Hierarchically Interconnected Piezoceramic Textile with a Balanced Performance in Piezoelectricity,Flexibility, Toughness,and Air Permeability

Softening of piezoelectric materials facilitates the development of flexible wearables and energy harvesting devices. However, as one of the most competitive candidates, piezoelectric ceramic-polymer composites inevitably exhibit reduced power-generation capability and weak mechanical strength due to the mismatch of strength and permittivity between the two phases inside. Herein a flexible, air-permeable, and high-performance piezoceramic textile composite with a mechanically reinforced hierarchical porous structure is introduced. Based on a template-assisted sol-gel method, a three-order hierarchical ceramic textile is constructed by intertwining submillimeter-scale multi-ply ceramic fibers that are further formed by twisting micrometer-scale one-ply ceramic fibrils. Theoretical analysis indicates that large mechanical stress can be easily induced in the multi-order hierarchical structure, which greatly benefits the electrical output. Fabricated samples generate an open-circuit voltage of 128 V, a short-circuit current of 120 µA, and an instantaneous power density of 0.75 mW cm⁻², much higher than the previously reported works. The developed multi-order and 3D-interconnected piezoceramic textile shows satisfactory piezoelectricity (d₃₃ of 190 pm V⁻¹), air permeability (45.1 mm s⁻¹), flexibility (Young's modulus of 0.35 GPa), and toughness (0.125 MJ m⁻³), collectively. The design strategy of obtaining balanced properties promotes the practicality of smart/functional materials in wearables and flexible electronics.     

Moist-Electric Generator with Efficient Output and Scalable Integration Based on Carbonized Polymer Dot and Liquid Metal Active Electrode

Moisture-enabled electricity generation (MEG) is highly promising in next-generation energy conversion. However, the practical applications of existing MEG devices are limited due to their low current and voltage outputs, strong dependence on high moisture, and inflexible nature. Herein, an efficient MEG integrated with flexible, all-weather, and scalable fabrication characteristics based on the rational combination of carbonized polymer dots (CPDs) and liquid metal (LM) active electrodes is developed for the first time. Remarkably, the fabricated MEG device can produce a stable voltage output of 800 mV and a record high current density of 1640 µA cm⁻². Even at a low air humidity of 15%, the MEG device can provide a high voltage output of 0.65 V and a considerable current density of 12 µA cm⁻². The prompted diffusion of hydrogen ions in CPDs and the additional metal ions ionized from the LM electrode contribute synergistically to the high electricity generation. Additionally, the device can be easily integrated on various flexible substrates and generate an ultrahigh voltage of 210 V to power commercial electronics, showing great potential in large-scale fabrication and application.     

Ultrahigh-Areal Capacitance Flexible Supercapacitors Based on Laser Assisted Construction of Hierarchical Aligned Carbon Nanotubes

Electrochemical energy storage is a key technology for a clean and sustainable energy supply. In this respect, supercapacitors (SC) have recently received considerable attention due to their excellent performance, including high-power density and long-cycle life. However, the poor binding strength between the active materials and substrate, the low active material loading, and small specific capacitance hinder the overall performance improvement of the device. In this study, an ultrahigh-areal capacitance flexible SC based on the Al micro grid-based hierarchical vertically aligned carbon nanotubes (VACNTs) is studied. Interestingly, the Al micro grid-based VACNTs exhibit ultrahigh loading (13 mg cm⁻²), and the as-fabricated VACNTs electrode display outstanding electrochemical performance, including an impressive areal capacitance of 1,300 mF cm⁻² at the current density of 13 mA cm⁻² and excellent stability with a retention ratio of 90% after 20,000 cycles at the current density of 130 mA cm⁻². Furthermore, the hierarchical VACNT electrodes show excellent mechanical flexibility when assembled into quasi-solid-state SC using Na₂SO₄-PVA gel as the electrolyte. The capacitance of this device is hardly changed bending different angles, even 180°. This study demonstrates the tremendous potential of Al micro grid-based hierarchical VACNTs as electrodes for high-performance flexible and wearable energy storage devices.     

Bioinspired and Hierarchically Textile-Structured Soft Actuators for Healthcare Wearables

Soft pneumatic actuators possess the increasing potential for various healthcare applications, such as smart wearable devices, safe human-robot interaction, and flexible manipulators. However, it is difficult to translate the existing technologies to commercial applications due to their inefficient volumetric power, sophisticated control with high operation pressure, slow production, and high cost. To overcome these issues, herein, a caterpillar-inspired actuator using hierarchical textile architectures based on simple fabrication and low-cost strategy is designed. Unlike the existing textile-based pneumatic actuators, the designed actuators are constructed by combining boucle fancy yarns with a novel trilayer-knit architecture. The as-prepared actuators concurrently possess fast response (1100° s⁻¹), large bending actuation strain (1080° m⁻¹), high-power density (272 W m⁻³), mechanical robustness, easy-programmable motions, and human-tactile comfort, which outperforms currently reported textile-based pneumatic actuators. Furthermore, due to the geometrical transition of the engineered hierarchical structure, the developed actuators exhibit superior dual-stiffness effect with stress evolution, providing a facile approach to addressing the conflict of flexibility and force output in soft fluidic actuators. This concept as a paradigm provides new insights to develop soft actuators with outstanding design flexibility, adaptability, and multifunctionality using engineered textile-structure, which has great potential for real-world applications in medical rehabilitation, physiotherapy, and soft robotics.     

Ultrasound‐Induced Wireless Energy Harvesting for Potential Retinal Electrical Stimulation Application

Retinal electrical stimulation for people with neurodegenerative diseases has shown to be feasible for direct excitation of neurons as a means of restoring vision. In this work, a new electrical stimulation strategy is proposed using ultrasound‐driven wireless energy harvesting technology to convert acoustic energy to electricity through the piezoelectric effect. The design, fabrication, and performance of a millimeter‐scale flexible ultrasound patch that utilizes an environment‐friendly lead‐free piezocomposite are described. A modified dice‐and‐fill technique is used to manufacture the microstructure of the piezocomposite and to generate improved electrical and acoustic properties. The as‐developed device can be attached on a complex surface and be driven by ultrasound to produce adjustable electrical outputs, reaching a maximum output power of 45 mW cm^?2. Potential applications for charging energy storage devices and powering commercial electronics using the device are demonstrated. The considerable current signals (e.g., current >72 µA and current density >9.2 nA µm^?2) that are higher than the average thresholds of retinal stimulation are also obtained in the ex vivo experiment of an implanted environment, showing great potential to be integrated on implanted biomedical devices for electrical stimulation application.     

Wearable Biosupercapacitor: Harvesting and Storing Energy from Sweat

This work demonstrates the first example of sweat-based wearable and stretchable biosupercapacitors (BSCs), capable of generating high-power pulses from human activity. The all-printed, dual-functional, conformal BSC platform can harvest and store energy from sweat lactate. By integrating energy harvesting and storage functionalities on the same footprint of a single epidermal device, the new wearable energy system can deliver high-power pulses and be rapidly self-charged by bioenergy conversion of sweat lactate generated from human activity while simplifying the design and fabrication. The mechanical robustness and conformability of the device are realized through island-bridge patterns and strain-enduring inks. The enhanced capacitance of the BSC is realized by the synergistic effect of carbon nanotube ink with electrodeposited polypyrrole on the anode and of porous cauliflower-like platinum on the cathode. In the presence of lactate, the BSC shows high power in pulsed output and stable cycling performance. Furthermore, the wearable device can store energy and deliver high-power pulses long after the perspiration stopped. The self-charging hybrid wearable device obtained high power of 1.7 mW cm⁻² in vitro, and 343 µW cm⁻² on the body during exercise, suggesting considerable potential as a power source for the next generation of wearable electronics.     

Multilevel Structure Engineered Lead-Free Piezoceramics Enabling Breakthrough in Energy Harvesting Performance for Bioelectronics

The prevalence of wearable/implantable medical electronics together with the rapid development of the Internet of Medicine Things call for the advancement of biocompatible, reliable, and high-efficiency energy harvesters. However, most current harvesters are based on toxic lead-based piezoelectric materials, raising biological safety concerns. What hinders the application of lead-free piezoelectric energy harvesters (PEHs) is the low power output, where the key challenge lies in obtaining a high piezoelectric voltage constant (g₃₃) and harvesting figure of merit (d₃₃ × g₃₃). Here, micron pores are introduced into phased boundary engineered high-performance (K, Na)NbO₃-based ceramic matrix, resulting in the state-of-the-art g₃₃ and the highest d₃₃ × g₃₃ values of 57.3 × 10⁻³ Vm N⁻¹ and 20887 × 10⁻¹⁵ m² N⁻¹ in lead-free piezoceramics, respectively. Concomitantly, ultrahigh energy harvesting performances are obtained in porous ceramic PEHs, with output voltage and power density of 200 V and 11.6 mW cm⁻² under instantaneous force impact and an average charging rate of 14.1 µW under high-frequency (1 MHz) ultrasound excitation, far outperforming previously reported PEHs. Porous ceramic PEHs are further developed into wearable and bio-implantable devices for human motion sensing and percutaneous ultrasound power transmission, opening avenues for the design of next-generation eco-friendly WIMEs.     

Flexible Thermoelectric Devices of Ultrahigh Power Factor by Scalable Printing and Interface Engineering

Printing is a versatile method to transform semiconducting nanoparticle inks into functional and flexible devices. In particular, thermoelectric nanoparticles are attractive building blocks to fabricate flexible devices for energy harvesting and cooling applications. However, the performance of printed devices are plagued by poor interfacial connections between nanoparticles and resulting low carrier mobility. While many rigid bulk materials have shown a thermoelectric figure of merit ZT greater than unity, it is an exacting challenge to develop flexible materials with ZT near unity. Here, a scalable screen‐printing method to fabricate high‐performance and flexible thermoelectric devices is reported. A tellurium‐based nanosolder approach is employed to bridge the interfaces between the BiSbTe particles during the postprinting sintering process. The printed BiSbTe flexible films demonstrate an ultrahigh room‐temperature power factor of 3 mW m^?1 K^?2 and ZT about 1, significantly higher than the best reported values for flexible films. A fully printed thermoelectric generator produces a high power density of 18.8 mW cm^?2 achievable with a small temperature gradient of 80 °C. This screen‐printing method, which directly transforms thermoelectric nanoparticles into high‐performance and flexible devices, presents a significant leap to make thermoelectrics a commercially viable technology for a broad range of energy harvesting and cooling applications.     

Highly Stretchable and Flexible Electrospinning-Based Biofuel Cell for Implantable Electronic

With the emerging demand of implantable microelectronics, it essentially requires the fully integrated and reliable power supplies. The study reports a stretchable and flexible electrospinning-based glucose/O₂ biofuel cell with glucose oxidase bioanode, Pt/C cathode and thermoplastic polyurethane substrate, which is capable for adapting to the various stresses and strains caused by individual movement. The rigid benzene rings and elastic chain segments of thermoplastic polyurethane ensure its superior tensile property. Furthermore, the stable covalent connections between the activated carbon nanotubes (CNTs-COOH) and glucose oxidase inside 3D thermoplastic polyurethane network are established by amide reaction to ensure the rapid direct electron transfer of bioanode and stable power output of device in flexible environments. The biofuel cell exhibits an open circuit voltage of 0.575 V, and high-power density of 57 µW cm⁻² in 5 mM glucose. Moreover, the power-generation properties of implantable biofuel cell keep steady, and its power density exhibits limited fluctuations on the dorsum of rat when bending, stretching, and twisting in 28 days. There is no obvious local inflammation or systemic abnormalities in rats. It satisfies the impressive biocompatible requirement, demonstrating the promising potential of electrospinning-based biofuel cell as a robust self-sustained power source for implantable electronics.     

Ultraprecise 3D Printed Graphene Aerogel Microlattices on Tape for Micro Sensors and E-Skin

3D printed graphene aerogels hold promise for flexible sensing fields due to their flexibility, low density, conductivity, and piezo-resistivity. However, low printing accuracy/fidelity and stochastic porous networks have hindered both sensing performance and device miniaturization. Here, printable graphene oxide (GO) inks are formulated through modulating oxygen functional groups, which allows printing of self-standing 3D graphene oxide aerogel microlattice (GOAL) with an ultra-high printing resolution of 70 µm. The reduced GOAL (RGOAL) is then stuck onto the adhesive tape as a facile and large-scale strategy to adapt their functionalities into target applications. Benefiting from the printing resolution of 70 µm, RGOAL tape shows better performance and data readability when used as micro sensors and robot e-skin. By adjusting the molecular structure of GO, the research realizes regulation of rheological properties of GO hydrogel and the 3D printing of lightweight and ultra-precision RGOAL, improves the sensing accuracy of graphene aerogel electronic devices and realizes the device miniaturization, expanding the application of graphene aerogel devices to a broader field such as micro robots, which is beyond the reach of previous reports.     

Inkjet Printing Flexible Thermoelectric Devices Using Metal Chalcogenide Nanowires

Development of flexible thermoelectric devices offers exciting opportunities for wearable applications in consumer electronics, healthcare, human–machine interface, etc. Despite the increased interests and efforts in nanotechnology-enabled flexible thermoelectrics, translating the superior properties of thermoelectric materials from nanoscale to macroscale and reducing the manufacturing costs at the device level remain a major challenge. Here, an economic and scalable inkjet printing method is reported to fabricate high-performance flexible thermoelectric devices. A general templated-directed chemical transformation process is employed to synthesize several types of 1D metal chalcogenide nanowires (e.g., Ag₂Te, Cu₇Te₄, and Bi₂Te_2.7Se_0.3). These nanowires are made into inks suitable for inkjet printing by dispersing them in ethanol without any additives. As a showcase for thermoelectric applications, fully inkjet-printed Ag₂Te-based flexible films and devices are prepared. The printed films exhibit a power factor of 493.8 µW m⁻¹ K⁻² at 400 K and the printed devices demonstrate a maximum power density of 0.9 µW cm⁻² K⁻², both of which are significantly higher than those reported in state-of-the-art inkjet-printed thermoelectrics. The protocols of metal chalcogenide ink formulations, as well as printing are general and extendable to a wider range of material systems, suggesting the great potential of this printing platform for scalable manufacturing of next-generation, high-performance flexible thermoelectric devices.     

In Vivo Self‐Powered Wireless Transmission Using Biocompatible Flexible Energy Harvesters

Additional surgeries for implantable biomedical devices are inevitable to replace discharged batteries, but repeated surgeries can be a risk to patients, causing bleeding, inflammation, and infection. Therefore, developing self‐powered implantable devices is essential to reduce the patient's physical/psychological pain and financial burden. Although wireless communication plays a critical role in implantable biomedical devices that contain the function of data transmitting, it has never been integrated with in vivo piezoelectric self‐powered system due to its high‐level power consumption (microwatt‐scale). Here, wireless communication, which is essential for a ubiquitous healthcare system, is successfully driven with in vivo energy harvesting enabled by high‐performance single‐crystalline (1 ? x )Pb(Mg_1/3Nb_2/3)O₃?(x )Pb(Zr,Ti)O₃ (PMN‐PZT). The PMN‐PZT energy harvester generates an open‐circuit voltage of 17.8 V and a short‐circuit current of 1.74 µA from porcine heartbeats, which are greater by a factor of 4.45 and 17.5 than those of previously reported in vivo piezoelectric energy harvesting. The energy harvester exhibits excellent biocompatibility, which implies the possibility for applying the device to biomedical applications.     

High-Performance Flexible Schottky DC Generator via Metal/Conducting Polymer Sliding Contacts

Dynamic Schottky direct-current (DC) generators hold great promise for ambient mechanical energy harvesting as it overcomes the low-current output limitation in conventional approaches. However, the lack of a fundamental understanding of DC generation in conducting polymer-based Schottky generators has hindered their application for self-powered wearable and implantable electronics. Here, a high-performance, flexible Schottky DC generator with metal/conducting polymer sliding contact system is demonstrated, which exhibits a large current density (J) up to 20 A m^–2 for single contact geometry and a scaled-up DC output reaching 200 µA (J = 0.73 A m^–2) and 0.8 V. The design of flexibility in such a Schottky DC generator is inherited from the long-chain polymer concept, leading to the demonstration of a variety of device configuration of free-standing thin film, supported thin film and nanocomposite prototype toward practical applications. It is revealed that the sliding junctions may exhibit a different mechanical energy conversion mechanism compared to the compressive conducting polymer Schottky junctions. It is also proven that the magnitude and polarity of DC generation is determined by the Schottky contact formation and interfacial electric field. The concept of a flexible Schottky generator not only shows great promise for next-generation, self-powered wearable devices, but also provides potential mechanisms for developing novel wearable sensors.     

A Flexible and Safe Planar Zinc-Ion Micro-Battery with Ultrahigh Energy Density Enabled by Interfacial Engineering for Wearable Sensing Systems

Aqueous zinc-ion micro-batteries (ZIMBs) have attracted considerable attention owing to their reliable safety, low cost, and great potential for wearable devices. However, current ZIMBs still suffer from various critical issues, including short cycle life, poor mechanical stability, and inadequate energy density. Herein, the fabrication of flexible planar ZIMBs with ultrahigh energy density by interfacial engineering in the screen-printing process based on high-performance MnO₂-based cathode materials is reported. The Ce-doped MnO₂ (Ce-MnO₂) exhibits significantly enhanced capacity (389.3 mAh g⁻¹), considerable rate capability and admirable cycling stability than that of the pure MnO₂. Importantly, the fabrication of micro-electrodes with ultrahigh mass loading of Ce-MnO₂ (24.12 mg cm⁻²) and good mechanical stability is achieved through optimizing the interfacial bonding between different printed layers. The fabricated planar ZIMBs achieve a record high capacity (7.21 mAh cm⁻² or 497.31 mAh cm⁻³) and energy density (8.43 mWh cm⁻² or 573.45 mWh cm⁻³), as well as excellent flexibility. Besides, a wearable self-powered sensing system for environmental monitoring is further demonstrated by integrating the planar ZIMBs with flexible solar cells and a multifunctional sensor array. This work sheds light on the development of high-performance planar ZIMBs for future self-powered and eco-friendly smart wearable electronics.     

All‐Printed Porous Carbon Film for Electricity Generation from Evaporation‐Driven Water Flow

Converting environmental “waste energies” into electricity via a natural process is an ideal strategy for environmental energy harvesting and supplying power for distributed energy‐consuming devices. This paper reports that evaporation‐driven water flow within an all‐printed porous carbon film can reliably generate sustainable voltage up to 1 V with a power density of ≈8.1 µW cm^?3 under ambient conditions. The output performance of the device can be easily scaled up and used to power low‐power consumption electronic devices or for energy storage. Furthermore, the device is successfully used without electric storage as a direct power source for electrodeposition of silver microstructures. Because of the ubiquity of water evaporation in nature and the low cost of materials involved, the study presents a novel avenue to harvest ambient energy and has potential applications in low‐cost, green, self‐powered devices and systems.     

Ultrahigh‐Strength Ultrahigh Molecular Weight Polyethylene (UHMWPE)‐Based Fiber Electrode for High Performance Flexible Supercapacitors

Flexible fiber‐based supercapacitor (FSC) with excellent electrochemical performance and high tensile strength and modulus is strongly desired for some special circumstances, such as load‐bearing, abrasion resistant, and anticutting fabrics. Here, a series of ultrahigh‐strength fiber electrodes are prepared for flexible FSCs based on ultrahigh molecular weight polyethylene fibers, on which the polydopamine, Ag, and poly (3,4‐ethylene dioxythiophene): poly(styrenesulfonate) are deposited in sequence. The modified fiber‐based electrode exhibits superhigh strength up to 3.72 GPa, which is the highest among fiber‐based electrodes reported to date. In addition, FSCs fabricated with the optimized fiber electrode shows a specific areal capacity as high as 563 mF cm^?2 at 0.17 mA cm^?2, which corresponds to a high areal energy density of ≈50.1 µWh cm^?2 at a power density of ≈124 µW cm^?2. The specific areal capacity only decrease 8% after 1000 times bending test, indicating the outstanding bending performance of this composite fiber electrode. Furthermore, several FSCs can be connected in series or in parallel to get higher working voltage or higher capacity respectively, which demonstrates its potential for broad applications in flexible devices.     

Reassembly of MXene Hydrogels into Flexible Films towards Compact and Ultrafast Supercapacitors

The freestanding MXene films are promising for compact energy storage ascribing to their high pseudocapacitance and density, yet the sluggish ion transport caused by the most densely packed structure severely hinders their rate capability. Here, a reassembly strategy for constructing freestanding and flexible MXene-based film electrodes with a tunable porous structure is proposed, where the Ti₃C₂T_x microgels disassembled from 3D structured hydrogel are reassembled together with individual Ti₃C₂T_x nanosheets in different mass ratios to form a densely packed 3D network in microscale and a film morphology in macroscale. The space utilization of produced film can be maximized by a good balance of the density and porosity, resulting in a high volumetric capacitance of 736 F cm⁻³ at an ultrahigh scan rate of 2000 mV s⁻¹. The fabricated supercapacitor yields a superior energy density of 40 Wh L⁻¹ at a power density of 0.83 kW L⁻¹, and an energy density of 21 Wh L⁻¹ can be still maintained even when the power density reaches 41.5 kW L⁻¹, which are the highest values reported to date for symmetric supercapacitors in aqueous electrolytes. More promisingly, the reassembled films can be used as electrodes of flexible supercapacitors, showing excellent flexibility and integrability.     

Performance Enhancement of Flexible Piezoelectric Nanogenerator via Doping and Rational 3D Structure Design For Self‐Powered Mechanosensational System

With the rapid development of the Internet of things (IoT), flexible piezoelectric nanogenerators (PENG) have attracted extensive attention for harvesting environmental mechanical energy to power electronics and nanosystems. Herein, porous piezoelectric fillers with samarium/titanium‐doped BiFeO₃ (BFO) are prepared by a freeze‐drying method, and then silicone rubber is filled into the microvoids of the piezoelectric ceramics, forming a unique structure based on silicone rubber matrix with uniformly distributed piezoelectric ceramic. When subjected to external force stimulation, compared with conventional piezocomposite films found on undoped BFO without a porous structure, the PENG possesses higher stress transfer ability and thus boosts output performance. The notable enhancement in the stress transfer ability and piezoelectric potential is proven by COMSOL simulations. The PENG can exhibit a maximum open‐circuit voltage (V_oc) of 16 V and short‐circuit current (I_sc) of 2.8 µA, which is 5.3 and 5.6 times higher than those of conventional piezocomposite films, respectively. The PENG can be used as a triggering signal to control the operation of fire extinguishers and household appliances. This work not only expands the application scope of lead‐free piezoelectric ceramic for energy harvesting, but also provides a novel solution for self‐powered mechanosensation and shows great potential application in IoT.     

A high-power GaAs MESFET with an experimentally optimized pattern

A high-power GaAs MESFET with a high packing density has been developed in order to increase the total gatewidth within limited practical device size. The gate-finger width was experimentally optimized to increase the packing density without deterioration of the power gain. The developed power MESFET is the crossover structure and has a total gatewidth of 15 mm with gate-finger width of 190 µm in a 2.2-mm-wide chip. The packing density was almost doubled, and the output powers of 25 W at 6 GHz, and 17 W at 8 GHz were obtained from the internally matched four-chip devices.     

Elastic-Connection and Soft-Contact Triboelectric Nanogenerator with Superior Durability and Efficiency

Triboelectric nanogenerator (TENG) has received tremendous attention in ambient energy harvesting, especially for ocean wave energy. However, the technology is generally challenged to obtain excellent durability and high efficiency simultaneously, which primarily overshadows their further industrial-scale applications. Here, a dual-mode and frequency multiplied TENG with ultrahigh durability and efficiency for ultralow frequency mechanical energy harvesting via the elastic connection and soft contact design is proposed. By introducing the spring and flexible dielectric fluff to the novel pendulum-like structural design, the surface triboelectric charges of TENG are replenished in soft contact mode under the intermittent mechanical excitation, while the robustness and durability are enhanced in non-contact working mode. The fabricated TENG results in a continuous electrical output for 65 s by one stimulus with a high energy conversion efficiency, as well as negligible change of output performance after a total of 2 000 000 cycles. Moreover, integrated with the power management circuit, the TENG array is demonstrated to drive the electronics by effectively harvesting wind and water wave energy as a sustainable energy source. This work paves a new pathway to enhance the robustness, durability, and efficiency of the TENG that resolves the bottleneck of its practical applications and industrialization.