreover, the lamellar structure of Illite generates directional channels in the PVA gel matrix, enabling the P-I2% hydrogel electrolyte to exhibit high ionic conductivity (41.9 mS cm-1). The specific discharge capacity of the supercapacitor assembled using the P-I2% hydrogel electrolyte was 116.97 mF cm-2 at a current density of 1 mA cm-2, and the capacitance retention rate of the P-I2%-based supercapacitor was 86.61% after 5000 working cycles at a current density of 5 mA cm-2. This work provides new ideas for clay minerals in the pathway to enhance the performance of hydrogel electrolytes.

Polypyrrole/carbon cloth flexible composite electrodes are prepared by growing polypyrrole on carbon cloth surface by vapour phase polymerization. This method is low-cost, scalable and does not require any conductive additives or adhesives during electrode fabrication. In addition, the influence of water vapour on electrode morphology and structure during the pyrrole vapour phase polymerization process was deeply studied. It was found that when water vapour was involved, the granular polypyrrole on the surface of carbon cloth was evenly distributed, and when the evaporation volume of water and pyrrole was 10:1, the electrode prepared has the best energy storage performance (1118.5mFcm-2 at 5 mA cm-2), when current density up to 20 mA cm-2, the electrode has 645.1 mF cm-2 capacitance, the corresponding capacitance retention is 57.6% exhibiting a good prospect in the application of flexible energy storage devices.

Aqueous Fe-ion hybrid capacitors, with high safety, low cost, and environmental friendliness, have attracted considerable attention as an emerging energy storage device. However, Fe-ion-based energy storage systems still face challenges, such as narrow voltage windows, limited energy density, and harsh fabrication conditions. To address these issues, this work fabricates an aqueous Fe-ion hybrid capacitor using low-cost activated carbon as the anode, manganese dioxide (MnO2) as the cathode, with an FeSO4 + NH4Cl aqueous electrolyte, successfully expanding the voltage window to 0-1.2 V. The atomic molecular dynamics simulations confirm the potential of MnO2 as a cathode material, and the spiny nanostructured MnO2 shows a large specific surface area and a stable tunnel structure, which facilitates the intercalation/deintercalation of Fe2+ ions. Consequently, the assembled device achieved a specific capacitance of 835 mF cm-2 at 1 mA cm-2 and a surface energy density of 167 μWh cm-2 with a capacitance retention of 97.2% after 3000 cycles. Furthermore, to meet wearable electronics requirements, a flexible device was assembled by integrating a carboxymethyl cellulose-poly(vinyl alcohol) hydrogel soft-packaging material. The results show that the flexible device exhibits excellent bending resistance. The further assembled flexible Fe-ion supercapacitors demonstrate a high energy storage potential. Under a current density test of 1 mA cm-2, the calculated specific capacitance is 682.4 mF cm-2, and the areal energy density is 136.48 μWh cm-2. The further assembled flexible Fe-ion supercapacitors demonstrate high energy storage potential. Under a current density test of 1 mA cm-2, the calculated specific capacitance is 682.4 mF cm-2, and the areal energy density is 136.48 μWh cm-2. Similarly, in the cycling performance test, the device retains 92.6% of its capacity after 3000 cycles. This study provides technical references for the development and practical application of flexible Fe-ion-based energy storage devices.

Laser-assisted reduction of graphene oxide (GO) has emerged as a promising method for fabricating conductive films and interdigitated electrodes onto flexible substrates, paving the way for high-performance flexible electronics and smart textiles. In this study, we demonstrate laser-reduced graphene oxide (LrGO) with an unprecedentedly low defect density (average D/G Raman band ratio of 0.1) onto bare heat-sensitive paper substrates. Under optimal lasing conditions, the paper-supported LrGO films exhibit a very low sheet resistance (<50 Ohm sq-1) and maintain good conductivity after multiple cycles of bending deformation. Increasing the laser power beyond the threshold required for GO reduction leads to a gradual decrease in defect density (as measured by Raman spectroscopy), while the surface chemistry (analyzed via X-ray Photoelectron Spectroscopy) remains largely unaffected. This suggests that excess photon energy primarily contributes to defect healing rather than further extending the reduction of LrGO. Three-electrode characterization in a 6 M KOH electrolyte revealed a maximum capacitance of 31.8 mF cm-2 at 10 mV s-1, while the capacitance of an interdigitated supercapacitor with PVA:H2SO4 electrolyte was 5.2 mF cm-2 at 0.02 mA cm-2. These values surpass those reported in recent studies on symmetric supercapacitors using LrGO electrodes on protected paper and other polymeric substrates, underlining the superior quality and potential of the electrodes developed in this work.

In this work, a simple, single-step electrochemical method is used to decorate a ternary Polypyrrole-Cu2O-MoO3 (PPy-Cu2O-MoO3) nanocomposite on Graphene Oxide (GO) nanosheets formed on a Graphite Foil Electrode (GFE). The characterization confirmed successful synthesis of ternary nanocomposite, and electrochemical tests showed the electrode performed well as both a supercapacitor and a hydrogen evolution reaction (HER). The investigation of the hydrogen production reaction by the PPy-Cu2O-MoO3/GO/GFE shows that this electrode has a smaller Tafel slope and overpotential. Additionally, the PPy-Cu2O-MoO3/GO/GFE has a specific capacitance of 1010.30 mF cm-2 at 1mA cm-2 in a 0.5 M H2SO4 electrolyte solution. The evaluation of the fabrication of a symmetric solid-state supercapacitor device shows that the constructed device has an excellent capacitance of 596.5 mF cm-2 at 1mA cm-2 and a cyclic stability of 82.4% after 6000 GCD cycles. For hydrogen evolution reaction, the electrode demonstrated an overpotential of 361 mV at 10mA cm-2 and a Tafel slope of 142 mV dec-1, indicating favorable electrocatalytic activity. These results highlight the potential of the synthesized nanocomposite as a multifunctional electrode material for both energy storage and clean energy production.

Manipulation of mechanical properties of monolayer molybdenum disulfide: Kirigami and hetero-structure based approach

Towards 3D knitted-fabric derived supercapacitors with full structural and functional integrity of fiber and electroactive materials

A facile and cost-efficient approach to functionalize raw carbon fiber paper (CFP) used for a self-standing capacitive electrode has been proposed here. Benefiting from the improved specific surface area and surface functional groups, the functionalized CFP (F-CFP) showed much enhanced capacitive performance, 3 orders of magnitude higher than that of the raw CFP. It delivered the areal capacitance of 1275 mF cm-2 at 5 mA cm-2 with a rather wide voltage window of 1.4 V (-0.4 to 1 V vs Ag/AgCl) in 0.5 M H2SO4. However, in a neutral 1 M Na2SO4 aqueous solution, although the areal capacitance of 1115 mF cm-2 at 3 mA cm-2 is slightly smaller, the potential window is much wider (2 V, -1 to 1 V vs Ag/AgCl), indicating a high overpotential of hydrogen evolution. The areal capacitance was still as high as 722 mF cm-2 at a very fast charge-discharge current density of 50 mA cm-2, and about 66% of the initial capacitance (at 3 mA cm-2) was remained in Na2SO4, indicating considerable rate capability.

Three dimensional (3-D) nanopores array has been widely regarded as the promising current collector for fabrication of pseudocapacitor electrodes, mainly due to its large surface area, efficient electron and ion transport, and strong structural stability. Typically, anodization of high purity aluminium (Al) is the facile method to achieve highly packed nanopores with straight channels, of which the structural parameters could be facilely tuned by anodization voltage and etching time. By deposition of conductive and active materials, each channel could serve as the unit cell to store the energy. Nevertheless, the drawbacks still exist in such structure from the following aspects: i) Each channel has the electronic connection only at the top of the nanopores, leading to long pathway for electron transport. ii) The ions diffusion pathway is cut off by the side walls of anodized aluminium oxide (AAO), resulting in the one dimensional diffusion way along the channel. iii) The volume/space occupied by AAO side walls has no contribution to the capacitance, resulting in the low efficient utilization of the nanostructure. To address above issues, we have engineered the 3-D interconnected nanopores array by anodization of unique Al alloy. In such an architecture, the side pores are uniformly distributed along the main channel of AAO, forming more porous and mechanically stable nanopores array. By controllable deposition of fluorine doped tin oxide (FTO) with the cost-effective method of ultrasonic spray pyrolysis, and electrochemical deposition of MnO2, the as-built pseudocapacitor electrode renders the highest areal capacitance of 322.6 mF cm-2 and volumetric capacitance of 80.65 F cm-3 at the discharging current density of 0.1 mA cm-2, and still maintains 236 mF cm-2 and 59 F cm-3 at the discharging current density of 1.5 mA cm-2. By contrast, the values for the pseudocapacitor electrode fabricated based on the traditional nanopores array current collector are 273.8 mF cm-2 and 68.45 F cm-3, respectively, and drastically degrade to 50 mF cm-2 and 12.5 F cm-3. The performance enhancement is much larger when the comparison falls on planar pseudocapacitor electrode. We ascribe the largely enhanced rate capability to two reasons: i) The interconnected nanopores structure offers more space, which benefits for loading of nanostructured MnO2. ii) The side pores allow ions to move freely into neighbouring channels, resulting in the faster ion diffusion. In this case, we regard such interconnected nanopores array as the superior current collector in pursuit of high performance pseudocapacitor electrode. Figure 1

Flexible supercapacitors with high electrochemical performance and stability along with mechanical robustness have gained immense attraction due to the substantial advancements and rampant requirements of storage devices. To meet the exponentially growing demand of microsized energy storage device, a cost-effective and durable supercapacitor is mandatory to realize their practical applications. Here, in this work, the fabrication route of novel electrode materials with high flexibility and charge-storage capability is reported using the hybrid structure of 1D zinc oxide (ZnO) nanorods and conductive polyvinylidene fluoride-tetrafluoroethylene (P(VDF-TrFE)) electrospun nanofibers. The ZnO nanorods are conformably grown on conductive P(VDF-TrFE) nanofibers to fabricate the light-weighted porous electrodes for supercapacitors. The conductive nanofibers acts as a high surface area scaffold with significant electrochemical performance, while the addition of ZnO nanorods further enhances the specific capacitance by 59%. The symmetric cell with the fabricated electrodes presents high areal capacitance of 1.22 mF cm-2 at a current density of 0.1 mA cm-2 with a power density of more than 1600 W kg-1 . Furthermore, these electrodes show outstanding flexibility and high stability with 96% and 78% retention in specific capacitance after 1000 and 5000 cycles, respectively. The notable mechanical durability and robustness of the cell acquire both good flexibility and high performance.