Self-powered Wearable Devices Research Articles

Silicone-incorporated nanoporous cobalt oxide and MXene nanocomposite-coated stretchable fabric for wearable triboelectric nanogenerator and self-powered sensing applications

Triboelectric nanogenerators (TENGs) provide a desirable solution to alleviate the expanding energy supply concerns in the development of self-powered wearable devices and sensors. Herein, a novel wearable, stretchable multifunctional double-layered TENG is fabricated by using a metal-organic framework-derived nanoporous cobalt oxide (NPCO)/silicone and MXene/silicone nanocomposite. The excellent nanoporosity of NPCO induces high charge accumulations that promote the electronegativity of the nanocomposite by fourfold. In addition, MXene/silicone with bifunctionality (charge trapping and charge transport) is incorporated into the intermediate layer to improve the charge trapping capability and electronegativity of the nanocomposite by nine times. Facile, hierarchical fabric-assisted micro/nanostructures on the nanocomposite are conceived to increase hydrophobicity and water resistivity. Conductive knitted fabric is employed as a flexible electrode to obtain high stretchability (230 %) and robustness. Owing to the synergistic effect of the optimized nanocomposite, the fabricated TENG delivers a high power density (10.4 W/m2), which is approximately 23 times higher than the pure silicone-based TENG. By exploiting the outstanding sensitivity (5.82 V/kPa), the TENG reveals an extraordinary self-powered biomotion sensor, and its practical applications in a foot pressure distribution sensor array and a self-powered wearable keyboard. This work provides new insights into the design of high-performance TENGs with high sensitivity and durability and facilitates their applications in biomechanical energy harvesting and self-powered wearable sensors.

3D printing stretchable core-shell laser scribed graphene conductive network for self-powered wearable devices

Graphene-based flexible electronics, particularly those with self-powered ability and stretchability, are greatly promising candidates in the applications of portable and wearable devices. However, complicated deformation of human body and harsh environment inevitably leads to the degradation of conductivity of wearable electronics due to the intrinsic brittleness and crack sensitivity of graphene. Herein, a metamaterial-inspired stretchable and stable conductive network fabricated by 3D printing polyether-ether-ketone (PEEK) and double-side laser scribing graphene (LSG) techniques is demonstrated, which is called LSGCN. The double-side LSG covers the outer surfaces of printed PEEK filaments and forms a special core-shell structure, and its conductivity is 2.72 times of traditional flat graphene. Moreover, the parametric design of LSGCN can increase the stretchability of the structure from 20% to 118%, while ensuring that the change rate of resistance is limited to 1.06 within the 60% strain range. Based on the triboelectric effect, we also demonstrate LSGCN-based self-powered devices, including wearable smart belts and human-computer interaction gloves. Particularly, the LSGCN glove integrates 21 interactive channels, and it can work as the input equipment to control the simulated calculator, display the slides and even play the 3D games. This hybrid-fabricating method of LSGCN provides a novel strategy to fabricate stretch-stable conductive structures for applications in bio-energy harvesting and self-powered sensing devices, which opens up a new avenue for the future Internet of Things.

Composite film with hollow hierarchical silica/perfluoropolyether filler and surface etching for performance enhanced triboelectric nanogenerators

Triboelectric nanogenerators (TENGs), capable of harvesting distributed energy from the environment, have provided a viable solution for self-powered wearable electronics. However, their low power density and susceptibility to contamination still severely limit their practical application. Herein, we reported a “two-step” strategy to implement a waterproof self-powered wearable electronic device based on TENG. Firstly, Perfluoropolyether (PF) and hollow hierarchical silica (H-SiO2) as fillers significantly improve the dielectric properties of polydimethylsiloxane (PDMS) composite films (PFS films) through polarization effect. Then the nano bumps of 10–30 nm are created on the surface of the films by surface etching, the bumps can increase the contact area of TENG. The voltage of TENG is improved from ∼ 67 V to ∼ 910 V and the current is improved from ∼ 1 μA to ∼ 25 μA. What’s more, the investigation of the surface structure of the PFS composite films by Atomic Force Microscope (AFM) revealed that the synergistic combination of multiple nanoscales (10–30 nm, 60–80 nm, 300–500 nm) is more favorable to achieve high performance of TENG. The surface structure composed of multiple nanoscales endows PFS with excellent superhydrophobicity. The PFS films remained fine performance after 40,000 drops of water and 90 days. This work achieves high performance and water resistance of TENG, demonstrating great potential in the field of self-powered wearable electronic devices.

Enhanced magneto-mechano-electric conversion in flexible multiferroic nanocomposites via slender magnetic nanofibers regulated by tailored carbon nanotubes

Flexible multiferroic materials play a key role in self-powered wearable devices and wireless sensing systems, due to their ability for magneto-mechano-electric (MME) coupling response. Here, a flexible multiferroic film with a high MME voltage coefficient modulated by the slender 1-D magnetic nanomaterials is presented. To prepare the 1-D magnetic nanomaterials, carbon nanotube (CNT) is tailored into a slender template to induce the directional arrangement of CoFe2O4 (CFO) nanoparticles. The slender CNT-CFO can yield enhanced MME conversion in poly(vinylidene fluoride-trifluoroethylene)-based nanocomposites due to the synergism of CFO on a 1-D structure and enlarged interface areas between magnetic phase and piezoelectric matrix. Thus, a high MME coupling coefficient of 39.5 mV·cm−1·Oe-1 and mechano-electric output signals of 9.4 V are observed in nanocomposite films when the filler addition is less than 15 wt%. The low ratio of magnetic nanofibers is in favor of realizing the flexibility of polymer-based nanocomposites Moreover, the mechano-electric output signal with ∼ 1.4 times enhancement can be observed when a magnetic field is applied. The work is expected to open up new opportunities for flexible multiferroic nanocomposites in multifunctional devices and self-powered systems.

A hybrid bioelectrochemical device based on glucose/O2 enzymatic biofuel cell for energy conversion and storage

In this work, combining poly (methylene green)/glucose dehydrogenase (PMG/GDH) bioanode with Prussian blue/glucose oxidase (PB/GOD) biocathode, we developed a hybrid bioelectrochemical device based on glucose/O2 enzymatic biofuel cell (EBFC) to achieve energy conversion and storage. Depending on the reversible redox behaviors, PMG and PB play roles of dual-functional nanomaterials, not only as mediators to accelerate electrons transport between enzymes and electrodes surface, but also as pseudocapacitive materials to achieve energy storage. As a result, this hybrid device exhibited superior performance towards energy storage with a specific capacitance of 158.5 mF cm−2 at the current density of 1 mA cm−2. Meanwhile, a maximum output power density of 783.5 μW cm−2 in the pulse mode could be obtained, which had a prominent increment than that of the prototypical EBFC (87.5 μW cm−2) in the steady state. Furthermore, this hybrid device also exhibited better operational stability in long-term charge/discharge cycles test, at the current pulse of 1 mA cm−2. Through the combination of bioelectrocatalysis and capacitive energy storage, this developed hybrid device achieves effective energy conversion and storage, and provides a high output power to address the insufficient power supply of traditional EBFCs, which may enlarge the practical application of EBFCs in self-powered implantable and wearable devices.

Self-Healable and Stretchable Ionic-Liquid-Based Thermoelectric Composites with High Ionic Seebeck Coefficient.

The advancement of wearable electronics, particularly self-powered wearable electronic devices, necessitates the development of efficient energy conversion technologies with flexible mechanical properties. Recently, ionic thermoelectric (TE) materials have attracted great attention because of their enormous thermopower, which can operate capacitors or supercapacitors by harvesting low-grade heat. This study presents self-healable, stretchable, and flexible ionic TE composites comprising an ionic liquid (IL), 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM:OTf); a polymer matrix, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP); and a fluoro-surfactant (FS). The self-healability of the IL-based composites originates from dynamic ion-dipole interactions between the IL, the PVDF-HFP, and the FS. The composites demonstrate excellent ionic TE properties with an ionic Seebeck coefficient (Si ) of ≈38.3mVK-1 and an ionic figure of merit of ZTi =2.34at 90% relative humidity, which are higher than the values reported for other IL-based TE materials. The IL-based ionic TE composites developed in this study can maintain excellent ionic TE properties under harsh conditions, including severe strain (75%) and multiple cutting-healing cycles.

Towards real-time self-powered sensing with ample redundant charges by a piezostack-based frequency-converted generator from human motions

This paper presents a piezostack-based frequency up-converting generator for scavenging ultra-low frequency (lower than 5 Hz) vibration energy associated with human motion. The generator, consisting of a force amplifier, a piezoelectric stack, a spring-mass system, and a spring limiter, realizes ultra-low frequency conversion mainly through the impact-induced frequency conversion effect. To estimate the output voltage of the generator numerically, we built a two-degree-of-freedom (2DOF) equivalent model based on the mechanical structure of the harvester. Moreover, we conducted five series of experiments to investigate the output performance of a fabricated prototype. The prototype generates an instantaneous peak-peak output power of 5.56 W (averaged power of 0.93 mW) excited by human running motions. A 'SHU' LED array was lighted up in real-time successfully. We then tested the performance of the prototype in a real-time self-powered system. The generator is able to power a watch and a thermometer in real-time. More importantly, when the excitation stops, they are powered by redundant charges for approximately 50 minutes and 1 minute, respectively. This research can make an essential contribution to ultra-low frequency vibration energy harvesting and the realization of real-time self-powered wearable devices.

Liquid-based nanogenerator fabricated by a self-assembled fluoroalkyl monolayer with high charge density for energy harvesting

<h2>Summary</h2> Liquid-based triboelectric nanogenerators (L-TENGs) have been considered as a promising tool to utilize clean energy. Here, we reported a tubular L-TENG (TL-TENG) based on fluoroalkyl monolayer-modified silica. It exhibited excellent electric output with an output voltage of 101.5 V, peak power density of 43.0 mW m⁻², and surface charge density of 500.3 μC m⁻². The electric output could be modulated by the thickness of the dielectric layer, types of liquid, and oscillation frequency, which was reasonably explained by our equivalent capacitor model. The hydrophobic fluoroalkyl monolayer could promote the electron transfer, and the dielectric layer could inhibit the leakage current perpendicular to the surface, both leading to the enhancement of electric output. A wearable TL-TENG was finally demonstrated to harvest body motion energy and power lighting devices efficiently. This kind of TL-TENG possesses great potential in the fields of energy harvesting and self-powered wearable devices in the wild.

High Interfacial Thermal Stability of Flexible Flake-Structured Aluminum Thin-Film Electrodes for Bi2Te3-Based Thermoelectric Devices.

Environmental thermal energy harvesting based on thermoelectric devices is greatly significant to the advancement of next-generation self-powered wearable electronic devices. However, the rigid electrodes and interface diffusion of electrodes/thermoelectric materials would lead to the wearable discomfort and performance degradation of the thermoelectric device. Here, a flake-structured Al thin-film electrode with high conductivity and excellent reliability is prepared by regulating the microstructure and crystallinity of the films. The as-prepared Al thin film not only maintains its robustness after 1000 bending cycles but also does not delaminate from the substrate when subjected to the 3M tape test, exhibiting excellent flexibility and adhesion to substrate. By comparing with the annealed interface of the double-layer Cu/Bi2Te3 film, the interface of the heat-treated Al/Bi2Te3 film has almost no element diffusion, demonstrating high interfacial thermal stability. Moreover, a thermoelectric temperature sensor based on the Al thin-film electrode is prepared. The sensitivity of the annealed sensor is still linear, and it can stably monitor the temperature variation, showing high reliability. This discovery could provide a facile and effective strategy to achieving highly reliable thermoelectric devices and flexible electronic devices without any additional diffusion barriers.

Fabrication and characterizations of Eu3+ doped PAN/BaTiO3 electrospun piezoelectric composite fibers

In this paper, Eu3+ doped PAN/BaTiO3 piezoelectric composite fibers were prepared by electrostatic spinning. The addition of filler contributes to the transformation of PAN from 31-helical conformation to planar zigzag conformation, thus improving the piezoelectric properties of PAN. The Φ value can be increased by 10% to ∼97.3%. The highest sensitivity (∼0.15 kPa−1), dielectric constant (3.5) and fluorescence characteristics (Eu3+). The prepared pressure sensor can produce up to ∼6 V voltage and ∼45 nA current at 12.5 kPa and 3 Hz. The results show that Eu3+ doped PAN/BaTiO3 piezoelectric composite fiber membranes can be effectively applied in the fields of flexible pressure sensors, wearable self-powered devices and optoelectronic devices.

Wearable Piezoelectric Nanogenerators Based on Core-Shell Ga-PZT@GaOx Nanorod-Enabled P(VDF-TrFE) Composites.

High-output flexible piezoelectric nanogenerators (PENGs) have achieved great progress and are promising applications for harvesting mechanical energy and supplying power to flexible electronics. In this work, unique core-shell structured Ga-PbZrxTi1-xO3 (PZT)@GaOx nanorods were synthesized by a simple mechanical mixing method and then were applied as fillers in a poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) matrix to obtain highly efficient PENGs with excellent energy-harvesting properties. The decoration of gallium nanoparticles on PZT @GaOx nanorods can amplify the local electric field, facilitate the increment of polar β-phase fraction in P(VDF-TrFE), and strengthen the polarizability of PZT and P(VDF-TrFE). The interfacial interactions of GaOx and P(VDF-TrFE) are also in favor of an increased β-phase fraction, which results in a remarkable improvement of PENG performance. The optimized Ga-PZT@GaOx/P(VDF-TrFE) PENG delivers a maximum open-circuit voltage of 98.6 V and a short-circuit current of 0.3 μA with 9.8 μW instantaneous power under a vertical force of 12 N at a frequency of 30 Hz. Such a PENG exhibits a stable output voltage after 6 000 cycles by the durability test. Moreover, the liquid gallium metal offers a mechanical matching interface between rigid PZT and the soft polymer matrix, which benefits the effective, durable mechanical energy-harvesting capability from the physical activities of elbow joint bending and walking. This research renders a deep association between a liquid metal and piezoelectric ceramics in the field of piezoelectric energy conversion, offering a promising approach toward self-powered smart wearable devices.

Printed multifunctional magnetically activated energy harvester with sensing capabilities

The exponential growth and ubiquitous use of mobile electronics supported by the Internet of Things (IoT) is leading to an increasing need of self-powered wearable electronic devices. In particular, converting electrical energy from magnetic fields is very appealing for the development of a sustainable power sources/sensing tools. Magneto-mechano-electric energy conversion is an effective way to convert magnetic fields into electricity for low power applications. The successful printing of such materials allows the design of customized structures, improved integration into devices and reduced materials waste. Here, a self-powered printed sensing device is presented, by exploiting piezoelectric/magnetic composites in response to magnetic stimuli via magneto-mechano-electric energy conversion. The printed magnetoactive device has the capabilities of harvesting magnetic energy with maximum output power density of 9.7 mW cm−3 as well as detecting magnetic fields with a r2 of 0.9991 and a sensitivity of 30 V T−1. Such sensing/harvesting performance allied to the Bluetooth connectivity offer great potential for applications in wearable electronics devices and IoT-related applications.

Development of a carbon nanofiber-attached flexible piezoelectric nanocomposite towards self-powered wearable devices

The flexible piezoelectric nanocomposite (PNC) has the tremendous opportunity in wearable and foldable devices for healthcare detection, artificial skin, human body motion, and robotics applications. The aim of this paper was to develop the polymer based piezoelectric nanocomposite using cast solution method, the carbon nanofiber (CNF) was mixed with poly(vinylidenefluoride) (PVDF) polymer as a solvent, to make a series of flexible piezoelectric nanocomposite (PNC) out of PVDF/CNF and investigate their dielectric characteristics across a frequency range of 20 Hz to 10 MHz. Moreover, the piezoelectric performance of PNCs is examined by bending machine with sufficient bending cycles. The dielectric properties of PNCs were analyzed using the impedance analyzer for the varying wt% of CNF. It was discovered that the 2 %wt CNF based PNC showed excellent dielectric properties and maximum piezoelectric voltage of 0.62 V at bending strain of 0.009. These fabricated PNCs can be used for piezoelectric nanogenerator for self-powered and wearable sensors.

Fluorinated graphite paper used for self-powered water speed sensors by immersion-type tribovoltaic effect-dominated triboelectric nanogenerators

The advancement of nanogenerators (NGs) enables self-powered wearable devices to respond to environmental parameters, which encourages new application scenarios to be explored. In the work, an immersion-type triboelectric NG (TENG) is fabricated to harvest mechanical energy from running water and acts as a novel self-powered water-speed sensor by fluorinated graphite paper (FGP). The oscillograms of output currents driven by flowing water are comprised of major direct current (DC) and minor alternative current (AC) signals. The DC signals are attributed to tribovoltaic mechanisms between the FGP and water, and the AC signals are attributed to triboelectric mechanisms between the FGP and ions in water, testified by subsequent experiments in NaCl(aq). The FGP-water TENG demonstrates the output current density and voltage of 3.3 μA/cm2 and 65 mV at a water speed of 4.2 cm/sec, showing 84 and 14-fold enhancements, respectively, compared with the GP-water TENG. The sensing of water speed by using the output current of the FGP-water TENG shows a linear calibration curve with R2 larger than 0.99. In addition to water speed sensing, bubble sensing in an aquarium, and energy harvesting in dynamic water by ultrasound are also demonstrated by the FGP-based device. The new applications and mechanisms involved in the work provide new insights into the triboelectric and tribovoltaic mechanisms in water and novel ideas to monitor and utilize water resources.

Highly wearable, machine-washable, and self-cleaning fabric-based triboelectric nanogenerator for wireless drowning sensors

Rapid developments of artificial intelligence have increasingly necessitated wearable and functionalized fabric-based triboelectric nanogenerators (F-TENGs). However, conventional F-TENGs are limited by low outputs, poor durability and washability. In this study, through simple liquid-phase fluorination with homemade urethane perfluorooctyl silane (NHCOO-PFOTS), functional fabrics were fabricated for highly wearable and machine-washable F-TENGs. By introducing fluorine atoms, the fabrics possess strong electron-accepting ability, excellent waterproof and anti-soil performances. Besides, fluorination provides excellent durability for F-TENGs since chemicals reacted inside the fibers and formed long-chain molecules that will not disappear upon subsequent washing and daily abrasion. F-TENG composed of fluorinated silk and nylon fabrics yielded a maximum output power of 2.08 W·m−2 at 10 MΩ with negligible decay after 45,000 cycles of contact-separation motions and 70 h of washing. Fluorinated silk can maintain hydrophobic (contact angle > 140°) in extreme environments for long durations. In addition, the F-TENG developed herein exhibits excellent anti-wear performances and self-healing of hydrophobicity and triboelectric performances through heating treatment. Further, F-TENGs sewed on clothing can drive a digital watch using electricity generated by arm swinging. A wireless drowning sensor was designed by utilizing human motion energy with a water-conducted switch in the circuit. The sensor gets triggered by water and instantaneously sends out real-time alarms and notifications to mobile devices. The excellent outputs and practicability of fluorinated fabrics make them excellent candidates for self-powered smart clothes and wearable devices for drowning prevention.

Experimentation of a Wearable Self-Powered Jacket Harvesting Body Heat for Wearable Device Applications

The development of special wearable/portable electronic devices for health monitoring is rapidly growing to cope with different health parameters. The emergence of wearable devices and its growing demand has widened the scope of self-powered wearable devices with the possibility to eliminate batteries. For instance, the wearable thermoelectric energy harvester (TEEH) is an alternate to batteries, which has been used in this study to develop four different self-powered wearable jacket prototypes and experimentally validated. It is observed that the thermal resistance of the cold side without a heat sink of prototype 4 is much greater than the rest of the proposed prototypes. Besides that, the thermal resistance of prototype 4 heat sinks is even lower among all proposed prototypes. Therefore, prototype 4 would have a relatively higher heat transfer coefficient which results in improved power generation. Moreover, an increase in heat transfer coefficient is observed with an increase in the temperature difference of the cold and hot sides of a TEEH. Thus, on the cold side, a heat flow increases which benefits heat dissipation and in turn reduces the thermal resistance of the heat sink. Besides that, the developed prototypes on people show that power generation is also affected by factors like ambient temperature, person’s activity, and wind breeze and does not depend on the metabolism. A different mechanism has been explored to maximize the power output within a 16.0 cm2 area, in order to justify the wearability of the energy harvester. Furthermore, it is observed that during the sunlight, any material covering the TEEH would improve the performance of prototypes. Prototypes are integrated into jacket and studied extensively. The TEEH system was designed to produce a maximum delivering power and power density of 699.71 μW and 43.73 μW/cm2, respectively. Moreover, the maximum voltage produced is 62.6 mV at an optimal load of 5.6 Ω. Furthermore, the TEEH (prototype 4) is connected to a power management circuit of ECT310 and LTC3108 and has been able to power 18 LEDs.

Fabrication and characterization of PVDF/BaTiO3 nanocomposite for energy harvesting application

Today’s world is surrounded by smart wireless devices that require a sustainable and eco-friendly power source. PENGs (Piezoelectric nanogenerators) is fast emerging as an extremely efficient, cost-effective, and easily fabricated source for producing battery-free devices. This study involves using nanomaterials as an essential component in manufacturing such a self-powered system. Nanocomposites of P(VDF)/BaTiO3 containing varying amounts of nanoparticles were fabricated by far-field electrospinning. The non-woven composites were characterized with the field emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In this paper, we report an approach that allows us to fabricate a PENG based on piezoelectric polymer and nanofiller material nanocomposite as an active layer that can capture energy from daily life human activity (pressing and bending). P(VDF)/BaTiO3 nanogenerators exhibited higher piezoelectric performance than the pristine P(VDF) PENG. These PENGs could be able to produce enough energy to run LED bulbs. The results of this study provide a basis for developing self-powered electrical wearable devices and systems.

Ion regulation in double-network hydrogel module with ultrahigh thermopower for low-grade heat harvesting

Harvesting low-grade heat as source of electrical power has emerged as a research frontier for self-powered wearable devices, as a promising route to overcome challenges associated with limited access to grid power. However, such promise is compromised by current attainable thermopowers and constraints of rigid or complicated thermoelectric systems. We report an ultrahigh thermopower of 19.32 mV K−1 on a stretchable thermoelectric module by the assembly of porous electrodes and hybrid hydrogel, containing 1-ethyl-3-methylimidazolium and tetrafluoroborate ions and polyethylene glycol. The anions act as charge carrier; for the first time, distinct ion mobilities are directly measured by 2D-diffusion-ordered nuclear magnetic resonance spectroscopy. By regulating ion transport via the synergy of selective ion-localization and thermo-osmotic mechanism, such design provides an effective strategy to increase thermopower, and our device is endowed with high output power density, tailorable architecture, and excellent stretchability, which is showcased in a thermoelectric wristband for body heat recovery.

On-demand bioenergy from a fingertip

Wearable biosensors can monitor biological vital signs of health continuously but require sustainable power technology to realize a paradigm shift towards connected healthcare anytime, anywhere. A recent article in <i>Joule</i> (Yin et al.) reports a fingertip-based self-powered wearable device that can harvest sustainable bioenergy more efficiently than previous technologies.

Soft Wearable Healthcare Materials and Devices.

In spite of advances in electronics and internet technologies, current healthcare remains hospital-centred. Disruptive technologies are required to translate state-of-art wearable devices into next-generation patient-centered diagnosis and therapy. In this review, recent advances in the emerging field of soft wearable materials and devices are summarized. A prerequisite for such future healthcare devices is the need of novel materials to be mechanically compliant, electrically conductive, and biologically compatible. It is begun with an overview of the two viable design strategies reported in the literatures, which is followed by description of state-of-the-art wearable healthcare devices for monitoring physical, electrophysiological, chemical, and biological signals. Self-powered wearable bioenergy devices are also covered and sensing systems, as well as feedback-controlled wearable closed-loop biodiagnostic and therapy systems. Finally, it is concluded with an overall summary and future perspective.