High‐Performance Flexible Piezoelectric Nanogenerator Based on Specific 3D Nano BCZT@Ag Hetero‐Structure Design for the Application of Self‐Powered Wireless Sensor System

Abstract

that people pursued are independent, sustainable, and maintenance free for power supply unit. However, these devices are still mainly powered by traditional batteries. The problems of battery power, such as replacement and waste disposal of battery, not only cause a lot of inconvenience to maintain devices, but also have a negative impact on environmental protection, which runs counter to people's design ideal. Therefore, the energy harvesting technique for self-powered device provides an effective pathway that could replace traditional battery power in IOT. [5][6][7][8][9] The piezoelectric nanogenerator (PENG) can realize the conversion of mechanical energy to electrical energy based on piezoelectric effect, which can harvest mechanical energy and produce electrical output under the mechanical stimulation, such as compression, tension, and twist. Compared with triboelectric generator, PENG has the advantages of little influence by environmental factors, long service life, and stable output performance, which has been considered as promising in the approach of IOT and self-powered sensors network. [10][11][12][13][14] However, the output performance of PENG is generally lower than as expected, and further research is needed to improve the performance of PENG.In general, the flexible PENG based on inorganic/organic composites is usually composed of piezoelectric ceramic fillers and polymer materials due to the composites can combine the favorable piezoelectric response of ceramics and excellent flexibility of polymer. For improving the performance of PENG, the most direct and effective way is to select doped ceramics with good piezoelectric performance. Up to present, there are various types of piezoelectric ceramic systems, such as Pb(Zr 1-x Ti x )O 3 (PZT), (K 0.5 Na 0.5 )NbO 3 (KNN), (Bi 0.5 Na 0.5 )TiO 3 (BNT), and BaTiO 3 (BT). [15][16][17][18][19][20] Among them, the Pb based piezoelectric ceramics have been widely applied in industry for decades, which attributes to their excellent and stable piezoelectric properties. However, with the requirement for environmentfriendly, the exploration of lead-free piezo-ceramics as inorganic fillers in flexible PENG has been in progress. The low-cost BT With the popularity of portable and miniaturized electronic devices in people's live, flexible piezoelectric nanogenerators (PENG) have become a research hotspot for harvesting energy from the living environment to power smallscale electronic equipment and systems because of its stability. For further enhancing output performance of PENG, chemical modification and structural design for piezoelectric fillers are effective ways. Thus, the 3D porous heterostructure fillers of BCZT@Ag are prepared by freeze-drying method and subsequent chemical seeding reduction. The silicone rubber as matrix is filled into the micro-voids of fillers to prepare specialized composite. The charge transport mechanism and stress transfer efficiency in PENG can be effectively improved through specialized design which is proven by experimental res...

Increasing Permittivity and Mechanical Harvesting Response of PVDF-Based Flexible Composites by Using Ag Nanoparticles onto BaTiO3 Nanofillers

“…As presented by various reviews mentioned in the introduction, the mechanism of combined tribo- and piezoelectric generation in the same material is not yet fully understood. Some publications suggested a few possible mechanisms to explain the beneficial role of the inorganic fillers (ferroelectric and metallic) in enhancing the output in composites with respect to ones of the pure polymer produced in the same conditions [ 28 , 29 , 31 ]. The improved output characteristics resulted in both PENG and PTENG configurations induced by the presence of inorganic fillers in the present composites with respect to the values of pure PVDF are first related to the beneficial role of BT ferroelectric nanofiller producing more electrical dipoles with a higher dipole moment (related to its ferroelectric spontaneous polarisation) inside the flexible thick film, which enhances the piezoelectric volume response and creates a larger specific interface between the PVDF matrix and ferroelectric filler (thus contributing also to augment the triboelectric output).…”

“…With respect to the pure polymer, all these dipoles would enhance permittivity, piezoelectric response, and triboelectric charge generation. The field concentration in some regions around the interfaces between the BT, and mostly the Ag inclusions, and polymer matrix generated as a result of the electrical boundary conditions [ 28 , 30 ], playing a positive role in increasing the piezoelectric response and creating a kind of local self-poling (i.e., without the need of an external poling [ 31 ]), as well as the triboelectric charge generation in such composites. Both Ag and BT fillers create rough external surfaces (as seen in the comparative AFM topographical images from Figure S4, Supplementary material ), thus promoting a larger friction interface for triboelectrification under the mechanical load and this is a major effect for enhancing the mechanical harvested output in the Configuration 2 with respect to the Configuration 1 ( Figure 8 ).…”

“…The increase of ferroelectric polarization and piezoelectric output was considered to be created by the field concentration around the conductive nanoparticles resulting in an enhancement of the overall polar character of the compound [ 28 , 30 ]. Combined with ferro/piezoelectric fillers, the presence of high conductivity nanoparticles (in particular noble metals) into the flexible insulating polymer was expected to improve the carrier transport mechanism and to enhance the partial voltage and polarization degree of piezoelectric grains during the polarization process, as it was shown in [ 30 , 31 ]. In [ 31 ], it was observed that the use of metal-piezoelectric core-shell nanofillers generates a further enhancement of the effective field in the polymer by reducing the surface energy of piezoelectric fillers, also diminishing the leakage currents.…”

“…Combined with ferro/piezoelectric fillers, the presence of high conductivity nanoparticles (in particular noble metals) into the flexible insulating polymer was expected to improve the carrier transport mechanism and to enhance the partial voltage and polarization degree of piezoelectric grains during the polarization process, as it was shown in [ 30 , 31 ]. In [ 31 ], it was observed that the use of metal-piezoelectric core-shell nanofillers generates a further enhancement of the effective field in the polymer by reducing the surface energy of piezoelectric fillers, also diminishing the leakage currents. By using 3D structures of Ag-BCTZ in a silicon rubber matrix, an output voltage of 38.6 V was produced [ 31 ].…”

“…In [ 31 ], it was observed that the use of metal-piezoelectric core-shell nanofillers generates a further enhancement of the effective field in the polymer by reducing the surface energy of piezoelectric fillers, also diminishing the leakage currents. By using 3D structures of Ag-BCTZ in a silicon rubber matrix, an output voltage of 38.6 V was produced [ 31 ]. From this point of view, it seems there is still a need to search for new combinations of hybrid fillers (metal—ferro/piezoelectric) in polymer matrices in order to increase the piezoelectric response of flexible composites.…”