Low-frequency Mechanical Energy Research Articles

High-sensitivity wearable multi-signal sensor based on self-powered MXene hydrogels

Developing high-performance wearable sensors with multi-sensing capabilities for different signals such as temperature, human motion and physiological signals remains a challenge. In this report, a novel catechol functionalization of PVA-CA/Poly(N-acryloyl glycinamide)/MXene hydrogels(PcNA-M) was fabricated by combining the thermosensitivity of Poly(N-acryloyl glycinamide)(PNAGA) hydrogel and the self-powered properties of the catechol functionalization of PVA(Pc)/MXene hydrogels. The mixing ratio of PNAGA and Pc was adjusted to impart the resulting PcNA-M with good tensile, compression, rebound properties, rapid self-healing and temperature sensing properties. In addition, the conductivity of the hydrogel was found to have contributions from ionic and electrical conductivity. To produce different forms of electrical signals for different signal sources, the PcNA-M sensor was utilized to monitor the resistive and voltage signals during body movements, switching temperature and handwriting motion. The PcNA-M sensor exhibits high sensitivity, identifiability, and reliability in applications of self-powered wearable sensors, and demonstrates great prospects in the field of low-frequency mechanical energy harvesting. This study opens a new possibility for wearable self-powered multi-signal sensors to monitor different signals related to human motion.

Electrostatic-driven self-assembled chitin nanocrystals (ChNCs)/MXene films for triboelectric nanogenerator

With the rapid development of smart wearable electronics, self-powered devices are urgently needed to overcome the limitations of conventional power sources. The single electrode triboelectric nanogenerator (TENG) attracts much attention owing to its simple fabrication, carrying convenience, and easy use as a power source for wearable electronic devices. Herein, a flexible, responsive, and multifunctional single electrode TENG based on renewable chitin nanocrystals (ChNCs) and MXene composite film (CM-TENG) is developed. ChNCs act as interfacial adhesives to facilitate the assembly of the MXene nanosheets, which significantly improves the composite film's mechanical properties and electrical conductivity. Positively charged ChNCs neutralize the negative charges of MXene nanosheet surfaces, enabling the composite film to rapidly transfer charges during the electrostatic induction process. The output performance of the CM-TENG can achieve 99.5 mW m−2 power density so it can be utilized for self-powered strain and tactile sensors. This work presents a new strategy for constructing stable and flexible power sources and self-powered sensors via electrostatic-driven self-assembled of ChNCs and MXene, which shows promising application in low frequency mechanical energy harvesting and self-powered wearable electronics.

Orange peel-like triboelectric nanogenerators with multiscale micro-nano structure for energy harvesting and touch sensing applications

With the continuous advancements in technology, triboelectric nanogenerators (TENGs) have gained significant traction as efficient harnessers of low-frequency mechanical energy to meet the escalating energy demands. Notably, employing solid polymer electrolyte (SPE) as a contact layer or optimizing the microstructural composition of the surface material represents a prevalent strategy for augmenting the output performance of TENGs. However, the fabrication of numerous microstructures poses significant challenges, particularly in terms of incorporating environmentally harmful materials. Moreover, the utilization of triboelectric nanogenerators is further constrained by limitations associated with electrode materials. Although various techniques are available for producing transparent and stretchable electrodes for such generators, these procedures can be intricate and necessitate the use of hazardous chemicals. In this study, we exploit Poly(vinyl alcohol) (PVA) and natural bacterial cellulose (BC) nanofibers to fabricate contact layers with OP structures characterized by micron-scale domes and nanoscale microcracks. The electrodes were fabricated using BC hydrogel and ionic liquids(ILs). Under the action of hydrogen bond topological network, a multi-scale structure is formed comprising of a molecular-scale interlacing network of hydrogen bonds and a nanoscale fiber skeleton, which synergistically confer the ionic gel with remarkable tensile strength and high ionic conductivity (up to 83.51mS/cm). The resulting OP-TENG exhibited an output open-circuit voltage of 280 V, a short-circuit current of 24μA, and a maximum power density of 5.6 W m−2, enabling it to illuminate up to 303 LEDs. A SSEM-TENG was devised by stacking two single electrode mode TENGs on top of each other using a single wire. This innovative design holds great potential for applications in wearable motion monitoring, high-precision writing stroke recognition, and low-frequency mechanical energy harvesting.

Enhancing PDMS-based triboelectric nanogenerator output by optimizing the microstructure and dielectric constant

Triboelectric nanogenerators possess the capability to convert low-frequency mechanical energy into electrical energy, thereby attracting significant attention due to their reliable performance, light weight nature, and simplistic structure.

(Invited) bionic Composite Films for Biomechanical Energy Harvesting and Self-Powered Sensing Applications

Triboelectric nanogenerators (TENGs) are novel and sustainable devices for harvesting ambient energy for many technological-based applications. However, extreme friction wear of triboelectric layers severely limits their long-term electrical stability and mechanical reliability, restricting the applicability of TENGs for low-frequency mechanical energy harvesting. Herein, we report novel bionic composite (BC) films, inspired by the structures and compositions of bioskins, as wear-resistant triboelectric contact layers for TENGs. We demonstrated that the proposed BC films has superior charge transfer capability, high wear resistance, and maintained long-term stable outputs compared to commercially available films. These works provide an effective strategy to reduce material abrasion by exploiting unique characteristics of the bionic materials, and lays a foundation for effective environmental energy harvesting toward practical applications. Figure 1

Ultrahigh Piezocatalytic Performance of Perovskite Ferroelectric Powder via Oxygen Vacancy Engineering.

Piezocatalysis has increasingly gained prominence due to its enormous potential for addressing energy shortages and environmental pollution issues. Nonetheless, the low piezocatalytic activity of state-of-the-art materials seriously inhibits the practical applications of piezocatalysis. Here, itis proposed to greatly enhance the piezocatalytic activity for a perovskite ferroelectric, i.e., Sm-doped 0.68Pb(Mg1/3 Nb2/3 )-0.32PbTiO3 (Sm-PMN-PT, a solid solution with ultrahigh piezoelectricity), by introducing oxygen vacancies (OVs). The results show that the presence of OVs promotes the production of reactive oxygen species while enhancing the adsorption and activation of organic pollutants to improve piezocatalytic performance. The OV-Sm-PMN-PT is found to possess a superior piezocatalytic degradation rate constant of 0.073 min-1 under ultrasonic vibration, which is ≈4.9 times higher than that of pristine Sm-PMN-PT. Furthermore, the OV-Sm-PMN-PT can efficiently remove RhB under 400rpm stirring, making it a promising candidate for water purification using low-frequency mechanical energy from nature. This research sheds light on the design of piezocatalytic materials via defect engineering.

Impact of external excitations on blinking enhanced synchronization in bistable vibrational energy harvesters.

Vibrational energy harvesters are capable of converting low-frequency broad-band mechanical energy into electrical power and can be used in implantable medical devices and wireless sensors. With the use of such energy harvesters, it is feasible to generate continuous power that is more reliable and cost-effective. According to previous findings, the energy harvester can offer rich complex dynamics, one of which is obtaining the synchronization behavior, which is intriguing to achieve desirable power from energy harvesters. Therefore, we consider bistable energy harvesters with periodic and quasiperiodic excitations to investigate synchronization. Specifically, we introduce blinking into the coupling function to check whether it improves the synchronization. Interestingly, we discover that raising the normalized proportion of blinking can initiate synchronization behaviors even with lower optimal coupling strength than the absence of blinking in the coupling (i.e., continuous coupling). The existence of synchronization behaviors is confirmed by finding the largest Lyapunov exponents. In addition, the results show that the optimal coupling strength needed to achieve synchronization for quasiperiodic excitations is smaller than that for periodic excitations.

Revisiting lead magnesium niobate-lead titanate piezoceramics for low-frequency mechanical vibration-based energy harvesting

Revisiting lead magnesium niobate-lead titanate piezoceramics for low-frequency mechanical vibration-based energy harvesting

Laser-Induced Graphene Formation on Chitosan Derivatives toward Ecofriendly Electronics

Laser-induced graphene (LIG) has aroused a wide range of research interests ranging from micro-nano energy devices to the Internet of Things (IoT). Nevertheless, the non-degradability of most-used synthetic polymer carbon sources poses a serious threat to the environment. In this work, ecofriendly chitosan-based derivatives, including carboxymethyl chitosan (CMCS), chitosan oligosaccharide, and chitosan hydrochloride, are successfully converted into LIGs for the first time via a convenient one-step CO2 laser engraving at ambient air. The obtained LIGs are characterized by a three-dimensional hierarchical porous structure and exhibit good sheet conductivity. The consecutive carbonization and graphitization mechanism of target precursors induced by laser heat accumulation is also deeply discussed. Besides, based on a mechanically reliable LIG/CMCS composite film and tribo-negative acrylic/polyimide anti-layers, two contact-separation mode triboelectric nanogenerators are built and their power densities range from 1.44 to 2.48 mW cm–2. These devices with long cycle life can be used for low-frequency mechanical energy harvesting and commercial capacitance charging, which could be potentially applied in the wireless sensor network nodes. Such a family of chitosan derivatives paves a new route for LIG synthesis and provides new ideas for ecofriendly LIG electronics.

Enhancing the Performance of Triboelectric Generator: A Novel Approach Using Solid-Liquid Interface-Treated Foam and Metal Contacts.

This work introduces a novel approach for enhancing the performance of a triboelectric generator (TEG) by using a solid-liquid interface-treated foam (SLITF) as its active layer, combined with two metal contacts of different work functions. SLITF is made by absorbing water into a cellulose foam, which enables charges generated by friction energy during the sliding motion to be separated and transferred through the conductive path formed by the hydrogen-bonded network of water molecules. Unlike traditional TEGs, the SLITF-TEG demonstrates an impressive current density of 3.57 A/m2 and can harvest electric power up to 0.174 W/m2 with an induced voltage of approximately 0.55 V. The device generates a direct current in the external circuit, eliminating the limitations of low current density and alternating current found in traditional TEGs. By connecting six-unit cells of SLITF-TEG in series and parallel, the peak voltage and current can be increased up to 3.2 V and 12.5 mA, respectively. Furthermore, the SLITF-TEG has the potential to serve as a self-powered vibration sensor with high accuracy (R2 = 0.99). The findings demonstrate the significant potential of the SLITF-TEG approach for efficiently harvesting low-frequency mechanical energy from the natural environment, with broad implications for a range of applications.

Research Progress in Intelligent Exercise Monitoring Based on Triboelectric Nanogenerator

The coming of the 5G era in the Internet of Things (IoT) opens progress in cross-sectoral research in multiple disciplines. All physiological indicators of the human body are collected through sensors to provide new ideas for developing innovative sports, wearable devices, and modern intelligent venues for IoT. Conventional sensors require an external power source and have a limited lifespan and maintenance cost. Triboelectric nanogenerators (TENG), a new self-powered sensing technology that collects mechanical energy from bodily motions, can break through these limitations and be used in intelligent sports applications. Firstly, TENG can capture kinematic, biochemical, electrophysiological, and tissue dynamics information from the human body. Secondly, the low-frequency mechanical energy of the human body is not only physiological information but can also be used to power microelectronic devices to transmit big data in sports. In conclusion, we discuss TENG-based wearable sensing systems’ challenges and future opportunities.

Enhanced piezo-catalytic H2O2 production over Bi0.5Na0.5TiO3 via piezoelectricity enhancement and surface engineering

The piezo-catalytic hydrogen peroxide (H2O2) production is a promising alternative to traditional anthraquinone oxidation process, but it remains a challenging task. The low conversion efficiency of mechanical energy and the limitedsurface-active sites are the challengings for improving reaction efficiency. Moreover, piezo-catalysts are difficult to prepare in large quantities, limiting the industrial application. To address this issue, this study utilized piezoelectricity enhancement and surface engineering to regulate the Bi0.5Na0.5TiO3 (BNT) for piezo-catalytic H2O2 production. We successfully synthesized an efficient and stable piezo-catalyst, Ag-loaded Bi0.5Na0.5TiO3-AgNbO3 solid solution (Ag/BNT-AN), that was applied to two-channel H2O2 production. The piezo-catalytic activity of Ag/BNT-AN piezo-catalyst was greatly improved through joint regulation of enhancing piezoelectricity by Ag and Nb co-substitution, as well as promoting O2 reduction and H2O oxidation reactions by surface modification with Ag nanoparticals and hydroxyl groups. The optimal Ag/BNT-AN piezo-catalyst displayed H2O2 production rates of 469 µmol g−1 h−1 under ultrasonic vibration, which was 13 times higher than pure BNT. Additionally, the study found that H2O2 could also be synthesized when the catalyst was subjected to simple stirring as mechanical stress, indicating the potential of Ag/BNT-AN to harness low-frequency mechanical energy. This work provides an effective strategy for regulating piezo-catalysts and presents a catalyst design paradigm at the kilogram level.

Broadband and Multi-Cylinder-Based Triboelectric Nanogenerators for Mechanical Energy Harvesting with High Space Utilization.

The development and utilization of new energy sources is an effective means of addressing the limits of traditional fossil energy resources and the problem of environmental pollution. Triboelectric nanogenerators (TENG) show great potential for applications in harvesting low-frequency mechanical energy from the environment. Here, we propose a multi-cylinder-based triboelectric nanogenerator (MC-TENG) with broadband and high space utilization for harvesting mechanical energy from the environment. The structure consisted of two TENG units (TENG I and TENG II) assembled by a central shaft. Both an internal rotor and an external stator were included in each TENG unit, operating in oscillating and freestanding layer mode. On one hand, the resonant frequencies of the masses in the two TENG units were different at the maximum angle of oscillation, allowing for energy harvesting in a broadband range (2.25-4 Hz). On the other hand, the internal space of TENG II was fully utilized, and the maximum peak power of the two TENG units connected in parallel reached 23.55 mW. In contrast, the peak power density reached 31.23 Wm-3, significantly higher than that of a single TENG unit. In the demonstration, the MC-TENG could power 1000 LEDs, a thermometer/hygrometer, and a calculator continuously. Therefore, the MC-TENG will have excellent application in the field of blue energy harvesting in the future.

The sealed bionic fishtail-structured TENG based on anticorrosive paint for ocean sensor systems

Triboelectric nanogenerators (TENGs) have attracted considerable research attention because of there ability to collect low-frequency mechanical energy. The sealed bionic fishtail-structured TENG (SBF-TENG) based on anticorrosive paint is presented for the first time in this paper because of its good maneuverability, stability and mechanical characteristics for harvesting blue energy. Meanwhile, the material characteristics of the SBF-TENG are systematically studied and engineered for optimizing triboelectric power generation, collecting the wave energy in the environment. The salinity of the ocean or solution can be sensitively detected by The SBF-TENG through the collection of ocean energy. Furthermore, the service life of metals in the ocean or solution can be increased through the cathodic protection system constructed by the SBF-TENG. This work provides a paradigm of combining TENGs with the biomimetic underwater robot, and it is of great importance for the application of TENGs in the field of metal cathodic protection and ocean sensor systems.

A PA66 lamellar crystal film with excellent triboelectric performance in vertical contact separation mode

Triboelectric nanogenerators (TENGs) are gaining tremendous attention as an environmentally friendly technology that converts low-frequency mechanical energy into electrical energy.

A Magnetic-Multiplier-Enabled Hybrid Generator with Frequency Division Operation and High Energy Utilization Efficiency.

The hybrid electromagnetic-triboelectric generator (HETG) is a prevalent device for mechanical energy harvesting. However, the energy utilization efficiency of the electromagnetic generator (EMG) is inferior to that of the triboelectric nanogenerator (TENG) at low driving frequencies, which limits the overall efficacy of the HETG. To tackle this issue, a layered hybrid generator consisting of a rotating disk TENG, a magnetic multiplier, and a coil panel is proposed. The magnetic multiplier not only forms the EMG part with its high-speed rotor and the coil panel but also facilitates the EMG to operate at a higher frequency than the TENG through frequency division operation. The systematic parameter optimization of the hybrid generator reveals that the energy utilization efficiency of EMG can be elevated to that of rotating disk TENG. Incorporating a power management circuit, the HETG assumes the responsibility for monitoring the water quality and fishing conditions by collecting low-frequency mechanical energy. The magnetic- multiplier-enabled hybrid generator demonstrated in this work offers a universal frequency division approach to improve the overall outputs of any hybrid generator that collects rotational energy, expanding its practical applications in diverse multifunctional self-powered systems.

An eccentric-structured hybrid triboelectric-electromagnetic nanogenerator for low-frequency mechanical energy harvesting

With the increasing aggravation of the environmental pollution and energy crisis, exploiting clean and renewable energy becomes imperative for human existence and development. In this paper, an eccentric-structured hybrid triboelectric-electromagnetic nanogenerator (EHNG) is proposed to harvest low-frequency mechanical energy. It mainly contains two parts, – a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG). Exploiting the unique eccentric structure, the EHNG can effectively transfer one-dimensional mechanical motion of an object to the rotation of the eccentric rotor, resulting in electricity generation. In comparison to a separate energy harvesting unit, the hybrid nanogenerator operates beyond the single energy harvesting mode, showing preferable electrical output performances including a broader output range and shorter time of voltage boosting. In terms of energy storage, the EHNG provides not only a higher saturation charging voltage and continuous charging from the TENG part, but also a rapid charging speed in the early charging phase from the EMG part. As a practical power source, the EHNG is shown to be capable of directly powering LEDs. The present work develops an effective and sustainable technique to maximally harvest mechanical energy from the environment.

A Multifunction Freestanding Liquid-Solid Triboelectric Nanogenerator Based on Low-Frequency Mechanical Sloshing.

A simple rectangular-structured freestanding liquid-solid triboelectric nanogenerator (LS-TENG) was fabricated, which used fluorinated ethylene propylene (FEP) films and deionized water (DI) as friction materials. The LS-TENG can effectively convert mechanical energy into electrical energy under the extremely low-frequency shaking of 2 Hz and shows greatly reliable stability. The influence of liquid volume and units on the output performance of the LS-TENG was studied, and the mechanism of the triboelectric electrification process of the LS-TENG was analyzed by COMSOL Multiphysics software. The results show that friction materials, liquid types, and number of units have a great effect on the output performance of the LS-TENG. Under the optimized conditions, the designed array LS-TENG shows high output performance with the open-circuit voltage, short-circuit current, and transferred charge of 120 V, 3.9 μA, and 133 nC, respectively. The LS-TENG can be applied in capacitive storage, AC power, signal acquisition, and self-powered sensor. The multifunctional LS-TENG provides a potentially practical route for harvesting low-frequency mechanical energy in natural environments and enabling multifunctional applications.

Matching Mechanism of Charge Excitation Circuit for Boosting Performance of a Rotary Triboelectric Nanogenerator.

The triboelectric nanogenerator (TENG) as an ideal low-frequency mechanical energy harvester has received extensive attention, while low output charge density limits its application. A charge excitation strategy is one of the techniques to effectively improve the surface charge density of the TENG. However, there is little in-depth research on the matching factors between the TENG and excitation circuit. Herein, a soft-contact charge excitation rotary TENG (SCER-TENG) is developed to explore the matching mechanism of different charge excitation strategies. The total output power transferred by the voltage-multiplying circuit (VMC) is 2.13 times that of the full-wave bridge rectifier, which effectively improves the output performance of the SCER-TENG. Moreover, through the established capacitor model and the theoretically calculated maximum output charge of the SCER-TENG with VMC and Zener diodes (VMC-Z), it is found that the output of the Main TENG is mainly affected by capacitors and Zener diodes. The theories have been verified by experiments. After optimization, the output charge of the Main TENG with VMC-Z (1.54 μC) is 3850% higher than that without excitation (0.04 μC). The SCER-TENG successfully harvests low-speed (2.5 m s-1) wind energy to form a self-powered system. This work has crucial instructive implications for using charge excitation strategies to improve the performance of the rotary TENG.

Breathable fabric-based triboelectric nanogenerators with open-porous architected polydimethylsiloxane coating for wearable applications

Triboelectric nanogenerators (TENGs), which can harvest low-frequency mechanical energy from human activities, are potential for wearable electronics, especially textile-based TENGs. Besides triboelectric performance, wearable comfort, like air permeability, is crucial for wearable electronics. However, the textile-based TENGs integrated with high performance and wearable comfort still remain challenging. Here, we construct the open porous architected PDMS coatings on fabric for breathable fabric-based TENG (oPF-TENG) based on the synergistic effect of insoluble NaCl, DBP and soluble silicone oil. The open porous structure constitutes the airflow channel with the air permeability of ∼73 mm/s. Meanwhile, the porous structure and the PVDF filler enhance the triboelectric output. The open circuit voltage, short circuit current and power density of oPF-TENG reach ∼600 V, ∼15 μA and 5.67 W/m2, respectively. The as-made oPF-TENG with good air permeability and triboelectric output can not only contribute to the human body energy harvesting but also show potential for wearable self-powered sensing.