Chemical functional groups on solid surfaces greatly influence contact electrification (CE) at water–solid interfaces. Previous studies of their effects mainly swapped materials or bonded related molecules to a substrate, introducing other factors of influence. This work aims at unambiguously demonstrating the role of functional groups in water-polymer CE. We study the contribution of functional groups, by using ion coupled plasma etching to modify a high-density polyethylene (HDPE) film, a polymer with a naturally quasi-null charge transfer ability. Fluoride (HDPE–F) and hydroxyl (HDPE–OH) functional groups are generated and endowed HDPE with charge withdrawing ability. HDPE–F withdraws 2.5–2.7 times more charges than HDPE–OH. Concurrently, the surface charges accumulated generate electrostatic forces, altering the droplets motion. This phenomenon provides another approach to study CE, helping to evaluate the contribution of electrons to solid–liquid CE. Finally, employing HDPE–F to perform contact-electro-catalysis shows its activity is 2.4 times higher than that of commercial fluorinated films.

As extremely important physiological indicators, respiratory signals can often reflect or predict the depth and urgency of various diseases. However, designing a wearable respiratory monitoring system with convenience, excellent durability, and high precision is still an urgent challenge. Here, we designed an easy-fabricate, lightweight, and badge reel-like retractable self-powered sensor (RSPS) with high precision, sensitivity, and durability for continuous detection of important indicators such as respiratory rate, apnea, and respiratory ventilation. By using three groups of interdigital electrode structures with phase differences, combined with flexible printed circuit boards (FPCBs) processing technology, a miniature rotating thin-film triboelectric nanogenerator (RTF-TENG) was developed. Based on discrete sensing technology, the RSPS has a sensing resolution of 0.13 mm, sensitivity of 7 P·mm⁻¹, and durability more than 1 million stretching cycles, with low hysteresis and excellent anti-environmental interference ability. Additionally, to demonstrate its wearability, real-time, and convenience of respiratory monitoring, a multifunctional wearable respiratory monitoring system (MWRMS) was designed. The MWRMS demonstrated in this study is expected to provide a new and practical strategy and technology for daily human respiratory monitoring and clinical diagnosis.