Increased Interfacial Area between Dielectric Layer and Electrode of Triboelectric Nanogenerator toward Robustness and Boosted Energy Output

2D Materials-based Electrochemical Triboelectric Nanogenerators

The integration of 2D materials in triboelectric nanogenerators (TENGs) is known to increase the mechanical-to-electrical power conversion efficiency. 2D materials are used in TENGs with multiple roles as triboelectric material, charge-trapping fillers, or as electrodes. Here, novel TENGs based on few-layers graphene (FLG) electrodes and stable gel electrolytes composed of liquid phase exfoliated 2D-transition metal dichalcogenides and polyvinyl alcohol are developed. TENGs embedding FLG and gel composites show competitive open-circuit voltage (≈ 300 V), instant peak power (530 mW m^-2 ), and stability (> 11 months). These values correspond to a seven-fold higher electrical output compared to TENGs embedding bare FLG electrodes. It is demonstrated that such a significant improvement depends on the high electrical double-layer capacitance (EDLC) of FLG electrodes functionalized with the gel composites. The wet encapsulation of the TENGs is shown to be an effective strategy to increase their power output further highlighting the EDLC role. It is also shown that the EDLC is dependent upon the transition metal (W vs Mo) rather than the relative abundance of 1T or 2H phases. Overall, this work lays down the roots for novel sustainable electrochemical-(e)-TENGs developed exploiting strategies typically used in electrochemical capacitors.

A Flexible TENG Based on Micro-Structure Film for Speed Skating Techniques Monitoring and Biomechanical Energy Harvesting

Wearable motion-monitoring systems have been widely used in recent years. However, the battery energy storage problem of traditional wearable devices limits the development of human sports training applications. In this paper, a self-powered and portable micro-structure triboelectric nanogenerator (MS-TENG) has been made. It consists of micro-structure polydimethylsiloxane (PDMS) film, fluorinated ethylene propylene (FEP) film, and lithium chloride polyacrylamide (LiCl-PAAM) hydrogel. Through the micro-structure, the voltage of the MS-TENG can be improved by 7 times. The MS-TENG provides outstanding sensing properties: maximum output voltage of 74 V, angular sensitivity of 1.016 V/degree, high signal-to-noise ratio, and excellent long-term service stability. We used it to monitor the running skills of speed skaters. It can also store the biomechanical energy which is generated in the process of speed skating through capacitors. It demonstrates capability of sensor to power electronic calculator and electronic watch. In addition, as a flexible electrode hydrogel, it can readily stretch over 1300%, which can help improve the service life and work stability of MS-TENG. Therefore, MS-TENG has great application potential in human sports training monitoring and big data analysis.

Enhancement of patterned triboelectric output performance by an interfacial polymer layer for energy harvesting application

Efficaciously scavenging waste mechanical energy from the environment is an emerging field in the self-powered and self-governing electronics systems which solves battery limitations. It demonstrates enormous potential in various fields such as wireless devices, vesture, and portable electronic devices. Different surface textured PET triboelectric nanogenerators (TENGs) were developed by the laser pattern method in the previous work, with the line textured TENG device showing improved performance due to a larger surface contact area. Here, a polyethylene oxide (PEO) and polyvinyl alcohol (PVA) coated line patterned PET-based TENG was developed for the conversion of mechanical energy into useful electric energy. The PEO layer boosted the TENG output to 4 times higher than that of the PA6-laser patterned PET TENG device (our previous report) and 2-fold higher than that of a pristine line patterned TENG. It generated an open-circuit voltage, short circuit current, and instantaneous power density of 131 V, 2.32 μA, and 41.6 μW cm^-2, respectively. The as-fabricated device was tested for 10 000 cycles for reliability evaluation, which shows no significant performance degradation. In addition, the device was deployed to power 10 LEDs with high intensity. Thus, this device can be used for ambient mechanical energy conversion and to power micro and nano-electronic devices.

Air-gap embedded triboelectric nanogenerator via surface modification of non-contact layer using sandpapers

With the increased number of small electronics and demand for their energy source, renewable energy sources have received much attention. Above all, a triboelectric nanogenerator (TENG) based on the combination of contact electrification and electrostatic induction has been researched as a method of converting mechanical energy into electricity. In order to increase the electrical output of TENGs with raising the surface charge density, a lot of researchers have focused on the fabrication methods to employ micro-/nano-structures onto a contact surface of the TENG, but have been facing several issues regarding the degradation of the output performance from the iterative operation process. Hence, it is highly required to introduce an approach to enhancing the performance of TENG, while minimally degrading the output power during the long-term operation. In this paper, an air-gap embedded TENG (AE-TENG), which contains a microstructure on the non-contact surface by means of a sandpaper, is proposed. These small air-gaps between the spin-coated polydimethylsiloxane and the non-contact surface can significantly boost the total surface charge density of the dielectric layer. Thus, the electrical output performance of the AE-TENG is enhanced without any surface engineering on the contact surface. Furthermore, the effect of the air-gap induced surface charges on the electric potential is systematically analyzed by not only experimentally electrical outputs, but theoretical and computational modeling based on the V-Q-x relationship and simulation software tool. This air-gap induced triboelectric effect opens a new perspective of the development of electrical outputs by providing a structural/theoretical understanding for TENGs.

Transparent Triboelectric Nanogenerator Based on Thermoplastic Polyurethane Films

This study aims at investigating flexible and transparent thermoplastic polyurethane (TPU) as a novel material for triboelectric nanogenerator (TENG) devices with a polyethylene terephthalate layer. Devices having TPU-either as a flat film or as electrospun micrometer-dimension fibers with varying concentrations of TPU-were tested. The best output performing device provided 21.4 V and 23 μA as open-circuit voltage and short-circuit current respectively, with the application of a small force of 0.33 N indicating the high efficiency of the device. Devices with flat films-obtained using the doctor-blade (DB) technique-have high transparency (80%) as well as high TENG output. The topography of the TPU layer, characterized by atomic force microscopy, reveals nanoscale roughness of the film surface. Finally, we demonstrate that gentle hand tapping on the TENG device can power upto 11 light-emitting diodes (LEDs). The high transparency, lightweight, simple fabrication, flexibility, and robust features of such device make it an added value for various optoelectronic applications.