Dual-Responsive MXene-Functionalized Wool Yarn Artificial Muscles

Fiber-based artificial muscles are promising for smart textiles capable of sensing, interacting, and adapting to environmental stimuli. However, the application of current artificial muscle-based textiles in wearable and engineering fields has largely remained a constraint due to the limited deformation, restrictive stimulation, and uncomfortable. Here, dual-responsive yarn muscles with high contractile actuation force are fabricated by incorporating a very small fraction (<1 wt.%) of Ti3C2Tx MXene/cellulose nanofibers (CNF) composites into self-plied and twisted wool yarns. They can lift and lower a load exceeding 3400 times their own weight when stimulated by moisture and photothermal. Furthermore, the yarn muscles are coiled homochirally or heterochirally to produce spring-like muscles, which generated over 550% elongation or 83% contraction under the photothermal stimulation. The actuation mechanism, involving photothermal/moisture-mechanical energy conversion, is clarified by a combination of experiments and finite element simulations. Specifically, MXene/CNF composites serve as both photothermal and hygroscopic agents to accelerate water evaporation under near-infrared (NIR) light and moisture absorption from ambient air. Due to their low-cost facile fabrication, large scalable dimensions, and robust strength coupled with dual responsiveness, these soft actuators are attractive for intelligent textiles and devices such as self-adaptive textiles, soft robotics, and wearable information encryption.

Towards high performance and durable soft tactile actuators

Soft actuators are gaining significant attention due to their ability to provide realistic tactile sensations in various applications. However, their soft nature makes them vulnerable to damage from external factors, limiting actuation stability and device lifespan. The susceptibility to damage becomes higher with these actuators often in direct contact with their surroundings to generate tactile feedback. Upon onset of damage, the stability or repeatability of the device will be undermined. Eventually, when complete failure occurs, these actuators are disposed of, accumulating waste and driving the consumption of natural resources. This emphasizes the need to enhance the durability of soft tactile actuators for continued operation. This review presents the principles of tactile feedback of actuators, followed by a discussion of the mechanisms, advancements, and challenges faced by soft tactile actuators to realize high actuation performance, categorized by their driving stimuli. Diverse approaches to achieve durability are evaluated, including self-healing, damage resistance, self-cleaning, and temperature stability for soft actuators. In these sections, current challenges and potential material designs are identified, paving the way for developing durable soft tactile actuators.

Functionalized MXene Films with Substantially Improved Low-Voltage Actuation

Ti3 C2 Tx MXene film is promising for low-voltage electrochemical actuators (ECAs) due to its excellent electrical conductivity, volumetric capacitance, and mechanical properties. However, its in-plane actuation is limited to little intralayer strain of MXene sheets under polarization. Here it is demonstrated that a simple tetrabutylammonium (TBA) functionalization of MXene improves the in-plane actuation strain by 337% and also enhances the mechanical property and stability in air and the electrolyte. Various in situ characterizations reveal that the improved actuation is ascribed to the co-insertion/desertion of TBA and Li ions into/from MXene interlayer galleries and inter-edge gaps that causes a large in-plane sliding of MXene sheets under negative/positive polarizations. The assembled bending actuator has a high strength and modulus and generates a peak-to-peak strain difference of 0.771% and a blocking force up to 51.5 times its own weight under 1 V. The designed soft robotic tweezer can grasp an object under 1 V and hold it firmly under 0 V. The novel sheet sliding mechanism resembling the filament sliding theory in skeletal muscles may inspire the design of high-performance actuators with other nanomaterials.

Triboelectric Nanogenerators Based on Fluid Medium: From Fundamental Mechanisms toward Multifunctional Applications

Fluid-based triboelectric nanogenerators (FB-TENGs) are at the forefront of promising energy technologies, demonstrating the ability to generate electricity through the dynamic interaction between two dissimilar materials, wherein at least one is a fluidic medium (such as gas or liquid). By capitalizing on the dynamic and continuous properties of fluids and their interface interactions, FB-TENGs exhibit a larger effective contact area and a longer-lasting triboelectric effect in comparison to their solid-based counterparts, thereby affording longer-term energy harvesting and higher-precision self-powered sensors in harsh conditions. In this review, various fluid-based mechanical energy harvesters, including liquid-solid, gas-solid, liquid-liquid, and gas-liquid TENGs, have been systematically summarized. Their working mechanism, optimization strategies, respective advantages and applications, theoretical and simulation analysis, as well as the existing challenges, have also been comprehensively discussed, which provide prospective directions for device design and mechanism understanding of FB-TENGs.

Encoding of multi-modal emotional information via personalized skin-integrated wireless facial interface

Human affects such as emotions, moods, feelings are increasingly being considered as key parameter to enhance the interaction of human with diverse machines and systems. However, their intrinsically abstract and ambiguous nature make it challenging to accurately extract and exploit the emotional information. Here, we develop a multi-modal human emotion recognition system which can efficiently utilize comprehensive emotional information by combining verbal and non-verbal expression data. This system is composed of personalized skin-integrated facial interface (PSiFI) system that is self-powered, facile, stretchable, transparent, featuring a first bidirectional triboelectric strain and vibration sensor enabling us to sense and combine the verbal and non-verbal expression data for the first time. It is fully integrated with a data processing circuit for wireless data transfer allowing real-time emotion recognition to be performed. With the help of machine learning, various human emotion recognition tasks are done accurately in real time even while wearing mask and demonstrated digital concierge application in VR environment.

Bioinspired structural hydrogels with highly ordered hierarchical orientations by flow-induced alignment of nanofibrils

Natural structural materials often possess unique combinations of strength and toughness resulting from their complex hierarchical assembly across multiple length scales. However, engineering such well-ordered structures in synthetic materials via a universal and scalable manner still poses a grand challenge. Herein, a simple yet versatile approach is proposed to design hierarchically structured hydrogels by flow-induced alignment of nanofibrils, without high time/energy consumption or cumbersome postprocessing. Highly aligned fibrous configuration and structural densification are successfully achieved in anisotropic hydrogels under ambient conditions, resulting in desired mechanical properties and damage-tolerant architectures, for example, strength of 14 ± 1 MPa, toughness of 154 ± 13 MJ m-3, and fracture energy of 153 ± 8 kJ m-2. Moreover, a hydrogel mesoporous framework can deliver ultra-fast and unidirectional water transport (maximum speed at 65.75 mm s-1), highlighting its potential for water purification. This scalable fabrication explores a promising strategy for developing bioinspired structural hydrogels, facilitating their practical applications in biomedical and engineering fields.

The Role of 3D Printing Technologies in Soft Grippers

Soft grippers are essential for precise and gentle handling of delicate, fragile, and easy-to-break objects, such as glassware, electronic components, food items, and biological samples, without causing any damage or deformation. This is especially important in industries such as healthcare, manufacturing, agriculture, food handling, and biomedical, where accuracy, safety, and preservation of the objects being handled are critical. This article reviews the use of 3D printing technologies in soft grippers, including those made of functional materials, nonfunctional materials, and those with sensors. 3D printing processes that can be used to fabricate each class of soft grippers are discussed. Available 3D printing technologies that are often used in soft grippers are primarily extrusion-based printing (fused deposition modeling and direct ink writing), jet-based printing (polymer jet), and immersion printing (stereolithography and digital light processing). The materials selected for fabricating soft grippers include thermoplastic polymers, UV-curable polymers, polymer gels, soft conductive composites, and hydrogels. It is conclude that 3D printing technologies revolutionize the way soft grippers are being fabricated, expanding their application domains and reducing the difficulties in customization, fabrication, and production.

Printed sustainable elastomeric conductor for soft electronics

The widespread adoption of renewable and sustainable elastomers in stretchable electronics has been impeded by challenges in their fabrication and lacklustre performance. Here, we realize a printed sustainable stretchable conductor with superior electrical performance by synthesizing sustainable and recyclable vegetable oil polyurethane (VegPU) elastomeric binder and developing a solution sintering method for their composites with Ag flakes. The binder impedes the propagation of cracks through its porous network, while the solution sintering reaction reduces the resistance increment upon stretching, resulting in high stretchability (350%), superior conductivity (12833 S cm-1), and low hysteresis (0.333) after 100% cyclic stretching. The sustainable conductor was used to print durable and stretchable impedance sensors for non-obstructive detection of fruit maturity in food sensing technology. The combination of sustainable materials and strategies for realizing high-performance stretchable conductors provides a roadmap for the development of sustainable stretchable electronics.

Size-Selective Ionic Crosslinking Provides Stretchable Mixed Ionic-Electronic Conductors

Mechanically compliant conductors are of utmost importance for the emerging fields of soft electronics and robotics. However, the development of intrinsically deformable organic conductors remains a challenge due to the trade-off between mechanical performance and charge mobility. In this study, we report a solution to this issue based on size-selective ionic crosslinking. This rationally designed crosslinking mediated by length-regulated oligo(ethylene glycol) pendant groups and metal ions simultaneously improved the softness and toughness and ensured excellent mixed ionic-electronic conductivity in poly(3,4-ethylenedioxythiophene):polystyrene sulfonate composite materials. Moreover, the added ions remarkably promoted accumulation of charge carriers in response to temperature gradient, thus offering a viable approach to stretchable thermoelectric generators with enhanced stability against humidity.

Effective Surface Modification of 2D MXene toward Thermal Energy Conversion and Management

Thermal energy management is a crucial aspect of many research developments, such as hybrid and soft electronics, aerospace, and electric vehicles. The selection of materials is of critical importance in these applications to manage thermal energy effectively. From this perspective, MXene, a new type of 2D material, has attracted considerable attention in thermal energy management, including thermal conduction and conversion, owing to its unique electrical and thermal properties. However, tailored surface modification of 2D MXenes is required to meet the application requirements or overcome specific limitations. Herein, a comprehensive review of surface modification of 2D MXenes for thermal energy management is discussed. First, this work discusses the current progress in the surface modification of 2D MXenes, including termination with functional groups, small-molecule organic compound functionalization, and polymer modification and composites. Subsequently, an in situ analysis of surface-modified 2D MXenes is presented. This is followed by an overview of the recent progress in the thermal energy management of 2D MXenes and their composites, such as Joule heating, heat dissipation, thermoelectric energy conversion, and photothermal conversion. Finally, some challenges facing the application of 2D MXenes are discussed, and an outlook on surface-modified 2D MXenes is provided.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Ferroelectric Modulation in Flexible Lead-Free Perovskite Schottky Direct-Current Nanogenerator for Capsule-Like Magnetic Suspension Sensor

Tribovoltaic nanogenerator (TVNG), a promising semiconductor energy technology, displays outstanding advantages such as low matching impedance and continuous direct-current output. However, the lack of controllable and stable performance modulation strategies is still a major bottleneck that impedes further practical applications of TVNG. Herein, by leveraging the ferroelectricity-enhanced mechanism and the control of interfacial energy band bending, we construct a lead-free perovskite-based [3,3-difluorocyclobutylammonium]₂ CuCl₄ ((DF-CBA)₂ CuCl₄ )/Al Schottky junction TVNG. The multiaxial ferroelectricity of (DF-CBA)₂ CuCl₄ enables an excellent surface charge modulating capacity, realizing a high work function regulation of ∼ 0.7 eV and over 15-fold current regulation (from 6 μA to 93 μA) via an electrical poling control. The controllable electrical poling leads to elevated work function difference between Al electrode and (DF-CBA)₂ CuCl₄ compared to traditional semiconductors and halide perovskites, which creates a stronger built-in electric field at the Schottky interface to enhance the electrical output. This TVNG device exhibits outstanding flexibility and long-term stability (> 20000 cycles) that can endure extreme mechanical deformations, and can also be used in a capsule-like magnetic suspension device capable of detecting vibration and weights of different objects as well as harvesting energy from human motions and water waves. This article is protected by copyright. All rights reserved.

Ultrafast, High-Strain, and Strong Uniaxial Hydrogel Actuators from Recyclable Nanofibril Networks

Polymer hydrogels mimic biological tissues and are suitable for future lifelike machines. However, their actuation is isotropic, so they must be crosslinked or placed in a turgor membrane to achieve high actuation pressures, severely impeding their performance. Here, it is shown that organizing cellulose nanofibrils (CNFs) in anisotropic hydrogel sheets leads to mechanical in-plane reinforcement that generates a uniaxial, out-of-plane strain with performance far surpassing polymer hydrogels. These fibrillar hydrogel actuators expand uniaxially by 250 times with an initial rate of 100-130% s^-1 , compared to <10 times and <1% s^-1 in directional strain rate for isotropic hydrogels, respectively. The blocking pressure reaches 0.9 MPa, similar to turgor actuators, while the time to reach 90% of the maximum pressure is 1-2 min, compared to 10 min to hours for polymer hydrogel actuators. Uniaxial actuators that lift objects 120 000 times their weight and soft grippers are showcased. In addition, the hydrogels can be recycled without a loss in performance. The uniaxial swelling allows adding channels through the gel for local solvent delivery, further increasing the actuation rate and cyclability. Thus, fibrillar networks can overcome the major drawbacks of hydrogel actuators and is a significant advancement towards hydrogel-based lifelike machines.

Melanin and Polypyrrole-Coated Nanocellulose Hydrogel Networks for Environmental Sensing and Energy Storage

Melanins are black-brown pigments of a specific class of poly indolequinones found in nature and in the human body. They are responsible for photoprotection, radical scavenging, and metal ion chelation. Recently, there has been significant interest in eumelanin as a functional material due to its macromolecular structure and the exploitation of the quinone-hydroquinone redox equilibrium. While eumelanin can be used in many promising applications, it is insoluble in most solvents, limiting its processing into homogeneous materials and coatings. A promising approach is to use a carrier system to stabilize eumelanin by incorporating cellulose nanofibrils (CNFs), a nanoscopic material that originates from plant biomass. In this work, a flexible network consisting of CNFs coupled with vapor-phase polymerized conductive polypyrrole (PPy) is utilized to form a functional eumelanin hydrogel composite (MelaGel) for environmental sensing and battery applications. Flexible sensors for detecting pH or metal ions made from MelaGel can detect both pH values in a range from 4 to 10 and metal ions like zinc(II), copper(II), and iron(III), paving the way for environmental and biomedical sensor applications. The reduced internal resistance in the MelaGel leads to improved charge storage ability compared to synthetic eumelanin composite electrodes. Other noteworthy advantages of the MelaGel are the amphiphilic nature of PPy and the additionally offered redox centers. Lastly, this material was tested in aqueous electrolyte zinc coin cells, where it was shown to have charge/discharge stability for over 1200 cycles, showcasing this MelaGel composite as a promising eumelanin-based composite hybrid sensor/energy storage material.

A supramolecular gel-elastomer system for soft iontronic adhesives

Electroadhesion provides a promising route to augment robotic functionalities with continuous, astrictive, and reversible adhesion force. However, the lack of suitable conductive/dielectric materials and processing capabilities have impeded the integration of electroadhesive modules into soft robots requiring both mechanical compliance and robustness. We present herein an iontronic adhesive based on a dynamically crosslinked gel-elastomer system, including an ionic organohydrogel as adhesive electrodes and a resilient polyurethane with high electrostatic energy density as dielectric layers. Through supramolecular design and synthesis, the dual-material system exhibits cohesive heterolayer bonding and autonomous self-healing from damages. Iontronic soft grippers that seamlessly integrate actuation, adhesive prehension, and exteroceptive sensation are devised via additive manufacturing. The grippers can capture soft and deformable items, bear high payload under reduced voltage input, and rapidly release foreign objects in contrast to electroadhesives. Our materials and iontronic mechanisms pave the way for future advancement in adhesive-enhanced multifunctional soft devices.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Multilayer Dielectric Elastomer with Reconfigurable Electrodes for Artificial Muscle

High-performance multilayer dielectric elastomer actuators (DEAs) are well-positioned to overcome the insufficient output force and energy density as artificial muscles. However, due to the fabrication process, the multilayer DEAs with nonmodifiable structures often suffer from the limitation of short lifespans and scalable preparation. Herein, reusable multilayer DEAs with the detachable and reconfigurable structure are fabricated. This is achieved by realizing scalable compliant electrodes using the continuous spatial confining forced network assembly (CSNA) method and combining the vacuum lamination (VL) approach to have good attachability and detachability with the VHB dielectric elastomer. The flexible roller-based CSNA method is used to prepare the large area compliant electrodes composed of α, ω-dihydroxy polydimethylsiloxane and electrically conductive nanoparticles. The fabricated electrodes can continuously work over 10 000 cycles at 40% strained stretching and maintain smooth surfaces to construct multilayer DEAs. Moreover, owing to the detachable configuration of the DEAs, the electrodes can also be recovered and reused for building new actuators. The lower limb assistive device is demonstrated by detachable multilayer spring roll DEAs, achieving approximately 3.1 degrees of flexion and extension movement of knee models under a voltage of 7 kV. The detachable and reconfigurable multilayer DEAs shed new light on the applications of wearable assistive devices.

Reliability of printed stretchable electronics based on nano/micro materials for practical applications

Recent decades have witnessed the booming development of stretchable electronics based on nano/micro composite inks. Printing is a scalable, low-cost, and high-efficiency fabrication tool to realize stretchable electronics through additive processes. However, compared with conventional flexible electronics, stretchable electronics need to experience more severe mechanical deformation which may cause destructive damage. Most of the reported works in this field mainly focus on how to achieve a high stretchability of nano/micro composite conductors or single working modules/devices, with limited attention given to the reliability for practical applications. In this minireview, we summarized the failure modes when printing stretchable electronics using nano/micro composite ink, including dysfunction of the stretchable interconnects, the stress-concentrated rigid-soft interfaces for hybrid electronics, the vulnerable vias upon stretching, thermal accumulation, and environmental instability of stretchable materials. Strategies for tackling these challenges to realize reliable performances are proposed and discussed. Our review provides an overview on the importance of reliable, printable, and stretchable electronics, which are the key enablers in propelling stretchable electronics from fancy demos to practical applications.

Rapidly Photocurable Solid-State Poly(ionic liquid) Ionogels For Thermally Robust and Flexible Electrochromic Devices

Formation of ionogels through in situ polymerization can effectively improve electrolyte processability; however, the curing process has been slow and oxygen-sensitive. Considering the low oxygen solubility of poly(ionic liquid)s (PILs), in situ polymerized ionogels are designed to realize excellent electrolytes. Herein, two in situ polymerized ionogels (PIL A & PIL B) are formulated, and they can be rapidly photocured within a minute. The ionogels are highly transparent, stretchable, and exhibit excellent physicochemical stability, including thermal, electrochemical, and air stability, allowing them to perform in various conditions. Benefitting from these properties, two high-performance electrochromic devices (ECDs) are assembled, with iron-centered coordination polymer (FeCP) and tungsten oxide (P-WO₃ ) electrochromic materials, achieving high color contrast (45.2% and 56.4%), fast response time (1.5/1.9 and 1.7/6.4 s), and excellent cycling endurance (>90% retention over 3000 cycles). Attributed to the thermal robustness of the ionogels, the ECDs can also be operated over a wide temperature range (-20 to 100 °C). With the use of deformable substrates (e.g., ultrathin ITO glass), curved electrochromic eye protector and flexible electrochromic displays are realized, highlighting their potential use in futuristic wearables.

Photothermal modulated dielectric elastomer actuator for resilient soft robots

Soft robots need to be resilient to extend their operation under unpredictable environments. While utilizing elastomers that are tough and healable is promising to achieve this, mechanical enhancements often lead to higher stiffness that deteriorates actuation strains. This work introduces liquid metal nanoparticles into carboxyl polyurethane elastomer to sensitize a dielectric elastomer actuator (DEA) with responsiveness to electric fields and NIR light. The nanocomposite can be healed under NIR illumination to retain high toughness (55 MJ m−3) and can be recycled at lower temperatures and shorter durations due to nanoparticle-elastomer interactions that minimize energy barriers. During co-stimulation, photothermal effects modulate the elastomer moduli to lower driving electric fields of DEAs. Bilayer configurations display synergistic actuation under co-stimulation to improve energy densities, and enable a DEA crawler to achieve longer strides. This work paves the way for a generation of soft robots that achieves both resilience and high actuation performance.

Al2O3/HfO2 Nanolaminate Dielectric Boosting IGZO-Based Flexible Thin-Film Transistors

HIGHLIGHTS

A stable laminated Al₂O₃/HfO₂ insulator is developed by atomic layer deposition at a relatively lower temperature of 150 °C. The flexible thin-film transistors (TFTs) with bottom-gate top-contacted configuration are fabricated on a flexible substrate with the Al₂O₃/HfO₂ insulator. The flexible TFTs present the carrier mobilities of 9.7 cm² V⁻¹ s⁻¹, ON/OFF ratio of ~ 1.3 × 10⁶, subthreshold voltage of 0.1 V, saturated current up to 0.83 mA, and subthreshold swing of 0.256 V dec⁻¹.

ABSTRACT

Flexible thin-film transistors (TFTs) have attracted wide interest in the development of flexible and wearable displays or sensors. However, the conventional high processing temperatures hinder the preparation of stable and reliable dielectric materials on flexible substrates. Here, we develop a stable laminated Al₂O₃/HfO₂ insulator by atomic layer deposition at a relatively lower temperature of 150 °C. A sputtered amorphous indium-gallium-zinc oxide (IGZO) with the stoichiometry of In_0.37Ga_0.20Zn_0.18O_0.25 is used as the active channel material. The flexible TFTs with bottom-gate top-contacted configuration are further fabricated on a flexible polyimide substrate with the Al₂O₃/HfO₂ nanolaminates. Benefited from the unique structural and compositional configuration in the nanolaminates consisting of amorphous Al₂O₃, crystallized HfO₂, and the aluminate Al–Hf–O phase, the as-prepared TFTs present the carrier mobilities of 9.7 cm² V⁻¹ s⁻¹, ON/OFF ratio of ~ 1.3 × 10⁶, subthreshold voltage of 0.1 V, saturated current up to 0.83 mA, and subthreshold swing of 0.256 V dec⁻¹, signifying a high-performance flexible TFT, which simultaneously able to withstand the bending radius of 40 mm. The TFTs with nanolaminate insulator possess satisfactory humidity stability and hysteresis behavior in a relative humidity of 60–70%, a temperature of 25–30 °C environment. The yield of IGZO-based TFTs with the nanolaminate insulator reaches 95%. [Image: see text]

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40820-022-00929-y.

Bond engineering of molecular ferroelectrics renders soft and high-performance piezoelectric energy harvesting materials

Piezoelectric materials convert mechanical stress to electrical energy and thus are widely used in energy harvesting and wearable devices. However, in the piezoelectric family, there are two pairs of properties that improving one of them will generally compromises the other, which limits their applications. The first pair is piezoelectric strain and voltage constant, and the second is piezoelectric performance and mechanical softness. Here, we report a molecular bond weakening strategy to mitigate these issues in organic-inorganic hybrid piezoelectrics. By introduction of large-size halide elements, the metal-halide bonds can be effectively weakened, leading to a softening effect on bond strength and reduction in polarization switching barrier. The obtained solid solution C₆H₅N(CH₃)₃CdBr₂Cl_0.75I_0.25 exhibits excellent piezoelectric constants (d₃₃ = 367 pm/V, g₃₃ = 3595 × 10⁻³ Vm/N), energy harvesting property (power density is 11 W/m²), and superior mechanical softness (0.8 GPa), promising this hybrid as high-performance soft piezoelectrics.

Improving piezoelectric strain and voltage constant generally compromises piezoelectric performance and mechanical softness. Here, the authors report a bond weakening strategy for organic-inorganic hybrid piezoelectrics and mitigated these issues.

Performance optimization strategies of halide perovskite-based mechanical energy harvesters

Halide perovskites, possessing unique electronic and photovoltaic properties, have been intensively investigated over the past decade. The excellent polarization, piezoelectricity, dielectricity and photoelectricity of halide perovskites provide new opportunities for the applications of mechanical energy harvesting. Although various studies have been conducted to develop halide perovskite-based triboelectric and piezoelectric nanogenerators, strategies for their electrical performance optimization are rarely mentioned. In this review, we systematically introduce the recent research progress of halide perovskite-based mechanical energy harvesters and summarize the different optimization strategies for improving both the piezoelectric and triboelectric output of the devices, bringing some inspiration to guide future material and structure design for halide perovskite-based energy devices. A summary of the current challenges and future perspectives is also presented, offering some possible directions for development in this emerging field.

Molecular-Level Methylcellulose/MXene Hybrids with Greatly Enhanced Electrochemical Actuation

Ti₃ C₂ T_x MXene film is promising for electrochemical actuators due to its high electrical conductivity and volumetric capacitance. However, its actuation performance is limited by the slow ion diffusion through the film and poor mechanical property in aqueous electrolytes. Here, molecular-level methylcellulose (MC)/MXene hybrid films are assembled with obviously enlarged layer distance, improved wet strength, and ambient stability. The hybrid films show significantly higher in-plane actuation strain in a liquid electrolyte. Based on direct strain measurements, in situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) analyses, the actuation enhancement can be ascribed to the enlarged layer distance allowing more water and ions to be intercalated/de-intercalated and MC-induced sliding of MXene sheets. The assembled soft actuator has a high Young's modulus of 1.93 GPa and can be operated in air, generating a peak-to-peak strain difference up to 0.541% under a triangular wave voltage of ±1 V and a blocking force of 4.7 times its own weight.

Natural Polymer in Soft Electronics: Opportunities, Challenges, and Future Prospects

Pollution caused by nondegradable plastics has been a serious threat to environmental sustainability. Natural polymers, which can degrade in nature, provide opportunities to replace petroleum-based polymers, meanwhile driving technological advances and sustainable practices. In the research field of soft electronics, regenerated natural polymers are promising building blocks for passive dielectric substrates, active dielectric layers, and matrices in soft conductors. Here, the natural-polymer polymorphs and their compatibilization with a variety of inorganic/organic conductors through interfacial bonding/intermixing and surface functionalization for applications in various device modalities are delineated. Challenges that impede the broad utilization of natural polymers in soft electronics, including limited durability, compromises between conductivity and deformability, and limited exploration in controllable degradation, etc. are explicitly inspected, while the potential solutions along with future prospects are also proposed. Finally, integrative considerations on material properties, device functionalities, and environmental impact are addressed to warrant natural polymers as credible alternatives to synthetic ones, and provide viable options for sustainable soft electronics.

Heat-Insulating Black Electrochromic Device Enabled by Reversible Nickel-Copper Electrodeposition

An electrochromic device (ECD), which can switch between black and transmissive states under electrical bias, is a promising candidate for smart windows due to its color neutrality and excellent durability. Most of the black ECDs are achieved through a reversible electrodeposition and dissolution mechanism; however, they typically suffer from relatively poor cycling stability and a slow coloration/bleaching time. Herein, we present a heat-insulating black ECD with a gel electrolyte that operates via reversible Ni-Cu electrodeposition and dissolution. With the adoption of a Cu alloying strategy and a compatible gel electrolyte, this two-electrode ECD (5.0 cm × 2.5 cm) can achieve a cycling stability of 1500 cycles with transmittance modulation up to 55.2% in short coloration (6.2 s) and bleaching times (13.2 s) at a wavelength of 550 nm. Additionally, the ECD can be switched from the transparent state (visible light transmittance: 0.566) to the opaque state (visible light transmittance: 0.003) within 1 min, reaching transmittance less than 5% across the visible-near-infrared spectrum (400-2000 nm) to efficiently block solar heat. Besides, in the voltage-off state, the black Ni-Cu alloy film can be sustained for more than 60 min (at room temperature, λ = 550 nm). Under infrared irradiation (170 W/m²) for 30 min, the black ECD blocks up to 35.0% of infrared radiation, which not only effectively prevents the heat transmission for energy management but also finds potential applications for promoting indoor human health and indoor farming.

Stretchable, Breathable, and Stable Lead-Free Perovskite/Polymer Nanofiber Composite for Hybrid Triboelectric and Piezoelectric Energy Harvesting

Halide-perovskite-based mechanical energy harvesters display excellent electrical output due to their unique ferroelectricity and dielectricity. However, their high toxicity and moisture sensitivity impede their practical applications. Herein, a stretchable, breathable, and stable nanofiber composite (LPPS-NFC) is fabricated through electrospinning of lead-free perovskite/poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and styrene-ethylene-butylene-styrene (SEBS). The Cs₃ Bi₂ Br₉ perovskites serve as efficient electron acceptors and local nucleating agents for the crystallization of polymer chains, thereby enhancing the electron-trapping capacity and polar crystalline phase in LPPS-NFC. The excellent energy level matching between Cs₃ Bi₂ Br₉ and PVDF-HFP boosts the electron transfer efficiency and reduces the charge loss, thereby promoting the electron-trapping process. Consequently, this LPPS-NFC-based energy harvester displays an excellent electrical output (400 V, 1.63 µA cm^-2 , and 2.34 W m^-2 ), setting a record of the output voltage among halide-perovskite-based nanogenerators. The LPPS-NFC also exhibits excellent stretchability, waterproofness, and breathability, enabling the fabrication of robust wearable devices that convert mechanical energy from different biomechanical motions into electrical power to drive common electronic devices. The LPPS-NFC-based energy harvesters also endure extreme mechanical deformations (washing, folding, and crumpling) without performance degradation, and maintain stable electrical output up to 5 months, demonstrating their promising potential for use as smart textiles and wearable power sources.

Crystallographic Anisotropy Dependence of Interfacial Sliding Phenomenon in a Cu(16)/Nb(16) ARB (Accumulated Rolling Bonding) Nanolaminate

Nanolaminates are extensively studied due to their unique properties, such as impact resistance, high fracture toughness, high strength, and resistance to radiation damage. Varieties of nanolaminates are being fabricated to achieve high strength and fracture toughness. In this study, one such nanolaminate fabricated through accumulative roll bonding (Cu(16)/Nb(16) ARB nanolaminate, where 16 nm is the layer thickness) was used as a test material. Cu(16)/Nb(16) ARB nanolaminate exhibits crystallographic anisotropy due to the existence of distinct interfaces along the rolling direction (RD) and the transverse direction (TD). Nanoindentation was executed using a Berkovich tip, with the main axis oriented either along TD or RD of the Cu(16)/Nb(16) ARB nanolaminate. Subsequently, height profiles were obtained along the main axis of the Berkovich indent for both TD and RD using scanning probe microscopy (SPM), which was later used to estimate the pile-up along the RD and TD. The TD exhibited more pile-up than the RD due to the anisotropy of the Cu(16)/Nb(16) ARB interface and the material plasticity along the TD and RD. An axisymmetric 2D finite element analysis (FEA) was also performed to compare/validate nanoindentation data, such as load vs. displacement curves and pile-up. The FEA simulated load vs. displacement curves matched relatively well with the experimentally generated load–displacement curves, while qualitative agreement was found between the simulated pile-up data and the experimentally obtained pile-up data. The authors believe that pile-up characterization during indentation is of great importance to documenting anisotropy in nanolaminates.

Wide-Spectrum Modulated Electrochromic Smart Windows Based on MnO2/PB Films

Inorganic materials have been extensively studied for visible electrochromism in the past few decades. However, the single inorganic electrochromic (EC) material commonly exhibits a single color change, leading to a narrow spectrum of modulation, which offsets or limits the maximally energy-saving ability. Here, we present a wide-spectrum modulated EC device designed by combining the complementary EC nanocomposite of manganese dioxide (MnO₂) and Prussian blue (PB) for enhanced energy savings. Porous MnO₂ nanostructures serve as host frameworks for the templated growth of PB, resulting in MnO₂/PB nanocomposites. The complementary optical modulation ranges of MnO₂ and PB enable a widen-spectrum modulation across the solar region with the development of the MnO₂/PB nanocomposite. The colored MnO₂/PB device exhibited an optical modulation of 32.1% in the wide solar spectrum range of 320-1100 nm and blocked 72.0% of the solar irradiance. Furthermore, fast switching responses (2.7 s for coloration and 2.1 s for bleaching) and a high coloration efficiency (83.1 cm²·C^-1) of the MnO₂/PB EC device are also achieved. The high EC performance of the MnO₂/PB nanocomposite device provides a new strategy for the design of high-performance energy-saving EC smart windows.

Magnetically Directed Co-nanoinitiators for Cross-Linking Adhesives and Enhancing Mechanical Properties

Magnetically directed localized polymerization is of immense interest for its extensive impacts and applications in numerous fields. The use of means untethered from an external magnetic field to localize initiation of polymerization to develop a curing system is a novel concept, with a sustainable, efficient, and eco-friendly approach and a wide range of potential in both science and engineering. However, the conventional means for the initiation of polymerization cannot define the desirable location of polymerization, which is often exacerbated by the poor temporal control in the curing system. Herein, the copper-immobilized dendrimer-based magnetic iron oxide silica (MNPs-G2@Cu²⁺) co-nanoinitiators are rationally designed as initiators for redox radical polymerization. The nanoinitiators are magnetically responsive and therefore enable localized polymerization using an external magnetic field. In this work, anaerobic polymerization of an adhesive composed of triethylene glycol dimethacrylate, tert-butyl peroxybenzoate, and MNPs-G2@Cu²⁺ as the magnetic co-nanoinitiators has been investigated. The use of a magnet locates and promotes redox free radical polymerization through the synergistic functions between peroxide and MNPs-G2@Cu²⁺ co-nanoinitiators. The mechanical properties of the resulting polymer are considerably reinforced because the MNPs-G2@Cu²⁺ co-nanoinitiators concurrently play another crucial role as nanofillers. This strategy provides a novel approach for magnetically tunable localized polymerization, which allows new opportunities to govern the formulation of advanced adhesives through polymerization under hazard-free conditions for various promising applications.

Continuous Tuning of the Fermi Level in Disorder-Engineered Amorphous Films of Li-Doped ZnO for Thermoelectric Applications

Amorphous metal-oxide semiconductors can be readily prepared by a solution process at low temperatures, and their energy band structures and carrier concentrations can be controlled based on the oxide composition or the addition of dopants in the design of thermoelectric (TE) materials. However, research on the correlation between the charge transport and TE performance of amorphous metal-oxide semiconductors is still in its infancy. Herein, we present the energy-dependent TE performance characteristics of Li-doped ZnO thin films with different doping levels and charge carrier concentrations. Thin films were prepared by the solution process, and the Li doping level was controlled by the Li precursor concentration added to a Zn precursor solution. Subsequently, a field-effect-modulated Seebeck coefficient measurement device was built to study the energy-dependent TE performance. Notably, the higher ratio of interstitial Li (Li_inter) and oxygen vacancies (O_va) in the Li-ZnO device indicates an improved n-type TE performance. To investigate more thoroughly the charge transport phenomena, the localized density of states (DOS) was derived from the temperature-dependent transfer curve; the higher ratio of interstitial Li (Li_inter) and oxygen vacancy (O_va) induces a reduction in the localized DOS and lowers the degree of disorder in their DOS. The determined energy-dependent TE characteristics can be used as guidance for the design of efficient TE devices with amorphous metal-oxide semiconductors.

Electropolymerized 1D Growth Coordination Polymer for Hybrid Electrochromic Aqueous Zinc Battery

Organic materials are always viewed as promising electrochromic (EC) materials due to their synthetic versatility, color tunability, ready processability, and derivability from sustainable feedstocks. Most organic materials, however, are prone to undesirable redox side reactions in the presence of oxygen and water. As such, redox-active organic layers are often used in tandem with organic electrolytes to preserve their electrochemical stability. With the growing interest in electronics that are environmentally sustainable and biologically safe, developing aqueous-compatible organic materials is gaining growing interest. Herein, a rationally designed iron terpyridyl coordination polymer (CP) is prepared by controlled electropolymerization for realization of aqueous compatible EC and energy storage applications. Detailed analysis is established, showing that the CP grows in a 1D fashion and exhibits a predominant capacitive behavior which is reflected from its rapid charge-transfer kinetics. Taking this as an advantage, an integrated hybrid electrochromic zinc battery device is demonstrated with high color contrast, fast response time, and good endurance.

Printable elastomeric electrodes with sweat-enhanced conductivity for wearables

We rationally synthesized the thermoplastic and hydrophilic poly(urethane-acrylate) (HPUA) binder for a type of printable and stretchable Ag flakes-HPUA (Ag-HPUA) electrodes in which the conductivity can be enhanced by human sweat. In the presence of human sweat, the synergistic effect of Cl- and lactic acid enables the partial removal of insulating surfactant on silver flakes and facilitates sintering of the exposed silver flakes, thus the resistance of Ag-HPUA electrodes can be notably reduced in both relaxed and stretched state. The on-body data show that the resistance of one electrode has been decreased from 3.02 to 0.62 ohm during the subject's 27-min sweating activity. A stretchable textile sweat-activated battery using Ag-HPUA electrodes as current collectors and human sweat as the electrolyte was constructed for wearable electronics. The enhanced conductivity of the wearable wiring electrode from the reaction with sweat would provide meritorious insight into the design of wearable devices.

Synergistic Effect of PVDF-Coated PCL-TCP Scaffolds and Pulsed Electromagnetic Field on Osteogenesis

Bone exhibits piezoelectric properties. Thus, electrical stimulations such as pulsed electromagnetic fields (PEMFs) and stimuli-responsive piezoelectric properties of scaffolds have been investigated separately to evaluate their efficacy in supporting osteogenesis. However, current understanding of cells responding under the combined influence of PEMF and piezoelectric properties in scaffolds is still lacking. Therefore, in this study, we fabricated piezoelectric scaffolds by functionalization of polycaprolactone-tricalcium phosphate (PCL-TCP) films with a polyvinylidene fluoride (PVDF) coating that is self-polarized by a modified breath-figure technique. The osteoinductive properties of these PVDF-coated PCL-TCP films on MC3T3-E1 cells were studied under the stimulation of PEMF. Piezoelectric and ferroelectric characterization demonstrated that scaffolds with piezoelectric coefficient d33 = -1.2 pC/N were obtained at a powder dissolution temperature of 100 °C and coating relative humidity (RH) of 56%. DNA quantification showed that cell proliferation was significantly enhanced by PEMF as low as 0.6 mT and 50 Hz. Hydroxyapatite staining showed that cell mineralization was significantly enhanced by incorporation of PVDF coating. Gene expression study showed that the combination of PEMF and PVDF coating promoted late osteogenic gene expression marker most significantly. Collectively, our results suggest that the synergistic effects of PEMF and piezoelectric scaffolds on osteogenesis provide a promising alternative strategy for electrically augmented osteoinduction. The piezoelectric response of PVDF by PEMF, which could provide mechanical strain, is particularly interesting as it could deliver local mechanical stimulation to osteogenic cells using PEMF.

Locomotion of Miniature Soft Robots

Miniature soft robots are mobile devices, which are made of smart materials that can be actuated by external stimuli to realize their desired functionalities. Here, the key advancements and challenges of the locomotion producible by miniature soft robots in micro- to centimeter length scales are highlighted. It is highly desirable to endow these small machines with dexterous locomotive gaits as it enables them to easily access highly confined and enclosed spaces via a noninvasive manner. If miniature soft robots are able to capitalize this unique ability, they will have the potential to transform a vast range of applications, including but not limited to, minimally invasive medical treatments, lab-on-chip applications, and search-and-rescue missions. The gaits of miniature soft robots are categorized into terrestrial, aquatic, and aerial locomotion. Except for the centimeter-scale robots that can perform aerial locomotion, the discussions in this report are centered around soft robots that are in the micro- to millimeter length scales. Under each category of locomotion, prospective methods and strategies that can improve their gait performances are also discussed. This report provides critical analyses and discussions that can inspire future strategies to make miniature soft robots significantly more agile.

Functional Fibers and Fabrics for Soft Robotics, Wearables, and Human-Robot Interface

Soft robotics inspired by the movement of living organisms, with excellent adaptability and accuracy for accomplishing tasks, are highly desirable for efficient operations and safe interactions with human. With the emerging wearable electronics, higher tactility and skin affinity are pursued for safe and user-friendly human-robot interactions. Fabrics interlocked by fibers perform traditional static functions such as warming, protection, and fashion. Recently, dynamic fibers and fabrics are favorable to deliver active stimulus responses such as sensing and actuating abilities for soft-robots and wearables. First, the responsive mechanisms of fiber/fabric actuators and their performances under various external stimuli are reviewed. Fiber/yarn-based artificial muscles for soft-robots manipulation and assistance in human motion are discussed, as well as smart clothes for improving human perception. Second, the geometric designs, fabrications, mechanisms, and functions of fibers/fabrics for sensing and energy harvesting from the human body and environments are summarized. Effective integration between the electronic components with garments, human skin, and living organisms is illustrated, presenting multifunctional platforms with self-powered potential for human-robot interactions and biomedicine. Lastly, the relationships between robotic/wearable fibers/fabrics and the external stimuli, together with the challenges and possible routes for revolutionizing the robotic fibers/fabrics and wearables in this new era are proposed.

Ferroelastic-switching-driven large shear strain and piezoelectricity in a hybrid ferroelectric

Materials that can produce large controllable strains are widely used in shape memory devices, actuators and sensors^1,2, and great efforts have been made to improve the strain output^3-6. Among them, ferroelastic transitions underpin giant reversible strains in electrically driven ferroelectrics or piezoelectrics and thermally or magnetically driven shape memory alloys^7,8. However, large-strain ferroelastic switching in conventional ferroelectrics is very challenging, while magnetic and thermal controls are not desirable for practical applications. Here we demonstrate a large shear strain of up to 21.5% in a hybrid ferroelectric, C₆H₅N(CH₃)₃CdCl₃, which is two orders of magnitude greater than that in conventional ferroelectric polymers and oxides. It is achieved by inorganic bond switching and facilitated by structural confinement of the large organic moieties, which prevents undesired 180° polarization switching. Furthermore, Br substitution can soften the bonds, allowing a sizable shear piezoelectric coefficient (d₃₅ ≈ 4,830 pm V^-1) at the Br-rich end of the solid solution, C₆H₅N(CH₃)₃CdBr_3xCl_3(1-x). The electromechanical properties of these compounds suggest their potential in lightweight and high-energy-density devices, and the strategy described here could inspire the development of next-generation piezoelectrics and electroactive materials based on hybrid ferroelectrics.

Recent Progress in Artificial Muscles for Interactive Soft Robotics

Artificial muscles are the core components of the smart and interactive soft robotic systems, providing the capabilities in shape morphing, manipulation, and mobility. Intense research efforts in the development of artificial muscles are based on the dielectric elastomer actuators, pneumatic actuators, electrochemical actuators, soft magnetic actuators, and stimulus responsive polymers. Recent progress has presented artificial muscles with impressive specific power output exceeding that of the natural muscles, dexterous shape morphing behavior that can be programmed and reconfigured, and exceptional high maneuverability to traverse surfaces with obstacles and different textures. Here, a succinct and critical summary is provided on the materials and strategies that have contributed to the important advancement of the artificial muscles in recent research. On that basis, the exciting opportunities are discussed in the integration of soft electronic devices with artificial muscles to enable smart and interactive soft robotic systems.

Breathable Nanogenerators for an On-Plant Self-Powered Sustainable Agriculture System

Building an intelligent interface between plants and the environment is of paramount importance for real-time monitoring of the health status of plants, especially promising for high agricultural yield. Although the advancement of various sensors allows automated monitoring, developing a sustainable power supply for these electronic devices remains a formidable challenge. Herein, a waterproof and breathable triboelectric nanogenerator (WB-TENG) is designed based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers embedded with fluorinated carbon nanotubes (F-CNT) microspheres, which was realized by simultaneous electrospinning and electrospraying, respectively. Using carbon nanotubes (CNT) as the electrode, the WB-TENG shows micro-to-nano hierarchical porous structures and high electrostatic adhesion, exhibiting a high output power density of 330.6 μW cm^-2, breathability, and hydrophobicity. Besides, the WB-TENG can be conformally self-attached to plant leaves without sacrificing the intrinsic physiological activities of plants, capable of harvesting typical environmental energy from wind and raindrops. Results demonstrate that the WB-TENG can serve as a sustainable power supply for a wireless plant sensor, enabling real-time monitoring of the health status of plants. This work realizes the concept of constructing a plant compatible TENG with environment adaptivity and energy scavenging ability, showing great potential in building a self-powered agriculture system.

Towards Control of the Size, Composition and Surface Area of NiO Nanostructures by Sn Doping

Achieving nanostructures with high surface area is one of the most challenging tasks as this metric usually plays a key role in technological applications, such as energy storage, gas sensing or photocatalysis, fields in which NiO is gaining increasing attention recently. Furthermore, the advent of modern NiO-based devices can take advantage of a deeper knowledge of the doping process in NiO, and the fabrication of p-n heterojunctions. By controlling experimental conditions such as dopant concentration, reaction time, temperature or pH, NiO morphology and doping mechanisms can be modulated. In this work, undoped and Sn doped nanoparticles and NiO/SnO2 nanostructures with high surface areas were obtained as a result of Sn incorporation. We demonstrate that Sn incorporation leads to the formation of nanosticks morphology, not previously observed for undoped NiO, promoting p-n heterostructures. Consequently, a surface area value around 340 m2/g was obtained for NiO nanoparticles with 4.7 at.% of Sn, which is nearly nine times higher than that of undoped NiO. The presence of Sn with different oxidation states and variable Ni3+/Ni2+ ratio as a function of the Sn content were also verified by XPS, suggesting a combination of two charge compensation mechanisms (electronic and ionic) for the substitution of Ni2+ by Sn4+. These results make Sn doped NiO nanostructures a potential candidate for a high number of technological applications, in which implementations can be achieved in the form of NiO-SnO2 p-n heterostructures.

Surface modification of liquid metal as an effective approach for deformable electronics and energy devices

The fields of flexible or stretchable electronics and energy devices, reconfigurable and compliant soft robotics, wearable e-textiles or health-care devices have paid significant attention to the need of deformable conductive electrodes due to its critical role in device performances. Gallium-based liquid metals, such as the eutectic gallium-indium (EGaIn) being an electrically conductive liquid phase at room temperature, have attracted immense interests as a promising candidate for deformable conductor. However, in the case of bulk liquid metal, there are several limitations such as the need of encapsulation, dispersion in a polymer matrix, or accurate patterning. For these reasons, the preparation of liquid metal particles in harnessing the properties in a non-bulk form and surface modification is crucial for the success of incorporating liquid metal into functional devices. Herein, we discuss the current progress in chemical surface modification and interfacial manipulations of liquid metal particles. The physical and chemical properties of the surface modification-assisted liquid metal polymer composite are also reviewed. Lastly, the applications of the surface-modified liquid metal particles such as flexible electrode, soft robotics, energy storage or harvester, thermal conductor, dielectric sensor, and bioelectronics are discussed, and the corresponding perspectives of deformable electronics and energy devices are provided. In particular, we focus on the functionalization method or requirement of liquid metal particles in each application. The challenging issues and outlook on the applications of surface-modified liquid metal particles are also discussed.

One-Dimensional π-d Conjugated Coordination Polymer for Electrochromic Energy Storage Device with Exceptionally High Performance

The rational design of previously unidentified materials that could realize excellent electrochemical-controlled optical and charge storage properties simultaneously, are especially desirable and useful for fabricating smart multifunctional devices. Here, a facile synthesis of a 1D π-d conjugated coordination polymer (Ni-BTA) is reported, consisting of metal (Ni)-containing nodes and organic linkers (1,2,4,5-benzenetetramine), which could be easily grown on various substrates via a scalable chemical bath deposition method. The resulting Ni-BTA film exhibits superior performances for both electrochromic and energy storage functions, such as large optical modulation (61.3%), high coloration efficiency (223.6 cm2 C-1), and high gravimetric capacity (168.1 mAh g-1). In particular, the Ni-BTA film can maintain its electrochemical recharge-ability and electrochromic properties even after 10 000 electrochemical cycles demonstrating excellent durability. Moreover, a smart energy storage indicator is demonstrated in which the energy storage states can be visually recognized in real time. The excellent electrochromic and charge storage performances of Ni-BTA films present a great promise for Ni-BTA nanowires to be used as practical electrode materials in various applications such as electrochromic devices, energy storage cells, and multifunctional smart windows.

A Quasi-Solid-State Tristate Reversible Electrochemical Mirror Device with Enhanced Stability

Reversible electrochemical mirror (REM) electrochromic devices with electrochemical tunability in multiple optical states are exciting alternatives to conventional electrochromic smart windows. Electrochromic devices are studied extensively, yet widespread adoptions have not been achieved due to problems associated with durability, switching speed, limited options on optical states, and cost. In this study, a REM electrochromic device based on CuSn alloy is developed, which offers highly reversible switching between transparent, greyish-blue, and mirror states via reversible electrodeposition and dissolution. The alloying element, Sn acts as an electrochemical mediator, which facilitates the electrodeposition and dissolution of Cu. The CuSn-based REM device shows superior cycling stability for 2400 cycles (transmittance mode) and 1000 cycles (reflectance mode). The electrodeposited CuSn alloy film is resistant to surface oxidation in ambient air, with a 2.9% difference in reflectance at 2000 nm after 3 days. In addition, the alloy film exhibits excellent NIR reflectance property with thermal modulation of 18.5 °C at a high temperature of 180 °C. The REM device with zero power consumption maintains its mirror state for at least 100 min, making it a promising candidate for energy-efficient applications.

Self-healable sticky porous elastomer for gas-solid interacted power generation

A previously unknown gas-solid interacted power generation is developed using triboelectric effect. We designed an adhesive, gas-tight, and self-healing supramolecular polysiloxane-dimethylglyoxime-based polyurethane (PDPU) porous elastomer based on segmented oxime-carbamate-urea. It is an intrinsically triboelectric negative material with trapped air within closed voids, exhibiting ultrahigh static surface potential and excellent compressibility. This porous PDPU generates electricity from interactions between the trapped air and the elastomeric matrix under periodical compression. The positively charged trapped air (or other gas) dominates the tribo-electrification with PDPU, inducing electron transfer from gas to the solid polymer for electricity generation. The self-healable elastomer renders gas-solid interacted triboelectric nanogenerator, GS-TENG, with high stretchability (~1200%). The inherently adhesive surface enables adherance to other substrates, allowing mechanical energy harvesting from deformations such as bending, twisting, and stretching. GS-TENG promises a freestanding wearable functional tactile skin for self-powered sensing of touch pressure, human motions, and Parkinsonian gait.

Photothermal actuated origamis based on graphene oxide-cellulose programmable bilayers

The design and construction of 3D architectures enabled by stimuli-responsive soft materials can yield novel functionalities for next generation soft-bodied actuating devices. Apart from additive manufacturing processes, origami inspired technology offers an alternative approach to fabricate 3D actuators from planar materials. Here we report a class of near-infrared (NIR) responsive 3D active origamis that deploy, actuate and transform between multistable structural equilibria. By exploiting the nonlinear coefficient of thermal expansion (CTE) of graphene oxide (GO), graphene oxide/ethylene cellulose (GO/EC) bilayers are readily fabricated to deliver precise origami structure control, and rapid low-temperature-triggered photothermal actuation. Complexity in 3D shapes is produced through heterogeneously patterning GO domains on 2D EC thin films, which allows us to customize 3D architectures that adapt to various robotic functions. The strategy also enables the construction of material systems possessing naturally inaccessible properties, such as remotely controlled mechanical metamaterials with auxetic behavior and bionic flowers with a rapid blooming rate. Harnessing deformability with multiple degrees of freedom (DOF) upon light irradiation, this work leads to breakthroughs in the design and implementation of shape-morphing functions with soft origamis.

Water-Processable, Stretchable, Self-Healable, Thermally Stable, and Transparent Ionic Conductors for Actuators and Sensors

For emerging biocompatible, wearable, and stretchable epidermal electronic devices, it is essential to realize novel stretchable conductors with the attributes of transparency, low-cost and nontoxic components, green-solvent processbility, self-healing, and thermal stabililty. Although conducting materials-rubber composites, ionic hydrogels, organogels have been developed, no stretchable material system that meets all the outlined requirements has been reported. Here, a series of P(SPMA-r-MMA) polymers with different ratios of ionic side chains is designed and synthesized, and it is demonstrated that the resulting stretchable ionic conductors with glycerol are transparent, water processable, self-healable, and thermally stable due to the chemically linked ionic side chain, satisfying all of the aforementioned requirements. Among the series of polymer gels, the P(SPMA_0.75 -r-MMA_0.25 ) gel shows optimum conductivity (6.7 × 10^-4 S cm^-1 ), stretchability (2636% of break at elongation), and self-healing (98.3% in 3 h) properties. Accordingly, the transparent and self-healable P(SPMA_0.75 -r-MMA_0.25 ) gels are used to realize thermally robust actuators up to 100 °C and deformable and self-healable thermal sensors.