Thermogalvanic hydrogel electrolyte for harvesting biothermal energy enabled by a novel redox couple of SO4/32- ions

Thermoelectric hydrogels can be used as energy conversion devices to convert low-grade heat into practical electricity for sustainable energy supply. However, current redox couple-based thermogalvanic gel electrolytes contain toxic metal elements, limiting their non-toxic and environmentally sustainable development. Here, a stretchable, flexible gel thermoelectric device is created by introducing a novel non-toxic redox couple of SO42-/SO32- for the first time, which exhibits a high Seebeck coefficient (Se) of 1.63 mV K−1 at the optimal redox couple concentration of 0.1 M. The tensile/compressive stress and deformation at break of the hydrogel electrolyte achieves a superior index due to the hybrid structure formed between PEDOT: PSS and SO42-/SO32- ion-promoted crosslinking PVA network. By subtly doping additional electrolyte ions, the gel affords a favorable ionic conductivity and thermoelectric performance. Furthermore, this PVA-SO4/32- hydrogel shows the capacity of harvesting biothermal energy for operating small electronics at body temperature. This work breaks with conventional redox couples and represents a step towards green sustainable self-powered wearables using a new redox couple with a favorable thermoelectric performance.