Thermochromic smart windows have gained increasing popularity in light modulation and energy management in buildings. However, the fabrication of flexible thermochromic smart windows with high luminous transmittance (T_lum), tailorable critical temperature (τ_c), strong solar modulation ability (ΔT_sol), and long-term durability remains a huge challenge. In this study, hydrogel-based thermochromic smart windows are fabricated by sandwiching thermochromic hydrogels of polyallylamine hydrochloride, polyacrylic acid, and carbonized polymer dots (CPDs) complexes between two pieces of transparent substrates. Benefiting from the incorporation of nanosized CPDs, the thermochromic hydrogel has an ultrahigh T_lum of ~98.7%, a desirable τ_c of ~24.2 °C, a ΔT_sol of ~89.3% and a rapid transition time of ~3 s from opaque state to transparent state. Moreover, the thermochromic hydrogel exhibits excellent anti-freezing ability, tight adhesion toward various substrates, and excellent self-healing capability. The self-healing capability enables the fabrication of large-area smart windows by welding multiple hydrogel pieces. The smart windows retain their original thermochromic properties after being stored under ambient conditions for at least 147 days or undergoing 10,000 uninterrupted heating/cooling cycles. The model houses with smart windows can achieve a temperature reduction of 9.2 °C, demonstrating the excellent indoor temperature modulation performance of the smart windows.

Patterning diversified properties and surface structure of polymer materials are of great importance toward their potential in biology, optics, and electronics. However, achieving both the patternability of stiffness and microstructure in a reconfigurable manner remains challenging. Here, we prepare amphigels crosslinked by dynamic disulfide bonds, which can be reversibly swollen by immiscible water or liquid paraffin. In the paraffingel form, the materials exhibited a high modulus of 130 MPa due to densified hydrogen bonds. Whereas swollen by water, the modulus fell over two orders of magnitude owing to the destruction of the hydrogen bonds. Via regionalized swelling of the solvents, well-controlled and rewritable soft/stiff mechanical patterns can be created. On the other hand, the dynamic exchange of the disulfide crosslinking enables mechanophoto patterning to fabricate sophisticated macrogeometries and microstructures. The reconfigurable stiffness-structure patterning can be manipulated orthogonally, which will create more application opportunities beyond conventional hydrogels and organogels.

Fluorescent poly(N-isopropylacrylamide-co-Nile blue) (pNIPAm-co-NB) microgels were synthesized that exhibited fluorescence intensity changes in a water temperature-dependent fashion. NB is well known to exhibit fluorescence intensity that depends on the hydrophobicity of the environment, while pNIPAm-based microgels are well known to transition from swollen (hydrophilic) to collapsed (relatively hydrophobic) at temperatures greater than 32 °C; hence, we attribute the above behavior to the hydrophobicity changes of the microgels with increasing temperature. This phenomenon is ultimately due to NB dimers (relatively quenched fluorescence) being broken in the hydrophobic environment of the microgels leading to relatively enhanced fluorescence. We went on to show that the introduction of cucurbit[7]uril (CB[7]) into the pNIPAm-co-NB microgels enhanced their fluorescence allowing them to be used for polyamine (e.g., spermine [SPM]) detection. Specifically, CB[7] forms a host–guest interaction with NB in the microgels, which prevents NB dimerization and enhances their fluorescence. When SPM is present, it forms a host–guest complex that is favored over the CB[7]-NB host–guest interaction, which frees the NB for dimerization and leads to fluorescence quenching. As a result, we could generate an SPM sensor capable of SPM detection down to ~0.5 µmol/L in complicated matrixes such as serum and urine.

Polymer ionogel (PIG) is a new type of flexible, stretchable, and ion-conductive material, which generally consists of two components (polymer matrix materials and ionic liquids/deep eutectic solvents). More and more attention has been received owing to its excellent properties, such as nonvolatility, good ionic conductivity, excellent thermal stability, high electrochemical stability, and transparency. In this review, the latest research and developments of PIGs are comprehensively reviewed according to different polymer matrices. Particularly, the development of novel structural designs, preparation methods, basic properties, and their advantages are respectively summarized. Furthermore, the typical applications of PIGs in flexible ionic skin, flexible electrochromic devices, flexible actuators, and flexible power supplies are reviewed. The novel working mechanism, device structure design strategies, and the unique functions of the PIG-based flexible ionic devices are briefly introduced. Finally, the perspectives on the current challenges and future directions of PIGs and their application are discussed.

This study marks the birth of visible and selective click covalent assembly. It is achieved by amplifying orthogonal alkyne−azide click chemistry through interfacial multisite interactions between azide/alkyne functionalized polymer hydrogels. Macroscopic assembly of hydrogels via host−guest chemistry or noncovalent interactions such as electrostatic interactions has been reported. Unlike macroscopic supramolecular assembly, here we report visible and selective “click” covalent assembly of hydrogels at the macroscale. LEGO-like hydrogels modified with alkyne and azide groups, respectively, can click together via the formation of covalent bonds. Monomer concentration-dependent assembly and selective covalent assembly have been studied. Notably, macroscopic gel assembly clearly elucidates click preferences and component selectivity not observed in the solution reactions of competing monomers.

Conductive-bridge random access memory (CBRAM) emerges as a promising candidate for next-generation memory and storage device. However, CBRAMs are prone to degenerate and fail during electrochemical metallization processes. To address this issue, herein we propose a self-repairability strategy for CBRAMs. Amorphous NbSe₂ was designed as the resistive switching layer, with Cu and Au as the top and bottom electrodes, respectively. The NbSe₂ CBRAMs demonstrate exceptional cycle-to-cycle and device-to-device uniformity, with forming-free and compliance current-free resistive switching characteristics, low-operation voltage, and competitive endurance and retention performance. Most importantly, the self-repairable behavior is discovered for the first time in CBRAM. The device after failure can recover its performance to the initially normal state by operating with a slightly large reset voltage. The existence of Cu conductive filament and excellent controllability of Cu migration in the NbSe₂ switching layer has been revealed by a designed broken-down point approach, which is responsible for the self-repairable behavior of NbSe₂ CBRAMs. Our self-repairable and high-uniform amorphous NbSe₂ CBRAM may open the door to the development of memory and storage devices in the future.

Transition metal carbides, including both MXene and non-MXene metal carbides, have enjoyed a soaring reputation in recent years. Benefitting from their intriguing physical and chemical characteristics, they shine in multifarious research fields and currently, they have emerged as promising nanomaterials for photocatalysis in energy and environmental science. Herein, based on the recent theoretical research and experimental studies, a systematic and comprehensive review of the expeditious advances of metal carbides and their nano-architectures in the flourishing arena of photocatalysis is presented. The fundamental mechanism involved in photocatalysis with metal carbides serving as semiconductors or cocatalysts is thoroughly discussed. Besides, we highlight the main synthetic strategies of MXene and non-MXene metal carbides and unravel the structural properties of the as-obtained metal carbides via different fabrication routes to establish and elucidate their intriguing role in ameliorating photocatalytic activity. Moreover, the state-of-the-art advancements of metal carbides in diverse photocatalytic applications, including hydrogen evolution reaction, oxygen evolution reaction, overall water splitting, and carbon dioxide reduction reaction, are summarized. In particular, insights into the structure–activity relationship of metal carbide in photocatalysis are elucidated. Finally, this review concludes with the ongoing challenges and perspectives on the future directions of metal carbides in the realm of photocatalysis.

Harvesting indoor light to power electronic devices for the Internet of Things has become an application scenario for emerging photovoltaics, especially utilizing organic photovoltaics (OPVs). Combined liquid- and solid-state processing, such as printing and lamination used in industry for developing indoor OPVs, also provides a new opportunity to investigate the device structure, which is otherwise hardly possible based on the conventional approach due to solvent orthogonality. This study investigates the impact of fullerene-based acceptor interlayer on the performance of conjugated polymer–fullerene-based laminated OPVs for indoor applications. We observe open-circuit voltage (V_OC) loss across the interface despite this arrangement being presumed to be ideal for optimal device performance. Incorporating insulating organic components such as polyethyleneimine (PEI) or polystyrene (PS) into fullerene interlayers decreases the work function of the cathode, leading to better energy level alignment with the active layer (AL) and reducing the V_OC loss across the interface. Neutron reflectivity studies further uncover two different mechanisms behind the V_OC increase upon the incorporation of these insulating organic components. The self-organized PEI layer could hinder the transfer of holes from the AL to the acceptor interlayer, while the gradient distribution of the PS-incorporated fullerene interlayer eliminates the thermalization losses. This work highlights the importance of structural dynamics near the extraction interfaces in OPVs and provides experimental demonstrations of interface investigation between solution-processed cathodic fullerene layer and bulk heterojunction AL.

Despite extensive efforts in designing and preparing switchable underwater adhesives, it is not easy to regulate the underwater adhesion strength locally and remotely. Here, we design and synthesize photoreversible copolymer of poly[dopamine methacrylamide-co-methoxyethyl-acrylate-co-7-(2-methacryloyloxyethoxy)-4-methylcoumarin]. Due to the dynamic formation and breaking of chemical crosslinking networks within the smart adhesives, the material shows widely tunable adhesion strength from ∼150 to ∼450 kPa and long-range reversible maneuverability under orthogonal 254 and 365 nm ultraviolet light stimulation via the coumarin dimerization and cycloreversion. Moreover, the adhesive exhibits good circulation performance and stability in an acid–base environment. It also demonstrated that the bolt can be coated with the smart adhesive material for on-demand bonding. This design principle opens the door to the development of remotely controllable high-performance smart underwater adhesives.

The remarkable successes of graphene have sparked increasing interest in elemental two-dimensional (2D) materials, also referred to as Xenes. Due to their chemical simplicity and appealing physiochemical properties, Xenes have shown particular potential for numerous (opto) electronic, iontronic, and energy applications. Among them, layered α-phase tellurene has demonstrated the most promise, thanks to the recent successes in the chemical synthesis of highly crystalline 2D tellurene. However, the general electronic and electrochemical properties of tellurene in electrolyte systems remain ambiguous, hindering their further development. In this work, we studied the electrostatic gating, electrocatalysis, and electrochemical stability of tellurene in electrolyte systems. Our results show that tellurene obtained from both hydrothermal and chemical vapor deposition methods, two mainstream synthetic approaches for Xenes, demonstrates thickness-dependent ambipolar transport with high hole mobility and stability in both aqueous electrolytes and ionic liquids. More importantly, the electrochemical properties of tellurene are investigated via the emerging on-chip electrochemistry. Pristine tellurene demonstrates hydrogen evolution reaction with low Tafel slopes and remarkable electrochemical stability in acidic electrolytes over a large potential window. Our study provides a comprehensive understanding of the iontronic and electrochemical properties of tellurene, paving the way for the broad adoption of Xenes in sensors, synaptic devices, and electrocatalysis.

Hybrid perovskites have attracted enormous attention in the next generation resistive switching (RS) memristor for the artificial synapses, owing to their ambipolar charge transport, long diffusion length, and tunable visible bandgap. However, the variable switch, limited reproducibility, and poor endurance are the obstacles to the practical application of the perovskite memristors. Herein, we reported a multilevel RS nonvolatile memory based on a 3D trigonal HC(NH₂)₂PbI₃ (α-FAPbI₃) perovskite layer modified by 1-cyanobutyl-3-methylimidazolium chloride ([CNBmim]Cl) and sandwiched between ITO and Au electrodes (Au/[CNBmim]Cl/α-FAPbI₃/SnO₂/ITO). In contrast to the bare memristor with failure switching from low resistance state (LRS) to high resistance state (HRS), the memristor device based on the α-FAPbI₃ modified with [CNBmim]Cl (Target device) shows the retention time over 10⁴ s with On/Off ratio (>10²) and endurance up to 550 cycles. The stable RS cycle benefits from the accelerated electrons de-trapping from the reduced defects and fast charge separation in the interface of α-FAPbI₃/electrode, leading to the rupture of conductive filaments and transition of LRS to HRS. As a two-terminal analog synaptic device, the target device can realize random handwritten digit recognition with an impressive accuracy of 89.3% on the condition of low learning phases (500 training cycles).

Research and development of novel fluorine-free materials to replace fluorinated aqueous film-forming foam (AFFF) are crucial for improving pool fire suppression performance and protecting the environment. In this study, we report the thermo-responsive fluorine-free foam stabilized by triblock PEO–PPO–PEO copolymers (EO)₁₀₀(PO)₆₅(EO)₁₀₀ for pool fire suppression. Small-angle X-ray scattering (SAXS) and reflected light interferometric techniques are conducted to study the molecular self-assembly in bulk and film thinning behavior, and the foaming kinetics of copolymer solution and thermophysical properties of the liquid foam are studied by dynamic surface tension and oscillatory rheology analysis. At room temperature, the amphipathic structure of PEO–PPO–PEO makes it possible to absorb at the air–liquid interface forming large-scale liquid foams containing the mobile films with a detergent state. Upon heating to the surface cooling temperature of burning oil, the mobile films can be actively switched into mechanically strong films with rigid surfaces. The in situ switching of the two interfacial states leads to the significant enhancement of the foam stability, especially under the dual defoaming effects of heat and oil. What's more, it is observed that the confinement of organized copolymer micelles in the Plateau borders and micellar self-layering in film confinement induce drainage delay of foam and film's stepwise thinning phenomenon, further increasing film thickness and enhancing the thermal stability of the foam. In standard fire-fighting tests, it is proved that the burnback performance exhibited by thermo-responsive copolymer foams is three times better than that for classical fluorine-free foams and almost 1.5 times higher than that for commercial AFFF.

Aqueous zinc-ion batteries (ZIBs) are regarded as among the most promising candidates for large-scale grid energy storage, owing to their high safety, low costs, and environmental friendliness. Over the past decade, vanadium oxides, which are exemplified by V₂O₅, have been widely developed as a class of cathode materials for ZIBs, where the relatively high theoretical capacity and structural stability are among the main considerations. However, there are considerable challenges in the construction of vanadium-based ZIBs with high capacity, long lifespan, and excellent rate performance. Simple widenings of the interlayer spacing in the layered vanadium oxides by pre-intercalations appear to have reached their limitations in improving the energy density and other key performance parameters of ZIBs, although various metal ions (Na⁺, Ca²⁺, and Al³⁺) and even organic cations/groups have been explored. Herein, we discuss the advances made more recently, and also the challenges faced by the high-performance vanadium oxides (V₂O₅-based) cathodes, where there are several strategies to improve their electrochemical performance ranging from the new structural designs down to sub-nano-scopic/molecular/atomic levels, including cation pre-intercalation, structural water optimization, and defect engineering, to macroscopic structural modifications. The key principles for an optimal structural design of the V₂O₅-based cathode materials for high energy density and fast-charging aqueous ZIBs are examined, aiming at paving the way for developing energy storage designed for those large scales, high safety, and low-cost systems.

Conductive polymer hydrogels have greatly improved the compatibility of electronic devices with biological tissues for human–machine interfacing. Hydrogels that possess low Young's modulus, low interfacial impedance, and high tensile properties facilitate high-quality signal transmission across dynamic biointerfaces. Direct incorporation of elastomers with conductive polymers may result in undesirable mechanical and/or electrical performance. Here, a covalent cross-linking network and an entanglement-driven network with conductive poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) have been combined. The triple-network conductive hydrogel shows high stretchability (with fracture strain up to 900%), low impedance (down to 91.2 Ω·cm²), and reversible adhesion. Importantly, ultra-low modulus (down to 6.3 kPa) and strain-insensitive electrical/electrochemical performance were achieved, which provides a guarantee for low current stimulation. The material design will contribute to the progression of soft and conformal bioelectronic devices, and pave the way to future implantable electronics.