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.