Triboelectric effect and triboelectric nanogenerator (TENG)
The triboelectric effect, which is when two materials become electrically charged after coming in contact with each other, is usually seen as a detrimental side effect in industry. For example, it can cause ignition hazard in the processing industry, engine element destruction in the aircraft industry, and electrostatic discharge (ESD) problem in the electronics industry. More recently, researchers began to develop device that takes advantage of the electro-mechanical conversion in the triboelectric effect by harvesting otherwise-wasted mechanical energy from the ambient environment to produce and store electrical charges, which is named as the Triboelectric Nanogenerator (TENG). Ever since the first TENG was published, efforts have been focused on enhancing the triboelectric output and improving the performance of TENGs, which include device structural modification, system and circuit design, surface texturing, and material optimization. Among the strategies mentioned above, material optimization is especially important since the triboelectric output is highly dependent on the materials involved. So far, the material optimization is purely based on a trial-and-error type approach since the fundamental physics behind the triboelectric effect is still in debate and not fully understood yet. Therefore, a fundamental and comprehensive understanding of the effects of material properties and geometric parameters on the triboelectric output is needed for making materials-driven discoveries, which is essential for developing and improving TENG.
In this study, the effects of material properties, i.e., electrical properties and mechanical properties, and the effects of thickness and surface roughness on the triboelectric output are investigated experimentally and computationally. 1) Filler-modified polymers, such as multi-wall carbon nanotube/ PDMS composite (MWCNT-PDMS) and ionic liquid-coated single-wall carbon nanotubes/ PDMS composite (SWCNT-IL-PDMS), are used to investigate the effects of dielectric permittivity and electrical conductivity on the triboelectric output. 2) PDMS with different crosslinking ratios and thermal treatment conditions is used to study the effects of mechanical properties on the triboelectric output. 3) Since it is difficult for one material to possess multiple optimum material properties simultaneously, a multi-layer TENG is fabricated and studied.
This study generalizes approaches for increasing the triboelectric output of polymers and their composites and proposes the mechanisms of the change in the triboelectric output of multi-layer materials with different material properties, paving the way for the practical use and wide adoption of TENGs in real-world applications.
