High Performance Eutectogel-Based Thermocell with a Wide Operating Temperature Range Through a Water-Containing Deep Eutectic Solvent Strategy

Flexible ionic thermoelectric (i-TE) quasi-solid cells provide an electrolyte leak free, easy-operation and mechanically adaptable route to low-grade heat harvest. However, limited by freezing and evaporation, the hydrogel-based thermocell exhibits environmental instability and has difficulty functioning at low temperatures. Herein, we develop a high-performance cryo-temperature i-TE eutectogel using a water-containing deep eutectic solvent (DES) strategy. The water containing DES is intentionally utilized to modulate the solvent shell structure of redox couple and expand the operation temperature range of i-TE eutectogel cell. Moreover, appropriate amount of water can increase the solubility of [Fe(CN)6]3-/4- , while maintaining the eutectic properties of DES. Subsequently, a double-network polymer gel is constructed to prevent liquid electrolyte leakage and provide the flexibility and operability of the i-TE cell. After synergistic optimization of the solvent and the polymer network, the Seebeck coefficient of the fabricated i-TE eutectogel cell reaches 2.06 mV/K. In a 20-cell prototype module, the current and voltage at Delta T = 8.3 K are 0.033 mA and 0.33 V, respectively. The DES endows this cell wide operable temperature ranging from-60 degrees C to 80 degrees C. The anti-freezing capability of this eutectogel cell offer a new strategy for fabricating gel-based thermocell required in frigid regions.