Design and Synthesis of Ferroelectric Metal-Ligand Architectures and their Piezoelectric Energy Harvesting

Abstract

Development of clean and renewable energy scavenging methods is of growing interest to meet the global mandate of reducing the carbon footprint. Mechanical force is an abundant resource of energy that is readily available in our environment and yet remains unprocessed. Miniaturized energy conversion systems (nanogenerators) based on ferroelectrics are attractive since materials with high remnant polarization and low rigidity are known to yield large piezoelectric responses. Until now, the majority of the commercial piezoelectric nanogenerators have been mainly assembled from traditional inorganic ceramics such as PZT and organic polymers such as (PVDF) because of their high polarization. Despite that, with the increasing demand for devices based on thin films, the use of inorganic ferroelectrics for this application is hampered by their complicated film forming procedures, while PVDF films require a high-voltage poling process. Thus, alternate materials such as single-component organics, two-component hybrids and metal-ligand assemblies have been investigated for their ferroelectric properties and nanogenerator applications. In this context, the use of polar metal-ligand systems is particularly attractive as they can be easily assembled from environmentally benign light-weight transition metal ions and simple organic ligands. This presentation will highlight the design and synthesis of metal-ligand ferroelectric assemblies by employing flexible di-and tripodal phosphoramide ligands containing suitable pyridyl and carboxylate ligands. By precise molecular tailoring and fine-tuning of intermolecular interactions, structures ranging from discrete to one- and two-dimensional networks were obtained in the crystalline lattice. Ferroelectric measurement performed on these materials rendered well resolved hysteresis loops with high remnant polarization values. As the piezoelectric coefficient is directly proportional to the electric polarization, several of these materials with high remnant polarization were employed towards the fabrication of composite piezoelectric nanogenerators with non-piezoelectric polymers such as polydimethylsiloxane and thermoplastic polyurethane. These composite devices demonstrated excellent output electromechanical responses such as output voltage, current- and power-density values under various impact forces and load resistances. All these results underscore a promising advancement for the use of ferroelectric metal-ligand assemblies in the domain of piezoelectric nanogenerators, which are envisioned to play a great role in future wearable and self-powered electronics.