Magneto-Responsive Switching of Liquid-Solid Triboelectrification for Self-Powered Magnetic Proximity Sensor

Water droplet-based triboelectric nanogenerators (WD-TENGs) harvest energy from triboelectrification between water drop and solid surface. WD-TENGs are highly advantageous to convert abundant rain drop energy.<br/>This study proposed a new concept for switching of liquid-solid triboelectrification by introduction of a magnetocontrollable lubricant-infused layer as a triboelectric layer. This layer was composed of magneto-responsive micropillars and lubricating oil. The micropillars showed two different aligning structure states that determine the continuity of lubricant layer. As the direction of the applied magnetic field changes, vertically standing micropillars start to lie down and the continuous lubricant layer is generated. The lubricant layer works for preventing liquid-solid triboelectrification. Triboelectric switching resulted from reversible change between these two states. The electrical outputs showed a difference of nearly three times, so it could be clearly defined as ON and OFF states. The triboelectric switching cycles assured excellent reversibility and stability even after almost one hundred cycles.<br/>The triboelectric switching has been analyzed in detail for factors that can affect the behavior of water droplets, such as the thickness of lubricant layer, drop height of water droplet and inclination angle of TENG.<br/>Also, switching characteristics showed reversible wettability change and it was utilized to recover the performance of WD-TENG even under high humidity environment. Unlike most WD-TENGs, our device can avoid surface wetting problems and generate sustainable electrical power in extreme condition. To extend the usability, the proposed device could work as a self-powered magnetic proximity sensor. Our work presents a new idea of magneto-responsive triboelectric switching, extending the TENG applicablity in low-power-consumption applications such as no-extra power supply-need switches and self-powered sensors.