Ionic liquid modified PVDF/BCZT nanocomposites for space charge induced mechanical energy harvesting performance.

Mechanical energy harvesting performances of poly(vinylidene fluoride) (PVDF) based composites are most often correlated with their polar phase and the individual piezoelectricity of the used filler materials. Here we show that the significant enhancement of space charge polarization of the said composites can play the key dominant role in determining their mechanical energy harvesting performance regardless of their polar phase and individual piezoelectricity of the used fillers. For this purpose, ionic liquid has been incorporated into PVDF/0.5(Ba0.7Ca0.3)TiO3-0.5Ba(Ti0.8Zr0.2)O3(BCZT) composites which led to a huge enhancement in space charge polarization. The gradual addition of ionic liquid into 10 wt% BCZT loaded PVDF (PBCZT) has helped in extraordinarily enhancing the conductivity gradually which has confirmed the huge enhancement of space charge polarization. However, after a certain limit of ionic liquid addition, the polar phase of the composite films is decreased. Despite this, the output voltages from the piezoelectric and piezo-tribo hybrid nanogenerators (PENGs and HNGs, respectively) fabricated by using the developed films have been found to be increased gradually with the increase in the ionic liquid amount in PBCZT composite. As the amount of BCZT filler was kept fixed for all the films, this result has confirmed the key role of space charge polarization of PVDF-based composites in determining their mechanical energy harvesting performances compared to the effect of polar phase and individual piezoelectricity of filler. The optimized PENG and HNG devices have shown the output voltage as high as 52 and 167 V, respectively, with power densities ∼85 and 152µW cm-2which predicted their excellent usability in real life energy conversion devices. This work also shows that the effect of extraordinarily enhanced space charge polarization is effective in improving the performance of all types of mechanical energy harvesting devices regardless of their mechanisms (piezoelectric or hybrid).

Electroactive properties and piezo-tribo hybrid energy harvesting performances of PVDF-AlFeO3 composites: role of crystal symmetry and agglomeration of fillers.

Inorganic filler-loaded PVDF-based composites have been very widely used for electrical and energy harvesting applications in recent times. In this regard, the effects of different parameters of fillers like size, shape, chemical states, distribution, functional properties, and many others on the output performance of PVDF have been widely studied. However, the effect of another important parameter, namely the crystal symmetry of the filler, in tuning the energy harvesting performance of PVDF has been rarely explored. Therefore, to explore this fact, here we develop PVDF-based composite films by using two types of AlFeO3 fillers, one with rhombohedral R3̄c symmetry (AFRH) and another with an orthorhombic Pc21n structure. Ferrite-based oxides have been chosen here as fillers due to their good dielectric compatibility with PVDF. On the other hand, AlFeO3 has been chosen due to the simplicity of synthesizing it with both centrosymmetric and non-centrosymmetric crystal structures and the scarcity of reports exploring the energy-harvesting performance of AlFeO3-based polymer composites. A significant difference in particle agglomeration has also been observed here between the mentioned two types of AlFeO3 fillers which was mainly due to their specific synthesis conditions. The electroactive properties of PVDF have been observed to be mostly dependent on filler agglomeration. However, the crystal symmetry has shown a strong effect on the piezoelectric energy harvesting performances. As a result of these facts, the piezo-tribo hybrid energy harvesting performance, which depends on both the dielectric permittivity and piezoelectric activity, has been observed to be better for the AFRH5-based hybrid device (AFRH5H) (with ∼72 V open circuit voltage and ∼45 µW cm-2 power density) compared to that of the AFOR5-based hybrid device (AFOR5H). The real-life applications of all the energy harvesting devices have also been demonstrated here.

Two-Dimensional Metal-Organic Framework Incorporated Highly Polar PVDF for Dielectric Energy Storage and Mechanical Energy Harvesting.

Here, we introduce a 2D metal-organic framework (MOF) into the poly(vinylidene fluoride) (PVDF) matrix, which has been comparatively less explored in this field. Highly 2D Ni-MOF has been synthesized in this regard via hydrothermal route and has been incorporated into PVDF matrix via solvent casting technique with ultralow filler (0.5 wt%) loading. The polar phase percentage of 0.5 wt% Ni-MOF loaded PVDF film (NPVDF) has been found to be increased to ~85% from a value of ~55% for neat PVDF. The ultralow filler loading has inhibited the easy breakdown path along with increased dielectric permittivity and hence has enhanced the energy storage performance. On the other hand, significantly enriched polarity and Young's Modulus has helped in improving its mechanical energy harvesting performance, thereby enhancing the human motion interactive sensing activities. The piezoelectric and piezo-tribo hybrid devices made up of NPVDF film have shown improved output power density of ~3.26 and 31 µW/cm2 compared to those of the piezoelectric and piezo-tribo hybrid devices comprising of neat PVDF (output power density ~0.6 and 17 µW/cm2, respectively). The developed composite can thus be considered an excellent candidate for multifunctional applications.

Enhanced dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of ZnO-PVDF composites induced by MWCNTs as an additive third phase.

The present work highlights an attempt of fabricating a nanocomposite by the addition of multi-walled carbon nanotubes (MWCNTs) as a third phase into flexible ZnO-poly(vinylidene fluoride) (ZnO-PVDF) composites. MWCNTs played a very important role in distributing ZnO fillers in the PVDF matrix more homogeneously and increased the connection capability. Enhancement of the piezoelectric phase, dielectric permittivity, ferroelectric polarization, energy storage density and mechanical energy harvesting performance of ZnO-PVDF composites after the addition of MWCNTs was confirmed from the respective characterization studies. The sensing capability was demonstrated by the generation of ∼22 V ac output voltage through the application of human finger tapping on 15 wt% ZnO and a 0.1 wt% MWCNT-loaded PVDF (15PZNT) based composite film. The rectified voltage from the fabricated 15PZNT film was used to charge a 10-µF capacitor up to ∼3 V which was used for the illumination of 30 commercial LEDs. The maximum power density from the film was found to be 21.41 µW cm-2 at 4 MΩ load resistance. The effect of the addition of MWCNTs was also verified by simulation using COMSOL Multiphysics software.

Hydroxylated BiFeO3 as efficient fillers in poly(vinylidene fluoride) for flexible dielectric, ferroelectric, energy storage and mechanical energy harvesting application.

Here we report the effect of surface hydroxylation of BiFeO3 fillers on the dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of poly(vinylidene fluoride). Surface hydroxylation helped to improve the interfacial interaction between the filler and PVDF matrix by introducing a strong hydrogen bonding between the -OH group of the hydroxylated BiFeO3 filler surface and the -CF2 dipole of PVDF in place of electrostatic interfacial interaction between non-hydroxylated BiFeO3 and the -CH2 dipole of PVDF. The amount of polar phase increased to around 91% for a 7 wt% hydroxylated BiFeO3 loaded PVDF film (7BFOH) by this new type of interfacial interaction. The dielectric, ferroelectric, energy storage and mechanical energy harvesting performance of the PVDF based composite films also improved by the above said technique. Upon repeated human finger tapping, the 7BFOH film delivered ∼18 V output peak to peak open circuit ac voltage (VOC). After rectification, the VOC of the 7BFOH film was able to charge a 10 µF capacitor up to ∼3 V which was able to light up some LEDs (connected in parallel) together instantaneously, which proved the real life applicability of the composite films in low power consuming self-powered electronic devices.

Nano-ZnO decorated ZnSnO3 as efficient fillers in PVDF matrixes: toward simultaneous enhancement of energy storage density and efficiency and improved energy harvesting activity.

Here, we report the effect of ZnO decoration on ZnSnO3 fillers on the dielectric property, energy storage behaviour and mechanical energy harvesting performance of PVDF matrixes. More enhanced dielectric constant and reduction in dielectric loss were achieved in PVDF-ZnO@ZnSnO3 (PVDF-ZNZS) films than in PVDF-ZnSnO3 (PVDF-ZS) films for the same concentration of filler loading. Similarly, PVDF-ZNZS films showed simultaneous enhancement in electrical energy storage density and storage efficiency compared to PVDF-ZS composites. As all the constituent materials (PVDF, ZnSnO3 and ZnO) were piezoelectric, the resulting composite film showed improved piezoelectric energy harvesting performance too. After rectification, the output ac voltage was used to charge a 10 µF capacitor up to ∼5 V dc which was further used to light up some LEDs. Furthermore, in order to exhibit improved sensitive output, a hybrid piezo-tribo nanogenerator was fabricated which was demonstrated as a motion sensor, a weight sensor and a human body movement sensor as part of a real life application.

Frequency dependent energy storage and dielectric performance of Ba-Zr Co-doped BiFeO3 loaded PVDF based mechanical energy harvesters: effect of corona poling.

Bi0.95Ba0.05Fe0.95Zr0.05O3 (BBFZO) nanoparticles were synthesized by a sol-gel technique to develop a filler material with lower leakage current and oxygen vacancies compared to the host BiFeO3. In this work, we report the enhanced dielectric, ferroelectric, energy storage and energy harvesting performance of BBFZO incorporated PVDF composites. 15 wt% BBFZO loaded PVDF (15BBFZO) exhibited improved polarity (F(EA) = 77.42%) compared to neat PVDF (F(EA) = 37.01%). At an applied field of ∼14 kV cm-1 (1 Hz), this film (15BBFZO) exhibited a maximum energy storage density of 151.18 µJ cm-3 (at 1 Hz). Upon repeated human finger tapping, an average open circuit peak to peak a.c. voltage (VOC) ∼ 20 V was obtained from 15BBFZO. A comprehensive study of frequency dependent D-E loops and an extensive study of the effect of electrical poling on the output performance of the developed composite films have been performed. An improvement of the dipolar polarization was established through a frequency dependent D-E loop study of unpoled and poled 15BBFZO and from other experiments. After poling the energy storage density and VOC of 15BBFZO were 154.66 µJ cm-3 (at 1 Hz) and ∼30 V, respectively. After rectification this output electrical signal was able to charge a 10 µF commercial capacitor up to ∼5.5 V. After poling, the energy storage efficiency (η) of 15BBFZO also improved from 52.49% to 67.85% (at 1 Hz). The frequency dependence of the storage efficiency for all the samples has also been extensively investigated here. At 1 kHz, η improved to 93.30% for poled 15BBFZO.

Role of suppressed oxygen vacancies in the BiFeO3 nanofiller to improve the polar phase and multifunctional performance of poly(vinylidene fluoride).

In the present work, we report the enhanced dielectric, ferroelectric, energy storage and energy harvesting performance of a citrate-gel synthesized Bi1-xBaxFeO3 (x = 0, 0.05, 0.10) incorporated poly(vinylidene fluoride) (PVDF) matrix. Doping with aliovalent ions has been shown to improve the multiferroic properties of BiFeO3. Though Ba2+ doping has been expected to introduce more oxygen vacancies, here we found a decrease in oxygen vacancies with increasing Ba2+ up to 10% doping. This suppression of oxygen vacancies through Ba2+ doping in BiFeO3 helped in the formation of the polar PVDF phase in the composite through interfacial interaction. The polar phase fraction (F(EA)) increases to 82.4% for the 7 wt% Bi0.9Ba0.1FeO3 incorporated PVDF film from 38.2% for the neat PVDF. This film also showed the highest energy storage density of 5.4 mJ cm-3 at a 110 kV cm-1 applied field and the highest energy harvesting performance of ∼20 V open circuit output voltage after application of repeated human finger tapping and releasing motion, due to its enhanced piezoelectric property. Here, we also demonstrate the enhanced energy harvesting capability of the said PVDF-Bi0.9Ba0.1FeO3 composite by charging a 10 µF commercial capacitor up to ∼5 V in 270 s, which can comfortably light up about 50 LEDs instantaneously.