Water–solid contact electrification and catalysis adjusted by surface functional groups

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.