Enlightening thermoelectric mastery: Bio-inspired cellulose gel containing eco-friendly deep eutectic solvents

Fossil fuel combustion typically harnesses a limited portion of available energy, making waste heat recovery a significant challenge. High-temperature waste heat recovery systems are established, but addressing low-temperature waste heat remains a challenge for conventional methods. Leveraging the Seebeck effect, we create flexible organic thermoelectric materials by integrating cellulose nanofibril (CNF) from plants with a deep eutectic solvent (DES). The achieved DES gel exhibits outstanding properties, including a high Seebeck coefficient (17.96 mV K−1), impressive ionic conductivity (7.16 mS cm−1), and low thermal conductivity (0.1847 W m−1 K−1) at room temperature with relative humidity of 60 %, marking a substantial advancement in thermoelectric performance. They also possess exceptional mechanical properties, with a tensile strain of up to 367 % and a tensile strength of 2.19 MPa. Given their remarkable versatility, DES gel shows promise as an active material in ionic thermoelectric capacitors, enabling efficient heat storage and offering potential in low-temperature waste heat recovery.