Negative thermopower anisotropic ionic thermoelectric hydrogels based on synergistic coordination and hydration for low-grade heat harvesting

To convert low-grade heat into valuable electricity, an efficient and cost-effective technology needs to be developed. In this context, the design of ultrasensitive ion thermopiles is particularly critical, as it plays an essential role in low-grade heat collection and temperature sensing. Modulation of the differential thermophoretic mobility of anions and cations in the electrolyte across temperature gradients is vital to achieving significant thermoelectric potentials. Here, we demonstrate an ionic hydrogel thermoelectric material obtained by synergistic coordination and hydration with a huge negative thermoelectric potential of −20.65 mV/K. Selective migration of conducting ions down thermal gradients is facilitated by subnanometer-scale confinement of ions in oriented aligned cellulose and polymer molecular chains. In addition, the oriented and ordered arrangement of the internal structure endows the hydrogel with excellent mechanical properties, and the tensile strength of the thermoelectric hydrogel reaches up to 2.89 MPa with a toughness of 22.5 MJ/m3. The combination of high ionic thermopotentials and excellent mechanical properties provides a new strategy for designing and applying high-performance ionic thermoelectric materials.