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. 2020 Jan 21;11(1):399.
doi: 10.1038/s41467-019-14278-9.

Quantifying Electron-Transfer in Liquid-Solid Contact Electrification and the Formation of Electric Double-Layer

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Free PMC article

Quantifying Electron-Transfer in Liquid-Solid Contact Electrification and the Formation of Electric Double-Layer

Shiquan Lin et al. Nat Commun. .
Free PMC article

Abstract

Contact electrification (CE) has been known for more than 2600 years but the nature of charge carriers and their transfer mechanisms still remain poorly understood, especially for the cases of liquid-solid CE. Here, we study the CE between liquids and solids and investigate the decay of CE charges on the solid surfaces after liquid-solid CE at different thermal conditions. The contribution of electron transfer is distinguished from that of ion transfer on the charged surfaces by using the theory of electron thermionic emission. Our study shows that there are both electron transfer and ion transfer in the liquid-solid CE. We reveal that solutes in the solution, pH value of the solution and the hydrophilicity of the solid affect the ratio of electron transfers to ion transfers. Further, we propose a two-step model of electron or/and ion transfer and demonstrate the formation of electric double-layer in liquid-solid CE.

Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1. Temperature effect on the CE between the DI water and the SiO2.
(a) The setup of the charging experiments, where the negative charges generated on the SiO2 surface could be electrons and O ions induced by surface ionization reaction. (‘O’ is the Oxygen atom, ‘Si’ is the silicon atom and ‘O’ is the Oxygen ion). (b) The setup of AFM platform for the thermionic emission experiments. (c) The decay of the CE charge (induced by contacting with the DI water at room temperature) on the SiO2 surface at different substrate temperatures. (d) The CE charge density on the SiO2 sample surface in the charging (contacting with the DI water at room temperature) and heating (at 513 K for 10 min) cycle tests. (Error bar are defined as s. d.).
Fig. 2
Fig. 2. Temperature effect on the CE between the SiO2 and aqueous solutions.
(a) The effects of the NaCl concentration on the CE between the SiO2 and the NaCl solutions. (b) The decay of the CE charge at 433 K which is induced by contacting with the NaCl solutions. (c) The CE charge density on the SiO2 sample surface in the charging (contacting with 0.4 M NaCl solution at room temperature) and heating (513 K for 10 min) cycle tests. (d) The decay of the CE charge at 433 K, which is induced by contacting with the pH 11 HCl solution and the pH 3 NaOH solution. The charging and heating cycle testes when the liquids are (e) the pH 11 NaOH solution and (f) the pH 3 HCl solution. (Error bar are defined as s. d.).
Fig. 3
Fig. 3. Temperature effect on the CE between the DI water and the solids.
The decay of CE charges (induced by contacting with the DI water at room temperature) on a MgO, b Si3N4, c Ta2O5, d HfO2, e Al2O3, and f AlN surfaces at 433 K, and the amount of the electron transfer and the ion transfer in the CE between the DI water and different insulators. g The relation between the electron transfer to the ion transfer ratio and the DI water contact angle (WCA) of the materials. h The schematic of WCA effects on the ion transfer and electron transfer in liquid–solid CE. γL, γS, and γL−S denote the liquid–gas interfacial tension, solid–gas interfacial tension and liquid–solid interfacial tension, respectively. (Error bar are defined as s. d.).
Fig. 4
Fig. 4. Mechanism of liquid–solid CE and formation of electric double-layer.
a The liquid contacts a virgin surface (before CE). b The water molecules and ions in the liquid impact the virgin surface and electron transfer between the water and the surface. c The surface is charged and the charge carriers are mainly electrons (WCA > 90°, pH = 7), some ions may be generated on the surface caused by the ionization reaction etc. d The opposite polarity ions are attracted to migrate toward the charged surface by the Coulomb force, electrically screening the first charged layer.

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