Wearable Piezoelectric Nanogenerators Based on Core-Shell Ga-PZT@GaOx Nanorod-Enabled P(VDF-TrFE) Composites

Electrospun Silver-Modified PZT/PVDF Composites for High-Performance Piezoelectric Energy Harvester

Piezoelectric materials based on polyvinylidene fluoride (PVDF) are widely regarded as ideal candidates for the fabrication of piezoelectric energy harvesters (PEHs). However, the relatively low power output of PVDF limits its widespread application and poses a significant challenge to the advancement of PEHs. To address this issue, we have designed a novel PEH using silver-modified lead zirconate titanate/PVDF (pPZT@Ag/PVDF), which achieves a remarkable balance between high output performance and long-term stability. The pPZT@60Ag/PVDF PEH generates a peak voltage of 14.33 V, which is about 2.6 times that of the pure lead zirconate titanate/PVDF (pPZT/PVDF) PEH. This enhancement is attributed to the confined structure within the PVDF fibers, as well as the enhancement in dipole orientation alignment and the local electric field induced by silver nanoparticle modification. Furthermore, the pPZT@60Ag/PVDF PEH demonstrates a peak power density of 0.58 μW/cm2, with negligible degradation in output voltage after 6000 bending cycles, and efficiently harvests mechanical energy from human movement. This study presents an effective method for fabricating high-performance PEHs, which is expected to advance the development of next-generation energy harvesting devices.

Boosting Energy Harvesting Performance in Piezoelectric Composites with Aligned Porosity via a Dual Structure Design Strategy

Porous piezoelectric materials have attracted much interest in the fields of sensing and energy harvesting owing to their low dielectric constant, high piezoelectric voltage coefficient, and energy harvesting figure of merit. However, the introduction of porosity can decrease the piezoelectric coefficient, which restricts the enhancement of output current and power density. Herein, to overcome these challenges, an array-structured piezoelectric composite energy harvester with aligned porosity was constructed via a dual structure design strategy to enhance the output current and power density. Silver metal particles were introduced into a porous barium calcium zirconate titanate (BCZT) ceramic matrix as a secondary phase to regulate the dielectric, ferroelectric, and piezoelectric properties. The optimal addition of silver particles can reduce the size of ferroelectric domains, which leads to an enhanced piezoelectric coefficient and energy harvesting figure of merit. Combined with the design of the array structure, the maximum output voltage and current of the piezoelectric composite energy harvester can reach 76 V and 340 μA, respectively, with a peak power density of 0.97 mW/cm2. Furthermore, the array-structured piezoelectric energy harvester can light 40 blue LED bulbs and power commercial low-power electronic devices. This work provides a strategy to boost the output current and power density of porous piezoelectric materials via a micro-macro structure design strategy for energy harvesting applications.

Recent Progress in the Auxiliary Phase Enhanced Flexible Piezocomposites

Piezocomposites with both flexibility and electromechanical conversion characteristics have been widely applied in various fields, including sensors, energy harvesting, catalysis, and biomedical treatment. In the composition of piezocomposites or their preparation process, a category of materials is commonly employed that do not possess piezoelectric properties themselves but play a crucial role in performance enhancement. In this review, the concept of auxiliary phase is first proposed to define these materials, aiming to provide a new perspective for designing high‐performance piezocomposites. Three different categories of modulation forms of auxiliary phase in piezocomposites are systematically summarized, including the modification of piezo‐matrix, the modification of piezo‐fillers, and the construction of special structures. Each category emphasizes the role of the auxiliary phase and systematically discusses the latest advancements and the physical mechanisms of the auxiliary phase enhanced flexible piezocomposites. Finally, a summary and future outlook of piezocomposites based on the auxiliary phase are provided.

Recent Progress on Flexible Self-Powered Tactile Sensing Platforms for Health Monitoring and Robotics

Over the past decades, tactile sensing technology has made significant advances in the fields of health monitoring and robotics. Compared to conventional sensors, self-powered tactile sensors do not require an external power source to drive, which makes the entire system more flexible and lightweight. Therefore, they are excellent candidates for mimicking the tactile perception functions for wearable health monitoring and ideal electronic skin (e-skin) for intelligent robots. Herein, the working principles, materials, and device fabrication strategies of various self-powered tactile sensing platforms are introduced first. Then their applications in health monitoring and robotics are presented. Finally, the future prospects of self-powered tactile sensing systems are discussed.

Giant Piezoelectric Output and Stability Enhancement in Piezopolymer Composites with Liquid Metal Nanofillers

Integrating nanomaterials into the polymer matrix is an effective strategy to optimize the performance of polymer-based piezoelectric devices. Nevertheless, the trade-off between the output enhancement and stability maintenance of piezoelectric composites usually leads to an unsatisfied overall performance for the high-strength operation of devices. Here, by setting liquid metal (LM) nanodroplets as the nanofillers in a poly(vinylidene difluoride) (PVDF) matrix, the as-formed liquid-solid/conductive-dielectric interfaces significantly promote the piezoelectric output and the reliability of this piezoelectric composite. A giant performance improvement featured is obtained with, nearly 1000% boosting on the output voltage (as high as 212 V), 270% increment on the piezoelectric coefficient (d33 ∼51.1 pC N-1 ) and long-term reliability on both structure and output (over 36 000 cycles). The design of a novel heterogenous interface with both mechanical matching and electric coupling can be the new orientation for developing high performance piezoelectric composite-based devices.

Wearable Triboelectric Nanogenerator with Ground-Coupled Electrode for Biomechanical Energy Harvesting and Sensing

Harvesting biomechanical energy for electricity as well as physiological monitoring is a major development trend for wearable devices. In this article, we report a wearable triboelectric nanogenerator (TENG) with a ground-coupled electrode. It has a considerable output performance for harvesting human biomechanical energy and can also be used as a human motion sensor. The reference electrode of this device achieves a lower potential by coupling with the ground to form a coupling capacitor. Such a design can significantly improve the TENG's outputs. A maximum output voltage up to 946 V and a short-circuit current of 36.3 μA are achieved. The quantity of the charge that transfers during one step of an adult walking reaches 419.6 nC, while it is only 100.8 nC for the separate single-electrode-structured device. In addition, using the human body as a natural conductor to connect the reference electrode allows the device to drive the shoelaces with integrated LEDs. Finally, the wearable TENG is able to perform motion monitoring and sensing, such as human gait recognition, step count and movement speed calculation. These show great application prospects of the presented TENG device in wearable electronics.

Self-poled and transparent polyvinylidene fluoride-co-hexafluoropropylene-based piezoelectric devices for printable and flexible electronics

Transparent and flexible energy supply devices are becoming increasingly important for human interfaces as the Internet of Things (IoT) continues to grow. In this study, self-poled and transparent piezoelectric nanogenerators (ST-PENGs) based on 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFOES) and polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP) composite films were prepared via extrusion printing, where PFOES induces the transformation of PVDF-HFP chains, exhibiting a higher β-phase content and remarkable piezoelectric properties. The hydrogen bonding interaction between the PVDF-HFP matrix and the PFOES agents causes a clear transition from phase to phase, as evidenced by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results. Moreover, the PFOES content influences the β-phase content, with 10 wt% of PFOES enabling the induction of the β-phase content up to 82.7%. The proposed ST-PENGs generate an excellent output voltage, power, and sensitivity of ∼6.2 V, ∼6.9 μW cm^-2, and ∼131.3 mV N^-1, respectively, exhibiting a record-high improvement compared with previously reported PENGs. These ST-PENGs also offer significant promise in tracking human activity and recovering biomechanical energy. This study may provide insight into the development of transparent and flexible piezoelectric devices to achieve high-performance self-powered electronics.

Flexible PVDF-TrFE Nanocomposites with Ag-decorated BCZT Heterostructures for Piezoelectric Nanogenerator Applications

Flexible piezoelectric nanogenerators are playing an important role in delivering power to next-generation wearable electronic devices due to their high-power density and potential to create self-powered sensors for the Internet of Things. Among the range of available piezoelectric materials, poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)-based piezoelectric composites exhibit significant potential for flexible piezoelectric nanogenerator applications. However, the high electric fields that are required for poling cannot be readily applied to polymer composites containing piezoelectric fillers due to the high permittivity contrast between the filler and matrix, which reduces the dielectric strength. In this paper, novel Ag-decorated BCZT heterostructures were synthesized via a photoreduction method, which were introduced at a low level (3 wt %) into the matrix of PVDF-TrFE to fabricate piezoelectric composite films. The effect of Ag nanoparticle loading content on the dielectric, ferroelectric, and piezoelectric properties was investigated in detail, where a maximum piezoelectric energy-harvesting figure of merit of 5.68 × 10^-12 m²/N was obtained in a 0.04Ag-BCZT NWs/PVDF-TrFE composite film, where 0.04 represents the concentration of the AgNO₃ solution. Modeling showed that an optimum performance was achieved by tailoring the fraction and distribution of the conductive silver nanoparticles to achieve a careful balance between generating electric field concentrations to increase the level of polarization, while not degrading the dielectric strength. This work therefore provides a strategy for the design and manufacture of highly polarized piezoelectric composite films for piezoelectric nanogenerator applications.

Enhancing the Piezoelectric Sensing of CFO@PDA/P(VDF-TrFE) Composite Films through Magnetic Field Orientation

Magnetic nanofiller is helpful for improving the piezoelectric properties of P(VDF-TrFE)-based composites, which shows promising potential as a flexible sensor or energy harvester. In this work, we use the interaction between the magnetic nanofiller and magnetic field to modify the structure of CoFe₂O₄ (CFO)@polydopamine (PDA)/P(VDF-TrFE) composite, in which CFO@PDA works as the nanofiller into the P(VDF-TrFE) matrix. It was found that the magnetic field orientation during polymer curing can significantly increase the content of the β-phase and d₃₃ of the composite. Regarding a typical composite film with 7 wt % CFO@PDA, the composite exhibits versatile sensing originated from the ball impact, hot-water droplet, bending, and pressing. In a noncontact magnetic field-driven experiment, the magnetic field oriented film produced the highest output voltages of 17.4 mV at 4 Hz and 12 mV at a drive amplitude of 19 Vpp, in contrast to the values of 7.1 mV and 7 mV for the film without magnetic field orientation, respectively. The LED without any charging capacitor can be instantaneously lighted through vertically pressing the oriented films. Thus, this work proposes a strategy of magnetic field orientation to improve the piezoelectric performance of the CFO@PDA/P(VDF-TrFE) multifunctional composite film.