Flexible Piezoelectric Nanogenerators Based on One-Dimensional Neutral Coordination Network Composites

Metal-organic coordination polymers are modular systems whose structures can be modified in numerous ways to introduce and influence non-linear optical and electrical properties. However, their full potential as piezoelectric nanogenerators for self-powered electronics is yet to be uncovered. Here, we report a Zn(II)-based ferroelectric one-dimensional coordination network {[Zn(L1)(bpy)]center dot (H2O)1.5}infinity (1) derived from a flexible dicarboxylate ligand [PhPO(NH-(C6H4COOH))2] (L1H2) and 2,2 '-bipyridine as a co-ligand. The origin of polarization in 1, despite its neutral structure, is due to the polyhedral distortions around the Zn(II) center as revealed by ab initio calculations. The presence of polarizable domains was visualized by piezoresponse force microscopy (PFM) experiments. Also, from the PFM studies, a sizable converse piezoelectric coefficient (d33) value of 19.4 pm/V was noticed for 1, which is unprecedentedly high for the class of neutral-network coordination polymers. Furthermore, flexible composite devices comprising a thermoplastic polyurethane (TPU) polymer with different weight percentages (wt %) of 1 were prepared and examined for application as piezoelectric nanogenerators. Notably, the champion device of this series (poled 5 wt % 1-TPU composite) exhibits a highest open-circuit voltage of 5.6 V and power density output of 14.6 mu W/cm2.