Advanced Microstructured BaTiO₃‑Embedded PVDF–HFP/PEO Film for Enhanced Triboelectric Interface in Self-Sufficient Energy Generation and Sensing

Abstract

The global reliance on fossil fuels and natural gas has largely dominated the energy production field, but due to finite resource depletion and escalating greenhouse gas emissions, the immediate exploration of sustainable energy alternatives to mitigate climate change and ensure resource security has been a major concern. There has been extensive research into other more renewable methods of energy production, such as wind and hydropower. Of these current energy generation types, there are many areas of untapped potential from the mechanical movements generated ambiently not only in the large scale of power generation but also on a smaller scale. The piezoelectric and triboelectric effects are phenomena where these ambient mechanical movements can generate electrical energy. Developing a hybrid system that leverages both mechanical stress and surface charges presents an ideal opportunity to exploit these untapped energy sources. Producing a hybrid PVDF–HFP/PEO film with perovskite BaTiO₃ (BTO) enables ambient power harvesting from both mechanical movement and surface charge. The optimized cell produced a potential of up to 15 V and a current of 200 nA with a 68 kΩ resistor, a substantial increase from a base system with an average of 2.1 V and 40 nA. These hybrid TENGs offer significant potential for energy harvesting in small-scale applications, such as health monitoring devices and indicators in electric circuits.

1. Introduction

Throughout history, human innovation has been closely tied to energy and the exploitation of available resources. Today, power production is predominantly dominated by nonrenewable resources like petroleum, coal, and natural gas. In the United States, nonrenewable energy sources account for 87.4% of the total energy production, with petroleum and natural gas leading the way, while renewable energy constitutes only about 12.6% as of April 2022. Globally, renewable energy is projected to account for 29% or 340 GW of the total energy production by the year 2022. There is a clear and urgent need for the expansion of renewable resources and ways to improve or supplement the production of energy for these methods. This demand has led to creative and innovative ways of power production to either generate power or act as supplemental power in addition to renewable resources that contain many moving parts, such as wind power. One of the new and upcoming methods of power production that has been receiving attention is the use of nanoscale technology. Nanogenerators have become a hot topic for many researchers as they can be compact and have a wide range of uses. A nanogenerator is a device that can use a variety of different methods, such as mechanical or thermal, to produce energy. Nanogenerators can be used in a variety of ingenious ways that may not have been thought of beforehand and now can make an impact in unconventional ways. There has been much work on triboelectric and piezoelectric nanogenerators as they offer much promise to integrate into a wide variety of systems.

The triboelectric effect is the concept of contact-induced power generation. This effect occurs in daily life. Triboelectricity, also known as the static effect, can be seen in daily occurrences such as rubbing socks on carpet or rubbing a balloon on a person’s hair. This type of generator was initially proposed by Wang and his team in 2012 , and detailed how taking advantage of the triboelectric effect enables novel and creative methods of scavenging lost potential energy from the environment at a relatively low cost. The triboelectric effect that he proposed works through the exchange of surface charges between one or more surfaces at the nanoscale, where physical contact and subsequent separation between materials with different electron affinities lead to charge transfer. Throughout daily life, there is mechanical energy being spent on tasks that normally are disregarded such as freely walking or bending elbows to cross arms or other ways of implementing mechanical movement into the system. − Apart from these, there are even greater sources of potential energy that are being spent and disregarded such as mechanical movements and impacts on mechanical equipment such as cars, heavy machinery, and even roads or walkways. Capitalizing on the triboelectric surface charge effect, triboelectric devices could be constructed and placed in strategic locations where power can be ambiently harvested at relatively low costs. In many renewable energy production methods, parts that connect to motors or gears may be able to host TENGs to act as a supplementary power source to what is already being produced. Since mechanical movement occurs in many different power generation methods, both phenomena have much utility in hybrid systems and other devices such as sensors that are readily seen in daily activities, leading to their adaptability to many different situations.

Current outputs for triboelectric nanogenerators vary per system and have many different energy outputs depending on the method of testing that is occurring. The first triboelectric nanogenerators fabricated by the Wang group back in 2012 were able to produce 3.3 V of ambient power. Current triboelectric nanogenerators are still able to maintain that reading of 3 V but have also been able to produce anywhere from 7.2 V to 328 V. One of the methods in which TENG energy is derived leads back to the fundamentals of the Maxwells displacement current. − Maxwells displacement current is defined as JD = ∂D/∂t = ε·∂E/∂t + ∂ρs/∂t 14, where d is the displacement field, E is the present electric field, Ps is the polarization that is present due to surface charges, and ε is the permittivity of the material medium. For the contact separation method for energy production of TENGs, there is a charge buildup that occurs when they encounter the opposing material due to the distance z. The charge buildup at the electrodes is ±σtr as it remains a function of z, allowing for the conversion of mechanical energy to electrical energy also seen as JD = ∂Dz/∂t = ∂σtr(z,t)/∂t. This fundamental theory and equations are the foundations for the method of energy production for the TENG and with some alterations PENGs as well.

One notable application that is the subject of much scientific interest is employing TENG as wearable nanogenerators; these provide a means to harvest electrical power from daily movements using flexible nanogenerator technology. , Introducing nanogenerators into daily items such as clothing and wearable devices allows for a wider network of technology to connect. Wearable technology is not unknown. In the modern day, many people wear devices such as watches, biosensors, and various phone parts. All of these devices currently operate on batteries and wireless networks. With the implementation of TENGs to wearable devices, the possibility of self-powered devices comes closer to reality and allows for more connections than ever. As the Internet continues to be a part of daily lives for many people, so does the opportunity for wearable devices and integration for larger systems. Current devices operate on batteries and must be changed or charged, often limiting how long a device can operate. This technology must be comfortable enough to not be noticed or hinder daily tasks and should be able to be placed into areas of high friction to be able to ambiently produce power. Wearable technology has a multitude of applications that range from health monitoring to power generation and allows for further connectivity. The method in which connectivity is enhanced provides a method for organizations to place sensors or devices onto uniforms to monitor workers in high-risk jobs. With the increase of interconnected smart devices, TENG-based systems provide an essential small-scale power solution to sustain continuous operation without dependence on conventional batteries.

The piezoelectric phenomenon is closely related to the triboelectric effect due to similar methods of energy production and usage in applications. This effect was discovered by physicist Pierre Curie in August 1880 alongside Jacques Curie and detailed how the symmetry of a crystal can be manipulated to produce power. For a material to be considered piezoelectric, there must be an unsymmetrical crystal or ceramic present. Since there is no full uniformity within an unsymmetrical crystal, there can be an internal polarization that occurs in response to external stress and can produce a voltage. The power production of these systems varies from as much as 25 to 370 V. Another characteristic defining a piezoelectric material is its propensity for forming ionic bonds and featuring distinctive structures, as seen in materials like quartz. Crystals alone are not the only materials that can have the piezoelectric properties, even monomers and polymers such as vinylidene fluoride (VDF), polyvinylidene fluoride (PVDF), and many more have displayed the piezoelectric effect, leading to a diverse selection of materials that can be used in these nanogenerators. Very much like triboelectricity, piezoelectric ,, can produce power through mechanical movements. Alongside having similar methods of power generation, another shared property is that many materials used contain both phenomena. An example of a piezoelectric material is barium titanate oxide (BTO) as it contains an unsymmetrical face-centered cubic structure. Previous research has extensively focused on enhancing energy generation through PVDF-based materials. In a 2021 study, a triboelectric nanogenerator (TENG) was developed using force-spun PVDF and thermoplastic polyurethane nanofiber membranes, achieving remarkable energy harvesting performance. Another study reported the fabrication of an electro-spun PVDF-TrFE/MXene nanofiber mat-based TENG, showcasing improved output performance due to the synergistic properties of the composite materials. Additionally, our recent work incorporated lithium tantalate and multiwalled carbon nanotubes into PVDF to create flexible piezoelectric nanogenerators, significantly enhancing energy harvesting and sensing capabilities. Collectively, these advancements underscore the potential of PVDF-based materials for developing flexible and efficient energy harvesting devices. Building on this foundation, this study goes further by optimizing material composition to achieve significant electrical performance gains. By the incorporation of BTO into a hybrid polymer blend and identification of the optimal filler ratio, this work demonstrates how targeted material engineering can dramatically enhance output performance, representing a tangible advancement toward real-world self-powered systems. BTO in polymer matrices significantly enhances their dielectric properties, making these composites supportive for various electronic applications. BTO is a ferroelectric ceramic known for its high dielectric constant, which when combined with polymers can improve the overall dielectric performance of the composite material. The theoretical models with experimental data suggest effective medium approximations for predicting the dielectric behavior of such composites.

This research introduces a novel composite approach by integrating BTO into a PVDF–HFP/PEO polymer matrix. Unlike previous studies that focused solely on PVDF-based or single-component systems, this work demonstrates a synergistic enhancement of the dielectric and triboelectric properties through material design. The resulting self-powered TENG presents a low-cost, flexible, and scalable solution for clean energy generation from ambient motion, marking a significant step toward the realization of autonomous, wearable energy systems and the broader implementation of nanogenerator-based renewable technologies.

In this paper, we report the findings of integrating BTO into the poly­(vinylidene fluoride-cohexafluoropropylene) (PVDF–HFP) polymer matrix with poly­(ethylene oxide) (PEO). Through various electrical tests, it was seen that 8 wt % was the optimal amount of microstructure filler integrated within the polymer matrix to produce a self-powering TENG. It was confirmed that the produced BTO was face-centered cubic-structured with some variation, and it was able to improve the system by 450% (going from 4 V to 18 maximum). The proposed TENG was then fixed onto several body parts, showing that it could be used as a power generator through replicating ambient movement for low-voltage devices such as sensors, allowing for it to add a wide range of possibilities.

2. Experimental Section

2.1. Materials

Poly­(ethylene oxide) (molecular weight of 200–300 K), poly­(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP), barium nitrate Ba­(NO₃)₂, titanium isopropoxide, sodium hydroxide pellets, and acetic acid were all purchased from Sigma-Aldrich. A Creality 3D printer was used along with its respective filament.

2.2. Synthesis of BTO Microparticles

The production of BTO was carried out in a 1:1 ratio of titanium isopropoxide to barium nitrate in a 3 molar solution and stirred in 15 mL of water for 30 min. After this, a solution of sodium hydroxide was then added dropwise and then stirred for another 30 min. Once mixing has finished, then the solution was placed into a 50 mL Teflon tube and allowed to sit in an oven at 150 °C for 12–24 h. Once this had ended, the solution was taken out and washed 5 times with 1 M acetic acid, DI water, and ethanol. Once the washing was finished, it was dried in an oven for 2–12 h.

2.3. Synthesis of PVDF–HFP Electrode Film

The preparation of the films involves two distinct processes. For PVDF–HFP, a 12 g solution is created, consisting of 20% PVDF–HFP by weight, with the remainder being dimethylformamide (DMF). They are mixed and allowed to sit under stirring conditions overnight. Once the solution is created for the base film, nothing is added, but as tests go on, the amount of BTO varied to 0, 4, 6, 8, and 12 wt % filler in the 12 g solution. Once the BTO is added, it is mixed via sonication for 1 min to ensure the dispersion of particles throughout the vial. Once the solution is ready, thin films can be made by pouring the solution into a spin coater that contains a copper sheet. The spin coater operated at two successive processing speeds: first at 20 × 10 rpm for 15 s, followed by 14 × 10 rpm for 12 s. After the polymer and particle have been dispersed, it is then allowed to dry in an ambient atmosphere in a fume hood, giving thin films on copper sheets.

2.4. Fabrication of Supporting PEO Electrode

For poly­(ethylene oxide) much like the PVDF–HFP, a polymer solution was created composed of a 12 g solution where 17 wt % was the PEO. The solvent for PEO was water in this case and allowed for a semiviscous solution. This solution was then taken to the spin coater and spun at 10 × 10 rpm for 30 s initially and then spun at 10 × 10 rpm for an additional 30 s. Like the PEO, it was allowed to dry at room temperature in the fume hood.

2.5. Assembling of TENG Structure

To fabricate the TENG systems, the circular disks that were collected were cut into 1.5 × 1.5 in. cubes and collected from each of the respective films and labeled properly as seen in Figure . This fabrication method consists of a 3D-printed housing that contains both the positive and negative layers of the TENG attached to a copper tape to act as the current/voltage collectors. The use of Styrofoam padding in each corner was also implemented for separating both polymers and allowing for separation. This method of testing takes advantage of the compression method for power production and allows for the complete separation of the different surface charges to occur (Figure ).

1.

Complete steps of film production starting from the production of hydrothermal partials to film production (photograph courtesy of “R.Y.”, free domain).

2.

Schematic of the proposed 3D-printed TENG housing with labeled internal layers.

2.6. Characterization Techniques

The surface of each film was observed using a FESEM Sigma VP instrument, Carl Zeiss, Jena, Germany. Parameters for voltage ranged between 2 and 5 kV with various magnifications. EDXS (energy-dispersive elemental analysis) was used as an attached detector with the SEM and allowed for detailed elemental dispersion of the film. Atomic force microscopy (AFM, Bruker nanoscale 8) was used for the analysis of films. To determine the open circuit voltage and capacitance, a TDS1001b digital oscilloscope was used. To determine current, a 6517b electrometer (KEITHLEY, a Tektronix company) was used.

3. Results and Discussion

This study specifically investigated the effect of introducing BTO into the negative layer of the TENG. Similar approaches have been applied using different polymers, such as poly­(dimethylsiloxane) (PDMS). The combination of PVDF–HFP, PEO, and BTO had not been previously explored, prompting various tests with different amounts of BTO micronanofiller. It is observed that the incorporation of BTO into PVDF films significantly enhances dielectric properties (Figures S1–S4). BTO’s high dielectric constant synergizes with PVDF’s piezoelectric characteristics, increasing the composite’s overall dielectric constant and improving polarization through better β-phase alignment. In association with the TENG effect, when an external vertical force is applied, the crystal structures of PVDF are disrupted, leading to the reorientation of electric dipoles within the material. This phenomenon, known as the stress-induced poling effect, aligns dipoles in a specific direction, generating a voltage difference between the two electrodes. The upper electrode develops a positive voltage due to its interaction with the positively oriented dipoles. Consequently, electrons move from the upper electrode to the bottom electrode, producing a positive voltage signal in the output. When the applied pressure is released, the piezoelectric potential dissipates, causing electrons to move back from the bottom electrode to the upper electrode, thereby generating a negative voltage signal. This leads to a higher energy storage density and dielectric strength with minimal loss when optimized. Additionally, PVDF’s flexibility ensures mechanical robustness, making these composites suitable for flexible electronics and energy devices. The combination is ideal for advanced applications such as energy harvesting and high-performance capacitors, leveraging the unique properties of BaTiO₃ and PVDF to create efficient and multifunctional dielectric materials (Figures S1 and S2). We argue that BTO modifies the electronic structure of the polymer by introducing high-permittivity regions, leading to enhanced polarization. BTO is a ferroelectric material and contributes to strong dipole moments, increasing charge storage capability. The interfacial regions between BTO and the polymer influence charge trapping and carrier mobility, affecting the dielectric loss and breakdown strength. The interfacial surface modifications alter energy band alignment, reducing charge recombination and optimizing conductivity pathways. The polymer’s intrinsic properties, BTO particle size, and dispersion further determine electron interactions, influencing the dielectric constant and overall performance. These factors potentially tailor the material’s electronic structure. The electrical testing methods included measurements of the open circuit voltage, short circuit current, and longevity. Each electrical test was performed on the basis of an oscilloscope and a fabricated tapping machine. From the gathered electrical test peak-to-peak voltage, capacitance, power was obtained to determine the capabilities of the fabricated TENG. The area that was pressed down in the tapping motion was 1 cm × 1 cm to simulate a finger pressing down on the proposed TENG. As mentioned previously, there are many different equations that can be used to calculate the theoretical , output of TENGs. Of these ways for a system that contains two dielectric materials, one set of eqs – that fits the models represented is the Maxwell–Poisson equation

$$\nabla D=p(r)$$ 1

where p is the charge density on the electrodes, and r is the position in the dielectric material that has the chance to be electrically active in the dielectric material present. Furthermore, from integration, the equation is fully flushed out to be

$$\mathrm{\Phi }(r)=\frac{1}{4\pi r\epsilon a}{\int }^{\mathrm{⧄}}p(r^{\prime })|r-r^1|\mathrm{d}V$$ 2

where each component is accounted for in a simplistic TENG, but for the main method of testing, contact separation can be solved analytically by the theoretical equation

$${\int }_{-(a/2)}^{a/2}{\int }_{-(b/2)}^{b/2}\frac{\mathrm{d}{x}^{\prime }\mathrm{d}{y}^{\prime }}{{(x^{\prime 2}+y^{\prime 2}+{(z-z_i)}^2)}^{3/2}}=\frac{4(z-z_i)}{\mathit{ab}}\arctan \left(\frac{\mathit{ab}}{4(z-z_i)\sqrt{\frac{a^2}{4}+\frac{b^2}{4}+{(z-z_i)}^2}}\right)$$ 3

In this equation, Z is the direction where the movement of the contact separation mechanism works. This equation considers the electric field of the two different dielectric materials but as a function of z, as that is the method in which external mechanical movement is applied. These equations have been used theoretically and offer as points to be used within this work.

3.1. Characterizations

To assess the morphological characteristics of the produced material, SEM imaging was conducted alongside various other techniques to characterize the BTO particles and PVDF–HFP films.

Figure shows the morphology of the produced particles via hydrothermal synthesis; each photo is taken at 20k× (Figure a) and 40k× (Figure b). The size of these particles is approximately 800 nm in length and 200 nm wide. While the uniformity of the particles is not completely consistent, this is a commonplace issue when it comes to hydrothermal synthesis as it can be difficult to maintain full control over the production process. What both images do convey is that the edge structures of these produced particles are well-defined and allow for the continual production of cube–cube-like particles, not just an amalgamation of particles without any defining structure. Figure a,b shows both ×20k (Figure a) and 40k× (Figure b) magnifications of the produced BTO particle, respectively, from the hydrothermal synthesis method. The aforesaid synthesis process produced some larger microparticles as evidenced in SEM images, which is also in agreement with the XRD analysis (vide infra). The size and structure of the synthesized BTO particles can be controlled through pH adjustment and variation of heating times in the hydrothermal reactor. A cross-sectional view of the PVDF–HFP film containing 8 wt % BTO is shown, alongside the 0 wt % film (controlled sample), for comparison (Figure c,e). Both images, captured at 40k× magnification, highlight structural differences between the two films, with their respective cross sections presented in Figure d,f. When comparing the cross section of the 0 wt % PVDF–HFP film to that of the 8 wt % BTO-integrated film, a noticeable reduction in void spaces is observed. The PVDF–HFP matrix in the 0 wt % film exhibits significant gaps (Figure d), whereas the 8 wt % BTO film (Figure f) appears more compact and filled. This enhanced structural density facilitates a more uniform distribution of charge, optimizing its interaction with the mechanical input and improving the overall energy conversion efficiency. The cross-sectional images provide insight into the BTO particle integration, nanoparticle–polymer interfacial interactions, surface compactness, and particle dispersionprimarily exhibiting homogeneous distribution. This uniform dispersion is indicative of enhanced dielectric properties (vide infra). The increased interfacial volume within the TENG cross section is believed to be the key factor contributing to the enhanced performance of the 8 wt % BTO cells. While the peak in the cross-sectional image of Figure f results from the resin-based fracture of the film, it still provides valuable insight into the internal structure. To further investigate the internal distribution of BTO particles within the PVDF–HFP matrix, elemental dispersion analysis was conducted. EDAX mapping (Figure g,h) confirms a uniform distribution of barium (Figure g) and titanium (Figure h) across the film surface. This homogeneous dispersion of BTO filler particles contributes to improved electrical conductivity and enhanced energy generation via the piezoelectric effect. The EDX mapping analysis 0% BTO and elemental composition were not shown here for the sake of brevity.

3.

SEM morphology of BTO (a, b) and films of PVDF–HFP (c) and PVDF–HFP with 8 wt % BTO, which is integrated incorporated as part of the internal structures, (e) with their respective cross-sectional internal view (d, f). EDXS film (8 wt % BTO) showing the surface dispersion of the elements barium (g) and titanium (h).

Figure consists of multiple images that are taken from atomic force microscopy, also known as AFM. AFM is a technique that is used to detail many things such as the height of a sample, the phase of which material is present at a given time, and the amount of voltage that can be allowed at the film at a given spot. Each film that is produced is about 0.005 mm thin and has a height of about 71 nm (Figure b). There are dips and grooves that are depicted according to the amplitude error graph (Figure c,d) as in the amplitude error depicts the variance from the height graph. The phase section in Figure e,f depicts a consistent phase present throughout the film with minimal change.

4.

Structural morphological analysis of the film with atomic force microscopy (AFM) imaging. The images with 8 wt % BTO film are only shown for the sake of brevity. Analysis parameter shows the surface roughness (a, b), amplitude error (c, d), and phase (e, f). The dimensions are within the 200 nm scale.

X-ray diffraction is largely used to determine the crystallinity of a sample and can provide you with unique features that are found specifically within compounds. In Figure , the spectra shown in red are the hydrothermally produced BaTiO₃ particle in comparison to the black line, which is a 1 to 1 match with the BTO catalog reference. It can also be seen that in the blue line in Figure , there were many sharp peaks that can be observed from the PVDF–HFP–BTO complex, showing that there was material present within the matrix. The presence of FCC structured material is confirmed by the peaks shown at 2θ = 23, 33, 38, 46, 57, 66, 71, 75, and 78°, which correspond to the (100), (110), (200), (210), (210), (220), (300), (310), and (311) planes that are present in the corresponding BTO file 000–005–626. Furthermore, the sharp peaks of major points such as 2θ = 33, 38, 46° are good indications that the produced material contains FCC crystals. It is known that typically FCC structured materials contain peaks at (111), (200), and (220) as clear indicators for FCC structured materials. To further support these structural, phase, and interface analyses, a comprehensive analysis of the optimized sample was conducted, reinforcing the conclusions drawn from interface and material characterizations (Figures S1 and S2). The structural properties of BaTiO₃ and BaTiO₃/interfaces are analyzed through band structure and optoelectronic property calculations. Figures S1 and S2 present the band structures of both materials with and without the Hubbard U (DFT+U) correction, highlighting modifications in electronic states. The optical properties, derived from density functional theory (DFT) calculations, reveal frequency-dependent variations in the dielectric function, refractive index, and reflectivity. Figures S3 and S4 illustrate these characteristics, distinguishing between perpendicular (⊥) and parallel (||) components relative to the c-axis. These insights provide a deeper understanding of the material’s electronic and interfacial interaction, which reveals that the optoelectronic property calculations on BaO-terminated BaTiO₃ show that the presence of PVDF–HFP decreases the dielectric constant of the matrix relative to BaTiO₃. This is in agreement with our experiment in which the BaTiO₃ surface is mostly Ti interfaced to the polymer. Advanced experimental methods like LEED and XPS also suggest that TiO₂ interaction-termination is predominant in many cases, particularly in thin-film growth. , For BaTiO₃ (001), the TiO₂ termination is generally more probable due to its lower surface energy and stability under common synthesis and processing conditions.

5.

(a) XRD of reference file 000–005–626 (black line), as-prepared BaTiO₃ (red line), and a polymer composite of 8 wt % BTP inside of PVDF–HFP (blue line); (b) BaTiO₃ as a standard face-centered cubic cell structure is shown with (c) an optimized structure of BaTiO₃ interfaced with a simple molecule H₄C₂O.

3.2. Electrical Outcomes

For TENGs, there are many ways to test the electrical performance of a system. Some of the methods of testing include wave motion, vibration, and many more vibration/motion-based testing methods. Currently, there is no one universal standard for the testing of TENGs and we have seen different methods of contact for energy conversion. To not rely on methods such as finger tapping, which could lead to different inconsistencies, a tapping machine was created where equal amounts of force and height could be consistently placed. The tapping machine utilizes the Hook law (F = −KX) primarily to determine how much force is being applied at a single instance. A spring with a known force can then be applied to the back end of the machine to act as the counterweight and provide a constant force. For the tests taken, a spring with a 1.3 lbs. of force constant was used to provide a constant force and allowed for an equal amount of pressure to be placed in the same location with every hit. Every single tap that was generated delivered about 5.6 N of force in the same location. To automate this testing method further, a motor was attached to the top of an added pulley system to deliver an equal amount of bpm at the operator’s discretion, removing another human factor compared to other systems. Each test for the TENG was carried out at various bpms being 60, 105, and 145 bpm or 1, 1.75, and 2.42 Hz.

The housing where each test was carried out can be seen in Figure and was optimized for the contact separation testing method. The housing was 3D-printed in the TPU filament to allow for as much flexibility to remain as the films in their original form without any restriction. Each test that was taken occurred at each of the previously mentioned speeds, but there was a noticeable decrease in performance when films would be tested at 145 bpm, and this was seen in many of the films showing a decrease in performance. To begin, a baseline was created, and PVDF–HFP was tested with PEO alone via simulated vertical finger tapping. Displayed tests were taken at 105 bpm (1.75 Hz) and seen to obtain a V _oc of ∼3 V with an average of ∼175 nanoampere (nA). A peak-to-peak average of about 1.7 V is seen in Figure . Varying amounts of BTO were integrated into the PVDF–HFP matrix via mixing and sonication. As the amount of BTO was introduced from 0–4 to 6–8 wt %, the interaction between the filler material and particle can best be defined to be a particulate composite and has an effect on the performance of the cell itself. The particulate can affect the integrity of the polymer, making it become more brittle or stiff eluding to the electrical performance that can be seen in Figure b where the past 8 wt % BTO added to the polymer matrix begins to underperform and has less output.

6.

(a) Combined section of all tests together at 105 bpm (1.75 Hz), (b) peak-to-peak average of multiple tests considered, and (c) current for each of the tests taken at 105 bpm (1.75 Hz).

The output of the TENG system increased from ∼3 to ∼15 V with a maximum of 18 V at 8 wt %. From peak to peak at 145 bpm, each cell was seen to have 1.7, 4.8, 4.4, 7.5, and 4.7 V. It can be noted that going from 60 to 105 bpm, there is a significant increase in performance, but at 145 bpm, there is a notable drop in performance that can be seen in each of the cells. This may be due to the stress of the spring that was used to perform the tests. It was seen that 8 wt % BTO in PVDF–HFP yielded the maximum amount of voltage and current from the fabricated devices. After 8 wt % BTO in PVDF–HFP, the number of deformities that have been introduced through the amount of nanofiller may be another factor that begins to decrease the overall performance of the system, sharply going from ∼15 to ∼5 V. To obtain current, a 7000 V electrometer was used along with the constructed inverse trebuchet. Along with voltage tests, the spring used was 1.3 lbs of force and calculated to be about 5.6 N of force delivered upon tapping. Tests ranging from 0–4 to 6–8 and 12 wt % were taken at 60, 105, and 145 bpm (1, 1.75, and 2.42 Hz). Each of the current test’s report that at 105 bpm 185, 360, 287, 545, and 78 nA showing that 8% was the most improved.

Power was calculated from the experimental results obtained by P = Ei (where P = power, E = voltage, and i = current). For power, it was observed that at 105 bpm, 0.31, 1.72, 1.2, 4.1, and 0.37 μW microwatts of power were produced. As with the other tests, there is a clear indication that 8 wt % BTO was the most improved and performed the best in contrast to the other varying amounts of particles introduced. Since 8 wt % BTO demonstrated the highest voltage (Figure a), current, and power generation, capacitance testing was focused exclusively on 8 wt % BTO at a frequency of 105 bpm (1.75 Hz). As shown in Figure b, the 8 wt % BTO composition was evaluated with various capacitors to determine its maximum capacitance. The max capacitance was seen to be at 4.7 μF, maintaining about 0.5 V and then was discharged using an LED lightbulb. This test proves that we can give power to energy storage devices, allowing different applications such as sensors. Many sensors operate in low-voltage/current systems with consumption ranges of 0.5 W and upward depending on application.

7.

(a) Power for each test at varying bpm/Hz. (b) Capacitance of each test with varying capacitors.

Along with other tests, the performance with constant pressure applied via the tapping machine was investigated at 105 bpm (1.75 Hz). The simulated finger tapping showed that the cell was moderately consistent, maintaining at ∼13.2 V over an extended duration as seen in Figure a, which indicated the cell sustainability. In terms of durability, the 8 wt % BTO film demonstrated exceptional resilience during testing, remaining intact and untorn throughout the process. The synthesized system (Figure a) demonstrated continuous operation for 400 s, showcasing its high longevity and stable performance. Throughout this duration, the cell maintained efficiency, generating energy without any noticeable degradation in output or performance. This highlights its capability for sustained long-term energy production. On the breadboard setup, glass diodes were used as rectifiers without the inclusion of capacitors or additional outlets, aside from the oscilloscope for measurement. The design choice ensured that the produced current remained direct current rather than the alternating current typically present in such systems. By eliminating unnecessary components, the setup effectively streamlined energy conversion while maintaining performance stability. The consistent operation without fluctuations or performance alterations further underscores the reliability of the system. This proof of concept indicates that the system is well-suited for extended use, reinforcing its potential applications in energy generation and electronic circuits requiring stable power output. However, the primary limitation of the cell was attributed to the fabricated PEO films. These films were spin-coated onto a thin copper sheet, leaving sufficient space for attaching copper tape to the remaining layer. This configuration allowed the copper tape to serve as an electrode, facilitating the extraction of excess energy. Despite the durability of the BTO film, optimizing the PEO layer and its integration remains essential for enhancing the overall efficiency and reliability of the device. At the intersection between the electrode and copper layer after extended periods of time, there is a tear that forms between each layer and runs down the middle, reducing the amount of energy that can be collected. A rectifier breadboard was created using diodes to allow voltage to flow in only one direction, as seen in Figure c.

8.

Durability test taken approximately 8 min with a breadboard rectifier (c) for the determination of performance as shown in panel (a) with a zoomed-in view (b).

3.3. Applications

Figure a–f shows a representation of various modes in which the fabricated TENG was tested. In Figures a,b and S5, walking was first tested, and the fabricated TENG was attached to the heel of a shoe and walked in at a normal everyday pace. This test showed a maximum voltage output of 16.2 V, with data acquisition performed using a digital storage oscilloscope connected via shielded flexible wires to the TENG output terminals. The subject walked a flat 10 m indoor path at a consistent speed, and voltage readings were logged continuously to capture peak and average output values. Next was jogging; jogging produced a maximum voltage of 8 V while placed at the bottom of the shoe. During jogging tests, the same oscilloscope setup was used. The subject jogged at a moderate pace along the same 10 m course, and data was collected over a 30 s interval to assess performance over repeated foot strikes. The third method of testing was jumping; it was seen that there was a maximum voltage of 17 V per instance jumped. Jumping tests involved vertical jumps from a standing position. Three jumps were executed at 5 s intervals to allow clear signal separation. The oscilloscope recorded individual voltage spikes generated during each impact phase. The next test conducted was wrist movement; wrist movement showed to have a maximum voltage output of 2.68 V when flexed and then unflexed. For this test, the TENG was fixed on a flexible wrist strap worn on the dorsal side of the wrist. The participant performed five slow and deliberate flexion–extension cycles while seated. A high-impedance oscilloscope captured the output to ensure accurate measurement of the relatively low-voltage signals. The next test was the bending of the elbow; this test showed a maximum output of 1.88 V per extension/decompress motion taken. The TENG was secured at the elbow joint using elastic fabric. The subject remained seated and carried out five full-range flexion–extension motions. Voltage signals were monitored continuously, and the peak voltage per motion was extracted from the time-series data. The final test conducted was the extension/compression of the knee. This testing method was seen to have a maximum output of 0.8 V. During this test, the subject was seated with their foot flat on the floor. The TENG was strapped across the front of the knee. Five full extension–compression cycles were performed in a controlled motion, and real-time voltage output was recorded for each cycle to determine peak signal values. These various tests showed that they can ambiently harvest energy through various means, even biomechanical, allowing for more avenues for low voltage and current energy harvesting. These devices demonstrate significant potential for use in advanced systems, including biomedical sensors and structural monitoring applications. In biomedical settings, they can provide precise and reliable data for health monitoring. In larger infrastructure, they can function as highly effective indication systems, detecting and signaling when structural components or machinery parts are moving in close proximity. By enabling the early detection of potential issues, these sensors enhance safety, operational efficiency, and maintenance planning, making them indispensable in both medical and industrial contexts.

9.

Depictions of various modes of movement with fabricated TENG attached: (a) walking at normal pace, (b) jogging at base speed, (c) jumping in place, (d) wrist movement, (e) arm bending at the elbow joint, and (f) bending of the front knee.

Apart from the typical testing method of TENGs such as contact taping in the previous graphs, these films offer an alternative source for ambient energy harvesting with daily motions. Thin films are easily placed in a wide range of locations such as the soles of shoes and within upper/lower body garments. To demonstrate that this was possible, the proposed TENG was attached to various parts of the human body to demonstrate the ambient power harvesting capabilities of the TENG. The parts chosen in this instance were the feet for walking, jogging, jumping, wrist for extension/compression, knee for extension/compression, and elbow for extension/compression. The device was tested as if the tester was under standard conditions to replicate normal ambient power generation.

4. Conclusions

In summary, an advanced integrated device utilizing both piezoelectric and triboelectric phenomena has been successfully fabricated, resulting in an improvement in its electrical output. Initially, the created TENG demonstrated the ability to produce 2–4 V with a current of 175 nA. However, by integrating a micronanofiller BTO into the negative polymer of the TENG, the electrical output significantly increased, reaching up to 18 V with a current of 750 nA. This integration of BTO into the PVDF–HFP polymer led to enhanced electrical output of TENG devices, enabling the utilization of low voltage/current energy harvesting options and opening up new avenues for small-scale power generation. Moreover, the fabricated devices were tested under ambient conditions and placed at various locations on the human body, demonstrating their capability to generate power and serve as sensors in diverse applications, including biomechanical systems.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c01183.

• Figures collectively provide insights into both the fundamental electronic properties of BaTiO₃-based systems and the practical application of triboelectric nanogenerators (TENGs) in urban infrastructure; comparing the electronic band structures and densities of states (DOS) of pristine BaTiO₃ and BaTiO₃/PEO composites, both without and with a Hubbard U correction (U = 8 eV), revealing that the interaction with PEO reduces the band gap in both cases; although DFT+U improves the theoretical band-gap value to 2.16 eV, it remains lower than the experimental benchmark, suggesting limitations in describing the conduction band accurately (Figures S1 and S2); frequency-dependent optical properties, highlighting that the BaTiO₃/PEO system exhibits reduced dielectric function peaks and a lower real dielectric response, indicating weaker optical transitions and diminished dielectric performance compared to pure BaTiO₃ (Figures S3 and S4); and transitions to application, illustrating a conceptual integration of a TENG beneath a sidewalk surface (Figure S5). This system harvests mechanical energy from pedestrian motion to generate and transmit electrical signals in real time. The figure demonstrates how such a setup could activate a traffic light in response to footstep pressure, exemplifying the utility of TENGs in creating self-powered, responsive infrastructure for smart cities. Together, these figures bridge theoretical material research with practical energy harvesting technologies for urban safety and automation (PDF)

The authors declare no competing financial interest.