Stable mechanical properties under cyclic mechanical loads are critical for the applications of hydrogels in flexible electronics and tissue engineering. However, most existing tough hydrogels still face obvious notch sensitivity and suffer from fatigue fracture under continuous load. Designing hydrogels with multifunctional properties, such as high stretchability, toughness, and excellent antifatigue fracture, through a facile strategy is on demand. In this work, the nanocomposite hydrogels with comprehensive mechanical properties were prepared by one-pot polymerization of acrylamide (AM), isocyanoethyl methacrylate-glutamine (IEM-Gln), and Laponite XLG nanosheets. Owing to the potent hydrogen bonds formed by urea groups in IEM-Gln and hydrogen-bonding interaction between the polymer chain and nanoclays, the presented nanocomposite hydrogels displayed excellent mechanical properties (tensile strength of 160 kPa, stretchability of 2600%, compressive strength of 2.3 MPa, and toughness of 3300 J/m2). It was noteworthy that the hydrogels exhibited excellent notch insensitivity and fatigue fracture resistance, and even after 50 cycles, there was no measurable crack propagation observed. In addition, the introduction of clay nanosheets into the gelation system endowed the composite hydrogels with outstanding hemostatic activity and tissue adhesiveness. The nanocomposite hydrogels could not only reduce the skin tension of the wound tissue by their high tensile properties but also accelerate hemostasis in the first stage of wound healing, both of which led to the fast healing of skin wound in mice.

Development of hydrogel-based flexible electronics with robust elasticity, low hysteresis, and excellent durability is still challenging. Herein, for the first time, B–N coordination was employed as the main driving force to promote gelation by free radical polymerization of acrylamide and 3-acrylamidophenylboronic acid. Owing to the outstanding stability of B–N coordination, the hydrogels could retain their initial stress (>95%) during 500 tension cycles (strain of 200%) with <10% hysteresis. Moreover, the addition of NaCl elevated the mechanical properties (break stress of 0.21 MPa and fracture strain of 1600%) and imparted high electrical conductivity (4.8 S/m) and superior gauge factor (10.2) to the hydrogels. The conductive hydrogels could accurately distinguish various deformations (2.5–200% tensile strain and 1–25 kPa compressive stress) and successively output reliable electrical signals with super durability (1000 tensile cycles with a strain of 100% and 1000 compressive cycles with a stress of 15 kPa). Combined with moderate tissue adhesiveness, the conductive hydrogels can monitor various human activities with constant outputs. This work offers a new solution to integrate high stretchability, robust elasticity, and low hysteresis into noncovalent cross-linked hydrogels, and may show vast potential in the development of flexible electronic devices.

Phosphorus-doped hollow carbon nanorods with high electronic conductivity can maintain excellent structural stability and endow outstanding electrochemical performance in sodium-based dual-ion batteries.

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An anion flow battery has recently emerged as an option to store electricity with high volumetric energy densities. In particular, fluoride ions are attractive for these batteries because they have the smallest size among anions, which is beneficial for charge transport. To date, reported fluoride ion batteries either operate with an ionic liquid, organic electrolyte or solid-state electrolyte at high temperatures. Herein, an aqueous fluoride ion flow battery is proposed that consists of bismuth fluoride as the anode, 4-hydroxy-TEMPO (TEMPO) as the cathode, and NaF salt solution as the aqueous electrolyte. During the charging process, bismuth fluoride electrochemically releases fluoride ions with the formation of bismuth metal, while TEMPO captures the fluoride ions. A reversible and stable discharge capacity of 89.5 mAh g −1 was achieved at 1000 mA g −1 after 85 cycles. The fluoride ion battery possesses excellent rate performance. To the best of our knowledge, this is the earliest demonstration that fluoride ion batteries can work in aqueous solutions, which can be used for future clean energy applications.

The Hoffmeister effect of inorganic salts is verified as a promising way to toughen hydrogels, however, the high concentration of inorganic salts may be accompanied by poor biocompatibility. In this work, it is found that polyelectrolytes can obviously elevate the mechanical performances of hydrogels through the Hoffmeister effect. The introduction of anionic poly(sodium acrylate) into poly(vinyl alcohol) (PVA) hydrogel induces the aggregation and crystallization of the PVA to boost the mechanical properties of the resulting double-network hydrogel: elevation of 73, 64, 28, 135, and 19 times in the tensile strength, compressive strength, Young's modulus, toughness, and fracture energy compared with poly(acrylic acid), respectively. It is noteworthy that the mechanical performances of the hydrogels can be flexibly tuned by the variation of polyelectrolyte concentration, ionization degree, relative hydrophobicity of the ionic component, and polyelectrolyte type in a wide range. This strategy is verified to work for other Hoffmeister-effect-sensitive polymers and polyelectrolytes. Also, the introduction of urea bonds into the polyelectrolyte can further improve the mechanical properties and antiswelling capability of hydrogels. As a biomedical patch, the advanced hydrogel can efficiently inhibit hernia formation and promote the regeneration of soft tissues in an abdominal wall defect model. IntroductionAs one of the most extensively studied soft and wet materials with adjustable physical and chemical properties, hydrogels have

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Fabrication of binder‐free electrodes is an effective way to increase the performance of electrochemical energy storage (EES) devices, such as rechargeable batteries and supercapacitors. In traditional electrodes, the binder is usually electrochemically inert and has weak interactions and interfaces between binder and the active material, which increase “dead mass” and directly affect the performance of energy storage system. The binder‐free electrode can provide well‐designed electrode material structure enables well connection between active materials themselves and current collectors. In addition, without insulating binder, electron and electrolyte ions can transfer more efficiently within the electrode materials. Here, we reviewed research efforts in using various techniques involving chemical, physical and electrical methods to fabricate binder‐free electrodes. For every technique, we first briefly describe their principle and involved factors that influence the performance of as‐fabricated binder‐free electrodes and summarize advantages and disadvantages. Next, we reviewed several works which have used this technique to fabricate binder‐free electrodes. Further, the effect of well‐crafted structure design on the properties of energy storage performances including rate capability, and cycle stability was highlighted. Last, we offer our perspectives on the challenges and potential future research directions in this area. We hope this review can stimulate more research to design and synthesize the binder‐free materials for EES devices.