Multidiscipline Applications of Triboelectric Nanogenerators for the Intelligent Era of Internet of Things

In the era of 5G and the Internet of things(IoTs),vari-ous human-computer interaction systems based on the integration of triboelectric nanogenerators(TENGs)and IoTs technologies dem-onstrate the feasibility of sustainable and self-powered functional systems.The rapid development of intelligent applications of IoTs based on TENGs mainly relies on supplying the harvested mechanical energy from surroundings and implementing active sensing,which have greatly changed the way of human production and daily life.This review mainly introduced the TENG applications in multidisci-pline scenarios of IoTs,including smart agriculture,smart industry,smart city,emergency monitoring,and machine learning-assisted artificial intelligence applications.The challenges and future research directions of TENG toward IoTs have also been proposed.The exten-sive developments and applications of TENG will push forward the IoTs into an energy autonomy fashion.

Design and Guideline Rules for the Performance Improvement of Vertically Integrated Nanogenerator

Piezoelectric nanowires have attracted much scientific interest in the last few years because of their enhanced piezoelectric coefficients at nanometer scale, with promises of efficient mechanical energy harvesters for autonomous integrated systems. This paper presents the design and, for the first time, guideline rules, based on simple analytical expressions, to improve the performance of a mechanical energy harvester integrating vertical ZnO piezoelectric nanowires. Additional simulations were carried out to account more realistically for device geometry. The authors discuss the prospects of such an approach, based on design and material improvement.

Piezotronic neuromorphic devices:principle,manufacture,and applications

With the arrival of the era of artificial intelligence(AI)and big data,the explosive growth of data has raised higher demands on computer hardware and systems.Neuromorphic techniques inspired by biological nervous systems are expected to be one of the approaches to breaking the von Neumann bottleneck.Piezotronic neuromorphic devices modulate electrical transport characteristics by piezopotential and directly associate external mechanical motion with electrical output signals in an active manner,with the capability to sense/store/process information of external stimuli.In this review,we have presented the piezotronic neuromorphic devices(which are classified into strain-gated piezotronic transistors and piezoelectric nanogenerator-gated field effect transistors based on device structure)and discussed their operating mechanisms and related manufacture techniques.Secondly,we summarized the research progress of piezotronic neuromorphic devices in recent years and provided a detailed discussion on multifunctional applications,including bionic sensing,information storage,logic computing,and electrical/optical artificial synapses.Finally,in the context of future development,challenges,and perspectives,we have discussed how to modulate novel neuromorphic devices with piezotronic effects more effectively.It is believed that the piezotronic neuromorphic devices have great potential for the next generation of interactive sensation/memory/computation to facilitate the development of the Internet of Things,AI,biomedical engineering,etc.

Advances in Triboelectric Nanogenerators for Blue Energy Harvesting and Marine Environmental Monitoring

Blue energy,which includes rainfall,tidal current,wave,and water-flow energy,is a promising renewable resource,although its exploitation is limited by current technologies and thus remains low.This form of energy is mainly harvested by electromagnetic generators(EMGs),which generate electricity via Lorenz force-driven electron flows.Triboelectric nano genera tors(TENGs)and TENG networks exhibit superiority over EMGs in low-frequency and high-entropy energy harvesting as a new approach for blue energy harvesting.A TENG produces electrical outputs by adopting the mechanism of Maxwell’s displacement current.To date,a series of research efforts have been made to optimize the structure and performance of TENGs for effective blue energy harvesting and marine environmental applications.Despite the great progress that has been achieved in the use of TENGs in this context so far,continuous exploration is required in energy conversion,device durability,power management,and environmental applications.This review reports on advances in TENGs for blue energy harvesting and marine environmental monitoring.It introduces the theoretical foundations of TENGs and discusses advanced TENG prototypes for blue energy harvesting,including TENG structures that function in freestanding and contact-separation modes.Performance enhancement strategies for TENGs intended for blue energy harvesting are also summarized.Finally,marine environmental applications of TENGs based on blue energy harvesting are discussed.

Biodegradable, Super-Strong, and Conductive Cellulose Macrofibers for Fabric-Based Triboelectric Nanogenerator

Electronic fibers used to fabricate wearable triboelectric nanogenerator(TENG) for harvesting human mechanical energy have been extensively explored. However, little attention is paid to their mutual advantages of environmental friendliness, mechanical properties, and stability. Here, we report a super-strong, biodegradable, and washable cellulose-based conductive macrofibers, which is prepared by wet-stretching and wet-twisting bacterial cellulose hydrogel incorporated with carbon nanotubes and polypyrrole. The cellulose-based conductive macrofibers possess high tensile strength of 449 MPa(able to lift 2 kg weights), good electrical conductivity(~ 5.32 S cm^(-1)), and excellent stability(Tensile strength and conductivity only decrease by 6.7% and 8.1% after immersing in water for 1 day). The degradation experiment demonstrates macrofibers can be degraded within 108 h in the cellulase solution. The designed fabric-based TENG from the cellulose-base conductive macrofibers shows a maximum open-circuit voltage of 170 V, short-circuit current of 0.8 μA, and output power at 352 μW, which is capable of powering the commercial electronics by charging the capacitors. More importantly, the fabric-based TENGs can be attached to the human body and work as self-powered sensors to effectively monitor human motions. This study suggests the potential of biodegradable, super-strong, and washable conductive cellulose-based fiber for designing eco-friendly fabric-based TENG for energy harvesting and biomechanical monitoring.

Fully Fabric-Based Triboelectric Nanogenerators as Self-Powered Human-Machine Interactive Keyboards

Combination flexible and stretchable textiles with self-powered sensors bring a novel insight into wearable functional electronics and cyber security in the era of Internet of Things.This work presents a highly flexible and self-powered fully fabric-based triboelectric nanogenerator(F-TENG)with sandwiched structure for biomechanical energy harvesting and real-time biometric authentication.The prepared F-TENG can power a digital watch by low-frequency motion and respond to the pressure change by the fall of leaves.A self-powered wearable keyboard(SPWK)is also fabricated by integrating large-area F-TENG sensor arrays,which not only can trace and record electrophysiological signals,but also can identify individuals’typing characteristics by means of the Haar wavelet.Based on these merits,the SPWK has promising applications in the realm of wearable electronics,self-powered sensors,cyber security,and artificial intelligences.

Self-charging power textiles integrating energy harvesting triboelectric nanogenerators with energy storage batteries/supercapacitors

Lightweight and flexible self-charging power systems with synchronous energy harvesting and energy storage abilities are highly desired in the era of the internet of things and artificial intelligences,which can provide stable,sustainable,and autonomous power sources for ubiquitous,distributed,and low-power wearable electronics.However,there is a lack of comprehensive review and challenging discussion on the state-of-the-art of the triboelectric nanogenetor(TENG)-based self-charging power textiles,which have a great possibility to become the future energy autonomy power sources.Herein,the recent progress of the self-charging power textiles hybridizing fiber/fabric based TENGs and fiber/fabric shaped batteries/supercapacitors is comprehensively summarized from the aspect of textile structural designs.Based on the current research status,the key bottlenecks and brighter prospects of self-charging power textiles are also discussed in the end.It is hoped that the summary and prospect of the latest research of self-charging power textiles can help relevant researchers accurately grasp the research progress,focus on the key scientific and technological issues,and promote further research and practical application process.

Ultralight Iontronic Triboelectric Mechanoreceptor with High Specific Outputs for Epidermal Electronics

The pursuit to mimic skin exteroceptive ability has motivated the endeavors for epidermal artificial mechanoreceptors.Artificial mechanoreceptors are required to be highly sensitive to capture imperceptible skin deformations and preferably to be self-powered,breathable,lightweight and deformable to satisfy the prolonged wearing demands.It is still struggling to achieve these traits in single device,as it remains difficult to minimize device architecture without sacrificing the sensitivity or stability.In this article,we present an all-fiber iontronic triboelectric mechanoreceptor(ITM)to fully tackle these challenges,enabled by the high-output mechano-to-electrical energy conversion.The proposed ITM is ultralight,breathable and stretchable and is quite stable under various mechanical deformations.On the one hand,the ITM can achieve a superior instantaneous power density;on the other hand,the ITM shows excellent sensitivity serving as epidermal sensors.Precise health status monitoring is readily implemented by the ITM calibrating by detecting vital signals and physical activities of human bodies.The ITM can also realize acoustic-to-electrical conversion and distinguish voices from different people,and biometric application as a noise dosimeter is demonstrated.The ITM therefore is believed to open new sights in epidermal electronics and skin prosthesis fields.

High-Efficiency Wastewater Purification System Based on Coupled Photoelectric–Catalytic Action Provided by Triboelectric Nanogenerator

It is of great importance to explore a creative route to improve the degradation e ciency of organic pollutants in wastewater.Herein,we construct a unique hybrid system by combining self-powered triboelectric nanogenerator(TENG)with carbon dots-TiO_(2)sheets doped three-dimensional graphene oxide photocatalyst(3 DGA@CDs-TNs),which can significantly enhance the degradation e ciency of brilliant green(BG)and direct blue 5 B(DB)owing to the powerful interaction of TENG and 3 DGA@CDs-TNs photocatalyst.The power output of TENG can be applied for wastewater purification directly,which exhibits a selfpowered electrocatalytic technology.Furthermore,the results also verify that TENG can replace conventional electric catalyst to remove pollutants e ectively from wastewater without any consumption.Subsequently,the unstable fragments and the plausible removal pathways of the two pollutants are proposed.Our work sheds light on the development of e cient and sustainable TENG/photocatalyst system,opening up new opportunities and possibilities for comprehensive utilization of random energy.

Human Machine Interface with Wearable Electronics Using Biodegradable Triboelectric Films for Calligraphy Practice and Correction

Letter handwriting,especially stroke correction,is of great importance for recording languages and expressing and exchanging ideas for individual behavior and the public.In this study,a biodegradable and conductive carboxymethyl chitosan-silk fibroin(CSF)film is prepared to design wearable triboelectric nanogenerator(denoted as CSF-TENG),which outputs of V_(oc)≈165 V,I_(sc)≈1.4μA,and Q_(sc)≈72 mW cm^(−2).Further,in vitro biodegradation of CSF film is performed through trypsin and lysozyme.The results show that trypsin and lysozyme have stable and favorable biodegradation properties,removing 63.1%of CSF film after degrading for 11 days.Further,the CSF-TENG-based human-machine interface(HMI)is designed to promptly track writing steps and access the accuracy of letters,resulting in a straightforward communication media of human and machine.The CSF-TENG-based HMI can automatically recognize and correct three representative letters(F,H,and K),which is benefited by HMI system for data processing and analysis.The CSF-TENG-based HMI can make decisions for the next stroke,highlighting the stroke in advance by replacing it with red,which can be a candidate for calligraphy practice and correction.Finally,various demonstrations are done in real-time to achieve virtual and real-world controls including writing,vehicle movements,and healthcare.

Epitaxial Lift-Off of Flexible GaN‑Based HEMT Arrays with Performances Optimization by the Piezotronic Effect

High-electron-mobility transistors(HEMTs)are a promising device in the field of radio frequency and wireless communication.However,to unlock the full potential of HEMTs,the fabrication of large-size flexible HEMTs is required.Herein,a large-sized(>2 cm^(2))of AlGaN/AlN/GaN heterostructure-based HEMTs were successfully stripped from sapphire substrate to a flexible polyethylene terephthalate substrate by an electrochemical lift-off technique.The piezotronic effect was then induced to optimize the electron transport performance by modulating/tuning the physical properties of two-dimensional electron gas(2DEG)and phonons.The saturation current of the flexible HEMT is enhanced by 3.15%under the 0.547%tensile condition,and the thermal degradation of the HEMT was also obviously suppressed under compressive straining.The corresponding electrical performance changes and energy diagrams systematically illustrate the intrinsic mechanism.This work not only provides in-depth understanding of the piezotronic effect in tuning 2DEG and phonon properties in GaN HEMTs,but also demonstrates a low-cost method to optimize its electronic and thermal properties.

MXene Lubricated Tribovoltaic Nanogenerator with High Current Output and Long Lifetime

Tribovoltaic nanogenerators(TVNGs)have the characteristics of high current density,low matched impedance and continuous output,which is expected to solve the problem of power supply for small electronic devices.However,wear occurrence in friction interface will seriously reduce the performance of TVNGs as well as lifetime.Here,we employ MXene solution as lubricate to improve output current density and lifetime of TVNG simultaneously,where a high value of 754 mA m^(-2)accompanied with a record durability of 90,000 cycles were achieved.By comparing multiple liquid lubricates with different polarity,we show that conductive polar liquid with MXene as additive plays a crucial role in enhancing the electrical output performance and durability of TVNG.Moreover,the universality of MXene solution is well demonstrated in various TVNGs with Cu and P-type Si,and Cu and N-GaAs as material pairs.This work may guide and accelerates the practical application of TVNG in future.

Ultra-Stable and Durable Piezoelectric Nanogenerator with All-Weather Service Capability Based on N Doped 4H-SiC Nanohole Arrays

Ultra-stable piezoelectric nanogenerator(PENG)driven by environmental actuation sources with all-weather service capability is highly desirable.Here,the PENG based on N doped 4H-SiC nanohole arrays(NHAs)is proposed to harvest ambient energy under low/high temperature and relative humidity(RH)conditions.Finite element method simulation of N doped 4H-SiC NHAs in compression mode is developed to evaluate the relationship between nanohole diameter and piezoelectric performance.The density of short circuit current of the assembled PENG reaches 313 nA cm^(-2),which is 1.57 times the output of PENG based on N doped 4H-SiC nanowire arrays.The enhancement can be attributed to the existence of nanohole sidewalls in NHAs.All-weather service capability of the PENG is verified after being treated at-80/80℃and 0%/100%RH for 50 days.The PENG is promising to be widely used in practice worldwide to harvest biomechanical energy and mechanical energy.

Scaling up blue energy harvesting:Transitioning from single generators to multiple generators

Original reference:iEnergy,2(2):93-99,2023 Droplet-based triboelectric nanogenerator(D-TENG)using liquid-solid contact electrification has been widely studied for harvesting raindrop energy and ocean energy due to its unique ability to effectively reduce friction between solids and improve durability.In 2020,a new-generation D-TENG with a“transistor-like”struc-ture was proposed,which first achieved ultra-high instantaneous power output(50 W/m2).Subsequently,D-TENG has been rapidly developed and is widely used in ocean wave energy power gener-ation and liquid-solid triboelectric power generation.Currently,although we have excellent D-TENGs to harvest energy from a single water droplet,but if multiple D-TENGs are simply connected in parallel for a large area usage,the output power of the whole power generation module will drop significantly due to the mutual influence between different individual generation units,which severely limits their applications in practice.Therefore,finding a reasonable topology to relieve the inherent constraints of D-TENGs is of great significance for realizing the large-scale rain-drop energy harvesting.

Cylindrical spiral triboelectric nanogenerator

In recent years, triboelectric nanogenerators have attracted much attention because of their unique potential in self-powered nanosensors and nanosystems. In this paper, we report a cylindrical spiral tdboelectric nanogenerator （S-TENG）, which not only can produce high electric output to power display devices, but also can be used as a self-powered displacement sensor integrated on a measurement ruler. At a sliding speed of 2.5 m/s, S-TENG can generate a short-circuit current （Isc） of 30 μA and an open-circuit voltage （Voc） of 40 V. As the power source, we fabricate a transparent and flexible hand-driven S-TENG. Furthermore, we demonstrate a self-powered S-TENG-based measuring tapeline that can accurately measure and display the pulled-out distance without the need for an extra battery. The results obtained indicate that TENG-based devices have good potential for application in self-powered measurement systems.

Contact Electrification by Quantum-Mechanical Tunneling

A simple model of charge transfer by loss-less quantum-mechanical tunneling between two solids is proposed.Te model is applicable to electron transport and contact electrifcation between e.g.a metal and a dielectric solid.Based on a one-dimensional efective-mass Hamiltonian,the tunneling transmission coefcient of electrons through a barrier from one solid to another solid is calculated analytically.Te transport rate(current)of electrons is found using the Tsu-Esaki equation and accounting for diferent Fermi functions of the two solids.We show that the tunneling dynamics is very sensitive to the vacuum potential versus the two solids conduction-band edges and the thickness of the vacuum gap.Te relevant time constants for tunneling and contact electrifcation,relevant for triboelectricity,can vary over several orders of magnitude when the vacuum gap changes by one order of magnitude,say,1˚A to 10˚A.Coulomb repulsion between electrons on the lef and right material surfaces is accounted for in the tunneling dynamics.

Scalable rolling-structured triboelectric nanogenerator with high power density for water wave energy harvesting toward marine environmental monitoring

In the context of advocating a green and low-carbon era,ocean energy,as a renewable strategic resource,is an important part of planning and building a new energy system.Triboelectric nanogenerator(TENG)arrays provide feasible and efficient routes for large-scale harvesting of ocean energy.In previous work,a spherical rolling-structured TENG with three-dimensional(3D)electrodes based on rolling motion of dielectric pellets was designed and fabricated for effectively harvesting low-frequency water wave energy.In this work,the external shape of the scalable rolling-structured TENG(SR-TENG)and internal filling amount of pellets were mainly optimized,achieving an average power density of 10.08 W∙m^(−3)under regular triggering.In actual water waves,the SR-TENG can deliver a maximum peak power density of 80.29 W∙m^(−3)and an average power density of 6.02 W∙m^(−3),which are much greater than those of most water wave-driven TENGs.Finally,through a power management,an SR-TENG array with eight units was demonstrated to successfully power portable electronic devices for monitoring the marine environment.The SR-TENGs could promote the development and utilization of ocean blue energy,providing a new paradigm for realizing the carbon neutrality goal.

Modeling and optimization of a spherical triboelectric generator

A detailed geometric analysis of spherical triboelectric nanogenerators is presented.In comparison with earlier works on spherical triboelectric generators,the general case where the moving dielectric rolls on the inside surface of the larger sphere of the TENG is discussed in terms of maximum energy harvesting.An optimization analysis of geometrical parameters allows various cases of electrode geometry,either in the form of a spherical circle,spherical ellipse,spherical rectangle,or spherical isosceles trapezium,to be solved.The analytical insight and computational effective models provided by differential geometry make the mathematical model superior compared to standard three-dimensional(3D)numerical methods.

Piezoelectric hydrogel for treatment of periodontitis through bioenergetic activation

The impaired differentiation ability of resident cells and disordered immune microenvironment in periodontitis pose a huge challenge for bone regeneration.Herein,we construct a piezoelectric hydrogel to rescue the impaired osteogenic capability and rebuild the regenerative immune microenvironment through bioenergetic activation.Under local mechanical stress,the piezoelectric hydrogel generated piezopotential that initiates osteogenic differentiation of inflammatory periodontal ligament stem cells(PDLSCs)via modulating energy metabolism and promoting adenosine triphosphate(ATP)synthesis.Moreover,it also reshapes an anti-inflammatory and pro-regenerative niche through switching M1 macrophages to the M2 phenotype.The synergy of tilapia gelatin and piezoelectric stimulation enhances in situ regeneration in periodontal inflammatory defects of rats.These findings pave a new pathway for treating periodontitis and other immune-related bone defects through piezoelectric stimulation-enabled energy metabolism modulation and immunomodulation.

3D interlocked all-textile structured triboelectric pressure sensor for accurately measuring epidermal pulse waves in amphibious environments

The performance degradation and even damage of the e-textiles caused by sweat,water,or submersion during all-weather health monitoring are the main reasons that e-textiles have not been commercialized and routinized so far.Herein,we developed an amphibious,high-performance,air-permeable,and comfortable all-textile triboelectric sensor for continuous and precise measurement of epidermal pulse waves during full-day activities.Based on the principle of preparing gas by acid-base neutralization reaction,a one-piece preparation process of amphibious conductive yarn(ACY)with densely porous structures is proposed.An innovative three-dimensional(3D)interlocking fabric knitted from ACYs(0.6 mm in diameter)and polytetrafluoroethylene yarns exhibit high sensitivity(0.433 V·kPa^(-1)),wide bandwidth(up to 10 Hz),and stability(>30,000 cycles).With these benefits,98.8%agreement was achieved between wrist pulse waves acquired by the sensor and a high-precision laser vibrometer.Furthermore,the polytetrafluoroethylene yarn with good compression resilience provides sufficient mechanical support for the contact separation of the ACYs.Meanwhile,the unique skeletonized design of the 3D interlocking structure can effectively relieve the water pressure on the sensor surface to obtain stable and accurate pulse waves(underwater depth of 5 cm).This achievement represents an important step in improving the practicality of e-textiles and early diagnosis of cardiovascular diseases.