Conventional Triboelectric Nanogenerator Research Articles

A compliant mechanism actuated bistable hybrid mode triboelectric nanogenerator

Abstract Triboelectric nanogenerators (TENGs) working in sliding mode offer higher power generation capability compared with those working in contact-separation mode (CS-TENGs). However, unlike CS-TENGs, sliding action can limit TENG lifespan due to wear and tear. A TENG combining both modes with intermittent sliding actions can overcome this limitation. In this study, we propose a bistable hybrid mode TENG (BHM-TENG) that can leverage the functionalities of the traditional sliding TENG and CS-TENG and achieve both durability and satisfactory performance, enabled by a compliant mechanism design. A self-rotating base introduces sufficient sliding during intermittent contact, leading to significant improvement in charge transfer (44%) and voltage output (58%) compared with the conventional TENGs while minimising wear and tear. The prototyped device, excited using compliant beams, can be effectively actuated even at extremely low input frequencies (<0.1 Hz), as explained by a mathematical model. The real-world energy harvesting applications enabled by BHM-TENG is proposed based on the output of BHM-TENG.

Biodegradable, stretchable, and high-performance triboelectric nanogenerators through interfacial polarization in bilayer structure

The increasing demand for wearable electronics has led to the development of triboelectric nanogenerators (TENGs) as a promising energy harvesting and sensing technology. However, conventional TENGs often utilize non-biodegradable materials, contributing to environmental pollution. In this work, we present a stretchable and biodegradable TENG based on hydroxyethyl cellulose (HEC) and gelatin (HG-TENG). The HG-TENG features a bilayered structure, where the large difference in their relative permittivity between HEC and gelatin induces interfacial polarization, effectively mitigating charge recombination and enhancing triboelectric performance. The optimized HG-TENG achieves an open-circuit voltage (Voc) of 93 V, a maximum power density of 57.8 µW/cm2, and can power 38 blue light-emitting diodes. The device exhibits a stretchability of 150 % and biodegrades within 3 hours in phosphate-buffered saline. Furthermore, we demonstrate the application of the HG-TENG as a wearable sensor by modifying it with trichloro(1H, 1H, 2H, 2H-perfluorooctyl)silane (FOTS) (FHG-TENG). The FHG-TENG-based smart glove, integrated with machine learning algorithms, enables real-time monitoring of blood pressure waveforms and finger motions, showcasing its potential for human-machine interfaces. The smart glove, equipped with five FHG-TENGs on the proximal interphalangeal joints of each finger, detects diverse finger gestures and generates voltage signals that control a robotic hand in real-time, demonstrating effective human-machine interaction through synchronized motion. Moreover, the smart glove achieves a high recognition accuracy of 96.15 % for 10 different hand sign languages.

Triboiontronics with temporal control of electrical double layer formation

The nanoscale electrical double layer plays a crucial role in macroscopic ion adsorption and reaction kinetics. In this study, we achieve controllable ion migration by dynamically regulating asymmetric electrical double layer formation. This tailors the ionic-electronic coupling interface, leading to the development of triboiontronics. Controlling the charge-collecting layer coverage on dielectric substrates allows for charge collection and adjustment of the substrate-liquid contact electrification property. By dynamically managing the asymmetric electrical double layer formation between the dielectric substrate and liquids, we develop a direct-current triboiontronic nanogenerator. This nanogenerator produces a transferred charge density of 412.54 mC/m2, significantly exceeding that of current hydrovoltaic technology and conventional triboelectric nanogenerators. Additionally, incorporating redox reactions to the process enhances the peak power and transferred charge density to 38.64 W/m2 and 540.70 mC/m2, respectively.

Rationally Improved Surface Charge Density of Triboelectric Nanogenerator with TiO2-MXene/Polystyrene Nanofiber Charge Trapping Layer for Biomechanical Sensing and Wound Healing Application.

Triboelectric nanogenerators (TENGs) have become reliable green energy harvesters by converting biomechanical motions into electricity. However, the inevitable charge leakage and poor electric field (EF) of conventional TENG result in inferior tribo-charge density on the active layer. In this paper, TiO2-MXene incorporated polystyrene (PS) nanofiber membrane (PTMx NFM) charge trapping interlayer is introduced into single electrode mode TENG (S-TENG) to prevent electron loss at the electrode interface. Surprisingly, this charge-trapping mechanism augments the surface charge density and electric output performance of TENGs. Polyvinylidene difluoride (PVDF) mixed polyurethane (PU) NFM is used as tribo-active layer, which improves the crystallinity and mechanical property of PVDF to prevent delamination during long cycle tests. Herein, the effect of this double-layer capacitive model is explained experimentally and theoretically. With optimization of the PTMx interlayer thickness, S-TENG exhibits a maximum open-circuit voltage of (280V), short-circuit current of (20µA) transfer charge of (120 nC), and power density of (25.2 µW cm-2). Then, this energy is utilized to charge electrical appliances. In addition, the influence of AC/DC EF simulation in wound healing management (vitro L929 cell migration, vivo tissue regeneration) is also investigated by changing the polarity of trans-epithelial potential (TEP) distribution in the wounded area.

Aqueous-Aqueous Triboelectric Nanogenerators Empowered Multifunctional Wound Healing System with Intensified Current Output for Accelerating Infected Wound Repair.

Triboelectric nanogenerators (TENGs) have emerged as promising devices for generating self-powered therapeutic electrical stimulation over multiple aspects of wound healing. However, the challenge of achieving full 100% contact in conventional TENGs presents a substantial hurdle in the quest for higher current output, which is crucial for further improving healing efficacy. Here, a novel multifunctional wound healing system is presented by integrating the aqueous-aqueous triboelectric nanogenerators (A-A TENGs) with a functionalized conductive hydrogel, aimed at advancing infected wound therapy. The A-A TENGs are founded on a principle of 100% contact interface and efficient post-contact separation of the immiscible interface within the aqueous two-phase system (ATPS), enhancing charge transfer and subsequently increasing current performance. Leveraging this intensified current output, this system demonstrates efficient therapeutic efficacies over infected wounds both in vitro and in vivo, including stimulating fibroblast migration and proliferation, boosting angiogenesis, enhancing collagen deposition, eradicating bacteria, and reducing inflammatory cells. Moreover, the conductive hydrogel ensures the uniformity and integrity of the electric field covering the wound site, and exhibits multiple synergistic therapeutic effects. With the capability to realize accelerated wound healing, the developed "A-A TENGs empowered multifunctional wound healing system" presenting an excellent prospect in clinical wound therapy.

A Triboelectric-Electromagnetic Hybrid Nanogenerator with Magnetic Coupling Assisted Waterproof Encapsulation for Long-Lasting Energy Harvesting.

Ocean energy harvesting based on a triboelectric nanogenerator (TENG) has great application potential, while the encapsulation of triboelectric devices in water poses a critical issue. Herein, a triboelectric-electromagnetic hybrid nanogenerator (TE-HNG) consisting of TENGs and electromagnetic generators (EMGs) is proposed to harvest water flow energy. A magnetic coupling transmission component is applied to replace traditional bearing structures, which can realize the fully enclosed packaging of the TENG devices and achieve long-lasting energy harvesting from water flow. Under the intense water impact, magnetic coupling reduces the possibility of internal gear damage due to excessive torque, indicating superior stability and robustness compared to conventional TENG. At the waterwheel rotates speed of 75rpm, the TE-HNG can generate an output peak power of 114.83mW, corresponding to a peak power density of 37.105Wm-3. After 5h of continuous operation, the electrical output attenuation of TENG is less than 3%, demonstrating excellent device durability. Moreover, a self-powered temperature sensing system and a self-powered cathodic protection system based on the TE-HNG are developed and illustrated. This work provides a prospective strategy for improving the output stability of TENGs, which benefits the practical applications of the TENGs in large-scale blue energy harvesting.

Ionic liquid with hydrogen bonding reducing leakage charge for enhancing triboelectric performance

Refining the dielectric layer of a triboelectric nanogenerator (TENG) has been shown to maximize its output performance. Among the available strategies, utilizing an ionic dielectric can improve the output performance notably through the internal formation of an electrical double layer (EDL). However, ions dispersed in the ionic dielectric inevitably cause leakage charge between the surface charged layer and electrode of the ionic dielectric; this reduces the charge density, directly affecting output performance. Here, we investigate optimization of the ionic dielectric of a TENG using various ionic liquids (ILs), with the alkyl chain lengths of the cations and fluoride of anions with different size, to achieve power enhancement based on the EDL effect while concurrently suppressing leakage charge via hydrogen bonding. To elucidate the power enhancement working mechanisms within the ionic dielectric, we characterize the chemical, mechanical, and electrochemical properties of the ionic dielectric, including formation of hydrogen bonds, ionic conductivity, and dielectric constant. These parameters are investigated by varying the ion types, molecular sizes, and concentrations of the ILs within the ionic dielectric. As a results, our findings reveal that an IL of OMIM+PF6- dissolved in a base material of thermoplastic polyurethane (TPU) significantly enhances the voltage and current by 2.3 and 2.9 times, respectively, compared to those of a conventional TENG with TPU. These findings are expected to be implemented across a wide range of TENGs, paving the path for their advanced applications in next-generation energy harvesting.

Mechanical switches integrated sandwich triboelectric nanogenerator with high instantaneous output power

Triboelectric nanogenerator (TENG) has emerged as a promising energy harvester that converts random mechanical energy in the environment into electricity to enable self-powered system construction. However, the conventional TENG exhibits a large internal resistance resulting in a low output power across external loads for practical application. In this work, the travel mechanical switches were integrated into the TENG to boost output power, where the switches were turned on and off by the periodic motion between the triboelectric layers. Moreover, the triboelectric layers of TENG were developed as contact separation sandwich structures to work with mechanical switches, allowing the device to release the co-accumulated charges from the dual triboelectric layer to yield giant instantaneous discharge. Compared to a conventional TENG, the device offers ~2.8 times more transfer charge in one cycle and ~106 times more instantaneous power at an external load of 500 Ω, which renders the internal impedance match almost negligible. As a result, the high-power source demonstrates the ability to illuminate the commercial lamps in parallel (total power: 50 W). Such a unique TENG with high output power for low resistance load could greatly enrich the practical application fields of self-powered systems.

Free-Standing Electrode and Fixed Surface Tiny Electrode Implemented Triboelectric Nanogenerator with High Instantaneous Current.

Conventional triboelectric nanogenerators (TENGs) face challenges pertaining to low output current density at low working frequencies and high internal impedance. While strategies, such as surface modification to enhance surface charge density, permittivity regulation of materials, and circuit management, have partially mitigated these issues. However, they have also resulted in increased complexity in the fabrication process. Therefore, there is an urgent demand for a universal and simplified approach to address these challenges. To fulfill this need, this work presents a free-standing electrode and fixed surface tiny electrode implemented triboelectric nanogenerator (FFI-TENG). It is fabricated by a straightforward yet effective method: introducing a tiny electrode onto the surface of the tribo-negative material. This approach yields substantial enhancements in performance, notably a more than tenfold increase in output current density, a reduction in effective working frequencies, and a decrease in matching resistance as compared to vertical contact-separation TENGs (CS-TENGs) or single-electrode TENGs (SE-TENGs). Simultaneously, a comprehensive examination and proposition regarding the operational mechanism of FFI-TENG, highlighting its extensive applicability are also offered. Significantly, FFI-TENG excels in mechanical energy harvesting even under ultra-low working frequencies (0.1Hz), outperforming similar contact-separation models. This innovation positions it as a practical and efficient solution for the development of low-entropy energy harvesters.

Charge Dispersion Strategy for High-Performance and Rain-Proof Triboelectric Nanogenerator.

Triboelectric nanogenerator (TENG) is becoming a sustainable and renewable way of energy harvesting and self-powered sensing because of low cost, simple structure, and high efficiency. However, the output current of existing TENGs is still low. It is proposed that the output current of TENGs can be dramatically improved if the triboelectric charges can distribute inside the triboelectric layers. Herein, a novel single-electrode conductive network-based TENG (CN-TENG) is developed by introducing a conductive network of multiwalled carbon nanotubes in dielectric triboelectric layer of thermoplastic polyurethane (TPU). In this CN-TENG, the contact electrification-induced charges distribute on both the surface and interior of the dielectric TPU layer. Thus, the short-circuit current of CN-TENG improves for 100-fold, compared with that of traditional dielectric TENG. In addition, this CN-TENG, even without packing, can work stably in high-humidity environments and even in the rain, which is another main challenge for conventional TENGs due to charge leakage. Further, this CN-TENG is applied for the first time, to successfully distinguish conductive and dielectric materials. This work provides a new and effective strategy to fabricate TENGs with high output current and humidity-resistivity, greatly expanding their practical applications in energy harvesting, movement sensing, human-machine interaction, and so on.

Direct Current Triboelectric Nanogenerators, a Perspective from Material Selections

With the global energy shortages, sustainable energy scavenging from the natural environment is desperately needed. Unlike solar cell or wind power, which depends heavily on weather conditions, triboelectric nanogenerator (TENG) has received extensive attention as an efficient all–weather energy–harvesting technology. Based on the coupling principle of contact electrification (CE) and electrostatic induction, conventional TENGs convert mechanical energy into an alternating current (AC) output. However, the typically distributed sensor systems in the ubiquitous Internet of Things (IoTs) request a direct current (DC) input. Direct current triboelectric nanogenerators (DC-TENGs) with the constant output characteristic are critical to satisfy the above requirements. Here, DC-TENGs were reviewed from the perspective of material selections. As device performance is mainly determined by material properties, the development of DC-TENGs could be divided into three categories based on dielectric materials, semiconductor materials, and materials for iontronic rectifications. The operating mechanism and influencing factors of various types of DC-TENG were summarized, representative applications were demonstrated, and the main challenges of future developments were also discussed.

Multi-Layered Triboelectric Nanogenerators with Controllable Multiple Spikes for Low-Power Artificial Synaptic Devices.

In the domains of wearable electronics, robotics, and the Internet of Things, there is a demand for devices with low power consumption and the capability of multiplex sensing, memory, and learning. Triboelectric nanogenerators (TENGs) offer remarkable versatility in this regard, particularly when integrated with synaptic transistors that mimic biological synapses. However, conventional TENGs, generating only two spikes per cycle, have limitations when used in synaptic devices requiring repetitive high-frequency gating signals to perform various synaptic plasticity functions. Herein, a multi-layered micropatterned TENG (M-TENG) consisting of a polydimethylsiloxane (PDMS) film and a composite film that includes 1H,1H,2H,2H-perfluorooctyltrichlorosilane/BaTiO3 /PDMS are proposed. The M-TENG generates multiple spikes from a single touch by utilizing separate triboelectric charges at the multiple friction layers, along with a contact/separation delay achieved by distinct spacers between layers. This configuration allows the maximum triboelectric output charge of M-TENG to reach up to 7.52 nC, compared to 3.69 nC for a single-layered TENG. Furthermore, by integrating M-TENGs with an organic electrochemical transistor, the spike number multiplication property of M-TENGs is leveraged to demonstrate an artificial synaptic device with low energy consumption. As a proof-of-concept application, a robotic hand is operated through continuous memory training under repeated stimulations, successfully emulating long-term plasticity.

WS2-based inorganic triboelectric nanogenerators with light-enhanced output and excellent anti-aging ability

Conventional triboelectric nanogenerators (TENGs) usually use polymer as friction layers, because polymer usually has large electronegativity differences and reliable frictional recovery properties. In recent years, inorganic material-based TENG has drawn attention due to its much higher resistance to high-temperature aging, light aging, and fatigue resistance than polymer. However, the performance of TENG with aging has not been fully studied. In this work, pure inorganic TENG based on WS2 and ITO glass was prepared, achieving a short-current (ISC) of 0.3 μA and an open voltage (VOC) of 30 V in the dark. Particularly, the current output of the nanogenerator could be enhanced to 0.61 μA under illumination. In addition, accelerated aging experiments indicated that the inorganic nanogenerator had a good improvement in performance degradation compared to most conventional polymeric nanogenerators. Based on this work, WS2-based inorganic TENGs have stability advantages and may be fully used in a wider range of environments.

Output Behavior of Fall Detection Sensor Using Brush-Based Triboelectric Nanogenerator Depending on Fiber Characteristics

In Japan, a huge portion of the population is aged people, who are prone to various diseases and injuries on a regular basis. Injuries due to falls are one of the biggest risk factors. Consequently, the demand for fall detection sensors, especially the ones that used a triboelectric nanogenerator (TENG) has recently increased. In a previous study, our group reported the development of a wearable sensor for fall detection with privacy protection using the principle of TENG. Conventional TENGs use polymer films as friction material. However, it is difficult for film-based TENGs to harvest output from various angles of contact separation, as the films have two-dimension structures. Consequently, our previous study focused on developing brush-based TENG (B-TENG), and B-TENG harvested output from various angles of contact-separation. However, the B-TENGs we developed were not sensitive enough to detect signals of lower contact force, and thereby could not be used in fall detection sensors. In this study, we focused on improving the performance of B-TENG by investigating the properties of the brushes and the effect of various external parameters on the harvested output voltage of B-TENGs. Consequently, we have constructed an optimized B-TENG, which harvests almost 18 times higher output voltage than the previous one developed by our group. Thus, this optimized B-TENG has the potential for practical use in fall detection sensors.

(Invited) empowering Triboelectric Nanogenerator with Functional Polymers for Environment Monitoring

Triboelectric nanogenerator (TENG) proves useful as self-powered sensor. Integration of TENG with functional polymers empowers TENG to exhibit new functionalities and stimuli responsiveness. This study describes the evaluation of spiropyran-functionalized polymer (P1) and guanidinium-functionalized polymers (2 Gdm.) as new materials for TENG, which both show tunable triboelectric output voltage in response to various environmental cues including UV irradiation, humidity change, metal ions and the presence of bacteria. Spiropyran isomerizes to merocyanine upon UV irradiation for 100s (6-8W), resulting in a decrease in output voltage from 100 V to 65 V. In addition, the output voltage is inversely proportional to the irradiation time. Noting high humidity (RH) generally limits the performance of conventional TENGs, such that the output voltage decreases as RH increases. The output voltage of P1 decreases by 48% (from 100V to 52V) and the output voltage of 2 Gdm. decreases by 85% (from 100V to 15V) as the RH changes from 25% to 88%, which is a common behavior of TENG under high humidity. In contrast, the output voltage of the UV irradiated P1 TENG increases by 30% (from 65V to 80V). Because merocyanine is capable of chelating with metal ions to form metal complexes, we also evaluate the effect of metal chelation on triboelectric voltage output. Chelation with copper(II) ions result in restoration of output voltage to ~100V, suggesting the relative position in triboelectric series can be modulated by metal complexation. For guanidinium-functionalized polymers, 2Gdm., the inherent antimicrobial properties of guanidinium side groups enables TENG to be sensitive to both gram-positive and gram-negative bacteria at a concentration of 105 CFU/mL, resulting in decreasing output voltage as bacteria concentration increases. These results demonstrate that the functionalized polymers can be used as a responsive motif to realize smart TENG systems, which exhibits sensitivity to UV irradiation, changes in humidity, and the presence of metal ions or bacteria.

A cerebral cortex-like structured metallized elastomer for high-performance triboelectric nanogenerator

The advancement of wearable electronics, particularly triboelectric nanogenerators (TENGs), relies on the development of flexible, stretchable, and compressible electrodes that possess a large active surface area, high electrical conductivity, and excellent mechanical stability and deformability. However, existing elastomeric electrodes face challenges in meeting all of these requirements. Herein, we present a novel approach to address these limitations and create electrodes with elastomeric properties, stable metal-like electrical conductivity, and an expanded active surface area. For this goal, we perform an assembly of metal nanoparticles (NPs) in toluene and amine-functionalized organic linkers in alcohol onto the thiol-functionalized, embossed-structured elastomer. Particularly, the assembly process involves ligand exchange reaction-mediated metal NPs and subjecting them to solvent-swelling/deswelling of the embossed PDMS. This process induces the formation of cerebral cortex-like structured elastomer electrode, which is subsequently electroplated with Ni. The resulting electrodes exhibit metal-like electrical conductivity, elastomer-like flexibility, and cerebral cortex-like structure with substantially large surface area and high stress relieving properties. When combined with an intaglio-structured dielectric PDMS electrode, the device exhibits impressive TENG performance, surpassing the performance of conventional TENGs. This approach provides a basis for developing and designing a variety of high-performance flexible electronics, including TENGs.

Optimization of electromagnetic-triboelectric wind energy harvester based on coaxial reversed mechanism with tip discharge

In recent years, the development of triboelectric-electromagnetic composite energy harvesters has revolutionized low-power urban devices by providing a cost-effective and high-output energy solution. However, most triboelectric nanogenerators (TENGs) have limited current output in the μA range, restricting their widespread application. Additionally, existing electromagnetic structures lack compactness and portability. To address these challenges, this paper proposes a compact triboelectric-electromagnetic composite wind energy harvester based on a coaxial reversing mechanism and tip discharge. It achieves gas ionization and increases the TENG's output current by utilizing TENG charge accumulation during rotation through a sidewall tip-copper structure. Compared to conventional TENGs, this harvester elevates the current from the μA level to the mA level. Moreover, it improves the output performance of the small volume electromagnetic generator (EMG) structure through the synchronous reversal of the magnet and coil at the same wind speed using two coaxial reversing propellers, intensifying the magnetic flux variation. Notably, the EMG structure outperforms a single rotating coil or magnet, achieving a remarkable 12% increase in output performance. At average urban wind speeds, this wind energy harvester can charge capacitors of 33 μF, 100 μF, and 220 μF to 2.5 V in 1.6 s, 2 s, and 3.6 s. Furthermore, it can power over 500 small LEDs and support the operation of temperature and humidity sensors. With its efficient wind energy harvesting technology, the proposed harvester holds great promise for self-powered Internet of Things (IoT) applications.

A paradigm-shift self-powered optical sensing system enabled by the rotation driven instantaneous discharging triboelectric nanogenerator (RDID-TENG)

Simultaneously achieving laser sensing and communication in a self-powered and wireless manner benefits a great variety of applications especially for the places with limited electrical supply, such as inhabited islands, etc. Regarded as a promising technology, triboelectric nanogenerators (TENGs) harvest mechanical energies with the environmental motion information revealed. However, until now, few TENG-triggered laser sensing and communication systems have been reported since the current required by the laser is several number orders higher than that of TENGs featuring high impedance and low current. This work reports a revolutionary paradigm using the tailored TENG to drive a laser to achieve environmental sensing and wireless communication in the meanwhile. Unlike conventional TENGs transporting the charge continuously during the friction, the developed rotation driven instantaneous discharging TENG (RDID-TENG) releases the whole accumulated charge by the triboelectric layer in extremely short time (i.e. lower than 500 μs), yielding a periodic and ultrahigh instantaneous current, which is 1000 times higher than that of regular rotational TENGs, making it an excellent pulsed electrical power source to drive the laser. The mechanical to electrical to optical signal conversion was achieved employing such a self-powered sensing system, where both rotational speed and medium contamination information can be extracted from the optical signal. This study proposes a new strategy to regulate the charge transportation of TENGs showing its effectiveness in demonstrated environmental online monitoring.

3D Printed SnS2/SnS-Based Nanocomposite Hydrogel as a Photoenhanced Triboelectric Nanogenerator

Recent advancements in printing technologies have led to new fabrication techniques for the development of various flexible, compact, wearable, and portable energy harvesters and self-powered devices. In particular, the three-dimensional printing (3DP) technology for a nanogenerator has become advantageous due to its low cost, simplicity, and high precision in fabricating complicated structures. Therefore, we report a 3DP-based photoinduced triboelectric nanogenerator (PTNG) fabrication, a hybrid version of a conventional triboelectric nanogenerator. Here, a 3D printed poly(vinyl alcohol) (PVA) nanocomposite hydrogel (3DPH) with photoactive SnS2/SnS nanoflakes is used as a tribo-positive material and copper foil as a tribo-negative material for PTNG application. Under light illumination, the as-fabricated PTNG with an optimized weight percentage of SnS2/SnS displays the open-circuit voltage (Voc) enhancement from 29 to 37.5 V and short-circuit current (Isc) enhancement from 1.23 to 1.58 μA. In addition, the power density of the device is observed at 5.4 μW/cm2 under illumination conditions at the external load of 60 MΩ. This enhanced performance of the as-fabricated PTNG is attributed to the mutual coupling effect and improved interfacial interactions between the SnS2/SnS nanoflakes and PVA under the influence of light illumination, leading to a charge-trapping mechanism. The outstanding performance and stability of the as-fabricated PTNG surpassing all similar recent reports, establish it as an effective hybrid platform for constructing multifunctional self-powered devices.

Discharge domains regulation and dynamic processes of direct-current triboelectric nanogenerator

Direct-current triboelectric nanogenerators arising from electrostatic breakdown can eliminate the bottleneck problem of air breakdown in conventional triboelectric nanogenerators, offering critical benefits of constant-current output, resistance to electromagnetic interference, and high output power density. Previous understanding is that its output characteristics are described by a capacitor-breakdown model or dictated by one or two discharge domains in direct-current triboelectric nanogenerators. Here, we demonstrate that the former holds only for ideal conditions and the latter cannot fully explain the dynamic process and output performance. We systematically image, define, and regulate three discharge domains in direct-current triboelectric nanogenerators, then a “cask model” is developed to bridge the cascaded-capacitor-breakdown dynamic model in ideal conditions and real outputs. Under its guidance, the output power is increased by an order of magnitude within a wide range of resistive loads. These unexplored discharge domains and optimization methods revolutionize the output performance and potential applications of direct-current triboelectric nanogenerators.