Effects of Metal Work Function and Contact Potential Difference on Electron Thermionic Emission in Contact Electrification

Triboelectric nanogenerator (TENG) is a direct measure of the surface charge density, thus providing a novel and powerful tool to study the essential mechanism of contact electrification (CE). A variety of TENGs including a Pt-Al2O3 TENG, Au-Al2O3 TENG, Ti-Al2O3 TENG, Al-Al2O3 TENG, and SiO2-Al2O3 TENG are prepared in this study. After introducing initial charges on the Al2O3 surface of the TENGs, the long-term evolution of surface charge quantity is investigated at different temperatures. The results show that charge variation of all the TENGs is analogous to exponential decay and is in accord with the thermionic emission model, verifying the electron transfer dominated mechanism of CE. Additionally, it is explored for the first time that the potential barrier of materials can be regulated by changing the contacting metals or dielectrics. Regulation of the barrier at high temperatures fully excludes the influence of ions from moisture and functional groups, which further indicates the dominant role played by electron transfer in CE. Surface state models for explaining barrier regulation during CE for both metal-dielectric and dielectric-dielectric pairs are proposed. This study provides a new perspective of the exploration of CE, and a novel method for further increasing or rapidly eliminating electrification of charged materials.