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Flexible, lead-free piezoelectric nanogenerators are gaining prominence as viable alternatives with remarkable potential in the backdrop of increasing demand for sustainable energy solutions, particularly in the field of microelectronic systems and sensing technologies. In this context, the synergistic impact of utilizing reduced graphene oxide (rGO) nanosheets decorated with zinc oxide (ZnO) nanorods, in conjunction with a low-temperature phase-inversion technique aimed at augmenting the polar β-phase of poly-(vinylidene fluoride) (PVDF) was explored. The nanofiller concentrations of rGO and ZnO were systematically varied to ascertain the optimal concentration in the PVDF matrix. These optimal concentrations were further used to fabricate PVDF/ZnO/rGO hybrid and PVDF/ZnO-decorated rGO nanocomposites. Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction analysis (XRD), and differential scanning calorimetry (DSC) characterizations were employed to examine the electroactive crystal phase in synthesized nanocomposites, confirming enhancement in polar β-phase and crystallinity, thereby improving piezoelectric, dielectric, and ferroelectric properties of the nanocomposites as confirmed by a dielectric broadband spectrometer (BDS) and piezoresponse force microscopy (PFM). A comparative analysis of optimized nanocomposites supplemented with related characterizations was performed to assess their piezoelectric performance. Additionally, systematic variations in force and frequency were carried out to understand their correlation with the piezoelectric performance of PENGs. The optimized PENG showcased the exceptional piezoelectric energy harvesting potential, generating an open circuit voltage of 23 V (at 1 Hz and 1 N), 98 V (at 5 Hz and 10 N), and 153 V (at 15 Hz and 50 N). Further, the PENG produced an instantaneous power density of ∼28 μW/cm2, charged a range of capacitors, sensed human body motions, successfully illuminating 50 LEDs in series and 36 in combination of series and parallel connections. This fabricated PENG henceforth showcases the immense potential for energy harvesting applications. [ABSTRACT FROM AUTHOR]

Existing self-powered generators with substantial volume can generate tens of V using triboelectric, piezoelectric, and pyroelectric effects. However, there is a growing need for more robust, cost-effective, smaller-sized, and easier-to-produce generators for onboard and distributed sensor applications. In this article, we introduce for the first time a minute renewable energy source based on a single zinc oxide nanowire (ZnONW) to power multiple common bulk sensors. A nanomanipulator within a scanning electron microscope (SEM) was utilized to manipulate and provide mechanical energy by deforming a single suspended ZnONW under specific scenarios. Piezoelectric properties of the ZnONW, including the effects of deformation magnitude and bending frequency, were investigated. A voltage output of up to 22.3 mV was obtained and was used to power external sensing elements practically for the first time, with the sensing signal measured using the voltage-division principle. 0–180° bending angle of a flexible strain gauge (sensitivity: −1.07 mV/rad), 30–90 °C temperature, and light on/off were successfully tested. Simulations were conducted to evaluate the influence of the mass block on the first resonant frequency of the nanogenerator and to enhance power generation performance. Our work offers a fresh method for studying the piezoelectric properties of a single ZnONW-based nanogenerator and demonstrates its potential for self-powered microdevices in various real-time, flexible, and portable sensing applications. [ABSTRACT FROM AUTHOR]

The present work reports an enhanced magnetoelectric (ME) effect at room temperature (RT) and above in a nanocomposite of LaYFe2O6/poly-(vinylidene fluoride)–hexafluoropropylene [LaYFe2O6/P-(VDF-HFP)], which is prepared by the solution-casting method. Field-emission scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy reveal excellent phase-to-phase connectivity and an enhanced beta-phase fraction in the PVDF matrix by the incorporation of 10 wt % antiferromagnetic nanoparticles (NPs). This is also substantiated by the improved ferroelectric (electric-field-dependent polarization) response by a 10 wt % sample. At RT, this nanocomposite manifests a first-order ME coupling coefficient of ∼2.92 mV cm–1 Oe–1 and a second-order ME coupling coefficient of ∼0.051 μV cm–1 Oe–2 (significantly 1 order higher than that of pristine LaYFe2O6). The enhanced ME coefficient at RT and above makes it a viable candidate to address the challenges of ME-based device applications. A flexible, portable, lightweight, cost-effective magnetoelectric nanogenerator (MENG) fabricated from the nanocomposite film is able to harvest the wasted magnetic energy with an efficiency of 1.5%. As a demonstration, the harvested electric energy is stored in a capacitor, which, in turn, is used to power a light-emitting diode (LED). The present work hence suggests the deployment of this material for self-powered wearable devices. [ABSTRACT FROM AUTHOR]

In low-dimensional material systems, augmented physical and chemical properties may be witnessed through a unique morphological evolution. Here, we report the development of an optimized nanowall network of ZnO for the fabrication of a flexible single-electrode triboelectric nanogenerator (STENG)-based tactile and gesture sensors. The chemically grown nanowall network with an adequate pore area endows superior triboelectric output (current ∼0.6 μA and power ∼20 μW/cm 2 ) by offering an optimum surface area and dielectric constant for pressure sensing applications. The rational comparison of the triboelectric properties of nanowall and nanorod structures of ZnO reveals that the higher surface area offered by the hollow walls leads to superior output characteristics. The demonstration of pressure sensitivity of the STENG ∼1 V/N is promising for self-powered tactile sensing applications. The array of STENG sensors, when attached to a user hand, generates distinguishable signals while holding objects of varying curvature and mass. Again, the observation of sensitivity of ∼0.1 V per degree during finger movement activity indicates the gesture sensing ability of the nanowall-based TENG system, facilitating sign language expression through the movement of fingers. Further, the generated electrical signals during tactile and gesture sensing can be classified and recognized through the deployment of machine learning (ML) techniques. In fact, the implementation of Random Forest and K-Nearest Neighbor models has offered an accuracy of 96% while recognizing the output signals generated by the sensor arrays. The demonstration of superior sensing characteristics with the optimized nanowall network may be advantageous in innovating prototype sensors for the differently abled people to distinguish or classify objects on the basis of material, morphology, and mass during their regular activities.

Tourmaline is known for its natural negative ion effect and far-infrared radiation function, which promote human blood circulation, relieve pain, regulate the endocrine system, and enhance immunity and other functions. These functions motivate the use of this material for enhanced sensitivity of wearable sensors. In this work, taking advantage of the unique multifunctions of tourmaline nanoparticles (Tur), highly boosted piezoelectricity was achieved by incorporating polydopamine (PDA)-modified Tur in PVDF. The PDA@Tur nanofillers not only effectively increased the β-phase content of PVDF but also played a major role in significantly enhancing piezoelectricity, wettability, elasticity, air permeability, and stability of the piezoelectric sensors. Especially, the maximum output voltage of the fiber membrane with 0.5 wt % PDA@Tur reached 31.0 V, being 4 times that of the output voltage of the pure PVDF fiber membrane. Meanwhile, the sensitivity reached 0.7011 V/kPa at 1-10 N, which was 3.6 times that of pure PVDF film (0.196 V/kPa). The power intensity reached 8 μW/cm 2 , being 5.55 times that of the pristine PVDF PENG (1.44 μW/cm 2 ), and the piezoelectric coefficient from d33 m/PFM is 5.5 pC/N, higher than that of pristine PVDF PENG (3.1 pC/N). Output signal graphs corresponding to flapping, finger, knee, and elbow movements were detected. The response/recovery time of the sensor device was 24/19 ms. The piezoelectric nanogenerator (PENG) was capable of charging multiple capacitors to 2 V within a short time and lighting up 15 light-emitting diodes bulbs (LEDs) simultaneously with a single beat. In addition, a 4 × 4 row-column multiplexed sensor array was made of PENGs, which showed distinct responses to different stress areas in different sensor modules. This study demonstrated high-performance PDA@Tur PVDF-based PENG being capable of energy harvesting and sensing, providing a guideline for the design and buildup of wearable self-powered devices in healthcare and human-computer interaction.

The advent of liquid-solid triboelectric nanogenerators (LS-TENGs) has ushered in a new era for harnessing and using energy derived from water. To date, extensive research has been conducted to enhance the output of LS-TENGs, thereby improving water utilization efficiency and facilitating their practical application. However, in contrast to intricate chemical treatment methods and specialized structures, a straightforward operational process and cost-effective materials are more conducive to the widespread adoption of LS-TENGs in practical applications. This work presents a novel method to enhance the output of LS-TENGs by increasing the liquid-solid contact area. The approach involves creating roughness on the solid surface through sandpaper grinding, which is simple in design and easy to operate and significantly reduces the cost of the experiment. The theory is applied to the solid triboelectric layer commonly used in the LS-TENG, demonstrating its universality and wide applicability to improve the output of the LS-TENG. The practical performance of the device is demonstrated by charging the capacitor and external load and driving the hygrometer and commercial 5 W LED light bulb, which can directly light up 300 commercial light-emitting diodes (LEDs) driven by a drop of water. This work provides a new method for the optimization of LS-TENGs and contributes to the wide application of LS-TENGs. This is a significant step forward in the field of energy harvesting and utilization.

Electrical stimulation therapy (EST) has been established as an effective strategy to accelerate wound healing by stimulating cell proliferation and migration, ultimately promoting re-epithelialization and vascularization, two key processes that significantly influence the rate of wound healing. Phosphatase and tensin homologue (PTEN), a widely expressed protein in somatic cells, works as a "brake" regulating cell differentiation, proliferation, and migration. Given that this "brake" also works in cell electrical responses, there is a hypothesis that PTEN inhibition may amplify the efficacy of EST in wound treatment. However, long-term inhibition of PTEN may result in DNA damage and reduce DNA repair, which poses a significant challenge to the safe use of PTEN inhibitors. To address this issue, we developed a system that combines PTEN inhibitor loaded electro-responsive hydrogel (BPV@PCP) with a wearable direct current pulse piezoelectric nanogenerator (PENG). The PENG converts the rat's motions into electric fields that synchronously charge the wound edge tissue and BPV@PCP. Electric field intensity was lower when the rat was quiet or anesthetized, which is insufficient to trigger an effective PTEN inhibitor release. However, when the rat was in action, the electric field intensity exceeded 625 mV/mm, resulting in a rapid drug release. This on-demand PTEN inhibition accelerated wound healing by amplifying cell electric responsiveness while avoiding negative effects associated with continuous overinhibition of PTEN. Notably, this system improves vascularization not only by improving endothelial cell electric responsiveness but also through the paracrine pathway, in which electrical stimulation and PTEN inhibition synergically promote VEGF secretion.

In this work, we decorated piezoresponsive atomically thin ZnO nanosheets on a polymer surface using additive manufacturing (three-dimensional (3D) printing) technology to demonstrate electrical-mechanical coupling phenomena. The output voltage response of the 3D-printed architecture was regulated by varying the external mechanical pressures. Additionally, we have shown energy generation by placing the 3D-printed fabric on the padded shoulder strap of a bag with a load ranging from ∼5 to ∼75 N, taking advantage of the excellent mechanical strength and flexibility of the coated 3D-printed architecture. The ZnO coating layer forms a stable interface between ZnO nanosheets and the fabric, as confirmed by combining density functional theory (DFT) and electrical measurements. This effectively improves the output performance of the 3D-printed fabric by enhancing the charge transfer at the interface. Therefore, the present work can be used to build a new infrastructure for next-generation energy harvesters capable of carrying out several structural and functional responsibilities.

The sustainable operation of wearable sensors plays an important role in continuous and longtime health monitoring. Conventional batteries, which are bulky and rigid, do not satisfy these requirements and, rather, cause additional economic burdens and environmental problems by regular replacement of power sources. This article provides a review on an alternative solution in the form of self-powered devices that can harvest energy from the surrounding environment to support the operation of the wearable sensor. The Review starts with an introduction of the self-powered triboelectric nanosensors (TENSs) and its two independent modules: the energy harvester and the sensing module. The Review continues with the TENS-related bioinspired designs for wearable applications, while providing a bird's-eye view of their characteristics and applications. The ongoing challenges and prospects for providing personal healthcare with self-powered TENS are presented and discussed.

Since the beginning of the COVID-19 pandemic, the use of face masks has become not only mandatory in several countries but also an acceptable approach for combating the pandemic. In the quest for designing an effective and useful face mask, triboelectric nanogenerators (TENGs) have been recently proposed. Novel functionalities are provided with the use of TENGs in face masks due to the induced triboelectrification generated by the exhaled and inhaled breath, allowing their use as an energy sensor. Nonetheless, within the face mask, the presence of nontextile plastics or other common triboelectric (TE) materials can be undesired. Herein, we propose the use of an all-fabric TENG (AF-TENG) with the use of high molecular weight polyethylene (UHMWPE) and cotton fabric as negative and positive triboelectric layers, respectively. With these materials, it is possible to detect the breathing of the patient, which in the case of not detecting a signal over a few minutes can trigger an alarm locally, providing valuable time. Also, in this article, we have sent breathing signals locally and remotely to distances up to 20 km via Wi-Fi and LoRa, the same as warning signals in the case of detecting anomalies. This work reveals the use of TENGs in smart face masks as an important tool to be used in difficult epidemiological periods to the general public, bringing much more comfort and relaxation to patients and elderly in today's society, and based on pristine eco-friendly materials.

The piezoelectric effect has been widely observed in biological systems, and its applications in biomedical field are emerging. Recent advances of wearable and implantable biomedical devices bring promise as well as requirements for the piezoelectric materials building blocks. Owing to their biocompatibility, biosafety, and environmental sustainability, natural piezoelectric biomaterials are known as a promising candidate in this emerging field, with a potential to replace conventional piezoelectric ceramics and synthetic polymers. Herein, we provide a thorough review of recent progresses of research on five major types of piezoelectric biomaterials including amino acids, peptides, proteins, viruses, and polysaccharides. Our discussion focuses on their structure- and phase-related piezoelectric properties and fabrication strategies to achieve desired piezoelectric phases. We compare and analyze their piezoelectric performance and further introduce and comment on the approaches to improve their piezoelectric property. Representative biomedical applications of this group of functional biomaterials including energy harvesting, sensing, and tissue engineering are also discussed. We envision that molecular-level understanding of the piezoelectric effect, piezoelectric response improvement, and large-scale manufacturing are three main challenges as well as research and development opportunities in this promising interdisciplinary field.

Diphenylalanine (FF) is a piezoelectric material that is widely known for its high piezoelectric constant, self-assembly characteristics, and ease of manufacture. Because of its biocompatible nature, it is useful for implantable applications. However, its use in real applications is challenging because it degrades too easily in the body due to its solubility in water (0.76 g/mL). Upon incorporation of hydrophobic and biocompatible porphyrins into the FF, the degradability of the piezoelectric FF and their piezoelectric nanogenerators (PENGs) is controlled. Porphyrin-incorporated FFs are also formed as piezoelectric nanostructures well aligned on the substrate through self-assembly, and their piezoelectric properties are comparable to those of FF. The FF-based PENG degrades in only 5 min, whereas the FF-porphyrin-based PENG produces a stable output for >15 min in phosphate-buffered saline. This strategy for realizing biodegradable functional materials and devices with tunable degradation rates in the body can be applied to many implantable electronics.

In this work, MXene films incorporating cellulose nanofibers (CNFs) with a spider-web-like structure were fabricated using a facile vacuum-assisted filtration method. The CNFs significantly improved the flexibility and stability of the MXene membranes. The resulting composites functioned well as electrodes and friction layers in triboelectric nanogenerators (TENGs) when paired with either polytetrafluoroethylene (PTFE) as an electropositive material or nylon as an electronegative material. A membrane containing 20 wt % CNFs in conjunction with PTFE was extremely effective during the prolonged operation of a TENGs, generating an output voltage in excess of 1120 V at a frequency of 3.5 Hz. The surface charge density of this device was as high as 100 μC m -2 . When paired with nylon, the MXene/CNF film produced a surface charge density of over 60 μC m -2 . The microstructures on the rough surface of these membranes, together with the presence of -F and other polar terminations on the MXene, are responsible for the high performance of the nanocomposite. This work demonstrates that MXenes are not necessarily equivalent to PTFE within the triboelectric series and suggests that the MXene-based friction layer could greatly enhance the performance of TENGs.

Enhancing the output power of a nanogenerator is essential in applications as a sustainable power source for wireless sensors and microelectronics. We report here a novel approach that greatly enhances piezoelectric power generation by introducing a p-type polymer layer on a piezoelectric semiconducting thin film. Holes at the film surface greatly reduce the piezoelectric potential screening effect caused by free electrons in a piezoelectric semiconducting material. Furthermore, additional carriers from a conducting polymer and a shift in the Fermi level help in increasing the power output. Poly-(3-hexylthiophene) (P3HT) was used as a p-type polymer on piezoelectric semiconducting zinc oxide (ZnO) thin film, and phenyl-C61-butyric acid methyl ester (PCBM) was added to P3HT to improve carrier transport. The ZnO/P3HT:PCBM-assembled piezoelectric power generator demonstrated 18-fold enhancement in the output voltage and tripled the current, relative to a power generator with ZnO only at a strain of 0.068%. The overall output power density exceeded 0.88 W/cm3, and the average power conversion efficiency was up to 18%. This high power generation enabled red, green, and blue light-emitting diodes to turn on after only tens of times bending the generator. This approach offers a breakthrough in realizing a high-performance flexible piezoelectric energy harvester for self-powered electronics. [ABSTRACT FROM AUTHOR]

The notable out-of-plane piezoelectric effect caused by the large electronegativity of the constituent elements makes two-dimensional (2D) group III nitrides appealing for nanoscale energy-harvesting applications. Here, we demonstrate by extensive density functional theory investigations that the vertical piezoelectricity is enhanced significantly in 2D XN (X = B, Al, Ga) bilayers due to in-plane interlayer sliding. The sliding operation generates tribological energy from the vertical resistance force between the monolayers. A maximum shear strength between the monolayers of 1-25 GPa is recorded during vertical sliding. We elucidate the tribo-piezoelectricity generation mechanism of XN bilayers using the tribological energy conversion to overcome the interfacial sliding barrier. The strongest out-of-plane piezoelectricity is found when the bilayers are in the A-A stacking arrangement. Any reduction in the interlayer distance between group III nitride bilayers enhances out-of-plane polarization due to the increase in sliding energy resistances, leading to an increased inductive voltage output. An induced voltage of ∼3.5 V is achieved during vertical compressive sliding of the upper layer. Using these phenomena, we present a compression-slide XN bilayer nanogenerator strategy capable of tuning the produced tribo-piezoelectric energy through sliding and compression.

The discovery of piezoelectricity in self-assembled peptide nanostructures opens an avenue to a new regime of piezoelectric materials and enables the fundamental investigation of electromechanical coupling in biomaterials. However, strategies for fabricating peptides with desired properties are still lacking. We find that a peptide-based coassembly process effectively controls the properties of peptide nanomaterials and demonstrates their application potential in nanogenerators. The composing peptides and their concentration influence the morphology, molecular property, and physical property of coassembled crystals. Compared with self-assembled diphenylalanine peptides, the coassembled peptides of diphenylalanine and phenylalanine-tryptophan show a 38% increase in piezoelectric coefficient, and the resulting harvesting device shows nearly a 3-fold increase in open-circuit voltage outputs.

Triboelectric nanogenerator (TENG) has the great potential to harvest the electrostatic energy and mechanical energy of raindrops. However, raindrops are small and scattered, and it is difficult to harvest their mechanical energy effectively. In this paper, a gridding triboelectric nanogenerator (G-TENG) with an area of 81 cm 2 is designed and developed to effectively harvest the mechanical energy of raindrops on a large scale. Its peak output power density is 8.56 mW/m 2 , which is 245 times the value of 35 μW/m 2 of a general TENG without gridding. Each unit of the G-TENG can work independently, which can effectively decrease the mutual counteraction of elastic deformation among the adjacent positions of the raindrop impacting layer and avoid the accumulation of raindrops. Under the impact of simulated raindrops from a shower at a flow rate of 0.137 mL/(cm 2 ·s), the open-circuit voltage ( V oc ) and the short-circuit current density ( J sc ) of the G-TENG reach 400 V and 2.5 mA/m 2 , respectively. The peak output power density reaches 110 mW/m 2 , which is 42 times the reported maximum value of 2.6 mW/m 2 of raindrop energy harvesting TENGs with the size larger than 10 cm 2 . Moreover, the G-TENG can harvest the mechanical energy of raindrops at a wide range of raindrop flow rates from 0.055 to 0.219 mL/(cm 2 ·s). This work contributes to the raindrop mechanical energy harvesting on a large scale.

It is known that the suspended liquid droplets in clouds can generate electrostatic charges, which finally results in the lightning. However, the detailed mechanism related to the contact-electrification process on the liquid-gas (L-G) interfaces is still poorly understood. Here, by introducing an acoustic levitation method for levitating a liquid droplet, we have studied the electrification mechanism at the L-G interface. The tribo-motion between water droplets and air induced by the ultrasound wave leads to the generation of positive charges on the surface of the droplets, and the charge amount of water droplets (20 μL) gradually reaches saturation within 30 s. The mixed solid particles in droplets can increase the amount of transferred charge, whereas the increase of ion concentration in the droplet can suppress the charge generation. This charge transfer phenomenon at L-G interfaces and the related analysis can be a guidance for the study in many fields, including anti-static, harvesting rainy energy, micro/nano fluidics, triboelectric power generator, surface engineering, and so on. Moreover, the surface charge generation due to L-G electrification is an inevitable effect during ultrasonic levitation, and thus, this study can also work for the applications of the ultrasonic technique.

Fiber-based nanogenerators have great potential applications in wearable electronics such as portable nanodevices, e-skin, and artificial intelligence system. Here, we report a kind of fiber-based electret nanogenerator (FENG) with a semisupported core-shell structure. Owing to its unique structure, the open-circuit voltage and short-circuit current of the FENG reach 40 V and 0.6 μA, respectively, under a short working distance (∼25 μm). No obvious degradation of the output performance under a long-time continuous work (>16 h) and different humidity environments (20-95%) is observed, which demonstrates the FENG's good reliability and stability. Many universal materials, such as cotton rope, conductive sewing thread, and polyvinyl chloride tube, have been successfully used to fabricate FENG. Meanwhile, the FENG-based wearable fabric has been successfully developed to effectively harvest mechanical energy of human motion. The FENG is highly effective, reliable, and stable, promoting the development of fiber-based nanogenerators and their applications in self-powered wearable electronics.

Temperature effects on the contact electrification (CE) is of great interest. Here, different kinds of substoichiometric oxide films, such as TiO 2- x , Al 2 O 3- x , Ta 2 O 5- x , and Cr 2 O 3- x , are deposited and annealed at different temperatures, and the CE between the films and a Pt-coated tip is performed by using Kelvin probe force microscopy (KPFM). An intriguing finding is that the polarity on the TiO 2- x surface changes from negative to positive with the increase of the sample annealing temperature in air atmosphere. Such a result is attributed to the fact that annealing under an oxidative atmosphere repairs oxygen vacancies and helps upgrade the low valency of Ti 3+ to a stable high valency of Ti 4+ . On the contrary, after annealing occurs in an Ar/H 2 atmosphere, the polarity on the TiO 2- x surface reverses from positive to negative. This is mainly due to the increase of oxygen vacancies after annealing in reducing atmosphere. Through the KPFM results of Al 2 O 3- x , Ta 2 O 5- x , and Cr 2 O 3- x films, the effect of oxygen vacancies is further confirmed, that is, the decrease of oxygen vacancies eases the films at capturing positive charges. Based on this, TiO 2- x -based identical material triboelectric nanogenerators (IM-TENGs) are designed and prepared for the first time to control the current direction. Moreover, a surface state model for explaining the CE mechanism between the metal and annealed dielectric is proposed. This study is conducive to the development of the IM-TENGs which regulate the current direction or voltage output accurately in the future and also provides a further understanding of the dominant mechanism of electron transfer in the CE.

Multiple biological barriers in solid tumors severely restrict the penetration of nanomedicines, which is a main cause for therapeutic failure in traditional tumor treatment. Here, a tumor-specific nanogenerator of peroxynitrite (ONOO - ), prepared by loading cisplatin and sodium nitroprusside into poly(d,l-lactide- co -glycolide) polymersomes, was designed to improve drug delivery and enhance tumor chemotherapy. After a cascade of nicotinamide adenine dinucleotide phosphate oxidases catalysis and glutathione reduction, the nanogenerator, namely, PMCS, could selectively induce the generation of ONOO - in tumor. The generated ONOO - could not only strengthen vascular permeability significantly but also improve the accumulation and penetration of PMCS in tumor by activating matrix metalloproteinases-mediated degradation of extracellular matrix. Along with endocytosis, PMCS released cisplatin to induce tumor cell apoptosis. Moreover, free cisplatin liberated from dead cells infected neighboring tumor cells quickly via ONOO - -mediated up-regulated copper transporter 1, further amplifying chemotherapeutic efficacy. This study advances ONOO - as a potent modality to address the main issues of therapeutic delivery, including but not limited to chemotherapy.

Poly(vinylidene difluoride) (PVDF) has become the polymer matrix of choice for fabrication of wearable electronics and physiological monitoring devices. Despite possessing a high piezoelectric constant, additives are required to increase the charge transfer from PVDF matrix to connected signal readout units. Many of these additives also stabilize the β-phase of PVDF, which is associated with highest piezoelectric coefficients. However, most of the additives used are often brittle ceramic-phase materials resulting in decreased flexibility of the devices and offsetting the gain in β-phase content. Intrinsically conducting polymers (ICP), on the other hand, are ideal candidates to improve the device-related properties of PVDF, due to their higher flexibility than ceramic fillers as well as ability to form conducting network in PVDF membranes. This work reports the performance and device feasibility of PVDF-polycarbazole (PCZ) electrospun nanofiber membranes. A higher β-phase was observed by FTIR spectroscopy in PVDF/PCZ compared to other PVDF phases. Moreover, a higher open-circuit potential was recorded over PVDF/polyaniline composites, which were studied for comparison. The addition of PCZ reduced the flexibility of pure PVDF nanofibers by 20% only. Besides, the work investigated the bacterial biofouling and cell compatibility of the matrix, as essential properties to examine any putative medical device application. PVDF/PCZ membranes were then used to develop a nanogenerator, which was capable of instantly lighting an entire LED array employing the rectified output power, and charged up a 2.2 μF capacitors using a bridge rectifier through a vertical compressive force applied periodically. Finally, the nanogenerator demonstrated electrical energy harvesting from movements of various parts of the human body, such as toe and heel movement and wrist bending. In conclusion, PCZ can be considered as an attractive, biocompatible, and anti-biofouling conducting polymer for electrical actuation and flexible electronic device applications.

Fibrous energy-autonomy electronics are highly desired for wearable soft electronics, human-machine interfaces, and the Internet of Things. How to effectively integrate various functional energy fibers into them and realize versatile applications is an urgent need to be fulfilled. Here, a multifunctional coaxial energy fiber has been developed toward energy harvesting, energy storage, and energy utilization. The energy fiber is composed of an all fiber-shaped triboelectric nanogenerator (TENG), supercapacitor (SC), and pressure sensor in a coaxial geometry. The inner core is a fibrous SC by a green activation strategy for energy storage; the outer sheath is a fibrous TENG in single-electrode mode for energy harvesting, and the outer friction layer and inner layer (covered with Ag) constitute a self-powered pressure sensor. The electrical performances of each energy component are systematically investigated. The fibrous SC shows a length specific capacitance density of 13.42 mF·cm -1 , good charging/discharging rate capability, and excellent cycling stability (∼96.6% retention). The fibrous TENG shows a maximum power of 2.5 μW to power an electronic watch and temperature sensor. The pressure sensor has a good enough sensitivity of 1.003 V·kPa -1 to readily monitor the real-time finger motions and work as a tactile interface. The demonstrated energy fibers have exhibited stable electrochemical and mechanical performances under mechanical deformation, which make them attractive for wearable electronics. The demonstrated soft and multifunctional coaxial energy fiber is also of great significance in a sustainable human-machine interactive system, intelligent robotic skin, security tactile switches, etc.

The large piezoelectricity of monolayer MoSe 2 , which is predicted to be stronger than that of all of the other group VIB transition-metal dichalcogenides (including MoS 2 ), has only been theoretically investigated. Here, we report experimental evidence of in-plane piezoelectricity in MoSe 2 . Monolayer single-crystalline MoSe 2 flake derived from chemical vapor deposition demonstrates a peak output voltage of 60 mV at 0.6% strain, which is ∼50% larger than that of MoS 2 . Piezoelectric signal along the armchair orientation of MoSe 2 is ∼6 times larger than that along the zigzag orientation, indicative of strong anisotropic piezoelectricity. Piezoelectric nanogenerator based on a single MoSe 2 flake illustrates remarkable electromechanical conversion ability, and thus is able to noninvasively monitor vital health signs, such as respiratory rate and heart rate. Despite the extremely small size, MoSe 2 nanogenerator is able to drive pH sensor based on MoS 2 and photodetector based on MoS 2 /WSe 2 heterojunction due to the outstanding piezoelectricity of MoSe 2 and the ultralow power consumption of two-dimensional (2D) material sensors. The self-powered, solely 2D-material-based sensor units demonstrate superb sensing performance. Therefore, the discovery of piezoelectricity in monolayer MoSe 2 provides a route for achieving self-powered atomic-scale electromechanical systems that could stimulate further fundamental research and potential applications.

As emerging ambient energy harvesting technology, triboelectric nanogenerators (TENGs) have proven to be a robust power source and have demonstrated the unique ability to power micro-nano electronics autonomously to form self-powered devices. Although four working modes of TENGs have been developed to promote the feasibility of self-powered micro-nano systems, the relatively complicated structure composed of multilayer and movable components limits the practical applications of TENGs. Herein, we propose a single-layer triboelectric nanogenerator (SL-TENG) based on ion-doped natural nanofibrils. Compared with the simplest mode of currently existing TENGs, i.e., the single-electrode type, this novel single-electrode TENG further simplifies the configuration by the removal of the dielectric layer. The underlying mechanism of the proposed SL-TENG is comprehensively investigated through electrical measurements and the analysis of the effect of ion species at different concentrations. In contrast to conventional TENGs that require electrodes to realize charge transfer, it is revealed that the ions doped into natural nanofibrils effectively realize charge transfer due to the separation and migration of cations and anions. This new working principle based on the combination of electrons and ions enables TENGs to show greater potential for applications since the ultrasimple single-layer configuration enables them to be more easily integrated with other electronic components; additionally, the whole device of the proposed SL-TENG is biodegradable because the natural nanofibrils are completely extracted from carrots.

This work presents a characterization study of the electrode interface in polypropylene ferroelectret nanogenerators. An emphasis is made on the comparison of carbon nanotube fiber electrodes with traditional metallic thin film electrodes. Multiple experiments were performed on samples with the same electrode dimensions for a range of applied pressures. Results showed higher open-circuit voltage peak values for the thin film metal electrodes, regardless of the applied pressure. Interestingly, the difference in short-circuit current values between metal and carbon nanotube-based fiber electrodes was not as significant. The carbon nanotube fiber electrode was further investigated by post-treating the fiber with acetone and comparing the results with untreated carbon nanotube film electrodes and thin film metal electrodes. In an effort to enable a monolithic integration of ferroelectret energy harvesters with flexible energy storage elements, this work also presents studies on generation and leakage of induced free charge in the electrodes of flexible ferroelectret energy harvesters. It was found the current leakage through parasitic elements is a faster process than dipole relaxation in the polypropylene film. Finally, an electrode reliability study shows no significant difference in the electrical output of the devices with metallic thin film electrodes after single folding but shows a significant deterioration after crumpling; meanwhile, these processes had no effect on the performance of similar devices with carbon nanotube fiber-based electrodes.

The current trend for smart, self-sustainable, and multifunctional technology demands for the development of energy harvesters based on widely available and environmentally friendly materials. In this context, ZnSnO 3 nanostructures show promising potential because of their high polarization, which can be explored in piezoelectric devices. Nevertheless, a pure phase of ZnSnO 3 is hard to achieve because of its metastability, and obtaining it in the form of nanowires is even more challenging. Although some groups have already reported the mixing of ZnSnO 3 nanostructures with polydimethylsiloxane (PDMS) to produce a nanogenerator, the resultant polymeric film is usually flat and does not take advantage of an enhanced piezoelectric contribution achieved through its microstructuration. Herein, a microstructured composite of nanowires synthesized by a seed-layer free hydrothermal route mixed with PDMS (ZnSnO 3 @PDMS) is proposed to produce nanogenerators. PFM measurements show a clear enhancement of d 33 for single ZnSnO 3 versus ZnO nanowires (23 ± 4 pm/V vs 9 ± 2 pm/V). The microstructuration introduced herein results in an enhancement of the piezoelectric effect of the ZnSnO 3 nanowires, enabling nanogenerators with an output voltage, current, and instantaneous power density of 120 V, 13 μA, and 230 μW·cm -2 , the performance of this nanogenerator enables lighting up multiple LEDs and other small electronic devices, thus proving great potential for wearables and portable electronics.2 , the performance of this nanogenerator enables lighting up multiple LEDs and other small electronic devices, thus proving great potential for wearables and portable electronics.

Here, we demonstrate the utilization of biocompatible Prussian blue (PB) active coatings onto polyester-carbon nanotube (CNT) threads to enable a fiber-based platform for both power harvesting and continuous motion sensing. First, we show experimental evidence supporting that the mechanistic power generating mechanical-electrochemical coupling in an electrochemical generator (ECG) is best achieved with K-ion insertion, in contrast to the expected preference for Li-ion insertion for batteries. We then construct KPB fibers and demonstrate power generation in an ECG device up to 3.8 μW/cm 2 at low frequencies relevant to human motion in either an aqueous or polymer gel electrolyte media. Further, by stitching these yarns into gloves or arm sleeves, our results show the continuous monitoring of finger or arm motion, respectively, during slow and repetitive human motion. Overall, our work demonstrates an ECG platform that overcomes the performance and integration barriers toward combined textile integration and human motion sensing while leveraging common materials and understanding extending from alkali metal-ion batteries.

In complex environments, there are often toxic and harmful conditions, and so self-powered sensors that use wireless access have a huge advantage. However, there is still a risk of short circuit for self-powered sensors in harsh environments. A single-electrode self-powered sensor was designed, which can be used to monitor body movements such as walking and running, as well as monitoring the motion of some mechanical devices, such as peristaltic pumps, door, and window switches. By using a threshold delay algorithm, this self-powered sensor can be connected to the phone to warn the phone user to check for theft or illegal intrusion when the door and window are opened. Further research shows that the single-electrode configuration can avoid the short-circuit behavior caused by device damage so that the self-powered sensor can still work even if it is pierced. Therefore, the wireless single-electrode self-powered sensor system has better reliability and is more applicable to harsh environments.

This work introduces a piezoelectric-pyroelectric nanogenerator (P-PNG) based on methylammonium lead iodide (CH 3 NH 3 PbI 3 ) incorporated electrospun poly(vinylidene fluoride) (PVDF) nanofibers that are able to harvest mechanical and thermal energies. During the application of a periodic compressive contact force at a frequency of 4 Hz, an output voltage of ∼220 mV is generated. The P-PNG has a piezoelectric coefficient ( d 33 ) of ∼19.7 pC/N coupled with a high durability (60 000 cycles) and quick response time (∼1 ms). The maximum generated output power density (∼0.8 mW/m 2 ) is sufficient to charge up a variety of capacitors, with the potential to replace an external power supply to drive portable devices. In addition, upon exposure to cyclic heating and cooling at a temperature of 38 K, a pyroelectric output current of 18.2 pA and a voltage of 41.78 mV were achieved. The fast response time of 1.14 s, reset time of 1.25 s, and pyroelectric coefficient of ∼44 pC/m 2 K demonstrate a self-powered temperature sensing capability of the P-PNG. These characteristics make the P-PNG suitable for flexible piezoelectric-pyroelectric energy harvesting for self-powered electronic devices.

Applying flexible materials for energy scavenging from ambient mechanical vibrations is a clean energy solution that can help alleviate electrical power demands in portable devices and wearable electronics. This work presents fundamental studies on a flexible ferroelectret polymer with a strong piezoelectric effect and its interface with self-powered and energy storage systems. A single-layered device with a thickness of 80 μm was used for characterizing the device's output voltage, current, transferred charge, and energy conversion efficiency. The potential capability of harvesting mechanical energy and delivering to system load is demonstrated by integrating the device into a fully integrated power management system. The theory for determining the harvested energy that is ultimately delivered to external electronic loads (or stored in a battery) is discussed. The maximum power delivery is found to be for a 600 MΩ load, which results in a device power density of 14.0 W/m 3 for input mechanical forces with a frequency around 2 Hz.

Skin wound healing is a major health care issue. While electric stimulations have been known for decades to be effective for facilitating skin wound recovery, practical applications are still largely limited by the clumsy electrical systems. Here, we report an efficient electrical bandage for accelerated skin wound healing. On the bandage, an alternating discrete electric field is generated by a wearable nanogenerator by converting mechanical displacement from skin movements into electricity. Rat studies demonstrated rapid closure of a full-thickness rectangular skin wound within 3 days as compared to 12 days of usual contraction-based healing processes in rodents. From in vitro studies, the accelerated skin wound healing was attributed to electric field-facilitated fibroblast migration, proliferation, and transdifferentiation. This self-powered electric-dressing modality could lead to a facile therapeutic strategy for nonhealing skin wound treatment.

Based on porous carbon nanotube/polyaniline composite (CNT/PANI) and poly(vinyl alcohol) gel, we fabricated centimeter-sized hydrocapacitors with dual functions of energy conversion and storage with an efficient low-cost method. Owning to excellent hydrophily and large specific capacitance of CNT/PANI, the hydrocapacitors can easily convert energy from water movement induced by capillarity, gravity, or air pressure difference into electricity and store the generated electricity. Especially, sandwich-like hydrocapacitors outputted large current of 1.65 mA through an external load of 100 Ω, and hydrocapacitors showed good extendibility by connecting in series. To explain the mechanism of hydrocapacitors in this work, a possible model based on capillarity and traditional streaming potential was proposed and discussed. Hydrocapacitors here also provide a reference for future integration of nanogenerators and energy storage parts.

Flexible pressure sensors possess promising applications in artificial electronic skin, intelligence robot, wearable health monitoring, flexible physiological signal sensing, etc. Herein, we design a flexible pressure sensor with robust stability, high sensitivity, and large linear pressure region on the basis of tetrafluoroethylene-hexafluoropropylene-vinylide (THV)/cyclic olefin copolymer (COC) piezoelectret nanogenerator. According to the theoretical analysis for piezoelectret nanogenerators with imbalanced charge distribution, THV and COC are utilized to promote the electric field inside the piezoelectret for output voltage enhancement. Meanwhile, the compression property of the piezoelectret nanogenerator is facilely tuned. Owing to high inner electric field and optimized compression property, the THV/COC piezoelectret nanogenerator exhibits a high sensitivity of 30 mV/kPa, which is 10 times higher than that of the traditional cellular polypropylene piezoelectret. Simultaneously, the linear pressure region reaches 150 kPa with excellent linearity ( R 2 = 0.99963). The device is demonstrated to realize wearable pressure sensing with a wide pressure range from finger typing to fist hammering. This study presents a fabrication strategy for piezoelectret nanogenerators with high sensitivity and large linear pressure region, paving the way for development of wearable and flexible pressure sensing networks.

In this work, a new approach to modifying poly(dimethylsiloxane) (PDMS) as a negative triboelectric material using graphene oxide (GO) and a sodium dodecyl sulfate (SDS) surfactant was reported. A porous PDMS@GO@SDS composite triboelectric nanogenerator (TENG) could deliver an output voltage and current of up to 438 V and 11 μA/cm 2 , respectively. These values were 3-fold higher than those of the flat PDMS. The superior performance is attributed to the intensified negative charges on PDMS from the oxygen functional groups of GO and anionic head groups of the SDS molecules. The outstanding performance and straightforward, low-cost fabrication process of the PDMS@GO@SDS TENG would be beneficial for the further development of powerful NGs integrated into wearable electronics and self-charging power cells.

We demonstrate a thermo-magneto-electric generator (TMEG) based on second-order phase transition of soft magnetic materials that provides a promising pathway for scavenging low-grade heat. It takes advantage of the cyclic magnetic forces of attraction and repulsion arising through ferromagnetic-to-paramagnetic phase transition to create mechanical vibrations that are converted into electricity through piezoelectric benders. To enhance the mechanical vibration frequency and thereby the output power of the TMEG, we utilize the nonlinear behavior of piezoelectric cantilevers and enhanced thermal transport through silver (Ag) nanoparticles (NPs) applied on the surface of a soft magnet. This results in large enhancement of the oscillation frequency reaching up to 9 Hz (300% higher compared with that of the prior literature). Optimization of the piezoelectric beam and Ag NP distribution resulted in the realization of nonlinear TMEGs that can generate a high output power of 80 μW across the load resistance of 0.91 MΩ, which is 2200% higher compared with that of the linear TMEG. Using a nonlinear TMEG, we fabricated and evaluated self-powered temperature-mapping sensors for monitoring the thermal variations across the surface. Combined, our results demonstrate that nonlinear TMEGs can provide additional functionality including temperature monitoring, thermal mapping, and powering sensor nodes.

Advances in mobile networks and low-power electronics have driven smart mobile medical devices at a tremendous pace, evoking increased interest in household healthcare, especially for those with cardiovascular or respiratory disease. Thus, flexible battery-free pressure sensors, with great potential for monitoring respiration and heartbeat in a smart way, are urgently demanded. However, traditional flexible battery-free pressure sensors for subtle physiological signal detecting are mostly tightly adhered onto the skin instead of working under the pressure of body weight in a noncontact mode, as the low sensitivity in the high-pressure region can hardly meet the demands. Moreover, a hollow microstructure (HM) with higher deformation than solid microstructures and great potential for improving the pressure sensitivity of self-powered sensors has never been investigated. Here, for the first time, we demonstrated a noncontact heartbeat and respiration monitoring system based on a flexible HM-enhanced self-powered pressure sensor, which possesses the advantages of low cost, a high dynamic-pressure sensitivity of 18.98 V·kPa -1 , and a wide working range of 40 kPa simultaneously. Specific superiority of physiological detection under a high pressure is also observed. Continuous reliable heartbeat and respiration information is successfully detected in a noncontact mode and transmitted to a mobile phone.

Amorphous KNbO 3 (KN) film containing KN nanocrystals was grown on TiN/SiO 2 /Si substrate at 350 °C. This KN film showed a dielectric constant (ε r ) and a piezoelectric strain constant (d 33 ) of 43 and 80 pm/V at 10 V, respectively, owing to the existence of KN nanocrystals. Piezoelectric nanogenerators (PNGs) were fabricated using KN films grown on the TiN/polyimide/poly(ethylene terephthalate) substrates. The PNG fabricated with the KN film grown at 350 °C showed an open-circuit output voltage of 2.5 V and a short-circuit current of 70 nA. The KN film grown at 350 °C exhibited a bipolar resistive switching behavior with good reliability characteristics that can be explained by the formation and rupture of the oxygen vacancy filaments. The KN resistive random access memory device powered by the KN PNG also showed promising resistive switching behavior. Moreover, the KN film shows good biocompatibility. Therefore, the KN film can be used for self-powered biomedical devices.

We report the development of a piezopotential-programmed nonvolatile memory array using a combination of ion gel-gated field-effect transistors (FETs) and piezoelectric nanogenerators (NGs). Piezopotentials produced from the NGs under external strains were able to replace the gate voltage inputs associated with the programming/erasing operation of the memory, which reduced the power consumption compared with conventional memory devices. Multilevel data storage in the memory device could be achieved by varying the external bending strain applied to the piezoelectric NGs. The resulting devices exhibited good memory performance, including a large programming/erasing current ratio that exceeded 10 3 , multilevel data storage of 2 bits (over 4 levels), performance stability over 100 cycles, and stable data retention over 3000 s. The piezopotential-programmed multilevel nonvolatile memory device described here is important for applications in data-storable electronic skin and advanced human-robot interface operations.

Piezoelectric and triboelectric nanogenerators have been developed as rising energy-harvesting devices in the past few years to effectively convert mechanical energy into electricity. Here, a novel hybrid piezo/triboelectric nanogenerator based on BaTiO 3 NP/PDMS composite film was developed in a simple and low-cost way. The effects of the BTO content and polarization degree on the output performance were systematically studied. The device with 20 wt % BTO in PDMS and a 100-μm-thick film showed the highest output power. We also designed three measurement modes to record hybrid, triboelectric, and piezoelectric outputs separately with a simple structure that has only two electrodes. The hybrid output performance is higher than the tribo- and piezoelectric performances. This work will provide not only a new way to enhance the output power of nanogenerators, but also new opportunities for developing built-in power sources in self-powered electronics.

Highly conductive n-type Bi 2 Te 3 films on a flexible substrate were prepared via electrodeposition followed by a transfer process using an adhesive substrate. The growth of the Bi 2 Te 3 crystals was precisely controlled by an electrochemical deposition potential (V dep ), which was critical to the preferred orientation of the crystal growth along the (110) direction and thus to the properties of a flexible thermoelectric generator (FTEG). A Bi 2 Te 3 film prepared under V dep of 0.02 V showed high electrical conductivity (691 S cm -1 ) with a maximum power factor of 1473 μW m -1 K -2 , which is the highest among the Bi 2 Te 3 films prepared by the electrodeposition methods. As-prepared FTEG was bendable, showing only a small resistance change after 300 repeated bending cycles. Combined with the n-type Bi 2 Te 3 FTEG, a prototype p-n-type flexible thermoelectric (pn-FTEG) was prepared using p-type poly(3,4-ethylene dioxythiophene)s. The pn-FTEG (5-couples) generated an output voltage of 5 mV at ΔT = 12 K with high output power of 56 nW (or 105 nWg -1 ). These results indicate that the FTEG can reproducibly work well in a bent state and has high application potential for harvesting thermal energy from curved sources such as human body temperature.