Enhancing the Thermoelectric Performance of Sustainable Cellulose‐Based Ionogels Through Water Content Regulation

Abstract Ionogels are widely studied as promising ionic thermoelectric (i‐TE) materials to harvest low‐grade waste heat into electrical energy due to their huge thermopower and good ionic conductivity, providing a feasible way to sustainable development. Herein, a p‐type i‐TE cellulose ionogel (CIG) based on Soret effect is prepared by dissolving cellulose in an ionic liquid (IL) and subsequent water‐absorbing induced gelation. Its morphological structure and IL distribution are intuitively investigated through cryo‐focused ion beam‐scanning electron microscope. Experimental characterizations and molecular dynamic simulation studies elucidate that the regulation of water content induces the hydration of 1‐butyl‐3‐methylimidazolium cation and the swelling of CIG, which greatly promotes the ions diffusion and expands the difference in mobility between anions and cations. The proposed CIG exhibits superior thermoelectric properties: an ionic conductivity of 51.2 mS cm −1 , an ionic Seebeck coefficient of 20.7 mV K −1 , and an ionic figure of merit zT i of 2.36 at 30 °C, respectively. A CIG‐based i‐TE device is designed and assembled to demonstrate its great potential for wearable body heat‐to‐electricity conversion. The cellulose skeleton in CIG is completely biodegradable in nature and the used IL is recyclable and reusable, providing a green and sustainable strategy for energy harvesting.