High-Performance Flexible Piezoelectric Nanogenerator Based on Electrospun PVDF-BaTiO3 Nanofibers for Self-Powered Vibration Sensing Applications

Boosting piezoelectric properties of PVDF nanofibers via embedded graphene oxide nanosheets

Tremendous research efforts have been directed toward developing polymer-based piezoelectric nanogenerators (PENG) in a promising step to investigate self-charging powered systems (SCPSs) and consequently, support the need for flexible, intelligent, and ultra-compact wearable electronic devices. In our work, electrospun polyvinylidene fluoride (PVDF) nanofiber mats were investigated while graphene oxide (GO) was added with different concentrations (from 0 to 3 wt.%). Sonication treatment was introduced for 5 min to GO nanosheets before combined PVDF solution. A comprehensive study was conducted to examine the GO incremental effect. Microstructural and mechanical properties were examined using a scanning electron microscope (SEM) and a texture analyzer. Moreover, piezoelectric properties were assessed via various tests including impulse response, frequency effect, d33 coefficient, charging and discharging analysis, and sawyer tower circuit. Experimental results indicate that incorporation of GO nanosheets enhances piezoelectric properties for all concentrations, which was linked to the increase in β phase inside the nanofibers, which has a significant potential of enhancing nanogenerator performance. PVDF-GO 1.5 wt.% shows a notably higher enhancing effect where the electroactive β-phase and γ-phase are recorded to be boosted to ~ 68.13%, as well as piezoelectric coefficient (d33 ~ 55.57 pC/N). Furthermore, increasing impact force encouraged the output voltage. Also noted that the delivered open circuit voltage is ~ 3671 V/g and the power density is ~ 150 µw/cm2. It was observed that GO of concentration 1.5 wt.% recorded a conversion efficiency of ~ 74.73%. All results are in line, showing better performance for PVDF-GO 1.5 wt.% for almost all concentrations.

High Performance Piezoelectric Nanogenerators Based on Polyvinylidene Fluoride-Graphene Nanoribbon Composite Thin Films

In this study, a highly efficient, sensitive, and lightweight piezoelectric nanogenerator (PENG) is developed using graphene nanoribbons (GNRs) incorporated into the polyvinylidene fluoride (PVDF) matrix. Unzipping multi-walled carbon nanotubes is an effective and scalable strategy for synthesizing graphene nanoribbons. The synthesized GNRs are employed to prepare nanometer-scale piezoelectric polymer composite films showing higher piezoelectric performance than neat PVDF. The impact of GNR concentration in the PVDF matrix on the electroactive phase content and piezoelectric properties of the composites is systematically investigated. X-ray diffraction (XRD) and Fourier-transformed infrared spectroscopy (FT-IR) analysis demonstrate an increase in the electroactive β and γ phases of PVDF by incorporating GNRs in the composites. With the optimized concentration of GNRs (1 wt%), the fabricated piezoelectric device can generate open-circuit voltage and an output power density of 26 V and 16.52 µWcm2, respectively. It is also found that the PVDF-GNR 1 nanogenerator can be used to generate electrical power by converting mechanical energy from different human activities such as wrist bending, palm tapping, and toe tapping. The findings indicate that (PVDF-GNR 1) PENG can be applied in self-powered portable and wearable electronic devices.

Self-Powering Gas Sensing System Enabled by Double-Layer Triboelectric Nanogenerators Based on Poly(2-vinylpyridine)@BaTiO3 Core-Shell Hybrids with Superior Dispersibility and Uniformity

Current core-shell hybrids used in diverse energy-related applications possess limited dispersibility and film uniformity that govern their overall performances. Herein, we showcase superdispersible core-shell hybrids (P2VP@BaTiO3) composed of a poly(2-vinylpyridine) (P2VP) (5-20 wt %) and a barium titanate oxide (BaTiO3), maximizing dielectric constants by forming the high-quality uniform films. The P2VP@BaTiO3-based triboelectric nanogenerators (TENGs), especially the 10 wt % P2VP (P2VP10@BaTiO3)-based one, deliver significantly enhanced output performances compared to physically mixed P2VP/BaTiO3 counterparts. The P2VP10@BaTiO3-based double-layer TENG exhibits not only an excellent transferred charge density of 281.7 μC m-2 with a power density of 27.2 W m-2 but also extraordinary device stability (∼100% sustainability of the maximum output voltage for 54,000 cycles and ∼68.7% voltage retention even at 99% humidity). Notably, introducing the MoS2/SiO2/Ni-mesh layer into this double-layer TENG enables ultrahigh charge density of up to 1228 μC m-2, which is the top value reported for the TENGs so far. Furthermore, we also demonstrate a near-field communication-based sensing system for monitoring CO2 gas using our developed self-powered generator with enhanced output performance and robustness.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Advancements in Bio-inspired Self-Powered Wireless Sensors: Materials, Mechanisms, and Biomedical Applications

The rapid maturation of smart city ecosystems is intimately linked to advances in the Internet of Things (IoT) and self-powered sensing technologies. Central to this evolution are battery-less sensors that are critical for applications such as continuous health monitoring through blood metabolites and vital signs, the recognition of human activity for behavioral analysis, and the operational enhancement of humanoid robots. The focus on biosensors that exploit the human body for energy-spanning wearable, attachable, and implantable variants has intensified, driven by their broad applicability in areas from underwater exploration to biomedical assays and earthquake monitoring. The heart of these sensors lies in their diverse energy harvesting mechanisms, including biofuel cells, and piezoelectric, triboelectric, and pyroelectric nanogenerators. Notwithstanding the wealth of research, the literature still lacks a holistic review that integrates the design challenges and implementation intricacies of such sensors. Our review seeks to fill this gap by thoroughly evaluating energy harvesting strategies from both material and structural perspectives and assessing their roles in powering an array of sensors for myriad uses. This exploration offers a comprehensive outlook on the state of self-powered sensing devices, tackling the nuances of their deployment and highlighting their potential to revolutionize data gathering in autonomous systems. The intent of this review is to chart the current landscape and future prospects, providing a pivotal reference point for ongoing research and innovation in self-powered wireless sensing technologies.

3D Printing of Flexible BaTiO3/Polydimethylsiloxane Piezocomposite with Aligned Particles for Enhanced Energy Harvesting

With the rapid development of human-machine interactions and artificial intelligence, the demand for wearable electronic devices is increasing uncontrollably all over the world; however, an unsustainable power supply for such sensors continues to restrict their applications. In the present work, piezoelectric barium titanate (BaTiO3) ceramic powder with excellent properties was prepared from milled precursors through a solid-state reaction. To fabricate a flexible device, the as-prepared BaTiO3 powder was mixed with polydimethylsiloxane (PDMS) polymer. The BaTiO3/PDMS ink with excellent rheological properties was extruded smoothly by direct ink writing technology (DIW). BaTiO3 particles were aligned due to the shear stress effect during the printing process. Subsequently, the as-printed composite was assembled into a sandwich-type device for effective energy harvesting. It was observed that the maximum output voltage and current of this device reached 68 V and 720 nA, respectively, for a BaTiO3 content of 6 vol %. Therefore, the material extrusion-based three-dimensional (3D) printing technique can be used to prepare flexible piezoelectric composites for efficient energy harvesting.

Hybrid Piezoelectric/Triboelectric Wearable Nanogenerator Based on Stretchable PVDF-PDMS Composite Films

Hybrid piezoelectric/triboelectric nanogenerators combine the merits of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs), possessing enhanced electrical output and sensitivity. However, the structures of the majority of hybrid nanogenerators are rather complex in integrating both functions, limiting their practical application in wearable electronics. Herein, we propose to construct a piezoelectric/triboelectric hybrid nanogenerator (PT-NG) with a simple structure based on a composite film to simultaneously achieve the coupling of piezoelectric charge generation and triboelectrification with improved energy conversion efficiency. The composite film consists of electrospun PVDF nanofibers embedded in the surface of the PDMS film, which not only forms a rough nanomorphology on the surface of PDMS but also provides structural protection to the PVDF nanofibers by PDMS during compressive deformation. The results have shown that the PT-NG can generate much higher electrical outputs than individual TENG and PENG devices. The PT-NG devices exhibit a high level of mechanical-to-electrical energy conversion efficiency with superior performance in charging capacitors and functioning as self-powered wearable sensors for the detection of different signals from finger movement, the recognition of various gestures, and the monitoring of respiration. More importantly, the composite device possesses an impressive structure durability, maintaining its layered structure over 5000 testing cycles without noticing any obvious damage on the nanofibers or detachment between the layers. Our results have demonstrated that the combining of piezoelectric nanofibers and triboelectric substrate is an efficient way to fabricate highly efficient energy harvesting devices for intelligent identification and health monitoring.

Energy storage and catalytic behaviour of cmWave assisted BZT and flexible electrospun BZT fibers for energy harvesting applications

High-performance lead-free Barium Zirconium Titanate (BZT) based ceramics have emerged as a potential candidate for applications in energy storage, catalysis for electro chemical energy conversion and energy harvesting devices as presented in this work. In the present study hybrid microwave sintered BZT are studied for dielectric, ferroelectric and phase transition properties. BZT ceramic exhibits tetragonal structure as confirmed by the Retvield refinement studies. XPS studies confirms the elemental composition of BZT and presence of Zr. Polarization versus electric field hysteresis loops confirms the ferroelectric behaviour of BZT ceramic. Encouragingly, the BZT showed a moderate energy storage efficiency of 30.7 % and relatively good electro chemical energy conversion (HER). Excellent catalytic activity observed for BZT electrode in acid medium with low Tafel slope 77 mV dec-1. Furthermore, electrospun nanofibers made of PVDF-HFP and BZT are used to make flexible piezoelectric nano generators (PENGs). FTIR studies show that the 16 wt% BZT composite ink exhibits a higher electroactive beta phase. The optimized open-circuit voltage and short circuit current of the flexible PENG exhibits 7Vpp and 750 nA under an applied force of 3N. Thus, flexible and self-powered BZT PENGs are alternative source of energy due to its reliability, affordability and environmental-friendly nature.

Nanocellulose-based nanogenerators for sensor applications: A review

With the rapid development of the Internet of Things, nanogenerator as a green energy collection technology has attracted great attention in various fields. Specifically, the natural renewable nanocellulose as a raw material can significantly improve the environmental friendliness of the nanocellulose-based nanogenerators, which also makes the nanocellulose based nanogenerators expected to further develop in areas such as wearable devices and sensor networks. This paper mainly reports the application of nanocellulose in nanogenerator, focusing on the sensor. The types, sources and preparation methods of nanocellulose are briefly introduced. At the same time, the special structure of nanocellulose highlights the advantages of nanocellulose in nanogenerators. Then, the application of nanocellulose-based nanogenerators in sensors is introduced. Finally, the future development prospects and shortcomings of this nanogenerator are discussed.

Enhanced Piezoelectricity of PVDF-TrFE Nanofibers by Intercalating with Electrosprayed BaTiO3

Over the past few decades, flexible piezoelectric devices have gained increasing interest due to their wide applications as wearable sensors and energy harvesters. Poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE), as one of piezoelectric polymers, has caught considerable attention because of its high flexibility, high thermal stability, and biocompatibility. However, its relatively lower piezoelectricity limits its broader applications. Herein, we present a new approach to improving the piezoelectricity of PVDF-TrFE nanofibers by integrating barium titanate (BTO) nanoparticles. Instead of being directly dispersed into PVDF-TrFE nanofibers, the BTO nanoparticles were electrosprayed between the nanofiber layers to create a sandwich structure. The results showed that the sample with BTO sandwiched between PVDF-TrFE nanofibers showed a much higher piezoelectric output compared to the sample with BTO uniformly dispersed in the nanofibers, with a maximum of ∼ 457% enhancement. Simulation results suggested that the enhanced piezoelectricity is due to the larger strain induced in the BTO nanoparticles in the sandwich structure. Additionally, BTO might be better poled during electrospraying with higher field strength, which is also believed to contribute to enhanced piezoelectricity. The potential of the piezoelectric nanofiber mats as a sensor for measuring biting force and as a sensor array for pressure mapping was demonstrated.

A Piezoelectric-Driven Electrochromic/Electrofluorochromic Dual-Modal Display Device

Electrochromic (EC) reflective displays offer great advantages in delivering information and providing visual data, but are limited in dark environments. Reflective/emissive dual-modal displays capable of electrochemically-induced color and fluorescence change simultaneously are highly desirable, especially possessing rapid response speed as well as long-term durability. Herein, an electroactive fluorescent ionic liquid based on triphenylamine and imidazole (EFIL-TPA) has been synthesized for reflective/emissive dual-modal display. The resultant device exhibits outstanding electrochromic/electrofluorochromic (EC/EFC) performance with low driving voltage (below 1.0 V), fast switching speed (0.57-1.8 s), and remarkable cycling durability (91% retention for 10 000 cycles). A piezoelectric nanogenerator (PENG) driven EC/EFC integrated system is fabricated to harvest energy from human motion and visually drive the color/fluorescence change for human motion indication in both bright and dark environments. This innovative EC/EFC dual-modal display device based on EFIL-TPA supports a huge space for the development of self-powered human motion visualized indication in all-light conditions.