Triboelectric Nanogenerators (TENGs) have emerged as a promising and innovative technology to generate electricity from friction, with the advantage of low cost and high output voltage. Recently, a group of researchers from Xiamen University Malaysia revealed the untapped potential of TENGs by harnessing dielectric and piezoelectric properties of polyvinylidene fluoride (PVDF) polymers. 

Entitled “High Performance Composition-tailored PVDF Triboelectric Nanogenerator Enabled by Low Temperature-induced Phase Transition”, the result of this research has just been published on Nano Energy, an SCI Q1 journal with an impact factor of 19.069.

This research is spearheaded by Dr. Tan Swee Tiam and Dr. Gan Wee Chen from XMUM School of Energy and Chemical Engineering. Involved in the team are Daniel Ong Tze Kheng, the first author, Jason Koay Soon Chye and Sim Moh Terng - all master’s students at New Energy Science and Engineering Programme.

It is a collaborative effort with University of Auckland and Tokyo University of Science.

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The minds behind the research to unleash friction. From left to right: Dr. Gan Wee Chen, Jason Koay Soon Chye, Daniel Ong Tze Kheng, Sim Moh Terng, Dr. Tan Swee Tiam

PVDF polymers are widely used in TENGs due to their excellent dielectric and piezoelectric properties. In this work, the team used a range of PVDF, co- and terpolymers to assess the distinct contributions of dielectric and piezoelectric properties on the TENG’s output, to further increase the performance and explain the phenomena behind.

“This project is based on our previous research conducted in 2020, with piezoelectric as the focus,” introduced Daniel Ong Tze Kheng. With the title “Maximizing the Output Power Density Enhancement of Solid Polymer Electrolyte Based-Triboelectric Nanogenerators via Contact Electrification-Induced Ionic Polarization”, the above-mentioned research was published on Nano Energy in 2021.

As explained by the researchers, PVDF copolymer serves as a piezoelectric tribomaterial due to its β-rich phase, while PVDF terpolymer is utilized as dielectric tribomaterial due to its high dielectric constant. The mechanism of the two properties is differentiated via surface potential measurements and a modified overlapped electron cloud (OEC) model. In this research, the piezoelectric property was found to shift electron energy levels before contact electrification (CE) while the dielectric property hindered electron backflow after CE. 

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Figure 1 (a) The graphs show the electric field-induced dielectric constant as it cools down from 25   (dielectric dominant) to -40   (piezoelectric dominant). Included are the proposed ferroelectric domains at these temperatures. (b) 94 LEDs arranged in “KELIP KELIP” lit up by the PVDF-TrFE-CTFE TENG.

Simple and effective, the surface potential observations are further confirmed by temperature-dependence electrical measurement, which takes advantage of the change of PVDF terpolymers from dielectric-dominant to piezoelectric-dominant due to temperature change. This provides guidelines on material selection and paves the way for potential low-temperature TENG applications. 

The research team would like to acknowledge Collaborative Research in Engineering, Science and Technology Centre (CREST), Malaysia and Xiamen University Malaysia (IENG/0039), Malaysian Industry-Government Group for High Technology (MIGHT) (EENG/0029), Hengyuan International Sdn. Bhd. (EENG/0003) and the Xiamen University Malaysia Research Fund (grant number: XMUMRF/IENG/0043) in making this research successful. 
 

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The article can be accessed at https://doi.org/10.1016/j.nanoen.2023.108555.