Flexible hydrogel with a coupling enhanced thermoelectric effect for low-grade heat harvest

Harvesting abundant and ubiquitous low-grade thermal energy and simultaneously converting it into electrical energy hold the potential of solving the existing energy crisis. Advances in thermoelectric materials now allow thermoelectric ionogel electrolyte to enhance the energy conversion and storage capacities under a thermal gradient. Here, we report an ionic thermoelectric (i-TE) material based on polyacrylamide (PAM) carboxymethyl cellulose (CMC) double network gel substrate with flexible and high thermal-electrical conversion properties. By combining the thermodiffusion effect of lithium sulfate (Li2SO4) ions and the thermogalvanic effect of [Fe(CN)64−/Fe(CN)63−], which achieved a coupled ionic Seebeck effect of up to 11.58 mV/K, exhibiting a high ionic conductivity (18.4 mS cm−1) and low thermal conductivity (0.47 W m−1/K), resulting in a high ionic power factor (198.2 μW m−1K−2) at room temperature. It exhibited an excellent tensile property (634%) and adhesion, and avoids electrolyte leakage to a large extent. Moreover, the application in ionic capacitors also demonstrates the superior thermoelectric conversion capability of i-TE gels. We believe that i-TE materials will pave a new pathway for low-grade thermal harvesting and self-driven flexible wearable electronics.