Next-gen wearable energy harvester using PVDF-doped CuO composite nanofiber-based piezoelectric nanogenerators

Next-gen wearable energy harvester using PVDF-doped CuO composite nanofiber-based piezoelectric nanogenerators | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Next-gen wearable energy harvester using PVDF-doped CuO composite nanofiber-based piezoelectric nanogenerators Bindhu Amrutha, Ponnan Sathiyanathan, Mohammad Shamim Reza, Hongdoo Kim, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7423207/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Flexible piezoelectric nanogenerators (PENGs) based on electrospun (ES) nanofibers (NFs) have gained significant attention for their ability to convert mechanical energy into electrical power. This study focuses on enhancing the piezoelectric performance of PENG devices fabricated from polyvinylidene fluoride (PVDF) ES NFs infused with varying concentrations (0, 1, 3, 5, and 7 wt%) of copper oxide (CuO) nanoparticles. Structural changes and the proportion of β -phase within the fibers were examined by FTIR and XRD measurements. Surface morphology and roughness were observed from FE-SEM and AFM analyses, respectively. Electrical output, including voltage and current was evaluated under mechanical pressure using a customized setup applying 1.0 kgf at 1.0 Hz. Pristine PVDF-based PENG generated a modest output of 1.7 V and 0.53 µA, while the composite fiber with 5 wt% CuO (5PCu) delivered a significantly enhanced output of 13.7 V and 1.6 µA. The 5PCu device was further tested for wearable applications, successfully detecting human activities such as tapping, wrist movements, walking, and jumping, demonstrating its potential in self-powered wearable electronics. PVDF CuO Nanocomposite fiber Piezoelectric nanogenerator Wearable sensors Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction In comparison to other sustainable energy sources (nuclear, wind, solar etc.), energy harvesting from physical activities such as bending, walking, jumping, and twisting, and also human biomechanical processes such as respiration, heartbeat, etc. have created a great deal of attention in transportable wearable electronics and sensors [ 1 , 2 ]. In this context, piezo and triboelectric materials that can convert mechanical energy into electrical energy have gained greater interest among researchers [ 3 , 4 ]. Several methods to develop portable and flexible electronics based on piezoelectric materials having high efficiency for converting mechanical energy to electrical energy have been previously published. Wang et al. [ 5 ] developed the very first piezoelectric nanogenerator (PENG) using arrays of zinc oxide nanowires. After that, significant research findings were published on PENGs utilizing diverse piezoelectric materials including organic and inorganic components. Lead zirconate titanate (PZT) was the initial and most commonly utilized material because of its strong piezoelectric coefficient. PVDF/PZT nanofibers (NFs) fabricated through electrospinning (ES) by doping with varying quantities of PZT have been observed to have a greater β -crystalline phase than neat PVDF NF. A 10% concentration of PZT doping gives the greatest output voltage of 79.7 mV at a resistive load [ 6 , 7 ] PZT is one of the most extensively used highly efficient piezoelectric materials. However, it is harmful to nature because it has a high concentration of lead. As a result, there is an increasing interest in using lead-free ceramic substances as piezoelectric additives to circumvent these limitations. In recent times, researchers are more focused in piezoelectric sensor materials for power harvesting, health assessment and environmental monitoring applications because of their lightweight, cost-effectiveness, adaptability, and biological compatibility properties [ 8 , 9 ]. Polyvinylidene fluoride (PVDF) is one among the frequently utilized material for piezoelectric applications [ 10 – 12 ]. The fundamental aspect affecting PVDF piezoelectricity is its crystalline phase, which comes in five different forms, viz. α, β, γ, δ , and ε [ 13 – 15 ]. Out of these, α -phase exhibits insignificant piezo performance and is electrically inert. In contrast, β -phase is highly electroactive and exhibits the greatest piezoelectricity because of the parallel dipole arrangement of CH 2 and CF 2 groups. Various techniques including physical stretching, annealing under high temperature, poling, structural designing, casting process, filler doping, ES, etc. have been employed to enhance the polar β -phase [ 16 , 17 ]. Contrary to other methods, stretching and high-temperature annealing are challenging procedures that only slightly enhance the piezo properties of PVDF. Polarization in a strong electric field is a successful technique for increasing the β -crystalline phase in PVDF [ 18 ]. However, restriction of the polarization direction results in an absence of structural flexibility, and the preparation processes are extremely difficult and tedious. In order to improve the piezoelectric characteristics of PVDF, further post-processing steps are required after casting, thermal treatment and coating [ 19 , 20 ]. A rapid and effective ES method can produce superfine fibers with sizes ranging from a few nanometers to a few micrometers, which makes it easier to add various dopants into the resultant PVDF fibers. ES technique uses high voltage to generate polymer fibers [ 21 ]. Its setup comprises a syringe pump that fills and keeps the ES solution, and in the front portion of the syringe, a solid collection plate is mounted. The gap between the syringe and the collecting plate is adjustable. The solution’s electrostatic repulsion and its surface pressure combine to generate a conical shape of drop at the syringe tip which is known as a Taylor cone [ 22 ]. As the field strength increases, an electrically charged jet of the solution is expelled from the tip, and the polymer fiber falls onto the collecting plate, after vaporizing the solvent. When it comes to the fabrication of NFs from piezoelectric polymers, ES serves as both deposition and conventional poling methods. According to a recent report, ES fibers can achieve superior piezoelectric characteristics without the use of an additional polarization step [ 23 ]. ES is used to fabricate polymer nanocomposite (NC) fibers based on PVDF [ 24 ]. When compared to other ceramic materials, PVDF-based ES NFs have the following advantages: biocompatibility, versatility, lightweight, and simplicity of production at various thicknesses. Additionally, PVDF ES NFs have already been the subject of numerous studies because of their enhanced piezoelectric potential [ 1 , 6 – 8 , 12 – 14 , 22 – 24 ]. β -phase in PVDF is produced by doping a variety of inorganic fillers, such as metal or metal oxide nanoparticles (NPs) and inorganic polar materials. However, there is a need to improve their electrical properties for effective use in piezoelectric energy harvesting applications. In our earlier study, synthesis of CuO NPs by co-precipitation method and its influence on enhancing the β -phase of ES PVDF NF based triboelectric nanogenerators were reported [ 25 ]. The present research study investigates the morphological and piezoelectric characteristics of CuO doped PVDF NCs and their suitability as wearable sensors for monitoring a variety of human motions. The results are reported in detail in the following sections. 2 Materials and Methods 2.1 Materials Commercial PVDF powder (MW ~ 370,000) was bought from Solvay, Republic of Korea. Acetone along with dimethylformamide (DMF) supplied from Merck, India. Solueta Co. Ltd. (Republic of Korea) supplied Ni-Cu-infused electrodes. Sodium hydroxide (98%) and Copper sulfate pentahydrate (CuSO 4 ·5H 2 O) were purchased from Sigma Aldrich (USA). All of the compounds were employed without any further purification. 2.2 Synthesis of CuO NPs Figure 1 a shows the step-wise synthesis of CuO NPs using the chemical co-precipitation method. Initially, CuSO 4 ·5H 2 O precursor material was dissolved in distilled water and continuously stirred for 2 h. Followed by NaOH (0.1 M) solution added dropwise to the precursor solution till the pH becomes 14 and the precipitate starts to form. After the complete formation of the precipitate, the resultant solution mixture was centrifuged and washed with distilled water. Lastly, the precipitate was calcinated at 500 o C for 5 h [ 26 , 27 ]. 2.3 Fabrication of ES CuO-PVDF NFs Neat PVDF and CuO-PVDF composite NF were fabricated using an ES technique. For preparing the spinning solution 1.2 g of PVDF powder (12 wt%) was dissolved in an acetone/DMF solvent mixture (2:3) and stirred continuously for 3 h, 500 rpm at ambient temperature. Then, four different weight percentages of CuO NPs (1, 3, 5, and 7 wt%) were added to the PVDF solution and stirred continuously for 10 h followed by 3 h ultrasonicated to prepare a homogeneous solution. Lastly, the prepared solution was taken in a 10 ml syringe with a 21 G needle for spinning. A Teflon sheet was used for collecting the NF, and the spinning conditions were 18 kV applied voltage, 10 cm distance from needle to collector, and a flow rate of 1.0 ml/h. After 5 h of spinning the fibers were taken out and characterized. The neat and 1, 3, 5, and 7 wt% CuO- PVDF NFs were named as 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu. The preparation procedure is graphically depicted in Fig. 1 b. The photographic images of the neat and composite fibers are shown in Fig. 2 a. Compared to neat NF, its composite NFs showed a dark color. 2.4 Fabrication and working principle of PENG device Figure 2 b depicts the PENG device configuration, in which Ni-Cu-coated conductive materials (2 × 2 cm 2 ) function as top and bottom electrodes. CuO NP doped ES PVDF composite NF was placed between the two electrodes. The size of the NF layer is larger than that of the electrodes to prevent short-circuiting between the electrodes. Under a dynamic external mechanical force, the sensor creates a pulse-type electric pattern. There is no electrical output in the absence of external mechanical force because of the net dipole being zero. The presence of vertical stress changes the arrangement of dipoles within the composite, resulting in the production of piezoelectric voltage, which is illustrated graphically in Fig. 2 c. The electrodes create positive as well as negative charges to analyze the piezoelectric output, resulting in the development of a positive voltage generated by the nanogenerator matching the initial positive peak. Whenever the vertical pressure is removed, the dipole orientation inside the NC is distorted, and simultaneously, the potential between the electrodes decreases. As a result, the generated charges are carried backward in the opposite direction, generating a negative peak [ 28 , 29 ]. 2.5 Characterization of CuO NPs and PVDF ES composite fiber The crystalline nature and functional group present in the prepared CuO NPs were reported in our previous work [ 25 ]. The morphological study of the NPs was analyzed using FE-SEM and EDS mapping. The presence of crystalline phases and percentage of β crystallinity in the undoped and NPs doped PVDF NFs were analyzed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Morphological study of ES neat PVDF and composite NFs were studied using field emission scanning electron microscopy (FE-SEM) after sputter coating with gold. The surface roughness of ES NFs was analyzed using atomic force microscopy (AFM). Hydrophobic nature of the fibers was confirmed by water contact angle (WCA) analysis studied with a sessile drop technique coupled with KRÜSS ADVANCE software. Output piezoelectric output such as voltage (V) current (µA) was evaluated using a digital Tektronix oscilloscope (DPO4104, Tektronix, USA). The sensitivity of the PENG device toward body movements was studied using a BIOPAC MP-150 system under 100 MΩ input resistance and 0Db gain. The data were saved in Acknowledge 4.2 software. 3 Results and discussion 3.1 Surface morphology and elemental analysis The surface morphology of the CuO NPs was studied using FE-SEM analysis. Figure 3 a shows the surface morphology of the NPs with 500 nm magnification. The NPs have uniform morphology with a nanorod structure. Figure 3 b illustrates the NP’s elemental mapping and composition with the presence of Cu and O elements in 76 and 24%, respectively. This confirms the successful synthesis of CuO NPs. FE-SEM images of 0PCu ES NF are shown in Fig. 3 c. The spinning conditions used in this experiment were perfect because the 0PCu NF exhibited an even surface devoid of beads. Similarly, the CuO-PVDF composite fiber 5PCu surface morphology was displayed in Fig. 3 e. The incorporation of the nanofiller is visible on the composite fiber surface. As the weight percentage of CuO increases from 1 to 7 wt%, the fiber diameter progressively reduces, which was further verified by the ImageJ software. It was performed by calculating the diameters of thirty separate fibers and then measuring their average diameter. The values are shown in Table S1 in Supporting Information (SI). The average fiber diameter of 0PCu is 365 nm. The composite fibers 1PCu to 7PCu start to decrease from 310 nm to 210 nm, respectively. This could be an effect of the polymer solutions’ greater conductivity. Similarly, the standard deviation (SD) value decreased from 105 nm to 48 nm. These lower SD values suggest that the fibers’ size got more uniform. The EDS visuals of 0PCu and 5PCu NFs are displayed in Fig. 3 d and f , respectively. This confirms the successful doping of CuO NP on the surface of PVDF NF [ 30 ]. 3.2. XRD Pattern As seen in Fig. 4 a, the Miller indices of (002), (111), and (202) correspond to the identified peaks of CuO at 35.6°, 38.71°, and 48.67°. This outcome resembles JCPDS no. 45–0937 [ 30 ]. The XRD analysis was performed on both neat and CuO-incorporated PVDF ES NFs (Fig. 4 b). In the case of the neat (0PCu) NF, characteristic diffraction peaks corresponding to both α- (non-polar) and β- (polar) crystalline phases were observed. For the composite fibers, additional diffraction peaks were seen due to the presence of CuO nanofiller, along with the α- and β -phases. A specific diffraction peak at 18.4° corresponds to the (020) plane, which signifies the α -phase. Similarly, the peak at 20.6° is associated with the (200) plane, indicating the formation of the electroactive β -phase. Notably, the intensity of the β -phase peak increased with the inclusion of CuO, suggesting that the nanofiller play a significant role in promoting the electroactive phase within the PVDF matrix. 3.3 FTIR studies The FTIR characterization verified the presence of functional groups within the CuO NPs (Fig. 4 c). The Cu-O vibrational deformation was exhibited by peak at 608 cm -1 . The absorption peak of 1646 cm -1 shows both symmetric and asymmetric stretching of Cu-O. The C-O plane was attributed to the 1060 peak. The peaks nearly matched the values found in the literature. Figure 4 d displays the FTIR spectra of the synthesized fibers. The absorption peaks observed at 840 cm -1 , 1276 cm -1 , and 1400 cm -1 correspond to the polar β -phase of PVDF, whereas the peak at 766 cm -1 is associated with the α-phase. In the case of the 0PCu fiber, the α -phase peak is distinctly visible; however, this peak gradually weakens in the composite fibers as the CuO content increases. To quantify the β -phase content in the PVDF fibers, the Lambert-Beer law (Eq. (1 ) ) was employed, utilizing the absorbance intensities at 766 cm -1 and 840 cm -1 . F( β )=[(A β )/((1.26×A α ) + A β )]×100 …(1) In this analysis, A α and A β denote the absorbance values at 766 cm⁻¹ and 840 cm⁻¹, respectively. The β -phase content in the 0PCu NF was found to be 79%. For the PVDF/CuO composite fibers, the β -phase percentages increased to 81%, 83%, 86%, and 84% for CuO concentrations of 1 wt%, 3 wt%, 5 wt%, and 7 wt%, respectively, as illustrated in Fig. 4 e. As the CuO content rose from 0 to 5 wt%, the proportion of the β -phase also increased from 79–86%, as detailed in Table S2 in SI. This enhancement is attributed to the strong interaction between the negatively charged surface of CuO and the positively charged CH₂ dipoles of the PVDF chains, which promotes the alignment of chains in a trans–trans–trans conformation. 3.4 WCA measurement Materials with hydrophilic surfaces tend to absorb moisture from surrounding air, leading to the formation of thin layer of water molecules on the fiber surface, which can influence their electrical behavior [ 31 ]. To evaluate the hydrophilic or hydrophobic characteristics of undoped PVDF and CuO-doped NFs, WCA measurements were conducted. Fiber samples cut into 1 cm × 1 cm pieces were mounted on glass slides, and 2 mL droplet of DI water was placed on their surfaces. WCA was recorded at 10 seconds intervals, and the results for both neat and composite fibers are illustrated in Fig. 5 a–f. WCA values observed for 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu were 111°, 120°, 122°, 126°, and 130°, respectively. Figure 5 g presents the quantitative comparison of WCA values. The increasing WCA with CuO NPs addition indicates an enhancement in the hydrophobic nature of the PVDF matrix. This improved hydrophobicity makes the fibers suitable for applications in humid conditions. According to the Wenzel model, the elevated WCA in the 5PCu sample can be attributed to its increased surface roughness, which contributes to greater hydrophobic behavior [ 26 , 32 ]. The wettability of the fiber plays a crucial role in practical applications, and the WCA analysis confirms that a hydrophobic surface is more desirable. 3.5 AFM analysis Using 2-D and 3-D AFM images, the surface roughness of neat PVDF and PVDF/CuO composite NFs were analyzed and compared ( Fig. S1 in SI). The average roughness (Ra) and root mean square roughness (Rq) values for both neat PVDF and the PVDF/CuO composites are detailed in Table S3 in SI . The measured Ra values were 170 nm, 510 nm, 824 nm, 1161 nm and 568 nm for 0PCu, 1PCu, 3PCu, 5PCu and 7PCu, respectively. It was observed that increasing the NPs content in the PVDF matrix led to a progressive rise in surface roughness. Among all the samples, 5PCu displayed the highest Ra value. This enhanced roughness may contribute to an increased surface area, potentially enabling more charge accumulation and generation of additional surface charges [ 34 ]. Thus, the AFM results confirmed that NPs incorporation increases the surface roughness, a key factor influencing electrical behavior. 3.6 Electrical measurements Using a custom-built setup, the fabricated piezoelectric devices were tested under repeated mechanical pressure. The electrical signals from the conductive Ni/Cu electrodes were collected through additional wires connected to the electrodes. The output peak-to-peak voltage ( V p-p ) of both neat and composite PVDF-based piezoelectric devices was measured under consistent loading conditions (1.0 kgf force at 1.0 Hz frequency). As the fiber thickness significantly influenced the sensor’s voltage output, the measured voltages were normalized. The sensor made from neat PVDF produced an output of 1.7 V, whereas the composite PENG devices exhibited higher output voltages, as shown in Fig. 6 a–e: 4.6 V for 1PCu, 6.8 V for 3PCu, 13.7 V for 5PCu, and 7.7 V for 7PCu. Among all the samples, 5PCu demonstrated 8 times improvement in piezoelectric voltage output over 0PCu. Figure 6 f-j depicts the short-circuit current ( I sc ) generated by the various PENG sensors. Compared to the 0PCu sensor ( I sc = 0.5 µA), the nanocomposite-based devices exhibited improved current output: 1PCu = 0.7 µA, 3PCu = 1.0 µA, 5PCu = 1.6 µA and 7PCu = 1.2 µA, thereby confirming the enhanced electrical performance upon the incorporation of NPs into the PVDF matrix. The quantitative voltage and current outputs of the tested devices are illustrated in Fig. 6 k. This indicates that the 5PCu device has strong potential for energy harvesting applications. 3.7 Applications of 5PCu-based PENG device 3.7.1 Wearable applications The optimized 5PCu flexible piezoelectric sensor was tested by placing it on various contact points such as the elbow, fingers, chair, and the shoe sole. The device’s output was evaluated using a 100 MΩ load resistance and 0 Db input impedance. As depicted in Fig. 7 a, voltage outputs recorded for different body motions were 4.2 V for tapping, 16.2 V for bending, 16.4 V for twisting, and 12.5 V for rolling (refer to Video S1 in SI). Among these, twisting elicited the highest voltage, indicating the sensor’s strong responsiveness to such deformation. The sensor was fixed near the joint to study elbow movement, and voltage variations were observed during periodic arm stretches. Figure 7 b shows that when the arm’s movement angle increased from 30° to 180°, the sensor’s voltage rose from 6.4 V to 10.8 V. Additionally, an output of 16.2 V was recorded while the subject was sitting as illustrated in Fig. 7 c. For motion detection during walking and running, the sensor was attached to the sole of a shoe, producing voltages of 5.2 V and 9.1 V, respectively, as shown in Fig. 7 d. These results highlight the potential of the developed PENG device for broader biomedical applications, particularly in neurological rehabilitation, such as assisting with hand function recovery and gait training following a stroke or traumatic brain injury. 3.7.2 Energy harvesting application To evaluate the real-time energy-harvesting capabilities of the PENG device, experiments were conducted using a 1 kgf applied force at a frequency of 1 Hz to power light-emitting diodes (LEDs) [ 33 , 34 ]. As shown in Fig. 7 e, the 5PCu-based PENG was able to successfully illuminate 10 LEDs simultaneously. The device was connected to the LEDs through a bridge rectifier, demonstrating its ability to directly power electronic components. The operation of the LEDs can be viewed in Video S2 in SI. 4 Conclusions This study presents the synthesis of CuO NPs, ES of CuO-incorporated PVDF NFs (ranging from 0PCu to 7PCu), fabrication of PENG devices and their evaluation for wearable technology applications. XRD and FTIR spectroscopy analyses revealed that CuO doping promotes the formation of the electroactive β -phase in PVDF. SEM analysis confirmed the uniform distribution of CuO NPs within the PVDF matrix and consistent NF morphology. The inclusion of 5 wt% CuO (5PCu) increased the β -phase content to 86%, compared to 79% in undoped PVDF, though higher concentrations (7PCu) led to a decline due to the agglomeration effect. Performance enhancement due to CuO was evident in the PENG output: 5PCu device generated V p-p = 13.7 V, approximately 8 times higher than undoped PVDF (0PCu sensor, V p-p = 7.7 V) when tested under 1.0 kgf force at 1.0 Hz. Additionally, 5PCu device achieved I sc = 1.6 µA, which is 2 times higher than 0PCu ( I sc = 0.7 µA). One of the major limitations in existing PENG technologies has been low electrical output, which is successfully addressed in this work. The developed sensors were effectively utilized to detect a variety of human motions, including walking, running, tapping, jumping, and elbow flexion. When compared to existing wearable sensors, the PVDF/CuO-based PENG demonstrated superior voltage performance. Owing to these capabilities, the device shows strong promise for use in neurological rehabilitation, particularly in aiding hand mobility and gait training following stroke or severe brain injury, and has wide-ranging potential in biomedical applications. Declarations Competing interests The authors declare no competing interests. Funding The authors (B.A and A.A.P) thank VIT for providing a “VIT SEED GRANT (SG20230088 dt. 23.06.2023)’’ for supporting this research work. Author Contribution B.A.: Conceptualization, methodology and writing - original draft, P.S.: Writing – review and editing, M.S.R.: data curation, resources and visualization, H.K.: resources, validation and supervision, A.PA: resources, supervision, writing – review and editing. All authors reviewed the manuscript. Data Availability Statement No datasets were generated or analysed during the current study. References Choi M, Murillo G, Hwang S, Woong J, Hoon J, Chen C, Lee M (2017) Mechanical and electrical characterization of PVDF-ZnO hybrid structure for application to nanogenerator. Nano Energy 33:462–468. https://doi.org/10.1016/j.nanoen.2017.01.062 Su Y, Chen C, Pan H, Yang Y, Chen G, Zhao X, Li W, Gong Q, Xie G, Zhou Y, Zhang S, Tai H, Jiang Y, Chen J (2021) Muscle fibers inspired high-performance piezoelectric textiles for wearable physiological monitoring. Adv Funct Mater 31:2010962. https://doi.org/10.1002/adfm.202010962 Deng X, Wu Z, Yu X, Wang M, Zang D, Long Y, Guo N, Weng L, Liu Y, Gao J (2025) Preparation and properties of triboelectric nanogenerator based on PVDF-TrFE/PMMA electrospun film. Adv Compos Hybrid Mater 8:19. https://doi.org/10.1007/s42114-024-01103-1 Wu Z, Ding X, Chen X, Chen J, Chang X, Liu Z, Song L, Huang J, Zhu Y (2025) Recent progress of polymer-based piezoelectric nanogenerators. Adv Compos Hybrid Mater 8:225. https://doi.org/10.1007/s42114-025-01225-0 Wang ZL, Song J (2006) Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science 312:242–246. https://doi.org/10.1126/science.112400 Pradhan SK, Kumar A, Sinha AN, Kour P, Pandey R, Kar M, Kumar P (2020) Piezoelectric and mechanical properties of PVDF-PZT composite. Ferroelectrics 558:59–66. https://doi.org/10.1080/00150193.2020.1735889 Chamankar N, Khajavi R, Yousefi AA, Rashidi A, Golestanifard F (2020) A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications. Ceram Int 46:19669–19681. https://doi.org/10.1016/j.ceramint.2020.03.210 Khadka A, Samuel E, Joshi B, Aldalbahi A, Periyasami G, Lee H, Yoon SS (2025) Integrating PVDF-based piezoelectric nanogenerators with highly conductive carbon nanofibers for energy-harvesting applications. Nano Energy 139:110991. https://doi.org/10.1016/j.nanoen.2025.110991 Ziaee S, Montazer M, Bagherzadeh R (2025) Flexible copper/nickel carbon composite fabrics as electrodes for wearable PVDF/BaTiO 3 composite piezoelectric nanogenerators. Nano Energy 357:1188688. https://doi.org/10.1016/j.compstruct.2025.118868 Hari AM, Karumuthil SC, Rajan L (2023) Optimization of PVDF nanocomposite based flexible piezoelectric tactile sensors: A comparative investigation. Sens Actuators Phys 353:114215. https://doi.org/10.1016/j.sna.2023.114215 Kar E, Maity S, Kar A (2024) Agricultural waste rice husk/poly(vinylidene fluoride) composite: a wearable triboelectric energy harvester for real-time smart IoT applications. Adv Compos Hybrid Mater 7:87. https://doi.org/10.1007/s42114-024-00896-5 Bagla A, Kulkarni ND, Kumari P, Saha A (2025) Development and characterization of a sustainable bamboo – polyvinylidene fluoride electro spun piezoelectric nanogenerator device for smart health monitoring. ACS Appl Polym Mater 7:5584–5597. https://doi.org/10.1021/acsapm.5c00408 Ghafari E, Jiang X, Lu N (2018) Surface morphology and beta-phase formation of single polyvinylidene fluoride (PVDF) composite nanofibers. Adv Compos Hybrid Mater 1:332–340. https://doi.org/10.1007/s42114-017-0016-z Verma K, Kumar A, Sharma R (2024) Fabrication of lead–free PVDF/KNNLTS/MWCNT piezoelectric nanogenerator: Role of MWCNT in the piezoelectric performance of nanogenerator for energy-harvesting application. J Electron Mater 53:7574–7592. https://doi.org/10.1007/s11664-024-11463-5 Das T, Tripathy S, Kumar A, Kar M (2025) Flexible piezoelectric nanogenerator as a self-charging piezo-supercapacitor for energy harvesting and storage application. Nano Energy 136:110752. https://doi.org/10.1016/j.nanoen.2025.110752 Bindhu A, Arun AP, Pathak M (2024) Review on polyvinylidene fluoride-based triboelectric nanogenerators for applications in health monitoring and energy harvesting. ACS Appl Electron Mater 6:47–72. https://doi.org/10.1021/acsaelm.3c01297 Nazar AM, Xu H, Huang M (2024) Revolutionizing wind energy: exploring triboelectric and piezoelectric nanogenerators for sustainable power generation. J Zhejiang Univ Sci A 25:889–907. http://doi.org/10.1631/jzus.A2300530 Wang S, Yu Z, Wang L, Wang Y, Yu D, Wu M (2023) A core-shell structured barium titanate nanoparticles for the enhanced piezoelectric performance of wearable nanogenerator. Appl Energy 351:121835. https://doi.org/10.1016/j.apenergy.2023.121835 Han Y, Song L, Du H, Wang G, Zhang T, Ni L, Li Y (2024) Enhancing structural response via macro-micro hierarchy for piezoelectric nanogenerator and self-powered wearable controller. Chem Eng J 481:148729. https://doi.org/10.1016/j.cej.2024.148729 Deng J, Sun Q, Wu Z, Wang Y (2024) Enhanced self-driven flexible piezoelectric nanogenerator sensor based on NaNbO 3 /P(VDF-TrFE) films for security applications. Surf Interfaces 53:105001. https://doi.org/10.1016/j.surfin.2024.105001 Venkatesan HM, Woo I, Yoon JU, Prasad G, Arun AP, Bae JW (2025) Unveiling the latent potential: Ni/CoFe 2 O 4 -loaded electrospun PVDF hybrid composite-based triboelectric nanogenerator for mechanical energy harvesting applications. Adv Compos Hybrid Mater 8:221. https://doi.org/10.1007/s42114-025-01296-z Wang Y, Shen N, Zhu Z, Liu J, Qi X, Liu Z, Zhu Y, Wang X, Long Y, Xiang H (2025) Electrospun 3D nanofibrous materials and their applications in orthopaedics. Adv Compos Hybrid Mater 8:62. https://doi.org/10.1007/s42114-024-01120-0 Zhao Y, Jia M, Wang X, Sun X, Li Z (2024) Enhanced output performance piezoelectric nanogenerators based on highly polarized PVDF/TBAHP tree-like nanofiber membranes for energy harvesting. Polymer 293:126681. https://doi.org/10.1016/j.polymer.2024.126681 Zhu Q, Song X, Chen X, Li D, Tang X, Chen J (2024) A high performance nanocellulose-PVDF based piezoelectric nanogenerator based on the highly active CNF@ZnO via electrospinning technology. Nano Energy 127:109741. https://doi.org/10.1016/j.nanoen.2024.109741 Amrutha B, Prasad G, Sathiyanathan P, Reza MS, Kim H, Pathak M, Prabu AA (2023) Fabrication of CuO-NP-doped PVDF composites based electrospun triboelectric nanogenerators for wearable and biomedical applications. Polymers 15:2442. https://doi.org/10.3390/polym15112442 Rahmah MI, Garallah ET (2022) Preparation of copper oxides/polyvinyl alcohol nanocoatings with antibacterial activity. Chem Data Collect 39:100869. https://doi.org/10.1016/j.cdc.2022.100869 Tahir M, Zeb M, Alamgeer A, Hussain S, Sarker M, Khan DN, Wahab F, Md Ali SH (2022) Cuprous oxide nanoparticles: synthesis, characterization, and their application for enhancing the humidity-sensing properties of poly(dioctylfluorene). Polymers 14:1503. https://doi.org/10.3390/polym14081503 Gunasekhar R, Anand Prabu A (2023) Polyvinylidene fluoride/aromatic hyperbranched polyester 2nd generation based triboelectric sensor for polysomnographic and health monitoring applications. Sens Actuators Phys 355:114311. https://doi.org/10.1016/j.sna.2023.114311 Prasad G, Lin X, Liang J, Yao Y, Tao T, Liang B, Lu SG (2023) Fabrication of intra porous PVDF fibers and their applications for heavy metal removal, oil absorption and piezoelectric sensors. J Materiomics 9:174–182. https://doi.org/10.1016/j.jmat.2022.08.003 Wu R, Ma Z, Gu Z, Yang Y (2010) Preparation and characterization of CuO nanoparticles with different morphology through a simple quick-precipitation method in DMAC–water mixed solvent. J Alloys Compd 504:45–49. https://doi.org/10.1016/j.jallcom.2010.05.062 Bindhu A, Yoon JU, Woo I, Prasad G, Prabu AA, Bae JW (2024) Performance optimization of MoS 2 -doped PVDF-HFP nanofiber triboelectric nanogenerator as sensing technology for smart cities. Appl Mater Today 41:102503. https://doi.org/10.1016/j.apmt.2024.102503 Niranjana VS, Yoon JU, Woo I, Gajula P, Bae JW, Prabu AA (2024) Exploring a new class of PVDF/3-aminopropyltriethoxysilane (core) and 2,2-bis(hydroxymethyl)butyric acid (monomer)-based hyperbranched polyester hybrid fibers by electrospinning technique for enhancing triboelectric performance. Adv Sustain Syst 8:2400311. https://doi.org/10.1002/adsu.202400311 Thakur P, Kool A, Amin N, Bagchi B, Khatun F, Biswas P, Brahma D, Roy S, Banerjee S, Das S (2018) Superior performances of in situ synthesized ZnO/PVDF thin film based self-poled piezoelectric nanogenerator and self-charged photo-power bank with high durability. Nano Energy 44:456–467. https://doi.org/10.1016/j.nanoen.2017.11.065 Gunasekhar R, Bindhu A, Reza MS, Arun AP, Kim KJ, Kim H (2024) Piezoelectric and triboelectric contributions by aromatic hyperbranched polyesters of second-generation/PVDF nanofiber-based nanogenerators for energy harvesting and wearable electronics. ACS Appl Electron Mater 6:5036–5049. https://doi.org/10.1021/acsaelm.4c00556 Additional Declarations No competing interests reported. Supplementary Files ACHMSupportingInformation.docx Fig. S1: (a- f) High-resolution 2-D AFM images of 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu NFs; (a’-f’) 3-D AFM images of corresponding NFs. Table S1: Fiber diameter distribution of neat and composite PVDF NFs. Table S2: β-phase content of neat and composite PVDF NFs. Table S3: Surface morphology (AFM) study of neat and composite PVDF NFs. ACHMVideoS1.mp4 Video S1: Voltage outputs of 5PCu PENG device recorded for different body motions like tapping, bending, twisting and rolling. ACHMVideoS2.mp4 Video S2:Operation of the LEDs using the charge generated from 5PCu PENG device. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7423207","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":510476990,"identity":"29119600-252f-478c-be99-2e6db79ada6d","order_by":0,"name":"Bindhu Amrutha","email":"","orcid":"","institution":"Vellore Institute of Technology","correspondingAuthor":false,"prefix":"","firstName":"Bindhu","middleName":"","lastName":"Amrutha","suffix":""},{"id":510476991,"identity":"46e4a61a-d420-4cb9-a1cb-1845fc467f97","order_by":1,"name":"Ponnan Sathiyanathan","email":"","orcid":"","institution":"Vel Tech Rangarajan Dr.Sagunthala R\u0026D Institute of Science \u0026 Technology","correspondingAuthor":false,"prefix":"","firstName":"Ponnan","middleName":"","lastName":"Sathiyanathan","suffix":""},{"id":510476992,"identity":"72ee4f40-f600-483f-9e63-c28b57c80f59","order_by":2,"name":"Mohammad Shamim Reza","email":"","orcid":"","institution":"Kyung Hee University","correspondingAuthor":false,"prefix":"","firstName":"Mohammad","middleName":"Shamim","lastName":"Reza","suffix":""},{"id":510476993,"identity":"e6953702-d4ff-41aa-affc-9bbb2de37ee0","order_by":3,"name":"Hongdoo Kim","email":"","orcid":"","institution":"Kyung Hee University","correspondingAuthor":false,"prefix":"","firstName":"Hongdoo","middleName":"","lastName":"Kim","suffix":""},{"id":510476994,"identity":"472c2c05-0540-4a6e-a3a6-efc75102b241","order_by":4,"name":"Arun Anand Prabu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYLACHiA2YGA+wJAA5jI2EKuFLYEhIYE0LTwGDFBr8AP+2c3PHrzdcU/eXCLnm8TDHwzy/A3MbQ/waZG4c8zccO6ZYsOdM3K3SQAdZjjjAGO7AV5rbiSYSfO2JTBuuJG72QCohXEDA2ObBD4d8jfSv4G02G+4kfMYpMWeoBaDGzlgWxKBWhgfALUkEtRieCOnTHLumYTknT3PDB8kpEkkzzhMQIvcjfRtEm93JNhuZ09+cPCHjY1tf3v7M7xawAAp7oCKmQmqZyAuukfBKBgFo2AEAwA/J0maVVnmqAAAAABJRU5ErkJggg==","orcid":"","institution":"Vellore Institute of Technology","correspondingAuthor":true,"prefix":"","firstName":"Arun","middleName":"Anand","lastName":"Prabu","suffix":""}],"badges":[],"createdAt":"2025-08-21 07:08:31","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7423207/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7423207/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90837333,"identity":"5195fd51-3a1e-42ec-b886-0edebcfff7ce","added_by":"auto","created_at":"2025-09-08 18:07:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":313111,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea \u003c/strong\u003eVisual representation of CuO NP preparation.\u003cstrong\u003e b \u003c/strong\u003eproduction of CuO-doped ES PVDF NF\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/c57146cf2b1939272de36c73.png"},{"id":90837032,"identity":"8b002fba-e251-4b59-a6f8-9b35c6b0f181","added_by":"auto","created_at":"2025-09-08 17:59:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":480141,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e Images of the fabricated ES NFs. \u003cstrong\u003eb\u003c/strong\u003e graphic illustration of the layer orientation. \u003cstrong\u003e(c)\u003c/strong\u003e Charge generating mechanism in the PENG device\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/cbd2f6e389c7760b0f0ad91c.png"},{"id":90837036,"identity":"81a1dbb6-4b78-4205-9608-d8eea495fc28","added_by":"auto","created_at":"2025-09-08 17:59:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":753900,"visible":true,"origin":"","legend":"\u003cp\u003eFE-SEM image and EDS analysis of \u003cstrong\u003ea-b\u003c/strong\u003e CuO NP. \u003cstrong\u003ec-d\u003c/strong\u003e0PCu NF. \u003cstrong\u003ee-f\u003c/strong\u003e 5PCu NF, respectively\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/f45313537d217677f8634355.png"},{"id":90837334,"identity":"e6ef3479-810b-4bc9-ab37-2447dc491dc9","added_by":"auto","created_at":"2025-09-08 18:07:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":222497,"visible":true,"origin":"","legend":"\u003cp\u003eXRD pattern of \u003cstrong\u003ea\u003c/strong\u003e CuO NPs. \u003cstrong\u003eb\u003c/strong\u003e Neat PVDF and CuO-doped PVDF NF. FTIR analysis of \u003cstrong\u003ec \u003c/strong\u003eCuO NPs. \u003cstrong\u003ed\u003c/strong\u003e Neat and composite NFs. \u003cstrong\u003ee\u003c/strong\u003e Quantitative analysis of \u003cem\u003eβ\u003c/em\u003e-phase content (%)\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/d2205281ac137c758014d54d.png"},{"id":90838370,"identity":"3e301550-11ec-4ed1-954b-515882350c9f","added_by":"auto","created_at":"2025-09-08 18:23:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":323621,"visible":true,"origin":"","legend":"\u003cp\u003eWCA of \u003cstrong\u003ea\u003c/strong\u003e 0PCu. \u003cstrong\u003eb\u003c/strong\u003e 1PCu. \u003cstrong\u003ec\u003c/strong\u003e 3PCu. \u003cstrong\u003ed\u003c/strong\u003e5PCu. \u003cstrong\u003ee\u003c/strong\u003e 7PCu. \u003cstrong\u003eF \u003c/strong\u003eQuantitative analysis of WCA\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/fb40cdb8985783853578fc27.png"},{"id":90837035,"identity":"a41a3020-9324-4ba6-b0ce-f7162de23603","added_by":"auto","created_at":"2025-09-08 17:59:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":238839,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea-e\u003c/strong\u003e Piezoelectric output voltage. \u003cstrong\u003ef-j\u003c/strong\u003e Output current of 0PCu, 1PCu, 3PCu, 5PCu and 7PCu, respectively. \u003cstrong\u003ek\u003c/strong\u003e Quantitative analysis of output voltage and current of the PENG devices.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/58cc623dcc277304135797ad.png"},{"id":90837771,"identity":"dbe34183-fcd6-418a-8851-8b6a9aba8f97","added_by":"auto","created_at":"2025-09-08 18:15:31","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":405285,"visible":true,"origin":"","legend":"\u003cp\u003eReal-time wearable applications of \u003cstrong\u003e(a)\u003c/strong\u003e tapping; \u003cstrong\u003e(b)\u003c/strong\u003e elbow movement; \u003cstrong\u003e(c)\u003c/strong\u003eperiodic sitting; \u003cstrong\u003e(d)\u003c/strong\u003e walking and jumping; \u003cstrong\u003e(e)\u003c/strong\u003e the optical images of 10 LEDs before and after connecting to the 5PCu PENG device.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/85431653877a3b7416fb287a.png"},{"id":91972796,"identity":"3cf097e0-dfe8-48b6-bbf6-e86a15dbfd61","added_by":"auto","created_at":"2025-09-23 09:24:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3511911,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/a6d04250-850c-4c12-93fd-13c46be9b2b0.pdf"},{"id":90837340,"identity":"c9e332bc-0749-4e34-93e5-fe090c48c820","added_by":"auto","created_at":"2025-09-08 18:07:31","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1547006,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eFig. S1\u003c/strong\u003e: \u003cstrong\u003e(a- f) \u003c/strong\u003eHigh-resolution 2-D AFM images of 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu NFs; \u003cstrong\u003e(a’-f’)\u003c/strong\u003e 3-D AFM images of corresponding NFs.\u003cstrong\u003e Table S1:\u003c/strong\u003e Fiber diameter distribution of neat and composite PVDF NFs. \u003cstrong\u003eTable S2:\u003c/strong\u003e β-phase content of neat and composite PVDF NFs. \u003cstrong\u003eTable S3:\u003c/strong\u003e Surface morphology (AFM) study of neat and composite PVDF NFs.\u003c/p\u003e","description":"","filename":"ACHMSupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/768452065f72cb69ca0b59b3.docx"},{"id":90837348,"identity":"e2aeae3c-ba99-4a55-b762-ea2e2b38773b","added_by":"auto","created_at":"2025-09-08 18:07:34","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":6942220,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVideo S1:\u003c/strong\u003e Voltage outputs of 5PCu PENG device recorded for different body motions like tapping, bending, twisting and rolling.\u003c/p\u003e","description":"","filename":"ACHMVideoS1.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/3e84fa756ee65df5788a2a28.mp4"},{"id":90837038,"identity":"2bca8f32-7249-4f17-8ed4-cc288deb7231","added_by":"auto","created_at":"2025-09-08 17:59:31","extension":"mp4","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1860643,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eVideo S2:\u003c/strong\u003eOperation of the LEDs using the charge generated from 5PCu PENG device.\u003c/p\u003e","description":"","filename":"ACHMVideoS2.mp4","url":"https://assets-eu.researchsquare.com/files/rs-7423207/v1/429f9b8af45f47bc50819884.mp4"}],"financialInterests":"No competing interests reported.","formattedTitle":"Next-gen wearable energy harvester using PVDF-doped CuO composite nanofiber-based piezoelectric nanogenerators","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eIn comparison to other sustainable energy sources (nuclear, wind, solar etc.), energy harvesting from physical activities such as bending, walking, jumping, and twisting, and also human biomechanical processes such as respiration, heartbeat, etc. have created a great deal of attention in transportable wearable electronics and sensors [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. In this context, piezo and triboelectric materials that can convert mechanical energy into electrical energy have gained greater interest among researchers [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Several methods to develop portable and flexible electronics based on piezoelectric materials having high efficiency for converting mechanical energy to electrical energy have been previously published. Wang \u003cem\u003eet al.\u003c/em\u003e [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] developed the very first piezoelectric nanogenerator (PENG) using arrays of zinc oxide nanowires. After that, significant research findings were published on PENGs utilizing diverse piezoelectric materials including organic and inorganic components. Lead zirconate titanate (PZT) was the initial and most commonly utilized material because of its strong piezoelectric coefficient. PVDF/PZT nanofibers (NFs) fabricated through electrospinning (ES) by doping with varying quantities of PZT have been observed to have a greater \u003cem\u003eβ\u003c/em\u003e-crystalline phase than neat PVDF NF. A 10% concentration of PZT doping gives the greatest output voltage of 79.7 mV at a resistive load [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] PZT is one of the most extensively used highly efficient piezoelectric materials. However, it is harmful to nature because it has a high concentration of lead. As a result, there is an increasing interest in using lead-free ceramic substances as piezoelectric additives to circumvent these limitations.\u003c/p\u003e\u003cp\u003eIn recent times, researchers are more focused in piezoelectric sensor materials for power harvesting, health assessment and environmental monitoring applications because of their lightweight, cost-effectiveness, adaptability, and biological compatibility properties [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Polyvinylidene fluoride (PVDF) is one among the frequently utilized material for piezoelectric applications [\u003cspan additionalcitationids=\"CR11\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The fundamental aspect affecting PVDF piezoelectricity is its crystalline phase, which comes in five different forms, viz. \u003cem\u003eα, β, γ, δ\u003c/em\u003e, and \u003cem\u003eε\u003c/em\u003e [\u003cspan additionalcitationids=\"CR14\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Out of these, \u003cem\u003eα\u003c/em\u003e-phase exhibits insignificant piezo performance and is electrically inert. In contrast, \u003cem\u003eβ\u003c/em\u003e-phase is highly electroactive and exhibits the greatest piezoelectricity because of the parallel dipole arrangement of CH\u003csub\u003e2\u003c/sub\u003e and CF\u003csub\u003e2\u003c/sub\u003e groups. Various techniques including physical stretching, annealing under high temperature, poling, structural designing, casting process, filler doping, ES, etc. have been employed to enhance the polar \u003cem\u003eβ\u003c/em\u003e-phase [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Contrary to other methods, stretching and high-temperature annealing are challenging procedures that only slightly enhance the piezo properties of PVDF. Polarization in a strong electric field is a successful technique for increasing the \u003cem\u003eβ\u003c/em\u003e-crystalline phase in PVDF [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. However, restriction of the polarization direction results in an absence of structural flexibility, and the preparation processes are extremely difficult and tedious. In order to improve the piezoelectric characteristics of PVDF, further post-processing steps are required after casting, thermal treatment and coating [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eA rapid and effective ES method can produce superfine fibers with sizes ranging from a few nanometers to a few micrometers, which makes it easier to add various dopants into the resultant PVDF fibers. ES technique uses high voltage to generate polymer fibers [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Its setup comprises a syringe pump that fills and keeps the ES solution, and in the front portion of the syringe, a solid collection plate is mounted. The gap between the syringe and the collecting plate is adjustable. The solution\u0026rsquo;s electrostatic repulsion and its surface pressure combine to generate a conical shape of drop at the syringe tip which is known as a Taylor cone [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. As the field strength increases, an electrically charged jet of the solution is expelled from the tip, and the polymer fiber falls onto the collecting plate, after vaporizing the solvent. When it comes to the fabrication of NFs from piezoelectric polymers, ES serves as both deposition and conventional poling methods. According to a recent report, ES fibers can achieve superior piezoelectric characteristics without the use of an additional polarization step [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. ES is used to fabricate polymer nanocomposite (NC) fibers based on PVDF [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. When compared to other ceramic materials, PVDF-based ES NFs have the following advantages: biocompatibility, versatility, lightweight, and simplicity of production at various thicknesses. Additionally, PVDF ES NFs have already been the subject of numerous studies because of their enhanced piezoelectric potential [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR7\" citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. \u003cem\u003eβ\u003c/em\u003e-phase in PVDF is produced by doping a variety of inorganic fillers, such as metal or metal oxide nanoparticles (NPs) and inorganic polar materials. However, there is a need to improve their electrical properties for effective use in piezoelectric energy harvesting applications.\u003c/p\u003e\u003cp\u003eIn our earlier study, synthesis of CuO NPs by co-precipitation method and its influence on enhancing the \u003cem\u003eβ\u003c/em\u003e-phase of ES PVDF NF based triboelectric nanogenerators were reported [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The present research study investigates the morphological and piezoelectric characteristics of CuO doped PVDF NCs and their suitability as wearable sensors for monitoring a variety of human motions. The results are reported in detail in the following sections.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e"},{"header":"2 Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Materials\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eCommercial PVDF powder (MW\u0026thinsp;~\u0026thinsp;370,000) was bought from Solvay, Republic of Korea. Acetone along with dimethylformamide (DMF) supplied from Merck, India. Solueta Co. Ltd. (Republic of Korea) supplied Ni-Cu-infused electrodes. Sodium hydroxide (98%) and Copper sulfate pentahydrate (CuSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO) were purchased from Sigma Aldrich (USA). All of the compounds were employed without any further purification.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Synthesis of CuO NPs\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea shows the step-wise synthesis of CuO NPs using the chemical co-precipitation method. Initially, CuSO\u003csub\u003e4\u003c/sub\u003e\u0026middot;5H\u003csub\u003e2\u003c/sub\u003eO precursor material was dissolved in distilled water and continuously stirred for 2 h. Followed by NaOH (0.1 M) solution added dropwise to the precursor solution till the pH becomes 14 and the precipitate starts to form. After the complete formation of the precipitate, the resultant solution mixture was centrifuged and washed with distilled water. Lastly, the precipitate was calcinated at 500 \u003csup\u003eo\u003c/sup\u003eC for 5 h [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Fabrication of ES CuO-PVDF NFs\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eNeat PVDF and CuO-PVDF composite NF were fabricated using an ES technique. For preparing the spinning solution 1.2 g of PVDF powder (12 wt%) was dissolved in an acetone/DMF solvent mixture (2:3) and stirred continuously for 3 h, 500 rpm at ambient temperature. Then, four different weight percentages of CuO NPs (1, 3, 5, and 7 wt%) were added to the PVDF solution and stirred continuously for 10 h followed by 3 h ultrasonicated to prepare a homogeneous solution. Lastly, the prepared solution was taken in a 10 ml syringe with a 21 G needle for spinning. A Teflon sheet was used for collecting the NF, and the spinning conditions were 18 kV applied voltage, 10 cm distance from needle to collector, and a flow rate of 1.0 ml/h. After 5 h of spinning the fibers were taken out and characterized. The neat and 1, 3, 5, and 7 wt% CuO- PVDF NFs were named as 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu. The preparation procedure is graphically depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. The photographic images of the neat and composite fibers are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. Compared to neat NF, its composite NFs showed a dark color.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 Fabrication and working principle of PENG device\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb depicts the PENG device configuration, in which Ni-Cu-coated conductive materials (2 \u0026times; 2 cm\u003csup\u003e2\u003c/sup\u003e) function as top and bottom electrodes. CuO NP doped ES PVDF composite NF was placed between the two electrodes. The size of the NF layer is larger than that of the electrodes to prevent short-circuiting between the electrodes. Under a dynamic external mechanical force, the sensor creates a pulse-type electric pattern. There is no electrical output in the absence of external mechanical force because of the net dipole being zero. The presence of vertical stress changes the arrangement of dipoles within the composite, resulting in the production of piezoelectric voltage, which is illustrated graphically in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. The electrodes create positive as well as negative charges to analyze the piezoelectric output, resulting in the development of a positive voltage generated by the nanogenerator matching the initial positive peak. Whenever the vertical pressure is removed, the dipole orientation inside the NC is distorted, and simultaneously, the potential between the electrodes decreases. As a result, the generated charges are carried backward in the opposite direction, generating a negative peak [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e].\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e2.5 Characterization of CuO NPs and PVDF ES composite fiber\u003c/h2\u003e\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThe crystalline nature and functional group present in the prepared CuO NPs were reported in our previous work [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The morphological study of the NPs was analyzed using FE-SEM and EDS mapping. The presence of crystalline phases and percentage of \u003cem\u003eβ\u003c/em\u003e crystallinity in the undoped and NPs doped PVDF NFs were analyzed using X-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). Morphological study of ES neat PVDF and composite NFs were studied using field emission scanning electron microscopy (FE-SEM) after sputter coating with gold. The surface roughness of ES NFs was analyzed using atomic force microscopy (AFM). Hydrophobic nature of the fibers was confirmed by water contact angle (WCA) analysis studied with a sessile drop technique coupled with KR\u0026Uuml;SS ADVANCE software. Output piezoelectric output such as voltage (V) current (\u0026micro;A) was evaluated using a digital Tektronix oscilloscope (DPO4104, Tektronix, USA). The sensitivity of the PENG device toward body movements was studied using a BIOPAC MP-150 system under 100 MΩ input resistance and 0Db gain. The data were saved in Acknowledge 4.2 software.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"3 Results and discussion","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Surface morphology and elemental analysis\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe surface morphology of the CuO NPs was studied using FE-SEM analysis. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the surface morphology of the NPs with 500 nm magnification. The NPs have uniform morphology with a nanorod structure. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb illustrates the NP\u0026rsquo;s elemental mapping and composition with the presence of Cu and O elements in 76 and 24%, respectively. This confirms the successful synthesis of CuO NPs. FE-SEM images of 0PCu ES NF are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec. The spinning conditions used in this experiment were perfect because the 0PCu NF exhibited an even surface devoid of beads. Similarly, the CuO-PVDF composite fiber 5PCu surface morphology was displayed in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee. The incorporation of the nanofiller is visible on the composite fiber surface. As the weight percentage of CuO increases from 1 to 7 wt%, the fiber diameter progressively reduces, which was further verified by the ImageJ software. It was performed by calculating the diameters of thirty separate fibers and then measuring their average diameter. The values are shown in \u003cstrong\u003eTable \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/strong\u003e in Supporting Information (SI). The average fiber diameter of 0PCu is 365 nm. The composite fibers 1PCu to 7PCu start to decrease from 310 nm to 210 nm, respectively. This could be an effect of the polymer solutions\u0026rsquo; greater conductivity. Similarly, the standard deviation (SD) value decreased from 105 nm to 48 nm. These lower SD values suggest that the fibers\u0026rsquo; size got more uniform. The EDS visuals of 0PCu and 5PCu NFs are displayed in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed \u003cstrong\u003eand f\u003c/strong\u003e, respectively. This confirms the successful doping of CuO NP on the surface of PVDF NF [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2. XRD Pattern\u003c/h2\u003e\n \u003cp\u003eAs seen in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea, the Miller indices of (002), (111), and (202) correspond to the identified peaks of CuO at 35.6\u0026deg;, 38.71\u0026deg;, and 48.67\u0026deg;. This outcome resembles JCPDS no. 45\u0026ndash;0937 [\u003cspan class=\"CitationRef\"\u003e30\u003c/span\u003e]. The XRD analysis was performed on both neat and CuO-incorporated PVDF ES NFs (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb). In the case of the neat (0PCu) NF, characteristic diffraction peaks corresponding to both \u003cem\u003e\u0026alpha;-\u003c/em\u003e (non-polar) and \u003cem\u003e\u0026beta;-\u003c/em\u003e (polar) crystalline phases were observed. For the composite fibers, additional diffraction peaks were seen due to the presence of CuO nanofiller, along with the \u003cem\u003e\u0026alpha;-\u003c/em\u003e and \u003cem\u003e\u0026beta;\u003c/em\u003e-phases.\u003c/p\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eA specific diffraction peak at 18.4\u0026deg; corresponds to the (020) plane, which signifies the \u003cem\u003e\u0026alpha;\u003c/em\u003e-phase. Similarly, the peak at 20.6\u0026deg; is associated with the (200) plane, indicating the formation of the electroactive \u003cem\u003e\u0026beta;\u003c/em\u003e-phase. Notably, the intensity of the \u003cem\u003e\u0026beta;\u003c/em\u003e-phase peak increased with the inclusion of CuO, suggesting that the nanofiller play a significant role in promoting the electroactive phase within the PVDF matrix.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 FTIR studies\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe FTIR characterization verified the presence of functional groups within the CuO NPs (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec). The Cu-O vibrational deformation was exhibited by peak at 608 cm\u003csup\u003e-1\u003c/sup\u003e. The absorption peak of 1646 cm\u003csup\u003e-1\u003c/sup\u003e shows both symmetric and asymmetric stretching of Cu-O. The C-O plane was attributed to the 1060 peak. The peaks nearly matched the values found in the literature. Figure \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed displays the FTIR spectra of the synthesized fibers. The absorption peaks observed at 840 cm\u003csup\u003e-1\u003c/sup\u003e, 1276 cm\u003csup\u003e-1\u003c/sup\u003e, and 1400 cm\u003csup\u003e-1\u003c/sup\u003e correspond to the polar \u003cem\u003e\u0026beta;\u003c/em\u003e-phase of PVDF, whereas the peak at 766 cm\u003csup\u003e-1\u003c/sup\u003e is associated with the \u0026alpha;-phase. In the case of the 0PCu fiber, the \u003cem\u003e\u0026alpha;\u003c/em\u003e-phase peak is distinctly visible; however, this peak gradually weakens in the composite fibers as the CuO content increases. To quantify the \u003cem\u003e\u0026beta;\u003c/em\u003e-phase content in the PVDF fibers, the Lambert-Beer law (Eq.\u0026nbsp;(1\u003cstrong\u003e)\u003c/strong\u003e) was employed, utilizing the absorbance intensities at 766 cm\u003csup\u003e-1\u003c/sup\u003e and 840 cm\u003csup\u003e-1\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eF(\u003cem\u003e\u0026beta;\u003c/em\u003e)=[(A\u003csub\u003e\u003cem\u003e\u0026beta;\u003c/em\u003e\u003c/sub\u003e)/((1.26\u0026times;A\u003csub\u003e\u003cem\u003e\u0026alpha;\u003c/em\u003e\u003c/sub\u003e)\u0026thinsp;+\u0026thinsp;A\u003csub\u003e\u003cem\u003e\u0026beta;\u003c/em\u003e\u003c/sub\u003e)]\u0026times;100 \u0026hellip;(1)\u003c/p\u003e\n \u003cp\u003eIn this analysis, A\u003csub\u003e\u003cem\u003e\u0026alpha;\u003c/em\u003e\u003c/sub\u003e and A\u003csub\u003e\u003cem\u003e\u0026beta;\u003c/em\u003e\u003c/sub\u003e denote the absorbance values at 766 cm⁻\u0026sup1; and 840 cm⁻\u0026sup1;, respectively. The \u003cem\u003e\u0026beta;\u003c/em\u003e-phase content in the 0PCu NF was found to be 79%. For the PVDF/CuO composite fibers, the \u003cem\u003e\u0026beta;\u003c/em\u003e-phase percentages increased to 81%, 83%, 86%, and 84% for CuO concentrations of 1 wt%, 3 wt%, 5 wt%, and 7 wt%, respectively, as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ee. As the CuO content rose from 0 to 5 wt%, the proportion of the \u003cem\u003e\u0026beta;\u003c/em\u003e-phase also increased from 79\u0026ndash;86%, as detailed in \u003cstrong\u003eTable \u003cspan class=\"InternalRef\"\u003eS2\u003c/span\u003e\u003c/strong\u003e in SI. This enhancement is attributed to the strong interaction between the negatively charged surface of CuO and the positively charged CH₂ dipoles of the PVDF chains, which promotes the alignment of chains in a trans\u0026ndash;trans\u0026ndash;trans conformation.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\n \u003ch2\u003e3.4 WCA measurement\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eMaterials with hydrophilic surfaces tend to absorb moisture from surrounding air, leading to the formation of thin layer of water molecules on the fiber surface, which can influence their electrical behavior [\u003cspan class=\"CitationRef\"\u003e31\u003c/span\u003e]. To evaluate the hydrophilic or hydrophobic characteristics of undoped PVDF and CuO-doped NFs, WCA measurements were conducted. Fiber samples cut into 1 cm \u0026times; 1 cm pieces were mounted on glass slides, and 2 mL droplet of DI water was placed on their surfaces. WCA was recorded at 10 seconds intervals, and the results for both neat and composite fibers are illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea\u0026ndash;f.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eWCA values observed for 0PCu, 1PCu, 3PCu, 5PCu, and 7PCu were 111\u0026deg;, 120\u0026deg;, 122\u0026deg;, 126\u0026deg;, and 130\u0026deg;, respectively. Figure \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eg presents the quantitative comparison of WCA values. The increasing WCA with CuO NPs addition indicates an enhancement in the hydrophobic nature of the PVDF matrix. This improved hydrophobicity makes the fibers suitable for applications in humid conditions. According to the Wenzel model, the elevated WCA in the 5PCu sample can be attributed to its increased surface roughness, which contributes to greater hydrophobic behavior [\u003cspan class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e32\u003c/span\u003e]. The wettability of the fiber plays a crucial role in practical applications, and the WCA analysis confirms that a hydrophobic surface is more desirable.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\n \u003ch2\u003e3.5 AFM analysis\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eUsing 2-D and 3-D AFM images, the surface roughness of neat PVDF and PVDF/CuO composite NFs were analyzed and compared (\u003cstrong\u003eFig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/strong\u003e in SI). The average roughness (Ra) and root mean square roughness (Rq) values for both neat PVDF and the PVDF/CuO composites are detailed in \u003cstrong\u003eTable \u003cspan class=\"InternalRef\"\u003eS3\u003c/span\u003e in SI\u003c/strong\u003e. The measured Ra values were 170 nm, 510 nm, 824 nm, 1161 nm and 568 nm for 0PCu, 1PCu, 3PCu, 5PCu and 7PCu, respectively. It was observed that increasing the NPs content in the PVDF matrix led to a progressive rise in surface roughness. Among all the samples, 5PCu displayed the highest Ra value. This enhanced roughness may contribute to an increased surface area, potentially enabling more charge accumulation and generation of additional surface charges [\u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. Thus, the AFM results confirmed that NPs incorporation increases the surface roughness, a key factor influencing electrical behavior.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\n \u003ch2\u003e3.6 Electrical measurements\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eUsing a custom-built setup, the fabricated piezoelectric devices were tested under repeated mechanical pressure. The electrical signals from the conductive Ni/Cu electrodes were collected through additional wires connected to the electrodes. The output peak-to-peak voltage (\u003cem\u003eV\u003c/em\u003e\u003csub\u003ep-p\u003c/sub\u003e) of both neat and composite PVDF-based piezoelectric devices was measured under consistent loading conditions (1.0 kgf force at 1.0 Hz frequency). As the fiber thickness significantly influenced the sensor\u0026rsquo;s voltage output, the measured voltages were normalized. The sensor made from neat PVDF produced an output of 1.7 V, whereas the composite PENG devices exhibited higher output voltages, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ea\u0026ndash;e: 4.6 V for 1PCu, 6.8 V for 3PCu, 13.7 V for 5PCu, and 7.7 V for 7PCu. Among all the samples, 5PCu demonstrated 8 times improvement in piezoelectric voltage output over 0PCu.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ef-j depicts the short-circuit current (\u003cem\u003eI\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e) generated by the various PENG sensors. Compared to the 0PCu sensor (\u003cem\u003eI\u003c/em\u003esc\u0026thinsp;=\u0026thinsp;0.5 \u0026micro;A), the nanocomposite-based devices exhibited improved current output: 1PCu\u0026thinsp;=\u0026thinsp;0.7 \u0026micro;A, 3PCu\u0026thinsp;=\u0026thinsp;1.0 \u0026micro;A, 5PCu\u0026thinsp;=\u0026thinsp;1.6 \u0026micro;A and 7PCu\u0026thinsp;=\u0026thinsp;1.2 \u0026micro;A, thereby confirming the enhanced electrical performance upon the incorporation of NPs into the PVDF matrix. The quantitative voltage and current outputs of the tested devices are illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003ek. This indicates that the 5PCu device has strong potential for energy harvesting applications.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.7 Applications of 5PCu-based PENG device\u003c/h2\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e3.7.1 Wearable applications\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eThe optimized 5PCu flexible piezoelectric sensor was tested by placing it on various contact points such as the elbow, fingers, chair, and the shoe sole. The device\u0026rsquo;s output was evaluated using a 100 MΩ load resistance and 0 Db input impedance. As depicted in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ea, voltage outputs recorded for different body motions were 4.2 V for tapping, 16.2 V for bending, 16.4 V for twisting, and 12.5 V for rolling (refer to \u003cstrong\u003eVideo S1\u003c/strong\u003e in SI). Among these, twisting elicited the highest voltage, indicating the sensor\u0026rsquo;s strong responsiveness to such deformation. The sensor was fixed near the joint to study elbow movement, and voltage variations were observed during periodic arm stretches. Figure \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eb shows that when the arm\u0026rsquo;s movement angle increased from 30\u0026deg; to 180\u0026deg;, the sensor\u0026rsquo;s voltage rose from 6.4 V to 10.8 V. Additionally, an output of 16.2 V was recorded while the subject was sitting as illustrated in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ec. For motion detection during walking and running, the sensor was attached to the sole of a shoe, producing voltages of 5.2 V and 9.1 V, respectively, as shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ed. These results highlight the potential of the developed PENG device for broader biomedical applications, particularly in neurological rehabilitation, such as assisting with hand function recovery and gait training following a stroke or traumatic brain injury.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n \u003ch2\u003e3.7.2 Energy harvesting application\u003c/h2\u003e\n \u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eTo evaluate the real-time energy-harvesting capabilities of the PENG device, experiments were conducted using a 1 kgf applied force at a frequency of 1 Hz to power light-emitting diodes (LEDs) [\u003cspan class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e34\u003c/span\u003e]. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003ee, the 5PCu-based PENG was able to successfully illuminate 10 LEDs simultaneously. The device was connected to the LEDs through a bridge rectifier, demonstrating its ability to directly power electronic components. The operation of the LEDs can be viewed in \u003cstrong\u003eVideo S2\u003c/strong\u003e in SI.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Conclusions","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eThis study presents the synthesis of CuO NPs, ES of CuO-incorporated PVDF NFs (ranging from 0PCu to 7PCu), fabrication of PENG devices and their evaluation for wearable technology applications. XRD and FTIR spectroscopy analyses revealed that CuO doping promotes the formation of the electroactive \u003cem\u003eβ\u003c/em\u003e-phase in PVDF. SEM analysis confirmed the uniform distribution of CuO NPs within the PVDF matrix and consistent NF morphology. The inclusion of 5 wt% CuO (5PCu) increased the \u003cem\u003eβ\u003c/em\u003e-phase content to 86%, compared to 79% in undoped PVDF, though higher concentrations (7PCu) led to a decline due to the agglomeration effect. Performance enhancement due to CuO was evident in the PENG output: 5PCu device generated \u003cem\u003eV\u003c/em\u003e\u003csub\u003ep-p\u003c/sub\u003e = 13.7 V, approximately 8 times higher than undoped PVDF (0PCu sensor, \u003cem\u003eV\u003c/em\u003e\u003csub\u003ep-p\u003c/sub\u003e = 7.7 V) when tested under 1.0 kgf force at 1.0 Hz. Additionally, 5PCu device achieved \u003cem\u003eI\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e = 1.6 \u0026micro;A, which is 2 times higher than 0PCu (\u003cem\u003eI\u003c/em\u003e\u003csub\u003esc\u003c/sub\u003e = 0.7 \u0026micro;A). One of the major limitations in existing PENG technologies has been low electrical output, which is successfully addressed in this work. The developed sensors were effectively utilized to detect a variety of human motions, including walking, running, tapping, jumping, and elbow flexion. When compared to existing wearable sensors, the PVDF/CuO-based PENG demonstrated superior voltage performance. Owing to these capabilities, the device shows strong promise for use in neurological rehabilitation, particularly in aiding hand mobility and gait training following stroke or severe brain injury, and has wide-ranging potential in biomedical applications.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eCompeting interests\u003c/h2\u003e\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThe authors (B.A and A.A.P) thank VIT for providing a \u0026ldquo;VIT SEED GRANT (SG20230088 dt. 23.06.2023)\u0026rsquo;\u0026rsquo; for supporting this research work.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eB.A.: Conceptualization, methodology and writing - original draft, P.S.: Writing \u0026ndash; review and editing, M.S.R.: data curation, resources and visualization, H.K.: resources, validation and supervision, A.PA: resources, supervision, writing \u0026ndash; review and editing. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eData Availability Statement\u003c/h2\u003e\u003cp\u003eNo datasets were generated or analysed during the current study.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eChoi M, Murillo G, Hwang S, Woong J, Hoon J, Chen C, Lee M (2017) Mechanical and electrical characterization of PVDF-ZnO hybrid structure for application to nanogenerator. Nano Energy 33:462\u0026ndash;468. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2017.01.062\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2017.01.062\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eSu Y, Chen C, Pan H, Yang Y, Chen G, Zhao X, Li W, Gong Q, Xie G, Zhou Y, Zhang S, Tai H, Jiang Y, Chen J (2021) Muscle fibers inspired high-performance piezoelectric textiles for wearable physiological monitoring. Adv Funct Mater 31:2010962. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/adfm.202010962\u003c/span\u003e\u003cspan address=\"10.1002/adfm.202010962\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDeng X, Wu Z, Yu X, Wang M, Zang D, Long Y, Guo N, Weng L, Liu Y, Gao J (2025) Preparation and properties of triboelectric nanogenerator based on PVDF-TrFE/PMMA electrospun film. Adv Compos Hybrid Mater 8:19. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-024-01103-1\u003c/span\u003e\u003cspan address=\"10.1007/s42114-024-01103-1\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWu Z, Ding X, Chen X, Chen J, Chang X, Liu Z, Song L, Huang J, Zhu Y (2025) Recent progress of polymer-based piezoelectric nanogenerators. Adv Compos Hybrid Mater 8:225. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-025-01225-0\u003c/span\u003e\u003cspan address=\"10.1007/s42114-025-01225-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang ZL, Song J (2006) Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science 312:242\u0026ndash;246. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1126/science.112400\u003c/span\u003e\u003cspan address=\"10.1126/science.112400\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePradhan SK, Kumar A, Sinha AN, Kour P, Pandey R, Kar M, Kumar P (2020) Piezoelectric and mechanical properties of PVDF-PZT composite. Ferroelectrics 558:59\u0026ndash;66. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/00150193.2020.1735889\u003c/span\u003e\u003cspan address=\"10.1080/00150193.2020.1735889\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eChamankar N, Khajavi R, Yousefi AA, Rashidi A, Golestanifard F (2020) A flexible piezoelectric pressure sensor based on PVDF nanocomposite fibers doped with PZT particles for energy harvesting applications. Ceram Int 46:19669\u0026ndash;19681. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ceramint.2020.03.210\u003c/span\u003e\u003cspan address=\"10.1016/j.ceramint.2020.03.210\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKhadka A, Samuel E, Joshi B, Aldalbahi A, Periyasami G, Lee H, Yoon SS (2025) Integrating PVDF-based piezoelectric nanogenerators with highly conductive carbon nanofibers for energy-harvesting applications. Nano Energy 139:110991. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2025.110991\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2025.110991\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZiaee S, Montazer M, Bagherzadeh R (2025) Flexible copper/nickel carbon composite fabrics as electrodes for wearable PVDF/BaTiO\u003csub\u003e3\u003c/sub\u003e composite piezoelectric nanogenerators. Nano Energy 357:1188688. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.compstruct.2025.118868\u003c/span\u003e\u003cspan address=\"10.1016/j.compstruct.2025.118868\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHari AM, Karumuthil SC, Rajan L (2023) Optimization of PVDF nanocomposite based flexible piezoelectric tactile sensors: A comparative investigation. Sens Actuators Phys 353:114215. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.sna.2023.114215\u003c/span\u003e\u003cspan address=\"10.1016/j.sna.2023.114215\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eKar E, Maity S, Kar A (2024) Agricultural waste rice husk/poly(vinylidene fluoride) composite: a wearable triboelectric energy harvester for real-time smart IoT applications. Adv Compos Hybrid Mater 7:87. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-024-00896-5\u003c/span\u003e\u003cspan address=\"10.1007/s42114-024-00896-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBagla A, Kulkarni ND, Kumari P, Saha A (2025) Development and characterization of a sustainable bamboo\u0026thinsp;\u0026ndash;\u0026thinsp;polyvinylidene fluoride electro spun piezoelectric nanogenerator device for smart health monitoring. ACS Appl Polym Mater 7:5584\u0026ndash;5597. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsapm.5c00408\u003c/span\u003e\u003cspan address=\"10.1021/acsapm.5c00408\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGhafari E, Jiang X, Lu N (2018) Surface morphology and beta-phase formation of single polyvinylidene fluoride (PVDF) composite nanofibers. Adv Compos Hybrid Mater 1:332\u0026ndash;340. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-017-0016-z\u003c/span\u003e\u003cspan address=\"10.1007/s42114-017-0016-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVerma K, Kumar A, Sharma R (2024) Fabrication of lead\u0026ndash;free PVDF/KNNLTS/MWCNT piezoelectric nanogenerator: Role of MWCNT in the piezoelectric performance of nanogenerator for energy-harvesting application. J Electron Mater 53:7574\u0026ndash;7592. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11664-024-11463-5\u003c/span\u003e\u003cspan address=\"10.1007/s11664-024-11463-5\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDas T, Tripathy S, Kumar A, Kar M (2025) Flexible piezoelectric nanogenerator as a self-charging piezo-supercapacitor for energy harvesting and storage application. Nano Energy 136:110752. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2025.110752\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2025.110752\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBindhu A, Arun AP, Pathak M (2024) Review on polyvinylidene fluoride-based triboelectric nanogenerators for applications in health monitoring and energy harvesting. ACS Appl Electron Mater 6:47\u0026ndash;72. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsaelm.3c01297\u003c/span\u003e\u003cspan address=\"10.1021/acsaelm.3c01297\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNazar AM, Xu H, Huang M (2024) Revolutionizing wind energy: exploring triboelectric and piezoelectric nanogenerators for sustainable power generation. J Zhejiang Univ Sci A 25:889\u0026ndash;907. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://doi.org/10.1631/jzus.A2300530\u003c/span\u003e\u003cspan address=\"10.1631/jzus.A2300530\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang S, Yu Z, Wang L, Wang Y, Yu D, Wu M (2023) A core-shell structured barium titanate nanoparticles for the enhanced piezoelectric performance of wearable nanogenerator. Appl Energy 351:121835. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.apenergy.2023.121835\u003c/span\u003e\u003cspan address=\"10.1016/j.apenergy.2023.121835\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eHan Y, Song L, Du H, Wang G, Zhang T, Ni L, Li Y (2024) Enhancing structural response via macro-micro hierarchy for piezoelectric nanogenerator and self-powered wearable controller. Chem Eng J 481:148729. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2024.148729\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2024.148729\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eDeng J, Sun Q, Wu Z, Wang Y (2024) Enhanced self-driven flexible piezoelectric nanogenerator sensor based on NaNbO\u003csub\u003e3\u003c/sub\u003e/P(VDF-TrFE) films for security applications. Surf Interfaces 53:105001. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.surfin.2024.105001\u003c/span\u003e\u003cspan address=\"10.1016/j.surfin.2024.105001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eVenkatesan HM, Woo I, Yoon JU, Prasad G, Arun AP, Bae JW (2025) Unveiling the latent potential: Ni/CoFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e-loaded electrospun PVDF hybrid composite-based triboelectric nanogenerator for mechanical energy harvesting applications. Adv Compos Hybrid Mater 8:221. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-025-01296-z\u003c/span\u003e\u003cspan address=\"10.1007/s42114-025-01296-z\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWang Y, Shen N, Zhu Z, Liu J, Qi X, Liu Z, Zhu Y, Wang X, Long Y, Xiang H (2025) Electrospun 3D nanofibrous materials and their applications in orthopaedics. Adv Compos Hybrid Mater 8:62. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s42114-024-01120-0\u003c/span\u003e\u003cspan address=\"10.1007/s42114-024-01120-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhao Y, Jia M, Wang X, Sun X, Li Z (2024) Enhanced output performance piezoelectric nanogenerators based on highly polarized PVDF/TBAHP tree-like nanofiber membranes for energy harvesting. Polymer 293:126681. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.polymer.2024.126681\u003c/span\u003e\u003cspan address=\"10.1016/j.polymer.2024.126681\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eZhu Q, Song X, Chen X, Li D, Tang X, Chen J (2024) A high performance nanocellulose-PVDF based piezoelectric nanogenerator based on the highly active CNF@ZnO via electrospinning technology. Nano Energy 127:109741. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2024.109741\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2024.109741\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eAmrutha B, Prasad G, Sathiyanathan P, Reza MS, Kim H, Pathak M, Prabu AA (2023) Fabrication of CuO-NP-doped PVDF composites based electrospun triboelectric nanogenerators for wearable and biomedical applications. Polymers 15:2442. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/polym15112442\u003c/span\u003e\u003cspan address=\"10.3390/polym15112442\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eRahmah MI, Garallah ET (2022) Preparation of copper oxides/polyvinyl alcohol nanocoatings with antibacterial activity. Chem Data Collect 39:100869. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cdc.2022.100869\u003c/span\u003e\u003cspan address=\"10.1016/j.cdc.2022.100869\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTahir M, Zeb M, Alamgeer A, Hussain S, Sarker M, Khan DN, Wahab F, Md Ali SH (2022) Cuprous oxide nanoparticles: synthesis, characterization, and their application for enhancing the humidity-sensing properties of poly(dioctylfluorene). Polymers 14:1503. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/polym14081503\u003c/span\u003e\u003cspan address=\"10.3390/polym14081503\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGunasekhar R, Anand Prabu A (2023) Polyvinylidene fluoride/aromatic hyperbranched polyester 2nd generation based triboelectric sensor for polysomnographic and health monitoring applications. Sens Actuators Phys 355:114311. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.sna.2023.114311\u003c/span\u003e\u003cspan address=\"10.1016/j.sna.2023.114311\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003ePrasad G, Lin X, Liang J, Yao Y, Tao T, Liang B, Lu SG (2023) Fabrication of intra porous PVDF fibers and their applications for heavy metal removal, oil absorption and piezoelectric sensors. J Materiomics 9:174\u0026ndash;182. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmat.2022.08.003\u003c/span\u003e\u003cspan address=\"10.1016/j.jmat.2022.08.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eWu R, Ma Z, Gu Z, Yang Y (2010) Preparation and characterization of CuO nanoparticles with different morphology through a simple quick-precipitation method in DMAC\u0026ndash;water mixed solvent. J Alloys Compd 504:45\u0026ndash;49. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jallcom.2010.05.062\u003c/span\u003e\u003cspan address=\"10.1016/j.jallcom.2010.05.062\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eBindhu A, Yoon JU, Woo I, Prasad G, Prabu AA, Bae JW (2024) Performance optimization of MoS\u003csub\u003e2\u003c/sub\u003e-doped PVDF-HFP nanofiber triboelectric nanogenerator as sensing technology for smart cities. Appl Mater Today 41:102503. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.apmt.2024.102503\u003c/span\u003e\u003cspan address=\"10.1016/j.apmt.2024.102503\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eNiranjana VS, Yoon JU, Woo I, Gajula P, Bae JW, Prabu AA (2024) Exploring a new class of PVDF/3-aminopropyltriethoxysilane (core) and 2,2-bis(hydroxymethyl)butyric acid (monomer)-based hyperbranched polyester hybrid fibers by electrospinning technique for enhancing triboelectric performance. Adv Sustain Syst 8:2400311. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/adsu.202400311\u003c/span\u003e\u003cspan address=\"10.1002/adsu.202400311\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eThakur P, Kool A, Amin N, Bagchi B, Khatun F, Biswas P, Brahma D, Roy S, Banerjee S, Das S (2018) Superior performances of in situ synthesized ZnO/PVDF thin film based self-poled piezoelectric nanogenerator and self-charged photo-power bank with high durability. Nano Energy 44:456\u0026ndash;467. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nanoen.2017.11.065\u003c/span\u003e\u003cspan address=\"10.1016/j.nanoen.2017.11.065\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eGunasekhar R, Bindhu A, Reza MS, Arun AP, Kim KJ, Kim H (2024) Piezoelectric and triboelectric contributions by aromatic hyperbranched polyesters of second-generation/PVDF nanofiber-based nanogenerators for energy harvesting and wearable electronics. ACS Appl Electron Mater 6:5036\u0026ndash;5049. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1021/acsaelm.4c00556\u003c/span\u003e\u003cspan address=\"10.1021/acsaelm.4c00556\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"PVDF, CuO, Nanocomposite fiber, Piezoelectric nanogenerator, Wearable sensors","lastPublishedDoi":"10.21203/rs.3.rs-7423207/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7423207/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eFlexible piezoelectric nanogenerators (PENGs) based on electrospun (ES) nanofibers (NFs) have gained significant attention for their ability to convert mechanical energy into electrical power. This study focuses on enhancing the piezoelectric performance of PENG devices fabricated from polyvinylidene fluoride (PVDF) ES NFs infused with varying concentrations (0, 1, 3, 5, and 7 wt%) of copper oxide (CuO) nanoparticles. Structural changes and the proportion of \u003cem\u003eβ\u003c/em\u003e-phase within the fibers were examined by FTIR and XRD measurements. Surface morphology and roughness were observed from FE-SEM and AFM analyses, respectively. Electrical output, including voltage and current was evaluated under mechanical pressure using a customized setup applying 1.0 kgf at 1.0 Hz. Pristine PVDF-based PENG generated a modest output of 1.7 V and 0.53 \u0026micro;A, while the composite fiber with 5 wt% CuO (5PCu) delivered a significantly enhanced output of 13.7 V and 1.6 \u0026micro;A. The 5PCu device was further tested for wearable applications, successfully detecting human activities such as tapping, wrist movements, walking, and jumping, demonstrating its potential in self-powered wearable electronics.\u003c/p\u003e","manuscriptTitle":"Next-gen wearable energy harvester using PVDF-doped CuO composite nanofiber-based piezoelectric nanogenerators","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-08 17:59:26","doi":"10.21203/rs.3.rs-7423207/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"58920c65-f580-4da5-bfd8-dcd59e571d9d","owner":[],"postedDate":"September 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-09-23T09:24:06+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-08 17:59:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7423207","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7423207","identity":"rs-7423207","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}