Self-powered Electronic Devices Research Articles

Two-dimensional Be2P4 as a promising thermoelectric material and anode for Na/K-ion batteries.

Incredibly effective and flexible energy conversion and storage systems hold great promise for portable self-powered electronic devices. Owing to their large surface area, exceptional atomic structures, superior electrical conductivity and good mechanical flexibility, two-dimensional (2D) materials are recognized as an attractive option for energy conversion and storage application. In this work, we examined the stability, electronic, thermoelectric and electrochemical aspects of a novel 2D Be2P4 monolayer by adopting density functional theory (DFT). The Be2P4 monolayer exhibits a direct semiconductor gap of 0.9 eV (HSE06), large Young's modulus (∼198 GPa), high carrier mobility (∼104 cm2 V-1 s-1) and a low excitonic binding energy of 0.11 eV. Our calculated findings suggest that Be2P4 shows a lattice thermal conductivity of 1.02 W m K-1 at 700 K, resulting in moderate thermoelectric performance (ZT ∼ 0.7), encouraging its use in thermoelectric materials. In addition, a higher adsorption energy of -2.28 eV (-2.52 eV) and less diffusion barrier of 0.22 eV (0.17 eV) for Na(K)-ion batteries promote fast ion transport in the Be2P4 monolayer. This material also shows a high specific capacity and superior energy density of 8460 W h kg-1 (8883 W h kg-1) for Na(K)-ion batteries. Thus, our results offer insightful information for investigating potential thermoelectric and flexible anode materials based on the Be2P4 monolayer.

High Performance Piezoelectric Nanogenerators Based on Polyvinylidene Fluoride-Graphene Nanoribbon Composite Thin Films.

In this study, a highly efficient, sensitive, and lightweight piezoelectric nanogenerator (PENG) is developed using graphene nanoribbons (GNRs) incorporated into the polyvinylidene fluoride (PVDF) matrix. Unzipping multi-walled carbon nanotubes is an effective and scalable strategy for synthesizing graphene nanoribbons. The synthesized GNRs are employed to prepare nanometer-scale piezoelectric polymer composite films showing higher piezoelectric performance than neat PVDF. The impact of GNR concentration in the PVDF matrix on the electroactive phase content and piezoelectric properties of the composites is systematically investigated. X-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR) analysis demonstrate an increase in the electroactive β and γ phases of PVDF by incorporating GNRs in the composites. With the optimized concentration of GNRs (1 wt%), the fabricated piezoelectric device can generate open-circuit voltage and an output power density of 26V and 16.52 µWcm2, respectively. It is also found that the PVDF-GNR 1 nanogenerator can be used to generate electrical power by converting mechanical energy from different human activities such as wrist bending, palm tapping, and toe tapping. The findings indicate that (PVDF-GNR 1) PENGcan be applied in self-powered portable and wearable electronic devices.

Development of Highly Flexible Piezoelectric PVDF-TRFE/Reduced Graphene Oxide Doped Electrospun Nano-Fibers for Self-Powered Pressure Sensor.

The demand for self-powered, flexible, and wearable electronic devices has been increasing in recent years for physiological and biomedical applications in real-time detection due to their higher flexibility and stretchability. This work fabricated a highly sensitive, self-powered wearable microdevice with Poly-Vinylidene Fluoride-Tetra Fluoroethylene (PVDF-TrFE) nano-fibers using an electrospinning technique. The dielectric response of the polymer was improved by incorporating the reduced-graphene-oxide (rGO) multi-walled carbon nano-tubes (MWCNTs) through doping. The dielectric behavior and piezoelectric effect were improved through the stretching and orientation of polymeric chains. The outermost layer was attained by chemical vapor deposition (CVD) of conductive polymer poly (3,4-ethylenedioxythiophene) to enhance the electrical conductivity and sensitivity. The hetero-structured nano-composite comprises PVDF-TrFE doped with rGO-MWCNTs over poly (3,4-ethylenedioxythiophene) (PEDOT), forming continuous self-assembly. The piezoelectric pressure sensor is capable of detecting human physiological vital signs. The pressure sensor exhibits a high-pressure sensitivity of 19.09 kPa-1, over a sensing range of 1.0 Pa to 25 kPa, and excellent cycling stability of 10,000 cycles. The study reveals that the piezoelectric pressure sensor has superior sensing performance and is capable of monitoring human vital signs, including heartbeat and wrist pulse, masticatory movement, voice recognition, and eye blinking signals. The research work demonstrates that the device could potentially eliminate metallic sensors and be used for early disease diagnosis in biomedical and personal healthcare applications.

Innovative Integration of Triboelectric Nanogenerators into Signature Stamps for Energy Harvesting, Self-Powered Electronic Devices, and Smart Applications

In this manuscript, we present a novel approach for integrating Triboelectric Nanogenerators (TENGs) into signature stamps, termed Stamp TENG (S-TENG). We have modified a commercially available stamp holder to integrate triboelectric layers for multiple applications like effective energy harvesting, sensing, and embedded electronics for data prediction. S-TENG has been further explored in remote monitoring systems for elderly individuals and for gathering real-time statistics regarding persons or events at specific locations. The S-TENG is fabricated using FEP and Al as functional layers. It demonstrates an output voltage of 310 V, a current of 165 μA, and a power density of 14.8 W/m2. The simplicity of the S-TENG’s design is noteworthy. Its ability to generate energy through simple, repetitive stamping actions, which anyone can perform without specialized training, stands out as a key feature. The device is also designed for ease of use, being handheld and user-friendly. Its flexible and adaptable structure ensures that individuals with varying physical capabilities can comfortably operate it. An impressive capability of the TENG is its ability to illuminate 320 LEDs with each stamp press momentarily. Furthermore, using energy management circuits, the S-TENG can power small electronic gadgets such as digital watches and thermometers for a few seconds. In addition, when integrated with electronics, the S-TENG shows great potential in data prediction for various practical applications.

Supercapacitors and triboelectric nanogenerators based on electrodes of greener iron nanoparticles/carbon nanotubes composites

The development of supporting materials based on carbon nanotubes (CNTs) impregnated with iron nanoparticles via a sustainable and green synthesis employing plant extract of Punica granatum L. leaves was carried out for the iron nanoparticle modification and the following impregnation into the carbon nanotubes composites (CNT-Fe) that were also coated with polypyrrole (CNT-Fe + PPy) for use as electrode for supercapacitor and triboelectric nanogenerators. The electrochemical characterization of the materials by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) assays revealed that the CNT-Fe + PPy gave rise to better performance due to the association of double-layer capacitance behavior of carbon derivative in association with the pseudocapacitance contribution of PPy resulting in an areal capacitance value 202 mF/ cm2 for the overall composite. In terms of the application of electrodes in triboelectric nanogenerators, the best performance for the composite of CNT-Fe + PPy was 60 V for output voltage and power density of 6 μW/cm2. The integrated system showed that the supercapacitors can be charged directly by the nanogenerator from 0 to 42 mV in 300 s. The successful green synthesis of iron nanoparticles on CNT and further PPy coating provides a feasible method for the design and synthesis of high-performance SCs and TENGs electrode materials. This work provides a systematic approach that moves the research front forward by generating data that underpins further research in self-powered electronic devices.

A high performance triboelectric nanogenerator using assembled sugar naphthalimides for self-powered electronics and sensors

A new class of N-glycosyl naphthalimide ricinoleate (NGNR) amphiphiles were generated using environmentally friendly reaction conditions in good yields. To investigate the potential applications of NGNR amphiphiles within the realm of supramolecular materials, molecular self-assembly experiments were conducted extensively across a diverse range of solvents and oils and observed the gel formation. Molecular-level interactions and assembly patterns were investigated by employing FTIR, SAXRD, UV–vis, and fluorescence spectroscopy, and a plausible assembly mechanism was proposed. The morphology of the supramolecular architecture was identified by scanning electron microscopy. Additionally, rheological studies provided insight into these soft materials' strength and processability. Further, in the process of fabricating a triboelectric nanogenerator (TENG) device, silicone rubber serves as an electron acceptor and assembled NGNR serves as an electron donor. The developed TENG demonstrated a significant improvement in performance over TENG made with amorphous NGNR, with output voltage, current, and power density of 410 V, 100 µA, and 5.1 W/m2, respectively, highlighting the importance of the assembly process. Furthermore, TENG is used to continuously power up small electronic device (calculator), which is useful in building self-powered electronic devices. Lastly, due to its high sensitivity and stability, the TENG was used to detect the humidity of the environment in the food processing, textile, and agriculture sectors. The change in TENG response is notably significant up to 70 % relative humidity (RH). This work showcases the development of self-powered humidity sensors.

Finite Element Analysis and Design of a Flexible Thermoelectric Generator with a Rhombus Gap Structure.

Flexible thermoelectric generators (f-TEGs) offer an opportunity to realize wearable, self-powered electronic devices. A typical f-TEG consists of flexible electrodes and rigid thermoelectric (TE) legs in a flexible package. In the realm of f-TEGs utilizing flexible electrodes and TE cuboids, our unwavering objective lies in the attainment of enhanced flexibility and elevated energy conversion efficiency. In this paper, we employ a quasi-three-dimensional thermal model to design an f-TEG with a rhombus gap structure (E/A-RhTEG) with its optimized performance validated by simulation and experiment. Additionally, the lateral and vertical thermal resistances are introduced to further explain the optimizing principle in the f-TEG's output performance. Compared with the conventional TEG with a rectangular air gap structure (E/A-ReTEG), E/A-RhTEG demonstrates improved energy conversion efficiency to some extent. Simulation results indicate that the output power and energy conversion efficiency of a 25-np-pair E/A-RhTEG at a 30 K temperature gradient reach 8.45 mW and 2.55%, which represent a performance improvement of 3.09 and 6.28%, respectively, compared to E/A-ReTEG. To further elucidate the optimization principle in the performance of f-TEGs, additional considerations are given to the lateral and vertical resistances. In this study, E/A-RhTEG comprising 25 np pairs is fabricated utilizing TE cuboids. Experimental findings indicate that E/A-RhTEG exhibits a voltage output of 127.07 mV when subjected to a temperature difference of 30 K, which demonstrates a performance enhancement of 4.06% compared to E/A-ReTEG. Furthermore, this study also demonstrates its implementation when wrapped around a curved surface and successfully achieves a self-powered device system after device performance optimization.

Highly Semiconducting One-Dimensional Porous ZnO Nanorod Array Nanogenerators for Mechanical Energy Harvesting Functions

The development of energy harvesters based on inexpensive inorganic materials has attracted considerable attention to envisage next-generation self-powered electronic devices. In this work, we presented surface modification of ZnO nanorods (NRs) by thermochemical reaction using photoresist (PR) as an etching source. The morphological and microstructural properties of surface-etched ZnO NRs (M: ZnO) were systematically studied in detail through SEM and HRTEM. The morphological results show that the surface-etched NRs possess nanofiber-like porous structures and are penetrated throughout the NRs with high surface area. We fabricated triboelectric nanogenerators (TENG) using M: ZnO NRs with poly (dimethylsiloxane) (PDMS) as negative triboelectric material and mica as positive triboelectric material. The prepared M: ZnO NR TENG successfully delivered an output voltage of up to 20 V and a current density of 3.2 μA cm−2, which is ∼1.5 times higher than those observed for smooth ZnO NRs, respectively. The prepared M: ZnO NR TENG device can be able to lit 24 red light-emitting diodes (LEDs) as the power source. Finally, to demonstrate the practical applications of M: ZnO NR TENG, it was attached to the human body (elbow, knee, wrist, and heel) and efficiently harvested the energy from daily human activities.

One-dimensional KNN micro rods doping to facilitate the energy conversion performance of a KNN MRs/P(VDF-TrFE) composite

Piezoelectric self-powered electronic devices can convert ambient mechanical vibrations into electrical energy in an environmentally friendly manner, significantly alleviating the scarcity of non-renewable sources. This work prepares an one-dimensional potassium sodium niobate micro rods (1D KNN MRs) using the molten salt - topological chemical reaction method, showing the significant advantages over 0-dimension (0D) nanoparticles due to its anisotropy. Simultaneously, KNN MRs are introduced into poly (vinylidene fluoride-trifluoroethylene) to form a KNN MRs/P(VDF-TrFE) piezoelectric composite, effectively facilitating the piezoelectric β-phase in P(VDF-TrFE) film, and contributing to a high remnant polarization (Pr ∼12.3 μC/cm2) at 125 MV/m and a high piezoelectric constant (d33 = −28 pC/N). Interestingly, a piezoelectric sensor assembled by KNN MRs/P(VDF-TrFE) composite shows a considerable piezoelectric output of 17.6 V at a scene of 2.5 MPa stress, offering a novel route for designing the optimum ceramic/polymer combinations suitable for mechanical energy conversion and energy harvesting.

Recent progress in piezoelectric thin films as self-powered devices: material and application

Piezoelectric materials have become a key component in sensors and actuators in many industrial fields, such as energy harvesting devices, self-powered structures, biomedical devices, nondestructive testing, owing to the novel properties including high piezoelectric coefficient and electromechanical coupling factors. Piezoelectric thin films integrated on silicon substrates are widely investigated for their high performance and low manufacturing costs to meet the requirement of sensor networks in internet of things (IoT). The aim of this work is to clarify the application and design structure of various piezoelectric thin films types, synthesis methods, and device processes. Based on latest literature, the process of fabricating thin film sensors is outlined, followed by a concise overview of techniques used in microelectromechanical systems (MEMS) processing that can integrate more complex functions to obtain relevant information in surrounding environment. Additionally, by addressing piezoelectric thin films sensors as a cutting-edge technology with the ability to produce self-powered electronic devices, this work delivers incisive conclusions on all aspects of piezoelectric sensor related features. A greater understanding of piezoelectricity is necessary regarding the future development and industry challenges.

Compatible interface based self-charging fiber for wearable electronic

With the rapid development of wearable devices, there is an increasing demand for flexible, eco-friendly, and reliable power sources. The self-charging energy system, which integrates energy collection and storage, has emerged as one of the most promising sustainable energy sources, with an urgent need for its application and implementation. In this work, we proposed a fiber-shaped self-charging system based on supercapacitor (SC) and triboelectric nanogenerator (TENG). For the supercapacitor, a silver-decorated carbon fiber with PEDOT: PSS coated is used as the positive electrode, while carbon nanotube film/Fe2O3/MoS2 serves as the negative electrode. The assembled coaxial structure not only shortens the distance between the positive and negative electrodes, effectively improving charge transfer efficiency, but also ensures the flexibility and mechanical stability of the device. The designed supercapacitor exhibited a capacitance of 213.3 mF cm−2 and demonstrated excellent stability of 92 % retention rate even after 5000 cycles. Moreover, the negative electrode of the supercapacitor also serves as a compatible interface for the TENG, with silicone rubber coating acting as the friction layer, forming a single-electrode structure. This coaxial structure with a compatible interface allows for higher efficiency in charge capture and transfer, doubling the charging efficiency compared to incompatible structures, while also ensuring flexibility, making it more suitable for wearable applications. By weaving the TENG, it exhibits an open-circuit voltage of 150 V, a short-circuit current of 6 μA, and a high power density of 900 mW cm−2. In addition, it can also serve as a self-powered sensor, capable of accurately detecting human motion and current conditions. This research proposes an effective compatible interface architecture promising application prospect for advancing sustainable development of self-powered wearable electronic devices.

Moisture-driven energy generation by vertically structured polymer aerogel on water-collecting gel

In the realm of energy harvesting, free-standing, film-type, moisture-driven electricity generators (MEGs) based on polymer hydrogels with moisture-retaining capability are promising as a convenient and practical power source, making them potentially suitable for various self-powered, wearable, and patchable electronic devices. Their performance is, however, substantially degraded under low-humidity (<40%) conditions owing to the limited water supply to the device. This study presents a high-performance film-type MEG that functions at a low humidity of 20%. The MEG is based on an ion-selective polymer aerogel as an electricity-generating layer, constructed on a water-collecting gel as a water reservoir. The water-collecting gel in the bi-layered MEG absorbs moisture even under low-humidity conditions and efficiently delivers moisture to the electricity-generating aerogel layer. The energy-harvesting ability of the electricity-generating aerogel layer is further facilitated by its characteristic vertical microstructure, which comprises aerogel pores directionally grown on the frozen water-collecting gel during the freeze-drying process. The low humidity-tolerant MEG generated a stable open-circuit voltage of 1.1 V for more than 500 min even under dry conditions (20% relative humidity). Various self-powered electronic applications are demonstrated with the low-humidity-tolerant, bi-layered MEGs in dry environments. This study provides new insights for designing future MEGs for operation in low-humidity environments, further facilitating the development of green and sustainable power generation.

Ultra-stretchable and anti-freezing ionic conductive hydrogels as high performance strain sensors and flexible triboelectric nanogenerator in extreme environments

Conductive hydrogels have shown promising applications in a variety of portable smart wearable electronics and flexible sensors due to their high flexibility, stretchability, adjustable mechanical properties and excellent electrical conductivity. However, most of the current hydrogel-based flexible strain sensors and portable triboelectric nanogenerator (TENG) generally suffer from low stretchability/flexibility, poor mechanical properties, weak low-temperature tolerance and low power output. Herein, a multifunctional ionic conductive hydrogel (PPAVC-BA) with ultra-stretchability (∼1750%), high transparency (85%), high electrical conductivity (13.7 mS/cm), and outstanding anti-freezing properties (below −80°C without freezing). The strain sensor assembled from the PPAVC-BA hydrogel shows high sensitivity (GF=4.43) and ultra-wide sensing detection range (0%-1100%) as well as fast response time. Based on these properties, the PPAVC-BA hydrogel strain sensor can accurately recognize different joint movements of the human body as well as weak muscle beats. In addition, the PPAVC-BA hydrogel-based TENG (PPAVC-BA-TENG) exhibits excellent electrical output performance, with an open circuit voltage (Voc) of about 420 V, a short circuit current (Isc) of 23 μA, a short-circuit transfer charge (Qsc) of 112 nC and a maximum power density of 2246.03 mW/m2, which allows it to power small electronic devices. This PPAVC-BA-TENG also shows outstanding tensile performance and can output stable electrical signals at 200% strain. Impressively, the PPAVC-BA-TENG exhibits good electrical output performance even at low temperature of −50°C and high temperature of 80°C. The flexible strain sensors and stretchable TENG for high performance and multifunctionality reported in this work provide viable references in the development of motion detection, energy harvesting and self-powered electronic devices.

Silane-modified MXene/PVA hydrogel for enhanced streaming vibration potential in high-performance flexible triboelectric nanogenerators

To meet the growing demand for flexible, self-powered, and portable electronic devices—vital for advancing soft robots, electronic skins, and energy-harvesting technologies—we've refined our approach to creating polyvinyl alcohol (PVA) modulating polyethylene glycol (PEG) to facilitate cation movement along polymer chains, significantly boosting the hydrogel's performance in triboelectric nanogenerators (PPh TENG), which is further enhanced by adding with layered Ti3C2 nanosheets, serving as ionic conductors. These nanosheets introduce an efficient electrostatic mechanism known as the streaming vibration potential (SVP), significantly augmenting the device's functionality. Moreover, we used 3-chloropropyltrimethoxysilane (CPTMS) and 1 H, 1 H, 2 H, 2 H-perfluorooctyltriethoxysilane (FOTS) to modify the surface of MXene nanosheets to fabricate Cl-MXene and F-MXene hydrogel TENGs, as named by Cl-MPPh and F-MPPh TENGs, respectively. The SVP effect is enhanced by these modified MXene nanosheets in the hydrogel, which is more substantial than unmodified MXene nanosheets. This is attributed to the higher charge density in the electric double layer formed between the MXene nanosheets and water. The Cl-MPPh and F-MPPh TENGs demonstrate open-circuit voltages of 190 V and 212 V, respectively. Our theoretical calculations show a marked increase in the distribution of electric potential. This increase occurs on both sides of the MXene nanosheets as water molecules move through them. The F-MPPh TENG exhibits exceptional sensitivity to mechanical stimuli, which holds promising potential for integration into motion sensors designed to monitor human body movements, including the bending of elbows and wrists.

Noncovalent cross-linked engineering hydrogel with low hysteresis and high sensitivity for flexible self-powered electronics

In this study, the hydrogel network was reinforced by covalent-like hydrogen bonding, and the strong binding ability of boron–nitrogen coordination served as the main driving force. Among them, acrylamide (AM) and 3-acrylamidophenylboronic acid (AAPBA) were the main body, and the numerous hydroxyl groups in the trehalose (Treh) molecule and other polymer groups formed strong hydrogen bonding interactions to improve the mechanical properties of the PAM/PAAPBA/Treh (PAAT) hydrogel and ensured the simplicity of the synthesis process. The hydrogel possessed high strain at break (1239%), stress (64.7 kPa), low hysteresis (100% to 500% strain, corresponding to dissipation energy from 1.37 to 7.80 kJ/m3), and outstanding cycling stability (retained more than 90% of maximum stress after 200 tensile cycles). By integrating carbon nanotubes (CNTs) into PAAT hydrogel (PAATC), the PAATC hydrogel with excellent strain response performance was successfully constructed. The PAATC conductive hydrogel exhibited high sensitivity (gauge factor (GF) = 10.58 and sensitivity (S) = 0.304 kPa−1), wide strain response range (0.5%–1000%), fast response time (450 ms), and short recovery time (350 ms), excellent fatigue resistance, and strain response stability. Furthermore, the PAATC-based triboelectric nanogenerator (TENG) displayed outstanding energy harvesting performance, which shows its potential for application in self-powered electronic devices.

Optimizing Piezoelectric Energy Harvesting from Mechanical Vibration for Electrical Efficiency: A Comprehensive Review

In the current era, energy resources from the environment via piezoelectric materials are not only used for self-powered electronic devices, but also play a significant role in creating a pleasant living environment. Piezoelectric materials have the potential to produce energy from micro to milliwatts of power depending on the ambient conditions. The energy obtained from these materials is used for powering small electronic devices such as sensors, health monitoring devices, and various smart electronic gadgets like watches, personal computers, and cameras. These reviews explain the comprehensive concepts related to piezoelectric (classical and non-classical) materials, energy harvesting from the mechanical vibration of piezoelectric materials, structural modelling, and their optimization. Non-conventional smart materials, such as polyceramics, polymers, or composite piezoelectric materials, stand out due to their slender actuator and sensor profiles, offering superior performance, flexibility, and reliability at competitive costs despite their susceptibility to performance fluctuations caused by temperature variations. Accurate modeling and performance optimization, employing analytical, numerical, and experimental methodologies are imperative. This review also furthers research and development in optimizing piezoelectric energy utilization, suggesting the need for continued experimentation to select optimal materials and structures for various energy applications.

Wearable All-Fabric Hybrid Energy Harvester to Simultaneously Harvest Radiofrequency and Triboelectric Energy.

Distributed micro-energy harvesting devices offer the flexibility, sustainability, and multi-scenario applicability that will be critical to wearable electronic products in the Internet of Things. The radiofrequency and triboelectric (RF-TE) hybrid energy harvester (HEH) concept and prototype is presented for the first time, to simultaneously capture the energy from ambient electromagnetic waves and biological motions. The proposed hybrid energy harvesting system consists of a wearable rectenna, a triboelectric nanogenerator (TENG), and a power management circuit (PMC). Among them, the all-fabric rectenna exhibits good impedance matching characteristics in the ISM frequency. The flexible TENG unit can generate a maximum power density of 0.024µWcm-2. The designed multifunctional fabric-based PMC can considerably enhance the controllability of harvested hybrid energy. Additionally, a normalizable fabric circuit board quasi surface mount technology (FCB-SMT) is proposed to integrate all modules on the same fabric substrate in one step, making the entire system superior mechanical robustness. The proposed wearable fabric-based RF-TE hybrid energy harvester is capable of successfully driving consumer electronics (such as sensors, watches, etc.). It provides a new energy solution strategy for self-powered wearable electronic devices and is anticipated to encourage the efficient utilization of renewable energy.

Recent Advances in Flexible Wearable Technology: From Textile Fibers to Devices.

Smart textile fabrics have been widely investigated and used in flexible wearable electronics because of their unique structure, flexibility and breathability, which are highly desirable with integrated multifunctionality. Recent years have witnessed the rapid development of textile fiber-based flexible wearable devices. However, the pristine textile fibers still can't meet the high standards for practical flexible wearable devices, which calls for the development of some effective modification strategies. In this review, we summarize the recent advances in the flexible wearable devices based on the textile fibers, putting special emphasis on the design and modifications of textile fibers. In addition, the applications of textile fibers in various fields and the critical role of textile fibers are also systematically discussed, which include the supercapacitors, sensors, triboelectric nanogenerators, thermoelectrics, and other self-powered electronic devices. Finally, the main challenges that should be overcome and some effective solutions are also manifested, which will guide the future development of more effective textile fiber-based flexible wearable devices.

Boosted triboelectric output performance in g-C3N4 embedded P(VDF-TrFE) composite via a coupling of photocarrier and ferroelectric dipole

Innovative material design is one of the most plausible routes to sufficiently enhance triboelectric outputs for self-powered electronic devices. Herein, we reported a g-C3N4 embedded P(VDF-TrFE) composite as a strong candidate for boosting the output power via simultaneous harvesting of mechanical and light energies. Visible light-responsive g-C3N4 nanosheets are chemically bonded to the ferroelectric P(VDF-TrFE) polymer and increase the ferroelectric polarization and dielectric constant of the composite. Kelvin probe force microscopy and photoluminescence measurements reveal that the enhanced triboelectric output is related to the increased workfunction, the reduced recombination rate of electron-hole pairs, and the band bending-induced photocarrier movement. The up-poled g-C3N4@P(VDF-TrFE) composite-based photoactive triboelectric nanogenerator (PA-TENG) generates a power (power density) of 2.0 mW (0.125 mW/cm2) under a blue light illumination, which is 10 times larger than PA-TENG under a dark condition and 54 times larger than bare P(VDF-TrFE)-based TENG. The output power is continued for at least up to 1.5 months in ambient conditions and is enough to power light-emitting diodes, a thermo-hygrometer, and a digital watch, which would be quite useful for individuals in the dark underground. This work provides a novel approach to boost the triboelectric output via a coupling of photocarrier and ferroelectric dipole and a useful hint to realize self-powered small electronics for safety issues in dark environments like caves and tunnels.

A method to design contact-separation triboelectric nanogenerators (CS-TENG) for efficient vibration energy harvesting

The necessity of self-powered electronic devices for sensing and communication (IoT) has led to the development of methods for energy harvesting. Triboelectric Nanogenerators (TENG) are promising for harvesting mechanical energy from the environment, in particular energy from vibrations. The optimization of the efficiency of energy transfer from vibration energy into electrical energy is a crucial problem. This paper deals with a contact-separation TENG (CS-TENG) devoted to vibration harvesting. Optimization was carried out taking into account all the parameters of the TENG connected to a load resistance. The moving electrode of the CS-TENG was supposed to be sinusoidal. After transformation into dimensionless parameters and variables intervening in the problem, it appeared that the electrical dynamics of the TENG are intrinsically determined by only two dimensionless parameters. Consequently, the optimization of efficiency can be conducted in a two-dimensional space. It is shown that the maximum efficiency of a TENG permanently connected to the load resistance cannot be greater than 25%. However, the efficiency can be increased to nearly 100%, provided that a switch is used in series with the load resistance which opens and closes in synchronization with the electrode motion. The optimization method presented could be extended to design TENG energy harvesters operating in other modes and for arbitrary vibrations.