Mitigating the Negative Piezoelectricity in Organic/Inorganic Hybrid Materials for High-performance Piezoelectric Nanogenerators

Recent Advances in Polyvinylidene Fluoride with Multifunctional Properties in Nanogenerators

Amid the global energy crisis and rising emphasis on sustainability, efficient energy harvesting has become a research priority. Nanogenerators excel in converting abundant mechanical and thermal energy into electricity, offering a promising path for sustainable solutions. Among various nanogenerator's materials, Polyvinylidene fluoride (PVDF), with its distinctive molecular structure, exhibits multifunctional electrical properties including dielectric, piezoelectric and pyroelectric characteristics. These properties combined with its excellent flexibility make PVDF a prime candidate material for nanogenerators. In nanogenerators, this material is capable of efficiently collecting and converting energy. This paper discusses how PVDF's properties are manifested in three types of nanogenerators and compares the performance of these nanogenerators. In addition, strategies to improve the output performance of nanogenerators are demonstrated, including physical and chemical modification of materials, as well as structural optimization strategies such as hybrid structures and external circuits. It also introduces the application of this material in natural and human energy harvesting, as well as its promising prospects in medical technologies and smart home systems. The aim is to promote the use of PVDF in self-powered sensing, energy harvesting and smart monitoring, thereby providing valuable insights for designing more efficient and versatile nanogenerators.

Ultra-high electrostriction and ferroelectricity in poly (vinylidene fluoride) by 'printing of charge' throughout the film

Electrostriction is an important electro-mechanical property in poly (vinylidene fluoride) (PVDF) films, which describes the proportional relation between the electro-stimulated deformation and the square of the electric field. Generally, traditional methods to improve the electrostriction of PVDF either sacrifice other crystalline-related key properties or only influence minimal regions around the surface. Here, we design a unique electret structure to fully exploit the benefits of internal crystal in PVDF films. Through the 3D printing of charged ink, we have obtained the best electrostrictive and ferroelectric properties among PVDF-based materials so far. The optimized electrostrictive coefficient M33 (324 × 10-18 m2 V-2) is 104 times that of normal PVDF films, and the piezoelectric constant d33 (298 pm V-1) is close to 10 times its traditional limit. The proposed 3D electret structure and the bottom-up approach to 'print the charge' open up a new way to design and adapt the electroactive polymers in smart devices and systems.

Enhancing output current in degradable flexible piezoelectric nanogenerators through internal electrode construction

Conventional piezoelectric nanogenerators (PNGs) face challenges in terms of degradation and reusability, which have negative environmental implications. On the other hand, biocompatible and degradable piezoelectric materials often exhibit lower piezoelectric response. In this study, potassium sodium niobate (KNN) powder and the biodegradable polymer poly(ε-caprolactone) (PCL) were used to fabricate piezoelectric composite films through solution casting. By constructing staggered electrodes, the total polarized charges quantity is increased, achieving a larger current output. The three-unit PNG (3-PNG) based on the composite film with 15 wt% KNN powder, reaches a maximum output current of 0.85 μA, which exhibits higher charging efficiency compared to 1-PNG. Moreover, the prepared 3-PNG can effectively harvest mechanical energy from human activities and maintain a stable output after 10,000 cycles of bending and releasing. The film exhibits complete degradation when exposed to acidic, neutral, and alkaline solutions. This research provides a promising option for environmentally friendly piezoelectric materials selected and output performance enhanced through optimized structural designs, making them more suitable for practical applications.

Adsorption Performance of Heavy Metal Ions under Multifactorial Conditions by Synthesized Organic-Inorganic Hybrid Membranes

A series of hybridized charged membrane materials containing carboxyl and silyl groups were prepared via the epoxy ring-opening reaction and sol-gel methods using 3-glycidoxypropyltrimethoxysilane (WD-60) and polyethylene glycol 6000 (PEG-6000) as raw materials and DMF as a solvent. Scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analyzer/differential scanning calorimetry (TGA/DSC) analysis showed that the heat resistance of the polymerized materials could reach over 300 °C after hybridization. A comparison of the results of heavy metal lead and copper ions' adsorption tests on the materials at different times, temperatures, pHs, and concentrations showed that the hybridized membrane materials have good adsorption effects on heavy metals and better adsorption effects on lead ions. The maximum capacity obtained from optimized conditions for Cu²⁺ and Pb²⁺ ions were 0.331 and 5.012 mmol/g. The experiments proved that this material is indeed a new environmentally friendly, energy-saving, high-efficiency material. Moreover, their adsorptions for Cu²⁺ and Pb²⁺ ions will be evaluated as a model for the separation and recovery of heavy metal ions from wastewater.