Triboelectric Devices Research Articles

Reduced graphene-oxide acting as electron-trapping sites in the friction layer for giant triboelectric enhancement

The continuously seeking of approaches for enhancing the output of triboelectric nanogenerators (TENGs) has always been the goal of researchers attempting to harvest mechanical energy efficiently. Here a novel methodology for enhancing the output performance of the TENG by introducing electron traps into the common friction layer has been firstly developed. For this purpose, reduced graphene oxide (rGO) embedded in the friction layer has been used as electron traps. Because the triboelectric electrons generated on the surface of a polyimide layer can be efficiently captured and stored in rGO sheets due to the interaction between the rGO sheets and the polyimide layer, the loss of triboelectric electrons can be suppressed. The maximum output power density of a vertical contact-separation mode TENG containing rGO sheets reached 6.3W/m2, which was 30 times larger than that of a device without rGO sheets. We also showed that the output performance of the lateral sliding-mode TENG, which is the other fundamental working mode of the TENG, can be enhanced due to the advantage of additional electron trapping in the friction layer, indicating that the concept demonstrated in this work holds potential for providing significant enhancements in next-generation triboelectric devices.

Influence of MWCNTs on β-Phase PVDF and Triboelectric Properties

The surface of multiwalled carbon nanotubes (MWCNTs) was chemically modified using 1-pyrenebutyric acid (PBA) to improve its compatibility with polyvinylidene fluoride (PVDF). The carboxylic acid groups of the MWCNTs-PBA (PCNTs) provide a β-phase nucleation site to the fluorine of PVDF along their surface. The content of the β-phase crystalline structure of PVDF was found to be the highest at a concentration of 1.0 wt.% of PCNTs, and these PVDF-PCNTs composites were utilized as active layers in triboelectric devices. The maximum output voltage achieved was 16 volts at a concentration of 1.0 wt.% of PCNTs in the PVDF composites.

Nanogenerators: Boosting Power‐Generating Performance of Triboelectric Nanogenerators via Artificial Control of Ferroelectric Polarization and Dielectric Properties (Adv. Energy Mater. 2/2017)

In article number 1600988, Young Jun Park, Sang-Woo Kim, and co-workers report a large output performance from ferroelectric polymer-based triboelectric nanogenerators (TNG) embedded with dielectric nanoparticles. Compared with typical triboelectric material-based devices, the TNG achieves a boosted power generating performance improved by about 150 times. Thus, the results could facilitate practical application in a self-powered smartwatch, driven by high output current generation.

Comment on “An ultrathin stretchable triboelectric nanogenerator with coplanar electrode for energy harvesting and gesture sensing” by X. Chen, Y. Song, H. Chen, J. Zhang and H. Zhang, Journal of Materials Chemistry A, 2017, 5, 12361

The electrostatic charge issue in skin-contact type triboelectric energy harvesting devices can be overcome by an appropriate choice of materials.

Study of Triboelectric Micromechanism for Three Dimensional Energy Harvesting

Capturing mechanical energy from the surroundings is a potential strategy to power different sensor nodes and devices. In past few years, Triboelectric effect has been recently utilized in energy harvesting devices as a method to convert mechanical energy into electrical energy. One of the major limitations of the triboelectric mechanism based devices is that they are only responsive to stimulation in a single direction. This limitation hinders the application of triboelectric mechanism devices in various practical situations. In this paper, we present a novel design for triboelectric mechanism based devices which is sensitive to excitation in multiple directions.

Soft, thin skin-mounted power management systems and their use in wireless thermography

Power supply represents a critical challenge in the development of body-integrated electronic technologies. Although recent research establishes an impressive variety of options in energy storage (batteries and supercapacitors) and generation (triboelectric, piezoelectric, thermoelectric, and photovoltaic devices), the modest electrical performance and/or the absence of soft, biocompatible mechanical properties limit their practical use. The results presented here form the basis of soft, skin-compatible means for efficient photovoltaic generation and high-capacity storage of electrical power using dual-junction, compound semiconductor solar cells and chip-scale, rechargeable lithium-ion batteries, respectively. Miniaturized components, deformable interconnects, optimized array layouts, and dual-composition elastomer substrates, superstrates, and encapsulation layers represent key features. Systematic studies of the materials and mechanics identify optimized designs, including unusual configurations that exploit a folded, multilayer construct to improve the functional density without adversely affecting the soft, stretchable characteristics. System-level examples exploit such technologies in fully wireless sensors for precision skin thermography, with capabilities in continuous data logging and local processing, validated through demonstrations on volunteer subjects in various realistic scenarios.

Enhanced triboelectrification of the polydimethylsiloxane surface by ultraviolet irradiation

Study of the triboelectric charging effect has recently gained much attraction by proposing a new potential technical application in the field of energy harvesting. Transparent polydimethylsiloxane (PDMS) has some advantages in employing the triboelectric effect due to good conformity at nanometer scale and the simple fabrication process. In this study, we demonstrate that UV irradiation can enhance the performance of a PDMS-based nanotribogenerator. Contact atomic force microscopy combined with Kelvin probe force microscopy enables an in-depth investigation of the effect of UV illumination on local triboelectric charge generation and its decay in PDMS. We found that UV exposure not only facilitates triboelectric charge generation but also enhances charge redistribution, which is related to the wettability of the PDMS surface. This study provides insights into the fundamental understanding and design of triboelectric generator devices.

High output piezo/triboelectric hybrid generator.

Recently, piezoelectric and triboelectric energy harvesting devices have been developed to convert mechanical energy into electrical energy. Especially, it is well known that triboelectric nanogenerators have a simple structure and a high output voltage. However, whereas nanostructures improve the output of triboelectric generators, its fabrication process is still complicated and unfavorable in term of the large scale and long-time durability of the device. Here, we demonstrate a hybrid generator which does not use nanostructure but generates much higher output power by a small mechanical force and integrates piezoelectric generator into triboelectric generator, derived from the simultaneous use of piezoelectric and triboelectric mechanisms in one press-and-release cycle. This hybrid generator combines high piezoelectric output current and triboelectric output voltage, which produces peak output voltage of ~370 V, current density of ~12 μA·cm−2, and average power density of ~4.44 mW·cm−2. The output power successfully lit up 600 LED bulbs by the application of a 0.2 N mechanical force and it charged a 10 μF capacitor to 10 V in 25 s. Beyond energy harvesting, this work will provide new opportunities for developing a small, built-in power source in self-powered electronics such as mobile electronics.

Low temperature dependence of triboelectric effect for energy harvesting and self-powered active sensing

The triboelectric nanogenerator (TENG) has been proved as a simple, reliable, cost-effective, and efficient means to harvest ambient mechanical energy in a normal environment, although its performance evaluation under the room temperature is still lacking. Here, we systematically looked into the reliance of triboelectric nanogenerators output on the ambient temperature spanning from 77 K to 320 K. Employed the most commonly used Polytetrafluoroethylene (PTFE) and aluminum as two contact materials, both the output voltage and current show a tendency of increase with decreasing temperature. Applicability of triboelectric nanogenerator over a wide range of temperature was confirmed from 77 K to 320 K. And, an output enhancement of 79.3% was experimentally obtained at the temperature of 77 K compared to that at a temperature of 300 K. However, a reverse tendency was observed for the TiO2 nanotubes/PTFE and Al coated TiO2 nanotubes/PTFE based triboelectric nanogenerators. This work can contribute not only to the design and packaging of triboelectric devices to operate at extreme environmental temperatures but also to the fundamental understanding of the mechanism of triboelectric effect.

Investigation of contact electrification based broadband energy harvesting mechanism using elastic PDMS microstructures

Triboelectric energy harvesting has recently garnered a lot of interest because of its easy fabrication and high power output. Contact electrification depends on the chemical properties of contacting materials. Another important factor in contact electrification mechanism is surfaces’ elastic and topographical characteristics. One of the biggest limitations of resonant mechanism based devices is their narrow operating bandwidth. This paper presents a broadband mechanism which utilizes stiffness induced in the cantilever motion due to contact between two triboelectric surfaces. We have conducted experiments using polydimethylsiloxane (PDMS) micropad patterns to study the effect of micropad array configuration on the performance of triboelectric energy harvesting devices. The maximum power output measured from the device was observed to be 0.69 μW at an acceleration of 1 g. Due to the non-linearity introduced by contact separation mechanism, the bandwidth of the triboelectric energy harvester was observed to be increased by 63% at an acceleration level of 1 g. A hybrid energy harvesting mechanism has also been demonstrated by compounding the triboelectric energy harvester with a piezoelectric bimorph.

Effect of humidity and pressure on the triboelectric nanogenerator

Triboelectric nanogenerator (TENG) as a novel energy harvester has raised wide research interests recently, although the environmental effect on its performance is still lacking. This paper attempted to experimentally quantify the effect of the relative humidity (RH) as well as the pressure on the charge generated from a TENG. It was found that under the same mechanical excitation, the generated charge of the TENG increased more than 20% when RH decreased from 90% to 10% at the ambient pressure. However, the generated charge decreased as the air pressure decreased from atmospheric pressure to 50Torr at RH close to 0%, while the optimal pressure shifted to a lower level when the relative humidity was higher. This study can contribute not only to the design and packaging of triboelectric devices to operate in varying environments and extreme conditions, but also to the fundamental understanding of the mechanism of triboelectric effect.

Flow measurement in pneumatic transport of pulverized coal

The paper also deals with the measurement of particle velocity. Particle velocity is the most fundamental parameter in the study of solids' movement by gases. However, its experimental determination is difficult. In most of the investigations of pneumatic transport of solids, the particle velocity either was measured indirectly or was inferred from theory. More recently, various techniques, such as the LDV (Laser Doppler Velocimetry), the tagging technique, or the double-solenoid technique, were advanced to measure the particle velocity directly. However, the usefulness of these techniques was limited, e.g. the LVD method could be used only in the dilute phase, and the tagging method needed a clean and transparent pipe. Recently, Mathur and Klinzing have used a cross-correlation technique for the measurement of the particle velocity in a coal/gas system using signals from two Auburn Monitors. These devices were expensive, and a more economical solution of the problem was sought. The possibility of using an Auburn triboelectric instrument that is based on the static charge transfer technique, was explored. The device in its original form was capable of indicating a flow or no-flow condition of solids in the pipe. The triboelectric devices were modified for our application so as to provide two matching signals, which could then be cross-correlated to yield particle velocity. Preliminary results using triboelectric devices are quite encouraging.