Multilayered triboelectric nanogenerators (TENGs) are commonly used to improve the performance parameters of electronic devices. However, multilayered TENGs with a high volumetric charge distribution must be robust and flexible for effective mass production. Consequently, suitable material selection is crucial for the industrialization of multilayered TENGs.
Study: All-Printed Wearable Triboelectric Nanogenerator with Ultra-Charged Electron Accumulation Polymers Based on MXene Nanoflakes. Image Credit: Den photographer 1985/Shutterstock.com
A recent study published in the journal Advanced Electronic Materials focuses on this issue by presenting an all-printed, durable, and wearable TENG with ultra-charged electron accumulation polymers (EAPs) based on MXene nanoflakes. The as-prepared TENG with EAPs can effectively operate different compact electronics and pH measuring devices with a pH sensor.
Multilayered TENGs: Overview and Significance
Wearable triboelectric nanogenerators (TENGs) are becoming increasingly popular as electromechanical energy extractors for next-generation electronic devices. Several research institutes are actively striving to establish an efficient production process for manufacturing lightweight and cost-effective TENGs with a high energy capacity using different nanocomposite coatings and material modifications.
According to prior research on the relationship between the TENG output power and the transferable electronic charges, a synthetic charge infusion, such as corona release, increases the carrier concentration on the surface and the power output of TENGs.
However, satisfying many characteristics, such as strong electron attraction, high dielectric constant, and large surface area with a single substance or layer, is quite difficult. As a result, a multilayered TENG has recently been proposed to solve this critical problem.
Design of sustainable wearable TENG based on EAPs. a) Schematic image of layer-by-layer composition (left side) of TENG based on EAPs with charge accumulation mechanism (right side). b) Fabrication procedure of EAP-based TENG with bottom and top parts. c) Cross-sectional SEM image of TENG with the full thickness of ≈70 µm. d) Cross-sectional images of PTFE-THV (left top side), SWCNT:COOH-THV (right top side), MXene-THV (left bottom side), and Ag-SEBS (right bottom side). e) Photograph of folded EAP-based TENGs. © Kim, K. N. et al. (2022)
Fabrication Challenges Associated with Multilayer TENGs
Conventional electron transport materials such as carbon nanotubes (CNTs) and trapping compounds such as graphene oxide are insufficient for TENGs' high volumetric charge distribution. Moreover, several investigations on multilayered TENGs have revealed that their high rigidity makes them unsuitable for wearable electronics.
Additionally, TENGs must be resistant to humidity and distortion to deliver energy constantly and effectively operate commercial wearable electronics.
Although prior research employed encapsulation and interface modifications to alleviate these challenges, these techniques are still complex, and mass manufacturing of these systems is problematic.
If different solutions for limiting air exposure, such as multilayered structures and electron-trapping agents insulated by native oxide, were explored, a highly sustainable and low-cost TENG capable of working in extreme climatic circumstances might be readily produced.
MXene: The Future of Multilayer TENG Fabrication
MXene is a two-dimensional inorganic material composed of thin layers of transition metal carbides, nitrides, or carbonitrides. MXene, which was first reported in 2011, combines the metallic conductance of transition metal carbides with the hydrophilic characteristic of hydroxyl- or oxygen-terminated surfaces.
MXene has lately attracted a lot of interest in TENG applications because of its high electron-attracting capabilities. MXene has been employed as a tribo-negative substance in several studies for boosting transmitted electrons.
To create an effective TENG based on the MXene capturing layer, it is necessary to boost the volume carrier concentration of tribo-negative layers by using MXene's electron-trapping capabilities and designing the electron transfer layer to efficiently channel electrons toward the interior bulk. Surface treatment and functionalization are also necessary for maximizing electron transport through a confined electric field at the MXene interface.
Highlights and Key Developments of the Current Study
In this study, the researchers developed a flexible and robust TENG made entirely of printable electron-accumulated polymers (EAPs) with higher volumetric charge distribution and storage capabilities.
EAPs were made of 2D MXene with many electron-trapping locations, single-walled carbon nanotubes (SWCNTs) with excellent electrical conduction, and polytetrafluoroethylene (PTFE) with significant electron attraction and transfer properties. TENG's layers were created using a low-cost screen-printing technology with stretchy specialized inks.
To show the real-world application of EAP-based TENGs, a pH sensor device for measuring the pH range of human perspiration was built. This device includes a very sensitive screen-printed pH sensor as well as a display. The pH sensor gets an electrical voltage signal from capacitors charged by the TENG and delivers it to a single-board microprocessor attached to the seven-segment display.
The microprocessor takes the input from the pH sensor, transforms it into digital signals, and activates display segments through instruction coding. When synthetic sweat of pH three is put on top of the pH sensor, the screen shows the number "3," whereas pH 7 displays the number "7."
Importantly, these findings indicate that this unique approach to enhanced energy extractors and portable detectors, such as the pH sensor created in this research, may lead to the development of smart sensor network applications.
Kim, K. N. et al. (2022). All-Printed Wearable Triboelectric Nanogenerator with Ultra-Charged Electron Accumulation Polymers Based on MXene Nanoflakes. Advanced Electronic Materials. Available at: https://onlinelibrary.wiley.com/doi/10.1002/aelm.202200819