Power Generation by a Limestone-Contained Putty

A novel contact-separation triboelectric generator concept is proposed in this paper, which consists of a limestone-based mounting putty and a metallized polyester (PET/Al) sheet. This is an attempt to explore tacky materials for power generation and extend the operational frequency bandwidth compared to existing TriboElectric NanoGenerators (TENGs). Moreover, the proposed design is very cost-effective and easy to build. Unlike traditional TENGs, which generate power solely due to a charge developing on the surface, the putty also replies on charge developed inside the material. Parametric study was conducted to determine the optimal putty thickness in a shaker test at 40 Hz. It was found that a putty layer at 0.6 mm thick yielded maximum power generation. During the separation phase, the electrical breakdown between triboelectric layers allows most existing electrons to flow back from the ground due to rapid charge removal at the interface. We are able to achieve a peak power of 16 mW in a shaker test at 40 Hz with an electrical load of 8 MΩ, which corresponds to a power density of 25.6 W/m². A peak power of 120 mW in a manual prototype generator is achieved, which operates at approximately 2 Hz. Since putty material has less tackiness than double-sided tape, we are able to expand the frequency bandwidth up to 80 Hz, which is significantly higher than a TENG (typically <10 Hz). The mounting putty material contains limestone with approximate 31 nm of mean grain size mixed with synthetic rubber materials. Elasticity from rubber and the nanohardness of calcite crystallites allow us to operate a putty generator repeatedly without the concern of grain fracture. Also, a durability test was conducted with up to 250,000 contact-separation cycles. In summary, comparable performance is achieved in the proposed putty generator to benefit energy harvesting and sensor applications.