Opportunities and Challenges in Triboelectric Nanogenerator (TENG) based Sustainable Energy Generation Technologies: A Mini-Review

Operator-Based Triboelectric Nanogenerator Power Management and Output Voltage Control

In this paper, an operator-based voltage control method for TENGs is investigated, achieving output voltage tracking without compensators and uncertainty suppression using robust right coprime factorization. Initially, a comprehensive simulation-capable circuit model for TENGs is developed, integrating their open-circuit voltage and variable capacitance characteristics. This model is implemented to simulate the behavior of TENGs with a rectifier bridge and capacitive load. To address the high-voltage, low-current pulsating nature of TENG outputs, a storage capacitor switching model is designed to effectively transfer the pulsating energy. This switching model is directly connected to a buck converter and operates under a unified control strategy. A complete TENG power management system was established based on this model, incorporating an operator theory-based control strategy. This strategy ensures steady output voltage under varying load conditions without using compensators, thereby reducing disturbances. Simulation results validate the feasibility of the proposed TENG system and the efficacy of the control strategy, providing a robust framework for optimizing TENG energy harvesting and management systems with significant potential for practical applications.

Nanocomposite Electret Layer Improved Long-Term Stable Solid-Liquid Contact Triboelectric Nanogenerator for Water Wave Energy Harvesting

With the continuous rise of environmental pollution and energy crisis, the global energy revolution is risen. Development of renewable blue energy based on the emerging promising triboelectric nanogenerators (TENG) has become an important direction of future energy development. The solid-liquid contact triboelectric nanogenerator (TENG) has the advantages of flexible structure, easy manufacture, and long-term stability, which makes it easier to integrate and achieve large-scale conversion of wave mechanical energy. However, the electric power output is still not large enough, which limits its practical applications. In this work, a nanocomposite electret layer enhanced solid-liquid contact triboelectric nanogenerator (E-TENG) is proposed for water wave energy harvesting, which can effectively improve the electric output and achieve real-time power supply of wireless sensing. Through introducing a nanocomposite electret layer into flexible multilayer solid-liquid contact TENG, higher power output is achieved. The E-TENG (active size of 50 mm × 49 mm) shows desired output performance, a power density of 521 mW m-2. The generated electric energy can drive wireless temperature sensing by transmitting wireless signals carrying detection information at the period of ˂5.5 min. This research greatly improves the electric output and provides a solid basis for the industrialization of TENG in blue energy.

Powering the future: Exploring self-charging cardiac implantable electronic devices and the Qi revolution

The incidence and prevalence of cardiovascular diseases (CVD) have risen over the last few decades worldwide, resulting in a cost burden to healthcare systems and increasingly complex procedures. Among many strategies for treating heart diseases, treating arrhythmias using cardiac implantable electronic devices (CIEDs) has been shown to improve quality of life and reduce the incidence of sudden cardiac death. The battery-powered CIEDs have the inherent challenge of regular battery replacements depending upon energy usage for their programmed tasks. Nanogenerator-based  energy harvesters have been extensively studied, developed, and optimized continuously in recent years to overcome this challenge owing to their merits of self-powering abilities and good biocompatibility. Although these nanogenerators and others currently used in energy harvesters, such as biofuel cells (BFCs) exhibit an infinite spectrum of uses for this novel technology, their demerits should not be dismissed. Despite the emergence of Qi wireless power transfer (WPT) has revolutionized the technological world, its application in CIEDs has yet to be studied well. This review outlines the working principles and applications of currently employed energy harvesters to provide a preliminary exploration of CIEDs based on Qi WPT, which may be a promising technology for the next generation of functionalized CIEDs.

Advancements in Bio-inspired Self-Powered Wireless Sensors: Materials, Mechanisms, and Biomedical Applications

The rapid maturation of smart city ecosystems is intimately linked to advances in the Internet of Things (IoT) and self-powered sensing technologies. Central to this evolution are battery-less sensors that are critical for applications such as continuous health monitoring through blood metabolites and vital signs, the recognition of human activity for behavioral analysis, and the operational enhancement of humanoid robots. The focus on biosensors that exploit the human body for energy-spanning wearable, attachable, and implantable variants has intensified, driven by their broad applicability in areas from underwater exploration to biomedical assays and earthquake monitoring. The heart of these sensors lies in their diverse energy harvesting mechanisms, including biofuel cells, and piezoelectric, triboelectric, and pyroelectric nanogenerators. Notwithstanding the wealth of research, the literature still lacks a holistic review that integrates the design challenges and implementation intricacies of such sensors. Our review seeks to fill this gap by thoroughly evaluating energy harvesting strategies from both material and structural perspectives and assessing their roles in powering an array of sensors for myriad uses. This exploration offers a comprehensive outlook on the state of self-powered sensing devices, tackling the nuances of their deployment and highlighting their potential to revolutionize data gathering in autonomous systems. The intent of this review is to chart the current landscape and future prospects, providing a pivotal reference point for ongoing research and innovation in self-powered wireless sensing technologies.

Nanofibrous PAN-PDMS Films-Based High-Performance Triboelectric Artificial Whisker for Self-Powered Obstacle Detection

Avoiding collisions is a key necessity for any autonomous mobile robot, and obstacle mapping enables them to maneuver in an uncharted area. In this era of the Internet of Things, with the emerging need for a multitude of sensors, adopting self-powered technologies is more practically viable than batteries for powering the same. Herein, with the fabrication of a triboelectric artificial whisker (TAW), a self-powered obstacle detection is demonstrated via tactile perception. The mechanical contact with the obstacle gives rise to an electrical signal from the TAW owing to the embedded triboelectric sensor. In addition, the triboelectric nanogenerator (TENG) based on electrospun polyacrylonitrile (PAN) nanofibers and polydimethylsiloxane film, which facilitates this self-powered artificial sensation, generates an output voltage of 720 V and current density of 5 mA m-2 with 1.7 W m-2 of maximum power delivery from a force of 10 N. The electro-spinning aided enhancement in contact area of the PAN is responsible for the remarkable improvement in the performance of the TENG, 3.4 times enhancement in power density, when compared to the nonsurface-modified ones. In addition, the TENG is able to charge commercial capacitors up to appreciable values and demonstrates powering different electronic gadgets such as calculators and thermometers.

Implantable Triboelectric Nanogenerators for Self-Powered Cardiovascular Healthcare

Triboelectric nanogenerators (TENGs) have gained significant traction in recent years in the bioengineering community. With the potential for expansive applications for biomedical use, many individuals and research groups have furthered their studies on the topic, in order to gain an understanding of how TENGs can contribute to healthcare. More specifically, there have been a number of recent studies focusing on implantable triboelectric nanogenerators (I-TENGs) toward self-powered cardiac systems healthcare. In this review, the progression of implantable TENGs for self-powered cardiovascular healthcare, including self-powered cardiac monitoring devices, self-powered therapeutic devices, and power sources for cardiac pacemakers, will be systematically reviewed. Long-term expectations of these implantable TENG devices through their biocompatibility and other utilization strategies will also be discussed.

One Material-Opposite Triboelectrification: Molecular Engineering Regulated Triboelectrification on Silica Surface to Enhance TENG Efficiency

Molecular engineering is a unique methodology to take advantage of the electrochemical characteristics of materials that are used in energy-harvesting devices. Particularly in triboelectric nanogenerator (TENG) studies, molecular grafting on dielectric metal oxide surfaces can be regarded as a feasible way to alter the surface charge density that directly affects the charge potential of triboelectric layers. Herein, we develop a feasible methodology to synthesize organic-inorganic hybrid structures with tunable triboelectric features. Different types of self-assembled monolayers (SAMs) with electron-donating and withdrawing groups have been used to modify metal oxide (MO) surfaces and to modify their charge density on the surface. All the synthetic routes for hybrid material production have been clearly shown and the formation of covalent bonds on the MO's surface has been confirmed by XPS. The obtained hybrid structures were applied as dopants to distinct polymer matrices with various ratios and fiberization processes were carried out to the prepare opposite triboelectric layers. The formation of the fibers was analyzed by SEM, while their surface morphology and physicochemical features have been measured by AFM and a drop shape analyzer. The triboelectric charge potential of each layer after doping and their contribution to the TENG device's parameters have been investigated. For each triboelectric layer, the best-performing tribopositive and tribonegative material combination was separately determined and then these opposite layers were used to fabricate TENG with the highest efficiency. A comparison of the device parameters with the reference indicated that the best tribopositive material gave rise to a 40% increase in the output voltage and produced 231 V, whereas the best tribonegative one led to a 33.3% rise in voltage and generated 220 V. In addition, the best device collected ~83% more charge than the reference device and came up with 250 V that corresponds to 51.5% performance enhancement. This approach paved the way by addressing the issue of how molecular engineering can be used to manipulate the triboelectric features of the same materials.

Enhancement of a pyroelectric body energy harvesting scheme employing pulsed electric fields

This research utilizes waste heat energy as a sustainable energy source to enhance pyroelectric power output by combining pyroelectric nanogenerators with an external pulsed electric field. When the surface temperature of the pyroelectric body varies, applying different pulses of the external electric field results in maximum power accumulation. A novel power-generating experimental setup was developed to measure and compute pyroelectric power generation. A standard Fuji ceramic C-9 sample was used to generate pyroelectric energy in a 20 °C temperature range from 120 to 140 °C. The continuous temperature variation frequency was 0.05 Hz, and the pulsed electric field was applied when the temperature rose. Pulses of the electric field with widths of 10, 50, 100, and 200 ms were applied to the sample under different pulse amplitudes, and the amplitude of each pulse was 250, 500, 1000, or 1500 V/mm. The maximum power generated through the application of an external pulsed electric field under the above-mentioned conditions was evaluated. This system had the highest power density of 0.204 mJ cm-2 °C-1 kV-1. In addition, for the lowest input power, the maximum power generation condition was a 10 ms pulse width and an amplitude of 250 V mm-1 in the applied electric field. This state might power smart sensor modules, IoT devices, automobiles, and other waste heat energy applications. Nano-pulse electric field applications may reduce input power to its lowest level, dependent on net-producing power. Therefore, new researchers can use net-generation power efficiency to create a large-scale power source using multiple pyroelectric arrays.

Fundamental Understanding of Multicellular Triboelectric Nanogenerator with Different Electrical Configurations

The single-cell triboelectric nanogenerator (TENG) often produces insufficient energy, leading to the use of a multicellular TENG structure. This work experimented with and simulated a dual-cell TENG with various configurations in parallel and series arrangements. The working principle of charge generation during each phase of a contact-separation cycle was explained through the analysis and comparison of five electrical configurations of a dual-cell TENG. Our observations indicate that measuring the output charge of a TENG provides a more reliable performance comparison. Finally, multicellular TENG with four cells arranged in an X-shape (X-TENG), self-supporting structure is fabricated and further experimented with, validating our conjectures derived from a dual-cell TENG.

Self-Repairing and Energy-Harvesting Triboelectric Sensor for Tracking Limb Motion and Identifying Breathing Patterns

The increasing prevalence of health problems stemming from sedentary lifestyles and evolving workplace cultures has placed a substantial burden on healthcare systems. Consequently, remote health wearable monitoring systems have emerged as essential tools to track individuals' health and well-being. Self-powered triboelectric nanogenerators (TENGs) have exhibited significant potential for use as emerging detection devices capable of recognizing body movements and monitoring breathing patterns. However, several challenges remain to be addressed in order to fulfill the requirements for self-healing ability, air permeability, energy harvesting, and suitable sensing materials. These materials must possess high flexibility, be lightweight, and have excellent triboelectric charging effects in both electropositive and electronegative layers. In this work, we investigated self-healable electrospun polybutadiene-based urethane (PBU) as a positive triboelectric layer and titanium carbide (Ti3C2Tx) MXene as a negative triboelectric layer for the fabrication of an energy-harvesting TENG device. PBU consists of maleimide and furfuryl components as well as hydrogen bonds that trigger the Diels-Alder reaction, contributing to its self-healing properties. Moreover, this urethane incorporates a multitude of carbonyl and amine groups, which create dipole moments in both the stiff and the flexible segments of the polymer. This characteristic positively influences the triboelectric qualities of PBU by facilitating electron transfer between contacting materials, ultimately resulting in high output performance. We employed this device for sensing applications to monitor human motion and breathing pattern recognition. The soft and fibrous-structured TENG generates a high and stable open-circuit voltage of up to 30 V and a short-circuit current of 4 μA at an operation frequency of 4.0 Hz, demonstrating remarkable cyclic stability. A significant feature of our TENG is its self-healing ability, which allows for the restoration of its functionality and performance after sustaining damage. This characteristic has been achieved through the utilization of the self-healable PBU fibers, which can be repaired via a simple vapor solvent method. This innovative approach enables the TENG device to maintain optimal performance and continue functioning effectively even after multiple uses. After integration with a rectifier, the TENG can charge various capacitors and power 120 LEDs. Moreover, we employed the TENG as a self-powered active motion sensor, attaching it to the human body to monitor various body movements for energy-harvesting and sensing purposes. Additionally, the device demonstrates the capability to recognize breathing patterns in real time, offering valuable insights into an individual's respiratory health.

MXene-Based Nanocomposites for Piezoelectric and Triboelectric Energy Harvesting Applications

Due to its superior advantages in terms of electronegativity, metallic conductivity, mechanical flexibility, customizable surface chemistry, etc., 2D MXenes for nanogenerators have demonstrated significant progress. In order to push scientific design strategies for the practical application of nanogenerators from the viewpoints of the basic aspect and recent advancements, this systematic review covers the most recent developments of MXenes for nanogenerators in its first section. In the second section, the importance of renewable energy and an introduction to nanogenerators, major classifications, and their working principles are discussed. At the end of this section, various materials used for energy harvesting and frequent combos of MXene with other active materials are described in detail together with the essential framework of nanogenerators. In the third, fourth, and fifth sections, the materials used for nanogenerators, MXene synthesis along with its properties, and MXene nanocomposites with polymeric materials are discussed in detail with the recent progress and challenges for their use in nanogenerator applications. In the sixth section, a thorough discussion of the design strategies and internal improvement mechanisms of MXenes and the composite materials for nanogenerators with 3D printing technologies are presented. Finally, we summarize the key points discussed throughout this review and discuss some thoughts on potential approaches for nanocomposite materials based on MXenes that could be used in nanogenerators for better performance.

3D printed triboelectric nanogenerator for underwater ultrasonic sensing

The underwater ultrasound power measurement has become necessary due to the rapid development of sonochemistry and sonocatalysis. This article presents construction of novel triboelectric nanogenerator (TENG) and its application for a detection of ultrasonic waves in water. The device was 3D printed using widely available and cost-effective materials. TENG consisted of the device housing and movable polymer pellets confined between flat electrodes. The device housing and pellets were 3D printed via stereolithography (SLA) and fused deposition modelling (FDM) methods, respectively. The pellets moved periodically driven by the ultrasonic waves leading to generation of an alternating voltage signal. The electric response of TENG was calibrated using a commercially available ultrasonic power sensor. The open-circuit voltage output of TENG was registered in different sections of the ultrasonic bath in order to determine the distribution of the acoustic power. TENG electric responses were analyzed by applying the fast Fourier transform (FFT) and fitting the theoretical dependence to experimental data. The main peaks in the frequency spectra of the voltage waveforms corresponded to the fundamental excitation frequency of the ultrasonic bath. TENG device, presented in this paper, can be successfully applied as a self-powered sensor for detection of ultrasonic waves. It enables precise control of the sonochemical process and reduction of power losses of the ultrasonic reactor. 3D printing technology has been confirmed to be fast, easy, and scalable method of fabrication of the ultrasonic sensors.

Modular Design in Triboelectric Sensors: A Review on the Clinical Applications for Real-Time Diagnosis

Triboelectric nanogenerators (TENGs) have garnered considerable interest as a promising technology for energy harvesting and stimulus sensing. While TENGs facilitate the generation of electricity from micro-motions, the modular design of TENG-based modular sensing systems (TMSs) also offers significant potential for powering biosensors and other medical devices, thus reducing dependence on external power sources and enabling biological processes to be monitored in real time. Moreover, TENGs can be customised and personalized to address individual patient needs while ensuring biocompatibility and safety, ultimately enhancing the efficiency and security of diagnosis and treatment. In this review, we concentrate on recent advancements in the modular design of TMSs for clinical applications with an emphasis on their potential for personalised real-time diagnosis. We also examine the design and fabrication of TMSs, their sensitivity and specificity, and their capabilities of detecting biomarkers for disease diagnosis and monitoring. Furthermore, we investigate the application of TENGs to energy harvesting and real-time monitoring in wearable and implantable medical devices, underscore the promising prospects of personalised and modular TMSs in advancing real-time diagnosis for clinical applications, and offer insights into the future direction of this burgeoning field.

Silicone-Based Multifunctional Thin Films with Improved Triboelectric and Sensing Performances via Chemically Interfacial Modification

The development of triboelectric nanogenerators (TENGs) technology has advanced in recent years. However, TENG performance is affected by the screened-out surface charge density owing to the abundant free electrons and physical adhesion at the electrode-tribomaterial interface. Furthermore, the demand for flexible and soft electrodes is higher than that for stiff electrodes for patchable nanogenerators. This study introduces a chemically cross-linked (XL) graphene-based electrode with a silicone elastomer using hydrolyzed 3-aminopropylenetriethoxysilanes. The conductive graphene-based multilayered electrode was successfully assembled on a modified silicone elastomer using a cheap and eco-friendly layer-by-layer assembly method. As a proof-of-concept, the droplet-driven TENG with the chemically XL electrode of silicone elastomer exhibited an output power of approximately 2-fold improvement owing to its higher surface charge density than without XL. This chemically XL electrode of silicone elastomer film demonstrated remarkable stability and resistance to repeated mechanical deformations like bending and stretching. Moreover, due to the chemical XL effects, it was used as a strain sensor to detect subtle motions and exhibited high sensitivity. Thus, this cheap, convenient, and sustainable design approach can provide a platform for future multifunctional wearable electronic devices.

Adaptive Triboelectric Nanogenerators for Long-Term Self-Treatment: A Review

Triboelectric nanogenerators (TENGs) were initially invented as an innovative energy-harvesting technology for scavenging mechanical energy from our bodies or the ambient environment. Through adaptive customization design, TENGs have also become a promising player in the self-powered wearable medical market for improving physical fitness and sustaining a healthy lifestyle. In addition to simultaneously harvesting our body's mechanical energy and actively detecting our physiological parameters and metabolic status, TENGs can also provide personalized medical treatment solutions in a self-powered modality. This review aims to cover the recent advances in TENG-based electronics in clinical applications, beginning from the basic working principles of TENGs and their general operation modes, continuing to the harvesting of bioenergy from the human body, and arriving at their adaptive design toward applications in chronic disease diagnosis and long-term clinical treatment. Considering the highly personalized usage scenarios, special attention is paid to customized modules that are based on TENGs and support complex medical treatments, where sustainability, biodegradability, compliance, and bio-friendliness may be critical for the operation of clinical systems. While this review provides a comprehensive understanding of TENG-based clinical devices that aims to reach a high level of technological readiness, the challenges and shortcomings of TENG-based clinical devices are also highlighted, with the expectation of providing a useful reference for the further development of such customized healthcare systems and the transfer of their technical capabilities into real-life patient care.

High-Performance Triboelectric Nanogenerators Based on Commercial Textiles: Electrospun Nylon 66 Nanofibers on Silk and PVDF on Polyester

A high-performance textile triboelectric nanogenerator is developed based on the common commercial fabrics silk and polyester (PET). Electrospun nylon 66 nanofibers were used to boost the tribo-positive performance of silk, and a poly(vinylidene difluoride) (PVDF) coating was deployed to increase the tribo-negativity of PET. The modifications confer a very significant boost in performance: output voltage and short-circuit current density increased ∼17 times (5.85 to 100 V) and ∼16 times (1.6 to 24.5 mA/m2), respectively, compared with the Silk/PET baseline. The maximum power density was 280 mW/m2 at a 4 MΩ resistance. The performance boost likely results from enhancing the tribo-positivity (and tribo-negativity) of the contact layers and from increased contact area facilitated by the electrospun nanofibers. Excellent stability and durability were demonstrated: the nylon nanofibers and PVDF coating provide high output, while the silk and PET substrate fabrics confer strength and flexibility. Rapid capacitor charging rates of 0.045 V/s (2 μF), 0.031 V/s (10 μF), and 0.011 V/s (22 μF) were demonstrated. Advantages include high output, a fully textile structure with excellent flexibility, and construction based on cost-effective commercial fabrics. The device is ideal as a power source for wearable electronic devices, and the approach can easily be deployed for other textiles.

Structural Flexibility in Triboelectric Nanogenerators: A Review on the Adaptive Design for Self-Powered Systems

There is an increasing need for structural flexibility in self-powered wearable electronics and other Internet of Things (IoT), where adaptable triboelectric nanogenerators (TENGs) play a key role in realizing the true potential of IoT by endowing the latter with self-sustainability. Thus, in this review, the topic was restricted to the adaptive design of TENGs with structural flexibility that aims to promote the sustainable operation of various smart electronics. This review begins with an emphatical discussion of the concept of flexible electronics and TENGs, and continues with the introduction of TENG-based self-powered intelligent systems while placing the emphasis on self-powered flexible intelligent devices. Self-powered healthcare sensors, e-skins, and other intelligent wearable electronics with enhanced intelligence and efficiency in practical applications due to the integration with TENGs are illustrated, along with an emphasis on the design strategy of structural flexibility of TENGs and the associated integration schemes. This review aims to cover recent achievements in the field of self-powered systems, and provides information on how flexibility or adaptability in TENGs can be adopted, their types, and why they are required in promoting advanced IoT applications with sustainability and intelligence algorithms.