Experimental Study of the Thermoelectric Properties in Ionic Liquid + Organic Solvent Hybrid System

The addition of organic solvents has proven to be an effective strategy for enhancing the thermoelectric performance of ionic thermoelectric materials. However, systematic studies on how organic solvents influence the thermoelectric properties of ionic liquids remain limited. Based on molecular structure and polarity considerations, four ionic liquid + organic solvent systems─(1-ethyl-3-methylimidazolium dicyanamide ([EMIM][DCA])/1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]) + Dimethyl sulfoxide (DMSO)/Propylene carbonate (PC))─were selected. A two-wire 3ω method was employed to measure thermal conductivity, along with a temperature gradient system for Seebeck coefficient measurements. The thermal conductivity, electrical conductivity, and Seebeck coefficient of the hybrid systems were investigated across various mass fractions and temperatures. The results indicate that selective solvation effects between ionic liquids and solvents can significantly enhance both electrical conductivity and Seebeck coefficient. At 25 °C, [EMIM][DCA] exhibited a 1.64-fold increase in the figure of merit with DMSO and a 0.90-fold increase with PC, while [EMIM][BF₄] showed corresponding improvements of 1.62 and 0.92 times, respectively. Hybrid systems combining aprotic polar solvents with ionic liquids composed of asymmetric and highly polar ion pairs tend to exhibit superior thermoelectric performance.