Energy Harvesting of Droplet-based Triboelectric Nanogenerators: From Mechanisms toward Performance optimizations

Triboelectric Nanogenerator (TENG), which couples the contact electrification (CE) and electrostatic induction effects, provides a promising route to efficiently harvest energy from droplets. Despite the seemingly modest energy derived from individual droplet, its widespread and abundant nature across diverse scenarios, including rainfalls, misty environments, water-logged and altitude variations ground, presents significant untapped energy potential. This underscores the practical importance of harvesting droplet energy as a vital component in fulfilling the demand for sustainable energy. Herein, we delve into the recent advancements in droplet energy harvesting using TENG. Initially, the electric double layer (EDL) of droplet-based TENGs is discussed in-depth, including the "two-step" formation process of EDL, as well as the sources and influencing factors of electrostatic charges on solid surface. Subsequently, three common work modes of droplet-based TENGs are introduced, and the energy harvesting process and the maximum efficiency of DEG which possess the droplet-characteristic feature are detailed description. Additionally, the performance and advantages of droplet-based TENGs are outlined, followed by a summary of strategies aimed at enhancing the output performance of droplet-based TENGs. Finally, potential applications and future prospects of droplet-based TENGs are discussed, that are essential for propelling the advancement in the field of droplet energy harvesting via TENG.