Contact electrification at the solid–liquid transition interface

Contact electrification (CE) is a well-known phenomenon that ubiquitously exists in the charge transfer between solid–solid (S-S) or solid–liquid (S-L) and plays pivotal roles in energy harvesting and self-powered sensing. However, little is known about the CE mechanism during the phase transition. Here, we investigated the mechanism of charge transfer between a representative crystalline ice and a dielectric material during the solid-to-liquid phase transition. This study aimed to determine how the phase transition affects the charge transfer efficiency. Before ice starts melting, electron transfer within S-S contact predominated. As the melted micro-droplets smoothed the rough surface of the ice, the contact area between the materials increased, resulting in a roughly 6-fold enhancement of charge transfer. When the ice melted, droplets condensed on the surface and established S-L contact with the dielectric material. It resulted in the formation of an electrical double layer (EDL) composed of ions and electrons at the contact interface, effectively shielding the surface net charge of the dielectric material and impeding charge transfer between the materials. After the complete melting of ice into water, a stable S-L contact was established, and the EDL formed a stable and strong screening effect, resulting in the lowest level of charge transfer. The findings contributed to enhancing knowledge about interaction and charge transfer between different substances in dynamic phase transition scenarios. It could also provide valuable insights into the optimization and advancement of CE-based triboelectric nanogenerators for energy harvesting and self-powered sensing.