Designing a piezoelectric energy harvester (PEH) with high power density and high fatigue resistance is essential for the successful replacement of the currently using batteries in structural health monitoring (SHM) systems. Among the various designs, the PEH comprising of a cantilever structure as a passive layer and piezoelectric single crystal-based fiber composites (SFC) as an active layer showed excellent performance due to its high electromechanical properties and dynamic flexibilities that are suitable for low frequency vibrations. In the present study, an effort was made to investigate the reliable performance of hard and soft SFC based PEHs. The base acceleration of both PEHs is held at 7 m/s² and the frequency of excitation is tuned to their resonant frequency (f_r) and then the output power (P_rms) is monitored for 10⁷ fatigue cycles. The effect of fatigue cycles on the output voltage, vibration displacement, dielectric, and ferroelectric properties of PEHs was analyzed. It was noticed that fatigue-induced performance degradation is more prominent in soft SFC-based PEH (SS-PEH) than in hard SFC-based PEH (HS-PEH). The HS-PEH showed a slight degradation in the output power due to a shift in f_r, however, no degradation in the maximum power was noticed, in fact, dielectric and ferroelectric properties were improved even after 10⁷ vibration cycles. In this context, the present study provides a pathway to consider the fatigue life of piezoelectric material for the designing of PEH to be used at resonant conditions for long-term operation.

Developing functional solid polymer electrolytes (SPEs) is crucial for flexible, lightweight, and portable supercapacitors. This work presents an electrospinning approach to fabricate SPEs using poly(vinyl alcohol)-sodium chloride (PVA-NaCl) nanofibers (PNNF). CuNi₂O₃ nanoparticles deposited on nitrogen-doped omnichannel carbon nanofibers (CuNi₂O₃@N-OCCFs), coated onto a carbon cloth (CC), serve as the positive electrode, enhancing faradaic capacitance. Meanwhile, the rationally designed N-OCCFs, also coated onto CC, function as the negative electrode, providing a high-surface-area, and facilitating rapid electron transport. Comprehensive characterization revealed insights into the morphology and chemical composition of both electrodes and the PNNF electrolyte. An all-solid-state asymmetric flexible supercapacitor (AFSC) device, CuNi₂O₃@N-OCCFs-1.5//N-OCCFs-1.5, was assembled using PNNF as both the electrolyte and separator and evaluated against devices employing gel and aqueous electrolytes. The PNNF electrolyte enabled a wider potential window (2.2 V) compared to gel (2.0 V) and liquid (1.8 V) electrolytes. The AFSC achieved an impressive energy density of 63.6 Wh kg⁻¹ at a power density of 1100 W kg⁻¹, with 96.2% capacitance retention after 6000 charge/discharge cycles at 10 A g⁻¹. When two devices were connected in series, they powered a red LED for 5.33 min and a blue LED for 1.43 min, demonstrating practical applicability. This study provides a simple and effective strategy for fabricating high-energy–density AFSCs with excellent cycling stability and broad potential for flexible electronics. Graphical Abstract

This comprehensive review of (K,Na)NbO ₃ -based perovskites explores design strategies, mechanisms, and applications in piezocatalysis and photo-piezocatalysis for sustainable environmental and energy solutions.