Ionic Liquid-based Thermoelectric Generator: Links between Liquid Data and Generator Characteristics

Abstract

The unfavorable link between electrical- and thermal conductivity limits the choice of solid-state materials for thermoelectric generators (TEG). An interesting alternative for solid-state TEG materials is the choice of ionic liquids (IOLs) that exhibits less thermal conductivity, and has the potential for being designed for delivering optimal thermoelectric properties. Further, Seebeck coefficients(S) as high as 1 mV/K could be shown by previous work [1], [2]. It appears that the key factor that limits the electro-thermal conversion efficiency for IOL-based TEGs must not only be seen in the conductivity but rather in the carrier extraction at the liquid-solid interface of the electrodes. The objective of the paper is to study the dominating mechanisms for free charge generation, free carrier separation and current extraction. A link between macroscopic IOL data (viscosity, electrical conductivity)and the generator performanceis aimed to be drawn. It is shown that viscosity and electrical conductivity of the liquids are linked via intermolecular mechanical, thermal and electrostatic forces. The polarity of the Seebeck Coefficients seems to be due to a specific affinity of one ion type to the heated electrode and the necessary thermal activation energy to initiate the oxidation and reduction process is reduced by the created electric field.