Recent advances in stretchable triboelectric nanogenerators for use in wearable bioelectronic devices

Wearable bioelectronic devices have the capacity for real-time human health monitoring,the provision of tailored services,and natural interaction with smart devices.However,these wearable bioelectronic devices rely on conventional rigid batteries that are frequently charged or replaced and are incompatible with the skin,leading to a discontinuity in complex therapeutic tasks related to human health monitoring and human-machine interaction.Stretchable triboelectric nanogenerator(TENG)is a high-efficiency energy harvesting technology that converts mechanical into electrical energy,effectively powering wearable bioelectronic devices.This study comprehensively overviews recent advances in stretchable TENG for use in wearable bioelectronic devices.The working mechanism of stretchable TENG is initially explained.A comprehensive discussion presents the approaches for fabricating stretchable TENG,including the design of stretchable structures and the selection of stretchable materials.Furthermore,applications of wearable bioelectronic devices based on stretchable TENG in human health monitoring(body movements,pulse,and respiration)and human-machine interaction(touch panels,machine control,and virtual reality)are introduced.Ultimately,the challenges and developmental trends regarding wearable bioelectronic devices based on stretchable TENG are elaborated.

Application of different fiber structures and arrangements by electrospinning in triboelectric nanogenerators

In recent years,nanogenerators(NGs)have attracted wide attention in the energy field,among which triboelectric nanogenerators(TENGs)have shown superior performance.Multiple reports of electrospinning(ES)-based TENGs have been reported,but there is a lack of deep analysis of the designing method from microstructure,limiting the creative of new ES-based TENGs.Most TENGs use polymer materials to achieve corresponding design,which requires structural design of polymer materials.The existing polymer molding design methods include macroscopic molding methods,such as injection,compression,extrusion,calendering,etc.,combined with liquid-solid changes such as soluting and melting;it also includes micro-nano molding technology,such as melt-blown method,coagulation bath method,ES method,and nanoimprint method.In fact,ES technology has good controllability of thickness dimension and rich means of nanoscale structure regulation.At present,these characteristics have not been reviewed.Therefore,in this paper,we combine recent reports with some microstructure regulation functions of ES to establish a more general TENGs design method.Based on the rich microstructure research results in the field of ES,much more new types of TENGs can be designed in the future.

Gel-Based Triboelectric Nanogenerators for Flexible Sensing:Principles,Properties,and Applications

The rapid development of the Internet of Things and artificial intelligence technologies has increased the need for wearable,portable,and self-powered flexible sensing devices.Triboelectric nanogenerators(TENGs)based on gel materials(with excellent conductivity,mechanical tunability,environmental adaptability,and biocompatibility)are considered an advanced approach for developing a new generation of flexible sensors.This review comprehensively summarizes the recent advances in gel-based TENGs for flexible sensors,covering their principles,properties,and applications.Based on the development requirements for flexible sensors,the working mechanism of gel-based TENGs and the characteristic advantages of gels are introduced.Design strategies for the performance optimization of hydrogel-,organogel-,and aerogel-based TENGs are systematically summarized.In addition,the applications of gel-based TENGs in human motion sensing,tactile sensing,health monitoring,environmental monitoring,human-machine interaction,and other related fields are summarized.Finally,the challenges of gel-based TENGs for flexible sensing are discussed,and feasible strategies are proposed to guide future research.

Fabricating AC/DC nanogenerators based on single ZnO nanowires by using a nanomanipulator in a scanning electron microscope

Single zinc oxide nanowires(ZnO NWs)are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties,but characterizing the latter efficiently is challenging.As reported here,an electrical breakdown strategy was used to construct single ZnO NWs with a specific length.With the high operability of a nanomanipulator in a scanning electron microscope,ZnO-NW-based twoprobe and three-probe structures were constructed for fabricating AC/DC nanogenerators,respectively.For a ZnO NW,an AC output of between−15.31 mV and 5.82 mV was achieved,while for a DC nanogenerator,an output of24.3 mV was realized.Also,the three-probe structure’s output method was changed to verify the distribution of piezoelectric charges when a single ZnO NW is bent by a probe,and DC outputs of different amplitudes were achieved.This study provides a low-cost,highly convenient,and operational method for studying the AC/DC output characteristics of single NWs,which is beneficial for the further development of nanogenerators.

Recent advances in fabricating high-performance triboelectric nanogenerators via modulating surface charge density

Triboelectric nanogenerators(TENGs),a type of promising micro/nano energy source,have been arousing tremendous research interest since their inception and have been the subject of many striking developments,including defining the fundamental physical mechanisms,expanding applications in mechanical to electric power conversion and self-powered sensors,etc.TENGs with a superior surface charge density at the interfaces of the electrodes and dielectrics are found to be crucial to the enhancement of the performance of the devices.Here,an overview of recent advances,including material optimization,circuit design,and strategy conjunction,in developing TENGs through surface charge enhancement is presented.In these topics,different strategies are retrospected in terms of charge transport and trapping mechanisms,technical merits,and limitations.Additionally,the current challenges in high-performance TENG research and the perspectives in this field are discussed.

Advances in magnetic-assisted triboelectric nanogenerators:structures,materials and self-sensing systems

Triboelectric nanogenerators(TENG),renowned for their remarkable capability to harness weak mechanical energy from the environment,have gained considerable attention owing to their cost-effectiveness,high output,and adaptability.This review provides a unique perspective by conducting a comprehensive and in-depth analysis of magnetically assisted TENGs that encompass structures,materials,and self-powered sensing systems.We systematically summarize the diverse functions of the magnetic assistance for TENGs,including system stiffness,components of the hybrid electromagnetic-triboelectric generator,transmission,and interaction forces.In the material domain,we review the incorporation of magnetic nano-composites materials,along with ferrofluid-based TENG and microstructure verification,which have also been summarized based on existing research.Furthermore,we delve into the research progress on physical quantity sensing and human-machine interface in magnetic-assisted TENGs.Our analysis highlights that magnetic assistance extends beyond the repulsive and suction forces under a magnetic field,thereby playing multifaceted roles in improving the output performance and environmental adaptability of the TENGs.Finally,we present the prevailing challenges and offer insights into the future trajectory of the magnetic-assisted TENGs development.

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.

Recent advances in high charge density triboelectric nanogenerators

Triboelectric materials with high charge density are the building-block for the commercial application of triboelectric nanogenerators(TENGs).Unstable dynamic processes influence the change of the charge density on the surface and inside of triboelectric materials.The charge density of triboelectric materials depends on the surface and the internal charge transfer processes.The focus of this review is on recent advances in high charge density triboelectric materials and advances in the fabrication of TENGs.We summarize the existing strategies for achieving high charge density in triboelectric materials as well as their fundamental properties.We then review current optimization methods for regulating dynamic charge transfer processes to increase the output charge density:first,increasing charge injection and limiting charge dissipation to achieve a high average surface charge density,and second,regulating the internal charge transfer process and storing charge in triboelectric materials to increase the output charge density.Finally,we present the challenges and prospects in developing high-performance triboelectric materials.

Harvesting Environment Mechanical Energy by Direct Current Triboelectric Nanogenerators

As hundreds of millions of distributed devices appear in every corner of our lives for information collection and transmission in big data era,the biggest challenge is the energy supply for these devices and the signal transmission of sensors.Triboelectric nanogenerator(TENG)as a new energy technology meets the increasing demand of today’s distributed energy supply due to its ability to convert the ambient mechanical energy into electric energy.Meanwhile,TENG can also be used as a sensing system.Direct current triboelectric nanogenerator(DC-TENG)can directly supply power to electronic devices without additional rectification.It has been one of the most important developments of TENG in recent years.Herein,we review recent progress in the novel structure designs,working mechanism and corresponding method to improve the output performance for DC-TENGs from the aspect of mechanical rectifier,tribovoltaic effect,phase control,mechanical delay switch and air-discharge.The basic theory of each mode,key merits and potential development are discussed in detail.At last,we provide a guideline for future challenges of DC-TENGs,and a strategy for improving the output performance for commercial applications.

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.

Advances in self-powered sports monitoring sensors based on triboelectric nanogenerators

The new era of the internet of things brings great opportunities to the field of intelligent sports.The collection and analysis of sports data are becoming more intelligent driven by the widely-distributed sensing network system.Triboelectric nanogenerators(TENGs)can collect and convert energy as selfpowered sensors,overcoming the limitations of external power supply,frequent power replacement and high-cost maintenance.Herein,we introduce the working modes and principles of TENGs,and then summarize the recent advances in self-powered sports monitoring sensors driven by TENGs in sports equipment facilities,wearable equipment and competitive sports specialities.We discuss the existing issues,i.e.,device stability,material sustainability,device design rationality,textile TENG cleanability,sports sensors safety,kinds and manufacturing of sports sensors,and data collection comprehensiveness,and finally,propose the countermeasures.This work has practical significance to the current TENG applications in sports monitoring,and TENG-based sensing technology will have a broad prospect in the field of intelligent sports in the future.

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.

Hybrid Triboelectric-Electromagnetic Nanogenerators for Mechanical Energy Harvesting:A Review

Motion-driven electromagnetictriboelectric energy generators(E-TENGs) hold a Hybrid triboelectric-electromagnetic generators C A Bgreat potential to provide higher voltages,higher currents and wider operating bandwidths than Cantilever generators1 μm both electromagnetic and triboelectric generators Rotating generatorsSliding generators standing alone. Therefore,they are promising solutions to autonomously supply a broad range of Flexible blade generators Magnetoelectric highly sophisticated devices. This paper provides generators a thorough review focused on major recent breakLinear generators Multidimensional generators throughs in the area of electromagnetic-triboelectric vibrational energy harvesting. A detailed Pendulum generators analysis was conducted on various architectures including rotational,pendulum,linear,sliding,cantilever,flexible blade,multidimensional and 1 cm magnetoelectric,and the following hybrid technologies. They enable highly e cient ways to harvest electric energy from many forms of vibrational,rotational,biomechanical,wave,wind and thermal sources,among others. Open-circuit voltages up to 75 V,short-circuit currents up to 60 mA and instantaneous power up to 144 mW were already achieved by these nanogenerators. Their transduction mechanisms,including proposed models to make intelligible the involved physical phenomena,are also overviewed here. A comprehensive analysis was performed to compare their respective construction designs,external excitations and electric outputs. The results highlight the potential of hybrid E-TENGs to convert unused mechanical motion into electric energy for both large-and small-scale applications.Finally,this paper proposes future research directions toward optimization of energy conversion e ciency,power management,durability and stability,packaging,energy storage,operation input,research of transduction mechanisms,quantitative standardization,system integration,miniaturization and multi-energy hybrid cells.

Nanogenerators for Self-Powered Gas Sensing

Looking toward world technology trends over the next few decades, self-powered sensing networks are a key field of technological and economic driver for global industries. Since 2006, Zhong Lin Wang's group has proposed a novel concept of nanogenerators(NGs), including piezoelectric nanogenerator and triboelectric nanogenerator, which could convert a mechanical trigger into an electric output. Considering motion ubiquitously exists in the surrounding environment and for any most common materials used every day, NGs could be inherently served as an energy source for our daily increasing requirements or as one of self-powered environmental sensors. In this regard, by coupling the piezoelectric or triboelectric properties with semiconducting gas sensing characterization, a new research field of self-powered gas sensing has been proposed. Recent works have shown promising concept to realize NG-based self-powered gas sensors that are capable of detecting gas environment without the need of external power sources to activate the gas sensors or to actively generate a readout signal. Compared with conventional sensors, these self-powered gas sensors keep the approximate performance.Meanwhile, these sensors drastically reduce power consumption and additionally reduce the required space for integration,which are significantly suitable for the wearable devices. This paper gives a brief summary about the establishment and latest progress in the fundamental principle, updated progress and potential applications of NG-based self-powered gas sensing system. The development trend in this field is envisaged, and the basic configurations are also introduced.

Woven fabric triboelectric nanogenerators for human-computer interaction and physical health monitoring

Triboelectric nanogenerator(TENG)converts mechanical energy into valuable electrical energy,offering a solution for future energy needs.As an indispensable part of TENG,textile TENG(T-TENG)has incredible advantages in harvesting biomechanical energy and physiological signal monitoring.However,the application of T-TENG is restricted,partly because the fabric structure parameter and structure on T-TENG performance have not been fully exploited.This study comprehensively investigates the effect of weaving structure on fabric TENGs(F-TENGs)for direct-weaving yarn TENGs and post-coating fabric TENGs.For direct-weaving F-TENGs,a single-yarn TENG(Y-TENG)with a core-sheath structure is fabricated using conductive yarn as the core layer yarn and polytetrafluoroethylene(PTFE)filaments as the sheath yarn.Twelve fabrics with five different sets of parameters were designed and investigated.For post-coating F-TENGs,fabrics with weaving structures of plain,twill,satin,and reinforced twill were fabricated and coated with conductive silver paint.Overall,the twill F-TENGs have the best electrical outputs,followed by the satin F-TENGs and plain weave F-TENGs.Besides,the increase of the Y-TENG gap spacing was demonstrated to improve the electrical output performance.Moreover,T-TENGs are demonstrated for human-computer interaction and self-powered real-time monitoring.This systematic work provides guidance for the future T-TENG’s design.

Self-powered systems by nanogenerators and smart MEMS by piezotronics

Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery, without which most of the sensor network may be impossible. The pie- zoelectric nanogenerators have the potential to serve as self-sufficient power sources for micro/nano systems. For wurtzite structures that have non-central symmetry, such as ZnO, GaN and InN, a piezoelectric potential （piezopotential） is created in the crystal by applying a strain. The nanogenerator is invented by using the piezopotential as the driving force for electrons to flow in respond to a dynamic straining of piezoelectric nanowires. A gentle straining can produce an output voltage of up to 20 - 50 V from an integrated nanogenerator. Furthermore, piezopotential in the wurtzite structure can serve as gate voltage that can effectively tune/control the charge transport across an interface/junction; electronics fabricated based on such a mechanism is coined as piezotronics, with applications in force/pressure triggercd/controlled electronic devices, sensors, logic units and memory. By using the piezotronic effect, it is showed that the optoelectronic devices fabricated using wurtzite materials can have superior performance as solar cell, photon detector and light emitting diode. Piezotronie is likely to serve as ＂mechanosensation＂ for directly interfacing biomechanieal action with silicon based technology and active flexible electronics. The paper gives a brief review about the basis of nanogenertors and piezotronics and their potential applications in smart MEMS （micro-electro-mechanical systems）.

Triboelectric nanogenerators for self-powered neurostimulation

The burgeoning field of soft bioelectronics heralds a new dawn in medical treatment for neurological and psychiatric conditions,presenting innovative methods for the stimulation,inhibition,and precise sensing of neuronal activities.Central to these advancements is the challenge of power supply;devices dependent on traditional batteries face limitations regarding miniaturization and require invasive surgeries for battery replacement.Triboelectric nanogenerators(TENGs),which generate power from biomechanical movements,offer a promising solution for developing self-powered neurostimulation devices without the need for an external power supply.This review delves into recent progress in TENGs,with a focus on their application in selfpowered neurostimulation systems.The utility of TENGs across various nervous systems—including the center,autonomic,and somatic nervous systems—is explored and presented,highlighting the potential for these devices to facilitate neurological treatments.By summarizing TENGs’operational details and the potential for clinical translation,this review also identifies challenges associated with the implantation and integration of neural electrodes and presents recent advances in solutions,aiming to reshape electric treatments for neurological diseases.

Highly stretchable kirigami-patterned nanofiber-based nanogenerators for harvesting human motion energy to power wearable electronics

Wearable electronics are advancing towards miniaturization and flexibility.However,traditional energy supply methods have largely hindered their development.An effective solution to this problem is to convert human mechanical energy into electricity to power wearable electronic devices.Therefore,it is greatly attractive to design flexible,foldable and even stretchable energy harvesting devices.Herein,we use the electrospinning and kirigami approach to develop a type of highly stretchable kirigami-patterned nanofiber-based triboelectric nanogenerator(K-TENG).Due to its innovative structural design,the K-TENG can achieve a tensile strain of 220%,independent of the tensile properties of the material itself.When a person swings their arms,the K-TENG fixed to the clothing can convert mechanical energy from human movement into electrical energy.The produced electricity can directly drive 50 LED lights and a digital watch,or be stored in a lithium battery to charge the smartwatch and smartphone,respectively.This study employs a new method to fabricate a stretchable triboelectric nanogenerator and demonstrates its promising applications in wearable power technology.

Beta-phase transformation of polyvinylidene fluoride with supersonically sprayed ZnSnO_(3) cuboids for flexible piezoelectric nanogenerators

Flexible self-powered electromechanical devices,such as piezoelectric nanogenerators(PENGs),which are used in wearable and implantable devices,are emerging as state-of-the-art clean energy sources.In this study,a scalable supersonic spraying technique was used to prepare flexible piezocomposite films of polyvinylidene fluoride(PVDF)and hydrothermally synthesized ZnSnO_(3)(ZSO)cubes for PENGs.Raman spectra confirmed that the transformation of the α-phase of PVDF to its β-phase was induced by the shear stress generated between the ZSO particles and PVDF polymer during supersonic spraying.The op-timized sample comprising 0.43 g of ZSO cubes and 1 g of PVDF produced a maximum piezopotential of 41.5 V and a short-circuit current,I_(sc),of 52.5 μA.A maximum power density of 50.6 μW cm-2 was ob-tained at a loading resistance of 0.4 MΩ,which matched the impedance of the PENG.Long-term tapping and bending cycles of N_(tap)=4200 and N_(bend)=600 yielded piezopotentials of 40.5 and 1.7 V,respectively.In addition,electrical poling for 2 h increased the piezopotential to 52 V owing to the alignment of the ferroelectric dipoles in the PVDF.