Direct ink writing technology is capable of using 2D MXene to construct 3D architectures for electrochemical energy storage (EES) devices that are normally difficult to achieve using conventional ...techniques. However, to meet specific rheological requirements for 3D printing, a large amount of MXene is needed in the ink, resulting in a severe self‐restacking structure after drying. Herein, a series of cellulose nanofibers (CNFs) with different morphologies and surface chemistries are applied to enhance the rheology of the MXene‐based inks with exceptional 3D printability. Various 3D architectures with superior shape fidelity and geometric accuracy are successfully printed using the optimized hybrid ink at a low solid content, generating self‐standing, hierarchically porous structures after being freeze‐dried, which improves surface area accessibility, ion transport efficiency, and ultimately, capacitive performance. A solid‐state interdigitated symmetrical supercapacitor is further 3D printed, which delivers an areal capacitance of 2.02 F cm−2 and an energy density of 101 μWh cm−2 at a power density of 0.299 mW cm−2, and maintains a capacitance retention rate of 85% after 5000 cycles. This work demonstrates the integration of 1D CNFs and 2D MXene in 3D printing technology to prepare customized, multiscale, and multidimensional architectures for the next generation of EES devices.
By rationally controlling the dimension and surface chemistry of cellulose nanofibers (CNFs), CNFs are successfully applied as rheology modifiers to formulate viscoelastic, 3D printable MXene‐based ink at a low solid concentration of 8 wt%. The freestanding, hierarchically porous MXene‐based electrode architectures can be achieved by 3D printing and freeze‐drying, which holds great potential in electrochemical energy storage devices.
This paper provides a comprehensive overview on the properties of electrospun nanofibers and their application as reinforcements in composites. The paper first introduces the remarkable properties of ...electrospun nanofibers including high aspect ratio and molecular orientation, large specific surface area, small pore size, as well as excellent mechanical performance. Next the fabrication methods for the electrospun nanofiber reinforced composites are described. Then different kinds of electrospun nanofiber reinforced composites are discussed in terms of the classifications of electrospun nanofibers. After that, the influences of the mechanical performance of fibers, fiber diameter, fiber amount, fiber/matrix interfacial interaction and the distribution of fibers in the matrix on the reinforcement of composites are discussed. At the end, the possible future challenges and conclusions for electrospun nanofiber reinforced composites are highlighted.
Directional freeze-drying is considered to regulate the structure of nanocellulose aerogels with special performances. In this work, TEMPO-oxidized cellulose nanofiber aerogels with high porosity (> ...99.5%) and low density (~ 7 mg/cm
3
) were produced by different freeze-drying methods. The effects of temperature, freezing reagents and freezing methods on the structure and properties of aerogels were investigated. Among them, an anisotropic cellulose aerogel was obtained using a simple and flexible directional freezing in ethanol of − 30 °C by a self-made directional freezer. Our results demonstrated that it could present honeycomb-like pores in the transverse direction and regular directional tunnels in the longitudinal direction, and some attractive features, such as high water adsorption (120 g/g) and stability in water. Compared with other aerogels, this anisotropic structure also provided the aerogel with excellent compressive property (15.2 kPa) and faster liquid transport (4.95 mm/s) in the longitudinal direction than in other directions. The distinctive aerogels based on nanocellulose by directional freeze-drying are also expected to be combined with multifunctional materials to achieve directional applications to meet the requirements of different fields.
Graphic abstract
Electroconductive hydrogels (ECHs) that integrate gel features and electrochemical properties are considered as promising tissue-like flexible materials important for broad applications. ...Nevertheless, realizing the synergistic features of self-healing capability, conductivity, biocompatibility, stretchability and malleability is challenging. Herein, a novel kind of versatile ECHs built on a borax-crosslinked polyvinyl alcohol (PVA) hydrogel system and conducting PANI@CNF (polyaniline-cellulose nanofiber) nanocomplexes which synergize the conductivity of PANI and the template feature of CNFs is reported. The PANI@CNF nanocomplexes are firstly prepared via in situ polymerization of anilines on CNFs, which are then evenly distributed into borax-crosslinked PVA gel system to fabricate free-standing PANI@CNF-PVA composite ECHs. Sustainable and renewable CNFs serve as flexible biotemplates and mediate the development of PANI into integrated PANI@CNF with good dispersity, enabling the establishment of an integrated conducting and reinforcing network. The dynamic multi-complexation and chain entanglements between PANI@CNF complexes, borax and PVA chains contribute to the development of a hierarchical network structure. The maximum compression stress (∼48.8 kPa) and storage modulus (∼31.5 kPa) of PANI@CNF-PVA hydrogel are about 3.5 and 400 times greater than those of pure PVA gel. These hydrogels also demonstrate appealing biocompatibility, mouldability, pH sensitivity, thermo-reversibility and fast self-healing ability within 15s. The hydrogel-based electrode with a conductivity of ∼5.2 S m−1 shows a maximum specific capacitance of 226.1 F g−1 and a capacitance retention of 74% after 3000 cycles. The integration of such remarkable features enables the promising applications of the as-prepared versatile ECHs in flexible, self-healing and implantable electronic devices.
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•Self-healable and biocompatible electro-conductive hydrogels are synthesized.•Nanostructured PANI@CNF complexes are homogeneously embedded in a viscoelastic PVA network.•Hydrogel-based electrode shows a specific capacitance of 226.1 F g−1 and a capacitance retention of 74% after 3000 cycles.
Recent development of flexible and self-healable electro-conductive hydrogels (ECHs) are considered as promising soft materials towards intelligent applications. Nonetheless, realizing the integrated ...features of high electro-conductivity, viscoelasticity and mechanical toughness, as well as inherent mouldability, fast self-healing ability, and ideal electrochemical properties is still challenging. Herein, we report a kind of multifunctional ECHs based on a polyvinyl alcohol-borax (PVAB) hydrogel and carbon nanotube-cellulose nanofiber (CNT-CNF) nanohybrids that combines the conductivity of CNTs and template function of CNFs. CNFs serve as dispersant to uniformly stabilize CNTs in suspension. As-prepared CNT-CNF nanohybrids are uniformly dispersed into PVAB to construct freeze-standing CNT-CNF/PVAB composite hydrogels. Owing to a conductive and reinforcing dual-network structure, the compression stress (∼93 kPa) and storage modulus (∼7.12 kPa) of CNT-CNF/PVAB are 2.7 and 1.9-fold larger than those of CNF/PVAB. CNT-CNF/PVAB also exhibits low density (∼1.1 g cm−3), high water content (∼95%), pH sensitivity, intrinsic mouldability and 20s self-healing capability. The solid-state supercapacitor assembled by PVAB-based hydrogels has a specific capacitance of 117.1 F g−1 and a capacitance retention of 96.4% after 1000 cycles. The self-healable and flexible supercapacitor demonstrates an ideal capacitance retention (∼98.2%) after ten damaging/self-healing cycles and a capacitance retention (∼95%) after 1000 cycles under various deformation.
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•A combined reinforcing and conductive network with a 3D hierarchical structure was constructed in NR by introducing well-dispersed CNF-PANI complexes.•The CNF-PANI/NR elastomer ...exhibited high flexibility, strength, stretchability and conductivity.•The elastomer-based sensor could monitor the real-time motion of human body, and the elastomer-based electrode demonstrated promising electrochemical performances.
The wide-ranging applications of electroconductive elastomers in next-generation soft electronics demand more renewable bio-based materials derived from natural forest crops than the non-sustainable materials currently available. However, it still remains a critical challenge to construct an effective, stable and continuous conductive network in a non-conductive elastomer matrix with enhanced mechanical properties and desired electrochemical performances especially using natural polymer. Here, we report a novel type of electroconductive hybrid elastomers based on a natural rubber (NR) matrix and nanostructured CNF-PANI (cellulose nanofibers-polyaniline) complexes that synergizes the conductive nature of PANI and the biotemplate role of CNFs. The CNF-PANI complexes with ideal dispersity and high aspect ratio are synthesized through in situ oxidative polymerization of aniline monomers on the surface of CNF templates, which are further uniformly dispersed into NR latex to synthesize CNF-PANI/NR elastomers with a hierarchical 3D network structure through a latex cocoagulation process. The incorporation of sustainable and biodegradable CNFs can not only built a reinforcing network, but also support the hierarchical 3D conductive network in NR matrix. The final bio-based elastomers with a homogeneous texture exhibited intrinsic flexibility, enhanced mechanical properties (tensile strength up to 9.7 MPa, Young’s modulus up to 10.9 MPa), decent stretchability (elongation at break up to 511%), low density (∼1.16 g cm−3) and ideal conductivity (up to 8.95 × 10-1 S m-1). The highly sensitive and repeatable strain-sensor integrated by the elastomer with 8 phr of PANI could monitor the real-time motion of human body. The specific capacitance of elastomer-based electrode with 20 phr of PANI can reach up to 110 F g-1 at a current density of 0.3 A g-1, and its capacitance degradation is less than 22% after 1200 cycles, exhibiting promising electrochemical properties. The multifunctional elastomers synthesized through a facile, scalable and green approach in this work promotes the advanced applications of bio-based materials including CNFs and NR in prospective soft electronics, such as strain sensors and flexible electrodes.
Nanocellulose-based porous materials have been recently considered as ideal candidates in various applications. However, challenges on performances remain owing to the disorderly structure and the ...limited transport specificity. Herein, wood-inspired composite sponges consisting of cellulose nanofibrils (CNFs) and high-aspect-ratio silver nanowires (AgNWs) were generated with anisotropic properties by the directional freeze-drying. The obtained composite sponges exhibited attractive features, such as an excellent compressive stress of 24.5 kPa, low percolation threshold of 0.1 vol % AgNWs, and high electrical conductivity of 1.52 S/cm. Furthermore, the self-assembled ordered structure in the longitudinal direction and synergistic effect between CNFs and AgNWs benefited the sponge interesting anisotropic electrical conductivity, thermal diffusivity, ultrafast electrically induced heating (<5 s), sensitive pressure sensing (errors <0.26%), and electromagnetic interference (EMI) shielding for special practical demands. This multifunctional material inspired by natural woods is expected to broaden new applications as electronic devices for an intelligent switch or EMI shielding.
Conventional self‐charging systems are generally complicated and highly reliant on the availability of energy sources. Herein, a chemically self‐charging, flexible solid‐state zinc ion battery ...(ssZIB) based on a vanadium dioxide (VO2) cathode and a polyacrylamide‐chitin nanofiber (PAM‐ChNF) hydrogel electrolyte is developed. With a power density of 139.0 W kg‐1, the ssZIBs can deliver a high energy density of 231.9 Wh kg‐1. The superior electrochemical performance of the ssZIBs is attributed to the robust tunnel structure of the VO2 cathode and the entangled network of PAM‐ChNF electrolyte, which provide efficient pathways for ion diffusion. Impressively, the designed ssZIBs can be chemically self‐charged by the redox reaction between the cathode and oxygen in ambient conditions. After oxidation for 6 h in air, the ssZIBs manifest a high discharging capacity of 263.9 mAh g‐1 at 0.2 A g‐1, showing excellent self‐rechargeability. With the assistance of a small amount of acetic acid added to the hydrogel electrolyte, the galvanostatic discharging and chemical self‐charging cycles can reach 20. More importantly, such ssZIBs are able to operate well at chemical or/and galvanostatic charging hybrid modes, demonstrating superior reusability. This work brings a new prospect for designing flexible chemically self‐charging ssZIBs for portable self‐powered systems.
The robust tunnel structure of a vanadium dioxide cathode and the network of a polyacrylamide–chitin nanofiber hydrogel electrolyte provide efficient pathways for ion diffusion, lead to superior electrochemical performance for solid‐state zinc‐ion batteries. In addition, the flexible chemically self‐charging ssZIBs demonstrate excellent self‐rechargeability and superior reusability, which provide a facile route for portable self‐powered systems.
Nowadays, large-scale oriented functional porous materials have been sought after by researchers. However, regulation of the long-range uniform and oriented structures of the material remains a ...challenge. Herein, ultralong anisotropic cellulose nanofibril (CNF) aerogels with uniformly ordered structures of pore walls inspired by lotus petioles were constructed by applying external speeds to counterbalance the growth driving forces of ice crystals. Based on the growth law of ice crystals, the ice crystals grew at a stable rate when the applied external speed was 0.04 mm/s, ensuring the consistent orientation of the large-scale CNF aerogel. The aerogel exhibited a rapid long-range directional transport ability to different liquid solvents, delivering ethanol up to 40 mm from bottom to top within 50 s. Moreover, by introducing rectorites with good cation-exchange properties, the resulting long-range composite possessed an enhanced adsorption capacity for methylene blue. Furthermore, aerogel successfully achieved real-time dye purification at a long distance, such as fast dye adsorption or selective adsorption. This flexible and straightforward strategy of fabricating ultralong oriented CNF aerogel materials is expected to promote the development of functional aerogels in directional liquid transport and sewage treatment.
Abstract
Recent research on wood‐based solar evaporators has made great progress and significant breakthroughs have been made in using lignin as a photothermal material; however, the intensity change ...mechanism regarding the conjugate structure of lignin is almost never mentioned. This study innovatively proposes a mechanism to explain the changes in conjugate intensity that occur before and after lignin dissolution and fabricates a lignin/wood‐based solar evaporator (LWE) using an all‐wood‐based material that is salt‐tolerant and has long‐term serviceability. Lignin in the evaporator serves not only as a photothermal material for converting light energy into heat energy but also as a reinforcement for the evaporator's structural strength. Adding lignin changes the original structure of balsa wood, increasing the proportion of intermediate water in the LWE, thereby lowering the enthalpy of water evaporation. The optimized LWE with an enhanced desalination capability, dye removal property, and high stability exhibits full‐spectrum solar absorption of about 83.6%, a photothermal conversion efficiency of 91.74%, and an evaporation efficiency of 1.93 kg m
−2
h
−1
, which surpasses most wood‐based evaporators. This study demonstrates that all‐wood‐based materials can be used to prepare evaporators with excellent performance, providing a new approach to address freshwater depletion.
