Cooperative Contact Electrification enabled by Control Over Electron and Ion Transfer Directions

Contact electrification (CE) is a phenomenon that occurs when two materials are broungth into contact and exchange charges. Although recent studies show that CE between two solids including metals, semiconductors and nonionic polymers is basically due to electron transfer, the mechanism for CE involving ionic materials remains controversial. In this paper, the CE process between single-ion conducting materials (SICM) and fluorinated ethylene propylene (FEP) is systematically investigated to elaborate the electrification mechanism when ions are participating in CE. In the study, electron thermionic emission method was also used to separate the contributions of ion transfer and electron transfer in the total static charges when varying the environmental humidity. Furthermore, molecular dynamics simulations were performed to reveal the molecular interactions and dynamics of the polymer surfaces, mobile ions and water molecules at the interface. The results show that ion transfer is an important mechanism in the CE of FEP/SICM pairs and that higher humidity leads to more free ions and higher contribution of ion transfer in the total transferred charges. Our research not only provides new insights into the mechanism of contact electrification that involves ion transfer but also introduces a uniqu category of triboelectric materials that are single-ion conducting.