METAL-ORGANIC COORDINATION POLYMERS FOR THERMOELECTRIC APPLICATIONS AT LOWTEMPERATURE

Thermoelectric (TE) materials enable the direct conversion of heat into electricity through the Seebeck effect. With nearly 70% of consumed energy lost as low-temperature heat (<200 °C), advancing TE materials is essential for minimizing our carbon footprint.[1] Traditionally, most TE materials are inorganic (e.g., Bi2Te3), but they face challenges such as high thermal conductivity, costly and high-temperature fabrication processes, scarcity, brittleness, and toxicity. Recently, coordination polymers (CPs) such as poly[Kx(Ni-ett)] have emerged as promising TE materials for low-temperature energy harvesting.[2] CPs can be tailored by substituting either the metal center or the organic ligand. In the present case case, Ni- and Cu-based polymers were synthesized through a three-step process carried out under a controlled atmosphere. The obtained materials are metalsulfur coordination polymers in which the metal is bonded to thylenetetrathiolate (ett) or dithiolylidene-tetrakisthiolate (diett) anions. Even if insoluble, they have been effectively processed as dispersions in acetonitrile, without additives and have undergone thorough chemical and physical characterization. They appear as highly delocalized systems featuring low activation energies, high electrical conductivity, good thermo-oxidative stability, and interesting thermoelectric properties. The best-performing p- and n-type polymers were deposited on flat substrates, and the corresponding p-n planar modules were fabricated. The resulting Seebeck coefficient and power density matched the combined contributions of the individual p and n legs, demonstrating the functionality of this system. These results demonstrate that coordination polymers are well-suited for low-temperature energy harvesting, offering high performance, stability and adaptability to unconventional geometries.