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.

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.

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.

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.

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.

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.

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.

Flexo-photocatalysis in centrosymmetric semiconductors

The separation of photogenerated electron–hole pairs is vitally important for photocatalysis,which can be effectively promoted by polarization field.However,it only manifests in piezoelectric/pyroelectric/ferroelectric materials that have a non-centrosymmetric structure.Here,we demonstrate that the polarization enhanced photocatalysis(with wide spectra from ultraviolet(UV)light to visible light)can be achieved in centrosymmetric semiconductors,such asδ-MnO_(2) and TiO_(2) nanosheets integrated nanoflowers,by using the strain-gradient-induced flexoelectric polarization that is always overlooked in polarization-enhanced catalysis.Under ultrasonic and illumination excitation,the organic pollutants(methylene blue(MB),etc.)can be effectively degraded within 30 min with excellent stability and repeatability.Compared with photocatalysis,the flexo-photocatalytic performance of above centrosymmetric semiconductors is substantially increased by 85%.Moreover,the factors related to flexo-photocatalysis such as material morphology,mechanical stimuli source,and adsorption are explored to deeply understand the mechanism of flexo-photocatalysis.This work opens up a way for high-performance photocatalysis in centrosymmetric semiconductors.

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.

Atomscopic of ripple origins for two-dimensional monolayer transition metal dichalcogenides

During the development of ultrathin two-dimensional(2D)materials,the appearance of ripples has been widely observed.However,the formation mechanisms and their influences are still rarely investigated,especially their contributions to the electronic structures and optical properties.To compensate for the knowledge gap,we have carried out comprehensive theoretical studies on the monolayer WSe_(2) with a series of ripple structures from 0 to 12Åin different lattice sizes.The sensitivity of the formation energy,band structures,electronic structures,and optical properties to the ripple structures have been performed systematically for the first time.The formation of ripples in Armchair and zigzag simultaneously are more energetically favorable,leading to more flexible optimizations of the optoelectronic properties.The improved charge-locking effect and extension of absorption ranges indicate the significant role of ripple structures.The spontaneous formation of ripples is associated with orbital rearrangements and structural distortions.This leads to the unique charge carrier correlate inversion between W-5d and Se-4p orbitals,resulting in the pinning of the Fermi level.This work has supplied significant references to understand ultrathin 2D structures and benefit their future developments and applications in high-performance optoelectronic devices.

Magnetic-field-assisted triboelectric nanogenerator for harvesting multi-directional wave energy

Ocean wave energy is a significant and promising source of renewable energy.However,the energy harvesting is challenging due to the multi-directional nature of waves.This paper proposes a magnetic-field-assisted triboelectric nanogenerator(MFATENG)for harvesting multi-directional wave energy.By incorporating a magnetic field,the planar motion of the pendulum is converted into spatial motion,increasing the triggering of multilayered TENG(M-TENG)and enhancing the output energy of the MFA-TENG.Experimental results demonstrate that the output energy of the MFA-TENG is increased by 73%by utilizing the magnetic field.Moreover,a spring model based on the origami-structured M-TENG is established to analyze the effect of different equivalent stiffnesses on the performance of the M-TENG,aiming to obtain optimal output performance.The results showcase the impressive output performance of the M-TENG,generating outputs of 250 V,18μA,and 255 nC.Furthermore,the proposed MFA-TENG effectively harvests multi-directional wave energy under water-wave driven conditions.This study significantly enhances the ability of the MFA-TENG to harvest multi-directional wave energy and presents a promising approach for self-powered marine monitoring in the future.

Triboelectric nanogenerator integrated with a simple controlled switch for regularized water wave energy harvesting

Ocean is full of low-frequency,irregular,and widely distributed wave energy,which is suitable as the energy source for maritime Internet of Things(IoTs).Utilizing triboelectric nanogenerators(TENGs)to harvest ocean wave energy and power sensors is proven to be an effective scheme.However,in random ocean waves,the irregular electrical energy output by general TENGs restricts the applications.At present,achieving regularized water wave energy harvesting relies on rather complex mechanical structure designs,which is not conducive to industrialization.In this work,we proposed a novel mechanical controlled TENG(MCTENG)with a simple controlled switch to realize the regularization function.The structural parameters of the MC-TENG are optimized,and the optimal output voltage,output current,and transferred charge respectively reach 1684.2 V,85.4μA,and 389.9 nC,generating a peak power density of 38.46 W·m^(−3)·Hz^(−1).Under real water wave environment,the output of the MC-TENG is regularized and keeps stable regardless of any wave conditions.Moreover,the potential applications of the MC-TENG are demonstrated in powering environmental temperature,humidity,and wind speed sensors.This work renders a simple approach to achieve effective regularized ocean wave energy harvesting,promoting the TENG industrialization toward practical application of maritime IoTs.