Great Enhancement in the Thermopower of Ionic Liquid by a Metal‐Organic Framework

Abstract To efficiently harvest the abundant waste heat on earth is of great significance for sustainable development. Thermoelectric materials can be used to directly convert heat into electricity, and ionic thermoelectric materials like ionic liquids (ILs) are considered as the next‐generation thermoelectric materials. It is important to develop novel methods to improve the overall thermoelectric properties particularly the thermopower. Herein, the great enhancement in the thermopower of 1‐ethyl‐3‐methylimidazolium dicyanamide (EMIM:DCA) is reported that is an IL by introducing zeolitic imidazolate framework (ZIF‐8) that is a metal‐organic framework (MOF) for the first time. The presence of 40 wt.% ZIF‐8 can greatly increase the ionic thermopower of EMIM:DCA from 8.8 to 31.9 mV K⁻¹ at room temperature, and the ZIF‐8/EMIM:DCA mixture at the ZIF‐8 loading of 10 wt.% can exhibit a ZT_i value of 3.1, notably higher than that (0.59) of neat EMIM:DCA. The enhancement in the thermopower is attributed to the increase in the difference of the mobilities of EMIM⁺ and DCA⁻ by ZIF‐8. Because DCA⁻ is smaller while EMIM⁺ is larger than the pore size of ZIF‐8, the DCA⁻ transport is hindered by ZIF‐8, while EMIM⁺ can bypass ZIF‐8.