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HighlightsThis Review encompasses the role, requirement, and development direction of water-based electrolytes for sustainable, safe, high-performance Li-ion batteries.Water-based electrolytes (aqueous liquid and gel electrolytes) and their mechanisms are comprehensively summarized to widen the electrolyte electrochemical stability window and battery operating voltage and to achieve long-term operation stability.Current lithium-ion batteries (LIBs) rely on organic liquid electrolytes that pose significant risks due to their flammability and toxicity. The potential for environmental pollution and explosions resulting from battery damage or fracture is a critical concern. Water-based (aqueous) electrolytes have been receiving attention as an alternative to organic electrolytes. However, a narrow electrochemical-stability window, water decomposition, and the consequent low battery operating voltage and energy density hinder the practical use of aqueous electrolytes. Therefore, developing novel aqueous electrolytes for sustainable, safe, high-performance LIBs remains challenging. This Review first commences by summarizing the roles and requirements of electrolytes–separators and then delineates the progression of aqueous electrolytes for LIBs, encompassing aqueous liquid and gel electrolyte development trends along with detailed principles of the electrolytes. These aqueous electrolytes are progressed based on strategies using superconcentrated salts, concentrated diluents, polymer additives, polymer networks, and artificial passivation layers, which are used for suppressing water decomposition and widening the electrochemical stability window of water of the electrolytes. In addition, this Review discusses potential strategies for the implementation of aqueous Li-metal batteries with improved electrolyte–electrode interfaces. A comprehensive understanding of each strategy in the aqueous system will assist in the design of an aqueous electrolyte and the development of sustainable and safe high-performance batteries.

Hydrogels are major components of the human body. To replace a damaged hydrogel in the body or support/monitor its normal operation, artificial hydrogels similar to those found in nature are required. As the development of morphologically adaptable soft yet tough hydrogels such as double‐network (DN) and polyampholyte (PA) gels, they are applied to soft tissues such as the neural and epithelial tissues with elastic moduli ranging from a few pascals to several kilopascals. However, creating strong and stiff hydrogels emulating stiff load‐bearing connective tissues with elastic moduli in the MPa‐to‐GPa range remains challenging. Herein, recent strategies and potential methods for strengthening and stiffening tough DN and PA gels (such as the reinforcement addition, polymer chain alignment, and solvent exchange) as well as the reinforcing and fracture mechanisms of the resulting hydrogels are summarized. The objective is to provide some insights into the optimal strategy and method for fabricating hydrogels with a combination of strength, stiffness, and toughness, which can emulate natural load‐bearing tissues. Strengthening and stiffening tough double‐network (DN) or polyampholyte (PA) hydrogels are a promising approach to fabricate synthetic hydrogels emulating the natural load‐bearing tissues with elastic moduli in the MPa‐to‐GPa. Herein, several strategies for strengthening and stiffening the hydrogels are summarized, and their reinforcing and fracture mechanisms are outlined, providing future directions to develop hydrogels with desirable mechanical properties.

For the practical use of synthetic hydrogels as artificial biological tissues, flexible electronics, and conductive membranes, achieving requirements for specific mechanical properties is one of the most prominent issues. Here, we demonstrate superstrong, superstiff, and conductive alginate hydrogels with densely interconnecting networks implemented via simple reconstructing processes, consisting of anisotropic densification of pre-gel and a subsequent ionic crosslinking with rehydration. The reconstructed hydrogel exhibits broad ranges of exceptional tensile strengths (8–57 MPa) and elastic moduli (94–1,290 MPa) depending on crosslinking ions. This hydrogel can hold sufficient cations (e.g., Li + ) within its gel matrix without compromising the mechanical performance and exhibits high ionic conductivity enough to be utilized as a gel electrolyte membrane. Further, this strategy can be applied to prepare mechanically outstanding, ionic-/electrical-conductive hydrogels by incorporating conducting polymer within the hydrogel matrix. Such hydrogels are easily laminated with strong interfacial adhesion by superficial de- and re-crosslinking processes, and the resulting layered hydrogel can act as a stable gel electrolyte membrane for an aqueous supercapacitor. Specific mechanical properties are one of the most important issues for application of synthetic hydrogels as biological tissue, flexible electronics or in conductive membranes. Here, the authors demonstrate that a reconstruction process consisting of anisotropic densification of pre-gel and subsequent ionic crosslinking and rehydration leads to strong, stiff, and conductive alginate hydrogels with densely interconnecting networks.

Mechanical properties of synthetic hydrogels remain inferior to those of load-bearing tissues such as ligaments, one of the strongest and stiffest natural hydrogels in the human body. Inspired by biological structures and their mechanisms conferring high mechanical properties, we report strong, stiff, and tough hydrogels composed of fiber-shaped elements that can be assembled into parallel bundles, closely resembling natural ligaments. These hydrogel fibers, readily fabricated with diameters of a few hundred micrometers, comprise polymer–particle hybrid agglomerates embedded in a continuous, interconnected polymer matrix. Strong polymer–particle interactions combined with spatial confinement within the agglomerates enable efficient load transfer, resulting in significant load-transfer lengths and substantial energy dissipation across the network. This design overcomes the conventional trade-offs between strength/stiffness and toughness/stretchability in polymer composites, thereby achieving tensile strength of 61 ± 8 MPa, elastic modulus of 131 ± 15 MPa, toughness 135 ± 11 MJ m −3 , and stretchability exceeding 400%. When assembled into millimeter-scale hierarchical bundles, the hydrogels mimic the structural organization of ligaments, sustain loads of tens of kilograms, and function as strain sensors. Mechanical properties have potential in biomedical applications, but the mechanical properties are not comparable to load-bearing tissues. Here, the authors report the development of hydrogels composed of hydrogel fibers that assemble to give parallel bundles, formed from polymer-particle agglomerates.

Achieving a simple yet sustainable printing technique with minimal instruments and energy remains challenging. Here, a facile and sustainable 3D printing technique is developed by utilizing a reversible salting-out effect. The salting-out effect induced by aqueous salt solutions lowers the phase transition temperature of poly(N-isopropylacrylamide) (PNIPAM) solutions to below 10 °C. It enables the spontaneous and instant formation of physical crosslinks within PNIPAM chains at room temperature, thus allowing the PNIPAM solution to solidify upon contact with a salt solution. The PNIPAM solutions are extrudable through needles and can immediately solidify by salt ions, preserving printed structures, without rheological modifiers, chemical crosslinkers, and additional post-processing steps/equipment. The reversible physical crosslinking and de-crosslinking of the polymer through the salting-out effect demonstrate the recyclability of the polymeric ink. This printing approach extends to various PNIPAM-based composite solutions incorporating functional materials or other polymers, which offers great potential for developing water-soluble disposable electronic circuits, carriers for delivering small materials, and smart actuators. Here, the authors show a facile and sustainable 3D printing by utilizing a reversible salting-out effect on poly(N-isopropylacrylamide) (PNIPAM) solutions. Aqueous salt solutions lower the phase transition temperature of PNIPAM solutions below 10 °C and instantly solidify the PNIPAM solutions upon contact.

Flexible electronic technology has developed rapidly in recent years, showing broad application prospects in motion monitoring, wearable devices, and personalized medicine. Consequently, the demand for high sensitivity and wide sensing range has gradually increased. Conductive hydrogels have high flexibility, excellent conductivity, and good biocompatibility, making them ideal candidates for fabricating flexible sensors. However, conductive hydrogels exhibit weak mechanical stability, which limits their applications. Therefore, sufficient mechanical properties and fatigue resistance are usually needed to fulfill their application requirements. Herein, the research frontiers of sensors based on mechanically robust conductive hydrogels are reviewed. While published papers always focus on the configuration design and application of sensors and the improvement of sensing performance, research on the network design of hydrogels and their effects on mechanical properties and sensing performance are limited. It is attempted in this review to fill this gap by focusing on the design principles of mechanically enhanced conductive hydrogels and their applications in flexible electronic devices. Herein, hydrogels’ structural designs, toughening mechanisms, mechanical properties, and sensing applications are discussed. The different working mechanisms of flexible sensors composed of tough conductive hydrogels and their applications are also reviewed. Finally, the future development directions and challenges in this field are highlighted. Hydrogels have gained significant attention in the field of flexible sensors because of their outstanding conductivity and flexibility. This review aims to provide an overview of the design and fabrication of different types of conductive hydrogels, while also investigating the intricate relationships between their structure and performance. Their working mechanisms, sensing capabilities, and applications to flexible sensors are explored.

Synthetic tough hydrogels have received attention because they could mimic the mechanical properties of natural hydrogels, such as muscle, ligament, tendon, and cartilage. Many recent studies suggest various approaches to enhance the mechanical properties of tough hydrogels. However, directly comparing each hydrogel property in different reports is challenging because various testing specimen shapes/sizes were employed, affecting the experimental mechanical property values. This study demonstrates how the specimen geometry—the lengths and width of the reduced section—of a tough double-network hydrogel causes differences in experimental tensile mechanical values. In particular, the elastic modulus was systemically compared using eleven specimens of different shapes and sizes that were tensile tested, including a rectangle, ASTM D412-C and D412-D, JIS K6251-7, and seven customized dumbbell shapes with various lengths and widths of the reduced section. Unlike the rectangular specimen, which showed an inconsistent measurement of mechanical properties due to a local load concentration near the grip, dumbbell-shaped specimens exhibited a stable fracture at the reduced section. The dumbbell-shaped specimen with a shorter gauge length resulted in a smaller elastic modulus. Moreover, a relationship between the specimen dimension and measured elastic modulus value was derived, which allowed for the prediction of the experimental elastic modulus of dumbbell-shaped tough hydrogels with different dimensions. This study conveys a message that reminds the apparent experimental dependence of specimen geometry on the stress-strain measurement and the need to standardize the measurement of of numerous tough hydrogels for a fair comparison.

In reducing the high operating temperatures (≥800 °C) of solid-oxide fuel cells, use of protonic ceramics as an alternative electrolyte material is attractive due to their high conductivity and low activation energy in a low-temperature regime (≤600 °C). Among many protonic ceramics, yttrium-doped barium zirconate has attracted attention due to its excellent chemical stability, which is the main issue in protonic-ceramic fuel cells. However, poor sinterability of yttrium-doped barium zirconate discourages its fabrication as a thin-film electrolyte and integration on porous anode supports, both of which are essential to achieve high performance. Here we fabricate a protonic-ceramic fuel cell using a thin-film-deposited yttrium-doped barium zirconate electrolyte with no impeding grain boundaries owing to the columnar structure tightly integrated with nanogranular cathode and nanoporous anode supports, which to the best of our knowledge exhibits a record high-power output of up to an order of magnitude higher than those of other reported barium zirconate-based fuel cells. Protonic ceramic fuel cells are promising for energy applications, but maintaining high performance with long-term stability is an issue. Here the authors use a stable yttrium-doped barium zirconate electrolyte, achieving a power output one order of magnitude higher than existing protonic ceramic fuel cells.

Tilia species are valuable woody species due to their beautiful shape and role as honey trees. Somatic embryogenesis can be an alternative method for mass propagation of T. amurensis . However, the molecular mechanisms of T. amurensis somatic embryogenesis are yet to be known. Here, we conducted comparative transcriptional analysis during somatic embryogenesis of T. amurensis . RNA-Seq identified 1505 differentially expressed genes, including developmental regulatory genes. Auxin related genes such as YUC, AUX/IAA and ARF and signal transduction pathway related genes including LEA and SERK were differentially regulated during somatic embryogenesis. Also, B3 domain family ( LEC2, FUS3), VAL and PKL, the regulatory transcription factors, were differentially expressed by somatic embryo developmental stages. Our results could provide plausible pathway of signaling somatic embryogenesis of T. amurensis , and serve an important resource for further studies in direct somatic embryogenesis in woody plants.

Arsenic is an extremely toxic metalloid causing serious health problems. In Southeast Asia, aquifers providing drinking and agricultural water for tens of millions of people are contaminated with arsenic. To reduce nutritional arsenic intake through the consumption of contaminated plants, identification of the mechanisms for arsenic accumulation and detoxification in plants is a prerequisite. Phytochelatins (PCs) are glutathione-derived peptides that chelate heavy metals and metalloids such as arsenic, thereby functioning as the first step in their detoxification. Plant vacuoles act as final detoxification stores for heavy metals and arsenic. The essential PC—metal (loid) transporters that sequester toxic metal(loid)s in plant vacuoles have long been sought but remain unidentified in plants. Here we show that in the absence of two ABCC-type transporters, AtABCC1 and AtABCC2, Arabidopsis thaliana is extremely sensitive to arsenic and arsenic-based herbicides. Heterologous expression of these ABCC transporters in phytochelatin-producing Saccharomyces cerevisiae enhanced arsenic tolerance and accumulation. Furthermore, membrane vesicles isolated from these yeasts exhibited a pronounced arsenite [As(III)]—PC₂ transport activity. Vacuoles isolated from atabcc1 atabcc2 double knockout plants exhibited a very low residual As(III)—PC₂ transport activity, and interestingly, less PC was produced in mutant plants when exposed to arsenic. Overexpression of AtPCS1 and AtABCC1 resulted in plants exhibiting increased arsenic tolerance. Our findings demonstrate that AtABCC1 and AtABCC2 are the long-sought and major vacuolar PC transporters. Modulation of vacuolar PC transporters in other plants may allow engineering of plants suited either for phytoremediation or reduced accumulation of arsenic in edible organs.