Mica's homo-positive-charging behavior enabled porous elastomer TENG for energy harvesting in high humidity

Tribo-charges upon contact and separation originate from the properties of contacted materials and are of opposite polarities according to the conventional view. Interestingly, mica, as a representative of a series of inorganic materials, always carries positive tribo-charges when two pieces of mica come into contact. Similar homo-charging phenomena have also been observed in other inorganic particles, such as NaCl, quartz, and CaF2. These phenomena are typically encountered during mineral flotation and sand-dust formation and contain abundant triboelectric energy. However, harvesting this disordered and ubiquitous energy is challenging, and a detailed understanding of this homo-positive-charging behavior at the molecular level remains lacking. In this study, the dynamic nature of the homo-positive-charging behavior was verified, and the underlying mechanism for the enhanced evaporation of OH(H2O)n− on the surface of mica was elucidated. Furthermore, mica’s homo-positive-charging behavior was utilized to prepare a porous elastomer, resulting in an endogenous triboelectric nanogenerator (TENG) and an optimized contact–separation mode TENG. The maximum output power density was 55 mW/m2, and 83% of the original energy generation retained at a high humidity of 84.3%. This study contributes to the understanding of mica’s tribo-charging behavior and provides a generic method to optimize positive tribo-layer, especially in high-humidity environments, which show promise in a wide range of applications.