Preparation And Performance Of Electrospun Piezoelectric Nanofiber Membrane Based Nanogenerators

With the rapid development of the global economy,the structure and supply of energy have faced unprecedented challenges.Nanogenerator is a new type of energy collection device in recent 20 years.It is fabricated by materials with microstructure at the nanometer scale and can effectively convert mechanical energy with low power density into electricity.Compared with traditional generators,nanogenerators have the advantages of light quality,simple structure,and strong adaptability to the environment.Therefore,nanogenerators can be used in a variety of environments and have shown good application potential as power supplies for wearable devices,portable electronic equipment,and sensors.The piezoelectric nanogenerator is fabricated based on the principle of the piezoelectric effect.The piezoelectric material is the determinant of its performance.In this paper,we use electrospinning as the basic preparation technique,by adjusting the composition and structure of materials,to improve the piezoelectric properties of materials.The main content is divided into the following three parts:1.Electrospinning polyvinylidene fluoride(PVDF)nanofiber membrane based acoustoelectric nanogenerator:PVDF is the most widely used piezoelectric polymer,with a high piezoelectric coefficient,good stability,and low acoustic impedance.(1)the PVDF nanofiber membrane was prepared by the electrospinning method.By adjusting the concentration of the solution,the morphology,the diameter of the fibers,and the phase content of PVDF can be adjusted.The PVDF nanofiber membrane was made into a nanogenerator driven by a sound wave.The experiment results show that the nanogenerator can produce larger voltage outputs under lower frequency(<1000Hz)of sound and the maximum output voltage is up to 470 m V.The voltage outputs increase with the increase of volume.The maximum output power is up to 0.118 m W and the internal resistance is 1.2 M?.(2)The electrospun PVDF nanofiber membrane was used as the substrate,and ZnO was introduced into the fibers by the hydrothermal method.The ZnO nanorods grew perpendicular to the surface of the fibers,forming a hierarchical structure.The acoustoelectric nanogenerator made of PVDF-ZnO composite fiber membrane also produces larger voltage outputs under low frequency and higher volume.Under the condition of the optimization sound field(140 Hz,116d B),the nanogenerator can produce the maximum outputs of 1.12 V and 1.6?A and power density of 50?W cm^-3.Under the condition of this sound source,the electric energy generated by the prepared PVDF-ZnO nanogenerator can charge a capacitor to1.3 V in 3 minutes.The two kinds of acoustoelectric nanogenerators based on PVDF nanofibers are both suitable for converting sound waves of low frequency and high volume into electric energy,indicating the potential to collect noise energy and serve as power supplies for micro and nanodevices.2.Electrospinning PVDF/BaTiO₃composite fiber membrane based piezoelectric nano-generator.The composition of polyvinylidene fluoride(PVDF)with nanoparticles and lamellar two-dimensional materials is beneficial to increase the content of?-phase and thus improve the piezoelectric performance.In this paper,the piezoelectric properties are improved by introducing piezoelectric ceramic BaTiO₃nanoparticles and graphene nanosheets into PVDF fibers by co-electrospinning.(1)The PVDF/BaTiO₃composite fiber membrane was prepared by electrospinning and made into piezoelectric nanogenerator devices.When the content of BaTiO₃nanoparticles is 15 wt%,the PVDF/BaTiO₃nanogenerator has good piezoelectric output performance,and the output voltage can reach 4.2 V at the force of 2 Hz and 5N.PVDF/BaTiO₃nanogenerator has good flexibility and can be applied to the collection and conversion of mechanical energy such as human movement.(2)The PVDF/BaTiO₃/graphene composite fiber membrane was prepared by electrospinning method and made into piezoelectric nanogenerator devices.The addition of graphene further promoted the?phase formation of PVDF,enhanced the strain of the material,and improved the piezoelectric properties.With the content of graphene of 0.15 wt%,PVDF/BaTiO₃/graphene composite nanogenerator has good piezoelectric output performance,and the output voltage can reach 10.8 V at the force of 2 Hz and 5 N.3.Electrospinning cellulose acetate membrane based piezoelectric nanogenerator:Cellulose and its derivatives are abundant renewable materials,and there are piezoelectric crystalline areas in their structures.Cellulose acetate(CA)nanofiber membrane was prepared by electrospinning to prepare environmentally friendly and renewable piezoelectric materials.Cellulose nanocrystals(CNC)were introduced into the membrane to improve the piezoelectric properties.(1)CA nanofiber membrane was prepared by electrospinning technology and was made into nanogenerator devices.Due to the high degree of hydrolysis,cellulose acetate has low crystallinity.Thus,the output voltage of the nanogenerator prepared by cellulose acetate nanofibers is also relatively low.The maximum output voltage can reach 300 m V under the force of 2Hz and 5 N.Its piezoelectric properties still need to be further improved.(2)The CA/CNC composite nanofiber membrane was prepared by the electrospinning method.The addition of CNC increased the content of piezoelectric cellulose I crystallization and the mechanical deformation of the fiber,which significantly improved the piezoelectric properties of the material.When the content of CNC is 20 wt%,the CA/CNC nanogenerator has high piezoelectric conversion performance,and the output voltage can reach up to 1.2 V when it is subjected to 2 Hz and 5 N forces.In addition,the output voltage of the CA/CNC nanogenerator has a good linear relationship with the pressure,which indicates that the CA/CNC nanogenerator has the potential application as a piezoelectric sensor.In summary,three kinds of piezoelectric nanofiber membrane materials have been prepared in this paper.Through the design of composition and structure,the piezoelectric performance of these materials has been improved.All these materials can be prepared into nanogenerators,which were able to collect energy in the environment and have application prospects in the fields of micro-nano energy and wearable devices.