Synergistic Enhancement of Thermoelectric Performance in Non-Toxic Hydrogels Enabled by Lignosulfonate and SO42-/SO32- Redox Couples

Growing demand for sustainable energy harvesting drives research into thermoelectric materials that convert waste heat into electricity. Hydrogel-based systems offer advantages but are limited by toxic redox couples and poor mechanical-thermoelectric balance. Herein, we design and fabricate a highly stretchable, organic flexible gel-based photo-thermoelectric device by integrating biomass-derived sodium lignosulfonate (LS) and employing a novel non-toxic redox couple (SO 4 2- /SO 3 2- ). Unlike the usual method of introducing high salt or metal ions, this work uses the -SO 3 - groups in biomass LS to enhance the concentration gradient between SO 4 2- and SO 3 2- , thereby endowing the gel with high thermoelectric performance, achieving a thermal power of up to 2.6 mV K -1 . Moreover, benefiting from the superior photothermal conversion capability of LS, the as-prepared gel realizes integrated photo-thermoelectric conversion, which further elevates its thermal power to approximately 3.5 mV K -1 . The resulting gel is also capable of powering small electronic devices under practically achievable temperature gradients and can harvest human body heat. This work breaks from traditional toxic redox systems and represents a significant advance toward high-performance, environmentally benign thermoelectric devices based on sustainable biomass materials.