MWCNT@SiO2 Heterogeneous Nanofiller Based Polymer Composites

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MWCNT@SiO2 heterogeneous nanofiller based polymer composites: A single key to the high performance piezoelectric nanogenerator and X-band microwave shield Epsita Kar, Navonil Bose, Biplab Dutta, Nillohit Mukherjee, and Sampad Mukherjee ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00770 • Publication Date (Web): 31 Jul 2018 Downloaded from http://pubs.acs.org on August 2, 2018

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MWCNT@SiO2 Heterogeneous Nanofiller Based Polymer Composites: A Single Key to the High Performance Piezoelectric Nanogenerator and X-band Microwave Shield Epsita Kar1, Navonil Bose2*, Biplab Dutta1, Nillohit Mukherjee3*, Sampad Mukherjee1* 1

Department of Physics, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, West Bengal, India

2

Department of Physics, Supreme Knowledge Foundation Group of Institutions, Hooghly712139, West Bengal, India

3

Centre of Excellence for Green Energy and Sensor Systems, Indian Institute of Engineering Science and Technology, Shibpur, Howrah-711103, West Bengal, India

Corresponding

authors:

[email protected]

(N.

Bose),

[email protected]

(N.

Mukherjee), [email protected] (S. Mukherjee)

Abstract: We report the prototype fabrication of flexible, facile multiwalled carbon nanotube@ silica incorporated poly(vinylidene fluoride) (MWCNT@SiO2/PVDF) nanocomposite based piezoelectric energy harvester as the cheaper and cleaner source of alternative energy. In depth study of local piezoelectric and ferroelectric properties of the nanocomposites was performed by piezoresponse force microscopy (PFM) technique. The prototype piezoelectric nanogenerator scavenges low frequency biomechanical energy and abundant vibration energy of ambient environment to produce remarkable electrical power (can directly illuminate a panel of 55 commercial LEDs), without applying any external poling process. The flexible nanogenerator exhibits high performance with a maximum recordable output voltage of 45 V, current density 1.2 μA/cm2 and power density 5400 W/m3 under periodically vertical compression and release operations via biomechanical force. The high efficiency (15.4%) of the nanogenerator lead to a unit cost of electricity as low as 0.21 US$/kWh, which is extremely competitive to other energy sources. Again, the self-standing MWCNT@SiO2/PVDF nanocomposite film shows extremely well electromagnetic interference (EMI) shielding property in X-band, with the promise to block detrimental effect of microwave radiation on environment. The flexible films with thickness 400±5 μm were found to exhibit about 99% microwave shielding in the X-band (8.2-12.4 GHz) 1 ACS Paragon Plus Environment

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with a dominating fraction of absorption. These results undoubtedly expand the feasibility of such heterogeneous nanocomposites in energy and environment sectors for high performance energy harvesting devices as well as microwave shielding applications like wearable devices for power production from human body movements and simultaneously protecting human body from microwave radiation. Keywords: Green energy source; PVDF composite; Piezoresponse force microscopy; Flexible piezoelectric nanogenerator; X-band microwave shield; Introduction: A rapidly growing demand of ever expanding human population has triggered two serious issues, lack of fossil fuels and global warming [1-2]. It is well understood that today the world is facing the problem of global warming due to rapid industrialization and urbanization. Utter measures are required in such a critical time when the world is trying to cut CO2 emission amount and to solve the electricity deficit related problems simultaneously. To address these issues, efficient energy harvesting has developed as one of the most important technologies in today’s green and renewable energy science. Moreover, rapid growth of portable electronic devices such as mobile phones, bendable displays, wearable personal multimedia and some medical devices are increasingly looking for thin, lightweight and flexible energy generation technologies [3]. Energy harvesting from environment depends on the nature of energy sources, such as solar, thermal, electromagnetic and mechanical [4-8]. Among the different conversion methods; piezoelectric nanogenerator (NG) is a powerful and upcoming approach for converting low frequency mechanical energy into electricity that works through the piezoelectric potential created by an externally applied strain in a piezoelectric material for driving the flow of electrons to the external load [9-10]. Recently human-motion-based piezoelectric energy harvesters have attracted tremendous interest due to their potential applications in portable, embedded and wearable smart electronics that require a self-sufficient and sustainable power source [11-12]. On the other hand, the inexhaustible use of electronic and communication devices produces electromagnetic (EM) radiation as an offshoot and leads to a new kind of pollution, called electromagnetic interference (EMI). EMI is undesirable and has emerged as a significant problem in current era. This eventually leads to the malfunctioning of some precise instruments and also affects human health as well as surrounding flora and fauna [13-17]. The materials used 2 ACS Paragon Plus Environment

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for EMI shielding applications should have high microwave absorption properties as well as, they should be flexible and light weight. One answer to both the problems lies with the development of flexible, lightweight, self-standing polymer nanocomposite films having improved ‘ferro’ and ‘piezo’ electric properties, which may act as an attractive option for self-powering system (capable of harvesting energy from the ambient environment) and on the other hand can absorb EM radiation to stop the detrimental effect. Owing to their remarkable piezoelectric, ferroelectric and dielectric properties, poly(vinylidene fluoride) (PVDF) and its copolymers based nanocomposite films are considered as the smart options to be chosen [17-20] for fabricating piezoelectric nanogenerators and EMI shielding devices. Semicrystalline PVDF has at least five crystalline polymorphs: α, β, ,   . However, the electroactive β polymorph (with all ‘trans’ (TTT) planar zigzag conformation) stands out to be most suitable for piezoelectric nanogenerator and other dielectric, ferroelectric applications [21]. Recently different nanofillers were added to PVDF based polymer matrix to enhance the piezoelectric property and nanogenerator performance either by inducing large β phase in PVDF and/or adding the effect of inherent piezoelectric properties of those nanofillers. PVDF nanocomposites with nanofillers such as ZnSnO3[22], RGO:Fe[23], ZnO[24], FAPbBr3[10], BaTiO3[25], Ce3+/grapheme [26], AlO/RGO [12] and graphene-silver [27] were used to achieve enhanced nanogenerator output. But the limitations of these nanocomposites are associated with the facts like low output power density, low economic performance, less durability and the requirement of additional poling process by external high electric field. It is also widely accepted that filling of carbon nanotubes (CNTs) enables the induction of high fraction of β polymorph in PVDF via self-polarization technique [28-29] and there is no requirement of any external electric field for their performance as nanogenerator. Owing to its high tensile strength and extraordinary electron mobility, CNTs (both single-walled and multiwalled) can be used as ideal nanofillers for improving energy harvesting as well as microwave shielding properties [30-33] of its polymer composites by enhancing the β phase contents. But the main drawback associated with the use of multiwalled carbon nanotubes (MWCNTs) and other graphitic carbon nanomaterials as filler is related with the high agglomeration tendency as well as low percolation threshold. Improved properties of polymer nanocompositesmay be achieved by the discrete and uniform dispersion of highly anisotropic nanofillers in polymer matrix [31]. Thus to take advantage of the conductive properties of CNTs in composite, there is a 3 ACS Paragon Plus Environment

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strong need to prevent the agglomeration which can be achieved by adding some other oxide nanofillers along with CNT. It is worthwhile to mention that, in case of EMI shielding activities; only MWCNTs cannot be used as suitable filler as it gives a low absorption loss due to its low dielectric loss and poor magnetic properties [31]. Carbon nanotube loaded PVDF composite (CNT/PVDF) nanocomposite EMI shields were reported earlier by Biswas et al. [30] but typically the shielding mechanism is dominated by reflection rather than absorption for all the cases. To overcome these drawbacks and to obtain a better dispersion of CNTs in PVDF matrix, low cost and easily processable SiO2 nanoparticles can be used with CNTs as co-filler in the PVDF matrix. As a concern, it will be quite interesting to study the effect of the well dispersed CNT@SiO2 on the piezoelectric, dielectric and EMI shielding properties of PVDF. In this work, we report the synthesis of self-polarized MWCNT@SiO2/PVDF polymer composite films with enhanced piezoelectric, dielectric and ferroelectric properties and we have explored their performance as a flexible, high performance, cost effective and durable piezoelectric nanogenerator as well as EMI shielding material. The well dispersed MWCNT@SiO2 nanofiller endow the composite film with advantages of nanofiller without compromising the mechanical and thermal property of the PVDF. To the best of our knowledge, no work has been reported on piezoresponse of MWCNT@SiO2/PVDF nanocomposite by β phase stabilization so far. Energy harvester fabricated from the MWCNT@SiO2/PVDF composite shows high output voltage, high power density and high energy conversion efficiency and can be used to directly power 55 commercial LEDs. On the other hand EMI shield fabricated from the composite is able to block 99% incident EM radiation (in X-band) mainly through absorption mechanism. A general schematic of summary of the entire work is presented in Fig.1. Hence the composite simultaneously demonstrates great potential for simple and cost effective fabrication of high performance flexible piezoelectric nanogenerator and EMI shield.

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Fig.1: Schematic of summary of the entire work. 2. Results and Discussions 2.1. Structural analyses X-ray diffraction. TEM micrograph of MWCNT@SiO2 is shown in Fig.S1 of supplementary document. Fig.2a reveals the X-ray diffraction (XRD) pattern of neat PVDF (P-0) and MWCNT@SiO2 impregnated PVDF nanocomposite films c.a. C-0.25, C-0.5, C-0.75, C-1.0 and C-5.0 (0.25 , 0.5, .75, 1, 5 wt% filler loaded composites). The figure shows the semi-crystalline nature of the neat as well as composite films. A broad hump is observed due to the presence of amorphous SiO2 nanoparticles in the composites at the lower 2θ region around 2θ=23° for all the loaded samples [35]. The position of the SiO2nanoparticles related broad hump coincides with the characteristic peak (2θ~ 25°) [36] of MWCNT, which consequences in a masking phenomenon over that region. The peaks positioned at 2θ= 17.5° (100), 18.2° (020), 19.7° (021) and 26.6° [(201),(310)] of the P-0 film are assigned to the non-polar α phase of PVDF [37]. A gradual decrease in intensity of the non-polar α phase related peaks with increasing filler contents is observed from the XRD pattern, whereas a new peak positioned around 2θ= 20.3° [(200),(101)] is found to appear for the PVDF nanocomposite films, which can clearly be 5 ACS Paragon Plus Environment

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assigned to the formation of the polar β phase of PVDF [37]. The content dependence of the fraction I20.3°/I18.2° (Fig.S3) yields that the most intimate interaction of the filler with the polymer matrix is occurred for 1 wt% filler loading where maximum β phase nucleation is occurred. Beyond 1 wt% filler loading β phase fraction is reduced in the composites due to agglomeration of the filler particles resulting reduction in the interfacial surface area between filler and the polymer matrix. Thus this ratio imparts knowledge on the interaction of the filler with the polymer matrix [38]. Thus the incorporation of MWCNT@SiO2 filler in PVDF matrix leads to the enhancement of the electroactive β phase as well as reduction of the non-polar α phase of PVDF.

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Fig.2 (a) XRD patterns of the MWCNT@SiO2 loaded PVDF composite samples c.a. C-0, C0.25, C-0.5, C-0.75 C-1.0 and C-5.0; the signals according to the PVDF matrix are labeled [37]. (b) FTIR spectra for the MWCNT@SiO2 nanoparticles loaded PVDF composites within 400 to 1000 cm-1 region for P-0, C-0.25, C-0.5, C-0.75, and (c) C-1.0, C-3.0 , C-5.0 films. (d) Variation of electroactive beta phase fraction [F(β)] with filler concentration. Fourier transform infrared spectroscopy. Output performance of a polymer based piezoelectric nanogenerator mostly depends on the electroactive phase contents, as piezoresponse of a polymeric material increases with increasing electroactive phase content. Fourier transform infrared (FTIR) absorption spectroscopy was used to investigate the electroactive β phase content in the prepared PVDF composites. Fig.2b-c show the as-recorded FTIR absorption spectra of neat (P-0) and MWCNT@SiO2 loaded PVDF films c.a. C-0.25, C0.5, C-0.75, C-1.0, C-3.0 and C-5.0. The FTIR spectrum of P-0 shows the peaks at 488 (CF2 wagging), 532 (CF2 bending), 615 (CF2 bending), 764 (skeletal bending), 796 and 976 cm-1 (CH2 rocking), which are assigned to the IR bands of the non-polar α phase of PVDF [37]. The FTIR spectrum of P-0 also reveals the presence of small peaks positioned at 510 (CF2 stretching) and 840 cm-1 (CH2 rocking, CF2 stretching and skeletal C-C stretching) corresponding to the β phase of PVDF [37]. With the increase in filler loading, the relative intensities of the IR absorption peaks corresponding to the non-polar α phase of PVDF are gradually diminished and simultaneously the relative intensity of the peaks corresponding to the polar β phase of PVDF is increased. For the sample C-1.0 the peaks assigned to the α-phase of PVDF have almost disappeared and only the absorption peaks related to the electroactive β phase of PVDF were found to be dominating, which are positioned at 510, 600 (CF2 waging) and 840 cm-1 [37]. Therefore, the FTIR results strongly indicate that MWCNT@SiO2 fillers can control the nucleation of crystalline polymorph in PVDF and results in a transformation from α to β phase, i.e. no-polar to polar arrangement. To make a quantitative study of the phase transformation for the filler incorporated PVDF films, the β phase fraction (F(β)) is calculated using Eqn. (S1) of supporting document. The variation of the F(β) with filler loading is shown in Fig.2d. Maximum 81% of β phase fraction is obtained at 1.0wt% of filler loading. It should be highlighted that even a small amount of filler (0.25 wt%) can give rise to the F(β) value to 68%, which is really impressive in the context of electroactive phase content nucleation without using any traditional, power consuming electrical poling process [38]. Interaction between the filler and the polymer 7 ACS Paragon Plus Environment

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matrix plays the key role in the variation of F(β). Initially, at lower loading fractions, the interfacial area between the filler and the polymer is relatively low. Interfacial area increases with the increasing filler loading, leading to an improved interaction between the filler and the polymer matrix. As a consequence, the number of aligned chains with ‘all trans’ (TTT) conformation in PVDF increases, resulting in an increase in F(β) fraction. The most intimate interaction between the polymer and the filler occurs at the loading of 1 wt% MWCNT@SiO2 fillers in PVDF (sample C-1.0) resulting in highest β phase fraction among the lot. However, beyond1.0 wt% filler loading the excessive amount of MWCNT@SiO2 present in the PVDF matrix disrupt the regular “all trans” (TTT) orientation of the polymer chain

due to

agglomeration of the fillers and the number of aligned dipoles decreases, which leads to an overall decrease in the polar β phase fraction. The variation of α and β phase with the filler content in the composite films (Fig.S4) confirms the highest β phase content formation at 1.0wt% MWCNT@SiO2 loading. Surface Morphology. The FESEM image (Fig.3a) of the composite film having maximum β phase content (C-1.0 film) shows highly compact and uniform surface morphology without any crack and pinholes. Spherulites (marked by red circles) present on the surface of C-1.0 are different in nature from the α-spherulites of neat PVDF (Fig.S5). Uniformly distributed spherulites of C-1.0 have smaller average diameter (5 μm) than that of the neat PVDF (12μm) which reflects faster nucleation kinetics in composite due to the presence of additional nucleation centers i.e. MWCNT@SiO2 nanofillers. Most importantly the uniform distribution of spherulites over the surface indicates the homogeneous and discrete distribution of the MWCNT@SiO2 nanofillers in the PVDF matrix. More discussion on morphological analyses is made in section S2.2.3 of the supporting document.

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Fig.3 (a) FESEM image of the sample C-1.0. Red circles show the position of the spherulities. The two red straight lines reveal the presence of common boundary of neighboring spherulities. (b) Schematic representation of the electrostatic interaction between the negative surface charges of the MWCNT@SiO2 nanoparticles and the positive –CH2 bond of PVDF matrix. The results obtained from the XRD, FTIR, FESEM and thermal (Fig. S6a-e, section S2.2.4 of the supporting document) studies of the composites confirm the incorporation of MWCNT@SiO2 nanoparticles in the PVDF matrix leads to an increment in the electroactive β phase nucleation up to a certain critical weight percentage of the filler loading. The results also confirm that the most intimate interaction between the filler and the polymer matrix is occurring for sample C-1.0. The enhancement of the electroactive β phase contents in the nanocomposite films can be attributed to the interaction between the negatively charge surface (as shown by the zeta potential curve Fig.S2) of MWCNTs@SiO2 and positive –CH2 group of PVDF. In Fig.3b, the schematic indicates the electrostatic interaction between the negatively charged surface of MWCNTs@SiO2 nanofiller and –CH2 dipole which leads to the formation of β phase PVDF. The detail evidences and discussion regarding the β phase formation through surface charge dipole interaction are provided in the supplementary sections (S2.2.5 and S2.2.6). In light of this, the sample C-1.0 having maximum β phase fraction has been chosen for the flexible piezoelectric nanogenerator device fabrication. 2.2 Electric force microscopy

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Piezoresponse force microscopy (PFM) was deployed to investigate the local piezoelectric properties of the sample with maximum beta phase fraction, viz. C-1.0. In the PFM measurements, a conductive Au-coated Si tip (Model CSG10 with Au NT-MDT) was employed with a constant tip AC voltage of 1.0 V at resonance frequency mode (17 KHz) and the bottom of the test sample was grounded. In PFM spectroscopic study, a sweeping DC bias in the range of ±10 V was applied by the tip at the top surface of the polymer composite film. Fig.4a-b show the piezoresponse loop and rectangular phase hysteresis loop under the application of DC bias voltage of ±10 V respectively. In Fig.4b, the piezoresponse phase loop shows the 180° phase difference at opposite signals, which confirms the 180° ferroelectric domain switching by the applied DC bias [40]. The dipoles localized under the tip are switched either upward or downward directions by the opposing external electric field. This result confirms the ferroelectric behavior of the composite film. C-1.0 contains significant amount of β phase which is a thermodynamically meta-stable phase of PVDF having ‘all trans’ (TTT) conformation. On application of dc-bias across the C-1.0 film, electric dipoles due to C-F and C-H can be rotated around the carbon backbone causing ferroelectric property within it, which is confirmed by the switching phenomenon of the ferroelectric hysteresis loop. The PFM spectroscopy studies were performed at various locations on the sample surface to confirm the presence of ferroelectric hysteresis with switching characteristics (Fig.S9a). Fig.S9b shows the location at which the PFM spectroscopic measurement was performed corresponding to the Fig.4a-b.

Fig.4 (a) Piezoresponse loop (b) rectangular hysteresis loop of the sample C-1.0 under the application of DC bias in the range ±10 V. Piezoresponse hysteresis PR(E) is calculated and

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plotted using equation PR(E)=A(E)CosΦ(E), where A(E) is the amplitude and Φ(E) is the phase angle [40]. Fig.5a-c show the PFM results of the topography, amplitude and phase for the 1.0 wt% MWCNT@SiO2 loaded PVDF composite, respectively. The amplitude of the piezoresponse signal is related to the local piezoelectric coefficient originated due to electromechanical coupling in the prepared materials, while the polarization direction or orientations can be reflected by the phase [40]. The PFM amplitude and phase signals (Fig.5b-c) show both positive and negative values suggesting that the domains are mainly separated by 1800 walls [41].To further study the change in ferroelectric properties, vertical PFM phase image of the C-1.0 film was recorded under a tip bias of 10 V as shown in Fig.5d. Significant change with respect to nobias phase measurement (Fig.5c) was observed and much uniform distribution in the domain contrast is also evident which also indicates the polarization switching behavior. During PFM measurements, the applied electrostatic force alters the polymer chain, making the monomer to rotate in the direction of the applied electric field, thus leading the configuration to arrange in a more regular structure. The phase angle value (in Fig.5d) lies majorly between 220 to 440. This is in well agreement with phase hysteresis loops (Fig.4b, Fig.S9a) where the phase values are ~250at 10 V (beyond the coercive voltage). Fig.S9c shows the vertical PFM phase image of the C-1.0 film under a tip bias of – 10 V. PFM measurements confirm that the sample C-1.0 possesses good ferroelectric and piezoelectric properties, hence can be suitably used for piezoelectric nanogenerator application.

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Fig.5 PFM results of (a) topography (b) amplitude and (c) phase (no DC bias) for the sample C1.0. (d) PFM phase image of C-1.0 film (10µm x 10µm area) under tip bias of 10 V. The microscopy was performed at the same area corresponding to Fig.5c. 2.3. Piezoelectric nanogenerator 2.3.1. Fabrication of nanogenerator Sandwich structure based polymer composite nanogenerators (PCNGs) were fabricated by arranging the MWCNT@SiO2/PVDF films (thickness of the films 100±10 µm) in between two flexible electrodes (cross sectional FESEM image is shown in Fig.S19 of Supporting Information). The electrodes (with 1.52.5cm2 area) were taken from both sides of the polymer composite (PC) films by using adhesive carbon tape. Then the whole sample was laminated using Teflon and one sided adhesive tape. The corresponding schematic diagram is presented in Fig.6. A digital photograph of the fabricated device is also shown in Fig.6, which also reflects its flexibility. The electrodes were connected to a bridge diode to rectify the generated piezoelectric signal. The device performance was characterized by imparting a periodic pressure (peak amplitude 0.4 MPa) onto the NG using a wooden probe.

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Fig.6 Schematic of the fabrication procedure of the MWCNT@SiO2/PVDF based nanogenerator. (a) MWCNT@SiO2/PVDF nanocomposite film with high flexibility (b) fabricated nanogenerator and (c) flexibility of the PC nanogenerator. 2.3.2. Piezoelectric nanogenerator performance The piezoelectric energy harvesting properties, i.e. the nanogenerator (NG) performance of the prepared MWCNT@SiO2/PVDF composite films were investigated by repetitive manual imparting of wooden piece on the upper surface of the NG (as shown in video VS1a). The generated piezoelectric output voltage was measured under a periodically vertical compressing and releasing process exerted by the simple biomechanical pressure 0.4 MPa at the frequency of 4 Hz. The piezoresponses of the MWCNT@SiO2/PVDF composite films without electrical poling and with different filler loading were studied by measuring the output electrical performances of the NGs. Fig.S10 shows the measured output open circuit voltage and calculated instantaneous output current of the NGs at different filler loading. As expected, the NG containing 1.0 wt% of MWCNT@SiO2 showed most efficient piezoelectric nanogenerator performance among the lot, which is attributed to the maximum presence of the electroactive β phase in it. The NG containing neat PVDF was found to exhibit very low output [23].The output performance of the nanocomposite films gradually increased with filler loading and reaches its maximum value at 1.0 wt% MWCNT@SiO2 loading due to the largest β phase formation in

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PVDF at this filler fraction. But beyond 1.0 wt% loading, the output performance of the nanocomposites was found to be diminished. The reduced piezoelectric harvesting property at higher filler loading is associated with the excessive amount of filler concentration in the polymer matrix. Increased number of fillers increase the dielectric constant of the composites (as discussed in section S2.2.11 of the Supporting Information file and Table-SII), but may weaken the electromechanical coupling effect of the PVDF composites film [42]. Reduction of beta-phase fraction above 1.0 wt% filler loading is another reason for such behavior. As a promising outcome NG (with an effective electrode size of (1.5 × 2.5cm2) made of 1.0 wt% MWCNT@SiO2/PVDF film exhibited an high output voltage ~ 45 V (Fig.7a) under the periodic, vertical compressing and releasing process. Enlarged view of one cycle of output voltage under forward connections is shown in Fig.7a, exhibiting two sets of responses of positive and negative piezoelectric potentials under compressing and releasing processes. The first set is generated when compression is applied and subsequently the strain recovers to its initial position after releasing of compressive force, and the later set can be attributed to the damping effect in NG film [42]. The higher peak value of the positive voltage signal than the negative voltage signal supports the piezoelectric nature of the cycle [7]. Further, switching polarity test [27] was performed by reversing the electrode connection to verify piezoelectric origin of the output signal of the fabricated NG as shown in Fig.S11a. The figure shows identical amplitude of output voltage with reversed connection. The corresponding time varying rectified piezoelectric output voltage is shown in Fig.S11b (supporting information). The time varying short circuit current of PCNG is shown in Fig.7b. An instantaneous current of peak value as high as 4.0 μA is achieved for PCNG.

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Fig.7 (a) Piezoelectric output voltage of the nanogenerator fabricated with sample C-1.0. The corresponding digital images of the circuit connections are given with the enlarged views of the cycles. (b) Time varying short circuit current of PCNG. (c) Variation of average piezoelectric output voltage and corresponding power density of the nanogenerator fabricated from the sample C-1.0. Inset shows the circuit connection to measure the output voltage. (d) Variation of surface current density with resistance of the nanogenerator fabricated with the sample C-1.0. Self-poled MWCNT@SiO2/PVDF based NG exhibited outstanding output performance without applying any traditional electrical poling process. It is essential to check the power generation and accumulation parameters of the fabricated NG to explore the suitable real life applications of this type of generators. Fig.7c shows the variation of average output voltage and instantaneous power density (Power density =

  

=

 



where, area= 1.5  2.5 cm2,

thickness~100µm) with load resistance. The measurement circuit diagram is shown in the inset of the Fig.7c. It is evident from the figure that the average output voltage is increased gradually with increasing resistance and reached the maximum 45 Volt across a 10 MΩ resistance. Hence the output voltage value is saturated at the theoretically infinite load resistance similar to the open circuit voltage. At optimum power transfer condition the value of output power density of PCNG is ~ 5400 W/m3 which is ever largest value obtained so far for any carbon based PVDF composite nanogenerators operated under similar bio-mechanical force, as given in Table-I. Table-I: Comparison of performance of different previously reported nanogenerators. Name of the nanogenerator

Outpu t Voltag e (V)

Current/Curren t Density

Power/Pow er Density

Energy Conversion Efficiency (%)

Ref

PDMS/ZnSnO3/MWC NT

40

0.4 µA

10.8µW/cm3

0.27 (2.2 µF)

[32]

Cellulose/PDMS/MW CNT

30

500 nA

9 µW/cm3

--

[33]

PVDF/AlO-rGO1.0

36

0.8 µA

27.97

12.47 (2.2 µF)

[12]

--

[43]

µW/cm3 PVDF/Surface modified

1

125 µW/cm3

1.5 µA

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graphene/BaTiO3 Ce3+doped PVDF/graphene

12

6 nA/cm2

7 µW

--

[26]

ZNO/PVDF

24.5

1.7 μA

32.5 mW/cm3

2.61

[44]

BTZO/PVDF

11.9

1.35 μA

--

--

[45]

Methylammonium lead iodide (CH3NH3PbI3)/PVDF

1.6

80 nA

2.5 μW/cm2

FAPbBr3/PDMS

--

--

--

FAPbBr3/PVDF

30

6.5 μA/cm2

27.4

[46]

0.44

[40]

0.55

[42]

0.3

[47]

--

[48]

2

μW/cm FSB/PDMS

10

51 nA

4.15 μW/cm2

ZTO/PVDF

25.7

8.22

1.2 μA

μW/cm2 PVDF/TrFE nanowires

3

5.5 nA

--

11

[49]

PVDF/DNA

20

0.184 μA

11.5 μW/cm2

2.59

[50]

MWCNT@SiO2/ PVDF

45

4.8 µA

5400 W/m3

15.4 (2.2 µF)

This work

!

Fig.7d shows the variation of calculated current density ( =

#

" 

$

) from PCNG. The estimated

maximum surface current density is ~ 1.2µA/cm2 which was obtained at 10 kΩ. Energy producing capability of the reported NG with 1.0 wt% MWCNT@SiO2 loaded PVDF was studied by charging a capacitor (2.2 µF) through a full wave rectifier where mechanical energy (input energy) to NG was provided by similar wooden piece imparting as mentioned in earlier section. Fig.8a shows that the capacitor was gradually charged by the power generated from NG under periodic applied force. Inset of the figure shows the circuit diagram of the capacitor charging process. The voltage across the capacitor is attained at 20 V within only 250 seconds of imparting under the average pressure of 0.4 MPa at 4 Hz frequency and reached at 17 ACS Paragon Plus Environment

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steady state condition within 300 seconds. Based on the charging capability of the NG, the energy storage in the capacitor (2.2 µF) at steady state condition is also calculated by Ee =1/2 CV2, which is 440 µJ for the charging time of 1000 cycles during 250 sec. It is worthy to mention here that such a high charging performance of a NG is not reported so far for any PVDF nanocomposite based device without applying any external poling process or triboelectric process. The piezoelectric efficiency or energy conversion efficiency of the NG can be calculated from the relation η= Wout/Win (detail of the calculation procedure is mentioned in S2.2.8 of supporting information) where Wout is the output electrical energy stored in capacitor (Ee) and Win is the input mechanical energy. The efficiency of the 1 wt% MWCNT@SiO2 loaded PVDF NG was found to be 15.4% which manifests the viability of use of self-poled, facile MWCNT@SiO2/PVDF based piezoelectric nanogenerators in real life applications and large scale production. The efficiency of our fabricated device is much higher than any other recently reported piezoelectric nanogenerators as mentioned in Table-I (comparison of the energy conversion efficiency of our PCNG with the other carbon as well as non-carbon based nanogenerators). PCNG was used to generate electric power by human finger imparting as shown in video VS1b. A panel of 55 numbers of commercial blue LEDs was powered directly and instantly from the PCNG (imparting by human finger as well as wooden piece) without using any capacitor or storage as shown in video VS2. The output energy of the NG was also exploited to illuminate a panel of commercial LEDs via a capacitor as shown in the video VS3.Video VS4 in supplementary document shows the piezoelectric output from PCNG due to movement of human foot (covered by sock) and wrist twisting. Fig.8b show the digital images of piezoelectric voltage generation by our PCNG due to different biomechanical forces viz. hand imparting, manually wooden piece imparting, wrist bending and toe pressure.

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Fig.8 (a) Charging of the capacitor (2.2 µF) by the power generated from the NG under periodic imparting process using a full wave rectifier. Inset shows the circuit connection to charge the capacitor. 5 Red commercial LEDs can be lightened up by charging the capacitor upto 100 sec, also shown in the inset. The pointed figure shows discharging of the capacitor recorded through the digital storage oscilloscope. (b) Digital image of piezoelectric power generation (rectified output voltage) by PCNG due to (I) hand imparting, (II) wrist bending, (III) toe pressure (IV) manually wooden piece imparting, (V) A panel of 55 numbers of commercial blue LEDs was directly powered from the PCNG. 19 ACS Paragon Plus Environment

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Fig.9 (a) Initial random alignment of the electric dipoles in the MWCNT@SiO2/PVDF film (b) piezoelectric potential and electron flow are generated when the compressive force is applied on the device (c) as the compressive force released, the accumulated electrons flow back along the opposite direction (d) a weak forward piezoelectric potential and electron flow are produced due to damping effect (e) after returning to original state, a reverse piezoelectric signal is generated. The inset is the enlarged view for one cycle of output voltage under forward connection corresponding to Fig.7a.

PCNG can be considered as a charge source (q) in parallel with an internal resistance (Ri) and capacitor (Ci) as shown in inset of Fig.8a. Therefore it can be inferred that our PCNG can act as a good power source under external imparting and its output fits well with the linear circuit theory which evaluates that the value of the internal resistance (Ri) and capacitance (Ci) are 4.30 MΩ and 22.4 µF respectively (as discussed in supporting section S2.2.9). As a consequence, the PCNG with low internal impedance and high capacitance can be suitably used for the potential applications in flexible portable electronic devices. The outstanding performance of the MWCNT@SiO2/PVDF composite nanogenerator can be attributed to the presence of high fraction of polar β phase (81%) in the sample C-1.0, which is formed due to the induction of the surface charges on MWCNT@SiO2. This surface charge 20 ACS Paragon Plus Environment

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induced β phase formation is an amazing self-polarization technique where the PVDF molecules are self-polarized without applying any complex and energy consuming electrical process. Uniform and discrete dispersion of the fillers in the PVDF matrix plays the key role for the formation of high fraction of polar β phase. FESEM micrograph (Fig.3a) of the sample C-1.0 also confirms the homogeneous distribution of fillers in polymer matrix. Another aspect, the reduction of overall resistance of the composites due to the presence of MWCNTs may be responsible for easy hoping of the charges resulting in shorter lifetime (full width at half maxima of a peak in time-voltage spot) and high output voltage peak. Proposed working mechanism for the MWCNT@SiO2/PVDF composite nanogenerator is illustrated through the schematics in Fig.9. Strain induced piezoelectric potential across the electrodes is responsible for electric signal generation through scavenging the ambient mechanical energy. Zero electrical output from the nanogenerator is evident in absence of any external mechanical force onto it which is attributed to the zero net dipole momentum of the composite without any strain. When a vertical compressive force is applied, the total dipole moment of composite changes along the compressive force leading to the generation of a piezoelectric potential across the electrodes. External positive and negative charges are accumulated at the electrodes to screen this piezoelectric potential, consequently a positive voltage signal is generated from the nanogenerator corresponding to the first positive peak of voltage in Fig.7a. The vertical strain and the piezoelectric potential across the electrodes are diminished when the applied vertical compression force is withdrawn. Hence the accumulated charges are transported back in a reverse direction and a negative signal, corresponding to the first negative peak is generated. This process is followed by a weak damped piezoelectric potential across the electrodes, which is generated due to the elastic restoring force in the polymeric material. Then again similar motions and accumulation of the charges are occurred via the electrodes resulting two back to back weak positive and negative peaks as shown in Fig.7a. The durability of the fabricated NG was also investigated to prove the mechanical endurance under periodic pressing and releasing for 288,000 cycles (driving stress of 0.4 MPa) for continuous 8 weeks (~1200 cycles in 300 sec in each span, ~ 25 min/day). After 8 weeks, no notable decrease in average piezoelectric output voltage was observed as shown in Fig.S14 which is the recorded output of PCNG after 8 weeks. This indicates that the nanogenerator is stable enough even after exhaustive applications. The overall performance and durability of the 21 ACS Paragon Plus Environment

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fabricated nanogenerator prototype based on MWCNT@SiO2/PVDF composite indicates that the material is suitable for large scale production of piezoelectric energy harvesting device due to its high efficiency, high mechanical durability, low cost and simple fabrication pathway.

2.3.3. Economic performance analysis Economic performance analysis of a power generation system is much required for design and optimization of complex real power system and integration of the power generator with practical devices. Basic economic model to explore the economic performance of the nanogenerator is developed according to P Mondal et al [51]. The unit cost of electricity (UCOE) delivered by the NG is determined by the following equation [51,52], UCOE =

*+, -*.&0

(1)

1

Where, AC3 is the annualized capital cost, A4&5 is the annualized operation and maintenance

cost, P is the annualized effective electricity delivered by the nanogenerator. AC3 is evaluated

from the actual expenses to fabricate the NG which includes the materials cost and process cost. Annualized operation and maintenance cost for all the components of NG is considered as a fraction of capital cost of NG. Annualized effective electricity delivered (P) can be determined as [52], P= W x 8760 x CUF x (1-L)

(2)

Where, W=generated power in one hour, CUF is capital utilization factor which is related to actual working time of PCNG per day, L is the loss incurred due to transmission. CUF depends on the mechanical durability of the composite film i.e. lifetime of the MWCNT@SiO2/PVDF composite film. In our work no degradation is observed even after 2,88,000 cycles (P ~ 0.4 MPa, f ~ 4 Hz) of operation on a single MWCNT@SiO2/PVDF composite film PCNG. Though further longer duration study is required to check the lifetime of the nanocomposites film, here we can safely consider that a single fabricated PCNG can sustain 10,00,000 cycles of operations as previously other works [12] reported about the high durability of PVDF nanocomposites. S Karan et al [12] previously observed no degradation in performance of PVDF/AlO-rGO based nanogenerator even after 25,00,000 cycles. Considering lifetime of a MWCNT@SiO2/PVDF as 22 ACS Paragon Plus Environment

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69.44 hours (10,00,000 cycles of operation with a applied mechanical pressure having frequency 4 Hz), the calculated value of CUF is 0.008. The evaluated value of annualized effective electricity delivered by a single MWCNT@SiO2/PVDF PCNG is ~0.102 kWh. The annualized capital cost, i.e. fabrication cost of a single MWCNT@SiO2/PVDF PCNG in our lab becomes US$ 0.038 taking into account the standard market price of the materials of industrial grade, while use of highly pure raw material may increase the annualized capital cost upto US$ 0.31. For PCNG, AO&M is almost nil due to zero maintenance expenses of PCNG, though AO&M is considered as 10% of AC3 . Therefore,

AC3 + A4&5 = US$ 0.042

and UCOE= 0.21 US$/kWh. This minimal value of UCOE for lab scale power production of prototype PCNG is even comparable to the tariffs of very large scale solar power production (0.067 US$/kWh), biomass fired power system (0.12 US$/kWh [44]) in competitive market. Large scale production of MWCNT@SiO2/PVDF based PCNG and capital subsidy for green energy generation system will surely further lower this UCOE of the fabricated PCNG system. Hence fairly economically viable MWCNT@SiO2/PVDF based PCNG may set a pave in green energy generation technology through conversion of low frequency mechanical energy. 2.4. Electromagnetic interference shielding The

fabrication

of

state

of

the

artelectromagnetic

interference

(EMI)

shielding

compositematerials with reliable experimental protocols, filler sizes controllability, and high filler dispersity is one of the challenging issues in current technology. The attenuation of electromagnetic radiation by shielding material can be occurred via two major routes, reflection loss and absorption loss [53]. The third mechanism which also majorly contributes towards the attenuation is the internal multiple reflection [53]. In the case of polymer composites, conducting fillers are added to achieve sufficient electrical conductivity to increase the reflection related loss. Above a critical fraction of filler loading, the filler particles can form continuous conductive network within the polymer matrix by which the shielding efficiency is increased. But overloading of fillers may lead to the reduction of EMI shielding efficiency due to the agglomerations of fillers. This is attributed to the lowering of effective interfacial area between 23 ACS Paragon Plus Environment

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the polymer and filler during the agglomeration process. To prevent such agglomeration of the MWCNTs in PVDF at a higher filler concentration, SiO2 matrix was chosen as the host for the MWCNTs in this work. Again, shielding mechanism is dominated by reflection when MWCNTs are only considered as filler due to their low dielectric loss and poor magnetic properties [30]. Recently Biswas et al [30] reported a work on PVDF/MWCNT based EMI shield showing reflection dominating loss. In their work, a total loss of -24 dB was observed, where the reflection loss was -17 dB and absorption loss was -7 dB. This was achieved at 3.0 wt % of MWCNT loading. For real life use, such as stealth technology or LO technology; shielding materials with significantly higher absorption shielding effectiveness (SEA) and lower reflection shielding effectiveness (SET) is important. Inclusion of heterogeneous materials in polymer matrix can shift the shielding mechanism from reflection to absorption dominating phenomenon by introducing high dielectric loss parameter. Hence, the filler MWCNT@SiO2, a conductingnonconducting heterogeneous microstructure has been used in our present work to increase the absorption loss as well as total EMI shielding effectiveness. Flexible MWCNTs@SiO2/PVDF composite films with significant dielectric loss and ac conductivity values (C-1.0, C-3.0 and C5.0) have been chosen for the electromagnetic shielding application. The detailed dielectric properties of the MWCNT@SiO2/PVDF composite films are discussed in the section S2.2.10 of the supporting document. The total electromagnetic interference shielding effectiveness (SET=SER+SEA) of neat PVDF as well as MWCNT@SiO2/PVDF composites was measured in the Xband region (8.2-12.4 GHz) as shown in Fig.10a. More detail about EMI shielding measurement technique is discussed in section S2.2.10 of the supporting document. The neat PVDF film is almost transparent to the EM radiation in X band (SET~ 0). Fig.10a reveals how the value of SET of the composite films increases with the increasing filler loading. The variation of the absorption loss (SEA) and the reflection loss (SER) parameters are shown in the inset of Fig.S15a and Fig.S15b. These figures show that the increment in the reflection loss with the filler loading is almost negligible where a significant enhancement in the absorption loss with the filler loading can be seen from Fig.S15a. The values of SET, SEA and SER for sample C-5.0 at frequency 8.2 GHz are -20 dB,-17.25 dB and -2.75 dB respectively. It can be noted that 5.0 wt% of MWCNT@SiO2 loaded PVDF composite film (C-5) of thickness 400±5 µm can effectively block 99% of the incident electromagnetic radiation where the absorption loss is about 86.25 % and reflection loss is about13.75 %. As a consequence, it can be concluded that, in the case here, 24 ACS Paragon Plus Environment

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the EMI shielding by absorption is the dominating phenomenon over the reflection loss. Thickness and flexibility of the polymer shield films are the other two determinants for potential practical applications in portable, small, bendable modern electronics devices. Polymer composite films having high EMI shielding effectiveness, reduced film thicknesses, low density and good flexibility are the most attractive candidates for present day practical applications. Higher film thickness can simply lead to the high SET value but simultaneously it increases the volume and weight of the shield and lowers the flexibility, thus reducing the acceptance of the shielding materials for practical applications. A realistic parameter (SSE/t), specific EMI shielding effectiveness (SSE) divided by thickness (t) is highly valuable for determining the effectiveness of a material as it includes EMI shielding effectiveness, thickness and density [54]. The calculated value of SSE/t for 5.0 wt% MWCNT@SiO2 loaded PVDF composite film is 410 dBgm-1cm2.In our study excellent SET and SEA values (-20 dB, -17.25 dB) were obtained by using self-standing, flexible 5.0 wt% MWCNT@SiO2/PVDF composite film having thickness of only 400±5 µm and density 1.22 g/cm3. The comparison of performance of different carbon nanomaterial based PVDF as EMI shielding material is tabulated in Table-II, which shows that the prepared sample in this case exhibits much better performance in terms of higher shielding effectiveness, lower thickness and cost effectiveness (lower loading of MWCNT). The outcome is even better than our previous study on graphite submicron platelets [53].Hence, this low cost (low MWCNT content), thin, flexible and easily process able MWCNT@SiO2/PVDF composite films can pave the way for achieving excellent EMI shielding.

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Fig.10 (a)Variation of Total loss (SET) with frequency for the samples C-1.0, C-3.0 and C-5.0 within the frequency range 8-14 GHz (b) Schematic of electromagnetic shielding mechanism for the prepared PVDF composite Table-II. Performance of different carbon nanomaterial based PVDF as EMI shielding material Name of the composite PC/MWNT

Thickness

SET(dB) -21

SEA(dB) SER (dB) -5 -16

PVDF/MWNT

5 mm

-24

-7

-17

PVDF/PC/MWNT

-32

-14

-18

PC/PVDF/PANIMWNT-FE3O4+BT PVDF/GPs

-37

-34

-3

[31]

-16

--

--

[55]

PVDF/activated carbon -fibers

12-14 (0.1-1 -GHz)

--

[56]

PVDF/acid functionalized powder

--

-2.5

--

--

[57]

PVDF/acid functionalized MWCNT

0.5 mm

-21.6

--

--

[58]

MWCNT@SiO2/PVDF

0.4 mm

-20

-17.25

-2.75

This work

2.5mm

Ref [30]

graphite

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The significant enhancement of SET value is possible due to the addition of heterogeneous MWCNT@SiO2 in PVDF matrix. The heterogeneous micro structures in the composite play the key role for the enhancement of microwave absorption. Incident EM wave interact with the microscopic boundaries resulting in enhanced attenuation of the EM waves [31, 59] through internal multiple reflection. Electromagnetic waves are reflected and scattered for multiple times from the boundaries of the well-dispersed microstructured complexes formed within the PVDF matrix due to the addition of the filler. The reflected radiations are internally absorbed within the volume. The presence of the SiO2 reduces the chances of agglomeration of the MWCNTs in the PVDF matrix. This discrete distribution of the filler particles in the polymer leads to enhanced interfacial area between the filler and the polymer matrix; hence the EMI shielding is increased. Fig.10b shows the schematic of the electromagnetic shielding mechanism inside the prepared polymer composite. 3. Conclusion The MWCNT@SiO2/PVDF nanocomposite plays role of a single key to help two major issues in energy and environment field: it may provide opportunities and inspiration for fabrication of energy harvester in industrial scale, which scavenges low frequency biomechanical energy or abundant vibrational energy of ambient environment; on the other hand this self-standing, light weight, flexible nanocomposites may have immense potential for resisting detrimental effect of microwave on flora and fauna. Successful impregnation of MWCNT@SiO2 heterogeneous nanofillers in PVDF matrix enhances the polar beta-phase fraction in the polymer. The nonpolar component (SiO2) in the heterogeneous filler restricts agglomeration of MWCNTs in the polymer matrix up to a certain loading percentage. It has been established that 1.0 wt% loading of MWCNT@SiO2 in the PVDF matrix can give rise to as high as 81% beta-phase fraction which makes the material most suitable for piezoelectric nanogenerator applications. Microscopic (PFM) and macroscopic (impact measurement) study demonstrated the strong piezoelectric behavior and reversible polarization switching of the nanocomposites. An output energy density of 5400 W/m3 was obtained from the fabricated flexible, robust nanogenerator prototype without any external polarization, which is the best value so far for the carbon/PVDF based devices. The efficiency of the nanogenerator is estimated as 15.4% which is much higher in comparison to the 27 ACS Paragon Plus Environment

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other recently reported piezoelectric nanogenerator. Due to high efficiency the device was able to directly power a panel of 55 blue LEDs by scavenging mechanical energy from gentle human fingers imparting. The prototype device is found to cost only US$ 0.038 and UCOE becomes only 0.21 US$/kWh which is comparable with the other reported clean energy sources. In addition a significant increase in dielectric constant (28 times than neat PVDF) of nanocomposite was observed due to interfacial polarization. 5wt% MWCNT@SiO2 loaded PVDF films with thickness 400±5 µm was found to exhibit superb X-band (8.2-12.4 GHz) microwave shielding properties (nearly 99%) mainly through absorption mechanism. Hence the composite may be readily used in different hybrid applications including: EMI shielding-energy harvester cloth for protecting human body from microwave radiation and simultaneously producing electric power from human body parts movement; in computer keyboard for production of power from typing and protecting human body from the radiation of computer keyboard.

4. Experimental section 4.1. Materials Poly(vinylidene fluoride) (PVDF) pallets with molecular weight 275000 g/mol were procured from Aldrich, USA. Multiwalled carbon nanotube (MWCNT) (purity>90%, length ~20 µm) was procured from Sigma Aldrich. Dry N,N-dimethyl formamide (DMF, Merck, India), tetraethyl orthosilicate (TEOS, Merck, Schuchardt) ethanol (Merck, Germany) and aqueous ammonia (strength 30%, Merck, Germany) were also used in this work. All the materials were of analytical reagent (AR) grade and used without any further purification.

4.2. Synthesis of MWCNT@SiO2 MWCNTs@SiO2are synthesized by the modified Stӧber’s method [34]. In this typical procedure, initially a particular amount (25 mg) of MWCNTs was dispersed in distilled water (11 ml). After that, 40 ml of ethanol and 1.35 ml of aqueous ammonia was added to the mixture followed by an 11 hour ultrasonication. Then 250 µl of TEOS was added drop wise to the mixture, which was magnetically stirred for 12 hours at 30℃. After that the resulting mixture was dried (90℃) to obtain the required MWCNT@SiO2. 28 ACS Paragon Plus Environment

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4.3. Synthesis of PVDF/MWCNT@SiO2 composite films The target composite films were prepared by simple cost-effective solvent casting technique from a solution of PVDF in dry DMF containing MWCNT@SiO2. DMF as solvent was chosen for mainly two reasons: (a) it is sufficiently polar and an excellent solvent for PVDF and (b) a good dispersion of MWCNT@SiO2 can be achieved using DMF. Initially the PVDF pallets (1 gm) were immersed in DMF (15 ml) to prepare the stock solution, which was stirred continuously at 60℃until the complete dissolution of PVDF in DMF was achieved. Afterwards, different weight percentage (0.25, 0.5, 0.75,1,3 and 5with respect to PVDF) of MWCNT@SiO2 was added to the solution and ultrasonicated for 14 hours to obtain a well dispersed and homogeneous solution of MWCNT@SiO2 in PVDF. The polymer composite films were prepared by casting the mixture in a properly cleaned and dried petri-dish. Then the solvent was evaporated at 90℃ and kept in a vacuum desiccator for 24 hours for the complete evaporation of the solvent. Finally the dried films are pulled offfrom the substrate and named as C-0.25, C-0.5, C-0.75, C-1.0, C-3.0 and C-5.0 according to the MWCNT@SiO2 loading percentage as mentioned in Table-SIII. Bare PVDF films were also prepared following the same procedure without using the filler. ASSOCIATED CONTENT Supporting Information TEM image, Zeta potential distribution curve, FESEM micrograph, DSC heating curves, surface charge dipole interaction model and mechanism of β phase formation, mechanical propertiey, PFM phase image, output voltage and calculated current of the NGs, rectified output voltage of PCNG, calculation of energy conversion efficiency, durability testing, absorption loss (SEA) and reflection loss (SER), dielectric properties, Video VS1a: Generation of instantaneous output voltage (rectified) by imparting wooden piece. Video VS1b: Generation of piezoelectric voltage (rectified) due to human fingers imparting. Video VS2: Lighting of commercial blue LEDs (55 numbers) Video VS3: Lighting of the commercial LEDs by charging a capacitor of capacitance 2.2 µF. Video VS4: Generation of piezoelectric voltage due to human foot movement and twisting of wrist. 29 ACS Paragon Plus Environment

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Acknowledgements One of the author is thankful to INSPIRE, DST, Govt. of India (IF-140209) for providing partial financial support. Acknowledgement is also to Dr. Santanu Das, Department of Electronics and Tele communication Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah for his kind co-operation and suggestions. Authors are thankful to Dr. P Mondal, Supreme Knowledge Foundation Group of Institutions for his kind guidance.

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Table of Content

We report the prototype fabrication of a flexible polymer composite based piezoelectric energy harvester as the cheaper and cleaner source of alternative energy. The high efficiency (15.4%) of the nanogenerator leads to a unit cost of electricity as low as 0.21 US$/kWh, which is extremely competitive to other energy sources. The composite also shows extremely well (99%) electromagnetic interference shielding property in X-band, with the promise to block detrimental effect of microwave radiation on human body and environment.

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We report the prototype fabrication of a flexible polymer composite based piezoelectric energy harvester as the cheaper and cleaner source of alternative energy. The high efficiency (15.4%) of the nanogenerator lead to a unit electricity cost as low as 0.21 US$/kWH, which is extremely competitive to other energy sources. The material also showed extremely well (99%) electromagnetic interference (EMI) shielding property in Xband (8.2-12.4 GHz), with the promise to block detrimental effect of microwave radiation on environment. These results undoubtedly expand the feasibility of such heterogeneous nanocomposites in energy and environment sectors for high performance flexible, wearable energy harvesting devices as well as microwave shielding applications. 244x187mm (96 x 96 DPI)

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