Poly(vinylidene fluoride) (PVDF)/potassium sodium niobate (KNN)–based nanofibrous web: A unique nanogenerator for renewable energy harvesting and investigating the role of KNN nanostructures

Abstract

In the recent era, finding renewable energy sources that are environmentally benign the main focus of scientific community around the globe. There is a plenty of renewable energy sources that are currently being researched such as solar power, thermal energy, wind energy, salinity gradients, and kinetic energy. Polymer‐ceramic–based nanocomposite piezoelectric material is known for quite some time for energy harvesting, but the real challenge lies as it requires very high loading of the ceramic part to obtain the required property and thus almost makes the system nonflexible. Developed material needs to be poled later on to use it as an electric energy generator from ambient mechanical movement. This current study is the first time attempt to produce a simple yet unique lightweight energy harvester using polyvinylidene fluoride (PVDF)/potassium sodium niobate (KNN) nanostructures–based nanocomposite flexible fibrous web where the material is in situ poled during its production using an electrospinning setup. At the beginning, various parameters were identified to synthesize and modulate KNN as nanostructural materials having higher aspect ratio, which is intended to provide a unique connection between KNN once these are embedded within the fibrous matrix. The incorporated KNN nanostructure having higher aspect ratio was also found to act as a beta nucleating agent in PVDF matrix and enhances the β‐phase crystal into the resultant fibrous web, which in turn increases the piezoelectric energy‐harvesting capacity manifold as compared with bare PVDF fibrous web. The in situ alignment of the nanostructured KNN (with a minimum loading, 5% only) into the fibrous nanocomposite is another achievement to obtain higher output. X‐ray diffraction and Fourier transform infrared analysis confirmed the mixture of α‐ and β‐crystalline phase of pure PVDF, which gets converted into β phase once KNN nanostructures are incorporated inside the nanofibrous web. An output voltage of 1.9 V was obtained from PVDF/KNN nanocomposite–based web, which is significantly higher (38 times) than generated voltage (50 mV) from the pure PVDF nanoweb without any subsequent poling operation.

Influence of High Aspect Ratio Lead‐Free Piezoelectric Fillers in Designing Flexible Fibrous Nanogenerators: Demonstration of Significant High Output Voltage

“…Herein, an interesting finding has been demonstrated for inducing the electroactive β phase in the PVDF polymer by the incorporation of higher aspect ratio KNN NRs. In our previous study on the PVDF/KNN nanostructure electrospun web‐based piezoelectric nanogenerator, it has been detected that the β fraction value increases with the loading of KNN nanostructures where as in this study, interestingly, the β fraction values decrease with an increase in the percentage of higher aspect ratio KNN NRs into the PVDF polymer . However, the piezoelectric performance in terms of output voltage, current, and current density has been increased significantly as compared with any other previous studies as mentioned earlier.…”

“…The hydrothermal method as adopted in our previous report was used for the synthesis of KNN NRs. If we explain very briefly the synthesis process, at first, 0.006 mol of Nb 2 O 5 (Spectrochem Pvt.…”

“…As the β phase is more desirable for piezoelectricity, there is a need to change α to the β phase for the mother PVDF polymer. There are different techniques for transfer from α to β , such as the incorporation of fillers, mechanical stretching, electrospinning, and poling . In addition, mechanical stretching trailed by outward poling at the higher electric field at a higher temperature is the more espoused technique for conversion of the nonpolar α crystalline phase to the electroactive β phase.…”

A hybrid piezoelectric nanogenerator comprising of KNN/ZnO nanorods incorporated PVDF electrospun nanocomposite webs

“… k α and k β are the absorption coefficient of the α and β‐crystalline phases. The standard value for the k α and k β are 6.1 × 104 and 7.7 × 104 cm 2 mol −1 , respectively . Figure D reveals the symmetric and asymmetric band vibration of the CH 2 dipole in the PVDF polymer matrix corresponding to wavenumber of 2926 and 3029 cm −1 , respectively.…”

“…In our previous study, we have developed KNN nanostructures (mixture of particles and rods) and nanorods incorporated PVDF polymer‐based nanogenerator by different methods like solution cast films, melt‐spun filaments, and electrospun webs. PVDF/KNN NRs melt‐spun filament‐based nanogenerator generated 3.7 V output signal whereas for the PVDF/KNN nanostructures the generated voltage was 1.9 V . Also, surface modified KNN nanorods incorporated PVDF solution cast films have been explored in our previous work .…”