A new piezoelectric hybrid metal thiocyanide for energy harvesting and human motion sensing

Hybrid organic-inorganic piezoelectrics have received considerable attention in recent years owing to their fascinating performance, facile synthesis, and mechanical flexibility. However, the reported systems usually contain toxic heavy metals or are unstable due to sensitive metal halide bonds in air. In this context, eco-friendly and stable hybrid materials with excellent piezoelectric properties are highly sought after. Here, a new stable zero-dimensional hybrid piezoelectric, [Me-V]3Mn(SCN)5 (Me-V, 1-methyl-[4,4′]-bipyridinium), based on a pseudo-halogen environmentally friendly anion of SCN− was synthesized. More importantly, the mechanical energy harvesting properties of its flexible composite films, [Me-V]3Mn(SCN)5/PBAT (PBAT, polybutylene adipate terephthalate), with a series of weight ratios (1, 5, 10, 15, and 20 wt%) of [Me-V]3Mn(SCN)5 are reported. Experimental results demonstrate that the 15 wt% [Me-V]3Mn-(SCN)5/PBAT devices present an exceptional performance in energy harvesting, which can produce a maximum output voltage of 18.49 V and a power density of 7.88 µW cm−2 under an applied force of only 0.03 MPa, catching up with those of the state-of-the-art piezoelectric energy harvesting devices. Meanwhile, a typical device was demonstrated to exhibit excellent mechanical durability under 5500 cycles and environmentally stable over 60 days. Furthermore, the devices also show good sensitivity in monitoring human body motions, including finger tapping, wrist and elbow bending, and foot stepping. This work proves that lead- and halide-free hybrid piezoelectrics can serve as eco-friendly materials for flexible sensing and energy harvesting.