First-Principles Study on the Origin of Tribo-Negative Nature of Polytetrafluoroethylene

Triboelectric nanogenerator (TENG) is an energy harvesting device that converts mechanical energy into electricity based on the coupling of contact electrification and electrostatic induction. Fluorocarbon polymers, such as polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkane (PFA) are the widely used polymeric triboelectric materials, however, their tribo-negative nature has been poorly understood. Here, using first-principles calculations, we have systematically investigated the electronic structure of PTFE and PFA. It is revealed that the defects associated with carbon dangling bonds act as charge trapping centers during contact electrification. Furthermore, the simulation on the contact model of PTFE and nylon confirms that the charge transfer occurs when the distance between them is as near as the atomic orbitals overlap. In addition, the calculated work functions of polymeric materials are consistent with the triboelectric series, giving a powerful method to predict the triboelectric property of materials. We expect our study provides fundamental understandings on the origin of the triboelectric property of materials and the atomistic phenomena during contact electrification. Our results also give insight into triboelectric material designs with a strong electron-withdrawing property.