Spatial-Interleaving Graphene Supercapacitor with High Area Energy Density and Mechanical Flexibility

In Situ Laser Direct Writing of Graphene-Based Layered Hybrid Materials with Superhydrophilicity

Laser-induced graphene (LIG) has attracted extensive attention as an electrode material. However, it usually exhibits limited electrochemical performance in many applications due to the limited electrical conductivity and charge storage properties. Herein, we proposed a simple and environmentally friendly strategy for in situ preparation of flexible Au/LIG/PI layered hybrid materials using laser direct writing. The transformation from hydrophobic to superhydrophilic of hybrid materials was successfully achieved. At a laser power of 6.0 W during laser reirradiation, the contact angle of the prepared Au/LIG/PI layered hybrid material was 0°. Characterizations confirmed a formed continuous Au layer covered on the porous LIG skeleton with a uniform distribution. The superhydrophilicity resulting from this unique microstructure greatly enhanced the electrochemical performance of the microsupercapacitors (MSCs) designed and fabricated based on Au/LIG/PI hybrid materials. Meanwhile, this MSC demonstrated excellent flexibility due to the PI substrate. The in situ preparation of superhydrophilic Au/LIG/PI layered hybrid materials provides a strategy for improving the performance of LIG-based MSCs, thereby enhancing their application potential.

Highly capacitive MXene film by incorporating poly(3,4-ethylenedioxythiophene) hollow spheres prepared through an interfacial oxidation polymerization

Sheets stacking of Ti3C2Tx MXene dramatically reduces the ion-accessible sites and brings a sluggish reaction kinetics. While introducing transitional metal oxides or polymers in the MXene films could partially alleviate such issue, their enhanced performances are realized at the expense of electrode conductivity or cycling stability. Herein, we report an alternative spacer of conductive poly(3,4-ethylenedioxythiophene) (PEDOT) hollow spheres (HSs) which are fabricated by a facile template-assisted interfacial polymerization. The Fe3+ ions electrostatically adsorbed on the -SO3H groups of the sulfonated polystyrene spheres (S-PS) initiate the polymerization of uniform PEDOT shell, yielding uniform PEDOT HSs after dissolving the S-PS core. Introducing these PEDOT HSs in the MXene film generates the highly flexible MXene-PEDOT (MP) films featuring hierarchically porous network and high conductivity (283 S cm-1). Consequently, specific capacitance of 218 F g-1 at 3  mV s-1, along with a forty-folds decrease in relaxation time constant (1.0 vs 39.8 s) has been achieved. Moreover, the MP film also exhibits nearly thickness-independent capacitive performances with film thickness in the range of 10-46 μm. A maximal energy density of 21.2 μWh cm-2 at 1015 μW cm-2 together with 92 % capacitance retention over 5000 cycles are achieved for the MP-based solid-state supercapacitor. The intrinsic high conductivity, excellent mechanical flexibility and good structure integrity are responsible for such outstanding electrochemical behaviors.

Overview of recent developments in carbon-based nanocomposites for supercapacitor applications

Energy storage devices are recognized as environmentally friendly technologies. Supercapacitors, known for their high cycle stability, have been proposed as potential alternatives to fossil fuels. Recent studies have focused on selecting suitable electrode materials to achieve energy storage systems with high stability, high specific capacity, and biocompatibility. In particular, carbon-based electrode materials, such as graphene oxide, activated carbon, carbon nanotubes, and carbon-based quantum dots, have attracted considerable attention due to their intrinsic properties, such as high conductivity and stability. However, carbon materials alone exhibit limitations, such as low energy density and low specific capacitance. To address this limitation, the synergistic effect of carbon materials has been combined with other electroactive materials to develop electrode materials with enhanced supercapacitor properties. The present study also investigates the supercapacitor performance of carbon-based nanocomposites. It examines the effect of each carbon material (AC, CNT, GO, rGO) on improving the performance of other electroactive materials, including metal oxides, metal sulfides, MXenes, MOFs, and conductive polymers. This study provides valuable insights for further studies on carbon-based electrode materials for supercapacitor applications.

Fully Printed, High-Temperature Micro-Supercapacitor Arrays Enabled by a Hexagonal Boron Nitride Ionogel Electrolyte

The proliferation and miniaturization of portable electronics require energy-storage devices that are simultaneously compact, flexible, and amenable to scalable manufacturing. In this work, mechanically flexible micro-supercapacitor arrays are demonstrated via sequential high-speed screen printing of conductive graphene electrodes and a high-temperature hexagonal boron nitride (hBN) ionogel electrolyte. By combining the superlative dielectric properties of 2D hBN with the high ionic conductivity of ionic liquids, the resulting hBN ionogel electrolyte enables micro-supercapacitors with exceptional areal capacitances that approach 1 mF cm-2. Unlike incumbent polymer-based electrolytes, the high-temperature stability of the hBN ionogel electrolyte implies that the printed micro-supercapacitors can be operated at unprecedentedly high temperatures up to 180 °C. These elevated operating temperatures result in increased power densities that make these printed micro-supercapacitors particularly promising for applications in harsh environments such as underground exploration, aviation, and electric vehicles. The combination of enhanced functionality in extreme conditions and high-speed production via scalable additive manufacturing significantly broadens the technological phase space for on-chip energy storage.

Effects of Crumpling Stage and Porosity of Graphene Electrode on the Performance of Electrochemical Supercapacitor

The performance characteristics of supercapacitors composed of crumpled graphene electrodes and aqueous NaCl electrolytes are investigated through Molecular Dynamics (MD) simulations using a newly developed crumpled graphene-based supercapacitor model. Results suggest that the three-dimensional configuration of crumpled graphene boosts electrolyte-electrode interaction. This improved interaction, which includes a larger ion-accessible zone, increases the specific capacitance of the supercapacitor by roughly 400% (16.4 μF/cm2) compared to planar graphene electrodes. Examining the effect of different stages of crumpling and the inclusion of pores on the electrode surface shows that the stages of crumpling substantially influence the supercapacitor performance. A smaller crumpling radius, meaning fully crumpled stage, improves the performance as increased crumpling leads to better packing efficiency, which aids in more ion separation. Furthermore, adding pores on the surface of crumpled graphene improves the ion accessibility by creating additional adsorption sites. An exceptional capacitance of 19.8 μF/cm2 is obtained for a porosity of 20%. However, the results suggest that the in-plane-porosity of the electrode needs to be optimized as there is a decline in specific capacitance after that point (20% porosity), indicating a suboptimal relationship between the charge distribution, specific surface area (SSA) and the porosity of the electrode.

Laser-machined micro-supercapacitors: from microstructure engineering to smart integrated systems

With the rapid development of portable and wearable electronic devices, there is an increasing demand for miniaturized and lightweight energy storage devices. Micro-supercapacitors (MSCs), as a kind of energy storage device with high power density, a fast charge/discharge rate, and a long service life, have attracted wide attention in the field of energy storage in recent years. The performance of MSCs is mainly related to the electrodes, so there is a need to explore more efficient methods to prepare electrodes for MSCs. The process is cumbersome and time-consuming using traditional fabrication methods, and the development of laser micro-nano technology provides an efficient, high-precision, low-cost, and convenient method for fabricating supercapacitor electrodes, which can achieve finer mask-less nanofabrication. This work reviews the basics of laser fabrication of MSCs, including the laser system, the structure of MSCs, and the performance evaluation of MSCs. The application of laser micro-nanofabrication technology to MSCs and the integration of MSCs are analyzed. Finally, the challenges and prospects for the development of laser micro-nano technology for manufacturing supercapacitors are summarized.

Flexible electrochemical energy storage devices and related applications: recent progress and challenges

Given the escalating demand for wearable electronics, there is an urgent need to explore cost-effective and environmentally friendly flexible energy storage devices with exceptional electrochemical properties. However, the existing types of flexible energy storage devices encounter challenges in effectively integrating mechanical and electrochemical performances. This review is intended to provide strategies for the design of components in flexible energy storage devices (electrode materials, gel electrolytes, and separators) with the aim of developing energy storage systems with excellent performance and deformability. Firstly, a concise overview is provided on the structural characteristics and properties of carbon-based materials and conductive polymer materials utilized in flexible energy storage devices. Secondly, the fabrication process and strategies for optimizing their structures are summarized. Subsequently, a comprehensive review is presented regarding the applications of carbon-based materials and conductive polymer materials in various fields of flexible energy storage, such as supercapacitors, lithium-ion batteries, and zinc-ion batteries. Finally, the challenges and future directions for next-generation flexible energy storage systems are proposed.

FeNP@MIL-101(Fe)-Based Carbon Nanotube Composite for Energy Storage Applications

Metal-organic frameworks (MOFs) are of great interest for energy applications due to their high porosity, high charge storage capacity, and large number of active redox sites. It is important to enhance the performance of metal-organic frameworks through modification in order to increase their potential applications. Unique Fe nanoparticle (NP) in the Materials of Institute Lavoisier (MIL) series embedded in the carbon nanotube (CNT), FeNP@MIL-101(Fe)/CNT-based, nanocomposites have been synthesized using suitable hierarchical micromesoporous structures. These were fabricated by simple and straightforward solvothermal methods, and their electrochemical charge storage performance was investigated. The energy storage application using the FeNP@MIL -101(Fe)/CNT composite as a supercapacitor electrode was implemented for the first time. Various techniques were used to characterize this composite. It has excellent electrochemical properties when used as electrode material in 1 M KOH solution, including a high capacitance of up to 1305 F g-1 at 1 A g-1 and a long cycling stability of 95.7% capacitance retention after 10,000 cycles. Moreover, symmetric two-electrode electrochemical experiments showed that the composite achieved an energy density of 98.65 Wh kg-1 and a power density of 9000 W kg-1, The combination of microporous and mesoporous structures, increased surface area, and higher electrical conductivity are the main reasons for the high performance. The integration of FeNP@MIL-101(Fe) with the CNT creates new ion diffusion pathways, improves the hierarchical pore properties, and exposes the FeNP@MIL-101(Fe) cluster to more redox active sites, which improves the charge storage performance.

Moisture-enabled self-charging and voltage stabilizing supercapacitor

Supercapacitor is highly demanded in emerging portable electronics, however, which faces frequent charging and inevitable rapid self-discharging of huge inconvenient. Here, we present a flexible moisture-powered supercapacitor (mp-SC) that capable of spontaneously moisture-enabled self-charging and persistently voltage stabilizing. Based on the synergy effect of moisture-induced ions diffusion of inner polyelectrolyte-based moist-electric generator and charges storage ability of inner graphene electrochemical capacitor, this mp-SC demonstrates the self-charged high areal capacitance of 138.3 mF cm-2 and ~96.6% voltage maintenance for 120 h. In addition, a large-scale flexible device of 72 mp-SC units connected in series achieves a self-charged 60 V voltage in air, efficiently powering various commercial electronics in practical applications. This work will provide insight into the design self-powered and ultra-long term stable supercapacitors and other energy storage devices.

Robust Graphene-based Aerogel for Integrated 3D Asymmetric Supercapacitors with High Energy Density

Three-dimensional asymmetric supercapacitors (3D ASC) have garnered significant attention due to their high operating window, theoretical energy density, and circularity. However, the practical application of 3D electrode materials is limited by brittleness and excessive dead volume. Therefore, we propose a controlled contraction strategy that regulates the pore structure of 3D electrode materials, eliminates dead volume in the 3D skeleton structure, and enhances mechanical strength. In this study to obtain reduced graphene oxide/manganese dioxide (rGO/MnO2) and reduced graphene oxide/carbon nanotube (rGO/CNT) composite aerogels with a stable and compact structure. MnO2 and CNT as nanogaskets, preventing the self-stacking of graphene nanosheets during the shrinkage process. Additionally, the high specific capacitor nanogaskets significantly enhance the specific energy density of the rGO aerogel electrode. The prepared rGO/MnO2//rGO/CNT 3D ASC exhibits a high mass-specific capacitance of 216.15 F g-1, a high mass energy density of 74 Wh kg-1 at 3.5 A g-1, and maintains a retention rate of capacitance at 99.89 % after undergoing 10,000 cycles of charge and discharge at 5 A g-1. The versatile and integrated assembly of 3D ASC units is achieved through the utilization of the robust mechanical structure of rGO-based aerogel electrodes, employing a mortise and tenon structural design.

Chemical vapor deposition growth of graphene and other nanomaterials with 3D architectures towards electrocatalysis and secondary battery-related applications

Recently, two-dimensional (2D) layered materials, such as graphene and transition metal dichalcogenides (TMDCs), have garnered a lot of attention in energy storage/conversion-related fields due to their novel physical and chemical properties. Constructing flat graphene and TMDCs nanosheets into 3D architectures can significantly increase their exposed surface area and prevent the restacking of adjacent 2D layers, thus dramatically promoting their applications in various energy-related fields. Chemical Vapor Deposition (CVD) is a low-cost, facile, and scalable method, which has been widely employed to produce high-quality graphene and TMDCs nanosheets with 3D architectures. During the CVD process, the morphologies and properties of the 3D architectures of such 2D materials can be designed by selecting substrates with different compositions, stacking geometries, and micro-structures. In this review, we focus on the recent advances in the CVD synthesis of graphene, TMDCs, and their hybrids with 3D architectures on different 3D-structured substrates, as well as their applications in the electrocatalytic hydrogen evolution reaction (HER) and various secondary batteries. In addition, the challenges and future prospects for the CVD synthesis and energy-related applications of these unique layered materials will also be discussed.

Ultrafast Ion Transfer of Metal-Organic Framework Interface for Highly Efficient Energy Storage

Flexible supercapacitors are favorable for wearable electronics. However, their high-rate capability and mechanical properties are limited because of unsatisfactory ion transfer kinetics and interfacial modulus mismatch inside devices. Here, we develop a metal-organic framework interface with superior electrical and mechanical properties for supercapacitors. The interfacial mechanism facilitates ultrafast ion transfer with an energy barrier reduction of 43% compared with that of conventional transmembrane transport. It delivers high specific capacity at a wide rate range and exhibits ultrastability beyond 30000 charge-discharge cycles. Furthermore, meliorative modulus mismatch benefited from ultrathin interface design that improves mechanical properties of flexible supercapacitors. It delivers a stable energy supply under various mechanical conditions like bending and twisting status and displays ultrastable mechanical properties with performance retention of 95.5% after 10 000 bending cycles. The research paves the way for interfacial engineering for ultrastable electrochemical devices.

Flexible Energy Storage Devices to Power the Future

The field of flexible electronics is a crucial driver of technological advancement, with a strong connection to human life and a unique role in various areas such as wearable devices and healthcare. Consequently, there is an urgent demand for flexible energy storage devices (FESDs) to cater to the energy storage needs of various forms of flexible products. FESDs can be classified into three categories based on spatial dimension, all of which share the features of excellent electrochemical performance, reliable safety, and superb flexibility. In this review, the application scenarios of FESDs are introduced and the main representative devices applied in disparate fields are summarized first. More specifically, it focuses on three types of FESDs in matched application scenarios from both structural and material aspects. Finally, the challenges that hinder the practical application of FESDs and the views on current barriers are presented.

Preparation of a High-Performance Asymmetric Supercapacitor by Recycling Aluminum Paper and Filter Components of Heated Tobacco

In this study, Al paper and cellulose acetate (CA) filters derived from heated tobacco waste were successfully converted into current collectors and active materials for a supercapacitor device. Typically, heated tobacco contains electrically discontinuous Al paper. First, Al was extracted from the tobacco waste using HCl to produce Lewis acid (AlCl3). This acid was then used in an Al electrodeposition process utilizing the chloroaluminate ionic liquid reaction between the acid and the base (RCl) at room temperature. To enhance the conductivity, a supplementary coating of Al metal was applied to the Al paper through electrodeposition, thus re-establishing the electrical continuity of the discontinuous parts and forming an Al-coated current collector. Moreover, the CA filters were carbonized under a nitrogen atmosphere, yielding carbon precursors (C-CA) for the supercapacitor electrodes. To further enhance the electrochemical performance, nickel oxide (NiO) was incorporated into C-CA, resulting in C-CA@NiO with pseudocapacitance. The specific surface area of CA increased with carbonization and the subsequent incorporation of NiO. The as-synthesized C-CA and C-CA@NiO materials were applied to an Al-coated current collector to obtain C-CA- and C-CA@NiO-based electrodes, exhibiting stable electrochemical behavior in the voltage range of -1.0 to 0 V and 0 to 1.0 V, respectively. An asymmetric supercapacitor (ASC) device was assembled with C-CA@NiO and C-CA as the positive and negative electrodes, respectively. This ASC device demonstrated a high specific capacitance of 40.8 F g-1, while widening the operating voltage window to 2.0 V. The high electrochemical performance of the device is attributed to the successful Al electrodeposition, which facilitates the electrical conductivity and increased porosity of the C-CA@NiO and C-CA materials. To the best of our knowledge, this is a pioneering study in regards to the conversion of biomass waste into current collectors and active materials to fabricate a practical ASC device. Our findings highlight the potential of reusing Al paper and CA filters from heated tobacco waste as essential components of energy storage devices.

Polymer Chainmail: Steric Hindrance and Charge Compensation of Anion-Doped PEDOT to Boost Stress Deformation of Compressible Supercapacitor

Conducting polymers with high theoretical capacitance and deformability are among the optimal candidates for compressible supercapacitor electrode materials. However, achieving both mechanical and electrochemical stabilities in a single electrode remains a great challenge. To address this issue, the "Polymer Chainmail" is proposed with reversible deformation capability and enhances stability because of the steric hindrance and charge compensation effect of doped anions. As a proof of concept, four common anions are selected as dopants for Poly(3,4-ethylenedioxythiophene) (PEDOT), and their effects on the adsorption and diffusion of H+ on PEDOT are verified using density functional theory calculations. Owing to the film formation effect, thePF 6 - ${{\rm{PF}}_6^- }$ doped PEDOT/nitrogen-doped carbon foam exhibits good mechanical properties. Furthermore, the composite demonstrates excellent rate performance and stability due to suitable anion doping. This finding provides new insights into the preparation of electrochemically stable conductive polymer-based compressible electrode materials.

Realizing Highly-Ordered Laser-Reduced Graphene for High-Performance Flexible Microsupercapacitor

Laser reduction of graphene oxide (GO) with direct-write technology is promising to develop miniaturized energy storage devices because of highly flexible, mask-free, and chemical-free merits. However, laser reduction of GO is often accompanied with deflagration (spectacular and violent deoxygenating reaction), leading reduced graphene oxide (rGO) films into brittle and irregular internal structure which is harmful to the applications. Here, a pre-reduction strategy is demonstrated to avoid this deflagration and realize a uniform laser-reduced GO (LrGO) matrix for the application of flexible micro-supercapacitors (MSCs).The pre-reduction process with ascorbic acid decreases the content of oxygen-containing functional groups on GO in advance, and thus relieves gases emission and avoids unconstrained expansion during the laser reduction process. In addition, a self-assembled skeleton with pre-reduced GO (PGO) nanosheets could be constructed which is a more appropriate aforehand framework for laser reduction to establish controllable rGO films with the homogenous porosity. The quasi-solid-state MSCs assembled with laser-reduced PGO exhibit the maximum areal capacitance of 88.32 mF cm-2 , good cycling performance (capacitance retention of 82% after 2000 cycles), and outstanding flexibility (no capacitance degradation after bending for 5000 times). This finding provides opportunities to enhance quality of LrGO which is promising for micro-power devices and beyond.

Recent Advances in Carbon-Based Electrodes for Energy Storage and Conversion

Carbon-based nanomaterials, including graphene, fullerenes, and carbon nanotubes, are attracting significant attention as promising materials for next-generation energy storage and conversion applications. They possess unique physicochemical properties, such as structural stability and flexibility, high porosity, and tunable physicochemical features, which render them well suited in these hot research fields. Technological advances at atomic and electronic levels are crucial for developing more efficient and durable devices. This comprehensive review provides a state-of-the-art overview of these advanced carbon-based nanomaterials for various energy storage and conversion applications, focusing on supercapacitors, lithium as well as sodium-ion batteries, and hydrogen evolution reactions. Particular emphasis is placed on the strategies employed to enhance performance through nonmetallic elemental doping of N, B, S, and P in either individual doping or codoping, as well as structural modifications such as the creation of defect sites, edge functionalization, and inter-layer distance manipulation, aiming to provide the general guidelines for designing these devices by the above approaches to achieve optimal performance. Furthermore, this review delves into the challenges and future prospects for the advancement of carbon-based electrodes in energy storage and conversion.

Understanding and Optimizing Capacitance Performance in Reduced Graphene-Oxide Based Supercapacitors

Reduced graphene-oxide (RGO)-based electrodes in supercapacitors deliver high energy/power capacities compared to typical nanoporous carbon materials. However, extensive critical analysis of literature reveals enormous discrepancies (up to 250 F g^-1 ) in the reported capacitance (variation of 100-350 F g^-1 ) of RGO materials synthesized under seemingly similar methods, inhibiting an understanding of capacitance variation. Here, the key factors that control the capacitance performance of RGO electrodes are demonstrated by analyzing and optimizing various types of commonly applied electrode fabrication methods. Beyond usual data acquisition parameters and oxidation/reduction properties of RGO, a substantial difference of more than 100% in capacitance values (with change from 190 ± 20 to 340 ± 10 F g^-1 ) is found depending on the electrode preparation method. For this demonstration, ≈40 RGO-based electrodes are fabricated from numerous distinctly different RGO materials via typically applied methods of solution (aqueous and organic) casting and compressed powders. The influence of data acquisition conditions and capacitance estimation practices are also discussed. Furthermore, by optimizing electrode processing method, a direct surface area governed capacitance relationship for RGO structures is revealed.

Liquid exfoliation of bulk g-C3N5 to nanosheets for improved photocatalytic antibacterial activity

Liquid exfoliation of bulk g-C₃N₅ was applied to synthesize g-C₃N₅ nanosheets. In order to characterize the samples, X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectra (XPS), UV-Vis absorption spectra (UV-Vis), and photoluminescence spectra (PL) were examined. g-C₃N₅ nanosheets exhibited enhanced performance in the inactivation of Escherichia coli (E. coli) with visible light irradiation relative to bulk g-C₃N₅ and promoted complete inactivation of E. coli within 120 min. h⁺ and •O₂^- were the principal reactive species in the antibacterial process. In the early stages, SOD and CAT played a defensive role in resisting oxidative damage of active species. With the prolonged light exposure time, the antioxidant protection system was overwhelmed leading to the destruction of the cell membrane. The leakage of cell contents such as K⁺, protein, and DNA caused bacterial apoptosis ultimately. The enhanced photocatalytic antibacterial performance of g-C₃N₅ nanosheets is ascribed to the stronger redox property by the upward shift of CB and downward shift of VB compared with bulk g-C₃N₅. On the other hand, larger specific surface area and better separation efficiency of photoinduced carriers are helpful to the improved photocatalytic performance. This study systematically revealed the inactivation process toward E. coli and expanded the application range of g-C₃N₅-based materials with abundant solar energy.

Recent advances in polyaniline-based micro-supercapacitors

The rapid development of the Internet of Things (IoTs) and proliferation of wearable electronics have significantly stimulated the pursuit of distributed power supply systems that are small and light. Accordingly, micro-supercapacitors (MSCs) have recently attracted tremendous research interest due to their high power density, good energy density, long cycling life, and rapid charge/discharge rate delivered in a limited volume and area. As an emerging class of electrochemical energy storage devices, MSCs using polyaniline (PANI) electrodes are envisaged to bridge the gap between carbonaceous MSCs and micro-batteries, leading to a high power density together with improved energy density. However, despite the intensive development of PANI-based MSCs in the past few decades, a comprehensive review focusing on the chemical properties and synthesis of PANI, working mechanisms, design principles, and electrochemical performances of MSCs is lacking. Thus, herein, we summarize the recent advances in PANI-based MSCs using a wide range of electrode materials. Firstly, the fundamentals of MSCs are outlined including their working principle, device design, fabrication technology, and performance metrics. Then, the working principle and synthesis methods of PANI are discussed. Afterward, MSCs based on various PANI materials including pure PANI, PANI hydrogel, and PANI composites are discussed in detail. Lastly, concluding remarks and perspectives on their future development are presented. This review can present new ideas and give rise to new opportunities for the design of high-performance miniaturized PANI-based MSCs that underpin the sustainable prosperity of the approaching IoTs era.

Fabrication of Flexible All-Solid-State Asymmetric Supercapacitor Device via Full Recycling of Heated Tobacco Waste Assisted by PLA Gelation Template Method

In this study, a flexible all-solid-state asymmetric supercapacitor (FASC) device has been successfully fabricated via full recycling of heated tobacco waste (HTW). Tobacco leaves and cellulose acetate tubes have been successfully carbonized (HTW-C) and mixed with metal oxides (MnO2 and Fe3O4) to obtain highly active materials for supercapacitors. Moreover, poly(lactic acid) (PLA) filters have been successfully dissolved in an organic solvent and mixed with the as-prepared active materials using a simple paste mixing method. In addition, flexible MnO2- and Fe3O4-mixed HTW-C/PLA electrodes (C-MnO2/PLA and C-Fe3O4/PLA) have been successfully fabricated using the drop-casting method. The as-synthesized flexible C-MnO2/PLA and C-Fe3O4/PLA electrodes have exhibited excellent electrical conductivity of 378 and 660 μS cm-1, and high specific capacitance of 34.8 and 47.9 mF cm-2 at 1 mA cm-2, respectively. A practical FASC device (C-MnO2/PLA//C-Fe3O4/PLA) has been assembled by employing the C-MnO2/PLA as the positive electrode and C-Fe3O4/PLA as the negative electrode. The as-prepared FASC device showed a remarkable capacitance of 5.80 mF cm-2 at 1 mA cm-2. Additionally, the FASC device manifests stable electrochemical performance under harsh bending conditions, verifying the superb flexibility and sustainability of the device. To the best of our knowledge, this is the first study to report complete recycling of heated tobacco waste to prepare the practical FASC devices. With excellent electrochemical performance, the experiments described in this study successfully demonstrate the possibility of recycling new types of biomass in the future.

Flexible Wood Enhanced Poly(acrylic acid-co-acrylamide)/Quaternized Gelatin Hydrogel Electrolytes for High-Energy-Density Supercapacitors

Hydrogels with good flexibility and strong hydrophilicity can be candidates for excellent flexible electrolyte materials. However, the poor structural stability, uncontrollable swelling, and lower potential window of hydrogel electrolytes need to be improved. This work combined quaternized gelatin with cross-linked poly(acrylic acid-co-acrylamide) to form a semi-interpenetrating network and gelatinized in situ in a flexible porous wood skeleton. The flexible wood (FW) skeleton enhances the hydrogel and limits the swelling of the hydrogel. In addition, quaternary ammonium groups and FW act synergistically to provide the composite hydrogel electrolyte with a high ionic conductivity of 5.57 × 10^-2 S cm^-1. The composite hydrogel electrolyte can enable the flexible supercapacitor to operate safely in a potential window of 0-2 V. The optimized supercapacitor has a high specific capacitance of 286.74 F g^-1 and provides an outstanding energy density of 39.09 W h kg^-1. The flexible supercapacitor shows a capacitance retention of up to 94.6% after 10,000 charge-discharge cycles, indicating dramatic cycling stability. Simultaneously, a capacitance retention of nearly 90% can be maintained by the flexible supercapacitor after 180° bends for 1000 times. A viable idea for developing high-performance hydrogel electrolytes and flexible supercapacitors is provided in this research.

Ultrafast Synthesis of Metal-Layered Hydroxides in a Dozen Seconds for High-Performance Aqueous Zn (Micro-) Battery

Efficient synthesis of transition metal hydroxides on conductive substrate is essential for enhancing their merits in industrialization of energy storage field. However, most of the synthetic routes at present mainly rely on traditional bottom-up method, which involves tedious steps, time-consuming treatments, or additional alkaline media, and is unfavorable for high-efficiency production. Herein, we present a facile, ultrafast and general avenue to synthesize transition metal hydroxides on carbon substrate within 13 s by Joule-heating method. With high reaction kinetics caused by the instantaneous high temperature, seven kinds of transition metal-layered hydroxides (TM-LDHs) are formed on carbon cloth. Therein, the fastest synthesis rate reaches ~ 0.46 cm2 s-1. Density functional theory calculations further demonstrate the nucleation energy barriers and potential mechanism for the formation of metal-based hydroxides on carbon substrates. This efficient approach avoids the use of extra agents, multiple steps, and long production time and endows the LDHs@carbon cloth with outstanding flexibility and machinability, showing practical advantages in both common and micro-zinc ion-based energy storage devices. To prove its utility, as a cathode in rechargeable aqueous alkaline Zn (micro-) battery, the NiCo LDH@carbon cloth exhibits a high energy density, superior to most transition metal LDH materials reported so far.