Strong concentration gradient effect and weak solvation effect in thermopower enhancement in K3Fe(CN)6/ K4Fe(CN)6 aqueous electrolyte with ethanol addition.

• We elucidate the impact of organic solvents on the solubility of K 3 Fe(CN) 6 /K 4 Fe(CN) 6. • The impact of solvation effect and normalized concentration gradient effect on the thermopower was quantified. • A general strategy to enhance thermoelectric properties by designing solvents to construct large normalized concentration gradient. Emerging thermocells exhibit a significant potential in low-grade heat harvesting owe to their high mV-scale thermopower, low cost, and high robustness. Fundamentally, three effects contribute to the thermopower enhancement of liquid thermocells, i.e. original concentration effect, solvation effect, and normalized concentration gradient effect. Yet, the contribution of the solvation effects and the normalized concentration gradient in organic solvents remains a subject of debate. In this paper, we integrate experiments, spectral analysis, and electrochemical theory to demonstrate that the normalized concentration gradient dominates the enhancement of thermopower in the investigated organic solvents, whereas the solvation effect is weak. Further, the introduction of ethanol results in a thermosensitive solubility of K 4 Fe(CN) 6 and a minimal concentration at the cold end, which establishes a huge substantial normalized Fe(CN) 6 4- concentration gradient and increases the Seebeck coefficient to 3.4 mV/K. Simultaneously, the precipitation resulting from the introduction of an organic solvent notably diminishes the heat convection within the system. As a result, the optimized TC-35EtOH system yields a ZT value (0.094) and Carnot-relative efficiency (2.52 %) that are 7 times greater than those of its initial counterpart. Additionally, the system's high power density of 3.64 W/m2 suggests its potential for harnessing low-grade heat waste energy. [ABSTRACT FROM AUTHOR]