Highly conductive triple network hydrogel thermoelectrochemical cells with low-grade heat harvesting

Quasi-solid thermoelectrochemical cells (TECs) are promising candidates for wearable energy harvesting devices as they enable the continuous conversion of low-grade heat into electricity. However, the TEC performance remains limited by inadequate ionic conductivity. Herein, a triple-network hydrogel consisting of polyacrylamide/poly(vinyl alcohol)/cellulose nanofiber (PAAM/PVA/CNF) is synthesized via a freeze-thaw method, and soaked in the thermogalvanic redox couple Fe(CN)63−/4– as the electrolyte. By optimizing the polymer composition and soaking time, a superior ionic conductivity of 168 mS cm−1 is achieved while maintaining a thermopower of ∼1.69 mV K−1. The high ionic conductivity is provided by the fractal microstructure of the hydrogel, as revealed by small-angle X-ray scattering (SAXS). Moreover, the as-fabricated thermoelectric generator array exhibits an exceptional power output of 28.7 μW at a temperature difference of 11.9 K. This work provides insights on the development of wearable thermoelectric materials for practical and reliable energy harvesting applications.