Triboelectric nanogenerators have numerous applications in power sources, self-powered sensors and electronic systems. Unfortunately, Maximal benefit of triboelectric nanogenerators is yet to be fully realized due to the low power outputs up to milliwatts. To this end, improvement of the output power is highly desirable to fully achieve the full potential applications of triboelectric nanogenerators. This also means exploring the factors affecting the output power of triboelectric nanogenerators including operational conditions, circuits, materials and structure of devices. Alternatively, the surface charge density of the dielectric layer also has significance quadratic effects on the output power and thus should be taken into consideration.
Several approaches (material selection and modification and increasing reactive area) have been used to obtain high surface charge density. Alternatively, the theoretical models have been developed to predict maximum surface charge density. However, these models are limited to relatively small and positive calculated charge density. However, in contact-mode triboelectric nanogenerators, obtaining the maximum charge density on the interactive surfaces is dependent on the electric breakdown behavior. Therefore, understanding the field emission induced breakdown, surface charge density variation as well as influence on the outputs of triboelectric nanogenerators is highly desirable.
To this end, researchers at The Hong Kong University of Polytechnic led by Professor Xiao-ming Tao from the Nanotechnology Center of Functional and Intelligent Textiles and Apparel developed a new theoretical model for predicting the maximum limits for the outputs of triboelectric nanogenerators. They took into consideration the electric breakdown behavior of the field emission and gas-ionization. Briefly, the experimental work entailed: investigating the breakdown in the two regions of the dielectric layer divided by a critical effective thickness. Additionally, the efficiency of the triboelectric nanogenerators systems was taken as the product of the individual efficiencies associated with the triboelectric nanogenerators, storage devices, and harvesting circuits. The main aim was to increase the power output of the triboelectric nanogenerators. The work is published in the research journal, Nano Energy.
The authors observed a relatively high output power from the resultant triboelectric nanogenerator. Consequently, a constant surface charge density was observed on the dielectric layer with effective thickness lying below the critical value which resulted in more transferred charges. In addition, smaller effective dielectric layer thickness resulted in a corresponding relatively higher working efficiency.
In summary, The Hong Kong University of Polytechnic scientists successfully presented a novel model for predicting the upper limits for output performance of the contact mode triboelectric nanogenerators systems. To actualize their study, they conducted a case-study that revealed the scope and potential of further improving the output performance of the contact-mode triboelectric nanogenerators harvesting systems. Altogether, the study presents essential information that will pave the way for the design of high-performance triboelectric nanogenerators systems in terms of materials selection, modification, and energy storage.
Yang, B., Tao, X., & Peng, Z. (2019). Upper limits for output performance of contact-mode triboelectric nanogenerator systems. Nano Energy, 57, 66-73.