Core-shell heterostructured Ni(OH)2@activation Zn-Co-Ni layered double hydroxides electrode for flexible all-solid-state coaxial fiber-shaped asymmetric supercapacitors.

The increasing requirements for wearable and portable electronics are driving the interests of high performance fiber supercapacitor. Layered double hydroxide (LDH) is broadly used in electrode materials, owing to the adjustability of components and the unique lamellar structure. However, limited active sites and poor electrical conductivity hinder its applications. Herein, the core-shell heterostructured Ni(OH)2@activation Zn-Co-Ni layered double hydroxides (Ni(OH)2@A-ZnCoNi-LDH) electrode was fabricated by loading pseudocapacitance material on the A-ZnCoNi-LDH to improve the electrochemical performance. Significantly, benefits from the synergistic effect of the multi-metal ions and the core-shell heterostructure, the electrodes demonstrated a capacitance of 2405 mF·cm-2 at 1 mA·cm-2. Furthermore, Ni(OH)2@A-ZnCoNi-LDH was used as the core electrode and carbon nanotube (CNT) film coated with Fe2O3@reduced graphene oxide (rGO) was wrapped around the core electrode to assemble coaxial fiber asymmetric supercapacitor, which illustrated an ultrahigh energy density of 177.7 µWh·cm-2 at 0.75 mW·cm-2. In particular, after consecutive charging and discharging 7000 cycles, the capacitance retention of the device was 95 %, indicating the excellent cycling stability. Furthermore, the device with high flexibility can be woven into textiles in different shapes. The fabricated device has an excellent development prospect as an energy source in wearable electronic devices.

Lightweight, flame retardant Janus carboxymethyl cellulose aerogel with fire-warning properties for smart sensor.

Lightweight, flame retardant biomass aerogels combining with multi-functionalities are promising for thermal insulation, noise absorption and smart sensors. However, high flammability hinders the application of these aerogels in extreme condition. Herein, lightweight, flame retardant aerogel with fire-warning properties fabricated from resource-abundant graphite and green carboxymethyl cellulose (CMC) is reported. During sonicating expandable graphite (EG) in CMC solution, CMC not only fabricates the downsizing process via hydrogen bonding effect but also forms stable dispersions. Then biomass aerogel is fabricated by freeze-drying strategy and enhanced by metal ionic cross-linking method. This aerogel demonstrates Janus properties for electrical conductivity and thermal conductivity. Due to the synergistic flame retardant effect of graphite nanocomposite and metal ions with a barrier effect and catalytic carbonization capacity, the flame retardancy of these aerogels are enhanced with fire-warning properties. Furthermore, these aerogels are used for monitoring physical deformations as smart sensors, which provides inspiration and a sustainable solution for developing low-cost biomass aerogel with multifunction.

Effect of the pre-crosslinking of Ba2+ ions on wet spinning of agar fibers.

Decreased coagulation bath concentration and difficult recovery are classical issues observed during the wet spinning of fibers. In this paper, a novel method was presented for preparing environment-friendly agar fibers using deionized water as the coagulation and stretch baths. The addition of Ba2+ into the spinning solution increased the crosslinking time and improved the performance of spinning solution. The results showed that the introduction of Ba2+ in the spinning solution increased the viscosity of the spinning solution. Particularly, when the concentration of BaCl2 in the spinning solution was 7 wt%, the viscosity increased to 39.29 Pa·s, which made the molecular chain arrangement of agar more compact and ordered and promoted the gelation transformation of the spinning solution, resulting in an increase in the gel temperature from 0.2 °C (Ba-0/agar) to 5.4 °C (Ba-7/agar). The spinning solution was more conducive to the formation of fibers in deionized water. In addition, the physical and chemical properties of agar fibers were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, tensile testing, and scanning electron microscopy. The results showed that the use of deionized water as the coagulation bath can improve the color of fiber and solve the problem of fiber adhesion, whereas the mechanical strength of agar fibers with pre-cross-linking metal ions was also improved. For example, the breaking strength of Ba-7/agar/DIW was 0.73 cN/dtex while the breaking strength of Ba-0/agar/DIW was only 0.62 cN/dtex.

Preparation of high-strength photochromic alginate fibers based on the study of flame-retardant properties.

Color-changing fibers have attracted much attention for their wide applications in camouflage, security warnings, and anti-counterfeiting. The inorganic color-changing material tungsten trioxide (WO3) has been widely investigated for its good stability, controllability, and ease of synthesis. In this study, photochromic alginate fibers (WO3@Ca-Alg) were prepared by incorporating UV-responsive hybrid tungsten trioxide nanoparticles in the fiber production process. The prepared photochromic alginate fibers changed from white to dark blue after 30 min of UV irradiation and returned to their original color after 64 h. It can be seen that WO3@Ca-Alg has the advantage of long color duration. The strength of this fiber reached 2.61 cN/dtex and the limiting oxygen index (LOI) was 40.9 %, which indicates that the fiber exhibited mechanical resistance and flame-retardant properties. After the cross-linking of WO3@Ca-Alg by sodium tetraborate, a new core-shell structure was generated, which was able to encapsulate tungsten trioxide in it, thus reducing the amount of tungsten trioxide loss, and its salt and washing resistance was greatly improved. This photochromic alginate fiber can be mass produced and spun into yarn.

Skin-like cryogel electronics from suppressed-freezing tuned polymer amorphization.

The sole situation of semi-crystalline structure induced single performance remarkably limits the green cryogels in the application of soft devices due to uncontrolled freezing field. Here, a facile strategy for achieving multifunctionality of cryogels is proposed using total amorphization of polymer. Through precisely lowering the freezing point of precursor solutions with an antifreezing salt, the suppressed growth of ice is achieved, creating an unusually weak and homogenous aggregation of polymer chains upon freezing, thereby realizing the tunable amorphization of polymer and the coexistence of free and hydrogen bonding hydroxyl groups. Such multi-scale microstructures trigger the integrated properties of tissue-like ultrasoftness (Young's modulus <10 kPa) yet stretchability, high transparency (~92%), self-adhesion, and instantaneous self-healing (<0.3 s) for cryogels, along with superior ionic-conductivity, antifreezing (-58 °C) and water-retention abilities, pushing the development of skin-like cryogel electronics. These concepts open an attractive branch for cryogels that adopt regulated crystallization behavior for on-demand functionalities.

Versatile Liquid Metal/Alginate Composite Fibers with Enhanced Flame Retardancy and Triboelectric Performance for Smart Wearable Textiles.

Liquid metal (LM) shows the superiority in smart wearable devices due to its biocompatibility and electromagnetic interference (EMI) shielding. However, LM based fibers that can achieve multifunctional integrated applications with biodegradability remain a daunting challenge. Herein, versatile LM based fibers are fabricated first by sonication in alginate solution to obtain LM micro/nano droplets and then wet-spinning into LM/alginate composite fibers. By mixing with high-concentration alginate solution (4-6 wt.%), the LM micro/nano droplets stability (colloidal stability for > 30 d and chemical stability for > 45 d) are not only improved, but also facilitate its spinning into fibers through bimetallic ions (e.g., Ga3+ and Ca2+ ) chelation strategy. These resultant fibers can be woven into smart textiles with excellent flexibility, air permeability, water/salt resistance, and high temperature tolerance (-196-150 °C). In addition, inhibition of smoldering result from the LM droplets and bimetallic ions is achieved to enhance flame retardancy. Furthermore, these fibers combine the exceptional properties of LM droplets (e.g., photo-thermal effect and EMI shielding) and alginate fibers (e.g., biocompatibility and biodegradability), applicable in wearable heating devices, wireless communication, and triboelectric nanogenerator, making it a promising candidate for flexible smart textiles.

NiFe Nanoparticle-Encapsulated Ultrahigh-Oxygen-Doped Carbon Layers as Bifunctional Electrocatalysts for Rechargeable Zn-Air Batteries.

There is an urgent demand for developing highly efficient bifunctional electrocatalysts with excellent stability toward the oxygen evolution and reduction reactions (OER and ORR, respectively) for rechargeable Zn-air batteries (ZABs). In this work, NiFe nanoparticles encapsulated within ultrahigh-oxygen-doped carbon quantum dots (C-NiFe) as bifunctional electrocatalysts are successfully obtained. The accumulation of carbon layers formed by carbon quantum dots results in abundant pore structures and a large specific surface area, which is favorable for improving catalytic active site exposure, ensuring high electronic conductivity and stability simultaneously. The synergistic effect of NiFe nanoparticles enriched the number of active centers and naturally increased the inherent electrocatalytic performance. Benefiting from the above optimization, C-NiFe shows excellent electrochemical activity for both OER and ORR processes (the OER overpotential is only 291 mV to achieve 10 mA cm-2). Furthermore, the C-FeNi catalyst as an air cathode displays an impressive peak power density of 110 mW cm-2, an open-circuit voltage of 1.47 V, and long-term durability over 58 h. The preparation of this bifunctional electrocatalyst provides a design idea for the construction of bimetallic NiFe composites for high-performance Zn-air batteries.

Ultra-robust, Highly Stretchable, and Conductive Nanocomposites with Self-healable Asymmetric Structures Prepared by a Simple Green Method.

Flexible conductive polymer nanocomposites based on silver nanowires (AgNWs) have been extensively studied to develop the next generation of flexible electronic devices. Fiber materials with high strength and large stretching are an important part of high-performance wearable electronics. However, manufacturing conductive composites with both high mechanical strength and good stability remains challenging. In addition, the process of effectively dispersing conductive fillers into substrates is relatively complex, which greatly hampers its widespread application. Here, a simple green self-assembly preparation method in water is reported. The AgNW is evenly dispersed in aqueous, i.e., water-borne polyurethane (WPU) with water as the solvent, and a AgNW/WPU conductive nanocomposite film with an asymmetric structure is formed by self-assembly in one step. The film has high strength (≈49.2 MPa) and high strain (≈910%), low initial resistance (99.9 mΩ/sq), high conductivity (9968.1 S/cm), and excellent self-healing (93%) and adhesion. With good self-healing performance, fibers with a conductive filler spiral structure are formed. At the same time, the application of the conductive composite material with an asymmetric structure in intelligent wearability is demonstrated.

Tuning Electronic State and Charge Transport in B←N-Containing 2D Polymer Heterostructures with Efficient Photocatalytic Performance.

Linear-conjugated polymers (LCPs) are excellent semiconductor photocatalysts. However, its inherent amorphous structures and simple electron transport channels restrict efficient photoexcited charge separation and transfer. Herein, "2D conjugated engineering" is employed to design high-crystalline polymer photocatalysts with multichannel charge transport by introducing alkoxyphenyl sidechains. The electronic state structure and electron transport pathways of the LCPs are investigated using experimental and theoretical calculations. Consequently, the 2D B←N-containing polymers (2DPBN) exhibit excellent photoelectric characteristics, which enable the efficient separation of electron-hole and rapidly transfer photogenerated carriers to the catalyst surface for efficient catalytic reactions. Significantly, the further hydrogen evolution of 2DPBN-4F heterostructures can be achieved by increasing the fluorine content of the backbones. This study highlights that the rational design of LCP photocatalysts is an effective strategy to spur further interest in photofunctional polymer material applications.

A general route to strong, conductive and antibacterial curdlan-based purely natural eutectohydrogels with self-assembled layer-by-layer network structure.

To promote the application extension of curdlan from food industry- dominant to advanced flexible biomaterials, a novel group of purely natural curdlan gels with noticeable performance was developed through a simple heating-cooling approach, i.e., heating the dispersion of pristine curdlan in mixed acidic natural deep eutectic solvents (NADESs) and water at 60-90 °C, and cooling at ambient temperature. The NADESs employed are composed of choline chloride and natural organic acids (lactic acid as the representative). The as-developed gels (called eutectohydrogels) are not only compressible and stretchable but conductive, which traditional curdlan hydrogels are not attainable. The compressive stress at 90 % strain exceeds 2.00 ± 0.03 MPa, the tensile strength and fracture elongation reach 0.131 ± 0.002 MPa and 300 ± 9 % respectively, attributed to the distinctive, reciprocally linked self-assembled layer-by-layer network structure formed during gelation. An electric conductivity up to 2.22 ± 0.04 S‧m-1 is achieved. The excellent mechanics and conductivity confer them good strain-sensing behavior. Additionally, the eutectohydrogels display high antibacterial activity against S. aureus (a model Gram-positive bacterium) and E. coli (a model Gram-negative bacterium). The outstanding comprehensive performance together with the purely natural attribute makes them broad application prospects in biomedical fields like flexible bioelectronics.

Fabrication and Characterization of Carrageenan/ZnO/Chitosan Composite Films.

In this study, a high-performance carrageenan/ZnO/chitosan composite film (FCA/ZnO/CS) was fabricated by the solution/dispersion casting method and layer-by-layer method. The first layer was nano-ZnO dispersed in carrageenan solution, and the second layer was chitosan dissolved in acetic acid. The morphology, chemical structure, surface wettability, barrier properties, mechanical properties, optical properties, and antibacterial activity of FCA/ZnO/CS were evaluated compared with a carrageenan film (FCA) and carrageenan/ZnO composite film (FCA/ZnO). This study revealed that the Zn element in FCA/ZnO/CS existed in the form of Zn2+ in FCA/ZnO/CS. There existed electrostatic interaction and hydrogen bonding between CA and CS. As a result, the mechanical strength and transparency of FCA/ZnO/CS were enhanced and the water vapor transmittance of FCA/ZnO/CS was decreased compared with that of FCA/ZnO. Furthermore, the addition of ZnO and CS greatly enhanced the antibacterial activity of Escherichia coli and also had a certain inhibitory effect on Staphylococcus aureus. FCA/ZnO/CS is expected to be a potential candidate material for food packaging, wound dressings, and various surface antimicrobial coatings.

Fabrication of a lamellar alginate-based aerogel decorated with carbon quantum dots for controlled fluorescence behaviors.

This study aimed to construct an alginate aerogel doped with carbon quantum dots and investigate the fluorescence properties of the composites. The carbon quantum dots with the highest fluorescence intensity were obtained using a methanol-water ratio of 1 : 1, a reaction time of 90 minutes, and a reaction temperature of 160 °C. The fluorescent carbon quantum dot sodium alginate-based aerogel (FCSA) obtained by compounding alginate and carbon quantum dots exhibited excellent fluorescence properties when the concentration of nano-carbon quantum dot solution was 10.0 vol%. By incorporating nano-carbon quantum dots, the fluorescence properties of the lamellar alginate aerogel can be easily and efficiently adjusted. The alginate aerogel decorated with nano-carbon quantum dots exhibits promising potential in biomedical applications due to its biodegradable, biocompatible, and sustainable properties.

Copper-Coordinated Cellulose Fibers for Electric Devices with Motion Sensitivity and Flame Retardance.

Nanocomposite conductive fibers are of great significance in applications of wearable devices, smart textiles, and flexible electronics. Integration of conductive nanomaterials into flexible bio-based fibers with multifunctionality remains challenging due to interface failure, poor flexibility, and inflammability. Although having broader applications in textiles, regenerated cellulose fibers (RCFs) cannot meet the requirements of wearable electronics owing to their intrinsic insulation. In this study, we constructed conductive RCFs fabricated by coordinating copper ions with cellulose and reducing them into stable Cu nanoparticles coated on their surface. The Cu sheath offered excellent electrical conductivity (4.6 × 105 S m-1), electromagnetic interference shielding, and enhanced flame retardance. Inspired by plant tendrils, the conductive RCF was wrapped around an elastic rod to develop wearable sensors for human health and motion monitoring. The resultant fibers not only form stable conductive nanocomposites on the fiber surface by chemical bonds but also exhibit a huge potential for wearable devices, smart sensors, and flame-retardant circuits.

Wet-spinning fluorescent alginate fibres achieved by doping PEI modified CPDs for multiple anti-counterfeiting.

Carbonized polymer dots (CPDs) with satisfactory excitation-dependent-emission and biocompatibility had great potential in anti-counterfeiting fibres field. However, it was difficult for CPDs to combined into the fibres due to the unstable interaction between CPDs and spinnable polymer matrix. Polyethyleneimine (PEI) was used to modify CPDs (namely PEI-CPDs) for achieving stable interactions with sodium alginate (SA) by a simple method, which including the physical interaction between the amino groups of PEI-CPDs and carboxyl groups of SA and the chain entanglement between two types of polymer chains. Then alginate fibres based on PEI-CPDs (PEI-CPDs/CaALG fibres) were successfully prepared by wet-spinning for the first time with less loss of PEI-CPDs. The high mechanical strength, excellent thermal stability and good biocompatibility achieved by PEI-CPDs/CaALG fibres. Furthermore, the fibres exhibited the excitation-dependent-emission property. Anti-counterfeiting of the fibres was conducted on both textile and papers, which showed higher security than the existing anti-counterfeiting fibres.

Metal-Free Carbon-Based Covalent Organic Frameworks with Heteroatom-Free Units Boost Efficient Oxygen Reduction.

Accurate identification of carbon-based metal-free electrocatalyst (CMFE) activity and enhancing their catalytic efficiency for O2 conversion is an urgent and challenging task. This study reports a promising strategy to simultaneously develop a series of covalent organic frameworks (COFs) with well-defined heterocyclic-free biphenyl or fluorenyl units. Unlike heteroatom doping, the developed method not only supplies methyl-induced molecular configuration to promote activity, but also provides a direct opportunity to identify heteroatom-free carbon active centers. The introduction of methyl groups (MGs) with reversible valence bonds into a pristine biphenyl-based COF results in an excellent performance with a half-wave potential of 0.74 V versus the reversible hydrogen electrode (RHE), which is among the highest values for CMFE-COFs as oxygen reduction reaction (ORR) electrocatalysts. Combined with in situ Raman spectra and theoretical calculations, the MG-bound skeleton (DAF-COF) is found to produce ortho activation, confirming the ortho carbon (site-5) adjacent to MGs as active centers. This may be attributed to the opening and binding of MGs, which effectively regulate the molecular configuration and charge redistribution, as well as improve charge transfer and reduce the energy barrier. This study provides insight into the design of highly efficient metal-free organic electrocatalysts via the regulation of valence bonds.

Zero-Carbon Emission Chemical Method to Remove Formaldehyde without Catalyst by Highly Porous Polymer Composites at Room Temperature.

Herein, the fabrication of reduced graphene oxide (RGO)-templated polymer composites for chemical removal of gaseous formaldehyde under ambient conditions is presented. The chemical removal of formaldehyde is achieved by a nucleophilic addition reaction between formaldehyde and aminooxy groups on the polymer chain ends to form the oxime bonds with the only byproduct of H2 O. RGO is essential since it not only has an ultralarge surface area but also can act as a perfect template for immobilizing pyrene-terminated and aminooxy-functionalized polymers via strong π-π stacking interactions, while melamine foam provides a three-dimensional skeleton for loading RGO/polymer composites to afford a porous 3D structure for efficient formaldehyde removal. Since the oxime bond can be cleaved into aminooxy group in acidic media, the RGO/polymer composite can be regenerated for repeatable usage, which shows an excellent performance of adsorbing 14 mg of formaldehyde by 100 mg of the polymer at ambient condition.

Alginate Fiber-Grafted Polyetheramine-Driven High Ion-Conductive and Flame-Retardant Separator and Solid Polymer Electrolyte for Lithium Metal Batteries.

Traditional polymer-based separators and solid polymer electrolytes (SPEs) often suffer from inherent poor flame retardancy and unsatisfied ionic conductivity, which seriously affect the safety and energy storage performance of lithium metal batteries (LMBs). Inspired by the mechanism of Li+ conductivity, an alginate fiber (AF)-grafted polyetheramine (AF-PEA) separator with efficient Li+ transport and excellent flame retardancy is dedicatedly designed, which also can act as the backbone for PEO-based SPEs (PEO@AF-PEA). Based on the intrinsic flame retardancy of the AF, the AF-PEA shows self-extinguishing ability, and its Li+ transport ability (1.8 mS cm-1 at 25 °C) is enhanced by grafting the ion-conductive PEA chain segment. By simulating the transport and distribution of Li+ in the AF-PEA, the PEA with 7-segment chain lengths can uniformly fill the Li+ transport space between the alginate backbone to promote the Li+ adsorption and the utilization of Li+ anchoring points in PEA side chains, increasing the Li+ transport rate and migration capacity. The LiFePO4/Li solid-state battery assembled using PEO@AF-PEA SPEs exhibits high safety and excellent cycling performance (exceeding 100 mAh g-1 after 1500 cycles at 2 C current density and 80 °C with less than 0.016% capacity decay for each cycle).

A zero-carbon emission chemical method to remove gaseous formaldehyde at room temperature by a renewable aminooxy-functionalized graphene composite.

We prepared a composite of aminooxy bifunctional molecules with graphene, which can decompose 91 mg of HCHO by 1 g of bifunctional molecules at room temperature with the only byproduct of water. Moreover, the composite can be regenerated under acidic conditions and 83.5% capacity is retained after 10 cycles.

Transportable, Endurable, and Recoverable Liquid Metal Powders with Mechanical Sintering Conductivity for Flexible Electronics and Electromagnetic Interference Shielding.

Liquid metals (LMs, e.g., EGaIn) promise a vast potential in accelerating the development of flexible electronics, smart robots, and wearable and biomedical devices. Although a variety of emerging processing methods are reported, they suffer several risks (e.g., leakage, weak adhesion, and low colloidal and chemical stability) because of their excellent fluidity, high surface tension, and rapid oxidation. Herein, liquid metal powders (LMPs) are fabricated based on a versatile method by vigorously stirring EGaIn with nonmetallic or organic particles through interfacial interactions. During the mixing process, EGaIn microdroplets are wrapped with a nonmetallic or an organic shell by electrostatic adsorption, and a more sticky oxide layer is constantly generated and then broken owing to the shearing friction. These transportable powders exhibit superior stability under extreme conditions (e.g., water and high temperature), being capable of recovering electrical conductivity and strong adhesion on different substrates upon mechanical sintering. A flexible, robust, and conductive coating can be constructed via swabbing with an integrated Joule heating effect and excellent electromagnetic interference shielding performances, and it is applicable in flexible wearable electronics, microcircuits, and wireless power transmission systems.

Hierarchical nano-helix as a new reinforcing unit for simultaneously ultra-strong and super-tough alginate fibers.

Fabricating alginate fibers of high strength and toughness remains a great challenge because of the difficulty in improving both strength and toughness simultaneously. Herein, this work reported the hierarchical assembly of sodium alginate nano-helix and its potential application as a new reinforcing unit for alginate fibers. Contributed from the hierarchical structures of α-helix, ß-sheet and tertiary helical alignment of nanofibrils, nano-helix improved the tensile strength of fibers with enhanced modulus, and prolonged elongation through unravelling the tertiary structures. Thus, the strength, elongation and toughness of alginate fibers were all enhanced by >200 %, solving the tradeoff of strength and toughness. The mechanical performance of nano-helix engineered alginate fibers is superior to present alginate fibers and even some other biomass-based fibers. The assembly of nano-helix provides a feasible reinforcing strategy for polysaccharide based materials, achieving simultaneous improvement of strength and toughness.