Giant Thermoelectric Properties of Ionogels with Cationic Doping

Although ionic thermoelectric (iTE) materials can have very high thermopower, it is of great significance to develop novel methods to further improve the ionic thermopower and figure of merit (ZT(i)). Here, significant improvement in the thermopower and thus the ZT(i) value of an ionogel by cationic doping, is reported. Doping sodium dicyanamide (Na:DCA) into the ionogels of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and 1-ethyl-3-methylimidazolium dicyanamide (EMIM:DCA) that is an ionic liquid can greatly enhance the thermopower. This is attributed to the interactions between the doped Na+ cations and DCA(-) anions, thereby increasing the difference in the mobilities of EMIM+ cations and DCA(-) anions. Moreover, through the combination with the solid networks engineering by an anti-solvent to PVDF-HFP, the PVDF-HFP/EMIM:DCA ionogel doped with 0.5 mol% Na+ with respect to EMIM+ exhibits an ionic thermopower of 43.8 +/- 1.0 mV K-1, ionic conductivity of 19.4 +/- 0.3 mS cm(-1) and thermal conductivity of 0.183 W m(-1) K-1 at the relative humidity of 85% and room temperature. The corresponding ZT(i) value thus reaches 6.1 +/- 0.4, much higher than the previous ZT(i) records of iTE materials. These ionogels can be used in the iTE capacitors for the thermoelectric conversion.

Automated summary

Significant improvement in the thermopower and figure of merit of an ionogel is reported through cationic doping. The doped ionogel exhibits higher thermopower, ionic conductivity and thermal conductivity. These ionogels have a high ZT(i) value and show potential for thermoelectric conversion in iTE capacitors.