Flexible Piezoelectric Nanogenerator with a Ferroelectric Metal–Ligand Cage for Self-Powered Sensor Applications

Ferroelectric materials have emerged as promising candidates for piezoelectric nanogenerators, attributed to their superior energy conversion efficiency derived from inherent polarization characteristics. Polar metal–ligand assemblies represent advantageous alternatives to conventional inorganic ceramics and organic polymers, offering tunable electronic properties, environmental benignity, and enhanced energy conversion capabilities. We demonstrate an octahedral [[Co₆(H₂O)₁₂(TPTA)₈](NO₃)₁₂·50H₂O] cage assembly exhibiting pronounced ferroelectric behavior, characterized by a P–E hysteresis loop with a remnant polarization of 6.84 μC cm^–2. The ferroelectric and piezoelectric properties of 1 were unambiguously confirmed through the visualization of electrical domains in single crystals and crystalline thin films via piezoresponse force microscopy (PFM). Single-point, bias-dependent PFM spectroscopy measurements revealed characteristic amplitude-butterfly and phase-hysteresis loops, substantiating the piezoelectric nature of the material. Piezoelectric energy harvesting investigations conducted on polydimethylsiloxane (PDMS) composite materials revealed a maximum peak output voltage of 12.20 V and a power density of 14.85 μW cm^–2 for the optimized 20 wt % 1-PDMS composite device. The practical utility was validated through the implementation of a smart pressure sensor, wherein a mat device, constructed from five parallel-connected independent devices, successfully functioned as a sensor capable of illuminating a commercial LED under gentle mechanical stimulation. These findings establish the potential of this cage system for integration into self-powered sensor technologies.