Synthesis and Optimization of Poly(Nickel-Ethylenetetrathiolate) for High Performance n-Type Thermoelectric Polymers

Abstract

Thermoelectric generators directly convert heat into electricity via the Seebeck effect, which creates a voltage in response to an applied temperature gradient. Thermoelectric generators have been limited to niche applications due to their high system costs. Electrically conducting polymers are an attractive class of materials, particularly for low-grade waste heat recovery applications. Furthermore, they are inexpensive owing to their abundance and potential to process from solution via printing techniques, and they have an inherently low thermal conductivity. Thermoelectric polymers are often compared by their power factor, which is a function of the electrical conductivity and the Seebeck coefficient. In this work, I investigate the thermoelectric properties of metallo-organic poly[Kx(Ni-ett)], which is one of the highest performing organic n-type TE materials. However, it is produced as a powder that is insoluble in common solvents such as methanol and water; previous attempts to solution process the material have resulted in significantly reduced thermoelectric properties. In this work, we optimize the synthesis of this polymer and fabricate a composite film by suspending poly[Kx(Ni-ett)] in a polymer matrix. This is achieved by optimizing the air exposure time and reducing the amount of polyvinylidene fluoride matrix needed to form a film. The obtained thin-film properties show a room temperature power factor that is several times higher than that of films reported in literature and shows excellent stability in air. Additionally, alternative polymer matrices are investigated to further improve thermoelectric properties.