Significant Enhancement in the Thermoelectric Properties of Ionogels through Solid Network Engineering

Thermoelectric (TE) materials are significant for sustainable development because they can be used to directly harvest heat into electricity. Recently, ionic TE materials emerged as very promising materials mainly due to their high thermovoltage that can be higher than the Seebeck coefficient of electronic TE materials by 2–3 orders in magnitude. However, their conductivity is very low. Here, the significant improvement in the ionic conductivity and thus the overall TE properties of ionogels is reported by engineering their solid networks, which immobilize the ionic liquid in the ionogels. An antisolvent of poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) is added into the acetone solution of 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA) that is an ionic liquid and PVDF‐HFP prior to the ionogel formation. This can significantly change the solid networks formed by PVDF‐HFP and thus the microstructure of the EMIM:DCA/PVDF‐HFP ionogels, thereby facilitating ionic transport. As a result, the ionic conductivity of the ionogels can be increased from 7.0 to 17.6 mS cm−1. The ionogels can exhibit a high ionic figure of merit (ZTi) of 1.8 with the ionic Seebeck coefficient of 25.4 mV K−1 and the thermal conductivity of 0.190 W m−1 K−1. This is the highest recorded ZTi value for ionic conductors. The addition of antisolvent into solution can engineer the solid networks and the microstructure of ionogels. This can greatly increase the ionic conductivity and thus the overall thermoelectric properties of ionogels. The ionic conductivity can be increased from 7.0 to 17.6 mS cm−1, and the ionogels can exhibit a high ionic figure of merit (ZTi) of 1.8.