Revisiting Contact Electrification at Polymer–Liquid Interfaces

Abstract

Contact electrification (CE) occurs naturally at all interfaces between solids and solids, solids and liquids, solids and gasses, and so forth. It has been extensively studied for decades. While CE at a solid−solid interface has been demonstrated to be primarily caused by electron transfer, the underlying mechanism of CE at a liquid−solid interface remains controversial. In this paper, the CE process between polyethylene terephthalate (PET) and different inorganic solutions at different temperatures is studied to investigate the charge transfer mechanism. The observed temperature−CE charge relationship falls into two categories, that is, the general case and the special case. In the general case, the CE charge first increases negatively and then positively with the temperature. The CE charge increasing negatively could result from enhanced electron transfer at the interface, while the CE charge increasing positively may be caused by increasing adsorption of cations, which neutralize the negative charges on the PET surface. In contrast, the CE charge first increases positively and then negatively with the temperature in the special case. The CE charge increasing positively could be attributed to more cations being attracted to the negatively charged PET surface, while the charge increasing negatively may be caused by more anions being attracted to the PET due to enhanced cation adsorption. Supported by the surface charge and dynamic charge transfer at different PET−solution interfaces and solution temperatures, our study provides a plausible interpretation of the temperature-dependent CE at the polymer−liquid interfaces.

Influence of Wettability and Geometry on Contact Electrification between Nonionic Insulators

“…Since TENG-based portable and wearable electronic devices will usually operate in varying environmental conditions across the globe, relative humidity is one of the most studied factors that affect tribocharging. − The power output is enhanced with increasing RH until reaching a material-dependent optimum that typically lies around 40% RH. ,, Above this optimum, the electric output decreases with increasing RH, which can be ascribed to water present at the interface. As the RH changes, water molecules adsorb on the surface, transforming the contact configuration from a single solid–solid interface to a double solid–liquid interface. ,,− Consequently, the charge transfer mechanism also changes; from electron transfer (at solid–solid interactions) to a combination of both electron and ion transfer (at solid–liquid interfaces). , Given that water has the ability to charge solid surfaces upon contact, it is thriving as a promising strategy for the massive development of solid–liquid TENGs, droplet-based TENGs, moisture-enabled electric nanogenerators, and generation of hydrogen peroxide, to harvest green and renewable electricity from the abundantly present water on Earth.…”

Recent Progress of Solid–Liquid Interface-Mediated Contact-Electro-Catalysis

“…Specifically, when the catalyst and the target organic ion had opposite electrical properties (e.g., Nitrile Butadiene Rubber (NBR,+) for MO(−), or FEP(−) for Rhodamine B (RhB,+)), the occurrence of physical adsorption significantly reduced the degradation efficiency of organic pollutants during the CEC process. This could be attributed to the excessive adsorption of organic ions, which might have diminished the active sites for the catalytic reaction, consequently reducing the efficiency of the electron transfer at the interface. − This research not only contributes to characterizing the optimal conditions, but also further enhances our fundamental understanding of CEC technology.…”

Contact-electro-catalysis (CEC)

“…The charge transfer process when PTFE contacts with DI water is different from the process when it comes into contact with NaCl aqueous solution, which can be partly attributed to the duality of ions. On the one hand, the free ions in the solution would prohibit the electron transfer by the screen effect and most ions will flow with liquids 67–69 On the other hand, a slight increase of the ion concentration in DI water would promote the ion transfer process, and ion transfer also contributes to the charge transfer process during CE. Therefore, the quantity of transferred charges first increases with an appropriate increase of the NaCl concentration (within 10 −5 mol L −1 in this case), and then decreases with further increase of the NaCl concentration.…”