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(<b>L¹</b>)­(bpy)]·(H₂O)_1.5}_∞ (<b>1</b>) derived from a flexible dicarboxylate ligand [PhPO­(NH-(C₆H₄COOH))₂] (<b>L¹H₂</b>) and 2,2′-bipyridine as a co-ligand. The origin of polarization in <b>1</b>, 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 (<i>d</i>₃₃) value of 19.4 pm/V was noticed for <b>1</b>, 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 <b>1</b> were prepared and examined for application as piezoelectric nanogenerators. Notably, the champion device of this series (poled 5 wt % <b>1</b>-TPU composite) exhibits a highest open-circuit voltage of 5.6 V and power density output of 14.6 μW/cm².