Development Of Triboelectric Nanogenerators Research Articles

Boosting the triboelectric performances of biowaste chitosan keratin triboelectric nanogenerator using carbon composite film as charge storage and charge recombination blocking intermediate layer

Environmental conservation efforts are promoting energy-generation technologies that avoid the use of highly polluting fuels and promote the reuse of waste materials. Advances in triboelectric nanogenerators (TENGs) have led to the progress in harvesting energy from ambient mechanical sources and powering small devices and sensors while being compact, flexible, biocompatible, and eco-friendly. Nevertheless, the practical applications of TENG have limitations. Therefore, the development of TENG with excellent tribological performance, eco-friendliness, and low cost is crucial. Consequently, an environmentally friendly, inexpensive TENG device with outstanding triboelectric performance was designed using keratin-enhanced chitosan as a tribo-positive material, a carbon film as an intermediate layer, and polytetrafluoroethylene as a triboelectric negative material. The device was purposely designed to simultaneously play a role in waste treatment and efficient green energy harvesting. Therefore, keratin was extracted from recycled fur, and a carbon film was selected to enhance the triboelectric performance because of its excellent electrical conductivity and dielectric constant. The triboelectric properties of a chitosan keratin intermediate layer (CKI)-TENG were systematically investigated. Practical applications of the CKI-TENG in charging electronic devices and waste-noise harvesting were also studied. The developed CKI TENG exhibited outstanding triboelectric performance compared to a TENG device without an intermediate layer. Particularly, the charge transfer, output voltage and power density was improved by 19%, 46%, and 60%, respectively, compared to the output of the chitosan-keratin (CK) TENG device. It also exhibited outstanding cyclic and charging-discharging stabilities. In addition, the power density of the developed CKI TENG was higher than that of previously reported TENG devices. Thus, it can play a significant role in green and clean energy generation and the utilization of the harvested energy in practical applications, such as biomedical sensors, charging electronic devices, smart textiles, and sensors.

A vortex-induced vibration device based on MG-TENG and research of its application in ocean current energy harvesting

In recent years, with the extensive research on the application of triboelectric nanogenerators (TENGs) by scholars all over the world, the development of TENGs in harvesting and utilization of ocean energy has attracted more and more attention according to the advantages of TENGs in low-frequency energy harvesting. As a kind of ocean energy, the development and utilization of ocean current energy is of great significance to the diversification of energy sources, the promotion of sustainable energy development, the protection of ecological environment and the response to climate change. In this work, a novel device based on the combination of vortex-induced vibration (VIV) and multi-grating TENG (MG-TENG) is proposed for energy harvesting in low-speed ocean currents. The device consists of an up and down moving float driving the TENG to convert kinetic energy into electrical energy. The result shows that the system has a maximum average output power of nearly 20 μW under the condition of 8 grating TENG. This work demonstrates the ability of devices based on the combination of VIV and MG-TENG to drive low-power electronic components, demonstrating future applications for sensing, positioning, and more.

3D hierarchical microcubic morphological composite and its application for Bi-functional Humidity/Pressure sensing in TENG architecture

Harnessing the power of contact electrification, triboelectric nanogenerators (TENGs) are a cutting-edge energy technology, where output performance is greatly influenced by the micro/nano scale architectures of triboelectric layers. We present a study on the development of TENG by introducing an advanced 3D hierarchical microcubic morphological structure prepared by simple solution casting method, employing a renewable material, lignin, in combination with eco-friendly polyvinyl alcohol (PVA) matrix. The strategic incorporation of epichlorohydrin (EPCH) as a crosslinker enhances thermal stability, and crosslinking within the lignin/PVA composite (LPC) film. A remarkable outcome of this integration is the emergence of a 3D hierarchical microcubic structure within the LPC film. This structure, with its intricate 3D arrangement, emerges as the cornerstone that underpins the development of LPC-TENGs devices distinguished by their simple fabrication process, elevated output performance, and multifaceted applications. The LPC-TENG, adorned with its unique 3D hierarchical microcubic architecture, establishes new standards in energy harvesting and sensing capabilities with a maximum output power density of 135.4 mWm−2, a short-circuit current of 6.44 μA, and a maximum output voltage of 65 V (5 times higher than PVA-based TENGs). Additionally, the LPC-TENG showed exceptional performance as a self-powered bifunctional sensing system, providing a steady output voltage range of 0–10 V across various humidity levels (20–90 % RH) and a wide usable pressure range (0–162 kPa) with a low detection limit of 1 kPa. We demonstrated the application of the LPC-TENG in energy harvesting from human walking, enabling simultaneous measurements of environmental relative humidity, pressure, and illumination of 27 commercial LEDs. The unique 3D hierarchical microcubic architecture offers an unparalleled foundation for accommodating overall performance and diverse sensing functionalities.

Advances of Strategies to Increase the Surface Charge Density of Triboelectric Nanogenerators: A Review.

Triboelectric nanogenerators (TENGs) have manifested a remarkable potential for harvesting environmental energy and have the prospects to be utilized for various uses, for instance, self-powered sensing devices, flexible wearables, and marine corrosion protection. However, the potential for further development of TENGs is restricted on account of their low output power that in turn is determined by their surface charge density. The current review majorly focuses on the selection and optimization of triboelectric materials. Subsequently, various methods capable of enhancing the surface charge density of TENGs, including environmental regulation, charge excitation, charge pumping, electrostatic breakdown, charge trapping, and liquid-solid structure are comprehensively reviewed. Lastly, the review is concluded by highlighting the existing challenges in enhancing the surface charge density of TENGs and exploring potential opportunities for future research endeavors in this area.

Droplet energy harvesting system based on MXene/SiO2 modified triboelectric nanogenerators

Raindrops are an abundant micromechanical renewable energy source in nature, and raindrop energy harvesting has always been a research hotspot. Traditional hydropower generation is not suitable for low-frequency energy harvesting, and it is difficult to realize distributed energy harvesting. The development of triboelectric nanogenerator (TENG) is a promising strategy for converting raindrop energy in the environment into electrical energy. Polydimethylsiloxane (PDMS) composite has received much attention due to its excellent chemical stability and insulating properties for TENG. However, the deficiency of the low output performance and insufficient hydrophobicity of PDMS limits the application of PDMS in droplet energy capture. Modification of PDMS can improve the droplet energy collection capability of the liquid–solid contact triboelectric (LS-TENG). In this work, a new approach to modifying polydimethylsiloxane (PDMS) as a hydrophobic negative triboelectric material using a high dielectric constant MXene and a hydrophobic nano-SiO2 was reported. The as-prepared composites′ permittivity and triboelectric performance were remarkably promoted as compared to composites without interfacial modification. In addition, the use of composites for TENG assembly improved the open-circuit voltage and short-circuit current by a factor of 47.5 and 25.21, respectively, compared to pure PDMS. Application of the composite to the assembled TENG was employed as energy harvester to light up LEDs and charge a capacitor. In addition, a cathodic protection system was designed to demonstrate its potential application in the field of electrochemistry. This provides guidance for the practical implementation of TENGs in the field of electrochemical cathodic protection.

Triboelectric nanogenerators: theoretical calculations, materials, and applications in net-zero emissions

Triboelectric nanogenerators (TENGs) have shown great potential in converting discrete mechanical energy in the environment into electricity without producing any greenhouse gases in the process, and they have been regarded as one of the most powerful methods to achieve zero carbon emissions. It has been confirmed that the output performance is the main factor limiting the real-world applications of the TENGs. Establishing universal standards for quantity analysis TENGs’ outputs and seeking advanced dielectric materials to improve the charge density are the two priorities for boosting TENG outputs. Here, the working mechanisms of TENG and the quantitative analysis of TENG output performance are introduced to reveal the relationships of Q–V–I–x (charge-voltage-current-displacement) and the energy conversion efficiencies. Selecting suitable triboelectric materials is the key to enhancing the performance of TENG. Materials used as advanced friction or dielectric layers are elaborated, including metals, inorganic non-metallic materials, polymers, and composites. Moreover, the influences of performance improvement methods, such as ionization injection, intermediate layer, surface modification, and charge-excitation strategy, are discussed accordingly. Finally, applications to achieving the goal of net zero and future challenges of TENGs are presented. This review provides strategies for guiding the further development of TENGs toward higher performances and promoting the commercialization of TENG net-zero systems.

Advancements in Triboelectric Nanogenerators (TENGs) for Intelligent Transportation Infrastructure: Enhancing Bridges, Highways, and Tunnels.

The development of triboelectric nanogenerators (TENGs) over time has resulted in considerable improvements to the efficiency, effectiveness, and sensitivity of self-powered sensing. Triboelectric nanogenerators have low restriction and high sensitivity while also having high efficiency. The vast majority of previous research has found that accidents on the road can be attributed to road conditions. For instance, extreme weather conditions, such as heavy winds or rain, can reduce the safety of the roads, while excessive temperatures might make it unpleasant to be behind the wheel. Air pollution also has a negative impact on visibility while driving. As a result, sensing road surroundings is the most important technical system that is used to evaluate a vehicle and make decisions. This paper discusses both monitoring driving behavior and self-powered sensors influenced by triboelectric nanogenerators (TENGs). It also considers energy harvesting and sustainability in smart road environments such as bridges, tunnels, and highways. Furthermore, the information gathered in this study can help readers enhance their knowledge concerning the advantages of employing these technologies for innovative uses of their powers.

EVA/PZT‐Composite‐Based Triboelectric Nanogenerator for Energy Harvesting

The development of triboelectric nanogenerators (TENGs) has experienced rapid advancement in the past decade. In the present study, ethylene vinyl acetate (EVA) polymer and lead zirconium titanate (PZT) are taken as the host materials. The EVA–PZT elastomer composites are fabricated using different weight percentages (2.5%, 5.0%, 7.5%, and 10.0%) of PZT in EVA by solvent casting. The X‐ray diffraction investigation of these films reveals the presence of the PZT material and the formation of composites. TENGs have the potential to revolutionize energy harvesting and provide a sustainable energy source for a variety of applications. The electrical output performance of the single‐electrode‐mode‐based TENG is examined. The maximum output of 60 V and 165 nA is produced by the EVA–PZT 7.5 wt%/Al‐based TENG device. Further, TENG is used to power devices and gather biomechanical energy.

Engineering of electrodes with 2D Ti3C2Tx-MXene sheets and chloride salt for robust and flexible high electrical power triboelectric nanogenerator

This article focuses on the development of triboelectric nanogenerator (TENG) by utilizing advanced 2D nanomaterials with innovative design and easy fabrication method to achieve durable TENG with high-power density and improved cycling performance. Herein, we fabricated a layer-by-layer stacked vertical contact-separation (CS) mode TENG. In this unique design, we incorporated a thin film of micron-sized Ti3C2Tx-MXene ultrathin sheets (TMSs) into a polyethylene terephthalate (PET) based tribo-negative electrode. A tribo-positive layer was prepared by integrating an optimized amount of NaCl into a polyvinyl alcohol (PVA) matrix. After optimization of both triboelectric layers, the optimized TMS-TENG showed an open-circuit voltage (Voc) ∼ 390 V, short-circuit current (Isc) ∼ 96 μA, and power density of 6.66 W·m−2. The boosted performance is due to the synergistic effect of TMSs, used as a charge trapping layer on the electronegative side, and the impact of an NaCl:PVA impregnated layer on the electropositive side of the TENG. The ultrathin-layered structures of sandwiched TMS film serve bifunctionally as a charge accumulation and charge trapping entity simultaneously, increasing the charge separation due to high dielectric constant, and thus increasing the overall output power of the fabricated TENG. The prepared TMS-TENG was tested as a pressure sensor to monitor different sensitive physiological movements of the human body. Further applications of the designed TMS-TENGs have been revealed by powering more than 500 LEDs, an electronic calulator, and swiftly charging micro-capacitors by utilizing direct output power. By engineering electrodes, we can gain insight into the specific role that TMSs play in enhancing the performance of TENGs. This research provides a new avenue for designing self-powered pressure/motion sensors in robotics and harvesting biomechanical energy as electrical energy for sustainable electronics.

Functionalized thermoplastic polyurethane with tunable tribopolarity and biodegradability for high performance and biodegradable triboelectric nanogenerator

Triboelectric nanogenerators (TENGs) convert mechanical energy into electrical energy and have received considerable attention as a green energy technology to solve recently emerging global environmental issues. However, most high-power TENGs use polymers as active materials, which contributes to plastic pollution. Therefore, it is necessary to use eco-friendly and biodegradable materials while maintaining high output performance for further development of TENGs as a next-generation green energy technology. This study designs a biodegradable thermoplastic polyurethane (TPU) based on polycaprolactone diol. The TPU was modified using polydimethylsiloxane diol and a chain extender containing fluorine units, which controlled the modification, output performance, and biodegradability of the TENG. Biodegradability varies depending on the structure of the TPU, especially the chain extender. The output of the TENG fabricated based on the modified TPU was considerably increased with a voltage from 1.31 V to 74.03 V and current from 0.02 μA to 1.98 μA. Further, the maximum power density increased approximately 1423 times compared to that of the native TPU-based TENG to a value of 42.71 μW/cm2. This study provides a potential strategy for the development of environmentally friendly, high-powered next-generation TENGs by ensuring controlled biodegradability.

Nanotechnology Applied to Cellulosic Materials.

In recent years, nanocellulosic materials have attracted special attention because of their performance in different advanced applications, biodegradability, availability, and biocompatibility. Nanocellulosic materials can assume three distinct morphologies, including cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial cellulose (BC). This review consists of two main parts related to obtaining and applying nanocelluloses in advanced materials. In the first part, the mechanical, chemical, and enzymatic treatments necessary for the production of nanocelluloses are discussed. Among chemical pretreatments, the most common approaches are described, such as acid- and alkali-catalyzed organosolvation, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation, ammonium persulfate (APS) and sodium persulfate (SPS) oxidative treatments, ozone, extraction with ionic liquids, and acid hydrolysis. As for mechanical/physical treatments, methods reviewed include refining, high-pressure homogenization, microfluidization, grinding, cryogenic crushing, steam blasting, ultrasound, extrusion, aqueous counter collision, and electrospinning. The application of nanocellulose focused, in particular, on triboelectric nanogenerators (TENGs) with CNC, CNF, and BC. With the development of TENGs, an unparalleled revolution is expected; there will be self-powered sensors, wearable and implantable electronic components, and a series of other innovative applications. In the future new era of TENGs, nanocellulose will certainly be a promising material in their constitution.

Smart wearable triboelectric nanogenerator for self-powered bioelectronics and therapeutics

With the development of Triboelectric Nanogenerators (TENGs), the field of energy harvesting has experienced a new era of revolution following the trend to configure innovative materials, design, integrated sensing and high triboelectric output. Here, we investigated the electricity-generation process of TENG by conducting its finite-element analysis using COMSOL Multiphysics software. Further, the effect of different weight concentrations (0%, 2%, 4%, 6%) of multi-walled carbon nanotubes (MWCNT) into the Polydimethylsiloxane (PDMS) matrix was investigated. It has enabled us to find the optimal weight ratio of MWCNT and increase surface charge density, thereby enhancing triboelectric performance for realising smart wearable triboelectric nanogenerators (SW-TENG). On the other hand, a novel dynamic test platform was developed for automated tapping on TENG for quantified performance analysis of SW-TENG. The results indicate that 4 wt% is the optimal weight ratio for fabrication of MWCNT-PDMS based TENG as it recorded the highest open circuit voltage of 195.4 V revealing ∼79% enhancement in triboelectric output as compared to pure PDMS based TENG. Furthermore, SW-TENG was integrated with a bridge rectifier and 10 μF capacitor in order to power bioelectric devices such as a digital thermometer and a pulse sensor. Besides serving as a power source, the SW-TENG shows innovative sensing capabilities for delivering self-powered rehabilitation therapy augmenting the next generation healthcare systems.

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.

Flexible Vitrimers for Self‐healable Triboelectric Nanogenerators

AbstractDespite rapid advancements in the development of triboelectric nanogenerators (TENG), mechanical defects generated during their working condition limit the service lifetime of these devices. Polyester‐based vitrimers can offer a solution to solve this issue via their dynamic bond exchange reactions. However, they often require high temperatures and a long time to crosslink, rendering them not useful for large‐scale TENG fabrication. To solve these issues, a self‐healable vitrimer‐based triboelectric nanogenerator (VITENG) is developed based on diacrylate poly(dimethylsiloxane) (AA‐PDMS) via a fast thiol‐Michael reaction. By including 2,3‐dihydroxypropyl methacrylate (DHPMA), hydroxy end dangling side chains are generated in the matrix, which increase the PDMS network's flexibility and transesterification efficiency. Efficient transesterification occurs on the abundant dynamic β‐hydroxy ester bonds in the PDMS network, resulting in 100% efficient mechanical damage repair. The VITENG demonstrates a good performance with an output voltage of 135 V under a load of 10 N, demonstrating the potential for mechanical energy harvesters with long lifetimes and high design flexibility.

Superhydrophobic cellulosic triboelectric materials for distributed energy harvesting

The development of triboelectric nanogenerators (TENGs) has made it possible to collect large-scale distributed energy, and their applications in the field of energy harvesting are promising. However, the erosion of water molecules in humid environments is a major challenge limiting the application of triboelectric materials. In this study, superhydrophobic methylated cellulosic triboelectric materials were prepared and rectangular TENG with an internal grid structure was designed for distributed energy harvesting. Interfacial modification of the cellulose nanofibrils (CNF) surface by silica nanoparticles to form a nanoscale microstructured surface further enhances the hydrophobicity of the triboelectric material. It was found that the modified CNF triboelectric material has excellent super-hydrophobicity (WCA: 154.7°), surface roughness (RMS: 72.61), and low surface energy. In addition, the RT-TENG internal grid structure is designed to allow external impact forces to be applied more uniformly to the surface of the f triboelectric material, demonstrating excellent electrical output performance (120 V) and cycling stability (10,000 cycles) when applied to distributed energy harvesting. This study provides a novel strategy for the design and preparation of superhydrophobic triboelectric materials and guides the study of distributed energy harvesting.

Energy Conversion Analysis of Multilayered Triboelectric Nanogenerators for Synergistic Rain and Solar Energy Harvesting.

The triboelectric nanogenerator (TENG) is an emerging technology that offers excellent potential for the conversion of mechanical energy from rain into electricity for hybrid energy applications. However, a high-performance TENG is yet to be achieved because a quantitative analysis method for the energy conversion process is still lacking. Herein, a quantitative analysis method, termed the "kinetic energy calculation and current integration" (KECCI) method, which significantly improves the understanding of the mechanical-to-electrical energy conversion process, is presented. Based on the KECCI method, a high-performance TENG is developed by systematically optimizing a biomimetic surface structure and instant switch design, with 1.25mA short-circuit current (Isc ), 150V open-circuit voltage (Voc ), and a high energy-conversion efficiency of 24.89%. Furthermore, a multilayered TENG device is proposed for continuously harvesting the kinetic energy of raindrops for further improvement in the energy-conversion efficiency. Finally, the multilayered TENGs are integrated with organic photovoltaics, achieving all-weather energy harvesting. This work presents a validated theoretical basis that will guide further development of TENGs toward higher performances, which will promote the commercialization of hybrid TENG systems for all-weather applications.

A high output triboelectric nanogenerator integrated with wave-structure electrode for football monitoring

In recent years, the development of triboelectric nanogenerator (TENG) technology has made great progress. However, most of the work focuses on the improvement of triboelectric materials and the optimization of device structure. In this work, we introduced a novel triboelectric nanogenerator integrated with wave structure electrode (W-TENG). Compared to the TENG with traditional flat plate electrode, the W-TENG with wave structure electrode can achieve higher output performance. The maximum short-circuit current (Isc), transfer charge, and open-circuit voltage (Voc) of 2.56 μA, 29 nC, and 74 V were obtained at 300 N. Correspondingly, the instantaneous output power of W-TENG illustrates the maximum value of 0.94 mW at 6 Hz. In addition, the output voltage signal of W-TENG can clearly reflect the different postures in football, and the W-TENG can perform real-time football monitoring. This mechano-electrical energy harvester and the corresponding self-powered monitor can promote the intelligent sports development.

A novel ZnS nanosheets-based triboelectric nanogenerator and its applications in sensing, self-powered electronics, and digital systems

The development of triboelectric nanogenerators (TENGs) based on inexpensive inorganic materials has attracted significant attention to envisage next-generation self-powered electronic devices and sensors. In this research work, the fabrication of a triboelectric nanogenerator (TENG) based on ZnS nanosheets arrays was investigated for the first time. This TENG was fabricated with ZnS nanosheets films, polydimethylsiloxane (PDMS) as active tribo-layers. The originality of this work lies in the choice of materials; pure ZnS nanosheets and PDMS-Al cover foils. By hand excitation force, the developed TENG (5 ×5 cm2) produced an output voltage and a short-circuit current of ~8 V and ~7.12 µA respectively. In addition, the present TENG with pure ZnS nanosheets on Al substrate produced an output voltage almost twice than TENG that involved only Al substrate. In this current study, introducing ZnS nanosheets on Al substrate increased the surface area and roughness, resulting in improved performance. The study of TENG parameters confirms that the TENG (10 ×10 cm2) with 2 cm spacing between tribo layers, applied force frequency of ~ 4–5 Hz were optimum to obtain the maximum output voltage of ~33 V. The high stability of TENG was confirmed by testing TENG response over 1000 cycles. Further, TENG was used to power portable electronic devices such as a digital watch, thermometer, calculator, and 64 LEDs when coupled to a capacitor. Finally, TENG was demonstrated for sensing force and pressure, TENG output response was used as a clock pulse for the digital circuits. The proposed TENG is easy to handle, simple and economical, and ZnS-based TENG's performance can be improved using other tribo-materials instead of PDMS.

A triboelectric nanogenerator for mechanical energy harvesting and as self-powered pressure sensor

Recently, the development of triboelectric nanogenerators (TENGs) based on the natural material have aroused widespread concern. Here, we report a novel bamboo stick-based triboelectric nanogenerator (B-TENG) that can both harvest biomechanical energy and act as a self-powered pressure sensor. The polydimethylsiloxane (PDMS) layer and bamboo stick layer form the triboelectric layers, and the conductive copper is used as the conductive electrode. According to the results, the output power of B-TENG can achieve the maximum value (about 217.38 μW) and the internal resistance of B-TENG is 40 MΩ. Besides, the B-TENG can realize the open-circuit voltage (Voc) of 169.75 V and short-circuit current (Isc) of 3.6 μA, respectively. Furthermore, the B-TENG can also play the role of a self-powered pressure sensor to reflect the change of pressure. We believe this work will promote the development of TENG devices and self-powered sensor.

Hydrogel‐based triboelectric nanogenerators: Properties, performance, and applications

The development of triboelectric nanogenerators (TENGs) in 2012 revolutionized the vision of environmental energy harvesting. Nowadays, TENG assembly, working mode, and material selection are investigated continuously in order to obtain high-performance and long-lasting devices. Hydrogels are flexible and stretchable water-swollen 3D polymer networks, which can be tailored to conduct electricity and render outstanding mechanical properties. Hydrogels have been used to develop novel flexible wearable TENGs. Here, we review the current knowledge concerning hydrogel-based TENGs, including an overview of relevant hydrogel characteristics, hydrogel-based TENG performance, and their practical applications. The single-electrode TENG working mode is the most popular in hydrogel-based TENGs as they can be easily attached and stretched for biomechanical energy harvesting. Hydrogel-based TENGs have demonstrated to be capable of delivering high electrical output (250-400 V, ≥10 μA) and being robust enough for devices that last for several months. Biomechanical energy sensing and harvesting, smart farming, biomedical, and human–machine control interfaces are investigated as potential applications of hydrogel-based TENGs. Interestingly, energy harvesting from human motion is of particular interest for this type of TENG due to its outstanding stretchability, strength, and additional physical properties, such as self-healing ability. In most cases, the devices are capable of powering small electronics entirely from harvested biomechanical energy. Biomedical applications involved wound healing acceleration driven by TENG-powered electrical stimuli and disease monitoring, including implantable devices. Despite showing promising electrical performance, controlling water evaporation is still challenging to maintain the mechanical and conductive properties of hydrogel-based TENGs. On the other hand, fully biodegradable TENGs are largely unexplored, as well as many applications, such as blue energy harvesting, the internet of things, and others. The next steps in this line of research must focus on addressing the main challenges of hydrogel-based TENGs and filling the application knowledge gaps.