LAUSR

The liquid‐solid contact electrification mechanism has been explored in the aqueous solution system, but there are few systematic studies on oil‐solid triboelectrification. Herein, an oil droplet triboelectric nanogenerator (Oil‐droplet TENG) is designed as the probe to investigate the charge transfer properties at oil‐solid interface. The charge transfer kinetics process is disclosed by the electrical signals produced, showing that the electron species initially predominated the oil‐solid triboelectrification. The molecular structure and electronic properties of oil also affect triboelectric performance. Further, the charge transfer principle in multi‐component liquid mixture during the electric double layer (EDL) development process is proposed to explain the component competition effect. As a proof of concept, a tubular‐TENG is designed as a self‐powered sensor for transformer oil trace water detection. The device demonstrates high water sensitivity with a detection limit of 10 µL L−1 and a response range of 10–100 µL L−1. This work not only reveals the oil‐solid triboelectric and charge transfer competition mechanism in EDL, but also open up a new channel for real‐time online monitoring of trace water in transformer oil, which holds promise for information perception and intelligent operation of transformers in the power industry.