The unique design of the core-shell heterostructure is significant for obtaining electrode materials with excellent electrochemical properties. In this paper, porous carbon nanofibers (NPC@PPZ) embedded with N-doped porous carbon nanoparticles are used to construct flexible electrodes (NPC@PPZ@Bi2O3). Zeolite imidazole skeleton (ZIF)-8 and poly(methyl methacrylate) (PMMA) derived porous carbon fibers and Bi2O3 nanosheets, were utilized as the porous core and multilayer shell, respectively. The unique core and shell result in abundant pores and channels for fast ion transport and storage, high specific surface area, and additional electroactive sites. This perfect structural design enables the NPC@PPZ@Bi2O3 composite electrode to have excellent electrochemical performance. The results show that this electrode can obtain a high specific capacitance of 697 F g- 1 at a current density of 1 A g- 1 and a stable cycling performance at a high current density of 5 A g- 1. The strategy developed in this study provides a new approach for the design and fabrication of flexible supercapacitors by electrostatic spinning combined with hierarchical porous structures.

The unique design of the core–shell heterostructure is significant for obtaining electrode materials with excellent electrochemical properties. In this paper, porous carbon nanofibers (NPC@PPZ) embedded with N-doped porous carbon nanoparticles are used to construct flexible electrodes (NPC@PPZ@Bi2O3). Zeolite imidazole skeleton (ZIF)-8 and poly(methyl methacrylate) (PMMA) derived porous carbon fibers and Bi2O3 nanosheets, were utilized as the porous core and multilayer shell, respectively. The unique core and shell result in abundant pores and channels for fast ion transport and storage, high specific surface area, and additional electroactive sites. This perfect structural design enables the NPC@PPZ@Bi2O3 composite electrode to have excellent electrochemical performance. The results show that this electrode can obtain a high specific capacitance of 697 F g−1 at a current density of 1 A g−1 and a stable cycling performance at a high current density of 5 A g−1. The strategy developed in this study provides a new approach for the design and fabrication of flexible supercapacitors by electrostatic spinning combined with hierarchical porous structures.

Silicon-based (Si-based) materials offer more possibilities for generating new portable electronic devices due to their high specific capacities. However, their inferior electrical conductivity and volume expansion during cycling seriously limit their development. The optimum solution is to select specific materials to establish an exceptionally conductive and volume buffer structure, which can assist Si materials in developing their excellent lithium storage properties. In this study, Si particles were confined in TiO2 carbon fibers (TiO2 CFs) via electrospinning, after which they were encapsulated with MXene and Co-MoS2 (CMS) nanosheets to fabricate hierarchical ST-2@MXene@CMS films. TiO2 CF, MXene and CMS were employed to establish a coherent conductive network with one-, two- and three-dimensional electronic pathways to permit the unimpeded flow of electrons inside the electrode material. TiO2 CF, MXene and CMS acted precisely as multilayered buffers to ameliorate the volume change of Si particles during cycling. In addition, the CMS nanosheets were involved in lithium storage, contributing to the final electrochemical performance. Ultimately, the ST-2@MXene@CMS films served as free-standing electrodes, avoiding the impact of inactive interfaces on the electrochemical performance and fulfilling the lightweight requirement for new energy storage devices.

The booming development of electronic devices has promoted the in-depth research on flexible supercapacitors. The structural design of core@shell can be regarded as an effective method of achieving excellent electrochemical performance and outstanding flexibility of electrode materials. Herein, a special structure of core@shell hybrid Bi2O3-x@carbon fiber@poly (3, 4-ethylenedioxythiophene) (Bi2O3-x@CF@PEDOT) electrode derived from a Bi-metal-organic framework (Bi-MOF) is fabricated by using the electrospinning technique, and using the stabilization, pyrolyzation and polymerization procedures. The amount of Bi-MOF is regulated to obtain an optimized flexible substrate (Bi2O3-x@CF). The free space of the hollow Bi2O3 microrod can effectively alleviate the volume expansion during long cycling processes and further promote ion diffusion. The effective optimizations for the structure and content could significantly improve the conductivity and electrochemical performance of the constructed electrode. The prepared Bi2O3-0.5@CF@PEDOT electrode exhibits a satisfied specific capacitance of 460 F g-1 (1 A g-1) and great cycling stability. The assembled symmetric supercapacitor yields a desired energy density (i.e., 16.4 Wh kg- 1) and power density (i.e., 500.34 W kg- 1), and remarkable cycling performance (i.e., 99 % capacitance retention after 8500 cycles). Moreover, the excellent flexibility of the device is demonstrated by folding the supercapacitor into different angles and without obvious capacitance loss. This work provides a special structural design method of constructing high-performance flexible electrodes.

Silicon-based (Si-based) materials have aroused extensive attention owing to their ultra-high theoretical specific capacity, while the huge volume expansion and inferior electronic conductivity have impeded their practical application in lithium-ion batteries (LIBs). Rational structural design has been regarded as a fascinating strategy, especially for yolk-shell structures. Herein, Si nanoparticles (Si NPs) were encapsulated in ZIF-67 metal–organic frameworks to obtain Si@ZIF-67 particles, which were wrapped in one-dimensional carbon fibers (CFs) by simple processes of electrospinning, vulcanization and carbonization to obtain a free-standing Si@Co9S8 CF electrode. The yolk-shelled Si@Co9S8 particles could remarkably ameliorate the volume variation of Si materials during the lithiation/de-lithiation cycling and the introduction of CFs endowed an efficient one-dimensional electronic pathway accurately to improve the conductivity of composite materials. In addition, it was not negligible that the as-obtained Si@Co9S8 CF films could be as a self-supporting electrode, which avoided the traditional cumbersome procedure of the electrode preparation. The resulting composite electrodes possess an excellent rate performance and an ultra-stable cycling lifespan. We hope this work can provide some novel insights for the development of the self-supporting Si-based electrode materials.

Lightweight, flexible, patterned, and environmentally friendly electronic devices should be developed to meet the requirements of future high-tech systems such as smart wearables, internet of things and smart cities. Herein, MXene and citrus-based carbon nanosheet composites (MX/CCNS) with excellent energy storage properties and cyclic stability are prepared via electrostatic self-assembly. MX/CCNS can be easily fabricated as flexible self-supporting electrodes by vacuum filtration and configured as ink for screen printing and large-scale contin-uous preparation of patterned electrodes. MX/CCNS film electrodes have high specific capacitance (up to 1825.6 mF/cm2 at a current density of 5 mA/cm2) and high cycling stability (99.82% capacity retention after 10,000 cycles). Meanwhile, MX/CCNS can be assembled into flexible all-solid-state and interdigital devices, all exhib-iting excellent capacitive performance. The capacitance (114.9 mF/cm2) and energy density (12.9 mu Wh/cm2) of the printed interdigital supercapacitors are competitive among MXene-based devices. MX/CCNS has great application prospects in scalable and sustainable production of next-generation wearable intelligent electronics.

Rational structure design and regulation are of paramount importance for obtaining electrode materials with desirable electrochemical performance. Here, a novel binder-free electrode with the hollow Co9 S 8 core@multi-shell structure (CS-x@MXene@Bi2O3) derived from metal-organic frameworks (MOFs) precursor is well designed by the electrospinning, sulfuration, carbonization, and hydrothermal processes. In this architecture, the concentration of Co9S8 (CS-x) is optimized for an ideal flexible substrate, which alleviates the dimensional variation for long cycle life. The unique cores and the MXene flakes engineered by Bi2O3 multiple shells can be responsible for the superior characteristics, including a fast electronic pathway, large specific surface area, enhanced electrical conductivity, and improved electrochemical performance. As expected, the obtained CS-2@MXene@Bi2O3 binder-free electrode exhibits a high discharge capacitance of 646.1 F g -1 (1 A g -1 ). Two binder-free electrodes can be assembled into a solid-state super capacitor with desirable energy and power density, and long-term cyclic stability is demonstrated through 50 0 0 cycles. Given these advantages, the CS-2@MXene@Bi2O3 is selected as the electrode in a foldable supercapacitor. More importantly, the specific capacitance is reserved after various deformations. Therefore, it is expected that binder-free electrode materials with the unique core@shell structure design could be applied in wearable and portable energy conversion devices.(c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Flexible supercapacitors have become a concern of flexible energy storage devices. In the process of exploring, the squid ink as N-doped biomass carbon was introduced to self-supporting flexible supercapacitors by elec-trospinning for the first time. By regulating the content of squid ink, the activation temperature, and the mass ratio of KOH-assisted activation, a N-doped porous biomass carbon@polyacrylonitrile (NPBC-1.5@PAN-800-2) with an ideal capacity and an excellent specific surface area (636.68 m2 g-1) was prepared. In addition, ZnO further optimized the capacity (422.7 F/g at 1 A g-1) and as an adhesive-free electrode for flexible asymmetric supercapacitor provided a relatively high specific capacitance, a satisfactory capacitance retention, and a wonderful energy density (48.01 Wh kg- 1 at 1124.43 W kg -1). The capacitance was thought to originate from a suitable microporous structure, N-doped, and metal-derived pseudocapacitance propertie.

As promising electrode material contender for supercapacitors, MXene has high conductivity, abundant surface functional groups, and large surface area. However, the self-restacking of MXene leads to poor ion-accessible surface area and restricted ion transport routes. Water-assisted proton channels contained by Polyoxometallate-based coordination polymer (POMCP) can improve the efficiency of ion transport between MXene layers, which is conducive to enhancing the storage capacity and rate performance. Herein, [PW12O40]@ [Cu6O(TZI)(3)(H2O)(6)] (4)center dot OH center dot 31H(2)O (CuCP) decorated Ti3C2Tx (CuCP/MX) was synthesized by in-situ hydrothermal method. Attribute to the extended interlayer space and enhanced ion transport efficiency, CuCP/MX exhibits excellent electrochemical energy storage properties. It is worth revealing that when assembling into an all-solidstate supercapacitor device (SC), excellent specific capacitance (380 mF/cm(2)) and energy density (68.4 mu Wh/cm(2) at 540 mu W/cm(2)) were exhibited. CuCP/MX is a considerable electrode material for supercapacitors for flexible electronic devices.

Silicon-based (Si-based) materials have been highlighted for their high specific capacity and abundant reserves. However, the limited electrical conductivity and the large volume expansion are critical barriers to their extensive application. The most targeted remedy is the incorporation of selected conductive materials and the tailored design of electrode structures. Herein, carbon-MXene (C-MXene) and poly(3,4-ethylenedioxythiophene) (PEDOT) were employed to decorate Si cores to obtain Si-x@C-MXene@PEDOT particles. Among them, the content of Si was regulated for an optimal electrochemical performance. More significantly, given that the common single-layer core-shell structure was inherently inadequate in resisting the volume change, the corebishell structure offered a robust buffer layer that consisted of a hard inorganic C-MXene and an organic PEDOT coating with an elastic conductive network, which collaboratively addressed the volume expansion issue. The resulting Si-2@C-MXene@PEDOT also possessed an excellent conductivity-promoting layer consisting of CMXene and PEDOT, which facilitated the rapid transport of electrons, thus significantly boosting the electrochemical performance of the final electrodes. Also, the core-bishell structure assisted in the formation of a thinner solid electrolyte interface (SEI) film, which avoided the massive consumption of Li+ and enhanced the lithium storage capability. This work was expected to open up possibilities for larger-scale applications of Sibased materials.

The design of the core@multi-shell metal sulfide hollow tube is of great importance for various supercapacitor electrodes. Herein, a hollow carbon tube (HCT) core@multi-shell with rich pores is developed for constructing the binder-free flexible electrodes (HCT-x@Co3O4@SnS2). The inner core-shell is derived from the zeolitic imidazole framework (ZIF)-8@ZIF-67 porous carbon tube and is engineered with vertically aligned SnS2 nanosheets. The unique inner core-shell and the outer-shell SnS2 contribute to the excellent characteristics, including abundant pores and channels for the rapid ion transport and storage, high specific surface area, improved electrical conductivity, and additional electroactive sites for the faradaic reaction. Thanks to the synergies between the unique 1D porous hollow structure and the different components, the as-fabricated HCT2@Co3O4@SnS2 electrode exhibits a high specific capacitance of 439 F/g at 1 A/g. Moreover, the assembled flexible supercapacitor also demonstrates a remarkable energy density of 40.22 Wh kg- 1, the corresponding power densities of 750.22 W kg- 1, and long cycle life. In addition, no structural deformation and capacitance loss are observed in the bended devices. The developed approach provides a facile structure design route for the flexible binder-free electrode preparation of flexible energy storage applications.

With the development of electronic technology, portable and wearable electronics are becoming increasingly indispensable in our lives, which promotes a high demand for flexible power supplies. To develop lightweight, flexible, and high performance energy storage devices, we have prepared MXene and Co-TCPP nanosheet composites (CoMX) with excellent electrochemical properties by electrostatic self-assembly. Co-TCPP is inserted between MXene layers and successfully improves ion accessibility and enhances electrochemical performance. CoMX film electrodes fabricated by vacuum filtration show high specific capacitance (1591.7 mF/cm2) and exhibit excellent cycling stability, with a capacity retention rate of 99.81 % after 8000 cycles. Flexible all-solidstate supercapacitors (SC) assembled with CoMX film and interdigital electrodes both exhibit excellent capacitance performance. The in-plane SC exhibits competitive specific capacitance (330.0 mF/cm2) and energy density (37.13 & mu;Wh/cm2 at 450 & mu;W/cm2). The specific capacitance and energy density of interdigital SC achieve 89.9 mF/cm2 and 12.9 & mu;Wh/cm2, respectively. The competitive performance of both devices makes them highly promising for flexible energy storage devices.

SnS is an ideal material for supercapacitors because of its unique layered structure and excellent electrochemical performance, but the research of SnS based electrode materials of flexible self-supporting supercapacitors has been rarely exploited. In this study, microsphere like Co doped SnS grown on carbon nanofibers (Co-SnS@CNF) was prepared by electrospinning, hydrothermal method and annealing treatment. Co-SnS@CNF has great flexibility, high specific capacitance, excellent rate performance and cycle stability. Specifically, the specific capacitance is 750 F g- 1 at the current density of 1 A g- 1. The special microsphere structure with more electrochemical active sites and lower resistance of ion and charge transfer by Co doping are responsible for the superior electrochemical performances. Furthermore, when assembled Co-SnS@CNF as the symmetrical supercapacitor device, the energy density of 20.89 Wh Kg-1 and the power density of 376 W Kg-1 are achieved at the current density of 1 A g- 1, while showing ultra-high cycle stability. Therefore, the Co-SnS@CNF offers excellent application potential for flexible self-supporting supercapacitors.

MXene can be used to create bifunctional materials for supercapacitors and electromagnetic wave absorbers by logical composition arrangement and microstructure design. The layered structure, high electrical conductivity, high capacitance, mechanical strength, and flexibility of Ti3C2Tx MXene all make it ideal for use as flexible energy storage devices and electromagnetic wave absorbers. In this study, MXene was innovatively intercalated with g-C3N4 and CNTs to produce MXCN/CNTs ternary hybrid film. The restacking is successfully avoided, and the layer spacing is increased. Meanwhile, g-C3N4 makes the interlayer charge density increase, and CNTs establish the interlayer conducting network, both of which greatly improve the charge transfer efficiency. These ternary hybrid films exhibit superior performance for both supercapacitor electrodes and electromagnetic wave absorbers. The specific capacitance of MXCN/CNTs electrode reaches 477.4 F/g at 1 A/g. The energy density of flexible symmetrical all-solid supercapacitor achieves 25.28 Wh/Kg at 449.99 W/Kg. When bent 180 degrees, the electrochemical performance remains constant. The MXCN/CNTs composites also show excellent electromagnetic wave absorption (EMA) performance. It achieves an optimized absorption intensity of -43.44 dB at 2.6 mm and shows an extremely wide effective absorption bandwidth (EAB) of 8.94 GHz. This work enhances the application studies of Ti3C2Tx MXene-based composite materials as multifunctional materials.

The large volume expansion effect and unstable solid electrolyte interface films of SiOx-based anode materials have hindered their commercial development. It has been shown that composite doping is a general strategy to solve critical problems. In this study, TiO2-doped core-shell SiOx/ TiO2@C composites were created using the sol-gel method. On the one hand, the uniformly dispersed TiO2 nanoparticles can alleviate the volume expansion of the SiOx active material during the lithiation process. On the other hand, they can react with Li+ to form LixTiO2, thereby increasing the ion diffusion rate in the composite material. The outer carbon shell acts as a protective layer that not only alleviates the volume expansion of the composite, but also improve the electron migration rate of the composite. The prepared SiOx/TiO2@C composite has a reversible capacity of 828.2 mA h g(-1) (0.2 A g(-1) 100 cycles). After 500 cycles, it still maintains a reversible capacity of 500 mA h g(-1) even at a high current density of 2 A g(-1). These findings suggest that SiOx/TiO2@C composites have a bright future in applications.

Flexible energy storage systems and electromagnetic pollution have become issues that need to be resolved in equipment research and development due to the widespread use of portable electronic devices and 5G networks. MXene is competent for supercapacitors and electromagnetic wave absorbers through sensible composite and microstructure design. Herein, Cu1.5Mn1.5O4 Hollow Nanosphere Decorated Ti3C2Tx MXene (CuMnHS@MX) was prepared by simple electrostatic self-assembly. Hybrid membranes can be quickly prepared by vacuum-assisted filtration. CuMnHS@MX exhibits excellent electromagnetic wave absorption performance and electrochemical energy storage properties. High specific capacitance (2089 mF/cm2 at 2.5 mA/cm2) and excellent cycle stability (99.89% after 8000 cycles) are achieved, which are attributed to the increased interlayer spacing and improved interlayer ion transport efficiency. When assembled into symmetrical flexible all-solid-state supercapacitor (SC), the device has a specific capacitance of 382.9 mF/cm2 and an energy density of 53.18 mu Wh/cm2 at a power density of 277.8 mu W/cm2. Meanwhile, CuMnHS@MX has advantageous absorbing properties. When the thickness is 4 mm, the minimum reflection loss (RLmin) is-53.42 dB at 6.08 GHz. Adjustable absorbing property is achieved, and the absorbing energy efficiency can cover X and most C, Ku bands. These excellent EMA properties are derived from the 3D structure and rich dipole/interface polarization. CuMnHS@MX is a promising bifunc-tional material for electrochemical energy storage and electromagnetic wave absorption.

Purity requirements for gas in daily life and industrial production have been increasing. Coordination polymer glass membranes can solve the problem of brittle and fragile inorganic membranes and retain some porosity. We obtained the novel CP material, to obtain self-supporting glass membranes by means of sheeting-melting-cooling, the selectivity of the agCd-P-dmbIm membrane in H2/CO2, H2/N2 and H2/CH4 are 68.8, 33.8 and 49.5 respectively. Its hydrogen permeance is 235 GPU, and its permeability is 73621 barrer. The results show that the diffusion coefficient of H2 is much greater than that of CO2. Relevant mechanism proved that the gas molecular size sieving properties of coordination polymers is the key factor to achieve efficient gas permeability and selectivity. agM-P-dmbIm is hydrogen purification membrane. Coordination polymer glass membranes have great potential in gas separation research.

A flexible Si@CNFs@1T/2H MoS2 film exhibits excellent rate capability and cycling performance with a high initial Coulombic efficiency of 94.5%, which indicates it can be used as a self-supporting electrode for lithium–ion batteries.

Carbon nanofibers (CNFs) have been playing an essential role in addressing the challenges of the flexibility in energy storage devices. However, the unsatisfactory electrochemical performance and poor electrical conductivity are often caused by insufficient physical contact points of CNFs. The design and implementation of unique electrodes are expected to overcome these issues. Here, the N-doped hierarchical porous carbon nanofibers (NCNFs) hollow framework derived from metal-organic frameworks (MOFs) is fabricated, which is decorated with high conductive reduced graphene oxide rGO and single-crystal ZnO nanorod for engineering the binder -free flexible electrodes NCNF@rGO-x@ZnO. The obtained NCNF@rGO-7@ZnO electrode exhibits the desired specific capacitance of 473 F g(-1). An assembled hybrid supercapacitor exhibits the high energy density of 35.16 Wh kg(-1) at the power density of 747.2 W kg(-1), and superior cycling life. Given these advantages, the NCNF@rGO-7@ZnO is selected as the electrode in a flexible and foldable supercapacitor. There is exceptional flexibility and no visible capacitance loss when the supercapacitor bending at different angles. Furthermore, a timer is suc-cessfully driven by two supercapacitor devices connected in series. Hence, a flexible binder-free electrode with excellent electrochemical performance can be obtained by engineering the structure into a hollow interconnected architecture and the rational design of materials.

Carbon nanofibers (CNFs) have attracted considerable attention because they make it possible for materials to have a variety of enhanced properities. However, the unsatisfied electrochemical performance of an individual component and the poor electrical conductivity caused by insufficient physical contact points become the fully addressing issues when CNFs are proposed as electrode material in a flexible supercapacitor. Hence, this paper proposes a feasible perspective on enhancing the electrochemical performance and flexibility via the method of electrostatic self-assembly and the "dipping and drying " strategy. The reduced graphene oxide (rGO) layer is uniformly anchored on the surface of SnCl2 modified carbon-based fiber polyacrylonitrile (PAN) fabricated by the electrospinning method. Pseudocapacitance material polypyrrole (PPy) is subsequently deposited and selected to design a composite PAN@rGO@PPy electrode. As expected, the as-constructed binder-free PAN@rGO@PPy electrode shows a specific capacitance of 203 F g(-1); the assembled flexible supercapacitor delivers a high energy density of 15 Wh kg(-1) together with a power density of 500 W kg -1, and displays remarkable cycling stability after 10,000 cycles. Finally, the flexibility via various deformations is discussed, meanwhile, the structural and compositional stability of the PAN@rGO@PPy electrode during long-term cycling test are demonstrated. In light of the facile preparation strategy and the excellent electrochemical performance, this work offers an instructive direction for the development of flexible energy storage devices.