Effect of ultraviolet irradiation on contact electrification at liquid-solid interface

Abstract

Liquid-solid triboelectric nanogenerator (L-S TENG) has demonstrated great potential in harvesting tiny mechanical energy from liquid. The saturated charge density of contact electrification (CE) at the liquid-solid interface is a key parameter to evaluate its performance. This study confirms that ultraviolet (UV) irradiation can enhance the saturated charge density of L-S CE, and the enhancement effect depends on the UV wavelength and intensity. The UV wavelengths that can further increase the saturated charge density of droplet -PTFE and droplet -FEP TENG are within 310-405 nm and 275-405 nm, respectively. In these wavelength ranges, high light intensity of UV irradiation favors L-S CE. The saturated charge density of FEP is up to -524 μC/m² under optimal irradiation conditions. A series of experiments are further conducted to explore the possible influences of UV irradiation on chemical change of solid surface, ionization of water, and so on. It is proposed that UV irradiation can excite electrons in water molecules to high-energy states and make them transfer to and be trapped by solid surface. Meanwhile, the electrons on the solid surface itself, as well as those that have been transferred to the solid surface, also can be excited under specific UV wavelength irradiation, resulting in charge dissipation at the L-S interface. Finally, the photo-excitation electron transfer theory is extended to quantitatively explain the influence mechanism of UV irradiation on L-S CE. This study not only contributes to further understanding of L-S CE, but also provide an effective technique to improve the performance of L-S TENG.