Effect of Surface Pre-Charging and Electric Field on the Contact Electrification between Liquid and Solid

Contact electrification at the solid-liquid interface is a ubiquitous phenomenon. In spite of the extensive studies about its origin, it remains difficult to reveal the mechanism of charge transfer under special conditions (e.g., in the case of pre-charging or applied electric field). Here, we measured the charge transfer between solids and liquids with different pre-charged pairs using an acoustic levitation-electric field measurement device. It is demonstrated that the interaction between the electronegativity and the electrostatic attraction by the net charge of the solid can facilitate or suppress the amount of transferred charges after contacting with the liquid. Considering that the pre-charges may affect the charge transfer by establishing an interfacial electric field, the effect of the applied electric field on the charge transfer at the solid-liquid interface was further explored. Particularly, charge transfer along the opposite direction of the driving electric-field force is observed, which is more likely due to electron transfer. The results are well explained using Wang's hybrid electric double layer model, which consists of transferred electrons, specifically oriented water molecules, and adsorbed ions.