Contact-mode Triboelectric Nanogenerators Research Articles

Development of flexible high-performance PDMS-based triboelectric nanogenerator using nanogratings

This article investigates the performance of a contact-mode Triboelectric Nanogenerator (TENG) utilizing polydimethylsiloxane (PDMS) with nano gratings as a dielectric in a metal-dielectric configuration. The evaluation encompasses the impact of gratings, tapping frequency, various load conditions, and contact area on the TENG performance. The fabrication involves spin-coating PDMS onto a master mold to create the device. Experimental measurements reveal a significant enhancement of 97% in open-circuit voltage by introducing gratings on PDMS. Furthermore, as the tapping frequency increases from 1 Hz to 3 Hz, there is a corresponding rise of 108% in output voltage. The influence of load resistance on TENG output performance demonstrates its ability to drive different loads efficiently. Moreover, enlarging the contact area of the device substantially increases the open-circuit voltage. A device with a 400 mm2 contact area can generate a voltage of 80 V at a low frequency of 3 Hz, indicating the importance of considering device size and contact area for specific applications. A practical circuit integrating a TENG with a full-wave bridge rectifier demonstrates energy harvesting capabilities by successfully illuminating a light-emitting diode (LED) and charging various capacitors. The fabricated devices exhibit better performance along with a cost-effective and easy fabrication process.

Dielectric-elastomer-enhanced triboelectric nanogenerator with amplified outputs

Dielectric elastomers are effective ambient motion energy harvesters due to their flexibility, high energy density, and their ability to match low frequency unsteady motions. However, the dielectric elastomer generator (DEG) is in reality a charge pump, which requires an external supply of electrical charge to work as an energy harvester. In this work, the DEG is coupled with a contact-mode triboelectric nanogenerator (TENG) to form a hybrid. The TENG autonomously produces charges by contact electrification and the DEG in turn amplifies the electrical output by raising the charges to a higher electrical potential. In addition, dielectric elastomer exhibits dielectric strength two orders of magnitude higher than air, thus enabling delivery of a higher output voltage than that by TENG only. Both the TENG and the DEG converts mechanical motion to electrical energy via capacitance change. This makes them physically compatible for easy integration. We first analyze the coupled system and identify the optimal conditions that maximizes output yield in the shortest amount of time. We found that, the maximum output was realized when the TENG and DEG were excited perfectly out-of-phase for same input frequency. We showed that the DEG is ideally able to amplify the voltage output from TENG that is proportional to the capacitance change ratio of the DEG. By the same token, the maximum power will also be amplified proportionally for a constant current system. Our experiment showed that 260% and 180% DEG capacitance change can produce saturation voltage amplification of 2.7 and 2, respectively. Our work demonstrated dielectric-elastomer-enhanced output of a TENG and presented the optimal conditions for maximal amplification.

An Ultrarobust and High-Performance Rotational Hydrodynamic Triboelectric Nanogenerator Enabled by Automatic Mode Switching and Charge Excitation.

The triboelectric nanogenerator (TENG) is an emerging technology for ambient mechanical energy harvesting, which provides a possibility to realize wild environment monitoring by self-powered sensing systems. However, TENGs are limited in some practical applications as a result of their low output performance (low charge density) and mechanical durability (material abrasion). Herein, an ultrarobust and high-performance rotational TENG enabled by automatic mode switching (contact mode at low speed and noncontact at high speed) and charge excitation is proposed. It displays excellent stability, maintaining 94% electrical output after 72000 cycles, much higher than that of the normal contact-mode TENG (30%). Due to its high electrical stability and large electrical output, this TENG powers 944 green light-emitting diodes to brightness in series. Furthermore, by harvesting water-flow energy, various commercial capacitors can be charged quickly, and a self-powered fire alarm and self-powered temperature and humidity detection are realized. This work provides an ideal scheme for enhancing the mechanical durability, broadening the range of working frequency, and improving the electrical output of TENGs. In addition, the high-performance hydrodynamic TENG demonstrated in this work will have great applications for Internet of Things in remote areas.

A whirligig-inspired intermittent-contact triboelectric nanogenerator for efficient low-frequency vibration energy harvesting

Triboelectric nanogenerator (TENG) has overwhelming dominance in the exploitation of low-frequency vibration energy, but the sparse pulsed output, material abrasion in contact-mode TENG and output decline in noncontact-mode TENG limit the output power and electrical stability. Herein, we report a rotational intermittent-contact TENG (IC-TENG) that is realized on the basis of a slideable rope-driven rotor to achieve efficient exploitation of low-frequency vibrations. The rope-driven rotor can start to spin and transform low-frequency vibrations to high-speed rotation through a whirligig-like dynamics mechanism without the requirement of any hand operation, which enables frequency-multiplied and high electric output of the IC-TENG. Moreover, owing to the constantly replenished tribo-charges produced by the intermittent sliding contact between the rotator and stator in the rope-driven rotor, the IC-TENG exhibits high electrical stability, whose normalized electric output stabilizes at around 81%, whereas the normalized electric output of noncontact-mode TENG attenuates continuously to 48% over a 10-day span. The frequency-multiplied electric output and superior electrical stability make the IC-TENG a promising technology for harnessing ambient low-frequency vibration energy. This work demonstrates a novel strategy for TENG to achieve high electric output and in the meanwhile long-term stability.

A Contact-Mode Triboelectric Nanogenerator for Energy Harvesting from Marine Pipe Vibrations.

Structural health monitoring is of great significance to ensure the safety of marine pipes, while powering the required monitoring sensors remains a problem because the ocean environment is not amenable to the traditional ways of providing an external power supply. However, mechanical energy due to the vortex-induced vibration of pipelines may be harvested to power those sensors, which is a convenient, economic and environmentally friendly way. We here exploit a contact-separation mode triboelectric nanogenerator (TENG) to create an efficient energy harvester to transform the mechanical energy of vibrating pipes into electrical energy. The TENG device is composed of a tribo-pair of dielectric material films that is connected to a mass-spring base to guarantee the contact-separation motions of the tribo-pair. Experimental tests are conducted to demonstrate the output performance and long-term durability of the TENG device by attaching it to a sample pipe. A theoretical model for the energy harvesting system is developed for predicting the electrical output performance of the device. It is established that the normalized output power depends only on two compound variables with all typical factors taken into consideration simultaneously. The simple scale law is useful to reveal the underlying mechanism of the device and can guideline the optimization of the device based on multi-parameters analyses. The results here may provide references for designing contact-mode TENG energy harvesting devices based on the vibration of marine pipes and similar structures.

Triboelectric and Piezoelectric Nanogenerators for Future Soft Robots and Machines.

SummaryThe triboelectric nanogenerator (TENG) and piezoelectric nanogenerator (PENG) are two recently developed technologies for effective harvesting of ambient mechanical energy for the creation of self-powered systems. The advantages of TENGs and PENGs which include large open-circuit output voltage, low cost, ease of fabrication, and high conversion efficiency enable their application as new flexible sensors, wearable devices, soft robotics, and machines. This perspective provides an overview of the current state of the art in triboelectric and piezoelectric devices that are used as self-powered sensors and energy harvesters for soft robots and machines; hybrid approaches that combine the advantages of both mechanisms are also discussed. To improve system performance and efficiency, the potential of providing self-powered soft systems with a degree of multifunctionality is investigated. This includes optical sensing, transparency, self-healing, water resistance, photo-luminescence, or an ability to operate in hostile environments such as low temperature, high humidity, or high strain/stretch. Finally, areas for future research directions are identified.

Direct current contact-mode triboelectric nanogenerators via systematic phase shifting

The intermittency and discontinuous nature of power generation in Triboelectric Nanogenerators (TENGs) are arguably their most significant drawback, despite the promise demonstrated in low-power electronics. Herein, we introduce a novel technology to overcome this issue, in which, built-in systematic phase shifting of multiple poles is used to design a pseudo direct-current TENG. Unlike previous attempts of constructing near direct-current TENGs that base on the segmentation of electrodes of a sliding mode TENG, this technology introduces a new method that depends on planned excitation of constituent TENG units at different time intervals to obtain the necessary phase shifts, achieved by their structural design that contains an asymmetric spatial arrangement. Therefore, the direct current generation for TENG, which was previously limited to the sliding mode TENG units, are expanded to contact-mode TENGs. The technology allows for continuous and smooth operation of the driven loads and paves the way for a new dawn in energy scavenging from mechanical sources. We use the distance-dependent electric field (DDEF) platform to design the systematic phase shifting technology, which is experimentally demonstrated via a free-standing mode TENG (FSTENG) based design, to power a number of prototype devices. The resultant power output of the TENG indicates a crest factor close to 1.1 at relatively low frequencies, the best reported values for TENGs with contact-mode basic units, to date. This work provides a highly awaited solution to overcome the intermittency and sporadic nature of TENG outputs, thus, promoting the field towards powering next generation autonomous and mobile electronics.

A novel rhombic-shaped paper-based triboelectric nanogenerator for harvesting energy from environmental vibration

Triboelectric nanogenerator (TENG) as a promising energy harvesting technology attracts much attention in recent years. Among others, the contact mode TENG is often given priority by virtue of its reliable robustness and high energy conversion efficiency. However, in most cases, the contact-mode TENG is only suitable for collecting energy from pressure-induced incentives because it requires a compression forces to drive. Here, we propose a rhombic-shaped paper-based triboelectric nanogenerator (RP-TENG) that may operate effectively under tensile conditions together with an enhanced contact force between the tribo-pair induced by the design of pressurizing braces. Mechanical tests were carried out to investigate the output performance of the RP-TENG under the activation of various applied forces. An integrated RP-TENG with four tribo-pairs were fabricated for optimizing the output performance. The novel design facilitates the device to achieve higher energy conversion efficiency and also expand its application circumstances. A theoretical model is developed to establish the correlation between the output voltage of the RP-TENG and the geometric characteristics as well as external excitations. The results suggest an effective strategy of using paper-based rhombic-shape design to enhance contact-mode TENGs and may serve as a guideline for structural and circuit design of this novel TENG devices.

Upper limits for output performance of contact-mode triboelectric nanogenerator systems

Intensive research efforts have been devoted to increasing output performance of triboelectric nanogenerators (TENGs) by selecting or modifying materials, increasing effective area, optimizing device structures and harvesting circuits. Considering field emission and gas-ionization for electric breakdown, this paper proposes new theoretical models to predict the upper limits for output performance of contact-mode TENG harvesting system. It reveals that a constant surface charge density exists on the dielectric layer with an effective thickness below a critical value. The resultant TENG exhibits a high output power. The working efficiency of the TENG harvesting system quantitatively highlights the scope and focus of improvement for high output power. The findings would provide a powerful tool to guide the experimental design in selection of materials, structure of TENG, harvesting circuits and storage device for intended applications.

Theoretical study on the oscillatory triboelectric charge density in a contact-mode triboelectric nanogenerator

We have analytically derived an oscillatory triboelectric charge density $ \sigma$ , induced by triboelectrification in a contact-mode triboelectric nanogenerator. We assumed that charge is conserved when $ \sigma$ reaches equilibrium state over time. A form of cycling operates between charges induced on the metal electrode and those on the dielectric surface, resulting in $ \sigma$ oscillations over time in a contact-mode triboelectric nanogenerator.

Power computation for the triboelectric nanogenerator

We consider, from a mathematical perspective, the power generated by a contact-mode triboelectric nanogenerator, an energy harvesting device that has been thoroughly studied recently. We encapsulate the behaviour of the device in a differential equation, which although linear and of first order, has periodic coefficients, leading to some interesting mathematical problems. In studying these, we derive approximate forms for the mean power generated and the current waveforms, and describe a procedure for computing the Fourier coefficients for the current, enabling us to compute the power accurately and show how the power is distributed over the harmonics. Comparisons with numerics validate our analysis.

Test bed for contact-mode triboelectric nanogenerator.

The triboelectric nanogenerator (TENG) has become one of the strongest candidates for sustainable power sources. The power of a TENG depends on factors such as contact area, contact parallelism, contact force, and contact speed. In order to evaluate the performance of the TENG precisely and quantitatively, it is necessary to apply consistent experimental conditions and measurement processes. In this paper, we propose a test bed capable of adjusting the contact area and contact parallelism and measuring the contact force, contact speed, current, and voltage in real time. The test bed consists of a 2-axis planar stage, a 2-axis tilting stage, a 1-axis vertical stage, a 3-degree-of-freedom (DOF) force/torque sensor, a capacitive displacement sensor, and a voice coil actuator. The 3-DOF force/torque sensor can provide feedback on the degree of parallelism and contact area alignment as well as contact force. With the proposed test bed, the effects of parallelism error, contact area, contact force, and contact speed on the performance of contact-mode TENGs are quantitatively analyzed. This test bed is expected to be used for the quantitative analysis of contact-mode TENGs with various new structures and for comparison among different devices.

Emulsion Electrospinning of Polytetrafluoroethylene (PTFE) Nanofibrous Membranes for High-Performance Triboelectric Nanogenerators.

Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoroethylene/polyethene oxide (PTFE/PEO) membranes were fabricated, followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilized against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which was further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilized peak-to-peak open-circuit voltage (Voc) of up to ∼900 V, a short-circuit current density (Jsc) of ∼20 mA m-2, and a corresponding charge density of ∼149 μC m-2, which are ∼12, 14, and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in the surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ∼9 W m-2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30 000 operation cycles, without any significant reduction in the output. The work thus introduces a relatively simple, cost-effective, and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and a direct ion-injection method which is able to dramatically improve the surface negative charge density of the PTFE fibrous membranes.

Relationship between triboelectric charge and contact force for two triboelectric layers

A relationship between triboelectric charge and contact force for two triboelectric layers is presented, by combining the theories of insulator contact charging and contact mechanics. Experimental verification has been successfully performed using contact-mode triboelectric nanogenerators (TENGs) in two cases: (a) under varying contact forces while keeping the surface roughness profile constant, and (b) under varying surface roughness profiles while keeping the contact force constant. The theory presented here can serve as an important guide in the design of triboelectric systems, particularly of a contact-mode TENG structure for specific applications and self-powered systems.

Using a synchronous switch to enhance output performance of triboelectric nanogenerators

Contact-mode triboelectric nanogenerators (TENGs) generally operate as a floating source with its two electrodes connected to an arbitrary external circuit forming a closed loop. In this work, a switch based contact-mode TENG (SW-TENG) is presented, wherein a switch is placed between a TENG electrode and an external circuit. By electrically isolating the TENG from the external circuit when the switch is open, charge leakage is prevented and the output performance of the TENG is enhanced while the transferred tribocharges per cycle remain the same. Effect of different switching frequencies while keeping the contact-separation frequency (fcs) and contact force constant at 1Hz and 0.5kgf, respectively, is presented. The versatility of the approach is presented via demonstrating the switching effect in three TENGs fabricated using different types of dielectric films – (a) bare polydimethylsiloxane (PDMS), (b) microdome patterned PDMS, and (c) PDMS-Carbon nanofiber (CNF) composite. When the switching frequency (fsw) is in sync with fcs, the output voltage is increased by a factor of up to 22, 17, and 90, in SW-TENGs made using samples (a), (b), and (c), respectively, compared to that obtained under typical TENG operation. In a 1μF capacitor charging experiment, it has been shown that synchronous switching can prevent a charge leakage of up to approximately 60%. Further, a maximum area power density of 3.4Wcm−2, 20Wcm−2, and 31.7Wcm−2 is achieved at an external load resistance of 56Ω, in SW-TENGs made using samples (a), (b), and (c), respectively. Compared with a typical TENG, the optimal load resistance is decreased by six orders of magnitude, from megaohms to ohms. The SW-TENG thus provides a new approach for mechanical energy harvesting.

Effect of surface density of states and dielectric constant on the transferred charges (Qsc) of triboelectric nanogenerators: Analytical and numerical study

ABSTRACTA theoretical model of the transferred charges from the contact-mode triboelectric nanogenerator (TENG) was performed in this work. Based on the analytical model, a triboelectric charge density consisting of structural parameters and averaged surface DOS () was used to calculate the transferred charges, (Qsc), and the relationship between the Qsc, the dielectric constant, and the was investigated. The model presented here is the first use of the parameter-dependent triboelectric charge density to derive the transferred charges. This can provide practical guidance on TENG design in energy harvesting application.

Theoretical study of contact-mode triboelectric nanogenerators: Analytical and numerical study for

ABSTRACTAn analytical and numerical analysis on contact-mode triboelectric nanogenerators (TENGs) was carried out in this work. Based on the analytical model, the time-dependent transferred charge and the relationship between the transferred charge and accelerated velocity were numerically analyzed. The approach used here is the general interpretation of the contact-mode TENG for the time-dependent transferred charge, which can be used as a guidance for a practical design of the TENG system.

The effect of dielectric constant and work function on triboelectric nanogenerators: Analytical and numerical study

In this study, an analytical model of triboelectric charge density and transferred charge density for simple contact-mode triboelectric nanogenerators (TENG) is constructed. The model comprises the characteristics of triboelectric materials, such as dielectric constants and work function, and structural parameters such as the thickness of the dielectric material and the separation distance between the metal and dielectric. The model presented in this paper is the analytical interpretation of the metal to dielectric contact-mode TENG and is intended to serve as a guideline for the design of TENGs in various applications.

Structural dependence of the transferred charge density in triboelectric nanogenerators: analytical and numerical study

The effect of the structure in a simple contact-mode triboelectric nanogenerator (TENG) was analyzed in this paper. Using the results of the finite-element method, a relationship between the transferred charges on the bottom and one side of the rectangular rod is derived. As the side of the top rectangular surface of the rod is increased, the amount of the transferred surface charge also increases. The numerical results presented here can serve as a rational guide for the practical design of the structure in TENG-based applications.

Hybridizing Triboelectrification and Electromagnetic Induction Effects for High-Efficient Mechanical Energy Harvesting

The recently introduced triboelectric nanogenerator (TENG) and the traditional electromagnetic induction generator (EMIG) are coherently integrated in one structure for energy harvesting and vibration sensing/isolation. The suspended structure is based on two oppositely oriented magnets that are enclosed by hollow cubes surrounded with coils, which oscillates in response to external disturbance and harvests mechanical energy simultaneously from triboelectrification and electromagnetic induction. It extends the previous definition of hybrid cell to harvest the same type of energy with multiple approaches. Both the sliding-mode TENG and contact-mode TENG can be achieved in the same structure. In order to make the TENG and EMIG work together, transformers are used to match the output impedance between these two power sources with very different characteristics. The maximum output power of 7.7 and 1.9 mW on the same load of 5 kΩ was obtained for the TENG and EMIG, respectively, after impedance matching. Benefiting from the rational design, the output signal from the TENG and the EMIG are in phase. They can be added up directly to get an output voltage of 4.6 V and an output current of 2.2 mA in parallel connection. A power management circuit was connected to the hybrid cell, and a regulated voltage of 3.3 V with constant current was achieved. For the first time, a logic operation was carried out on a half-adder circuit by using the hybrid cell working as both the power source and the input digit signals. We also demonstrated that the hybrid cell can serve as a vibration isolator. Further applications as vibration dampers, triggers, and sensors are all promising.