Zinc-iodine thermal charging cell engineered by cost-efficient electrolytes for low-grade heat harvesting

Emerging ionic thermoelectric devices (i-TEs), with synergistic effect of thermogalvanic effect and thermo-diffusion effect, are promising devices to achieve heat to electricity. We report a zinc-iodine thermal charging cell (ZITCC) enabled by cost-efficient electrolytes for low-grade heat harvesting. Efficient functional electrolytes are obtained through optimization from Zn(NO 3 ) 2 , Zn(CH 3 COO) 2 and ZnSO 4 electrolytes and introducing redox species (I − /I 3 − ). The ZITCCs generate electricity through thermo-diffusion effect of electrolyte ions, as well as the thermogalvanic effect involving I − to I 3 − conversion and Zn plating, enabling efficient heat-to-electricity conversion. The Seebeck coefficient of 19.2 mV K −1 , a high output voltage of ∼1 V and superior normalized maximum power density of 0.44 mW m −2  K −2 is obtained at temperature difference of 15 K. Meanwhile, ZITCCs have good energy storage capacity. In addition, a quasi-solid-state device delivers an 8.5 mW m −2 output power and impressive performance at temperature difference of 8 K can be acquired. This work provides a good strategy for the design of high-Seebeck coefficient, cost-effective i-TEs for low-grade heat harvesting.