A Highly Electrostrictive Salt Cocrystal and the Piezoelectric Nanogenerator Application of Its 3D-Printed Polymer Composite.

Ionic cocrystals with hydrogen bonding can form exciting materials with enhanced optical and electronic properties. We present a highly moisture-stable ammonium salt cocrystal [CHCHCH(CH)NH][CHCHCH(CH)NH][PF] () crystallizing in the polar monoclinic 2 space group. The asymmetry in was induced by its chiral substituents, while the polar order and structural stability were achieved by using the octahedral PF anion and the consequent formation of salt cocrystal. The ferroelectric properties of were confirmed through loop measurements. Piezoresponse force microscopy (PFM) enabled the visualization of its domain structure with characteristic "butterfly" and hysteresis loops associated with ferro- and piezoelectric properties. Notably, exhibits a large electrostrictive coefficient () value of 2.02 m C, higher than those found for ceramic-based materials and comparable to that of polyvinylidene difluoride. Furthermore, the composite films of with polycaprolactone (PCL) polymer and its gyroid-shaped 3D-printed composite scaled-up device, , were prepared and evaluated for piezoelectric energy-harvesting functionality. A high output voltage of 22.8 V and a power density of 118.5 μW cm have been recorded for the device. Remarkably, no loss in voltage outputs was observed for the devices even after exposure to 99% relative humidity, showcasing their utility under extremely humid conditions.