Contact electrification (frictional electrification) was discovered in ancient Greece. Although its discovery has been more than 2,600 years old, there are still many arguments on its principle. The most important of these is that in the electrification process, the charge transfer is achieved by the transfer of electrons or ions and why the generated charge can remain on the surface of the material for a long period of time. The contact between metal and metal or between metal and semiconductor is electrified. It is generally considered that electron transfer occurs and can be explained by the difference in work function or contact potential. By introducing the concept of surface states, electron transfer theory can also explain the contact electrification between metal and insulator to a certain extent. However, ion transfer can also be used to explain contact electrification, and is more suitable for electrification systems that contain polymers, for example where ions or functional groups dominate the generation of electrification phenomena. Almost all existing research relating to contact electrification has focused on the total amount of charge generated, and there has been little real-time detection or temperature-related investigation of surface electrostatic changes. To date, there is no convincing theory that can be used to reveal whether the dominant mechanism of contact electrification originated from electrons or ion transfer.
According to Maxwell's principle of displacement current, the triboelectric nanogenerator (TENG) technology, a foreign academician of the Chinese Academy of Sciences and the chief scientist of the Beijing Institute of Nano Energy and Systems, Chinese Academy of Sciences, can accurately characterize the surface charge density and can achieve different temperatures. Application, this provides a new idea for solving the above-mentioned problems in contact electrification. Recently, under the guidance of Wang Zhonglin, associate professors Xu Cheng, Dr. Ji Yunlong, and Ph.D. student Wang Qi have achieved real-time and quantitative measurement of surface charge density/charge by designing a TENG that can be operated at high temperatures, thus revealing contact electrification. Charge characteristics and underlying mechanisms in the process. The study designed different types of TENG and caused TENG to generate only a very small amount of charge during operation, so it can ignore the influence of its own generated charge. By introducing the initial charge, the evolution of the surface charge evolution over time at different temperatures is studied. The experimental and simulation results show that it is in accordance with the thermal electron emission equation and confirms the main source of contact electrification between the two different solid materials. Electronic transfer. In addition, the study also revealed that the surface of different materials has different barrier heights. It is precisely because of the existence of this barrier that the charge generated by the contact electrification can be stored on the surface without escape. Based on the electron-emission-dominated contact electrification mechanism described above, this study further proposes a universal electronic cloud-potential trap model, which for the first time achieves a unified interpretation of the principle of contact electrification between any two conventional materials. The method proposed in this study is conducive to a better understanding of the contact electrification effect and at the same time provides science for the development of frictional nanogenerators in micro- and nano-energy, blue energy, self-driven sensing, artificial intelligence, robotics and physics applications. basis.
The relevant research results were published in Advanced Materials.
(a)-(c), the states of electrons and potential wells (three-dimensional and two-dimensional drawings) of atoms of two different materials before, during, and after electrification; (d) at higher levels The state of discharge at temperature.
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