Advanced Bacterial Cellulose Ionic Conductors with Gigantic Thermopower for Low-Grade Heat Harvesting.

Ionic conductors such as polymer electrolytes and ionic liquids have high thermoelectric voltages several orders of magnitude higher than electronic thermoelectric materials, while their conductivity is much lower than the latter. This work reports a novel approach to achieve high-performance ionic conductors using calcium ion (Ca²⁺) coordinated bacterial cellulose (CaBC) through molecular channel engineering. Through the coordination of Ca²⁺ with cellulose molecular chain, the distance between the cellulose molecular chains is widened, so that ions can transport along the cellulose molecular chain. Therefore, we reported ionic thermoelectric (i-TE) material based on CaBC/NaCl with a relatively high ionic Seebeck coefficient of -27.2 mV K^-1 and high ionic conductivity of 204.2 mS cm^-1. This ionic hydrogel is promising in the design of high-thermopower i-TE materials for low-grade heat energy harvesting.