A strong, tough, and high-efficiency hydrogel thermocell for thermal energy harvesting

Hydrogel thermocells can directly convert low-grade thermal energy, such as industrial waste heat, solar heat, and human body heat, into electrical energy through redox reactions. However, existing hydrogel thermocells still face challenges in practical applications, including low output power density and poor mechanical properties. Inspired by the porous network structure of plant roots, a nanoporous hydrogel thermocell is designed through the synergy of co-nonsolvency effect and Hofmeister effect. The interconnected nanoporous network structure can serve as efficient ion-transport channels, enabling the hydrogel thermocells to achieve a high thermopower of 4.13 mV K⁻¹, a superior conductivity of 11.07 S m⁻¹, and a significantly enhanced normalized output power density of 5.34 mW m⁻² K⁻². Simultaneously, the densified porous network skeleton can effectively increase the mechanical properties of the hydrogel thermocells, with a tensile strength of 9.06 MPa and a stretchability of 1460 %. After connecting 20 thermocell units in series, it can output a voltage above 2 V to directly drive electronic devices, demonstrating tremendous application potential in the fields of thermal-electric energy conversion and self-powered flexible technology.