Antisolvent Engineering Enabled Stretchable and Transparent Thermogalvanic Hydrogels with High Thermoelectric Properties

ABSTRACT Ionic thermogalvanic hydrogels with high ionic thermopower are promising for wearable power supply. However, due to the presence of solid network, their ionic conductivities are still low, limiting their power densities. Herein, a facile and effective enhancement strategy on ionic conductivities and thus ionic thermoelectric properties of PVA(poly(vinyl alcohol))/CMC(carboxymethyl cellulose) hydrogels is proposed through antisolvent engineering. An antisolvent (ethanol) of PVA is introduced into PVA/CMC precursor solution prior to the hydrogel formation, which can change the conformation of PVA and CMC molecular chains as well as hydrogen bond network of prepared hydrogel. It can decrease PVA crystalline domains, and present higher water content and more sub‐micron porous structure through freeze‐thaw cycles to form stretchable and transparent hydrogel with faster ionic transport. This PVA/CMC hydrogel with antisolvent engineering presents the high ionic conductivity of 57.9 mS cm −1 and elongation at beak of 256%, which are 3.75 and 1.8 times higher than pristine hydrogel, respectively. This boosts its P max /∆ T 2 to a high value of 0.67 mW m −2 K −2 , higher than that of most PVA hydrogels. During this configuration with 27 hydrogels, it can output a high voltage of 718.1 mV under 10 K temperature difference, which is potential for wearable power supply.