Elucidating the Piezoelectric, Ferroelectric, and Dielectric Performance of Lead-Free KNN/PVDF and Its Copolymer-Based Flexible Composite Films

Ecofriendly, reliable, and high-performance piezoelectric materials are drawing huge interest in resolving the environmental problems arising due to consumption of fossil fuel energy. Among the lead-free ferroelectrics, potassium sodium niobate (KNN, (K,Na)NbO3) is one of the most promising piezoelectric ceramics that can replace Pb(Zr,Ti)O3. In the present work, the piezoelectric performance of KNN incorporated in poly(vinylidene fluoride) (PVDF) and its copolymers, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), has been compared. The films were fabricated by a solution casting method and were further polarized by a corona poling technique. The results confirmed that the nanocomposite film with 8 wt % KNN filler in PVDF-TrFE (PTK8) exhibited the highest F(β) value, maximum remnant polarization, and dielectric constant value than other nanocomposites. The relative β-phase contents in PTK8, PHK8, and PK8 composite films reached 85, 76, and 75.8%, respectively, indicating that KNN acts as the most suitable nucleating agent in PVDF-TrFE. Also, the piezoelectric voltage output of the PTK8-based nanogenerator was found to be remarkably higher (∼20 V) as compared to other nanocomposite-based piezoelectric nanogenerators. It also exhibited a maximum power density of 0.54 μW/cm2 that was significantly improved in comparison to other composites. This nanogenerator was found to be a promising power generation device promoting miniaturization of self-powered systems

Bio-molecule Assisted Aggregation of ZnWO₄ Nanoparticles (NPs) into Chain-like Assemblies: Material for High Performance Supercapacitor and as Catalyst for Benzyl Alcohol Oxidation

ZnWO₄ nanoparticles (NPs) that are assembled and aggregated together as chain-like morphology have been synthesized via the reaction of Zn­(II) salt solution with sodium tungstate in the presence of the DNA scaffold under 5 min of microwave heating. The reaction parameters have been tuned to control the size of the individual particles and diameter of the chains. The significance of different reaction parameters and specific growth mechanism for the formation of particles is elaborated. The DNA-ZnWO₄ nanoassemblies have been used in two potential applications for the first time, namely, supercapacitor and catalysis studies. Supercapacitor study revealed that DNA-ZnWO₄ nanoassemblies exhibited good electrochemical properties having high specific capacitance value ∼72 F/g at 5 mV s^–1, and electrodes possessed a good cyclic stability with more than 1000 consecutive times of cycling. Catalysis studies have been done for benzyl alcohol oxidation, and it was observed that DNA-ZnWO₄ nanoassemblies having smaller diameter gives better catalytic efficiency compared to other morphology. This is further authenticated from their BET surface area analysis. In the future, the self-assembled DNA-ZnWO₄ nanoassemblies could be a promising candidate for the synthesis of other mixed metal oxides and should be applicable in various emerging fields like Li ion batteries or photocatalysis, or as luminescent materials

Piezoelectric-Driven Self-Charging Supercapacitor Power Cell

In this work, we have fabricated a piezoelectric-driven self-charging supercapacitor power cell (SCSPC) using MnO₂ nanowires as positive and negative electrodes and a polyvinylidene difluoride (PVDF)–ZnO film as a separator (as well as a piezoelectric), which directly converts mechanical energy into electrochemical energy. Such a SCSPC consists of a nanogenerator, a supercapacitor, and a power-management system, which can be directly used as a power source. The self-charging capability of SCSPC was demonstrated by mechanical deformation under human palm impact. The SCSPC can be charged to 110 mV (aluminum foil) in 300 s under palm impact. In addition, the green light-emitting diode glowed using serially connected SCSPC as the power source. This finding opens up the possibility of making self-powered flexible hybrid electronic devices