Research On Contact Electrification Mechanism Of Solid-liquid Interface And Performance Optimization Of Drop Triboelectric Nanogenerator

The droplet triboelectric nanogenerator（D-TENG）is a novel energy harvesting device.Since it was proposed by the team of Academician Wang Zhong Lin at the Georgia Institute of Technology in 2014,it has attracted extensive attention from researchers because it can collect blue energy in nature such as raindrops and water droplets.The working principle of D-TENG mainly relies on contact electrification and electrostatic induction processes at the solid-liquid interface.How to optimize the above process is the key to improve the output performance of the D-TENG.It is well known that the contact electrification at the solid-liquid interface describes how triboelectric charges are generated and distributed.Although there is a long history of research on contact electrification at solid-liquid interfaces,the analysis of its mechanism is still not clear enough.In 2020,Academician Wang Zhong Lin’s team proposed Wang’s hybridization theoretical model:the electrification of water and polymer contact is likely to be dominated by electron transfer;while the general solid-liquid contact electrification phenomenon is likely to be attributed to both electron transfer and ion transfer.This physical model has been verified from the perspectives of the gradual saturation process of electricity generated by the contact between water droplets and polymers,and the potential distribution and change law of the solid surface.However,the chemical process is not clear enough,and there is little direct experimental evidence.In addition,D-TENG solves the problem that the triboelectric layer material of the traditional solid-solid triboelectric nanogenerator is damaged due to long-term contact friction,and also expands the working environment of the triboelectric nanogenerator,which has important research significance.However,the traditional D-TENG often adopts the output mode of single-electrode structure mode,which mainly relies on the electrostatic induction process,and the interface effect limits its further improvement.In 2020,the team of Professor Wang Zuankai at City University of Hong Kong developed a D-TENG with a switch structure,which can generate a large amount of instantaneous power.The introduction of the switch structure controls the connection and interruption of the entire circuit.At the moment when the circuit is connected,a high instantaneous charge output is generated to improve the instantaneous power density.However,the electrification rate of the polymeric triboelectric layer is still slow,and there is room for further improvement in the output performance of D-TENG.This paper takes D-TENG and D-TENG with switch structure as the main research objects,and discusses the contact electrification mechanism of solid-liquid interface and the performance optimization of D-TENG.The research content mainly includes the following two parts:（1）In order to understand the contact electrification mechanism of the solid-liquid interface,we constructed D-TENGs with different structures and used their power generation characteristics to determine whether the contact electrification or electrostatic induction process between the water droplet and the friction layer（PTFE）was carried out.At the same time,the water droplets that slipped from the surface of PTFE were dropped into 100μmol/L 4-carboxyphenylboronic acid solution,and the mass spectrometry method was used to detect that the water droplets after friction contained boric acid and p-hydroxybenzoic acid,which can prove that after friction The water droplets contain trace amounts of hydrogen peroxide（H₂O₂）.Using UV-vis spectroscopy to compare the standard curve of H₂O₂ titration with 0.1μmol/L potassium titanium oxalate（PTO,K₂Ti O（C₂O₄）₂·H₂O）solution,it is also verified that a small amount of H₂O₂ is produced in the water droplets sliding off the PTFE membrane.Finally,the electron paramagnetic resonance（EPR）technique showed that after the water droplet was in contact with the PTFE membrane,a 1:2:2:1quartet appeared in the water droplet,which verified that the strong oxidizing group hydroxyl was produced in the water droplet that lost electrons.Free radicals（?OH）.It can be seen that after the contact electrification between the water droplet and the PTFE membrane,the water droplet is reduced.In addition,by comparing with the UV standard curve of 0.1μmol/L PTO solution titration H₂O₂ reaction,it was found that a small amount of H₂O₂ was also produced after the water droplets were separated from the natural magnolia leaves.（2）Regarding the performance optimization of D-TENG,D-TENG with a switch structure was used as a prototype,and the surface of PTFE was modified with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane to prepare fluorine Silane-modified TENG（F-TENG）.The three-dimensional modification of the molecular brush is used to increase the contact area between the droplet and the friction layer of the F-TENG.After the first 10 drops of water rubbed against the modified PTFE,its surface potential reached 80%of the saturation state.When 100μL of deionized water was dropped on the surface of F-TENG from a height of 15 cm,the output current,transferred charge and open circuit voltage were 28.49μA,80.56 n C and 400 V,respectively.It can be seen that the output performance of the D-TENG is relatively excellent.And its energy conversion efficiency is 14.02%,which is much higher than that of previously reported D-TENG.The F-TENG with high instantaneous performance in this paper can light up 400 LEDs with a drop of water.Moreover,it could charge a 470μF capacitor to 13 V with one F-TENG,which can power a smartphone.