A Fully Verified Theoretical Analysis of Contact‐Mode Triboelectric Nanogenerators as a Wearable Power Source

Harvesting mechanical energy from human activities by triboelectric nanogenerators (TENGs) is an effective approach for sustainable, maintenance‐free, and green power source for wireless, portable, and wearable electronics. A theoretical model for contact‐mode triboelectric nanogenerators based on the principles of charge conservation and zero loop‐voltage is illustrated. Explicit expressions for the output current, voltage, and power are presented for the TENGs with an external load of resistance. Experimental verification is conducted by using a laboratory‐fabricated contact‐mode TENG made from conducting fabric electrodes and polydimethylsiloxane/graphene oxide composite as the dielectric layer. Excellent agreements of the output voltage, current, and power are demonstrated between the theoretical and experimental results, without any adjustable parameters. The effects of the moving speed on output voltage, current, and power are illustrated in three cases, that is, the motion with constant speed, the sinusoidal motion cycles, and the real walking cycles by human subject. The fully verified theoretical model is a very powerful tool to guide the design of the device structure and selection of materials, and optimization of performance with respect to the application conditions of TENGs.     

自驱动健康监测及生理功能调节器件的研究进展

纳米发电机(摩擦纳米发电机和压电纳米发电机)技术自被提出以来得到了迅速发展,该技术可将人体动能、风能、声波能、海洋能等各种机械能转化为电能,并应用于自驱动健康监测及生理功能调节,如脉搏传感、神经电刺激、心脏起搏等。文中综述了纳米发电机的结构、工作原理、输出性能及其在循环系统、神经系统、生物组织、睡眠及水下救援等方面的最新研究进展,并在此基础上进一步分析了纳米发电机技术应用到临床治疗所面临的挑战。未来纳米发电机有望成为辅助电源,甚至取代传统电池类电源用于驱动医疗电子器件,实现人体自驱动健康监测及生理功能调节。     

Self‐Powered Wireless Sensor Node Enabled by a Duck‐Shaped Triboelectric Nanogenerator for Harvesting Water Wave Energy

This paper presents a fully enclosed duck‐shaped triboelectric nanogenerator (TENG) for effectively scavenging energy from random and low‐frequency water waves. The design of the TENG incorporates the freestanding rolling mode and the pitch motion of a duck‐shaped structure generated by incident waves. By investigating the material and structural features, a unit of the TENG device is successfully designed. Furthermore, a hybrid system is constructed using three units of the TENG device. The hybrid system achieves an instantaneous peak current of 65.5 µA with an instantaneous output power density of up to 1.366 W m^?2. Following the design, a fluid–solid interaction analysis is carried out on one duck‐shaped TENG to understand the dynamic behavior, mechanical efficiency, and stability of the device under various water wave conditions. In addition, the hybrid system is experimentally tested to enable a commercial wireless temperature sensor node. In summary, the unique duck‐shaped TENG shows a simple, cost‐effective, environmentally friendly, light‐weight, and highly stable system. The newly designed TENG is promising for building a network of generators to harvest existing blue energy in oceans, lakes, and rivers.     

Boosting Power‐Generating Performance of Triboelectric Nanogenerators via Artificial Control of Ferroelectric Polarization and Dielectric Properties

Low output current represents a critical challenge that has interrupted the use of triboelectric nanogenerators (TNGs) in a wide range of applications as sustainable power sources. Many approaches (e.g., operation at high frequency, parallel stacks of individual devices, and hybridization with other energy harvesters) remain limited in solving the challenge of low output current from TNGs. Here, a nanocomposite material system having a superior surface charge density as a triboelectric active material is reported. The nanocomposite material consists of a high dielectric ceramic material, barium titanate, showing great charge‐trapping capability, together with a ferroelectric copolymer matrix, Poly(vinylidenefluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)), with electrically manipulated polarization with strong triboelectric charge transfer characteristics. Based on a contact potential difference study showing that poled P(VDF‐TrFE) has 18 times higher charge attracting properties, a fraction between two components is optimized. Boosting power‐generating performance is achieved for 1130 V of output voltage and 1.5 mA of output current with this ferroelectric composite‐based TNG, under 6 kgf of pushing force at 5 Hz. An enormously faster charging property than traditional polymer film‐based TNGs is demonstrated in this study. Finally, the charging of a self‐powering smartwatch with a charging management circuit system with no external power sources is demonstrated successfully.     

An Ultrathin Flexible Single‐Electrode Triboelectric‐Nanogenerator for Mechanical Energy Harvesting and Instantaneous Force Sensing

The trends in miniaturization of electronic devices give rise to the attention of energy harvesting technologies that gathers tiny wattages of power. Here this study demonstrates an ultrathin flexible single electrode triboelectric nanogenerator (S‐TENG) which not only could harvest mechanical energy from human movements and ambient sources, but also could sense instantaneous force without extra energy. The S‐TENG, which features an extremely simple structure, has an average output current of 78 μA, lightening up at least 70 LEDs (light‐emitting diode). Even tapped by bare finger, it exhibits an output current of 1 μA. The detection sensitivity for instantaneous force sensing is about 0.947 μA MPa^?1. Performances of the device are also systematically investigated under various motion types, press force, and triboelectric materials. The S‐TENG has great application prospects in sustainable wearable devices, sustainable medical devices, and smart wireless sensor networks owning to its thinness, light weight, energy harvesting, and sensing capacities.     

Triboelectric Nanogenerator Enabled Wearable Sensors and Electronics for Sustainable Internet of Things Integrated Green Earth

The advancement of the Internet of Things/5G infrastructure requires a low-cost ubiquitous sensory network to realize an autonomous system for information collection and processing, aiming at diversified applications ranging from healthcare, smart home, industry 4.0 to environmental monitoring. The triboelectric nanogenerator (TENG) is considered the most promising technology due to its self-powered, cost-effective, and highly customizable advantages. Through the use of wearable electronic devices, advanced TENG technology is developed as a core technology enabling self-powered sensors, power supplies, and data communications for the aforementioned applications. In this review, the advancements of TENG-based electronics regarding materials, material/device hybridization, systems integration, technology convergence, and applications in healthcare, environment monitoring, transportation, and smart homes toward the future green earth are reported.     

High Permittivity CaCu3Ti4O12 Particle‐Induced Internal Polarization Amplification for High Performance Triboelectric Nanogenerators

Here, a composite material based on the butylated melamine formaldehyde (BMF) and high permittivity CaCu₃Ti₄O₁₂ (CCTO) particles as a triboelectric dielectric material for stable high output triboelectric nanogenerators (TENGs) is proposed. CCTO particles, which have the high permittivity of 7500, can potentially result in the formation of strong internal polarization into the dielectric material under the electric field from triboelectric charges. As a consequence, the charge induction on the bottom electrode is enhanced thereby increasing the triboelectric output performance. A rotation‐type freestanding mode TENG based on BMF–CCTO 1 wt% composite material demonstrates high performance power output of a root‐mean‐square voltage and current density with 268 V and 25.8 mA m^?2, respectively. The strategy of incorporating the high permittivity CCTO particles can be universally applied to any triboelectric polymer matrix in order to enhance the output performance of TENGs.     

Biomechanical Energy‐Driven Hybridized Generator as a Universal Portable Power Source for Smart/Wearable Electronics

The fast growth of smart electronics requires novel solutions to power them sustainably. Portable power sources capable of harvesting biomechanical energy are a promising modern approach to reduce battery dependency. Herein, a novel elastic impact‐based nonresonant hybridized generator (EINR‐HG) is reported to effectively harvest biomechanical energy from diverse human activities outdoors. Through the rational integration of a nonlinear electromagnetic generator with two contact‐mode triboelectric nanogenerators, the proposed EINR‐HG generates hybrid electrical output simultaneously under the same mechanical excitations. By introducing a flux‐concentrator with a nanowire‐nanofiber surface modification, significant improvement in the energy harvesting efficiency of the EINR‐HG is achieved. After optimizing using simulations and vibration tests, the as‐fabricated EINR‐HG delivers an outstanding normalized power density of 3.13 mW cm^?3 g^?2 across a matching resistance of 1.5 kΩ at 6 Hz under 1 g acceleration. Under human motion testing, the EINR‐HG generates an optimal output power of 131.4 mW with horizontal handshaking. With a customized power management circuit, the EINR‐HG serves as a universal power source that successfully drives commercial smart electronics, including smart bands and smartphones. This work shows the massive potential of biomechanical energy‐driven hybridized generators for powering personal electronics and portable healthcare monitoring devices.     

Microdischarge‐Based Direct Current Triboelectric Nanogenerator via Accumulation of Triboelectric Charge in Atmospheric Condition

Direct conversion of mechanical energy into direct current (DC) by triboelectric nanogenerators (TENGs) is one of the desired features in terms of energy conversion efficiency. Although promising applications have been reported using the triboelectric effect, effective DC generating TENGs must be developed for practical purposes. Here, it is reported that continuous DC generation within a TENG itself, without any circuitry, can be achieved by triggering air breakdown via triboelectrification. It is demonstrated that DC generation occurs in combination with i) charge accumulation to generate air breakdown, ii) incident discharge (microdischarge), and iii) conveyance of charges to make the device sustainable. 10.5 mA m^?2 of output current and 10.6 W m^?2 of output power at 33 MΩ load resistance are achieved. Compared to the best DC generating TENGs ever reported, the TENG in this present study generates about 20 times larger root‐mean square current density.     

Sustainable Energy Source for Wearable Electronics Based on Multilayer Elastomeric Triboelectric Nanogenerators

Wearable electronics have attracted a wide range of attention with various functions due to the development of semiconductor industry and information technology. This work focuses on a triboelectric nanogenerator‐based self‐charging power system as a continuous energy source for wearable electronics. The triboelectric nanogenerator has a multilayer elastomeric structure with closely stacked arches as basic functional units. Owing to material and structural innovations, this triboelectric nanogenerator performs outstanding electric output with the maximum volume charge density ≈0.055 C m^?3 and practical properties for energy harvesting from body motions. Utilizing the triboelectric nanogenerator as outsole to harvest energy from walking or jogging, a pair of shoes is fabricated with the maximum equivalent charge current of each shoe being around 16.2 µA and specific fitness functions realized on each shoe separately without complex connections.     

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

The fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO₂) nanoparticles on Ti₃C₂T_x MXene nanosheets. The resulting RuO₂@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO₂ nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO₂@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm^?3 at 1 mV s^?1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm^?3 at 2000 mV s^?1), outstanding flexibility, remarkable energy (13.5 mWh cm^?3) and power density (48.5 W cm^?3).     

High‐Performance Triboelectric Nanogenerators Based on Solid Polymer Electrolytes with Asymmetric Pairing of Ions

In general, various kinds of surface modifications are utilized to enhance the power output performance of triboelectric nanogenerators (TENGs), but they typically have limited stability. Here, a new strategy of adding electrolytes with asymmetric ion pairing to polymer friction layers of TENGs is introduced in order to enhance their triboelectric property. Indeed, Kelvin probe force microscopy (KPFM) measurements show that an addition of phosphoric acid (H₃PO₄ ), an electrolyte with more cations than anions, to polyvinyl alcohol (PVA) can make it one of the most negative triboelectric materials; whereas, an addition of calcium chloride (CaCl₂ ), an electrolyte with more anions than cations, to PVA can make it one of the most positive triboelectric materials. Furthermore, the TENGs based on such solid polymer electrolytes (SPEs) produce significantly higher power output than typical metal‐polymer TENGs. Due to these unique features, SPEs are a promising triboelectric material for realizing high‐performance TENGs for self‐powered small electronics.     

A Soft and Robust Spring Based Triboelectric Nanogenerator for Harvesting Arbitrary Directional Vibration Energy and Self‐Powered Vibration Sensing

Vibration is a common mechanical phenomenon and possesses mechanical energy in ambient environment, which can serve as a sustainable source of power for equipment and devices if it can be effectively collected. In the present work, a novel soft and robust triboelectric nanogenerator (TENG) made of a silicone rubber‐spring helical structure with nanocomposite‐based elastomeric electrodes is proposed. Such a spring based TENG (S‐TENG) structure operates in the contact‐separation mode upon vibrating and can effectively convert mechanical energy from ambient excitation into electrical energy. The two fundamental vibration modes resulting from the vertical and horizontal excitation are analyzed theoretically, numerically, and experimentally. Under the resonant states of the S‐TENG, its peak power density is found to be 240 and 45 mW m^?2 with an external load of 10 MΩ and an acceleration amplitude of 23 m s^?2. Additionally, the dependence of the S‐TENG's output signal on the ambient excitation can be used as a prime self‐powered active vibration sensor that can be applied to monitor the acceleration and frequency of the ambient excitation. Therefore, the newly designed S‐TENG has a great potential in harvesting arbitrary directional vibration energy and serving as a self‐powered vibration sensor.     

Unity Convoluted Design of Solid Li‐Ion Battery and Triboelectric Nanogenerator for Self‐Powered Wearable Electronics

Wearable electronics suffer from severe power shortage due to limited working time of Li‐ion batteries, and there is a desperate need to build a hybrid device including energy scavenging and storing units. However, previous attempts to integrate the two units are mainly based on simple external connections and assembly, so that maintaining small volume and low manufacturing cost becomes increasingly challenging. Here a convoluted power device is presented by hybridizing internally a solid Li‐ion battery (SLB) and a triboelectric nanogenerator (TENG), so that the two units are one inseparable entity. The fabricated device acts as a TENG that can deliver a peak output power of 7.4 mW under a loading resistance of 7 MΩ, while the device also acts as an SLB to store the obtained electric energy. The device can be mounted on a human shoe to sustainably operate a green light‐emitting diode, thus demonstrating potential for self‐powered wearable electronics.     

In Situ Electrochemical Synthesis of MXenes without Acid/Alkali Usage in/for an Aqueous Zinc Ion Battery

The traditional method to fabricate a MXene based energy storage device starts from etching MAX phase particles with dangerous acid/alkali etchants to MXenes, followed by device assembly. This is a multistep protocol and is not environmentally friendly. Herein, an all‐in‐one protocol is proposed to integrate synthesis and battery fabrication of MXene. By choosing a special F‐rich electrolyte, MAX V₂AlC is directly exfoliated inside a battery and the obtained V₂CT_X MXene is in situ used to achieve an excellent battery performance. This is a one‐step process with all reactions inside the cell, avoiding any contamination to external environments. Through the lifetime, the device experiences three stages of exfoliation, electrode oxidation, and redox of V₂O₅. While the electrode is changing, the device can always be used as a battery and the performance is continuously enhanced. The resulting aqueous zinc ion battery achieves outstanding cycling stability (4000 cycles) and rate performance (97.5 mAh g^?1 at 64 A g^?1), distinct from all reported aqueous MXene‐based counterparts with pseudo‐capacitive properties, and outperforming most vanadium‐based zinc ion batteries with high capacity. This work sheds light on the green synthesis of MXenes, provides an all‐in‐one protocol for MXene devices, and extends MXenes’ application in the aqueous energy storage field.     

MXene‐on‐Paper Coplanar Microsupercapacitors

A simple and scalable direct laser machining process to fabricate MXene‐on‐paper coplanar microsupercapacitors is reported. Commercially available printing paper is employed as a platform in order to coat either hydrofluoric acid‐etched or clay‐like 2D Ti₃C₂ MXene sheets, followed by laser machining to fabricate thick‐film MXene coplanar electrodes over a large area. The size, morphology, and conductivity of the 2D MXene sheets are found to strongly affect the electrochemical performance due to the efficiency of the ion‐electron kinetics within the layered MXene sheets. The areal performance metrics of Ti₃C₂ MXene‐on‐paper microsupercapacitors show very competitive power‐energy densities, comparable to the reported state‐of‐the‐art paper‐based microsupercapacitors. Various device architectures are fabricated using the MXene‐on‐paper electrodes and successfully demonstrated as a micropower source for light emitting diodes. The MXene‐on‐paper electrodes show promise for flexible on‐paper energy storage devices.     

A Wireless Triboelectric Nanogenerator

A new “wireless” paradigm for harvesting mechanical energy via a 3D‐printed wireless triboelectric nanogenerator (W‐TENG) comprised of an ecofriendly graphene polylactic acid (gPLA) nanocomposite and Teflon is demonstrated. The W‐TENG generates very high output voltages >2 kV with a strong electric field that enables the wireless transmission of harvested energy over a distance of 3 m. The W‐TENG exhibited an instantaneous peak power up to 70 mW that could be wirelessly transmitted for storage into a capacitor obviating the need for hard‐wiring or additional circuitry. Furthermore, the use of W‐TENG for wireless and secure actuation of smart‐home applications such as smart tint windows, temperature sensors, liquid crystal displays, and security alarms either with a single or a specific user‐defined passcode of mechanical pulses (e.g., Fibonacci sequence) is demonstrated. The scalable additive manufacturing approach for gPLA‐based W‐TENGs, along with their high electrical output and unprecedented wireless applications, is poised for revolutionizing the present mechanical energy harvesting technologies.     

Enhancing the Output Performance of Triboelectric Nanogenerator via Grating‐Electrode‐Enabled Surface Plasmon Excitation

The surface charge density and the output impedance of triboelectric nanogenerators (TENGs) are two critical factors for TENGs to speed up their commercialization, so it is important to explore unique methods to reduce the output impedance and increase the surface charge density. Here, an approach is demonstrated to effectively boost the output performance of TENG while reducing the output impedance of TENGs by utilizing grating‐electrode‐enabled surface plasmon excitation. A sustainable and enhanced output performance of about 40 µA (short‐circuit current) and 350 V (peak‐to‐peak voltage at a resistance of 10 MΩ) is produced via grating‐coupled surface plasmon resonance on the TENG with the aluminum grating electrode in the line density of 600 lines mm^?1, and it delivers a peak output power of 3.6 mW under a loading resistance of 1 MΩ, giving over 4.5‐fold enhancement in output power and a 75% reduction in the output impedance. Finally a self‐powered ultrasonic ranging system is utilized to verify the capability of the TENG in powering portable electrics.     

Robust Triboelectric Nanogenerator Achieved by Centrifugal Force Induced Automatic Working Mode Transition

Material abrasion in contact‐based freestanding mode‐triboelectric nanogenerators (FS‐TENGs) seriously deteriorates device mechanical durability and electrical stability, which causes TENGs to be only applicable in the harvesting of mechanical energy at low‐frequency. Here, a wide‐frequency and ultra‐robust rotational TENG is reported that is composed of a built‐in traction rope structure and capable of transforming from contact mode to non‐contact mode automatically as driven by the centrifugal force. With optimizing the fixed x and y position on slider and center shaft, respectively, the mode transition threshold speed can be reduced to 225 rpm. Additionally, the automatic working mode transition TENG exhibits excellent electrical stability, which can maintain 90% electric output after over 24 h of continuous operation, while the contact and non‐contact mode TENGs only retain 30% and 2% output, respectively. The high stability and large output density ensure its usage in the fast and effective charging of commercial capacitors or electronics. This work provides a prospective strategy for rotational TENGs to extend the frequency operation region and mechanical durability for practical applications.     

Mechanical Regulation Triboelectric Nanogenerator with Controllable Output Performance for Random Energy Harvesting

Recycling of random mechanical energy in the environment has become an important research hotspot. The triboelectric nanogenerators (TENGs) were invented to harvest energy, and have been widely applied due to their simple structure, small size, and low cost. This paper reports a mechanical regulation triboelectric nanogenerator (MR‐TENG) for the first time with controllable output performance used to harvest random or irregular energy in the environment. It comprises a transmission unit, switch structure, generator unit, flywheel, and shell. Random linear motion or rocking motion is transferred via the transmission unit to the flywheel. The rotor of the generator unit fixed on the flywheel and the stator of the generator unit fixed on the shell combine. By controlling the storage and release of energy in the flywheel, the switch structure assists the flywheel to convert random or irregular energy into a controllable and stable energy output. The MR‐TENG can generate an open‐circuit voltage of 350 V, a short‐circuit current of 12 μA, a transfer charge of 130 nC, and a peak power of 2.52 mW. Furthermore, a thermometer and more than 300 light emitting diodes (LEDs) are separately powered by this MR‐TENG in simulated water waves, demonstrating its potential application in water wave energy harvesting.