Design Of Triboelectric Layers And Performance Of TENG Based On EVOH Nanofibers

Triboelectric nanogenerator(TENG)functioning via a combination of triboelectrification and electrostatic induction can convert mechanical energy into electricity,which is gradually regarded as a new type of energy-generating unit to construct self-powered wearable electronics.Specifically,the structural characteristics of triboelectric layers are important factors restricting the electrical output performance of TENG.Obtaining the triboelectric layers that can provide high contact aera and surface charge density will help enrich the adaptive development of devices.Poly(ethylene-co-vinyl alcohol)(EVOH)exhibits excellent wear resistance and flexibility.It is unique to be used as triboelectric layers because not only the built-in micro-nano structure of aggregates arising from its nanofibers,but also being easy to integrate with conventional fabrics prepared by thermoplastic polymers.At the same time,containing a large amount of hydroxyl groups to be functionalized is beneficial to explore the relationship between the electrical output performance of TENG and the properties of EVOH after modification.In this dissertation,EVOH nanofibers prepared by melt-blending extrusion were selected as the raw material,and then were assembled as nanofiber membranes and nanofiber aerogels via vacuum extraction filtering and freeze-drying methods,respectively.After improving the tribo-polarity of EVOH through various modification,a series of TENG devices based on such composite nanofiber aggregates were successfully obtained.For exploring the optimizing method of triboelectric layers to guide the fabrication of TENG based on thermoplastic polymer,the effects of morphology,structure,chemical composition and surface wettability of modified EVOH nanofiber aggregates on the electrical output performance of as-prepared device were deeply analyzed.The main research contents are as follows:1.Since EVOH having hydroxyl groups showed a certain tendency to lose electrons but weak tribo-electropositivity,PANI/EVOH composite nanofiber membranes(PANI-ECNMs)were developed as the tribo-electropositive layer by introducing PANI containing amino groups.Due to the stronger tendency of PANI to lose electrons and the obvious micro-nano structure caused by in-situ chemical oxidative polymerization,the output open-circuit voltage and short-circuit current of PANI-ECNMs/PTFE TENG were higher than that of EVOH/PTFE TENG,which increased to 150.4V and 22.4?A,respectively.Meanwhile,the maximum instantaneous power density was 1.43 W/m~2when the frequency of contact-separation was fixed at 10 Hz.And the effect of relative humidity on the electrical output performance of as-fabricated device was significantly decreased after surface hydrophobization by two-step dip-coating.In addition,it was also verified that the flexible TENG based on EVOH nanofibers could be used to scavenge irregular biomechanical energy generated by body motions.2.Compared to be modified by the component with stronger tribo-polarity,improving the surface charge density via introducing electret can make the triboelectric layer based on EVOH nanofiber membranes show tribo-electropositive or tribo-electronegative when matching with different tribo-polarity material to construct vertical contact-separation TENG,which will facilitate its use.Herein,SiO₂/EVOH composite nanofiber membranes(SECNMs)were developed as both the tribo-electropositive layer and the tribo-electronegative layer by introducing SiO₂ that possessed excellent charge retention ability.Due to the electret properties of SiO₂ enhancing surface charge density and the obvious micro-nano structure caused by in-situ hydrolysis-polycondensation,the output open-circuit voltage and short-circuit current of FPSECNMs/PTFE TENG increased to 144.9V and 23.7?A,respectively even after obtaining amphiphobicity by being modified with two-component fluorine-containing materials.Meanwhile,the maximum instantaneous power density was 2.14 W/m~2.On the other hand,the electrical output performance of as-fabricated Al/FPSECNMs TENG was also slightly higher than that of Al/EVOH TENG when FPSECNMs were used as the tribo-electronegative layer.In addition,the influence of humidity and antistatic agents on the electrical output performance of as-fabricated device would further be reduced because of not only remarkable amphiphobicity but also good stability.3.Although the triboelectric layer based on EVOH nanofiber membranes can show both tribo-electropositive and tribo-electronegative by introducing SiO₂,it's not obvious in increasing the tribo-electronegativity of EVOH.Also,the friction can't be effectively achieved based on the identity substrate,which will significantly limit the practical application.Herein,PEI/EVOH composite nanofibrous membranes(PEI-ECNMs)with improved tribo-electropositivity and PTFE/PVDF/EVOH composite nanofibrous membranes(PPECNMs)with enhanced tribo-electronegativity were developed by positive and negative post-fabrication modification to introduce PEI and PTFE/PVDF mixtures,respectively.Due to the abundant amino groups of branched PEI,the output open-circuit voltage and short-circuit current of PEI-ECNMs/PTFE TENG respectively increased to 235.7 V and 47.6?A.Because of the excellent tribo-electronegativity of fluorine-containing polymer and the obvious micro-nano structure caused by non-solvent induced phase separation,the output open-circuit voltage and short-circuit current of Al/PPECNMs TENG respectively increased to 145.5 V and 30.0?A.In addition,the above tribo-electropositive layer and tribo-electronegative layer both based on same EVOH nanofiber membrane showed large difference in tribo-polarity,providing a maximum instantaneous power density of 2.11 W/m~2 when constructing PEI-ECNMs/PPECNMs TENG.With remarkable flexibility,all-fiber TENG can be sewn on garment after using conductive fabrics as the back-coated electrodes for simulating friction between clothes to collect energy arising from body-motion.4.Although the electrical output performance of TENG based on nanofiber membranes has been improved after modification,the low porosity of substrate and the segmental dissipation of triboelectric charges on the non-contact surface seems to be harmful.Therefore,taking advantage of the higher porosity,MoS₂-NH₂/EVOH composite nanofibrous aerogels(MNECNFAs)with interconnect porous network were developed as the tribo-electropositive layer by introducing MoS₂-NH₂.Due to the increased transfer charge density caused by MoS₂-NH₂,the output open-circuit voltage and short-circuit current of MNECNFAs/PTFE TENG were higher than that of crosslinked EVOH NFAs/PTFE TENG,which increased to 169.5 V and 25.5?A,respectively.Meanwhile,the maximum instantaneous power density was 1.55 W/m~2.In addition,the as-fabricated device with excellent mechanical properties exhibited good stability and the ability to power LED,capacitor and hygrothermograph.